Surface Water CO₂ variability in the Gulf of Mexico (1996-2017)

Approximately 380,000 underway measurements of sea surface salinity, temperature, and carbon dioxide (CO₂) in the Gulf of Mexico (GoM) were compiled from the Surface Ocean CO₂ Atlas (SOCAT) to provide a comprehensive observational analysis of spatiotemporal CO₂ dynamics from 1996 to 2017. An empirical orthogonal function (EOF) was used to derive the main drivers of spatial and temporal variability in the dataset. In open and coastal waters, drivers were identified as a biological component linked to riverine water, and temperature seasonality. Air-sea flux estimates indicate the GoM open (- 0.06 ± 0.45 mol C m^-2 year^-1) and coastal (- 0.03 ± 1.83 mol C m^-2 year^-1) ocean are approximately neutral in terms of an annual source or sink for atmospheric CO₂. Surface water pCO₂ in the northwest and southeast GoM open ocean is increasing (1.63 ± 0.63 µatm  year^-1 and 1.70 ± 0.14 µatm year^-1, respectively) at rates comparable to those measured at long-term ocean time-series stations. The average annual increase in coastal CO₂ was 3.20 ± 1.47 µatm year^-1 for the northwestern GoM and 2.35 ± 0.82 µatm year^-1 for the west Florida Shelf. However, surface CO₂ in the central (coastal and open) GoM, which is influenced by Mississippi and Atchafalaya River outflow, remained fairly stable over this time period.