The Carbonate System in the Yucatan Platform in the Gulf of México

In this work, the spatial patterns of the variables of the carbonate system [i.e. dissolved inorganic carbon (DIC), total alkalinity (TA), pH_total and δ¹³C_DIC] in the platform of Yucatan were determined in order to identify the main processes that control its distribution. Data were generated from two campaigns: one in November (2015), representative month of the "nortes" season in winter, and the second in August (2016) representative of the rainy season in summer. CTD cast and discrete samples of seawater were taken at surface and bottom. In general, two oceanographic conditions were observed: 1) Summer sampling was characterized by the presence of Caribbean Surface Water (CSW) advected from the east side of the platform with a temperature >30 °C, salinity of ~36, low values of DIC (2020 μM km^-1) and TA (2380 μM km^-1), and high pH_total (~8.3). This water changes as it moves westward, acquiring greater salinity (~36.8), DIC (2120 μM km^-1) and TA (2410 μM km^-1); therefore, an east-west gradient was observed spatially. The δ¹³C_DIC also reflected this spatial gradient, with more enriched values (~1.24‰) distributed on the east side of the platform. 2) Winter sampling was characterized by submarine groundwater discharge (SDG), which determined both variability and high concentration of DIC (2490 μM km^-1), TA (2467 μM km^-1), and low pH_total (~7.5) values, generating a coast-ocean gradient. This was verified with the δ¹³C_DIC that presented values between -4.18 – 0.39‰. The most negative values correspond to the area associated with the coast. This δ¹³C_DIC values, together with the high DIC and TA, and low pH_total suggest that in the coastal zone, the process of dissolution is taking place due to the effect of SGD.