Physical and biogeochemical controls of the carbonate system of the Yucatan Shelf

The dynamics and distribution of the carbonate system and the processes that regulate it over the Yucatan Shelf (YS), a region of karst geology and high productivity that is influenced by submarine groundwater discharges (SGDs) and upwelling, were explored with data from two oceanographic cruises. The first oceanographic cruise was conducted in November 2015 during the Nortes season, a period of intense northerly wind activity, and a second cruise was conducted during the rainy season in August/September 2016. Notable biogeochemical differences were present between them. At the surface, Caribbean Surface Water (CSW) predominated over the shelf in both periods. During the Nortes cruise, a surface nearshore-offshore gradient showed high dissolved inorganic carbon (DIC; similar to 2470 mu mol kg(-1)) and total alkalinity (TA; similar to 2460 mu mol kg(-1)) values near the coast and average pH(Total) and pCO(2) values of 7.42 +/- 0.10 and 2206 +/- 546 mu atm, respectively. These geochemical characteristics were attributed to the influence of SGDs, punctuated by relatively low delta C-13(DIC) values between -4.18 parts per thousand and -2.49 parts per thousand, which reflects an important oxidation of organic carbon and the dissolution of carbonate minerals. The presence of upwelled water on the eastern side of the YS showed average DIC and pH(Tota)(l) values of 2260 +/- 15 mu mol kg(-1) and 7.69 +/- 0.08, respectively, which were lower than coastal values. During the rainy cruise, the advection of CSW by the Yucatan Current was traced by its thermohaline properties. However, the surface water carbonate system was relatively homogeneous, with average DIC, TA, pH(Tota)(l) and pCO(2) values of 2047 +/- 16 mu mol kg(-1), 2388 +/- 11 mu mol kg(-1), 8.02 +/- 0.02, and 440 +/- 27 mu atm, respectively. Lastly, the delta C-13(DIC) values during this cruise ranged from -1.21 parts per thousand to 1.25 parts per thousand, which suggests that the carbonate system is mainly regulated by organic matter production and respiration.