Atmospheric dust addition under elevated CO2 restructured phytoplankton community from the Arabian Sea: A microcosm approach

Abstract

Atmospheric dust deposition in the North Indian Ocean, particularly in the Arabian Sea significantly impacts phytoplankton productivity. Importantly, the steady increase in Sea Surface Temperature (SST) of the Arabian Sea may intensify oligotrophy and the significance of atmospheric dust input for phytoplankton growth may escalate in the future. Furthermore, the globally increasing atmospheric CO2 is simultaneously impacting the surface ocean by decreasing its pH called Ocean Acidification (OA). We present here the first experimental study showing the impacts of atmospheric dust input under the simulated OA scenario on the natural phytoplankton communities from the Arabian Sea (winter monsoon). Phytoplankton cell density and chlorophyll (Chla) contents were enhanced in response to dust addition. The external input of inorganic nitrogen and iron (from dust) were the key growth-promoting factors that increased the relative contribution of micro and nanophytoplankton irrespective of the CO2 levels, whereas picophytoplankton decreased. The predominance of pennate diatoms and non-diatoms was mostly due to low dissolved silicate (DSi) availability. The cell density of the pennate diatoms Pseudo-nitzschia sp., Nitzschia sp., and Cylindrotheca closterium increased by several orders of magnitude in response to dust addition under OA. The dinoflagellates, Alexandrium sp., and Gymnodinium sp. showed higher tolerance to OA and proliferated in response to dust input. The present experimental conditions can be compared to the future ocean scenario (low DSi, OA, and dust input) where the proliferation of non-palatable/ toxigenic phytoplankton taxa may be expected which has the potential to impact ecological processes like trophic transfer, carbon cycling, and fisheries.