Gulf of Mexico Response to Hurricane Katrina (2005)

Michelle M Gierach, University of South Carolina, mhite@geol.sc.edu
Subrahmanyam Bulusu, University of South Carolina, sbulusu@geol.sc.edu (Presenting)

Analysis of satellite observations and model simulations provided an opportunity to assess the biological and physical effects of Hurricane Katrina (2005) in the Gulf of Mexico. An area of maximum surface chlorophyll-a concentration and sea surface cooling was detected with peak intensities of 3 mg m-3 and 4-6°C to the right and left of Katrina’s track. The temperature of the mixed layer cooled approximately 2°C and the depth of the mixed layer deepened by approximately 33-52 m. The forced deepening of the mixed layer injected nutrients into the euphotic zone, generating phytoplankton blooms 3-4 days after passage of Hurricane Katrina.

This study was further investigated through the use of 1/25° horizontal resolution nested GoM HYbrid Coordinate Ocean Model (HYCOM) simulations. It is important that both simulations and observations be used to provide a complete spatial and temporal evolution of the biophysical responses exhibited. Satellite and/or model simulations depicted sea surface cooling of 3°-7°C, salinity freshening of 0.2-0.3 psu, and chlorophyll-a enhancement (i.e., increase in phytoplankton biomass accumulation at the ocean’s surface) of approximately 3 mg m-3 within a region from 23.5°-25.5°N and 85°-83°W. Model sea surface height and satellite sea surface height anomalies illustrated that the region transpired in a cold-core eddy, which contributed to the enhanced observed and simulated responses. Analysis of model surface and subsurface dynamics in this region revealed rapid upwelling/downwelling of 2-2.5 x 10-4 m s-1, hurricane force wind-driven currents dominating the surface circulation, and near-inertial oscillations following Hurricane Katrina.