Data_Sheet_1_Long-Term Trends in Estuarine Carbonate Chemistry in the Northwestern Gulf of Mexico.pdf

A four-decade dataset that spans seven estuaries along a latitudinal gradient in the northwestern Gulf of Mexico and includes measurements of pH and total alkalinity was used to calculate partial pressure of CO₂ (pCO₂), dissolved inorganic carbon (DIC), saturation state of aragonite (Ω_Ar), and a buffer factor (β_DIC, which measures the response of proton concentration or pH to DIC concentration change) and examine long-term trends and spatial patterns in these parameters. With the notable exception of the northernmost and southernmost estuaries (and selected stations near freshwater input), these estuaries have generally experienced long-term increases in pCO₂ and decreases in DIC, Ω_Ar, and β_DIC, with the magnitude of change generally increasing from north to south. At all stations with increasing pCO₂, the rate of increase exceeded the rate of increase in atmospheric pCO₂, indicating that these estuaries have become a greater source of CO₂ to the atmosphere over the last few decades. The decreases in Ω_Ar have yet to cause Ω_Ar to near undersaturation, but even the observed decreases may have the potential to decrease calcification rates in important estuarine calcifiers like oysters. The decreases in β_DIC directly indicate that these estuaries have experienced continually greater change in pH in the context of ocean acidification.