Surface Chlorophyll-a Distribution in the Southwestern Atlantic due to Mesoscale Eddies

MARTIN SARACENO; DAVID OKS

Simposio; 20 years of Progress in Radar Altimetry symposium; 2012

Eddies play a key role in promoting the growth of phytoplankton and in the large-scale redistribution of chlorophyll-a. In this study we combine satellite altimetry and surface chlorophyll-a to study their covariability within mesoscale eddies. The study is focused in the western South Atlantic between (35ºS- 52ºS, 62ºW-35ºW). The western South Atlantic presents a wide range of eddy kinetic energy (e.g. 102 to 2x103 cm2/s2) and sharp contrasts in chlorophyll concentration (0.05 to >10 mg/m3) and is therefore a good region to determine the impact of eddies on biological production in different environments. Eddies are detected applying a modified Okubo-Weiss method to satellite altimetry data for the period 1997- 2010. The satellite derived surface chlorophyll-a distribution associated with the eddy field is studied for the same period of time. On average chlorophyll-a concentrations increase (decrease) toward the center of cyclonic (anticyclonic) eddies. North of 45ºS this behavior holds in regions of low and high eddy-kinetic energy. South of 45ºS, surface chlorophyll-a concentrations are higher within the cores of anticyclonic eddies than within cyclonic eddies. Mechanisms to explain the above observations are discussed. The rate of cyclonic eddy-induced chlorophyll-a to the total concentration estimated as a function of location indicates that up to 30% of the total chlorophyll-a may be associated with cyclonic eddies