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Investigaciones marinas

versión On-line ISSN 0717-7178

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

http://dx.doi.org/10.4067/S0717-71782002030100015 

Comparative Analysis of Warm Events
in the Series 1970 - 2002 off the
Coast of Peru

Octavio Moron A.

Instituto del Mar del Perú (IMARPE), Apartado 22,
Callao, Perú, E-mail: omoron@imarpe.gob.pe

Introduction

The El Niño phenomenon is a recurrent event that maintains the scientific community around the world on permanent alert with the aim of forecasting its occurrence, characteristics and intensity and the effects that it can cause on marine life and on the continents.

Between May and September of 2001, different international organisations specialized on the subject, talked about a warm event occurring during the last few months of the year, changing and postponing their views later to just a small warming for the months of February and March of 2002 due to the renewal of cold conditions in the last few months of 2001.

What was observed off the Peruvian coast between February and May has not only been a slight warming, but has been accompanied by positive anomalies of up to +4°C with an intrusion of Equatorial Surface Waters (ESW) reaching 10°S. As a result of these anomalies in the Southeast Pacific, some have considered it a warm event without major importance, while others have termed it an El Niño event of moderate intensity.

The present study describes the evolution of this latest warm event along the South American coast, with emphasis on Peru, making use of information obtained via internet, and from research carried out by Instituto del Mar de Perú (IMARPE), as well as a comparison with other events labelled moderate, principally with that of 1992, with which a lot of similarity is found.

Results

Evolution of the Warm Event 2002

Between January and April of 2001 a small warming of waters presented itself over the northern coast of Peru reaching anomalies of up to 2,5°C in its main nucleus, associated with the projection of ESW up to 08°S beyond 40 nautical miles (N.M.), unusual since these waters are normally located north of 05°S during summer, returning northwards between austral autumn and winter.

Between the months of June and September the Central Equatorial Pacific showed the formation of a subsuperficial warm nucleus moving towards the South American coast, while off Peru, the Southern Extension of the Cromwell Current (SECC) presented an unusual projection to 12°S during the month of July, which then retreated considerably over the following months due to the intensification of coastal upwelling, which in turn showed great intensity north of 10°S and which, uncommonly, occurred between the months of September and October.

In turn, with the cooling of the Peruvian sea, the warm waters from the Equatorial Pacific fell back towards the west, although the thermal anomalies increased in the month of December to 3°C in the zone between 160°W and the international date line and between 100 and 200 m depth.

It was in January 2002, when cold conditions prevailed off the Peruvian coast close to the norm, that the warm water mass from the Equatorial Pacific projected itself quickly toward the eastern Pacific, mixing with?(or reaching) these waters in the month of February, resulting in temperatures of 27°C being registered an the station in Paita, with positive anomalies of 5°C over the monthly mean.

This warming has been associated with the projection of ESW towards the south, the same waters that reached a depth of 70 m off Paita and 30 m off Chimbote at the end of march (MOPFEN 0203), with predominant anomalies of 3 and 4°C over the mean. Likewise, during this month, the SECC presented a projection up to 13°S, which is reflected in the deepening of isotherms lower than 16°C and the relatively high content of dissolved oxygen in the sea water.

The Eureka LVII cruise, carried out between the 29th and 30th of April, showed a fall back of the ESW, although positive anomalies of up to 2,5°C remained beyond 40 nm between 6 and 10°S, diminishing towards the south. Likewise, a reactivation of coastal upwelling was observed as well as the presence of Subtropical Superficial Waters (SSW) which caused a great mixture of waters north of 10°S, with salinity values between 34,8 and 35,0 psu resulting in a confused interpretation.

Comparative Analysis

For the comparative analysis time series of sea surface temperatures off Paita, Chicama, and Callao have been selected for the years 1970 to 2002, as well as superficial maps and vertical sections from oceanographic cruises and corresponding operations, from 1976 (Report - Informe de la Exploración con boliches para el control costero de "El Niño" en febrero de 1976), Cr. 38 th R/V Dimitr Mendeleev (03-13 Feb. 1987) and Cr. BIC SNP-1 9201-02, all those carried out in years considered "Moderate Niños", including also the abundant information collected so far in 2002.

Conclusion

Due to the ongoing anomalous conditions off the Peruvian coast at the time this summary was written, there is still no conclusion of the real intensity of the last warm event, but from the thermal anomalies, the southward projection of the Equatorial Waters as well as the Southern Extension of the Cromwell Current and the effect on the marine resources have been deduced; the author considers that it could be named a moderate El Niño.

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