Seasonal and interannual variability of cross-shelf transports of chlorophyll in the Gulf of Mexico

The seasonal and interannual variability of offshore cross-shelf transports of chlorophyll-rich waters in the Gulf of Mexico is studied using Level-3, monthly SeaWiFS data and monthly NCEP/NCAR-Reanalysis winds for the period September 1997–August 2007. Offshore cross-shelf transports of chlorophyll-rich waters have a seasonal cycle mainly modulated by the component of the wind field along the coast. These transports are basically located at three regions: southwest of the Texas–Louisiana (LATEX) Shelf, the southern Bay of Campeche, and southeast of the Mississippi River mouth.Southwest of the LATEX Shelf and in the southern Bay of Campeche, the confluence of seasonal along-coast currents, produced by the convergence of the seasonal along-coast wind stress component, induces offshore cross-shelf transport of chlorophyll-rich waters, with maximum values of chlorophyll-a concentration occurring at these locations during May and October–November, respectively. On the slope, southeast of the Mississippi River mouth, the seasonal maximum of chlorophyll-a concentration is observed in July due to the prevailing southwesterly winds during this month.A large fraction of the interannual variability of the offshore cross-shelf transports of chlorophyll-rich waters in the southern Bay of Campeche is explained by anomalies of the convergence of the along-coast wind stress component. On the southwestern LATEX Shelf, in addition to this process, cyclonic and anticyclonic eddies reaching this region may contribute to the interannual variability by shifting the location of the offshore cross-shelf transports.