Outflow of Gulf of Mexico Waters Below 600 m Through the Western Yucatan Channel Suggested by Biogeochemical Tracers and Hydrography

Jose Augusto Valencia Gasti, Universidad Autonoma de Baja California, Instituto de Investigaciones Oceanológicas, Ensenada, BJ, Mexico, Victor F Camacho-Ibar, Autonomous University of Baja California- UABC, Instituto de Investigaciones Oceanológicas, Ensenada, Mexico, Jose Martin Martin Hernandez-Ayon, Autonomous University of Baja California, Instituto de Investigaciones Oceanológicas, Ensenada, BJ, Mexico and Leticia Barbero, University of Miami, Cooperative Institute for Marine and Atmospheric Studies, CIMAS, Miami, United States
Based on data collected during two summer cruises in the Gulf of Mexico (GoM), an extended optimum multiparameter analysis (eOMP) was applied in order to quantify the mixing of water masses and to estimate nutrient concentration changes through biogeochemical processes within the gulf. The eOMP results from the Yucatan Channel west of 85.9º W and the slope of the isopycnals were used to infer the inflow/outflow of water properties below the mixed layer. A decreasing gradient into the GoM in the contribution of the three water masses dominating the thermocline, i.e., the North Atlantic Subtropical Water, the Eighteen-degree Mode Water and the Tropical Atlantic Central Water, reflect the inflow of the Yucatan currents. Below 600 m, waters were characterized by relatively high nitrate and silicate concentrations indicating an enrichment within the GoM that is not explained only from mixing. The presence of nutrient enriched waters reflects an outflow between 700 and 1200 m, where the Antarctic Intermediate water mass has a large contribution (<70%) between 700-800 m and the North Atlantic Deep water mass dominates below 800 m. Particularly noticeable is the enrichment in silicate in the deep water of the basin where its concentration remains constant (≅25-26 μmol kg-1) below ∼1200 m, however, the source of enrichment has yet to be determined. Our results show that nutrients and dissolved oxygen are useful in tracing water mass exchange through the Yucatan Channel and can complement direct current measurements. However, higher spatial and temporal sampling resolution is required to better understand the complex water exchange with the Caribbean basins.