Increasing river alkalinity slows ocean acidification in the northern Gulf of Mexico

Abstract

Ocean acidification (OA) progression is affected by multiple factors, such as ocean warming, biological production, and 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.

Projected climate oligotrophication of the Adriatic marine ecosystems

“…The acidification trend obtained within the different regions of the Adriatic Sea is of the same order of changes detected at the global scale (e.g., Doney et al, 2009) as well as in the Mediterranean Sea (Cossarini et al, 2021;Hassoun et al, 2022;Reale et al, 2022;Solidoro et al, 2022;Kristiansen et al, 2024). The Northern Estuarine area stands out as more acidic than the others at present day, and at the same time less affected by acidification, hinting at the important role that rivers can play as sources of carbon and alkalinity, already observed in past studies (Müller et al, 2016;Butenschön et al, 2021;Gomez et al, 2021;Reale et al, 2022), and object of further research in future projects on the Adriatic Sea. Indeed, in the literature this behavior is associated with the fact that in the Northern Adriatic Sea the TA is in the upper range of that measured in the Mediterranean Sea, primarily because riverine inputs transport carbonates dissolved from Alpine dolomites and karstic watersheds (Brush et al, 2020).…”