Biological response to wind and terrestrial nitrate in the western and southern continental shelves of the Gulf of Mexico

Abstract

Abstract. In Mexico, 16 rivers directly discharge into the Gulf of Mexico. The Mexican rivers and those coming from the United States generate large regions in which phytoplanktonic primary production possesses a seasonal component that is linked to these nutrient-rich freshwater inputs. In the present study, new flow and daily nutrient data were obtained for the largest Mexican rivers. These data were integrated as forcing factors in a configuration of the hydrodynamic Coastal and Regional Ocean COmmunity model coupled to an N2PZD2 biogeochemical model. To correctly represent biological processes in coastal regions, a biological bottom condition was implemented in the biogeochemical model. With this condition, it was possible to represent remineralization on the continental shelf of the Gulf of Mexico. We present a 21 year simulation using two different configurations. The first included river forcing, and the second did not consider their influence. The results were validated with satellite images of the surface concentration of chlorophyll and compared with data from previous studies. The coupled model was able to realistically reproduce the seasonal dynamics of primary production in the Gulf of Mexico based on the concentration and distribution of chlorophyll, both at the surface and in the water column. Finally, the physical processes that influence the dynamics of primary production in the deep region and continental shelf of the gulf were defined. In the deep region, primary production was dominated by vertical mixing induced by the passage of cold fronts during winter and mesoscale structures. On the continental shelf, such dynamics were dominated by coastal upwelling and fluvial nutrient contributions.