Budget of the total nitrogen in the Yucatan Shelf: driving mechanisms through a physical-biogeochemical coupled model

Abstract. Continental shelves are the most productive areas in the seas with strongest implications for global Total Nitrogen (TN) cycling. The Yucatan shelf is the largest shelf in the Gulf of Mexico (GoM), however, its general TN budget has not been quantified. This is largely due to the lack of significant spatio-temporal in situ measurements and the complexity of the shelf dynamics, including the Yucatan Current, coastal upwelling, Coastal Trapped Waves (CTWs) and bottom Ekman transport. Through a nine years output of a coupled physical-biogeochemical model of the GoM, the TN budget in the Yucatan shelf is quantified. Results indicate that the main entrance of inorganic nitrogen is through its southern and eastern margins. The TN is then advected to the oligotrophic deep GoM and to the deep Campeche bay. The analysis also shows that the inner shelf (50 m isobath) is efficient in terms of TN, since all the DIN imported into the shelf is consumed by the phytoplankton. Rivers contribute 20 % of the TN, while denitrification removes up to 53 % of TN that enters into the inner shelf. The high-frequency variability of the TN fluxes are modulated by the Yucatan Current in the south and by bottom Ekman transport produced by this current against the shelf-break (250 m isobath) in the east. This current-topography interaction can help to maintain the upwelling of Cape Catoche, uplifting nutrient-rich water into the euphotic layer. The export of TN at both western and northwestern margins is modulated by CTWs with a mean period of 10 days in agreement with recent observational and modelling studies.