Increasing River Alkalinity Slows Ocean Acidification in the Northern Gulf of Mexico

• Published in: Geophysical research letters Vol. 48; no. 24
• Main Authors: Gomez, Fabian A., Wanninkhof, Rik, Barbero, Leticia, Lee, Sang‐Ki
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.12.2021
• Subjects: Acidification; Alkalinity; Anthropogenic factors; Aragonite; Biological activity; Biological production; Carbon; Carbon dioxide; Climate variability; Coastal plains; Coastal waters; Gulf of Mexico; Human influences; Mathematical models; Mississippi River; Numerical models; Ocean acidification; ocean alkalinity; ocean biogeochemical modeling; Ocean temperature; Ocean warming; Oceans; pH effects; river chemistry; River discharge; River flow; River runoff; Rivers; Runoff; Saturation; Sensitivity analysis; Spatial variability; Spatial variations; Trends; Uptake; Variability; United States > US; Mississippi; Gulf of Mexico
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL096521

Ocean acidification (OA) progression is affected by multiple factors, such as ocean warming, biological production, and river runoff. Here we used an ocean‐biogeochemical model to assess the impact of river runoff and climate variability on the spatiotemporal patterns of OA in the Gulf of Mexico (GoM) during 1981–2014. The model showed the expected pH and aragonite saturation state (ΩAr) decline, due to the increase in anthropogenic carbon, with trends close to values reported for the Subtropical North Atlantic. However, significant departures from the basin‐averaged pattern were obtained in part of the northern GoM shelf, where pH and ΩAr increased. Model sensitivity analyses showed that OA progression was counteracted by enhanced alkalinity from the Mississippi‐Atchafalaya River System. Our findings highlight that river alkalinity is a key driver of carbon system variability in river‐dominated ocean margins and emphasize the need to quantify riverine chemistry to properly assess acidification in coastal waters. Plain Language Summary Although ocean acidification (OA) is mainly driven by the ocean uptake of anthropogenic carbon dioxide from the atmosphere, multiple factors influence its temporal progression, including changes in ocean temperature, biological processes, and river discharge. Here we used numerical model outputs to describe historical OA trends across the Gulf of Mexico (GoM) and identify the main drivers of its spatial variability. We showed that changes in river runoff slowed OA over the northern GoM coast. This was mainly due to an increasing Mississippi river alkalinity concentration, a property related to the water capacity to neutralize acidification. Our results show the importance of alkalinity changes to quantify OA progression in the GoM. Key Points We simulated the spatiotemporal variability of ocean acidification progression over the Gulf of Mexico during 1981–2014 Model results showed positive trends in the surface ocean alkalinity, salinity, and temperature influencing acidification trends Increasing Mississippi river alkalinity substantially lessened the ocean acidification progression on the northern Gulf of Mexico shelf