Tropical storms trigger phytoplankton blooms in the deserts of north Indian Ocean

Abstract

Abstract As the phytoplanktons consume carbon dioxide, they significantly influence the global carbon cycle and thus, the global temperature by modifying sea surface temperature. Studies on the changes in chlorophyll–a (Chl-a) amount are therefore, key for understanding the changes in ocean productivity, global carbon budget and climate. Here, we report the cyclone-induced Chl-a blooms in the North Indian Ocean (NIO) using the ocean colour measurements from satellites for the past two decades (1997–2019). The average Chl-a concentration associated with cyclone-induced phytoplankton blooms is around 1.65 mg/m3, which is about 20–3000% higher than the average open ocean or pre-cyclone Chl-a levels, depending on the cyclones. In general, the phytoplankton bloom is inversely related to the translational speed (TS) of cyclones, as slower storms make intense Chl-a blooms. In addition to wind-induced upwelling and TS of cyclones, cold-core eddies also play a major role in enhancement of Chl-a when the cyclones encounter eddies on their track. It is observed that the cyclone-induced phytoplankton blooms are larger in the La Niña years than that in the El Niño and normal years. The amplitude of bloom is higher for the positive IOD years in Bay of Bengal, but for negative IOD years in Arabian Sea. Henceforth, this study provides new insights into the life cycle, seasonal changes, and magnitude of the cyclone-induced primary production, remote forcing and greenhouse mediated climate change in NIO.