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Gayana (Concepción)

versión impresa ISSN 0717-652Xversión On-line ISSN 0717-6538

Gayana (Concepc.) v.70  supl.1 Concepción oct. 2006

http://dx.doi.org/10.4067/S0717-65382006000300019 

Suplemento Gayana 70: 83-86, 2006



POSTER ABSTRACTS



MICRO-ORGANISMS ABOVE AND WITHIN THE OXYGEN MINIMUM ZONE OFF NORTHERN CHILE: STRUCTURE AND TROPHIC INTERACTIONS

MICRO-ORGANISMOS SOBRE Y EN LA ZONA DE MINIMO OXIGENO EN EL NORTE DE CHILE: ESTRUCTURA E INTERACCIONES TROFICAS

V. Anabalón1,2, C.E. Morales1,2 , G. Alarcón1, O. Ulloa1, , R. Escribano1,2

1. Center for Oceanographic Research in the Eastern South Pacific (FONDAP-COPAS), Department of Oceanography, University of Concepción, P.O. Box 160-C, Concepción, Chile.

2. Marine Biological Station, Dichato, University of Concepción, Concepción, Chile camorale@udec.cl

The horizontal (coastal-oceanic) and vertical (0-200 m) distribution and abundance of microbial assemblages (nano- and micro-plankton), and grazing upon pico-prokaryotes (bacterioplankton and cyanobacteria), were examined in two coastal upwelling areas off northern Chile. Oxic waters in the upper layer and suboxic waters were separated by a strong and shallow oxycline, providing an opportunity to assess the influence of oxygen and grazing on microbial abundance, both under natural and experimental conditions. Nano-flagellates numerically dominated the nanoplankton and were mostly concentrated in the oxic layer but also occurred in the OMZ. Diatoms dominated the microplankton and were mostly absent in the OMZ though their resting spores were found there. Using the selective inhibitors technique, grazing rates on bacteria were assessed and we discuss the impact of grazing by nano-heterotrophs in regulating the production of prokaryotes in oxic and suboxic waters.


LONG-TERM TRENDS IN APPARENT OXYGEN UTILIZATION AND REDFIELD RATIOS IN THE SOUTHERN CALIFORNIA CURRENT SYSTEM

TENDENCIAS DE LARGO TERMINO EN LA UTILIZACION APARENTE DEL OXIGENO Y DE LAS RELACIONES DE REDFIELD EN EL SISTEMA DE LA CORRIENTE DE CALIFORNIA

Steven J. Bograd1, Carmen G. Castro2, Curt A. Collins3 & Francisco P. Chávez4

1. NOAA/SWFSC/Environmental Research Division, Pacific Grove, CA, USA. steven.bograd@noaa.gov

2. Institute of Marine Research (CSIC), Vigo, Spain

3. Department of Oceanography, Naval Postgraduate School, Monterey, CA, USA.

4. Monterey Bay Aquarium Research Institute, Moss Landing, CA, USA,

We use historical hydrographic data from the California Cooperative Oceanic Fisheries Investigations (CalCOFI) program to explore the temporal variability of physical and chemical properties of slope waters impacted by the California Undercurrent (CUC) over the period 1984-2004. The upper water column (sq < 26.0) has experienced a strong warming trend, and is greatly impacted by El Niño events. At the depth of the CUC (sq = 26.4), there has been weaker interannual variability, but waters have become progressively warmer, saltier, and lower in oxygen content over the twenty years, leading to a significant increase in apparent oxygen utilization. There have also been increasing trends in nitrate and phosphate in CUC waters over this period, although at different rates, leading to highly significant declines in the NO3:PO4 and SiO4:NO3 ratios. Several mechanisms for the observed trends were considered. The most likely cause is temporal variability in the properties of CUC source waters, and changes in net transport into the Southern California Bight. Significant changes in the oxygen content and nutrient composition of CUC waters, which are upwelled upstream, could have important implications for the California Current ecosystem.


16S RIBOSOMAL RNA OF THE PLANKTOMYCETALES AND VERRUCOMICROBIA IN CHILEAN CONTINENTAL SHELF SEDIMENTS

RNA RIBOSOMAL 16S DE PLANKTOMICETALES Y VERRUCOMICROBIA DE SEDIMENTOS DE LA PLATAFORMA CONTINENTAL DE CHILE

Justin Blair1, Mark, A. Lever1, Victor A. Gallardo2 & Andreas Teske1

1. University of North Carolina at Chapel Hill, Dept. of Marine Sciences, Chapel Hill, NC 27599, USA, teske@email.unc.edu

2. Department of Oceanography & Center for Oceanographic Research in the Eastern South Pacific (FONDAP-COPAS), University of Concepción, Concepción, Chile

Nitrate-respiring, ammonia-producing, sulfur-oxidizing mats of Thioploca spp. constitute the dominant microbial community on Chilean continental shelf sediments. With the exception of the Thioploca spp. themselves, the general microbial community structure is just beginning to be explored, and remains to be linked to characteristic biogeochemical processes in the Thioploca sediments, such as sulfate reduction, and the anaerobic oxidation of ammonia that is characteristic for oxygen-depleted marine environments. In this study, the structure of the metabolically active sediment microbial communities in Thioploca-bearing sediments is analyzed by 16S rRNA extraction, reverse transcription to cDNA, cloning and sequencing. Sediments were sampled during a joint research cruise in January 2006, hosted by the University of Concepción with participation of the Max-Planck-Institute for marine Microbiology in Bremen, Delft Technical University, Aarhus University and Aalborg University. Near-surface sediments (0-1, 1-2, 2-3, 3-4, 7-8 and 12-13 cm sediment depth) from Station 18, ca. 20 km offshore northwest of the Bay of Concepción (88 m depth), and surficial sediments (0-1 cm) from nearshore Station 7 located in the entrance to the Bay of Concepción (37 m depth) near the municipal sewage outfall of the town of Tomé, were analyzed. PCR amplification was performed with 16S rDNA primers selective for the Planktomycetales in an effort to detect members of anaerobic ammonia-oxidizing bacteria that are members of the Planktomycetales phylum. Total RNA extraction was performed based on Biddle at al.'s method, with modification for removal of excess organic material using the chelator cetyl-trimethyl ammonium bromide (CTAB). The protocol prevents amplification of intra- and extracellular DNA by DNAse digest of nucleic acid extracts before reverse transcription. The resulting rRNA transcripts included several novel, distinct phylogenetic clusters within the phyla Planktomycetales, Verrucomicrobia and related phyla that are unrelated to cultured strains and species among the heterotrophic, oxygen-respiring genera Pirellula and Planktomyces, and the ammonia-oxidizing, anaerobic candidate genera Brocadia, Scalindua and Kuenenia. So far, the Chilean rRNA phylotypes emphasize the environmental diversity and activity of the recently defined PVC (Planktomycetales/Verrucomicrobia/Chlamydiae) superphylum within the Thioploca mat sediments. This potentially monophyletic group of multiple phylum-level bacterial lineages includes Planktomycetales, Verrucomicrobia, Chlamydiae and Lentisphaerae, groups with cultured representatives, and the currently uncultured Poribacteria and OP3 phyla. Representatives of the PVC superphylum are frequently recovered from aquatic environments. Suboxic/anoxic marine environments with conspicuous nitrate/nitrite/ammonia gradients, such as the Black Sea water column and surface sediments on the Chilean Pacific shelf harboring Thioploca spp., emerge as a major habitat that is characterized by active members of PVC lineages.


DISSOLVED METHANE IN THE AREA OF SILLS, GULF OF
CALIFORNIA, MEXICO

METANO DISUELTO EN LA ZONA DE UMBRALES, GOLFO DE CALIFORNIA, MEXICO

Karel Castro-Morales1, J. Vinicio Macías-Zamora1 & Roger A. Burke2

1. Institute of Oceanologic Research (IIO-UABC), Tijuana-Ensenada, P.O. Box. 453, Baja California, México, karelcm@gmail.com

2. U.S. Environmental Protection Agency, National Exposure Research Laboratory, Athens, GA, USA.

The northern part of the Gulf of California is physically separated from the rest of the Gulf by a series of sills and islands. Its waters are highly productive as several water masses interact with each other at the sills. One of the characteristics in the area is the presence of the oxygen minimum zone (OMZ) located just south of the sills. Its chemical manifestation can probably be best observed by methane concentrations in the water column. We measured the distribution of methane concentration in the water column in this area to serve as a tracer of mixing water masses.

High dissolved methane concentrations and super-saturation were found at two sites near the area of sills. One of them was located at the south, where a well-defined OMZ has been previously identified. The origin of this large volume of water with oxygen concentration below hypoxia is thought to be due to natural rather than anthropogenic causes.

The gulf is one of the most biologically productive areas in the world. In the north, high productivity, topographic features that isolate the upper part from the rest of the gulf, and upwelling events are important factors that favor the formation of Gulf of California Water mass (GCW). This water mass contains oxygen concentrations well above hypoxia.

Dissolved methane was measured in sea-water samples taken from 22 stations around the Gulf of California Islands, using a phase equilibration method between the aqueous and gas phase (Helium) under temperature and pressure standard conditions.

Our data show good association of the GCW mass with high dissolved methane concentration. Also, vertical methane distribution shows that dissolved methane is well associated with GCW and Sub-surface Subtropical Water mass (SSTW).

The "Canal de Ballenas" (Whales Channel) zone showed to be an important source of methane from the sea surface to the atmosphere due to high mixing water column with values around 80.3 to 201.5 mMol CH4 m-2 d-1. At the same time, high temperature in the water column promotes less solubility of gases. Highest dissolved methane concentrations were found in this channel (Sta. 7) at 50, 20 and 10m depth (49.1, 48.3 and 43.5 nM respectively), corresponding to the highest saturation values measured (2088, 2053 and 1848% respectively). Those values are higher than those measured at many other high productivity marine sites worldwide. Dissolved subsurface maximum were reached at 50 m in most of the stations.

Dissolved methane in the area of sills was a good water mass tracer indicating the water mass movement of the GCW.

PHYTOplankton community, VENTILATION AND CLIMATE changeS DURING THE MARINE ISOTOPE STAGE 5 in Peru Oxygen Minimum Zone SEDIMENTS INFERRED FROM bIOMARKERS PRESERVED AT ODP Site 1229 (~11ºS)

cambios en la COMUNIDAD FitoplanctOnica, el clima y la ventilaciOn durante el ESTADIO ISOTOPICO MARINO 5 EN SEDIMENTOS DE LA ZONA DE MINIMO OXIGENO de peru inferidos a travEs de biomarcadores preservados en el sitio odp 1229 (~11ºS)

S. Contreras1, S. Pantoja2, 3, M. Kuypers4, C. B. Lange2, 3 & G. Lavik4

1. Graduate Program in Oceanography, University of Concepcion, P.O. Box 160-C, Concepcion, Chile, sergiocontreras@udec.cl

2. Department of Oceanography, University of Concepcion, Concepcion, Chile.

3. Center for Oceanographic Research in the Eastern South Pacific (FONDAP-COPAS), University of Concepcion, Concepcion, Chile.

4. Nutrient Group, Max Planck Institute for Marine Microbiology, Bremen, Germany

A multi-proxy approach, using bulk geochemical indicators (i.e., TOC, TN, sedimentary d15N) and lipid biomarkers (long chain n-alkanes & n-alcohols, diols, lycopane, dinosterol, alkenones), was used to reconstruct sea surface temperatures, bottom water redox conditions, terrigenous input and plankton community changes in the Peruvian shelf-waters (ODP Site 1229E; 10º59'S, 77º57'W; 151m water depth) during the past ~200 kyrs (i.e., between 35 to 180 kyrs). The sea surface temperatures reconstructed using C37 alkenone unsaturation index (U K'37), vary between 20ºC and 24ºC with a maximum during marine isotope stage (MIS 5). The transition from the glacial MIS 6 to the interglacial warm phase (MIS 5) is associated with a positive shift in bulk d15N values of ~6‰. A similar shift in d15N values was previously reported from the Peruvian margin and was attributed to enhanced denitrification due to an increase in primary production and an intensification of the oxygen minimum zone during MIS 6-5 deglaciation. However, low and constant lycopane ratio values indicate that the bottom waters at Site 1229 remained oxic during the transition. Intriguingly, the high abundance of biomarkers specific for the diatom genus Proboscia indicates more stratified conditions with a decreased upwelling intensity at Site 1229 during MIS 5. Our combined results indicate that MIS 5 was associated with warm surface waters and reduced upwelling intensity with a more stratified water column.

N2O DISTRIBUTION ALONG THE EASTERN SOUTH PACIFIC (12°-55°S)

DISTRIBUCION DE N2O A LO LARGO DEL PACIFICO SUR-ORIENTAL (12°-55°S)

Marcela Cornejo*1; Laura Farías 1, 2, 3 & Mauricio Gallegos 2,3

1. Department of Oceanography, University of Concepción, P.O. Box 160-C, Concepcion, Chile mcornejo@profc.ude.cl

2. Center for Oceanographic Research in the Eastern South Pacific (FONDAP-COPAS), University of Concepción, Concepcion, Chile

3. Laboratory of Oceanographic Processes and Climate (PROFC), University of Concepcion, Concepcion, Chile

The global climate has experienced disturbances since the beginning of the industrial age. These disturbances have mainly been associated with increased greenhouse gases such as CO2, CH4, and N2O in the atmosphere. N2O is one of the most potent of these gases; it is able to influence the radiation balance of the planet and to participate in the destruction of stratospheric ozone. The ocean contributes 25% of the total N2O production, most of which (up to 75% of global oceanic production) comes from the so-called oxygen minimum zones (OMZ), which are also found associated with coastal upwelling areas. The occurrence of coastal upwelling events with different frequencies and intensities along the Peruvian and Chilean coast must also be considered as propitious conditions for intense N2O production and recycling.

In the eastern South Pacific, an oxygen-deficient layer is associated with Equatorial Subsurface Waters (ESSW) distributed southwards (up to ~45° S) by the Peru-Chile Countercurrent. Waters off Peru and northern Chile have a permanent upwelling and suboxic subsurface waters (OMZ), that is one of the shallowest and most severe (<5 µM O2) in the world. Coastal water off central Chile is characterized by seasonal upwelling and hypoxic subsurface waters; whereas, waters off southern Chile are completely oxygenated and the area is subject to strong instability of the mixed layer making it a highly dynamic zone.

Measurements of dissolved O2 and N2O, nutrients (NO3- and NO2-), and other variables and oceanographic parameters were taken in the water column between 12° and 55°S, from 2000 to the present. The study area includes: Callao, Pisco, Iquique, Mejillones, Coquimbo, Valparaiso, Concepcion, and Punta Arenas.

The vertical distribution of N2O showed three basic patterns in relation to water oxygenation in the first order and productivity in the second order. A sharp subsurface maximum (with saturation levels up to 1400%) was associated with a strong oxycline followed by an N2O consumption zone, where the O2 concentrations dropped below 11 µM (OMZ core). This condition is found off Peru and northern Chile (12°-23°S). When this core water is oxygenated to levels greater than 22.3 µM as it moves south, the N2O increases gradually with depth as found off central Chile (30°-36° S). In southernmost Chile, a slight increase in N2O with depth (up to 25 nM at 1000_2000m depth) was associated with high oxygenation and low primary production levels. Air-sea N2O fluxes reflect the hydrographic/oceanographic conditions of each region. Central Chile is without doubt the region with the strongest N2O flux to the atmosphere (annual mean N2O flux of 31.8 µmol·m-2·d-1), whereas the Peru and northern Chile regions have a summer mean flux of 23.4 µmol·m-2·d-1, showing the moderating effect of the OMZ where N2O consumption has been identified by canonical denitrification in the core. Contrary to northern and central Chile, southern Chile represents a slight N2O sink (in average of -3 µmol·m-2·d).

(*) Financial support: FONDECYT #1050743-FONDAP-COPAS

PRELIMINARY OBSERVATIONS ON BENTHIC MICROBES FROM THE GOLFO DULCE, COSTA RICA

OBSERVACIONES PRELIMINARES SOBRE MICROBIOS BENTONICOS DEL GOLFO DULCE, COSTA RICA

Jorge Cortés1, Carola Espinoza2 & Víctor A. Gallardo2, 3

1. Center for Research in Marine Sciences and Limnology (CIMAR), University of Costa Rica, San José, Costa Rica, jcortes@cariari.ucr.ac.cr

2. Department of Oceanography, University of Concepcion, Concepcion, Chile.

3. Center for Oceanographic Research in the Eastern South Pacific (FONDAP-COPAS), University of Concepcion, Concepcion, Chile.

On the Pacific coast, Golfo Dulce (GD), Costa Rica (8°27'-8°45'N; 83°07'-83°30'W) is a tropical fjord-like body of water where a sill favors the formation of deep oxygen-deficient waters. Based on the work hypothesis that such oceanographic conditions might favor the occurrence of similar giant bacterial communities as those found on the shelf and bays of the eastern South Pacific, we carried out a benthic survey with a mono-corer in the GD during September 2005. We here report on the preliminary findings stemming from this survey. While low dissolved oxygen waters were encountered close to the bottom (ca. 0.6 ml/L-1), contrary to our expectations, sediments were only slightly reduced. Nevertheless, although not forming a mat, giant bacteria and other microbes were encountered, among them: (1) filamentous, sulfur-granule-containing, sheath-less, vacuolated, Thioploca-like trichomes, judging by the diameters, possibly Th. araucae and Th. chileae, (2) filamentous, sulfur-granule-containing, non-vacuolated Beggiatoa-like trichomes, (3) spherical, sulfur-granule-containing, Thiomargarita-like spheres, (4) abundant spirochaetes, (5) an smaller version of the filamentous, non-granulose `anaconda', (6) a host of undetermined granulose and non-granulose big filaments, and 7) protists, e.g., diverse ciliates and flagellates (euglenoids). In summary, in the GD, similar microbial communities as those found in sediments under the OMZ off Chile were observed indicating that this microbial system including giant filamentous bacteria is more widely distributed than previously imagined, opening new lines for regional microbial cooperative research.

HYDROGEN SULPHIDE: A FACTOR IN THE NORTHERN BENGUELA UPWELLING SYSTEM OFF NAMIBIA.

SULFURO DE HIDROGENO: UN FACTOR EN EL SISTEMA DE SURGENCIAS DE BENGUELA NORTE COSTA AFUERA DE NAMIBIA

B. Currie1, K. Peard2, A. Utne-Palme3, A.V.G. Salvanes3 & D. Schiedeck4

1. Ministry of Fisheries and Marine Resources, NatMIRC, P.O. Box 912, Swakopmund, Namibia, a_b_currie@yahoo.co.uk

2. Ministry of Fisheries and Marine Resources, Lüderitz Research Station, Namibia

3. Department of Biology, University of Bergen, Norway

4. Institut für Ostseeforschung, Warnemünde, Germany

The northern Benguela is one of the most productive upwelling systems in the world. However, much of the intense primary production sinks unutilized to the seabed to form a thick belt of anoxic diatomaceous mud along the Namibian coast. Just centimeters below the sediment surface the intense decay processes result in the formation of hydrogen sulfide and methane. Extensive mats of sulfur bacteria (Thiomargarita namibiensis and Beggiatoa species) efficiently prevent sulfide from diffusing into the overlying water column.

On occasions the entire water column is pervaded by high concentrations of hydrogen sulfide which rapidly deplete the dissolved oxygen content to zero or near-zero, even at the water surface. Such events are a regular, short-lived but devastating feature of the Namibian central coast. They are evidenced by both their noxious smell and milky water which develops at the surface. Impacts on the local marine life vary. Whilst mortalities of fish and benthos are evidenced by wash-ups on the beach, some key fish species e.g., the pelagic goby Sufflogobius bibarbatus, as well as some invertebrates e.g., the indigenous mussels Perna perna and Semimytilus algosus, show resistance to sulfide exposure.

The outbreaks of hydrogen sulfide are a significant factor to be reckoned with by the mariculture activities in the shallow coastal areas of Namibia, where farmers build contingency plans into their farming activities to allow for such events.


CONSERVATION OF COASTAL ECOLOGY FOR TSUNAMI DISASTER MITIGATION - ISSUES ON ECOLOGICAL AND SOCIAL RISK IN OXYGEN MINIMUM ZONES : LESSONS FROM SOUTH ASIAN TSUNAMI ALONG INDIAN COAST

CONSERVACION DE LA ECOLOGIA COSTERA PARA LA MITIGACION DE LOS DESASTRES POR TSUNAMIS Y RIESGO SOCIAL EN ZONAS DE MINIMO OXIGENO: LECCIONES DEL TSUNAMI SUR-ASIATICO A LO LARGO DE LA COSTA INDIA

Lalit P. Chaudhari, A.G.Bhole, N.K.Choudhary, S. P. Yavalkar. M.D.Shivankar & others.

Institute for Sustainable Development & Research , ISDR, India, B-1-8, Narayan Pujari nagar, Worli, Bombay, 400018. INDIA, clkp123@yahoo.com

South Asia is more vulnerable to Geo-disasters and impacts of climate changes in recent years. On 26 December 2004 massive waves triggered by an earthquake surged into coastal communities in Asia and East Africa with devastating force. Hitting Indonesia, Sri Lanka, Thailand and India hardest, the deadly waves swept more than 200 000 people to their deaths. More than 20 million population in the Indian coastal region alone and 50 million all over the coastal zones are witnessing the social- economical and ecological risks and impacts due to Tsunami and related climate changes .

The economic losses to coastal ecosystem, agriculture, irrigation, aquaculture, drinking water resources, coastal industries and infrastructure are very high due to extreme geo-disasters that are linked with environmental and climate changes .The ecosystem, economic system, agriculture and aquaculture system in this region are severely affected and need systematic rehabilitation. Also mitigating the geo-disasters, marine hazards and rehabilitation during post tsunami period, scientific knowledge is needed, requiring experienced research communities who can train the local population during tsunami rehabilitation.

ISDR, AVCCE, India and CGSI jointly started the initiatives on the problem identifications in management of risks in geo-disasters, tsunami rehabilitation etc., to investigate problems related to social-economic and ecological risks and management issues resulting from the December tsunami and Geo-disaster, to aid mitigation planning in affected areas and to educate scientists and local populations to form a basis for sustainable solutions.

This presentation reviews the status and issues of ocean _atmosphere interactions, Geo-risks, marine risks along Indian coast focusing on technical issues, biodiversity related problems and damage arising from the tsunami in agriculture, aquaculture, irrigation, drinking water, coastal infrastructure, coastal ecosystems and coastal economic systems. This study signifies that climate changes and risk management, Geo-disasters and Tsunami education are needed for mitigating potential Geo-marine risks in this region for capacity building for oxygen minimum zones and conservation of coastal ecology based on local resources.

RELATIONSHIP BETWEEN VIRAL AND PROKARYOTIC ABUNDANCE ON THE "BAJO O'HIGGINS 1" SEAMOUNT (HUMBOLDT CURRENT SYSTEM OFF CHILE)

RELACION ENTRE LA ABUNDANCIA VIRAL Y PROCARIOTICA SOBRE EL MONTE SUBMARINO "BAJO O'HIGGINS 1" (SISTEMA DE LA CORRIENTE DE HUMBOLDT, CHILE)

Oscar E. Chiang1 & Renato A. Quiñones1, 2

1. Graduate Program in Oceanography, Department of Oceanography, University of Concepción, P.O. Box 160-C, Concepción, Chile, ochiang@udec.cl

2. Center for Oceanographic Research in the Eastern South Pacific (FONDAP-COPAS), Department of Oceanography, University of Concepción, Concepción, Chile.

The ecology of microbial communities living in the water column over seamounts is scarcely known. Here, for the first time, the spatial distribution and abundance of virus-like particles (VLP) are described over a seamount. The association between VLP distribution, prokaryotic abundance, and environmental variables is also analyzed. Sampling was conducted on board the R/V Koyo Maru (National Fisheries University, Japan) in December 2004 on the Bajo O'Higgins 1 seamount (32°54'S, 73°53'W) located in the Humboldt Current System off Chile. A minimum oxygen layer was clearly present between 130 and 280 m in the water column over the seamount. Water samples were taken with Niskin bottles at 10 oceanographic stations over the seamount at depths of 5, 20, 50, 75, 100, and 150 m and at the benthic boundary layer (BBL; 5 - 12 m over the sediments). Temperature, salinity, oxygen, chlorophyll a, and phaeopigments were measured at each station. Viral and prokaryotic abundance were determined with fluorochrome SYBR Green I. Viral abundance ranged from 1.53 x 109 VLP L-1 to 16.48 x 109 VLP L-1, whereas prokaryotic abundance ranged from 1.78 x 108 cell L-1 to 14.91 x 108 cell L-1. The virus-like particle/prokaryote ratio varied widely among the analyzed layers (i.e. surface, oxygen minimum zone, and BBL), probably due to the presence of different prokaryotic and viral assemblages in each layer. Our results indicate that the environmental conditions, mainly the concentration of dissolved oxygen in the water column over the "Bajo O'Higgins 1" seamount, shape the association between viral and prokaryotic abundance.

PREVAILING WINDS AT THE BAY OF CONCEPCION, CENTRAL CHILE

VIENTOS PREDOMINANTES EN LA BAHIA DE CONCEPCION, CHILE CENTRAL

Alejandro de la Maza

Chilean Navy, Talcahuano Meteorological Center, jmeteotlc@directemar.cl

According to oceanographers, prevailing winds in Concepción Bay come from the South in summer (due to the presence of the Pacific High Pressure Center), shifting to the North in winter (due to the passage of frontal systems).

Nevertheless, from a meteorological point of view, winter frontal systems seem irrelevant to determine the prevailing winds, because of their intermittent and irregular nature, which leaves High Pressure Centers to restore the coastal wind circulation almost during the entire year.

As a subject of a brief investigation, in Concepción Bay there are four Chilean Navy weather stations (two automated), which allow us to see what is happening every three hours (or every minute) and to make our daily marine weather forecasts and warnings.

The recorded basic data would be useful to study the behavior of the wind during the present winter season, by using the weather stations located at Quiriquina Island and Talcahuano Harbor.


PRESERVATION OF FISH SCALES IN SEDIMENTS OFF CALLAO (PERU) AND ITS RELATIONSHIP TO THE STRENGTH OF THE OXYGEN MINIMUM ZONE

PRESERVACION DE ESCAMAS DE PECES EN SEDIMENTOS RECOLECTADOS FRENTE A CALLAO (PERU) Y SU RELACION CON LA INTENSIDAD DE LA ZONA DE MINIMO OXIGENO

Javier A. Díaz-Ochoa1, Carina B. Lange2, Gert de Lange3, Silvio Pantoja2, Práxedes Muñoz4, 5 & Dimitri Gutiérrez5

1. Graduate Program in Oceanography, Department of Oceanography, University of Concepcion, P.O. Box 160-C, Concepcion, Chile, jadiaz@udec.cl

2. Department of Oceanography and Center for Oceanographic Research in the Eastern South Pacific (FONDAP-COPAS), University of Concepcion, Concepcion, Chile.

3. Department of Geochemistry, Institute of Earth Sciences, Utrecht University, Utrecht, The Netherlands.

4. Department of Marine Biology, Catholic Northern University, Coquimbo, Chile.

5. Oceanographic Research Directorate, Institute of the Sea of Peru (IMARPE), Callao, Perú.

Fish remains are found in high concentrations within sediments beneath the coastal upwelling area off Peru, an area characterized by high fish productivity and an Oxygen Minimum Zone (OMZ) that impinges on the shelf and slope sediments which favors preservation of fish remains due to inhibited bioturbation. We use fish scale concentrations in a gravity core collected off Callao (CAG030521-29; 12º 0.84'S, 77º41'W; water depth = 179 m; core length = 52 cm) to study their preservation as a function of sediment oxygenation during the last few centuries. We established a relative chronology based on a mass accumulation rate of 0.032 g cm-2 yr-1 derived from 210Pbxs, a discontinuity at 26-27 cm which likely represents a tsunami that occurred off Callao at AD 1746, as well as on increased Cu concentrations in the upper 5 cm attributable to the start of Peruvian industrial mining at ~AD 1900. This chronology is inside the 2s confidence intervals of two calibrated 14C ages at 13 cm (AD 1795 ±113) and 38 cm (AD 1383 ±82) core depths. Measurements of trace element concentrations show that terrigenous elements Al, Ti and Fe are depleted in the upper 17 cm of the core (representing the interval between ~AD 1840 and ~AD 1924) and simultaneously, Mo is augmented and Mn depleted. Al-normalized trace elements show a consistent increase of redox-sensitive elements V, Mo, Ni, Cu and Zn in this upper section, probably due to increased anoxia during most of the 19th and the early 20th centuries. A first principal component summarizing >70% of the total variance of redox-sensitive trace elements is significantly regressed to fish scales concentration (r2 = 0.44, p <<0.01). An analysis of phosphorus from fish remains (PFISH) from selected samples along the core further demonstrates that PFISH is more concentrated in the sediment size particles >150 µm during periods of more intense anoxia and when fish scale preservation would be enhanced.

VERTICAL DISTRIBUTION, DIVERSITY AND ENZYMATIC ACTIVITY OF CULTURABLE BACTERIA OF SUB-OXIC SEDIMENTS IN THE EASTERN ARABIAN SEA

DISTRIBUCION VERTICAL, DIVERSIDAD Y ACTIVIDAD ENZIMATICA DE BACTERIAS CULTIVABLES DE SEDIMENTOS SUB-OXICOS EN EL MAR DE ARABIA ORIENTAL

Baby Divya, V. S. Sijumon, Nair Shanta & P.A. Loka Bharathi

Microbiology Laboratory, National Institute of Oceanography, Dona Paula 403004, Goa, India bdivya@nio.org

The sub-oxic region in the eastern Arabian Sea extends from depth of 150 m to 1500 m where dissolved oxygen values are less than 0.5ml L-1. In this study an attempt was made to examine the vertical distribution, diversity and enzymatic activity of the culturable bacteria in five vertical sections 0-1cm, 1-3 cm, 3-5 cm, 5-7 cm and 7-10 cm from a sediment core collected from 400 m depth. The bacterial abundance was of the order of 109/gdw in all sections, while the direct viable counts were 108/gdw in all sections except 7-10 cm in which it was 107/gdw. The retrievability ranged from 104-105/gdw, with maximum counts in 3-5 cm, that is 2 105/gdw followed by 1-3 cm, 7-10 cm, 5-7 cm and 0-1 cm in that order. The main genera retrieved (100%: 108 isolates) in the whole of the core were Pseudomonas (41%) > Alcaligenes (26%) >Acinetobacter (15%) > Bacillus (12%) > Vibrio (4%) > Corynebacterium (2%) in the order of dominance. Pseudomonas, Acinetobacter and Alkaligenes are common in all the sections examined. Pseudomonas was higher in 0-1 and 7-10cm with 61% and 70% respectively. Alcaligenes constitute the first two layers (0-1cm and 1-3 cm) with more or less similar percentage i.e. 22 and 25%. Acinetobacter was found to be highest in 5-7 cm section (25%), Bacillus was observed in only the middle three sections 1-3 cm, 3-5 cm and 5-7 cm while Vibrio and Corynebacterium were present only in 7-10 cm (17%) and 5-7 cm (7%) sections respectively. All the isolates were examined for enzymatic activities and all the sections exhibited more or less similar patterns of profiles without any increasing or decreasing trends. A notable feature is the lack of gelatinase activity in any of the sections. Amylase activity is detected in all sections except 0-1 cm. In addition the caseinase activity is not detected in the deeper two sections. Phosphatase activity was present in all the sections, highest being in 0-1 cm. Though there was no significant trend in any of the parameters observed vertically, this work would serve as excellent baseline information for further microbiological studies in this region.

IMPACT OF LOW OXYGEN ON THE LIFE CYCLES OF ZOOPLANKTON IN THE BENGUELA CURRENT UPWELLING REGION

IMPACTO DEL BAJO OXIGENO SOBRE LOS CICLOS DE VIDA DEL ZOOPLANKTON EN LA REGION DE SURGENCIAS DE LA CORRIENTE DE BENGUELA

Werner Ekau1, Hans M. Verheye2, Wilhelm Hagen3, Holger Auel3, Fritz Buchholz4, Anja Kreiner5, Antonio da Silva6 & Sakhile V. Tsotsobe2

1. Center for Tropical Marine Ecology (ZMT), Fahrenheitstrasse 6, D-28359 Bremen, Germany. E-mail: wekau@zmt.uni-bremen.de

2. Marine and Coastal Management (DEAT), Cape Town, South Africa

3. Marine Zoology, University of Bremen, Bremen, Germany

4. Alfred Wegener Institute for Polar and Marine Research, Helgoland, Germany

5. National Marine Information and Research Center, Swakopmund, Namibia

6. National Institute for Fisheries Research, Luanda, Angola

The Benguela Current off southern Africa is one of the four major eastern boundary current systems of the world's oceans, characterized by coastal upwelling and high productivity supporting commercially valuable fisheries. Uniquely, it is bounded by warm-water frontal systems along its northern (the Angola-Benguela Front - ABF) and southern (the Agulhas Current Retroflection) borders, which both affect the living resources of the Benguela. Another feature of the Benguela is the extended area of oxygen-depleted water masses. In the north, there is an almost permanent hypoxic layer overlying the bottom. In some areas, oxygen concentrations <1 ml l-1 are also found in the pelagial at depths of 50 to 100 m and thus may be a limiting factor for many pelagic species, particularly their early life-history stages. This may be even more important than currents, temperature gradients or food limitation caused by weak upwelling. Until recently, information on the effects of oxygen depletion on pelagic species, their recruitment or migration and distribution patterns, was scarce. Research initiatives to redress this were started under the umbrella of the BENEFIT (Benguela Environment Fisheries Interaction and Training) Programme and the Germany-South Africa Bi-lateral Scientific and Technological Cooperation. Data were collected during capacity building and training cruises onboard the South African FRS Africana (1999 and 2002) and the German RV Alexander v. Humboldt (2004). We present data on horizontal and vertical distribution patterns of low-oxygen water and how hypoxic conditions affect the distribution of life-history stages of populations of zooplankton (e.g., the dominant copepod Calanoides carinatus) and commercial fish (e.g., larvae of sardine Sardinops sagax, anchovy Engraulis encrasicolus and horse mackerel Trachurus capensis). The observed large-scale patterns in the hydrography and plankton distributions suggest that the Benguela system comprises a number of sub-systems, distinguishable based on water-mass characteristics, productivity patterns and plankton communities. Consideration of oxygen as an important environmental factor in the life history of zoo- and ichthyoplankton species and communities opens new perspectives for explaining their life-history strategies. Tight correlations exist between oxygen concentration and stratification as well as ecological adaptations of copepods and larval fish. For instance, C. carinatus did not inhabit the intermediate oxygen minimum layer (IOML; <1 ml O2 l-1). Experimental and physiological studies showed strong differences between active, lipid-poor individuals at the surface and diapausing, lipid-rich copepodids C5 below the IOML with severely reduced metabolism and respiration rates. Clearly, the role of the different zooplankton components interlinking primary production with pelagic fish stock dynamics under various seasonal and environmental influences, especially oxygen deficiency, is not fully understood, warranting further investigation.

FLOPS (FLOTADORES DEL PACIFICO SURORIENTAL): AN ARGO PROJECT TO MONITOR HYDROLOGICAL VARIABILITY IN THE OMZ OF THE EASTERN SOUTH PACIFIC

FLOPS (FLOTADORES DEL PACIFICO SURORIENTAL: UN PROYECTO ARGO PARA EL MONITOREO DE LA VARIABILIDAD HIDROLOGICA EN LA ZMO DEL PACIFICO SURORIENTAL

Gérard Eldin1, Alexis Chaigneau2, Oscar Pizarro3, Carmen Grados4

1Laboratory of Geophysical and Oceanographic studies (LEGOS), 31400 Toulouse, France, eldin@ird.fr

2Laboratory of Ocean, Climate and numerical Analysis (LOCEAN), Paris, France & Institute of the Sea of Perú (IMARPE) Lima, Peru

3Department of Geophysics and Center for Oceanographic Research in the Eastern South Pacific (FONDAP-COPAS), University of Concepcion, Concepcion, Chile

4Institute of the Sea of Peru, (IMARPE), Lima, Peru.

The eastern South-Pacific (ESP), offshore northern Chile and Peru, is characterized by the presence of the most pronounced and extended oxygen minimum zone (OMZ) of the world ocean. Located at intermediate depths (<1000 m), this OMZ plays a crucial role on greenhouse gases exchanges between the ocean and the atmosphere, but also on the adaptation of ecosystems to such an anoxic environment. The ESP also exhibits a complex three dimensional T-S structure, with the presence in the upper 2000 m of distinct water masses originating from equatorial, subtropical, sub-Antarctic, and the Antarctic regions. Superimposed to these rather large-scale synoptic characteristics, the mesoscale activity is seen as an important factor for both the transfer of heat and salt from the offshore waters to the surface coastal layers, and for the offshore propagation of physical and biogeochemical properties from the coastal upwelling regions.

The ARGO network of profiling floats now provide an invaluable tool to evaluate spatial distribution and variability of the OMZ and the water masses in the ESP, and to determine the vertical structure of the mesoscale eddies in this region. To contribute to this network, a grant from the CORIOLIS funding agency will allow us to deploy 20 additional floats in the area in 2006-2007. Two floats have already been deployed, and 8 floats are currently being modified to include an oxygen concentration sensor.

As a preliminary step, a high resolution oceanic circulation model has been run, and a simulation of float deployments completed. It shows that floats deployed at 100-200 miles from the coast will follow different trajectories depending of their launch locations: some will be entrained in the general circulation flows and different water masses, and other be more influenced by meso-scale eddies.

Some studies related to hydrological variability have already started from the approximately 4000 ARGO profiles available from the area for the 2002-2006 period. Methods of quality control were developed through comparisons with existing climatologies. First results will be presented related to seasonal and interannual variability in different areas of the ESP.

INITIAL MOLECULAR WORK ON THE NEWLY DISCOVERED BENTHIC FILAMENTOUS BACTERIA OF THE HUMBOLDT CURRENT SYSTEM

INVESTIGACIONES MOLECULARES INICIALES SOBRE LAS RECIENTEMENTE DESCUBIERTAS BACTERIAS FILAMENTOSAS DEL SISTEMA DE CORRIENTES DE HUMBOLDT

Carola Espinoza1, Jeppe L. Nielsen2 & V. A. Gallardo1, 3

1. Center for Oceanographic Research in the Eastern South Pacific (FONDAP-COPAS), University of Concepcion, P.O. Box 160-C, Concepcion, Chile, carespin@udec.cl

2. Department of Biotechnology, Chemistry and Environmental Engineering, Aalborg University, Denmark.

3. Department of Oceanography, University of Concepción, Concepción, Chile.

The shelf sediments under the Humboldt Current System have provided new opportunities to study big marine bacteria which were supposed to be scarce in the world's ocean. Recent observations indicate that they are not only plentiful in today's oceans, in particular in sediments under the oxygen minimum systems but, judging from the paleobiological literature, they were also common in the Precambrian oceans. We present here information on their finding off Concepcion, central and northern Chile. These recent investigations which have been more of the field survey type and based exclusively on morphology through phase contrast microscopy and microphotography, have moved into the molecular realm. Present efforts on the most conspicuous of these newly found big filamentous bacteria, the so-called `anaconda', an autofluorescent, non-vacuolated, multicellular, filamentous organism, extracted from field samples by means of micromanipulation, have included so far their 16S rRNA genes subjected to PCR (polymerase chain reaction) amplification and screening by DGGE (denaturing gradient gel electrophoresis). The ecophysiology of the organism is being studied by microautoradiography (MAR) in combination with FISH (fluorescence in situ hybridization). Preliminary results indicate that this, still unidentified form, is an obligate anaerobe, capable of fixing CO2 and acetate under sulfide conditions.

FIXATION OF N2O WITHIN THE OMZ OFF PERU AND ITS INFLUENCE ON N2O BUDGETS AND AIR-SEA FLUXES

FIJACION DE N2O EN LA ZMO FRENTE A PERU Y SU INFLUENCIA SOBRE EL BALANCE DE N2O Y LOS FLUJOS OCEANO-ATMOSFERA

Laura Farías*1, 2, 3, Marcela Cornejo1 & Camila Fernández2

1. Department of Oceanography, University of Concepcion, P.O. Box 160-C, Concepcion, Chile, lfarias@profc.udec.cl

2. Laboratory of Oceanographic and Climate Processes (PROFC), University of Concepcion.

3. Center for Oceanographic Research in the eastern South Pacific (FONDAP-COPAS), University of Concepción, Concepción, Chile

The Humboldt Current System (HCS) and particularly the coastal area off Peru possess unique characteristics for studying the biogeochemical transformations of nitrogen due to the presence of an intense upwelling regime able to sustain high primary production rates. In addition, this area presents a permanent oxygen minimum zone (OMZ) that can occasionally reach the euphotic layer. It is known that air- sea exchanges of N2O are highly implicated in greenhouse gas cycling and climate. Strong accumulations of N2O occur in a narrow and shallow depth range of OMZ regions, being in part produced by dissimilative NO3- reduction process (denitrification), which can have a strong impact on N2O budgets in the water column. In order to put fluxes across the surface ocean in relation with N2O distribution within the OMZ off Peru, we present an N2O budget taking into account both assimilative and reducing processes. Experiments for N2O fixation (assimilative) and reduction (dissimilative) were performed at different depths between the upper oxycline and the core of the OMZ, using a highly sensitive isotope tracer (15N2O) and the acetylene blockage techniques, respectively.

Air-sea N2O fluxes estimated by discrete sampling showed high variability (-1.07 to 89.88 µmol·m-2·d-1). Negative values (assumed to indicate a local sink of atmospheric N2O) were obtained in southern stations off Peru (17º_15º S) while high out-gassing was estimated in the northern area (13ºS and 10ºS). Below the upper oxycline, a strong N2O accumulation was occasionally observed (up to 1284% N2O saturation). The estimated cross-thermocline flux related to this N2O accumulation ranged between 2.4 to 17.9 µMol·m-2·d-1, representing 10 to 120% of average air-sea N2O fluxes.

Results revealed that N2O was actively assimilated at the oxycline and in the core of the OMZ at all stations, with rates varying between 0.23 and 0.85 nM·d-1. Integrated rates from below the thermocline (15_50m depth) to 150m depth yielded a N2O fixation of 79.3 µmol·m-2·d-1, showing that this process could be balance up to 10% of denitrified N2O in the area.

We conclude that a large vertical N2O exchange across the thermocline is taking place in the study area and is suspected to be contributing to the surface N2O budget. N2O fixation rates are also retaining some N2O originated from denitrification process, preventing it from reaching the upper layer N2O budget. We demonstrate that N2O fixation exerts an important control on the N2O subsurface waters accumulation and therefore is an indirect control for cross-thermocline N2O fluxes toward the mixed layer and finally to the N2O exchange between the ocean and the atmosphere.

(*) Financial support: FONDECYT #1050743-FONDAP-COPAS


hYPOXIC PROCESSES in THE Central area of Conceição lagoon, SC, Brazil

PROCESOS HIPoXICOS EN EL AREA CENTRAL DE LA LAGUNA DE Conceição, SC, BRASIL

Maria Luiza S. Fontes & Ariane Laurenti

Department of Environmental Engineering, Universidade Federal de Santa Catarina (UFSC) Florianópolis/SC, Brazil, 88040-900, luaondas@yahoo.com.br

The Conceição lagoon receives an increased allochtonous load of nutrients and organic matter. The sampling cruises were conducted in summer and winter 2003. They focused on the hypoxic/anoxic events occurring in the central area of the lagoon which is connected to the Atlantic Ocean through a 2 km-long channel (Canal da Barra). The lagoons's maximum depth is 6 m and salinity varies between 22 and 33. In the absence of strong winds, there is the development of a termohalocline frequently associated with an oxycline at 4-5 m deep, favoring accumulation of organic matter and, consequently, heterotrophic bacterial growth. This leads to anoxic conditions in the bottom waters. The hypoxic/anoxic events are influenced by both biotic and abiotic factors, such as heterotrophic metabolism and wind. Hypoxia (<2 mg/L) in the deep water has been reported in the lagoon since 1980. These events were observed frequently in summer and winter, with the highest sulfide (>34 mM), chlorophyll a (32 mg/L) and phaeophytin a (69 mg/L) concentrations found in summer. These values were significantly higher than those measured in other sectors of the lagoon (p<0.05). We hypothesize that aerobic and anaerobic processes are spatially diverse in the lagoon water body and that heterotrophic and photosynthetic bacteria couples in the bottom waters from the central area of the Conceição lagoon since sunlight reaches the sediment.

TEMPORAL TRENDS in THE STRATIFIED water column of Conceição lagoon, SC, Brazil

TENDENCIAS TEMPORALES EN LA COLUMNA ESTRATIFICADA DEL AGUA DE LA LAGUNA DE CONCEIÇÃO, SC, BRASIL

Maria Luiza S. Fontes1, Alessandra Fonseca2 & Ângela Schu3

1. Postgraduate Course of Biological Oceanography, Fundação Universidade Federal do Rio Grande (FURG), Rio Grande, Brasil luaondas@yahoo.com.br

2. Estação Ecológica de Carijós, Florianópolis/SC, Brasil;

3. Graduate Course of Chemistry, UFSC, Florianópolis/SC, Brasil

The Conceição lagoon is a shallow lagoon located in Florianópolis island (2734' S - 4827'W). The present study aimed to evaluate the temporal variation of dissolved oxygen, ammonium, phosphate, chlorophyll a and phaeophytin a in the water column. The sampling cruises were conducted in 2001 (summer/winter), 2003 (summer), and 2005 (winter). A stratification pattern was observed in the central area (maximum depth = 6 m), where deep-water salinity was 8 units higher than that of surface waters. Heterotrophic micro-organisms consumed all the available oxygen (from 10 to 0 mg/L), favored by high organic matter concentrations found in sediment (up to 10%). In July 2001, after two days of intense winds (11 m/s), the stratification remained and the oxygen decreased from 1.86 to 0 mg/L during a 3-day sampling interval. The anoxic condition favored: i) phosphate desorption, increasing concentrations of phosphate from 0.32 to 1.86 µM; ii) chlorophyll a degradation as indicated by the high phaeophytin a concentration of 28 µg/L. In summer 2003, we also observed anoxic conditions right below the halocline and with high levels of sulfide (>34 µM), phaeophytin a (up to 69.9 µg/L), and an increase of ammonium and phosphate concentrations from 1 to 6.7 µM and from 0.2 to 0.6 µM, respectively. On the other hand, in winter 2005, the hypoxic conditions in bottom waters were related to the highest chlorophyll a concentrations (up to 11 µg/L), which may be indicative of the presence of anoxygenic photosynthetic bacteria. The mean chlorophyll a levels in the lagoon varied between 2.3 and 5 µg/L. Significant correlations between oxygen concentration and pigments suggest the importance of biological processes in oxygen dynamics of the deep waters of the lagoon, more than physical processes.

EVALUATION OF GENETIC DIVERSITY IN PRISOGASTER NIGER (GRAY 1839) ASSOCIATED TO THE ENVIRONMENTAL HETEROGENEITY

EVALUACION DE LA DIVERSIDAD GENETICA EN PRISOGASTER NIGER (GRAY 1839) ASOCIADO A LA HETEROGENEIDAD AMBIENTAL

Carmen Fuentealba & Ricardo Figueroa

Aquatic Systems Unit, EULA Center, University of Concepción, P.O. Box 160-C, Concepción, Chile, cfuentea@udec.cl

One of the most important threats to the biological and genetic diversity is habitats loss. Generally, this begins with fragmentation processes derived from human activities. This initiates an effective population size reduction and an increase in the level of isolation among populations. The understanding of such factors in population change rate is key to design effective conservation plans of a resource in danger of extinction. We determined the levels of variability and tendency of the population size by means of bottleneck analysis in iso-enzymes of P. niger from the harbors of Lebu (37º37'S; 73º40'W), Penco (36º44'S; 73º00'W) and Dichato (36º32'S; 72º57'W). The sampled areas present differences in the environmental pollution levels as a consequence of the industrial and urban activities. The results of this study showed a reduction of the populations, expressed in high homozygous levels, especially in the locality of Penco (Bay of Concepcion), where increases in the organic matter concentration have taken place in the last decades. These inputs have generated anoxia and organic-enrichment (eutrophication) problems. According to the Wright, fixation index statistics the average level was (FST): 0.060 indicating a moderate genetic structuring. The level of genetic distance (Nei) fluctuated between (D): 0.8923 and 0.9869, and that of genetic identity between (I): 0.1077 and 0.0131. Results in relation to the degree of environmental heterogeneity are discussed.

EVALUATION OF CHANGES IN THE MACROBENTHIC INFAUNA OF THE BAY OF CONCEPCION

EVALUACION DE LOS CAMBIOS EN LA INFAUNA MACROBENTONICA DE LA BAHIA DE CONCEPCION?

Carlos Franco1, Leandra Torres1, Daniela Pérez1 & Víctor A. Gallardo2

1. Marine Biology Program, University of Concepcion, P.O. Box 160-C, Concepcion, Chile, cfvsigma7@hotmail.cl

2. Department of Oceanography & Center for Oceanographic Research in the Eastern South Pacific, (FONDAP-COPAS), University of Concepcion, Concepcion, Chile

The loss of biodiversity and biological productivity from the seas are threats to sustainable life on the planet the society must urgently face. In the developing world, for economical and cultural reasons it is not common to have data that might be used to evaluate such changes. Fortunately, historical data is available for the Bay of Concepcion. An extensive quantitative benthic survey was performed in the Bay of Concepcion in the summer of 1969, during a cold ENSO phase regime. Major taxa abundances and biomass were then recorded from more than 100 sampling stations. The 1969 data set is considered to represent conditions mostly shaped by the natural oceanographic conditions of the region during a cold ENSO regime, i.e., high primary productivity in surface waters and the sporadic incursions of oxygen-deficient waters from the off-shore Sub-surface Equatorial water-mass (SSEW). During April 2006, also under cold ENSO conditions, we performed a limited quantitative survey to gather fresh data from the bay, applying the same technique as used in 1969. We here present data that suggest important down-ward changes in the composition, abundance, and biomass of the macrobenthos of the Bay of Concepcion as compared with the situation of 1969. The following questions arise are: Are these changes due to the new and increasing addition in the interim of anthropogenic organic matter, i.e., organic inputs from fish reducing plant coastal outfalls and the installation of municipal submarine outfalls within the bay? Or, do they reflect natural changes in a larger scenario, e.g., interdecadal changes or global climate change? However this may be, the need to establish a serious long-term monitoring program including not only benthic and oceanographic observations but also the assessment of operating conditions of inputs into the Bay of Concepcion, is proposed.

DISCOLORATION OF THE BAY OF CONCEPCION, CENTRAL CHILE, DUE TO HYPOXIA AND HYDROGEN SULFIDE ERUPTIONS DURING COLD ENSO PHASE SUMMERS

DESCOLORACION DE LA BAHIA DE CONCEPCION, CHILE CENTRAL, DEBIDO A HIPOXIA Y ERUPCIONES DE HIDROGENO SULFURADO DURANTE VERANOS DE LA FASE FRIA DE ENOS

Victor Ariel Gallardo1, 2, Luis Pinto2, Carola Espinoza2, & Lilian Muñoz2

1. Department of Oceanography, University of Concepcion, P.O. Box 160-C, Concepcion, Chile, vagallar@udec.cl

2. Center for Oceanographic Research in the Eastern South Pacific, (FONDAP-COPAS), University of Concepcion, Concepción, Chile

The peculiar discoloration of the waters of the Bay of Concepcion is a recurrent phenomenon during summers of non-El Niño years. The first report of such discoloration dates from the summer of 1956. During these occasions, the bay acquires from a milky to a turquoise coloration. The events appear to originate during the morning of sunny and warm summer days in the enclosed waters at the head of the bay. At the same time sulfide gas bubbling is observed and strong smell of sulfide is felt in the area. The smell of sulfide gas can be traced across the bay to several kilometers inland along the highway to the central valley. When the south-west wind, typical for the season, picks up in strength and speed towards midday, the discoloration plume spreads within the bay, at times to affect its entire surface. At the head of the bay sometimes the sulfide bubbles (probably including other gases such as methane) are big enough to float to the surface large chunks of black, reduced, sediments. Several cruises were made last summer during the process of discoloration aboard the B/C OTILIA, a boat of suitable size and easy handling for shallow water work. Water samples were collected with a Niskin bottle and sediment samples were secured with a 0.02 van Veen grab for macrofauna analyses and with a mono-corer to obtain undisturbed samples for the observation of giant filamentous bacteria.

CHANGES IN oxygen minimum zone PROPERTIES ACROSS THE GULF STREAM and into the gulf of st. lawrence

CAMBIOS EN LAS PROPIEDADES DE LA ZONA DE MINIMO OXIGENO A TRAVES DE LA CORRIENTE DEL GOLFO EN EL GOLFO DE ST. LAWRENCE

Denis Gilbert

Institut Maurice-Lamontagne, Mont-Joli, Québec, Canada, G5H 3Z4, gilbertd@dfo-mpo.gc.ca

Sharp oxygen gradients exist across the Gulf Stream. The oxygen minimum occurs at a depth of about 1000m in the subtropical waters to the south of this frontal system, but is about 250 to 300 m deep in the Slope Waters and into the Gulf of St. Lawrence. I will display maps of oxygen concentration and saturation extending from the Sargasso Sea to the Slope Water and the Gulf of St. Lawrence. I will also present data from two Argo floats equipped with oxygen sensors in this general area. Finally, I will show that the hypoxic waters (<30% saturation) of the St. Lawrence Estuary are intimately linked to the northwest Atlantic oxygen minimum system.

HOLOCENE OCEANOGRAPHY AND CLIMATE IN THE SOUTHERN GULF OF CALIFORNIA, MEXICO

OCEANOGRAFIA Y CLIMA DEL HOLOCENO EN EL SUR DEL GOLFO DE CALIFORNIA, MEXICO

Oscar E. González-Yajimovich1, Robert G. Douglas2 & Donn S. Gorsline2

1. School of Marine Sciences, University of Baja California, km 103 Carretera Tij-Eda. Ensenada, Baja California, México, yajimo@uabc.mx

2. Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA

Alfonso Basin on the western side of the Gulf of California and Pescadero Basin on the center slope of the east side are basins which have sills or shoreward slopes in the Oxygen Minimum Zone and preserve sediment laminations whose physical and geochemical characteristics yield information on climatic and oceanographic changes during the Holocene. Accumulation rates of 25-50 cm/kyr within the OMZ preserve a high-resolution record of biogenic (organic carbon, carbonate, opal) and terrigenous sedimentation. Major changes in sedimentation began in the early Holocene (circa 7,200 YBP) with major shifts occurring at 4,200 and 3,000 YBP and smaller changes at 1500, 950, and 400 YBP in both basins. X-radiographs of the laminated, hemipelagic mud reveals subtle shifts in bottom water dissolved oxygen concentrations. A stepwise decrease in mass accumulation rates correlates to northern hemisphere summer insolation and suggests stronger NW winds and decreasing rains. Biogenic records indicate a drop in productivity accompanied a long-term shift from wetter to dryer conditions. At 400 YBP a recovery suggests a return to wetter less windy conditions. Three general climatic periods are recognized. Spectral analysis shows a 1-2 kyr climate rhythm in the Gulf and mediated by the migration of the Intertropical Convergence Zone (ITCZ) due to orbital precession. The sediment record is marked by strong climate-ocean variability cycles at about 88, 155, 200 and 300 years that appear related to latitudinal shifts of the ITCZ, produced by solar cycles. The variability in all of the sediment records increases after about 2 ka.

SEASONAL AND INTERANNUAL VARIABILITY OF THE PERU UNDERCURRENT

VARIABILIDAD ESTACIONAL E INTERANUAL DE LA CORRIENTE SUB-SUPERFICIAL DEL PERU

C. Grados1, G. Eldin2, L. Vásquez1, B. Dewitte2, C. Estrada3 & Y. du Penhoat2

1Institute of the Sea of Peru (IMARPE), Callao, Perú, cgrados@imarpe.gob.pe

2Laboratory of Spatial Geophysical and Oceanographic Studies (LEGOS), Toulouse, France

3 Directorate for Hydrography and Navigation (DHN), Callao, Peru

Historical hydrographic cross-shelf sections data (1990-2006) from 5°S to 18°S off Peru, combined with coastal sea level, satellite altimeter data, Acoustic Doppler Current Profiler data and an equatorial Kelvin wave model are employed to investigate the seasonal and inter-annual variability of the Peru Undercurrent and its relationship to the equatorial Pacific. Three distinctive hydrographic features associated to the PUC are used, along with dynamic topography, to trace the mean path of the Equatorial Undercurrent and to investigate aspects of its seasonal variation. These features are the 13°C thermostad, the high-salinity core, and the high dissolved oxygen concentration.

In situ sea level data from six mareographic stations distributed alongshore Peru and temperature and salinity hydrographic data collected from the surface to 500 m depth in the 350 km band adjacent to the coast were used. Monthly and seasonal current fields were obtained using geostrophic approximation. These results were compared to ADCP measurements collected during some cruises of 2006 in order to validate the geostrophic calculation. These in situ data sets combined to the altimetric sea level are interpreted in the light of the estimates of the Kelvin wave amplitude along the equator as derived from linear model simulations and the SODA reanalyses. Results indicate that the propagating features as revealed by the in situ data are associated to the equatorial Kelvin wave impinging at the eastern boundary of the tropical Pacific. The southward extension and amplitude of the PUC variability varies with the frequency of the equatorial forcing, with the 1997-1998 El Niño imprinting the most dramatic change in the structure of the PUC. These changes superpose to some extent on the O2 concentration pattern that exhibits a marked latitudinal heterogeneity suggesting that the PUC participates to poleward transport of dissolved oxygen.

IMBER: INTEGRATED MARINE BIOGEOCHEMISTRY AND ECOSYSTEM RESEARCH

IMBER: BIOGEOQUIMICA MARINA E INVESTIGACION ECOSISTEMICA INTEGRADAS

Julie Hall1 & Sylvie Roy 2

1. National Institute of Water and Atmosphere Research Ltd., P.O. Box 11-115, Hamilton, New Zealand, j.hall@niwa.co.nz

2. European Institute for Marine Studies, Plouzané, France.

Human activities are rapidly altering Earth System processes that directly and indirectly influence society. Informed decisions require an understanding of which parts of the Earth Systems are most sensitive to change, and the nature and extend of anticipated impacts of global change. In response to this need, the new IGBP-SCOR Integrated Marine Biogeochemistry and Ecosystem Research (IMBER) project has been formed, to focus on ocean biogeochemical cycles and ecosystems. The IMBER vision is to provide a comprehensive understanding of, and accurate predictive capacity for, ocean responses to accelerating global change and the consequent effects on the Earth System and human society. To achieve this, the IMBER Science Plan and Implementation Strategy is structured around four major research themes. Theme 1 focuses on identifying and characterizing interactions of the key biogeochemical and ecosystem processes that will be impacted by global change. Central to IMBER goal, Theme 2 will develop a predictive understanding of how marine biogeochemical cycles and ecosystems respond to complex forcings, such as large-scale climatic variations, changing to physical dynamics, carbon cycle chemistry and nutrient fluxes, and the impacts of marine harvesting. Theme 3 investigates the roles of ocean biogeochemistry and ecosystems in impacting the larger Earth System through direct and indirect feedbacks. Finally, Theme 4 integrates natural and social sciences, drawing on information from the previous three themes to investigate key interactions with the human system and the options for mitigating or adapting to the impacts of global change on marine biogeochemical cycles and ecosystems.

DIEL VERTICAL MIGRATION OF THE COPEPODS EUCALANUS SPP AND THEIR INTERACTIONS WITH THE OXYGEN MINIMUM ZONE IN THE NORTHERN UPWELLING REGION OFF CHILE

MIGRACION VERTICAL CIRCADIAL DE LOS COPEPODOS EUCALANUS SPP Y SU INTERACCION CON LA ZONA DE MINIMO OXIGENO EN LA REGION DE SURGENCIAS DEL NORTE, COSTA AFUERA DE CHILE

P. Hidalgo1 & R. Escribano1,2

1. Center for Oceanographic Research in the Eastern South Pacific (FONDAP-COPAS), University of Concepción, P.O. Box 160-C, Concepción, Chile pahidalg@udec.cl

2. Department of Oceanography, University of Concepción, Marine Biological Station, Dichato, University of Concepción, Concepción, Chile

Eucalanus copepods comprise a remarkable and numerically abundant assemblage of zooplankton in the northern upwelling region off Chile. They have been found closely associated with the oxygen minimum zone (OMZ), mainly in relation with their vertical distribution and migration and influence on the carbon fluxes. Eucalanus species were identified (all development stages) and their abundance and diel vertical migration (DVM) examined, from samples obtained during the MinOx (oxygen minimum) cruise, carried out in March 2000 off Iquique (21° S) onboard AGOR Vidal Gormaz. Samples were collected at four stations and at 4 depth strata (day and night): the upper well-oxygenated layer (0-30 m), the oxycline (30-60 m), the upper boundary of the OMZ (60-200 m), and the main core of the OMZ (200-400 m).

Identified species, in order of abundance were, Eucalanus inermis, Subeucalanus subtenuis, Subeucalanus crassus and Eucalanus attenuatus. Different DVM patterns of ontogenetic behavior were found among species: S. subtenuis did not perform DVM at any stage, whereas S. crassus performed DVM at late stage C5 and adults. For E. attenuatus there were missing stages in the samples, such that it was difficult to reveal a pattern, although late copepodids and adults appear distributed in deeper layers compared to younger stages. E. inermis exhibited DVM between intermediate layers for almost all stages, although the young copepodids C1 seem to remain deep (>100 m) at both day and night conditions.

For the copepods studied here, the OMZ system can play a significant ecological role as acting as a refuge to avoid predation. The vertical movement between layers, on the other hand, may imply a significant role of these copepods in accelerating vertical fluxes of organic matter into deep waters at this coastal upwelling system.

DENITRIFICATION BY FORAMINIFERS IN AN OXYGEN MINIMUM ZONE

DENITRIFICACION POR FORAMINIFEROS EN UNA ZONA DE MINIMO OXIGENO

Signe Ingvardsen1, Lars Peter Nielsen1, Tomas Cedhagen2, Niels Peter Revsbech1

1. Department of Microbiology, University of Aarhus, DK-8000 Aarhus C Denmark, signe.ingvardsen@biology.au.dk

2. Department of Marine Ecology, University of Aarhus, Aarhus, Denmark,

Nitrate accumulation and reduction was studied in two dominating foraminifer species Nonionella cf. stella and Stainforthia sp. in the Chilean oxygen minimum zone. Nitrate was accumulated to high concentrations within the foraminiferal cell where nitrate reduction took place. Nonionella cf. stella had an average denitrification rate of 84 ± 33 pmol N d-1 indiv-1. Total foraminiferal denitrification was estimated to 164 µmol N d-1 m-2 on the site.

Despite extreme oxygen depletion foraminifera are known to thrive in oxygen minimum zones (OMZ) with increasing standing stocks in central OMZ areas. A release in predation and enhanced food supply are proposed to account for this pattern. Despite of the high abundances of foraminifers in low oxygen environments energy conservation by foraminifera living in anoxic environments is not well comprehended. Recent findings of intracellular nitrate accumulation and denitrification by Globobulimina pseudospinescens from a Swedish fjord motivated this study of nitrate metabolism in foraminifers inhabiting OMZ. We aimed to quantify nitrate respiration rates, internal nitrate pools, nitrate uptake rates and the vertical distribution of living nitrate accumulating foraminifers to investigate their nitrate dependent life strategy and assess the role of the foraminifer in OMZ nitrogen cycling.

Investigations were performed at Sta. 18* outside the Bay of Concepcion, Chile, January 2006. The two dominating species Nonionella cf. stella and Stainforthia sp. both accumulated nitrate with an average nitrate content of 186 pmol and 60 pmol amounting to internal concentrations of 35 mM and 180 mM.

Denitrification rate in Nonionella cf. stella where 84 ± 33 pmol N d-1 indiv-1 measured by N2O-microelectrodes and acetylene inhibition. Enumeration of Rose Bengal stained Nonionella cf. stella and Stainforthia sp. showed a density of more than 1.9 x 106 specimens m-2 at the site and total foraminifer mediated nitrate reduction was thus estimated to 164 µmol N d-1 m-2. Higher rates are to be expected since premature screening suggests that more species depend on nitrate accumulation. These findings present a new pathway in nitrogen cycling in OMZ environments and suggest the existence of nitrate dependent faunal communities in completely oxygen-free environments.

* Time-Series Station of the Center FONDAP-COPAS, University of Concepcion.

LIFE AT STABLE LOW OXYGEN LEVELS: ADAPTATIONS OF ANIMALS (FORAMINIFERA) TO OCEANIC OXYGEN MINIMUM LAYERS

LA VIDA EN NIVELES ESTABLES Y BAJOS DE OXIGENO: ADAPTACIONES DE ANIMALES (FORAMINIFERA) A CAPAS DE MINIMO OXIGENO OCEANICAS

N. Jayaraju

Dept of Geology, S.V.University, Tirupati 517 502, India, naddimi_raju@yahoo.com

Zones of minimum oxygen level are found at intermediate depths in most of the world's oceans and, although the oxygen partial pressure in some of these `oxygen minimum layers' is only a fraction of a kilopascal, populations of pelagic metazoans exist there. These oxygen minimum layers are areas of the water column and the associated benthos (Foraminifera _ protozoan microscopic animals) with stable conditions of continuously low oxygen level and low temperature at intermediate depths (400-1000m depth) over vast areas. Off the Indian East coast, where PO2 at the oxygen minimum is 0.7 kPa, there are abundant populations of animals both in the water column and on the bottom. Farther to the south in the eastern tropical Bay of Bengal, oxygen partial pressures of less than approximately 0.5 kPa result in very low biomasses and diversity of animals (foraminifera) at minimum layer depths. At the minimum oxygen levels found off the Indian East coast, most animals which inhabit the minimum zones appear to support their routine metabolic demands via aerobic metabolism. They do this by being very effective at removing oxygen from water. Among the adaptations of benthic forms to these conditions are: (1) enhanced ventilation abilities, (2) enhanced percentage removal of O2 from the ventilation stream, (3) large test surface areas, (4) short diffusion distances from the water to the shell, and (5) reproduction with a very high affinity for O2, high cooperation and large Bohr effects. The lower O2 consumption rates of many deeper-living species are also functionally adaptive in that they facilitate aerobic survival at low PO2. However, they are not adaptations to the minimum layer, since similarly low rates are found in the same and comparable species living at the same depths in regions without well-developed minima, and these animals are unable to survive at the low PO2 values of the minima. While anaerobic metabolism may be important for metabolic rates above the routine level for most foraminifera in the minimum layer, there is little evidence for the use of sustained anaerobiosis in the species studied. In summary, given the stable presence of very low O2 levels in the minima, the primary adaptations of animals living within them are those that support aerobic metabolism by giving the animals remarkable abilities to extract O2 from water. These abilities are notably better than those of animals adapted to unstable hypoxic environments, such as intertidal mudflats, while the latter animals rely on a much greater extent on anaerobiosis and perhaps on metabolic suppression to survive periods of anoxia.

BENTHIC COMMUNITIES OFF CENTRAL CHILE, BIOMASS AND METABOLIC SPECTRA IN THE OXYGEN MINIMUM ZONE

COMUNIDADES BENTONICAS DE CHILE CENTRAL, ESPECTROS DE BIOMASA Y METABOLISMO EN LA ZONA DE MINIMO OXIGENO

Gerdhard L. Jessen1 & Renato A. Quiñones1, 2

1. Graduate Program in Oceanography, Department of Oceanography, University of Concepcion, P.O. Box 160-C, Concepcion, Chile, gjessen@udec.cl

2. Center for Oceanographic Research in the Eastern South Pacific (FONDAP-COPAS), University of Concepcion, Concepcion, Chile.

The distribution of biomass by size has been widely used to describe the structure of pelagic and benthic communities. This approach is based on the size dependence of the flow of matter and energy in most organisms. Four oceanographic stations located on a transect from the inner Bay of Concepción to the mid-continental shelf were sampled with the purpose of analyzing the distribution of metabolism (aerobic and anaerobic) and biomass by size in benthic communities associated with the oxygen minimum zone (OMZ) off central Chile. This is the first time that empirical aerobic and anaerobic metabolic spectra are constructed in benthic communities worldwide. Biomass was estimated as total ATP concentration and the aerobic metabolic activity was assessed evaluating the ETS activity. The lactate dehydrogenase (LDH) activity was used as an indicator of anaerobic metabolism. Biomass, aerobic and anaerobic metabolism diminishes (log-log scale) with the increment of body size at the community level of organization. The negative slopes of the biomass spectra as well as those of the metabolic spectra demonstrate the importance, at the community level of organization, played by the smaller organisms both from the standpoint of biomass as well as metabolism (aerobic and anaerobic).

SEASONAL DISTRIBUTION OF OXYGEN MINIMUM LAYER IN THE EXCLUSIVE ECONOMIC ZONE OF THE WESTERN INDIAN OCEAN

DISTRIBUCION ESTACIONAL DE LA CAPA DE MINIMO OXIGENO EN LA ZONA ECONOMICA EXCLUSIVA DEL OCEANO INDICO OCCIDENTAL

Vijay John Gerson1 & Joseph Sebastian Paimpillil2

1. National Institute of Oceanography, Regional Center, Salim Ali Road, Cochin 18, India, daj@vsnl.com

2. Center for Earth Research and Environment Management, Cochin, India

The distributions of Oxygen Minimum Layer during the monsoon and non-monsoon months in EEZ of western Indian Ocean were investigated. Depletion in dissolved oxygen in the intermediate waters was observed in almost all the seasons. Except in summer monsoon, oxygen depletion dropped below 5µM along the northern part of the EEZ. The OMZ had a larger geographical extend in EEZ during winter, indicating its maximum horizontal shift. A rapid increase in thickness of OMZ occurred from 12 °N to 18 °N between 200 m and 750 m and this was accompanied by a steady northward decrease in oxygen reaching below 5 µM at northern most transect. The oxygen deficient waters <20 µM were observed along the entire transect between 100 and 1000 m depth during the winter season. The thicknesses of 20 µM patch along 22°N transect increased to 900m. The lob of 10 µM contours extended only up to 14°N along the open ocean transect This intermediate water deepened to 300 m while it was around 150 m in coastal transects. A corresponding deepening of the depth limit of 20 µM patch was also evident along the northern transect. A wide band of 5 µM observed in the coastal transect near the continental shelf, might be due to sedimentary action. During the north east monsoon, the renewal of the oxygen deficient waters was sluggish due to the restricted trans-equatorial transport of high oxygenated waters. The vertical and horizontal extend of the OMZ reduced considerably during the summer monsoon, with a 150 m thick band of OMZ traced with its southern limits at 17°N as the renewal of oxygen deficient waters is rapid during south west monsoon. The relative role of physical factors controlling the depth of thermocline, thickness of OMZ and its boundaries were identified.

THE OXYGEN MINIMUM ZONES IN THE EASTERN TROPICAL ATLANTIC AND PACIFIC OCEANS

LAS ZONAS DE MINIMO OXiGENO EN LOS OCEANOS ATLANTICO Y PACIFICO TROPICALES ORIENTALES

J. Karstensen, L. Stramma & M. Visbeck

IFM-GEOMAR Leibniz-Institut fuer Meereswissenschaften Kiel, Germany, jkarstensen@ifm-geomar.de

In the eastern tropical Atlantic and Pacific Oceans oxygen minimum zones (OMZ) exist in the depth range 100 to 900 m. The minimum oxygen values are reached at 300 to 500 m depth. Oxygen minimum values in the eastern Pacific become suboxic (below 4.5 mmol kg-1) with dissolved oxygen of less than 1mmol kg-1. The OMZ of the eastern Atlantic is not suboxic and has relatively high oxygen minimum values of about 40 mmol kg-1 in the North Atlantic and about 17 mmol kg-1 in the South Atlantic. Taking 45 m mol kg-1 (90 mmol kg-1) as an upper limit for an OMZ oxygen content for sq<27.2 kg m-3 , about 20% (40%) of the North Pacific volume is occupied with an OMZ. The numbers reduce to less than half for the South Pacific relative occupancy (7% and 13%, respectively), while they are considerably less (1% and 7%) for the South Atlantic and (~0% and 5%) for the North Atlantic relative occupancy. The vertical extent of the low oxygen layer is much higher in the Pacific compared to the Atlantic. Thermal domes characterized by upward displacements of isotherms are located near the centers of the OMZ in the northeastern Pacific and Atlantic but are not directly involved in the formation of the OMZs.

The OMZs are a consequence of a combination of ocean ventilation, which supplies oxygen, and respiration, which consumes oxygen. Approximating the oxygen supply in the outcrop area by a turn-over time, that is the ratio of volume to ventilation flux, and the respiration by an average age, based on an apparent oxygen utilization rate, it becomes apparent that the suboxic density range coincides with sluggish ventilation but can not be identified in the respiration based average age. We conclude that ventilation over the outcrop sets the constrain for the suboxic OMZ existence. The results are independent of details of ocean transport. However, the geographical location of the OMZ is determined in first order by: i) the patterns of upwelling, either through Ekman suction or equatorial divergence, ii) the regions of general sluggish horizontal flow at the eastern boundaries, and iii) the regions with high productivity as indicated by ocean color data. However, the extent of areas with high productivity (iii) is far beyond the OMZs indicating that ocean ventilation maintains an oxygen level above what is considered an OMZ.

ORGANIC CARBON DISTRIBUTION IN SEDIMENT CORES FROM THE SOUTHWESTERN MARGIN OF INDIA

DISTRIBUCION DEL CARBONO ORGANICO EN TESTIGOS DE SEDIMENTOS DEL MARGEN SUR-OCCIDENTAL DE INDIA

Pratima M. Kessarkar

National Institute of Oceanography, Dona Paula 403 004, Goa, India, pratimak@nio.org

The monsoons play an important role in controlling the physical and biogeochemical processes along the western continental margins of India. Here, upwelling during the SW monsoon induces high productivity in the surface waters. The oxygen minimum zone (OMZ) impinges on the continental slope at water depths of 150-1200 m, with its intensity and thickness decreasing towards the south. The controls on the formation of organic-rich sediments have been extensively debated for the past several years and the arguments basically revolve around two hypotheses: (a) higher productivity and (b) better preservation of organic matter.

To test these hypotheses, ten sediment cores collected within and below the OMZ from the south-western margin of India were studied. The organic carbon (OC) content decreases from south to north in all the cores occurring either at shallow (286 m-340 m) or deep depths (1380 m-2650 m) or, located within or below the OMZ. Between Mangalore and Cape Comorin, the OC content in core top sediments below the OMZ (4.0%-4.4%) and at the lower boundary of the OMZ (4.9% OC), is higher than within the OMZ (2.9-3.8%) The down-core variations of OC are identical in these cores. Relatively high OC content and low sedimentation rates correspond to the intervals of late Holocene and Last Glacial Maximum (LGM) and, low OC and high sedimentation rates to the early Holocene sediments.

In the present study area upwelling-related productivity seem to vary from south to north along the southwestern margin of India and plays a major role in the distribution of OC. Between Marmagao and Mangalore the high OC content may be the result of better preservation of OC in the OMZ sediments. We suggest that the variations in productivity and down-slope transport of sediment controls the OC enrichment.

PHYLOGENETIC AND METABOLIC DIVERSITY OF MICROBIAL COMMUNITIES ACROSS THE O2/H2S INTERFACE AND ANOXIC ZONE OF THE CARIACO BASIN

DIVERSIDAD FILOGENETICA Y METABOLICA DE LAS COMUNIDADES MICROBIANAS A TRAVES DE LA INTERFAZ O2/H2S Y ZONA ANOXICA DE LA CUENCA DE CARIACO

Vanessa Madrid1,2, María José Rodríguez1, Mary Scranton2, Gordon Taylor2 & Andrei Chistoserdov1

1. University of Louisiana at Lafayette, Louisiana, USA, vmadrida@ic.sunysb.edu

2. Stony Brook University, NY, USA

The Cariaco Basin is the second largest and the only truly marine permanently anoxic basin in the world. It has a depth of up to 1400 m and it is separated from the Caribbean Sea by a sill or shallow ridge about 100 m in depth, which prevents water circulation. Due to this particular bathymetry the vertical and horizontal mixing of the waters is limited, which creates a stratified environment with complete anoxic conditions after a specific depth, depending on the location. The basin's O2/H2S transition zone spans tens of meters and occurs in the aphotic zone, more than 150 m below the 0.1% light incidence level, attribute that makes this environment analogous to most marine sediments. These characteristics make of Cariaco's water column an ideal model for understanding processes across oxic-anoxic interfaces in general. The ecological significance of oxic-anoxic interfaces has yet to be fully explored, but clearly, these environments play an important role in biogeochemical cycles of many elements. In the present work we used and array of culture dependent and independent techniques for studying the microbial communities in the O2/H2S and anoxic zone of the Cariaco basin. Sequences of 16S rRNA genes retrieved from the interface as well as the anoxic zone indicate a vertical succession of several complex chemolithotrophic guilds. 16S rDNA sequences from just below the interface were dominated by sequences closely related to ectosymbionts of hydrothermal vents dwelling invertebrates, referred here as `epsilon symbiont relatives' (`ESR'). The deepest sample had the highest microbial diversity including archaeal and new candidate division sequences. Archaeal sequences are closely related to an archaeon able to oxidize methane anaerobically. Enrichments for autotrophic thiosulfate oxidizing/manganese-oxide reducing bacteria suggest that `ESR' are respiring MnO2 as electron acceptor. Autotrophic thiosulfate oxidizing manganese-oxide reducing bacteria, autotrophic elemental sulfur disproportionating bacteria, elemental sulfur-reducing bacteria and sulfate-reducing bacteria are present in the anoxic zone of the Cariaco Basin. Overall, the composition of microbial communities from the Cariaco Basin resembles that from several deep marine anaerobic sediments. Fingerprinting analysis (DGGE) profiles suggest that bacterial communities at the interface were very different from strictly oxic or deep anoxic zone communities. Interfacial bacterial communities appeared to be dissimilar in composition between locations although several prominent community members appeared in each of the interface samples. However, for each individual station, the microbial guilds from different depths across the O2/H2S transition were very similar to each other with slightly higher bacterial diversities some 20 m below the interface. Community composition data were also correlated with depth profiles of dark CO2 fixation and relevant redox-active compounds. We speculate that these taxa are responsible for observed dark CO2 fixation. The most prominent and ubiquitous bands on DGGE gels belonged to gamma- and delta-proteobacteria. However, a substantial number of minor DGGE bands, which vary from site to site, derive from alpha, gamma, and epsilon-proteobacteria. Comparison of DGGE profiles from several cruises indicated that in recent years the microbial community became more complex and lost one previously prominent epsilon-proteobacterial member. Quantification of genes involved in carbon fixation (RubisCO) and sulfate reduction (dsr) were quantified by real-time PCR. The high copy numbers of RubisCO genes and dsr at and below the interface clearly indicate the importance of redox-interfaces in the carbon and sulfur cycles. Additionally, given that these are extreme environments, unique microbial communities that elicit metabolisms not previously described may likely be found.

THE ROLE OF MICROBIAL COMMUNITIES IN THE BIOGEOCHEMISTRY OF TROPICAL DELTAIC NON-SULFIDIC MOBILE SEDIMENTS OF AMAZON-GUIANA MUD-BELT AND GULF OF PAPUA, PAPUA NEW GUINEA

EL ROL DE LAS COMUNIDADES MICROBIANAS EN LA BIOGEOQUIMICA DE LOS SEDIMENTOS DELTAICOS MOBILES NO SULFUROSOS DEL CINTURON DE FANGO DEL AMAZONAS-GUYANA Y DEL GOLFO DE PAPUA, PAPUA NUEVA GUINEA

Vanessa Madrid1,2, Robert Aller2, Josephine Aller2 & Andrei Chistoserdov1

1University of Louisiana at Lafayette, Louisiana USA vmadrida@ic.sunysb.edu

2State University of New York, USA

Marine deposits such as those studied here differ from typical marine sulfidogenic sediments in that they often exhibit no net sulfide production over extensive depth intervals. Although oxygen penetrates only a few mm below the sediment surface, physical mixing as a result of tidal currents, seasonal winds and local geomorphologic features, periodically reoxidize these deposits to a depth of >70 cm. During remobilization, large amounts of highly weathered and reactive oxidized debris are entrained from overlying waters, and redox conditions reset. Because of the relative abundance of oxidants, this reoxidized sediment layer passes through oxic and NO3- reducing conditions within a day followed by Mn reduction stages for several weeks and then remains in a suboxic Fe reduction stage for up to a year before becoming sulfidic. Since mobile marine sediments are basically deprived of oxygen traditional cultivation methods are inadequate for their study. Cultivation-independent techniques were therefore used for assessing the functional diversity and metabolic activity of microbes in mobile deltaic sediments from two different tropical locales-French Guiana in NE South America and the Gulf of Papua, Papua New Guinea in Oceania. The retrieval of 16S rRNA gene sequences from these environments first hinted at the presence of bacteria potentially involved in chemolithoautotrophic CO2 fixation and sulfur cycles. Also, 16S rRNA sequences revealed that mobile sediments off French Guiana are among the most microbiologically diverse in the world. Direct evidence of involvement of prokaryotes in the sulfur and carbon cycles was studied by characterization of key enzymes involved in carbon fixation and sulfate reduction. Direct evidence of sulfate reduction was found by 35SO4= radiotracer experiments and quantification and cataloging of genes encoding for dissimilatory sulfite reductase (dsr), one of the key enzymes involved in sulfate reduction. The retrieval, characterization and quantification of genes and transcripts of ribulose 1,5-biphosphate carboxylase/oxygenase genes (RubisCO, green-,red-like cbbL and cbbM) provided direct evidence for chemolithoautotrophic CO2 fixation. Gene expression was high and enhanced by frequent mixing of these sediments. These results directly imply that CO2 fixation could be an important source of CO2 removal and thus highlights the importance of redox-interfaces. These environments are highly complex, highly microbiologically diverse with a large percentage of uncultured members. Gene numbers and transcripts of genes studied are correlated with biogeochemical data and the role of different microbial pathways are discussed.

CARBON REGENERATION IN CARIACO TRENCH,S WATER, VENEZUELA, DURING THE PERIOD JANUARY 2002-SEPTEMBeR 2003

REGENERACION DEL CARBONO EN EL AGUA DE LA FOSA DE CARIACO, VENEZUELA DURANTE EL PERIODO ENERO 2002-SEPTIEMBRE 2003

Arístide Márquez1, William Senior1, Gregorio Martínez1, Julián Castañeda1 Frank Müller-Karger2, Ramón Valera3 & Aída Ríos4

1. Department of Oceanography, Oceanographic Institute of Venezuela, Cumana, Venezuela, aristide@sucre.udo.edu.ve

2. University of South Florida, College of Marine Science, St. Petersburg, FL,USA.

3. Marine Research Station of Margarita, La Salle Foundation of Natural Sciences, Punta de Piedras, Nueva Esparta, Venezuela.

4. Institute of Marine Research (CSIC), Vigo, Spain.

In this investigation the regeneration of carbon in waters of the Cariaco Trench is studied following Broecker & Peng's model (1982). This model uses the slope generated from the AT curve and CO2, where CO2 is the concentration of carbon dioxide and AT the total alkalinity. Additionally the primary productivity (PP) is estimated as a measurement of carbon produced by biological activity. The results indicate that the CO2 levels are minimum (1,962 µmol/kg) in the surface layer increasing through the anoxic threshold until a value of 2,451 µmol/kg is reached. At the same time, the primary productivity, was maximum in the first 7 m, with a seasonal cycle that increases the values up to 17 mgC/m3/h in the months of maximum upwelling, i.e., January-April. These increases are reflected in the integrated values, which surpass the 600 g C/m2/año. The regeneration model indicates that, 82% of carbon distribution is controlled by organic carbon from the soft material of the photosynthetic organisms, whereas 18% is of inorganic origin, from the chalky skeletons. Vertically, the regeneration of organic carbon (81-84%) is maximum in the surface layer in agreement with PP values; nevertheless, in the oxic-anoxic interface a second maximum of smaller intensity (70-80%) is detected, which is generated by bacterial processes of decomposition of organic matter that using chemoautotrophic mechanisms. The values regenerated in the anoxic zone are lower than those in the oxic zone because the decomposition under the aerobic conditions is more effective than those under the anaerobic ones.

OXYGEN MINIMUM PHENOMENON AND FISHERIES OF PAKISTAN

EL FENOMENO DE LA MINIMA DE OXIGENO Y LAS PESQUERIAS DE PAKISTAN

Mohammad Moazzam

Marine Fisheries Department, Government of Pakistan, Fish Harbour, West Wharf, Karachi 74000, Pakistan, mmoazzam@eworld.net.pk

Development of an oxygen minimum system is one of the important oceanographic features of the Arabian Sea. Low oxygen zone exists in the Arabian Sea between depths of 500 to 2000 m. With the cessation of monsoon in September, the oxygen minimum layers start moving toward the coastline forcing fishes to moves to shallow waters which results in an increase in fish catches of the local fishing boats. Since the oxygen minimum layers cover most part of the coastline by October/November, the catches of trawlers and bottom set gill-netters drop to a negligible level. An analysis of catch rate of local fishing boats and deep sea fishing vessels operating in waters of Pakistan will be presented which will confirm that the existence and movement of the oxygen minimum layer are the most important factors controlling abundance of fish in the Arabian Sea. The poster will also discuss the catch rates of various species which suggest that some commercially important species seem to be more tolerant to low oxygen and thus their distribution is not affected by the oxygen minimum system.

NITROSOSPIRA SPP. DOMINATE THE AMMONIA-OXIDIZING COMMUNITY WITHIN THE PROTEOBACTERIA IN THE OXYGEN MINIMUM ZONE OFF NORTHERN CHILE

NITROSOSPIRA SPP. DOMINAN LA COMUNIDAD AMONIO OXIDANTE DENTRO DE LAS b-PROTEOBACTERIAS EN LA ZONA DE MINIMO OXIGENO FRENTE AL NORTE DE CHILE

Verónica Molina1, Laura Farías1,2, Osvaldo Ulloa1,2, Homero Urrutia3, Salvador Ramírez1, Pilar Junier4 & Karl-Paul Witzel4

1. Laboratory for Oceanographic Processes and Climate (PROFC), University of Concepción, P.O. Box 160-C, Concepción, Chile, vemolina@udec.cl

2. Department of Oceanography and Center for Oceanographic Research in the Eastern South Pacific (FONDAP-COPAS), University of Concepción, Concepción, Chile

3. Department of Microbiology, University of Concepción, Concepción, Chile.

4. Max-Planck Institute for Limnology, Germany.

Ammonia oxidizing bacteria (AOB) have been found to contribute to the NH4+ removal and NO2- and N2O production in oxygen minimum zones (OMZs). However, so far, little is known about the community structure of AOB and the potential role of specific groups adapted to the low oxygen conditions found in these areas. The composition of AOB from the b-Proteobacteria subclass was studied in the upper oxycline (2-50 m depth; ~200-44 mM O2) and OMZ (50-400 m depth; <10 mM O2) of the eastern South Pacific off northern Chile. This study was carried out through cloning of genes encoding for 16S ribosomal RNA and the ammonia monooxygenase enzyme active subunit (amoA) which catalyses the aerobic oxidation of ammonium to hydroxylamine. Nitrosospira-like from Cluster 1 sequences were dominant in the 16S rDNA clone libraries constructed from both the upper oxycline and within the OMZ. Cluster 1 is exclusively conformed by yet-uncultivated AOB from marine environments. However, a single clone belonging to Nitrosospira-like from Cluster 0 was also found in the OMZ clone library. Cluster 0 groups AOB isolated from sand, soil and freshwater environments. The amoA clone libraries from the upper oxycline were grouped in a subcluster also marine with no cultured representatives. In contrast, all the amoA sequences originated from the OMZ were closely affiliated to cultured Nitrosospira from Cluster 0, and also to other yet uncultured AOB from soil and aerated_anoxic Orbal process plant, coinciding only with the single 16S rDNA sequence found in the OMZ. Our results thus show that the OMZ shares with the upper oxycline a similar type of AOB (i.e., Nitrosospira-like from Cluster 1) at the 16S rDNA phylogenetic level, which is widespread in marine systems, but also presented a particular functional group associated with Nitrosospira-like from Cluster 0, and therefore potentially specialized to the biogeochemical conditions of the OMZ.

THE VARIABILITY OF NATURAL HYPOXIA IN A COASTAL UPWELLING SYSTEM: OCEANIC PHYSICS OR SHELF BIOLOGY?

LA VARIABILIDAD DE LA HIPOXIA NATURAL EN UN SISTEMA DE SURGENCIA COSTERA: FISICA OCEANICA O BIOLOGIA DE LA PLATAFORMA CONTINENTAL?

P.M.S. Monteiro1, 2, A. van der Plas3, V. Mohrholz4, E. Mabille1, A. Pascall1 & W.R. Joubert1

1. CSIR, P.O. Box 320, Stellenbosch, South Africa, pmonteir@csir.co.za

2. Department of Oceanography, University of Cape Town, South Africa

3. NatMIRC, Swakopmund, Namibia

4. Baltic Sea Research Institute Warnemünde, Rostock, Germany

The incidence and scale of natural hypoxia and anoxia in temperate coastal oceans is raising concerns, particularly in the context of emerging uncertainties linked to climate change. Natural hypoxic events can have a devastating scale of impact on fisheries and ecosystem services. These include the major recruitment failure of the Namibian hake stock in 1992-1994, the periodic mass mortalities (>1000 tons) of rock lobsters in South Africa and most recently the dead zones off the Californian and Oregon upwelling systems. Emerging understanding of the incidence and variability of natural coastal hypoxia is divided between two main hypotheses: the biogeochemical oxygen demand linked to locally driven decaying organic matter or physically remotely sourced hypoxic waters. The precise trigger role of either mechanism has remained elusive. Here we report on the first combined methane and oxygen year-long hourly data time series in the Benguela upwelling system. They suggest that these systems may be responding to a complex interaction between the two alternative views. The data show how anoxia, as measured by the changes in dissolved methane, is initially triggered by remote equatorial hypoxic waters after which it can be sustained by a local biogeochemical flux of exported production. Crucially, without a remote trigger the local forcing could not develop anoxic conditions because the physical flux of oxygen would be too high. The robustness of this interpretation is further tested using a 10-year data set (1994-2003) with seasonal and interannual scales of variability. This result highlights the potentially increased vulnerability of temperate upwelling habitats and ecosystem services to pole-ward shifts of the equatorial low oxygen zones. Understanding the complexity of these dynamics should contribute to understanding how coastal upwelling ecosystems and their valuable fisheries may be shaped by climate change.

DENITRIFICATION OVER THE INDIAN SHELF

DENITRIFICACION SOBRE LA PLATAFORMA CONTINENTAL DE LA INDIA

Hema Naik, Wajih Naqvi & P.V.Narvekar

National Institute of Oceanography, Dona Paula, Goa, India, hema@nio.org

The Arabian Sea contains one of the world's three largest mesopelagic oxygen minimum zones (OMZs) within which O2 concentrations are low enough to support denitrification. This makes the Arabian Sea a globally important sink of combined nitrogen. In addition to the perennial open ocean sub-oxic zone, there also exists a seasonal sub-oxic zone over the western continental shelf of India, which is of natural origin. During the southwest monsoon, upwelling brings poorly oxygenated, nutrient-rich subsurface waters over the western Indian continental shelf close to the sea surface. But these waters are generally overlain by thin (~5-10 m thick) fresher water lens resulting from local precipitation making the water column highly stratified. This supports enhanced subsurface biological production that attains the maximal value of ~6 g C m-2 d-1 (highest value observed in the Arabian Sea). The eventual decay of organic matter leads to the removal of residual O2. The facultative bacteria then utilize the NO3- followed by SO42- as oxidants for degrading organic matter. Denitrification over the mid-shelf is often associated with large accumulation of NO2- (up to 16 µM) and N2O (up to ~0.8 µM) usually in the upper portion of the sub-oxic layer, with the removal of oxidized nitrogen forms occurring in the deeper anoxic portion.

Pelagic denitrification rates were estimated from repeat observations at a fixed station (the Candolim Time Series, CATS, site located off Goa at a water depth of ~28 m). The average rate calculated is 0.8 µM NO3- L-1 d-1. The overall rate for the entire shelf experiencing suboxia (area ~200,000 km2) comes to 1.3-3.8 Tg N yr-1, which corresponds to the 4-12% of the denitrification within the perennial sub-oxic zone.

We have also measured the sedimentary denitrification rates (SDR) at depths varying from 29 to 300 m following the acetylene block technique. SDR varied over the range 0.17-1.45 pmole NO3- cm-2 s-1 with the maximum occurring over the mid-shelf. The observed rates are quite modest and comparable with similar estimates from other areas. When extrapolated to the total area of continental shelves in the Arabian Sea (0.51 x 1012 m2), the total benthic denitrification rate works out to be 0.38-3.5 (average 1.33) Tg N yr-1, which is of the same order of magnitude as the pelagic denitrification rate over the Indian shelf. Thus, benthic denitrification over the Arabian Sea continental shelf acts as a moderate sink for combined nitrogen. Although denitrification has a potential to counter inputs of combined nitrogen due to human activities, the fact that a substantial fraction of nitrogen is reduced to N2O means that this process is of little environmental benefit.


THE 18O/16O RATIOS OF DISSOLVED OXYGEN IN THE PHILIPPINE SEA

LAS RAZONES 18O/16O DEL OXIGENO DISUELTO EN EL MAR DE FILIPINAS

N. Nakayama, H. Obata & T. Gamo

Ocean Research Institute, The University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokio 164-8639, Japan, noriko@ori.u-tokyo.ac.jp

The delta-18O is a useful tracer for chemical and biological processes not linearly related to oxygen utilization. The variations of delta-18O, therefore, will give us information about processes occurring in the interior ocean independently from dissolved oxygen itself. The purpose of this study is to quantify the physical and biological processes maintaining the OMZs in the Philippine Sea. We measured the 18O/16O ratios of oxygen dissolved in seawater of the Philippine Sea along 137°W collected between 2 to 13 June, 2006 on R/V Hakuho-Maru. Seawater samples were drawn from Niskin bottles mounted CTD rosette. For the isotope measurements, approximately 150 mL of water were collected in 300 mL pre-evacuated bottles that have been poisoned with 45ìl of saturated HgCl2 solution. These samples were prepared and analyzed by FinniganTM-DELTAplusXP according to the modified procedure described by E Barkan and B. Luz. The depth profile of delta-18O and dissolved O2 demonstrate the fundamental feature of the delta-18O distribution in seawater, enrichment with decreasing O2 concentration, and vice versa .We apply a well-known diffusion-reaction model (Kroopnick and Craig, 1976) to the water of the Philippine Sea to obtain the oxidation fractionation factor. The isotopic fractionation factor during the respiration process (ar) was determined to be 0.984 from the relation between vertical profile of the O2 concentration and delta-18O values.

OXYGEN SUPPLY TO THE OXYGEN MINIMUM ZONE BY THE PERSIAN GULF WATER AND ITS IMPACT ON DENITRIFICATION IN THE ARABIAN SEA

APORTE DE OXIGENO DEL AGUA DEL GOLFO PERSICO A LA ZONA DE MINIMO DE OXIGENO Y SU IMPACTO SOBRE LA DENITRIFICACION DEL MAR DE ARABIA

P.V. Narvekar & S.W.A. Naqvi

National Institute of Oceanography, Dona Paula, Goa, India, narvekar@nio.org

One of the most salty water masses in the oceans is formed in the Persian Gulf due to the large excess of evaporation over precipitation and river runoff. The Persian Gulf Water (PGW) flows out of the Gulf and spreads along sq = 26.2-26.8 at depths ranging from 200 to 350 m in the northern and central parts of the Arabian Sea. Apparently, isolated surveys do not give a complete picture of physico-chemical processes within the PGW and reports on the seasonal variations are found lacking in the literature. We have generated substantial data sets at fixed sites in the Arabian Sea to understand seasonal/inter-annual variations in both the T-S characteristics and chemical properties of the Persian Gulf core layer. Here we examine these data collected during 11 cruises spanning a period of 12 years (1992-2004). Going by the T-S distributions, the PGW mass was generally present in the Gulf of Oman, northern and central Arabian Sea. Seasonal trends in data were resolved by averaging values from the salinity maximum. The penetration depth of the PGW, judged from its salinity maximum, varied from 186 to 382 m. While both salinity and temperature decreased away from the source, the depth of penetration increased. The water is most dense during winter when the average temperature and salinity are the lowest.

Despite the advection from the south that is mostly responsible for the renewal of subsurface water, a lower supply and an enhanced demand for O2 combine to produce very intense O2 deficiency (Winkler O2<4 µM) over a wide depth range (150-1000 m) in the northern and central Arabian Sea. As compared to the waters of the southern origin, the volumetric contribution of the PGW to the subsurface renewal in the Arabian Sea is low. However, it makes a very significant impact on the O2 distribution. An O2 maximum

is often associated with the PGW in the northeastern Arabian Sea. We observed that O2 attained concentrations maxima of 10-12 µM during SW monsoon at two sites closer to the source. These levels are high enough to suppress denitrification. At the station located closest to the source of PGW, where a minimum in nitrite (NO2-) was found at the salinity peak in most cases, this effect appears to be most pronounced during the SW monsoon period. No intensification of denitrification appears to have occurred at this site since the GEOSECS survey carried out in 1977. Short-term time series measurements revealed large variations in T-S properties as well as chemical composition of the PGW. Variation in salinity was responsible for the associated rise and fall in density and hence the penetration depth of the water mass.

BIOGEOCHEMICAL ANOMALIES IN THE OMZ OFF CHILE

ANOMALIAS BIOGEOQUIMICAS EN LA OMZ A LO LARGO DE CHILE

A. Paulmier1, D. Ruiz-Pino1, V. Garcon2, L. Farias3 & O. Ulloa3

1. Université P&M Curie, 13 rue Crespin du Gast, 75011, Paris, France paulmier@ccr.jussieu.fr

2. LEGOS/CNRS, Toulouse, France

3. Department of Oceanography, Laboratory of Oceanographic and Climate Processes PROFC, University of Concepción, Concepción, Chile

The OMZs could be considered as an analog of reduced environment where life appears. Which biogeochemical perturbations related to the C and N cycles would induce the O2 deficit? Four cruises and a monthly monitoring (2000-2002) off Chile (21°-36°S) have included simultaneous low O2, carbon system parameters (CO2, pH, alkalinity) and N2O measurements. The Chilean OMZ is characterized by a shallow (5-80 m) and intense (>1 µM/m) oxycline intercepting the euphotic layer, and a core reaching the lowest O2 (<1 µM). The Total CO2 concentrations (up to 2500 µM) are among the highest in the intermediate ocean. The N2O shows a subsurface peak (>120 nM) up to 30% more intense than the maximal reported in open ocean of the Arabian Sea OMZ. Thus, the OMZ in the eastern South Pacific (ESP) could constitute a CO2 reserve (Carbon Maximum Zone: CMZ) with high N2O production at the oxycline, which could potentially induce a huge greenhouse gases source (12.2 GtCeq/yr), twice higher than the total ant hropogenic (CO2+N2O) releasing per year. In addition, the Chilean OMZ presents an extreme acidification reaching the lowest pH (7.5 SWS) and intense alkalinity variations (>100 µeq/L). The core of the OMZ and CMZ are locally maintaining thanks to a remineralization 2-5 times higher than in the oxygenated ocean. This remineralization leading to the OMZ formation paradoxally needs O2, and thus occurs at 75% in the oxycline, the biogeochemical OMZ "engine". The highest O2 consumption (active phase) occurs preferentially during weak stratification (O2 >30 µM) as offshore, spring and fall, and then shifts to passivity (lower O2 consumption), suggesting an OMZ remineralization control by O2 availability. This OMZ remineralization should be explored, considering the oxic/suboxic/well-lit oxycline allowing a possible co-existence of aerobic/anaerobic, photic/aphotic and autotrophic/heterotrophic processes, which usually occur at different depths: aerobic remineralization (70%); nitrification (20%); photosynthesis (6%); denitrification (4%). The highest N2O would be due to a possible denitrification and nitrification coupling, and acidification and alkalinity variations mainly induced by the intense aerobic remineralization. All these chemical OMZ anomalies would modify the `classical' oxygenated ecosystem, as the molar ratios (C/O=1.14±0.3; C/N=9±4) evaluated at the oxycline, up to 1.5 times higher than the Redfield ratios, could show. The ESP ecosystem, because of low O2 and pH near the surface and high heterotrophic bacterial activity, could become less productive and induce fewer fisheries.

HYDROGEN SULPHIDE ALONG THE NAMIBIAN COAST

SULFURO DE HIDROGENO A LO LARGO DE LA COSTA NAMIBIANA

K. R. Peard1, B. Currie2, K-C. Emeis3, S.J. Weeks4 & R. Endler5,

1. Ministry of Fisheries and Marine Resources, Lüderitz Research Station, P.O. Box 394 Lüderitz, Namibia, kpeard@mfmr.gov.na

2. Ministry of Fisheries and Marine Resources, Swakopmund, Namibia

3. Institut für Biogeochemie und Meereschemie, University of Hamburg, Hamburg, Germany

4. Pew Institute for Ocean Science, University of Queensland, Australia

5. Institut für Ostseeforschung, Warnemüende, Germany

Hydrogen sulfide outbreaks are regular features along the Namibian central coast. Intense and continuous primary production downstream of the world's strongest upwelling cell results in decay of phytoplankton on the seabed, forming a thick belt of diatomaceous mud along the inner shelf, where hydrogen sulfide and methane form in high concentrations close to the sediment surface. Sediment parasounding has revealed extensive gas pockets close to the sediment surface of these muds. Studies show doming as well as collapsed crater formation from gas gas-escape structures.

The ready supply of hydrogen sulfide at the sediment-water interface fuels dense mats of large sulfur bacteria (mainly Thiomargarita namibiensis and Beggiatoa species). These bacteria play the vital role of effectively regulating diffusion of sulfide into the overlying water. The relative abundance and distribution of these sulfur bacteria over the Namibian inner shelf showed considerable temporal and spatial variability over the period 2000-2004.

On occasions when hydrogen sulfide pervades the entire water column, causing anoxia and severe hypoxia, the surface water is discolored by dense microgranules as sulfide is oxidized to elemental sulfur. This discoloration is detected by satellite images to provide valuable information on the locality and extent of events.

oxygen MINIMUM IN THE EASTERN Japan Sea

EL MINIMO DE OXYGENO EN EL MAR ORIENTAL DE JAPON

Vladimir Ponomarev1, Lynne Talley2, Pavel Tishchenko1, Sergey Sagalaev1, Natalia Rudykh1, & Alexandr Nedashkovskii1

1. Pacific Oceanological Institute (POI), Far Eastern Branch of Russian Academy of Science, Baltiyskaya Street, Vladivostok, 690041 Russia, ponomarev@poi.dvo.ru

2. Scripps Institute of Oceanography (SIO), La Jolla, California, USA.

Both oceanographic and hydrochemical characteristics, including dissolved oxygen, of the Japan Proper Water (JSPW) have changed during the second half of the 20th century and especially during last decade of that century. This study is focused on the analyses of observation data on the Oxygen Minimum Layer (OML) and Oxygen Minimum Zone (OMZ) over the deep slope of the eastern Japan Sea (EJS) basins as found during Joint International Project of the Japan/East Sea Study 1999- 2000 (SOI, USA; FERHRY, POI, Russia). As earlier described, these OML and OMZ are similar to those existing over the slope bottom of the Arabian Sea.

The OMZ in the EJS is observed over the slope bottom and within the depth band corresponding to the deep Oxygen Minimum Layer. Oxygen concentrations about an absolute minimal value of 196.8 µM/kg for the JSPW are found in the near_bottom boundary layer over the north continental slope at depth 1078 m in the Tatarskii Strait. This is an unexpected fact because the Tatarskii Strait was earlier suggested as a main region for the deep basin bottom water formation. The maximal oxygen value over the trough of the Tatarskii Strait axes is 251.4 µM/kg, observed after winter ventilation during the same cruise at a depth of 1081 m in March 2000.

An expected seasonal variation is revealed in the water column from the upper mixed layer to the near-bottom boundary layer over the central area of the deep trough adjacent to the Tatarskii Strait. In the layer 0-600 m the difference between oxygen values in early spring (March) and in summer (August) over the trough axis is in the range of 20-40 µM/kg with a maximum of about 35-40 µM/kg at depth of 400-500 m. In the deep layer, 650-1350 m, this difference is about 15-20 µM/kg and in the thick bottom layer, 1350-1600 m it is about 10-15 µM/kg. The vertical density stratification substantially decreases from August to March but during the observation period it is definitely stable in deep areas under the upper mixed layer even in March. Nevertheless, the minimal oxygen value in near-bottom layer at the same section in the winter cruise of 2000 (196.8 µM/kg), is lower than in the summer cruise of 1999 (198.2 µM/kg).

Similar oxygen concentrations (197.8 µM/kg) were also found in the deep near-bottom layer of the southern eastern Japan Sea (EJS) area over the south-southwest Ulleung Basin deep slope situated in the subtropical sea area. However, the depth of this oxygen minimum pattern is about 2000 m, that is deeper than in the Tatarskii Strait adjacent area of the sub-arctic EJS zone. So, the same minimal oxygen values in the OMZ are observed in both sub-arctic and sub-tropic deep EJS regions characterized by different ventilation intensity. The prevailing OMZ over the deep slope in the certain sub-arctic EJS areas is caused by both increased (negative) oxygen sink in the boundary layer over the deep slope and upwelling of the bottom water from the deep basin during the deep water ventilation over the axes of the Tatarskii Strait trough (in comparison with the oxygen source related to the deep _slope- convection and water exchange with the upper sea layers). This could be controlled by benthic activity and organic matter decomposition at the top of sediments like in the Arabian Sea (according to the known publications). The areas with extreme OMZ are also characterized by high biological productivity in the upper layer and high organic matter transport to the deep basin slope from the shelf and seasonal pycnocline. It seems that the oxygen sink at the top of the sediment in the OMZ impacts the Deep Oxygen Minimum Layer formation and evolution in the eastern Japan Sea. Decadal variability of the OML, as well as influence of ventilation and circulation processes in different EJS areas is discussed.


PRELIMINARY OBSERVATIONS ON BIG BENTHIC BACTERIA COLLECTED OFF ANCON AND
CALLAO, PERU

OBSERVACIONES PRELIMINARES SOBRE GRANDES BACTERIAS BENTONICAS COLECTADAS FRENTE A ANCON Y AL CALLAO, PERU

Luis Quipúzcoa1, Carola Espinoza2, Juan Tarazona3 & Víctor A. Gallardo2, 4

1. Institute of the Sea of Peru (IMARPE), P.O. Box 22, Callao, Peru, lquipuzcoa@imarpe.gob.pe

2. Center for Oceanographic Research in the Eastern South Pacific (FONDAP-COPAS), University of Concepcion, Concepcion, Chile

3. Department of Hydrobiology and Fisheries, Faculty of Biological Sciences, University of San Marcos, Lima, Peru.

4. Department of Oceanography, University of Concepcion, Concepcion, Chile

The oxygen minimum zone of the eastern Pacific is one of the most extensive one. Recent analyses of the bathymetric distribution of dissolved oxygen data however indicate that along this region there are two areas, one north and one south of the Equator where these oxygen minima impinge the shelf. The northern area extends from about 5°N to about 25°N, while the southern area extends from about 5°S to about 37°S. Based on the working hypothesis that such oceanographic conditions might favor the occurrence of similar giant bacterial communities as those found on the shelf off central and northern Chile (off Iquique and Mejillones, northern Chile) and embayments (Bay of Concepcion and the Gulf of Arauco, central Chile), we carried out a benthic surveys off Peru (Independence Bay and off Callao). We here report on the preliminary findings from these Peruvian samplings. Both surveys utilized a monocorer for the retrieval of undisturbed samples. In both sampling areas strongly enriched and reduced sediments were encountered. Although not forming a defined mat, giant bacteria and other microbes were encountered in the sediments, among them: (1) large filaments containing numerous trichones of Thioploca araucae, (2) sheathes containing a variety of large filamentos bacteria of different diameters, (3) filamentous, sulfur-granule-containing, non-vacuolated Beggiatoa-like trichomes, (4) short filamentous granulose forms, (5) spirochaetes, (4) long, filamentous, non-granulose, green-pigmented `anacondas', (6) a host of filiform non-granulose filaments, and (7) protists, e.g., diverse ciliates and flagellates. In summary, in the sediments under the OMZ off Peru, similar microbial communities as those found under the OMZ off central, northern Chile and the Golfo Dulce in Costa Rica, were observed, indicating that this microbial system, including giant filamentous bacteria, is more widely distributed than previously imagined, opening new lines for regional microbial cooperative research.

HYDRODYNAMICS SIMULATION BY ENVIRONMENTAL FORCING IN THE BAY OF PARACAS, PISCO-PERÚ

SIMULACION DE LA HIDRODINAMICA EN LA BAHIA DE PARACAS, PISCO, PERU, UTILIZANDO FORZAMIENTO AMBIENTAL

J. Quispe1 , I. Ramírez2 , O. Morón3 , J. Tenorio3

1. Center for Research on Oceanographic and Fisheries Biology Modeling, Unit for Physical Oceanography , Institute of the Sea of Peru, P.O. Box 22, Callao, Perú , jquispe @imarpe.gob.pe

2. Department of Physical Oceanography, Center for Scientific Research, Ensenada B.C., Mexico

3. Directorate of Oceanographic Research, Unit of Physical Oceanography, Institute of the Sea of Perú , Callao, Perú

The aim of this study is to characterize the hydrodynamics of the Bay of Paracas (13°40' S, 76°20' W) located in Pisco, Perú. The three-dimensional hydrodynamic model ELCOM (Estuary and Lake Computer Model) was developed by B.R. Hodges from the Centre Water Research (CWR), of the University of Western Australia (UWA). In order to use ELCOM model in the Bay of Paracas, several campaigns of field measurements were performed to obtain the bathymetry of the bay and hydrographic data to establish initial and boundary conditions for the model. The model is solved on a rectangular Arakawa-C grid. The ELCOM model considers the Navier-Stokes equations with hydrostatic and Boussines approximations and the transport equation use turbulent viscosity in the horizontal.

The hydrodynamics simulation solves the momentum conservation equations for incompressible fluids using a semi-implicit scheme adapted from the family of TRIM models, which is based on the Euler-Lagrange quadratic method for momentum advection with a solution of conjugated gradient for the free surface. The size of the Cartesian rectangular grid (dx = dy) was 71 m. The model was forced with time series of tide, solar radiation, wind speed and direction, air temperature and relative humidity. Different initial and boundary conditions were imposed to the model to analyze its ability to reproduce environmental coastal conditions in the bay. Results comprise current velocities and temperature. The model includes both baroclinic and barotropic components, rotational effects, tide forcing, wind, surface heating and salt transport. Three-dimensional numerical simulations were use to investigate the behavior of the currents and temperatures by environmental forcing. Simulations are presented and compared with field data. These results contribute to a better understanding of the current and temperature variability in the Bay of Paracas.


NUMERICAL MODELING OF HYDRODYNAMIC PROCESSES FORCED BY WIND AND TIDE IN THE PARACAS BAY, PISCO-PERÚ

MODELADO NUMERICO DE LOS PROCESOS HIDRODINAMICOS FORZADOS POR EL VIENTO Y LAS MAREAS EN LA BAHIA DE PARACAS, PISCO-PERU

Jorge Quispe1 & Emmanuel Guzmán2

1. Institute of the Sea of Perú (IMARPE), P.O. Box 22, Callao, Perú, jquispe@imarpe.gob.pe

2. Universidad Nacional Mayor de San Marcos, Lima, Perú

The aim of this research is to study the hydrodynamics of the Paracas Bay, located in the province of Pisco, Perú. The model employed was the Princeton Ocean Model (POM), which was developed by George Mellor and Allan Blumberg at the Geophysical Fluid Dynamics Laboratory (GFDL). POM is a sigma coordinate model and solves the basic equations of fluid mechanics using an "Arakawa C" difference scheme for the horizontal grid. To establish the initial and boundary conditions hydrographic, oceanic and meteorological data were acquired and incorporated into the model to perform the simulations.

The hydrodynamic simulations were performed for 30 days using a Cartesian rectangular grid dx = dy = 390 m and time step dt = 40 s. The model was forced with time series of tide (with harmonic constituents) and winds (velocity and direction). The simulation scenes include the three-dimensional barotropic answer, rotational effects, and the results show the current fields (velocity and direction) in the bay. Three-dimensional numerical simulations were used to investigate the behavior of current dynamics and temperature by environmental forcing. Simulations are presented and compared with field data. The results contribute to a better understanding of current and temperature variability in the Paracas Bay.

SEASONAL AND ANTHROPOGENIC INFLUENCES FOR THE DECREASE IN DISSOLVED OXYGEN IN CIENFUEGOS BAY, CUBA

INFLUENCIAS ESTACIONALES Y ANTROPOGENICAS EN LA DISMINUCION DEL OXIGENO DISUELTO EN LA BAHIA CIENFUEGOS, CUBA

Mabel Seisdedo & Alain Muñoz

Cienfuegos Center for Enviromental Studies, Cienfuegos 55100, Cuba. mabel@ceacgrn.perla.inf.cu

Cienfuegos Bay constitutes one of the most important ecosystems in Cuba because it is a decisive element in the industrial development. Along the margins of the bay there are important industries, as well as other uses are developed, among them: fishing, tourism, nautical sports and the urban one. Often, these aquatic systems are threatened because anthropogenic activities transform them into receivers of all kinds of waste. Thus, since 1990 this ecosystem has a Hydrological Monitoring Program which allows the control of its waters quality and contributes to the management of this resource.

The objective of this work was to study the seasonal and anthropogenic influences on the decrease of dissolved oxygen in this bay. To study the seasonal influence, the correlation levels between the annual averages of precipitation, salinity and dissolved oxygen concentrations for the period 1990-2000 were analyzed. A cluster analysis was performed in order to study the associations of these two parameter behaviors per month. On the other hand, to analyze the anthropogenic influence the spatial distribution of the dissolved oxygen was studied taking into account the average concentrations for every season.

The correlation coefficients among average values of precipitation and of dissolved oxygen in bottom layer (r=-0.81, p<0.01) and among average values of precipitation and surface salinity (r=-0.86, p<0.01) were obtained. Significant correlations found can be related to the stratification process of this system, which is associated to the largest incorporation of suspended organic matter by silts removal during the rainy period. The degradation of the incorporated matter leads to a significant reduction (t=9.4, p <0.05), from average concentrations of dissolved oxygen from 5.77 mg/L to 3.38 mg/L, being this last value lower than 5 mg/L, criteria for good quality waters according to the NC.25:1999; while the relationship between the surface salinity and precipitation levels showed the influence of rain on the salinity decrease in the surface layer from average of 33.9 to 28.7, due to the increment in the contribution of fresh water to this system.

The cluster analysis among the monthly behaviors for both hydrological parameters defined two groups. The first group included the characteristic months of the dry period (November-May), and the other group included the months corresponding to the rainy period (June-October).

The spatial distribution of the oxygen that took into account both seasons, besides reflecting the seasonal influence, showed the positive influence in the areas near the channel entrance due to the exchange with waters of the adjacent sea, while the other areas were more affected by anthropogenic activities; the average concentrations in the deepest layer were even lower than 2 mg/L and on the other hand, the quick recovery of the ecosystem in the dry period.


FUNGAL BIODIVERSITY IN THE ANOXIC COASTAL MARINE SEDIMENTS OFF GOA, INDIA

BIODIVERSIDAD FUNGAL EN SEDIMENTOS MARINOS COSTEROS ANOXICOS COSTA AFUERA DE GOA, INDIA

J. Cathrine Sumathi, C.Raghukumar & S. Raghukumar

National Institute of Oceanography, Dona Paula-Goa 403 004, India, cathrine@nio.org

The marine sediments harbor a large diversity of microbes and the waters above it influence its biodiversity, they replenish the nutrients and supply oxygen. Sediments underlying oxygen-depleted waters are deprived of the regular oxygen supply and microorganisms living in these regions adapt alternate modes of respiration. The denitrifying bacteria can utilize nitrate and nitrite as the final electron acceptor in their respiratory cycle and release nitrogen gas to the atmosphere. Bacteria in the denitrification process reduce nitrate to nitrite and the reaction is carried out by the enzyme dissimilatory nitrate reductase (nar), nitrite is further reduced to nitric oxide by dissimilatory nitrite reductase (nir), nitric oxide reductase (nor) can reduce nitric oxide to nitrous oxide and the final step of nitrogen gas formation is catalyzed by the enzyme nitrous oxide reductase. The formation of nitrogen gas in the marine environment is a major sink of the fixed nitrogen and has a special significance. Fungi are also capable of being involved in the denitrification process and their role in the grassland ecosystem based on substrate-induced respiratory inhibition has shown that they account for nearly 80% of the nitrous oxide production. Screening of fungal isolates has shown that all the major groups of fungi are capable of denitrification process, though they predominantly form only nitrous oxide. Ammonia fermentation is another mode of alternate respiration observed in fungi during complete anoxic conditions. Studies on the denitrifying activities of Fusarium oxysporum have shown that they express diversified pathways of nitrate metabolism in response to environmental O2 tension, ammonia fermentation under anoxic conditions, denitrification when hypoxic, and oxygen respiration under aerobic conditions; thus showing that it is an eukaryote that can use a multimodal type of respiration (or ATP-producing) system to rapidly adapt to changes in the oxygen supply.

The Indian Ocean is a biogeochemically active region influenced largely by the southwest and northeast monsoon, which leads to upwelling and high productivity in these regions. A combination of high productivity and limited mixing leads to the development of a mid-water oxygen minimum zone. Apart from this, a seasonal anoxic zone in the coastal waters on the western Indian shelf has also been observed to develop during June to December (late summer to autumn), with the maximum intensity in September and October (2000). Low mid-water oxygen concentrations lead to reduction in consumer utilization and, as a result, much of the organic matter reaches the seabed relatively undegraded and impinges its effect on the seabed. Global quantification of naturally occurring hypoxic seabed, reveals that 764,000 km2 of shelf and sea floor is under the influence of the hypoxic overlying waters, where dissolved oxygen is 0.2 mL L-1; over half (63%) occurs in the Indian Ocean (Arabian Sea and Bay of Bengal). The coastal anoxic zone extends over the continental shelf, at shallower depths and directly influence on the sediments. Sedimentary denitrification in the continental shelf region is estimated to be 0.4 to 3.5 Tg N y-1. In our preliminary survey in this region we have studied the distribution of fungi in the anoxic coastal sediments, which proves to be a potent niche to study eukaryotic denitrification. The fungal biomass in the sediment was quantified using the fluorescent brightner (Calcoflour) to stain the fungal hyphae. Isolation of fungi was also carried out, and these isolates were screened for their ability to utilize nitrate and (or) nitrite under anoxic conditions. The results in comparison to the well-studied fungus Fusarium oxysporum will be discussed.

MODELING THE OCCURRENCE OF HYDROGEN SULFIDE IN THE SURFACE WATERS OFF NAMIBIA

MODELANDO LA OCURRENCIA DE SULFURO DE HIDROGENO EN LAS AGUAS SUPERFICIALES DE NAMIBIA

Martin Schmidt & Stefan Schäfer

Leibniz Institute of Baltic Sea Research Warnemünde, Rostock, Germany, martin.schmidt@io-warnemuende.de

The ecosystem of the Benguela Upwelling Area off Namibia experiences sporadic events with hydrogen sulfide in the water column, which could be even observed remotely from satellites. The processes which govern such events are investigated by means of a coupled biogeochemical model. The ocean model is based on the Modular Ocean Model (MOM-31), GFDL. The ecosystem component model is derived from the ERGOM code and is embedded in the ocean model. It considers the nitrogen and phosphorus cycle, the oxygen cycle and partially the sulfur cycle in the water column and in the sediment as well. It comprises primary producers, zooplankton, detritus and sediment.

A typical feature off Namibia is a thick mud belt as the result of high primary production facilitated by the nutrient supply from the more or less permanent upwelling due to the trade winds. Usually, the near bottom water on the Namibian shelf is ventilated by the poleward undercurrent and the wind driven Ekman compensation current, which is oxygen-depleted but carries ample nitrate. Hence, oxygen or nitrate is available for bacterial mineralization of organic matter. Occasionally, in response to relaxed trade winds these currents may weaken or disappear. Hence, if also nitrate is exhausted, sulfate is used as oxygen source and hydrogen sulfide is released, which may be upwelled with intensifying trades.

The model was run over six model years and validated with field data from several cruises. It resembles temperature and salinity distribution and the currents in the Benguela Upwelling System. A sediment distribution develops similarly to the observed mud belt. The model is able to reproduce hypoxia at the shelf and shows occasional hydrogen sulfide in the water column. The relevance of several processes for the ecosystem dynamics is shown and the sensitivity to varying reaction rates and model parameters is investigated.

OBSERVING AND MODELING THE OXYGEN MINIMUM ZONE IN THE EASTERN TROPICAL NORTH ATLANTIC

OBSERVACION Y MODELACION DE LA ZONA DE MINIMO OXIGENO EN EL ATLANTICO TROPICAL NOR-ORIENTAL

L. Stramma, P. Brandt, C. Eden, J. Fischer, A. Körtzinger, M. Visbeck

IFM-GEOMAR Leibniz-Institut fuer Meereswissenschaften, Duesternbrooker Weg 20, 24105 Kiel, Germany, lstramma@ifm-geomar.de

In the eastern tropical Atlantic Ocean an oxygen minimum zone (OMZ) exists in the area south of the Cape Verde Islands close to the Guinea Dome region. The OMZ extents from about 200 m to 900 m with the minimum located at the boundary between the Central Water and the Antarctic Intermediate Water. The North Atlantic OMZ is weaker than the corresponding OMZ's in the Pacific and the North Indian Ocean. An open question is the role of oxygen supply by the two eastward current bands of the North Equatorial Countercurrent as well as other zonal current bands for the relative weakness of the OMZ. Ship sections in July 2006 along 23°W south of the Cape Verde Islands and at 18°N with CTD, oxygen and nutrients measurements are used to describe the spatial distribution of the OMZ in the eastern tropical Atlantic. The oxygen minimum is located at about 450 m depth while phosphate and nitrate maxima are observed underneath at about 750 m depth. Related shipboard ADCP measurements of these cruises reaching down to about 1200 m depth as well as ARGO float trajectories are used to investigate supply and drainage paths of the OMZ. The zonal tropical flow structure appears to be of large importance for the ventilation and drainage of the oxygen minimum zone.

The simulated eastern equatorial zonal flow structure in an eddy-resolving FLAME model version with high horizontal resolution was coupled to a simple nitrate-based pelagic ecosystem model interacting with simulated O2 and CO2 concentrations assuming constant Redfield-stoichiometry. In the model results at 23°W a highly structured oxygen field shows up where the eastward flow appears to be linked to local O2 maxima while the westward flow is linked to local O2 minima. This confirms the observed role of the zonal currents for the ventilation and drainage of the OMZ.

Enhanced observations in the OMZ of the tropical eastern North Atlantic are planned for the next few years with oceanographic and biogeochemical measurements including a tracer release experiment, accompanied with high resolution modeling efforts.

LIVING (STAINED) BENTHIC FORAMINIFERA IN RECENT SEDIMENTS WITHIN AND BELOW THE OXYGEN MINIMUM ZONE OFF CONCEPCION, CENTRAL CHILE (~36ºS)

FORAMINIFEROS BENTONICOS VIVOS (TEÑIDOS) EN SEDIMENTOS RECIENTES DENTRO Y BAJO LA ZONA MINIMA DE OXIGENO DE CONCEPCION, CHILE CENTRAL (~36º)

Raúl Tapia1, 2, Carina B. Lange2, 3 & Margarita Marchant4

1. Graduate Program in Oceanography, Department of Oceanography, P.O.Box 160-C, University of Concepción, Concepción, Chile rtapia@udec.cl

2. Center for Oceanographic Research in the Eastern South Pacific (FONDAP-COPAS), University of Concepción, Concepción, Chile

3. Department of Oceanography, University of Concepción, Concepción, Chile

4. Department of Zoology, University of Concepción, Concepción, Chile

We examined the effects of bottom oxygen conditions and organic matter availability on the vertical distribution of living (Rose Bengal-stained) benthic foraminifera (>180 mm fraction) within 10-cm sedimentary columns from three stations along a bathymetric transect off Concepción, Chile (Sta. 18 = 88 m, Sta. 26 = 120 m, and Sta. 40 = 1030 m water depth) that includes sites within and below the Oxygen Minimum Zone. Calcareous foraminifera dominated the three stations. Onshore-offshore pattern revealed overall highest foraminiferal densities within the shelf Stas. 18 and 26 where bottom water dissolved oxygen was lowest (<1 ml L-1) and sediment labile organic matter was greatest. Within the sediment column, maximum abundances (50 and 60%) of living organisms were found in the first centimeters at o rganic-rich and oxygen-poor shelf stations 18 and 26 (average living depth = 1.08 cm and 1.86 cm, respectively), in contrast to the well-oxygenated slope station 40, where 70% of living foraminifera was observed deeper than the first centimeter (average living depth = 2.26 cm). The number of species and size of organisms increased offshore.

THE EASTERN TROPICAL PACIFIC OCEAN OF COLOMBIA: THE CHALLENGE OF STUDYING THE OXYGEN-DEFICIENT WATER SYSTEM

EL PACIFICO TROPICAL ORIENTAL DE COLOMBIA: EL DESAFIO DEL ESTUDIO DEL SISTEMA DE AGUAS DEFICIENTES EN OXIGENO

José Valencia-Gasti1, Efraín Rodríguez-Rubio2 & Alan Giraldo-López1, 2

1. University del Valle, Department of Biology, Cali, Valle, Colombia, oceanografia@univalle.edu.co

2. Research Group for Oceanographic and El Niño Phenomenon Studies, Division of Operational Oceanography, Center for the Control of the Contamination in the Pacific - CCCP-DIMAR, San Andrés de Tumaco, Nariño, Colombia.

Knowledge about physical and chemical properties of the water is a key element to the understanding of the transformation of particulate matter in the water column of the ocean. The ocean-atmosphere interaction in the eastern Tropical Pacific of Colombia (ETPC) generates that dissolved oxygen concentration (O2D) in the surface layer would be relatively high (>4.5 mL L-1), while in the subsurface zone (100 to 150 m) dissolved oxygen can reach values near suboxic levels (<0.5 mL L-1). During two oceanographic cruises in the ETPC (Pacific XLI _ September 2005 and Pacific XLII _ March 2006) on board ARC Malpelo, a water sampling procedure was carried out on 42 stations, at standard depths, in order to evaluate the O2D concentration dynamic in the basin and the variability along water column. Furthermore, the variability of temperature, salinity, density, nutrients and Chlor-a in a similar spatial and temporal scales was evaluated. During September a strong stratification in the water column was registered, detecting the oxycline at 30 m depth, while during March the oxycline was shallower (10 m) than in September. The registered O2D decayed gradually with increasing depth to values near 1 mL L-1 at 130 m depth during September and at 60 m depth in March. Considering the hydrodynamic characteristics of the study zone, the O2D concentration would be affected by: 1) local upwelling patterns at the northern portion of the study zone, and 2) the intensification of the Colombian Current during March due to the increment of the Southern Trade Winds. Both processes increase the availability of limiting nutrients (Nitrate and Phosphate) to phytoplankton, with the consequent increment of surface O2D product of photosynthesis processes. It is important to emphasize that N: P rate varied between September and March from 7.40:1.00 to 5.12:1.00, with an increased the oxygen consumption during March of 119 to 185 mol of oxygen by each mol of regenerated phosphate. This result suggests that the Colombian Current could be a potential center for particulate matter remineralization. This process would be modulated by the temporary contribution of nutrients to this system from coastal estuarine zones and the direct influences of the local pattern of circulation along near shore. These are research results from an instantaneous vision of the system at two different times, therefore the general answer of the system to big scale forces, like the ENSO, are not considered.

CLIMATE-BIOGEOCHEMICAL INTERACTION IN THE TROPICAL OCEAN: A RESEARCH CENTRE PROPOSAL AT THE UNIVERSITY OF KIEL

PROPUESTA PARA LA CREACION DE UN CENTRO DE INVESTIGACION EN LA UNIVERSIDAD DE KIEL PARA EL ESTUDIO DE LA INTERACCION CLIMATICA-BIOGEOQUIMICA EN EL OCEANO TROPICAL

D. Wallace & R. Schneider

Christian-Albrechts University Kiel, Kiel, Germany, dwallace@ifm-geomar.de

A special research center (Climate-Biogeochemical Interactions in the tropical oceans) which is currently proposed at the University of Kiel will be presented. The overall goal of the center is to improve our understanding of the coupling of tropical climate variability and circulation with the ocean's oxygen and nutrient balance as well as to assess consequences for the Ocean's future. In addition to examining the processes that are responsible for, and operating within, present Oxygen Minimum Zones, the SFB will work simultaneously on a detailed consideration of past climate-biogeochemistry linkages for two particular periods: the last Glacial-Interglacial (Holocene) cycle and the Cretaceous.

The main scientific questions are: (1) How does subsurface dissolved oxygen in the tropical oceans respond to variability in climate forcing and circulation? (2) What are the sensitivities and feedbacks linking low or variable oxygen levels with key nutrient source and sink mechanisms? In the benthos? In the water column? (3) What can we learn from the past and present ocean concerning the magnitudes and timescales of climate-forced variability of oceanic oxygen and nutrient levels? On the regional scale? On the global scale?

The research centre is divided into three collaborating `projects':

• Oxygen Supply Processes

• Processes at the switch point from oxic to sub-oxic

• New approaches to past changes

Progress on the scientific questions requires close collaboration between several traditional marine disciplines (physical oceanography and climate research, ocean chemistry and biology within biogeochemical research and marine geologic expertise for paleo-climatic research). Thus the proposed SFB research agenda builds on a set of shared scientific issues: (I) The Key Role of the Tropical Oceans. (II) Dissolved Oxygen as a Biogeochemical Switch, and (III) Coupling of Climate, Circulation, Biological Productivity and Oxygen in the Tropical Oceans.

ANALYSIS OF THE BIOGEOCHEMICAL PROCESSES IN THE BLACK SEA WATER COLUMN OXIC/ANOXIC INTERFACE WITH A REDOX LAYER MODEL

ANALISIS DE LOS PROCESOS BIOGEOQUIMICOS EN LA INTERFAZ OXICA/ANOXICA DE LA COLUMNA DE AGUA DEL MAR NEGRO MEDIANTE UN MODELO DE CAPA REDOX

E.V. Yakushev

Okeanologiya, Gelendzhik-7, 353467, Russia e_yakushev@yahoo.com

The goal of this 1D hydrophysical-biogeochemical O-N-S-P-Mn-Fe model was to study the processes of these chemical elements cycling in the water column in the Seas with suboxic and anoxic conditions. The biogeochemical processes of organic matter (OM) formation (photosynthesis and chemosynthesis), OM decay (aerobic decomposition, denitrification, sulfate reduction), nitrification, hydrogen sulfide oxidation, manganese and iron reduction and oxidation were considered. The following variables were considered: O2, H2S, S0, S2O-23, SO-24, NH+4, NO-2, NO-3, PON, DON, PO-34, POP, DOP, Mn(II), Mn(IV), Fe(II), Fe(III), phytoplankton, zooplankton, aerobic heterotrophic bacteria, aerobic autotrophic bacteria, anaerobic heterotrophic bacteria, anaerobic autotrophic bacteria. The time space evolution of the model compounds variables is described by a system of horizontally integrated vertical diffusion equations for non-conservative substances. To study the influence of the seasonal variability on the redox-layer structure we considered the influence of seasonal changes of organic matter production and intensity of mixing. The calculated spatial and temporal distributions of parameters agree reasonably well with the observations.

The oxidation of H2S in the model was realized with the following electron-acceptors: Mn(IV) _ 69.0%, NO-3 _ 23.8%, Fe(III) _ 5.7 %, and O2 _ 1.5%, in the mentioned proportions. This model justifies that particular M n (IV) can be the main oxidizer of hydrogen sulfide. Mn (IV) is being formed several meters higher via the reaction of dissolved Mn with O2. The intensive vertical transport of detrital particles with heavy Mn parts is a reason of the existence of a zone with the absence of significant concentrations of O2 that makes possi ble the processes of anoxic oxidation of reduced compounds (i.e., anammox). With this model we analyzed the roles of different processes on the O2 consumption in the oxygen-deficient conditions (from the concentrations of <50 µM to the sulfidic boundary, 60 _120 m). The share connected with the mineralization of OM was relatively small (about 7%) because in this layer the decomposition of OM should be connected with denitrification. The largest amount of O2 was consumed by nitrification (mainly ammonia oxidation _ 40%, and smaller value for nitrite oxidation _ 16%). Consumption for the reductants oxidation was about 36% (with 27% for Mn(II) and the latter for S0 and S2O-23). The calculations with the model clearly showed that the organic matter, formed during the summer bloom of the phytoplankton, essentially influenced the structure and the processes in the redox-interface. There should be a competition for the O2 between the supplying from the upper layers OM (particulate and dissolved) and supplying from the anoxic zone reductants. The result of this competition is that in summer the processes of OM mineralization become more intensive, that leads to the increase of the activity of heteroptophic bacteria (both in oxic and anoxic zones) and also of activity of aerobic autotrophic bacteria. The activity of the anaerobic chemolithoautotrophic organisms occurs reduced in summer, because lesser amount of oxidants (metal hydroxides, which formation require oxygen) are available for the reactions with anaerobic oxidation of sulfides and other reductants.

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