AUTHOR=McCutcheon Melissa R. , Hu Xinping 

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

JOURNAL=Frontiers in Marine Science

VOLUME=9

YEAR=2022

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2022.793065

DOI=10.3389/fmars.2022.793065

ISSN=2296-7745

ABSTRACT=<p>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<sub>2</sub> (<italic>p</italic>CO<sub>2</sub>), dissolved inorganic carbon (DIC), saturation state of aragonite (Ω<sub>Ar</sub>), and a buffer factor (β<sub>DIC</sub>, 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 <italic>p</italic>CO<sub>2</sub> and decreases in DIC, Ω<sub>Ar</sub>, and β<sub>DIC</sub>, with the magnitude of change generally increasing from north to south. At all stations with increasing <italic>p</italic>CO<sub>2</sub>, the rate of increase exceeded the rate of increase in atmospheric <italic>p</italic>CO<sub>2</sub>, indicating that these estuaries have become a greater source of CO<sub>2</sub> to the atmosphere over the last few decades. The decreases in Ω<sub>Ar</sub> have yet to cause Ω<sub>Ar</sub> 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<sub>DIC</sub> directly indicate that these estuaries have experienced continually greater change in pH in the context of ocean acidification.</p>