Although ocean acidification (OA) is mainly driven by the ocean uptake of anthropogenic carbon dioxide from the atmosphere, multiple factors including changes in ocean temperature, biological processes, and river discharge influence its temporal progression. In a new paper accepted in the Geophysical Research Letters, a team of researchers from the Northern Gulf Institute of the Mississippi State University, and NOAA’s Atlantic Oceanographic and Meteorological Laboratory used a regional ocean-biogeochemical model to describe historical OA trends across the Gulf of Mexico (GoM) and identify the main drivers of its spatial variability. This study showed that changes in river runoff slowed OA over the northern GoM coast. This was mainly due to an increasing Mississippi river alkalinity concentration during the study period (1981-2014), a property related to the water capacity to neutralize acidification. This finding highlights that river alkalinity is a key driver of carbon system variability in river-dominated ocean margins and emphasizes the need to quantify riverine chemistry to properly assess acidification in coastal waters.
Figure 1c. from Gomez et al., (2021): Surface trends of aragonite saturation state (ΩAR) in the northern GoM during 1981-2014, derived from the model hindcast. Black contour lines depict the 25 and 200 m isobaths. The 25 m isobath defines the limit between the inner and outer shelf. A decline in the saturation state of carbonate minerals, especially aragonite, is a good indicator of a rise in ocean acidification.
Gomez, F. A., Wanninkhof, R., Barbero, L., & Lee, S.-K. (2021). Increasing river alkalinity slows ocean acidification in the northern Gulf of Mexico. Geophysical Research Letters, 48, e2021GL096521. https://doi.org/10.1029/2021GL096521
Ocean to Climate 
River runoff creates a buffer zone for Ocean Acidification in the Gulf of Mexico
https://www.aoml.noaa.gov/news/river-runoff-creates-a-buffer-zone-for-ocean-acidification-in-the-gulf-of-mexico/