HR: 0800h
AN: OS51A-1286    [Abstracts]
TI: Seasonal Variability of the SeaWiFS Chlorophyll in the Western Tropical Pacific
AU: * Messi\'{e}, M
EM: messie@notos.cst.cnes.fr
AF: LEGOS, 18 avenue Edouard Belin, Toulouse cedex 9, 31401 France
AU: Radenac, M
EM: radenac@notos.cst.cnes.fr
AF: LEGOS, 18 avenue Edouard Belin, Toulouse cedex 9, 31401 France
AU: Gar\c{c}on, V
EM: garcon@notos.cst.cnes.fr
AF: LEGOS, 18 avenue Edouard Belin, Toulouse cedex 9, 31401 France
AB: We use Sea-viewing Wide Field-of-view Sensor (SeaWiFS) observations to document the seasonal cycle of surface chlorophyll concentration in the western tropical Pacific. Essentially, surface waters of this region can be divided into two contrasted ecosystems. The western end of the cold, salty waters of the equatorial divergence with High Nutrient Low Chlorophyll (HNLC) characteristics occupy most of the eastern part of the region while warm, fresh, and oligotrophic waters of the warm pool stand in the western part. Nevertheless, disruption of the oligotrophy may show up at different locations. We reconstruct the seasonal cycle of chlorophyll, SST, winds, and surface currents from satellite data and satellite-derived products by fitting the annual harmonic to the time-series at each grid point. The calculation is done for the 1999-2001 years in order to exclude the 1997-1998 and 2002-2003 ENSO events. An EOF analysis applied to the typical year highlights three major regions with coherent seasonal signal. [1] The oligotrophy/upwelling transition zone undergoes zonal and meridional seasonal displacements. The front is at its westernmost and northernmost (easternmost and southernmost) position during boreal spring (autumn). The equatorial displacements of the front can be explained in terms of advection, whereas the seasonal variability of chlorophyll along the northern (southern) boundary is mainly consistent with the seasonal cycle of the north and south equatorial countercurrents (NECC and SECC). [2] SeaWiFS images show enrichments in the western NECC, especially from February to June. The Chl maximum lags a maximum eastward velocity and a SST minimum, and occurs during the upwelling favorable phase of the wind stress curl. These enrichments can be attributed to advection and/or upwelling associated with current meandering. [3] Near the Solomon Islands, we observe enhancement of Chl concentration either east or southwest of the islands, depending on the direction of surface currents. This may be explained by the island mass effect.
DE: 4855 Plankton
DE: 4227 Diurnal, seasonal, and annual cycles
DE: 4231 Equatorial oceanography
DE: 4572 Upper ocean processes
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting