253-258A study on MODIS (Moderate Resolution imaging Spectroradiometer)-derived chlorophyll-a concentration data was carried out for 12 years (2003 to 2014), to know the reasons for two episodic phytoplankton bloom events occurred in 2005 and 2013. During the month of December 2005 and 2013, magnitude of the production increased to two to three times of climatological value over the south-western Bay of Bengal region. Reasons for the bloom were examined with the available satellite resources and it was identified that the strong cyclonic eddy, with long residence time, caused the increase of the production. This production intensified when cyclones passed through or were close to the eddy. The vertical mixing enhanced (2013) when very severe cyclonic storms passed through or moved close to the eddy compared to depressions passing over it which caused further intensification of the primary production
