Impact of dust storm on phytoplankton bloom over the Arabian Sea: a case study during March 2012.

Dust storms affect the primary productivity of the ocean by providing necessary micronutrients to the surface layer. One such dust storm during March 2012 led to a substantial reduction in visibility and enhancement in aerosol optical depth (AOD) up to ~ 0.8 (AOD increased from 0.1 to 0.9) over the Arabian Sea. We explored the possible effects and mechanisms through which this particular dust storm could impact the ocean's primary productivity (phytoplankton concentration), using satellite-borne remote sensors and reanalysis model data (2003-2016). The climatological analyses revealed anomalous March 2012 in terms of dust deposition and enhancement in phytoplankton concentration in the month of March during 2003-2016 over this region. The studied dust storm accounts for increase in the daily average surface dust deposition rate from ~ 3 to ~53 mg m-2 day-1, which is followed by a significant enhancement in the chlorophyll-a (Chl_a) concentration (~ 2 to ~9 mg m-3). We show strong association between a dust storm and an event of anomalously high biological production (with a 4-day forward lag) in the Arabian Sea. We suggest that the increase in biological production results from the superposition of two complementary processes (deposition of atmospheric nutrients and deepening of the mixed layer due to dust-induced sea surface temperature cooling) that enhance nutrient availability in the euphotic layer.