High-resolution model simulation of ocean acidification progression in the Gulf of Mexico during 1981-2014

Abstract:

Ocean Acidification (OA) progression in the Gulf of Mexico (GoM) remains poorly documented due to the lack of long observational records to discriminate long-term carbon chemistry trends. Here we used a high-resolution (~8 km) ocean-biogeochemical model to describe OA trend in the GoM during 1981-2014. The simulated basin-averaged trends for surface aragonite saturation state (Ω_Ar) and pH were –0.0086 yr^–1 and –0.0015 yr^–1, respectively. The largest differences from the mean basin patterns were observed over parts of the Louisiana inner shelf, where surface W_Ar and pH displayed positive trends. Our analysis suggests that a significant increase in total alkalinity (TA) in this region counteracted the expected OA patterns. Further analysis suggests that the increase in surface TA along the northern GoM shelf was largely caused by an increase in Mississippi river alkalinity. The model results also showed significant interdecadal changes in the magnitude of the OA trends before and after the Pacific climate regime shift in 1997-1998, due partly to the increasing atmospheric CO₂ trend, and changes in river runoff and sea surface temperature (SST). Our model results identify TA as one of the key drivers of the low frequency carbon system variability in the northern GoM shelf, and highlight the need for prescribing (or simulating) realistic river alkalinity fluxes to properly assess OA progression in coastal regions.