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.
Highlights
The Gulf of Mexico (GoM) is a semi-closed sea that covers an area of ∼ 1.5 × 106 km2
The annual cycle of the deep region of the Gulf of Mexico analyzed in this study is consistent with the model data that has been reported by Fennel et al (2011), Xue et al (2013), Gomez et al (2018b), and Damien et al (2018), cruise data analyzed by Hidalgo-González and Alvarez-Borrego (2008), and profiler data analyzed by Pasqueron de Fommervault et al (2017) for 185 both the surface and water column
This annual cycle appears to be stable and consistent in all simulation years. This cycle responds mainly to intense vertical mixing caused by winds associated with cold fronts that occur during October–March, mesoscale processes that are mainly associated with the Loop Current, and the eddies that emerge from the Loop Current and eject filaments of chlorophyll-rich water to the central region of the Gulf of Mexico
Summary
The Gulf of Mexico (GoM) is a semi-closed sea that covers an area of ∼ 1.5 × 106 km2 It is located between 18–30◦ N 20 and 82–98◦ W (Fig. 1) and connects with the Atlantic Ocean through the Yucatan Channel and the Straits of Florida. Of the 16 rivers that flow into the GoM from Mexican territory, the Grijalva, Usumacinta, Coatzacoalcos, Papaloapan, and Panuco rivers provide the majority of the freshwater to the gulf, with a combined flow of ∼ 2.2 × 106 m3 per year (Fig 2). This value constitutes ∼ 90% of the total runoff from Mexican territory into the GoM (CONAGUA, 2014). The identification of extraordinary events with regard to the responses of phytoplankton based on the new daily flow rate data were evaluated in the coupled model
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