Southwestward extent of chlorophyll-enriched waters from the peruvian and equatorial upwellings between Tahiti and Pananama

The transition zone between waters deriving from the Peruvian and Equatorial upwellings, and oligotrophic waters of the central South Tropical Pacific, was examined by sea-surface chlorophyll sampling carried out by merchant ships on the Tahiti-Panama track. The results from 118 transects (December 1979 to September 1985) show that this transition is generally associated with convergences between the Westward South Equatorial current and eastward flows, as indicated by contemporaneous temperature sections obtained from expendable bathythermographs. The transition position varies between 5 and 17°S and variations occur mostly on time scales of a month or less. The Tuamotu atolls (15 to22°S, 135 to 150°W) were observed to be reached by waters deriving from the upwellings on 14 % of the transects; this might help to explain the anomalous abundance of life on these atolls. The 1982-1983 El Nino resulted in a fall in chlorophyll concentrations in the eastern tropical Pacific, but dit not cause a significant change of the position of the transition. (Résumé d'auteur

Upper ocean water masses and transports in the Western Tropical Pacific (165°E)

As part of the international TOGA program, the ORSTOM Center in Nouméa (New Caledonia) initiated in January 1984 a series of semi-annual cruises along the 165°E meridian from 20°S to 10°N, across the equatorial current system of the western Pacific. This paper presents an analysis of the first six hydrographic (0-1000 m) and current (0-600 m) sections. A detailed description of "typical" January 1986 vertical structures of temperature, salinity and zonal measured velocity is offered. Differences are noted with structures previously obtained in the Tropical Pacific. Compared to the Central and Eastern Pacific, the 165°E data set evidences a much weaker equatorial upwelling and deeper surface isothermal layer and subsurface currents. Compared to the few Western Pacific measurements, the two speed cores of the Equatorial Undercurrent (EUC) previously reported at 100 and 200 m are not observed here. Special attention is given to the eastward equatorial jet (2°S-2°N; 0-75 m) measured in January 1985 when westerly winds were present from the north of New Guinea to 160°

Coupes verticales des structures océaniques physiques à 165°E observées au cours de dix campagnes SURTROPAC, 1984-1988

In, 1984, the SURTROPAC group from the ORSTOM Center in Noumea has undertaken a series of trans-equatorial biannual cruises, along the 165°E meridian, from 20°S-10°N. These cruises are now part of the international TOGA program, and are scheduled until 1994. Half-way of this series, this report presents sections of temperature (T), salinity (S), potential density, zonal geostrophic currents (Ug), and zonal (u) and meridional (v) components of measured currents, for each of the 10 cruises already carried out. Some indications on data processing and contouring algorithms are given before. Two different types of hydrology probes and current profilers were used for measurements : for cruises § 1-5, a Bisset-Berman model 9040 STD probe, and a more accurate Seabird model SBE9 CTD for cruises § 6-10; the 2 Düing-like profilers are based on Aanderaa currentmeters, and differ only by the shape of floats used ... To improve resolution of shallow structures, hydrology sections are presented twice, on 0-400m and 0-1000m vertical scales. For cruises § 7-10, CTD casts were deeper, and 0-2000m sections are also shown. Measured velocity sections are given on 0-400m, for comparisons with hydrology section

Des Açores à la Nouvelle-Calédonie : un demi-tour du monde de mesures avec un profileur acoustique à effet Doppler

Ce rapport présente les résultats des mesures au profileur de courant acoustique à effet Doppler (ADCP) effectuées au cours de la traversée Brest-Nouméa du navire océanographique LE NOROIT de décembre 1990 à mars 1991. Les données ont été recueillies durant le transit Atlantique des Açores à Panama, et pendant la campagne ALIZE 2 le long de l'équateur dans le Pacifique. Le principe de fonctionnement de l'ADCP est rappelé brièvement, et l'installation d'un modèle RDVM-150 fabriqué par RD Instruments sur LE NOROIT est décrite. Les méthodes d'acquisition et de traitement des données sont détaillés. Les résultats sont exposés sous forme de coupes verticales des composantes zonale et méridienne des courants, pour chaque partie de la traversée. (Résumé d'auteur

Sea level and dynamic topography in the Western Pacific during 1982-83 El Nino

Pendant le fort El Nino 1982-1983, deux réseaux d'observations océanographiques ont fourni des données continues dans le Pacifique tropical : le réseau de mesure du niveau de la mer créé et maintenu par l'Université d'Hawaii et le réseau XTB - navires marchands du groupe SURTROPAC, Centre ORSTOM de Nouméa - La topographie dynamique mensuelle 0-400 db est calculée le long de la route Nouméa-Japon (20°S-20°N, 150°E-165°E), en utilisant des relations T-S réelles, pour faire ressortir les anomalies interannuelles. Cette topographie est comparée aux valeurs mensuelles du niveau de la mer. Ce très bon accord obtenu entre les variations spatio-temporelles déduites des deux réseaux montre qu'ils se complètent utilement dans la surveillance des anomalies climatiques. (Résumé d'auteur

Effects of westerly wind bursts upon the Western Equatorial Pacific ocean, february-april 1991

In February-April 1991, episodes of 2 to 8 m s-1 westerly winds of 3 to 11 days' duration occurred in the Western Pacific warm pool. Resulting modifications of the upper ocean in current and hydrology are quantified using data from an equatorial mooring at 165°E and from three cruises within 30 days of one another along 165°E. During westerly wind bursts (WWB) stronger tha m s-1, the upper 50 m becomes isothermal to within O.1°C and sea surface temperature (SST) drops by 0.3.-0.4°C between 5°S and 2.5°N. Conversely, STT starts warming and the upper 50 m restratifies in 4-5 days after the end of WWB. In contrasts to previous observations, salinity between 0 and 50 m appears almost unaffected by WWB; it freshens by 0.4 practical salinity unit in March within an area of 1°-2° of latitude aroud the equator but not necessarily in direct response to WWB. As for zonal circulation, surface equatorial flow accelerates eastward jets both develop from 2°N to 2°S in the upper and lower halves of the temperature mixed layer, respectively. Changes in zonal mass transport in this layer were as much as 30 Sv between 2.5°S and 2.5°N from one cruise to the next. (Résumé d'auteur

Variation of the Western Equatorial Pacific ocean, 1986-1988

Twenty one oceanographic sections made along 165°E during 1984-1988 provide a unique picture of the 1986-1987 El Nino and the subsequent La Nina in the Western Equatorial Pacific. The mean of six cruises from January 1984 throught June 1986, a relatively normal period, provides a reference with which the later sections are compared... Changes in the stratification along 165°E were corresponddingly large, reflecting both the geostrophic balance of the strong zonal currents and the changes in the volume of warm water in the Western Equatorial Pacific. The anomaly of warm water volume corresponded closely to the time integral of the warm water transport across 165°E. Local wind forcing and remotely forced waves were both important causes of the transport fluctuations. Winds, precipitation, and currents were all important factors determining the depth of the surface mixed layer and the thickness of the underlying barrier layer. The way in which these factors interact is a strong function of latitude. (D'après résumé d'auteur