Carbonate Chemistry in Estuaries Along a Hydrological Gradient in the Northwestern Gulf of Mexico

Estuaries in the northwestern Gulf of Mexico span a dramatic climatic gradient in a relatively narrow latitudinal band. As a result of decreasing precipitation and increasing evaporation, these estuaries exhibit a strong spatial heterogeneity in terms of freshwater balance, which decreases by two orders of magnitude from northeast to southwest. In addition to the disparity in freshwater availability, drainage basin mineralogy plays an important role in determining the levels of weathering products delivered into these estuaries by rivers. A complex interplay among the freshwater input, estuarine residence time, and biogeochemical reactions renders these estuaries with distinctively different carbonate chemistry characteristics in water salinities that range from mesohaline to hypersaline. These estuaries provide a “natural laboratory” to examine the suitability of estuarine carbonate chemistry to calcifying organisms under the drier regional conditions projected due to climate change.