Connecting the Mississippi River with Carbon Variability in the Gulf of Mexico

To understand the linkage between landuse/land-cover change within the Mississippi basin and the carbon dynamics in the Gulf of Mexico, a three-dimensional coupled physical-biogeochemical model was used to the examine temporal and spatial variability of surface ocean pCO₂ in the Gulf of Mexico (GoM). The model is driven by realistic atmospheric forcing, open boundary conditions from a data-assimilative global ocean circulation model, and freshwater and terrestrial nutrient and carbon input from major rivers provided by the Dynamic Land Ecosystem Model (DLEM). A seven-year model hindcast (2004–2010) was performed and was validated against the recently updated Lamont-Doherty Earth Observatory global ocean carbon dataset. Model simulated seawater pCO₂ and air-sea CO₂ flux are in good agreement with in-situ measurements. An inorganic carbon budget was estimated based on the multi-year mean of the model results. Overall, the GoM is a sink of atmospheric CO₂ with a flux of 0.92 × 10¹² mol C yr^-1, which, together with the enormous fluvial carbon input, is balanced by carbon export through the Loop Current. In a sensitivity experiment with all biological sources and sinks of carbon disabled surface pCO₂ was elevated by ~70 ppm, suggesting that biological uptake is the most important reason for the simulated CO₂ sink. The impact from landuse and land-cover changes within the Mississippi River basin on coastal pCO₂ dynamics is also discussed based on a scenario run driven by river conditions during the 1904-1910 provided by the DLEM model.