Modeling pCO₂ variability in the Gulf of Mexico

A three-dimensional coupled physical-biogeochemical model was used to simulate and examine temporal and spatial variability of sea surface pCO₂ in the Gulf of Mexico (GoM). The model was driven by realistic atmospheric forcing, open boundary conditions from a dataassimilative global ocean circulation model, and observed freshwater and terrestrial nutrient and carbon input from major rivers. A 7-year model hindcast (2004-2010) was performed and validated against ship measurements. Model results revealed clear seasonality in surface pCO₂ and were used to estimate carbon budgets in the Gulf. Based on the average of model simulations, the GoM was a net CO₂ sink with a flux of 1.11±0.84×10¹² mol Cyr^-1, which, together with the enormous fluvial inorganic carbon input, was comparable to the inorganic carbon export through the Loop Current. Two model sensitivity experiments were performed: one without biological sources and sinks and the other using river input from the 1904-1910 period as simulated by the Dynamic Land Ecosystem Model (DLEM). It was found that biological uptake was the primary driver making GoM an overall CO₂ sink and that the carbon flux in the northern GoM was very susceptible to changes in river forcing. Large uncertainties in model simulations warrant further process-based investigations.