Study the Mechanism of Surface Chlorophyll–a Variability in the Southern Tropical Indian Ocean Using an OGCM

Abstract

Eleven years (1997–2007) of SeaWiFS observations and Ocean General Circulation Model sensitivity experiments are used to understand chlorophyll–a variability in the southern tropical Indian Ocean. The strong offshore Ekman transport forced by anomalous southeasterly winds are responsible for inducing higher chlorophyll-a in the eastern equatorial Indian Ocean. In the case of the southwest tropical Indian Ocean, Rossby waves and local upwelling are responsible for lifting the phytoplankton from deep chlorophyll maxima to the surface. Both intraseasonal dynamical response and interannual forcing are responsible for the phytoplankton blooming in the western basin, whereas the interannual forcing is mainly responsible in the east.

Keywords:

• Ocean General Circulation Model
• surface chlorophyll concentration
• Ekman transport
• Rossby waves

Acknowledgments

The first author acknowledges the Council of Scientific and Industrial Research (CSIR), India, for Junior/Senior Research Fellowships. We thank A. Deshpande for proofreading the manuscript. Financial support of Space Application Centre (SAC), Ahmedabad, India, and Indian National Centre for Ocean Information Services (INCOIS), Hyderabad, India, is acknowledged. TMI gridded SST data are produced by Remote Sensing Systems and are available at www.remss.com. The altimeter products were produced by Salto/Duacs and distributed by AVISO with support from CNES. We acknowledge the SeaWiFS Project Office for Chl–a data.