The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

Eddies are essential parts of the marine ecosystem and have a big impact on altering the physical and biological conditions of the ocean. More importantly, they are crucial for the distribution of chlorophyll (Chla), heat, salt, and energy, which directly influence ocean circulation patterns. Despite their importance, the periodic nature of eddies in the Indian Ocean, particularly around Sri Lanka (5°N–20°N, 75°E–90°E), has not been extensively studied. In this study, we investigate Chla variations impacted by nearshore and offshore eddies, focusing on periodic anticyclonic and cyclonic eddies in the Bay of Bengal (BoB). We utilized 20 years of data from the Archiving, Validation, and Interpretation of Satellite Oceanographic (AVISO) eddy trajectory data, the Moderate Resolution Imaging Spectroradiometer (MODIS – Aqua 1km), and additional satellite sources. Analysis of AE and CE composites from over 10,000 eddy realizations reveals that nearshore eddies exhibit greater horizontal advection than offshore eddies, suggesting a stronger Chla transport in coastal areas. Comparative analysis of Chla distribution shows that CE eddies have significant positive Chla anomalies at the eddy center, while AE eddies exhibit elevated Chla levels at their peripheries. Statistical examination of eddy occurrences shows that in June, there is a periodic cold eddy, characterized by occurrence probabilities exceeding 70%, which is identified as 'CE'. Conversely, a periodic warm eddy, termed 'AE', appears in September. Composite analysis indicates that AE results in a 48% increase in local chlorophyll along eddy peripheries, whereas CE leads to a 65% increase in chlorophyll concentration at the eddy center.
 

Chlorophyll (Chla); Periodic cold eddy; Periodic warm eddy; Bay of Bengal (BoB); Nearshore and Offshore eddies