ASSESSING THE EFFECTS OF THE PASSAGE OF COLD FRONTS ON SATELLITE-DERIVED CHLOROPHYLL IN THE SOUTH BRAZIL BIGHT

The South Brazil Bight (SBB) is oceanographically characterized by a strong vertical stratification during the austral summer and a more mixed water column during winter. Atmospheric mesoscale dynamics and circulation are highly dominated by the passage of cold fronts. Cold front passages cause wind intensification and a shift in its main quadrant direction, impacting on the dynamics of the water column and ocean circulation. However, the effects on biological processes are still poorly understood. In the present study, daily MODIS-Aqua chlorophyll-a concentration (chl) estimates were analyzed before and after the passage of cold fronts in the SBB region, between 01/2004-12/2008. The frontal systems were more frequent during spring, winter and fall, with 157 cold fronts identified in Cabo Frio and 192 in Santos, with mean frequencies of 2-4 events per month. The Wilcoxon-signed rank test showed that the increase in chl after the cold front passages were significant (p-value < 0.05) within 3 days in Cabo Frio and 8 days in Santos. Cloud cover was a limitation for obtaining daily MODIS data. Future work should test the use of different orbital sensors, complemented by in situ biophysical data and numerical simulations for better understanding the role of cold front passages on water column and phytoplankton dynamics.