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vol.30 número1  suppl.SympThe Role of El Niño, La Niña and Climate Change in the Pacific Eastern Boundary Currents: An Integrated Introductory ViewThe precipitation regimes along Chile and California at the extremes of the ENSO and ENSO-like cycles índice de autoresíndice de materiabúsqueda de artículos
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Investigaciones marinas

versión On-line ISSN 0717-7178

Investig. mar. v.30 n.1 supl.Symp Valparaíso ago. 2002 


Interdecadal and Centennial Variability
Underlying the El Niño/La Niña

Tim Baumgartner1, Luc Ortlieb2

1Centro de Investigación Científica y de Educación
Superior, CICESE, Km 107 Carr. Tijuana-Ensenada, Ensenada,
B.C., C.P. 22860, Mexico,
2Institut de Recherche pour le Développement, Centre
de recherche Ile de France, 32 avenue Henri-Varagnat,
F-93143 Bondy Cedex, France,

The regional dynamics of the Humboldt and California Current systems are linked through their response to basin-wide coupling of ocean and atmosphere circulation and thus exhibit similarities in the nature of their variability over interannual and interdecadal time scales. This presentation is focused on interdecadal to multi-centennial periods of climate and ecosystem changes that underlie the ENSO-scale, interannual variability. Reconstruction of paleoecological records preserved in the sediments of the California and Humboldt systems offers the potential to infer and compare the nature of changes in the character of the ecosystems and ocean climate over the interdecadal to centennial scales of the past 2000 years. Depositional sites in the ocean that provide such detailed histories of animal populations, however, are rare because of the suite of conditions which must prevail—the principal condition being the depletion of oxygen in the overlying bottom water—for good preservation of the biological remains within a detailed chronological framework of annual (or near-annual) layering. This presentation will describe the current state of development of the information about ecosystem history and climate contained in the natural archives of marine sediments from which we can resolve at least interdecadal (accuracy within ±10 calendar years in 1000 years of record) down to interannual variability (±2 yr) in the California and Humboldt systems.

Interdecadal variability in the Pacific occurs as climate shifts between basin-scale regime states related to tropical warming and cooling which persist for several decades. These longer-period changes in ocean climate over the Pacific Basin produce significant adjustments in the organization and dynamics of the large marine ecosystems. Such changes are manifested in the abundance, distribution and productivity of animal populations, often with shifts in dominant species that lead to cascading effects through the trophic structure of the biological community. One of the important sources of information derived from the high-resolution sediment records is the rate of deposition of fish scales of small schooling planktivorous species like sardine and anchovy which form important trophic links in these ecosystems. The large-scale change in ocean climate over the Pacific are associated with well-documented latitudinal expansions and contractions of the habitats of these fish, resulting in persistent increases/decreases in abundance and change in distribution of their populations. Studies on fish scale-depostion are working towards uncovering the variability in abundance, distribution and age structure of these populations over the past 2000 years. Related studies are focusing on other sources of environmental information in the paleo records that reflect changes in regional ocean climate associated with changes in the fish populations.

The longest (1600 years so far) and best known high-resolution record of fish-scale deposition is from the California Current found in the sediments of the nearshore Santa Barbara Basin off southern California. Two other sites under development are located at the southern and northern extremes of the California Current system—off southern Baja California, Mexico (150 years on record so far) and on the west coast of Vancouver Island, Canada (500 years on record). Comparison among the north-south sites within the California Current system suggests a pattern of range expansion and contraction of the sardine populations over the past 500 years of available record. The spectrum of the longer 1600-year record from the Santa Barbara Basin exhibits two major peaks in the interdecadal band of variability: a large peak representing a period of 50-70 years and a lesser peak at approximately 20 years. The Santa Barbara record also indicates centennial-scale change in the successive warming, cooling and warming of the coastal ocean along North America over the past 1000 years. This is associated with the Medieval Warm Period (950-1350 AD) and the Little Ice Age (1400-1800 AD) documented from European sources and the global warming trend which began at the end of the Little Ice Age.

High-resolution sites in the Peru-Chile system are known to occur off central and southern Peru (with population histories now reconstructed through the past 150 years). Preliminary work shows that these sites have well preserved records of habitat change of the Peruvian anchoveta since the 1870s that is clearly related to interdecadal changes in ocean climate. These latter two sites are also well located to track equatorward expansion of sardine habitat from the population center off northern Chile. The presence of coherent, lower resolution records of fish scale deposition off northern Chile hold the promise for developing higher resolution records of the past 2000 years for that region.

* Keynote presentation.

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