Tropical cyclones (TCs) can make the surface chlorophyll-a bloom in satellite observations, often interpreted as enhanced phytoplankton biomass. Using 44 cyclones in the Bay of Bengal (BoB), we found that surface chlorophyll-a increased rapidly during TC passage but declined within a few days, while depth-integrated chlorophyll-a over the upper 100 m showed no significant increase. This suggests that TCs may have a limited role in new phytoplankton biomass. The chlorophyll-a response exhibited strong spatial heterogeneity. Increases in both surface and column-averaged chlorophyll-a were weak in the central deep basin, likely because a thick barrier layer suppressed nutrient supply. Stronger surface responses occurred along the northwestern shelf and off Sri Lanka, but column-averaged changes were negligible along the shelf and significant off Sri Lanka, reflecting TC-induced onshore transport of low-chlorophyll-a water and stronger upwelling, respectively. These findings highlight regional controls on TC-driven new production.

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