Satellite data analysis of the upper ocean response to hurricanes Katrina and Rita (2005) in the Gulf of Mexico

The biological and physical effects of hurricanes Katrina and Rita (2005) on the upper ocean are analyzed using satellite observations and model simulations of the mixed layer in the Gulf of Mexico. Along the hurricanes' passages, the Moderate Resolution Imaging Spectroradiometer and Advanced Very High Resolution Radiometer instruments detected two areas of maximum surface chlorophyll-a (chl a) concentration and sea surface cooling. These areas had peak intensities ranging from 2-3 mg.m(-3) and 3 degrees C-4 degrees C. The depth of the mixed layer deepened by approximately 33-52 m, and the temperature of the mixed layer cooled approximately 2 degrees C. Hurricane wind fields intensified the oceanic cyclonic circulation, maximizing upwelling, surface cooling, and deepening the mixed layer. The forced mixed layer deepening injected nutrients into the surface layer, resulting in phytoplankton blooms three-five days later (i.e., higher chl a concentrations).