The influence of tropical Indian Ocean warming and Indian Ocean Dipole on the surface chlorophyll concentration in the eastern Arabian Sea

Abstract. This study examines the role of increased Indian Ocean warming and positive Indian Ocean Dipole (IOD) events on the surface chlorophyll concentration in the Eastern Arabian Sea (EAS) during the period 1998 to 2014. Remotely sensed surface chlorophyll concentration – during the month of October when IOD strength is maximum – at three selected areas in the EAS, viz., the central eastern Arabian Sea (CEAS, 73° E–76° E, 13° N–18° N), south eastern Arabian Sea (SEAS, 74° E–77° E, 8° N–13° N) and the southern tip of India (TIP, 74° E–78° E, 5° N–8° N) shows a steady decreasing trend, though not statistically significant. The EAS also has a higher warming trend when compared to the western basin during the study period. Our analysis has shown that in the EAS, local surface winds, remote forcing by equatorial winds and the surface and sub-surface oceanic circulation features are less (respectively more) favorable for inducing coastal upwelling during positive (respectively negative) IOD years. The Dipole Mode Index (DMI) and surface chlorophyll concentration in the EAS is significantly and negatively correlated, pointing to the fact that in the event of occurrence of frequent positive IOD years under a global warming regime, the surface chlorophyll concentration is likely to decrease during fall.