Long-Term Trends in Estuarine Carbonate Chemistry in the Northwestern Gulf of Mexico

• Published in: Frontiers in Marine Science 2022-03, Vol.9
• Main Authors: McCutcheon, Melissa R., Hu, Xinping
• Format: Article
• Language: English
• Subjects: Acidification; Alkalinity; Aragonite; Brackishwater environment; buffer capacity; Calcification; Carbon; Carbon dioxide; carbonate chemistry; Carbonates; Chemistry; Coasts; Dissolved inorganic carbon; Environmental quality; Estuaries; Estuarine environments; estuary; Freshwater; Inland water environment; Latitudinal variations; long-term trend; Marine molluscs; Metabolism; Oysters; pCO2; pH effects; Precipitation; Salinity; Saturation; Surface water; Trends; Water quality
• ISSN: 2296-7745; 2296-7745
• DOI: 10.3389/fmars.2022.793065

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 CO 2 ( p CO 2 ), 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 p CO 2 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 p CO 2 , the rate of increase exceeded the rate of increase in atmospheric p CO 2 , indicating that these estuaries have become a greater source of CO 2 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.