BACKGROUND AND OBJECTIVES: The southeast Indian Ocean is one of the areas where tropical cyclones formed. A comprehensive understanding of the cyclone impact in the Southeastern Indian Ocean is needed to anticipate future changes due to the warming trend. The present study investigates the influence of Cyclone Marcus on oceanographic processes in the subsurface and surface layers and its impact on temperature and Chlorophyll-a in the Southeastern Indian Ocean. The present study applies the Argo Float data located near the peak of the Cyclone Markus path and could capture the subsurface layer vertically that has never been reported previously.
METHODS: This study performs Copernicus data set and Argo Float data to analyze the oceanographic feature of the region before, during, and after Cyclone Marcus.
FINDINGS: The average surface current velocity increased almost two times during Cyclone Marcus, and the eddy was formed in the clockwise direction following the surface wind pattern. The Argo Float data presents that Cyclone Marcus could induce surface divergence (clockwise eddy) where the cold water and high salinity waters pumped up to the surface layer, starting 1 day after the peak of Cyclone Marcus, resulting in cooling surface temperature by 1.7 °C and deepening mixed layer depth up to 60 m. It implies that the lifted nutrient-rich water stays in the mixed layer depth for 11 days, and sea surface Chlorophyll-a concentration increase with time lags of 2.5 days and 5.6 days, respectively. The Chlorophyll-a concentration increases 2.5 times, and since then starts to decrease until its ‘normal concentration’ within two weeks.
CONCLUSION: Cyclone Marcus triggers the entrainment between the subsurface layer and the sea surface, forcing a phytoplankton growth, particularly in the path area. The future cyclone could increase in the category in the study area, as the warming trend in the Indian Ocean.
- The surface wind speed increased three times during Cyclone Marcus in a clockwise direction. The surface current velocity increased almost two times during Cyclone Marcus, and the eddy was formed in the clockwise direction following the surface wind pattern;
- The results show a decrease in SST and an increase in Chl-a along the path of Cyclone Marcus. Wind-induced eddy and Ekman pumping plays a vital role in the entrainments process. The Argo Float data presents that Cyclone Marcus could induce surface divergence (clockwise eddy) where the cold water and high salinity waters pumped up to the surface layer, starting 1 day after the peak of Cyclone Marcus;
- The research findings show a temperature difference of 1.7 °C, MLD deepening up to 60 m, the lifted nutrient-rich water stays in the MLD for 11 days, a Chl-a increases two weeks after the cyclone with Chl-a concentration almost three times in responding to the cyclone.
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