Abstract

Coastal ecosystems with karstic geology have a unique characteristic where the dissolution of carbonate rocks can increase total alkalinity (TA) and dissolved inorganic carbon (DIC). This results in higher inorganic carbon budgets in coastal areas. One such ecosystem is the Terminos Lagoon, the most extensive tropical estuarine lagoon system in Mexico, located in the karstic aquifer of the Yucatan Peninsula and connected to the southern Gulf of Mexico (sGoM). We measured TA and DIC to evaluate the variability in Terminos Lagoon's of the carbonate system. We also estimated pH, partial CO2 pressure (pCO2), and aragonite saturation (ohm Ar) along two transects from the main lagoon tributaries (Palizada and Candelaria rivers) to the coastal zone during the dry and rainy seasons. During the dry season, TA and DIC concentrations were significantly higher (3092 +/- 452 mu mol kg-1 TA, 2943 +/- 522 mu mol kg-1 DIC) than during the rainy season (2533 +/- 228 mu mol kg-1 TA, 2492 +/- 259 DIC mu mol kg-1). Our calculations indicate that the rainy season pCO2 (2532 +/- 2371 mu atm) seems higher than in the dry season (1534 +/- 1192 mu atm). This leads to a reduction in pH (7.9 +/- 0.3 to 7.8 +/- 0.3). These significant changes indicate that rain increases the flow of unsaturated river water into the lagoon. The results of this work contribute toward a dissolved inorganic carbon variability baseline in the sGoM and can be helpful to Terminos Lagoon decision-makers.