Observed chlorophyll-a bloom in the southern Bay of Bengal during winter 2006-2007

The analysis of 6-year chlorophyll-a data provided by the Moderate Resolution Imaging Spectral (MODIS) radiometer revealed anomalous chlorophyll-a bloom in the southern Bay of Bengal during the winter 2006-2007. The plausible causative mechanisms for such a large chlorophyll-a during the winter 2006-2007 are analysed through surface wind field, surface net heat flux and sea surface height anomaly (SSHA) data. The chlorophyll-a bloom developed in November 2006 near the northern tip of Sumatra. It was intensified and propagated slowly westward during December 2006 to January 2007 and then weakened by February 2007. The combined effect of shallowing of thermocline and weakening of barrier layer due to anomalous westward propagating upwelling Rossby waves associated with the Indian Ocean Dipole (IOD) event and relatively strong wind field causing entrainment of subsurface nutrient-rich water to euphotic zone leads to the bloom in the southern Bay of Bengal.