Program

Physical-biological interaction between chlorophyll (CHL) concentrations and cyclonic eddies has been well documented in literature. Four physical mechanisms, eddy stirring, eddy trapping, eddy pumping and eddy induced Ekman pumping, have been proposed to play key roles in near surface CHL variations in eddies. Previous studies mainly focused on the CHL spatial distribution within eddies. We study both temporal and spatial evolution of CHL within cyclonic eddies to promote a better understand underlying mechanisms. After analyzing 10-year sea level anomalies (SLA) from AVISO and sea surface CHL from NOBM between 1998 and 2007, 230 cyclonic eddies are identified in the subtropical Southeastern Pacific. Both dipolar and monopolar distributions of CHL and their associated temporal variations are classified based on self-organizing map (SOM). The four physical mechanisms indeed significantly contribute to CHL variations and the dominant mechanism is changing with eddy evolution. Particularly, eddy stirring accounts for more than 50% of sea surface CHL variations, which leads to a slightly negative CHL response in cyclonic eddy region. Besides, a new mechanism called eddy breakup (eddy shedding from big eddies) is found. It has a considerable contribution to CHL variations at eddy formation and decaying stages.