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

As phytoplankton consume carbon dioxide, they influence the global carbon cycle and climate by modifying sea surface temperature and ocean productivity. Using two decades (1997–2019) of satellite ocean colour observations, this study reports cyclone-induced chlorophyll-a (Chl-a) blooms in the North Indian Ocean (NIO). The average Chl-a associated with cyclone-induced blooms is about 1.65 mg/m³, representing 20–3000% increases above open-ocean or pre-cyclone levels depending on the event. Bloom magnitude is generally inversely related to cyclone translational speed (TS), with slower storms producing stronger blooms. Besides wind-driven upwelling and TS, interactions with cold-core eddies markedly enhance Chl-a when cyclones encounter them. Bloom amplitudes are larger during La Niña than El Niño and normal years. Positive IOD years favor higher blooms in the Bay of Bengal (BoB), while negative IOD years favor higher blooms in the Arabian Sea (AS). The work provides new insights into the life cycle, seasonal variability, and magnitude of cyclone-induced primary production and its links to remote forcing and greenhouse-gas-mediated climate change in the NIO.

J. Kuttippurath, N. Sunanda, M. V. Martin, Kunal Chakraborty