Ocean color variability of the tropical Indo-Pacific basin observed by SeaWiFS during 1997-1998

High-quality ocean color data (chlorophyll) provided by the Sea-viewing Wid e Field of view Sensor (SeaWiFS) satellite were analyzed for the first comp lete year of coverage (October 1997 to September 1998) in the tropical Indo -Pacific basin. This period coincides with the peak of one of the strongest Fl Nino events during December 1997 and the La Nina of 1998 that appeared dramatically in less than a month as a sea surface temperature (SST) change of over 6 degrees C in the central equatorial Pacific during June 1998, Th e tropical Indian Ocean also underwent a highly anomalous series of events with negative SST anomalies (SSTA) of over 3 degrees C in the eastern equat orial and coastal regions during October-December 1997 and warm SSTA in the west that peaked at over 2 degrees C during February 1998. The ocean color variability is interpreted using other satellite data such as sea level fr om TOPEX/Poseidon and also in terms of the dynamics and thermodynamics of t he region from simulations with an ocean general circulation model, The El Nino-related reductions in equatorial production and the off-equatorial inc rease in biological activity, and their basin scale evolution is clearly se en for the first time. Persistent northerly wind anomalies resulted in a no rthward shift of the equatorial divergence and the upwelling Kelvin wave wh ich signalled the end of the 1997-1998 El Nino. The anomalous surface chlor ophyll associated with this Kelvin wave was also clearly shifted north of t he equator by nearly 300 km and appeared more than a month before the negat ive sea level anomalies seen by TOPEX/Poseidon. On the equator near 165 deg rees E, the disappearance of the barrier layer appeared to coincide with a localized bloom that occurred in response to the easterly wind bursts over the western Pacific that lasted from December 1997 through the boreal summe r. The ecosystem response to the cold La Nina conditions is clearly seen as elevated chlorophyll during the boreal summer of 1998 in the equatorial Pa cific cold tongue region. In the Indian Ocean, an anomalous phytoplankton b loom was observed by SeaWiFS during October-December 1997 coincident with t he anomalous upwelling in the eastern equatorial region and off the coast o f Sumatra, A stronger than normal northeast monsoon is seen as higher than climatological values of surface chlorophyll. The open ocean Ekman pumping and the shoaling of the thermocline near 60 degrees E and 10 degrees S and the eastward extension of mixed layer entrainment in the same latitude band is seen as a region of higher biological activity during the boreal summer .