Upper ocean biogeochemical response of Arabian Sea to extremely severe cyclonic storm “Biparjoy”

Recent warming in the tropical oceans has increased tropical cyclone (TC) activity globally. The Arabian Sea (AS) in the northern Indian Ocean is such a basin with rising TC activity. TCs have the potential to favor the short-term productivity of the ocean through extensive mixing of the upper ocean, bringing about temporary variations in the biogeochemistry. The current study investigates the upper ocean biogeochemical response of AS to a TC utilizing data sets from six Bio-Argos, multi-satellite observations, and biogeochemical models from Copernicus Marine Services. The extremely severe cyclonic storm “Biparjoy”, one of the long-duration TCs in the basin was chosen as a case study. It formed during the onset of the Indian summer monsoon in June 2023 and persisted for eleven days (6^th to 16^th June 2023). Profiles obtained from the Bio-Argos around the storm track showed extensive cooling (~4 °C) in the upper surface. The strong TC also resulted in significant vertical mixing which brought cold, nutrient-rich water to the upper surface. Dissolved oxygen concentration was observed to have decreased during the cyclone, compared to pre- and post-cyclone periods. Eventually, an increased chlorophyll concentration, persisting for more than a week, was observed along the track in the sub-surface and surface waters after the passage of the storm. Biogeochemical model data was used to analyze the intricate variations in the upper ocean biogeochemistry of AS during the storm. Further analysis for a better understanding of the upper ocean response of the AS to cyclonic storms in recent years is in progress.