Abstract
Abstract. Uncertainties in carbon chemistry variability still remain large in the Gulf of Mexico (GoM), as data gaps limit our ability to infer basin-wide patterns. Here we configure and validate a regional high-resolution ocean biogeochemical model for the GoM to describe seasonal patterns in surface pressure of CO2 (pCO2), aragonite saturation state (ΩAr), and sea–air CO2 flux. Model results indicate that seasonal changes in surface pCO2 are strongly controlled by temperature across most of the GoM basin, except in the vicinity of the Mississippi–Atchafalaya river system delta, where runoff largely controls dissolved inorganic carbon (DIC) and total alkalinity (TA) changes. Our model results also show that seasonal patterns of surface ΩAr are driven by seasonal changes in DIC and TA, and reinforced by the seasonal changes in temperature. Simulated sea–air CO2 fluxes are consistent with previous observation-based estimates that show CO2 uptake during winter–spring, and CO2 outgassing during summer–fall. Annually, our model indicates a basin-wide mean CO2 uptake of 0.35 molm-2yr-1, and a northern GoM shelf (< 200 m) uptake of 0.93 molm-2yr-1. The observation and model-derived patterns of surface pCO2 and CO2 fluxes show good correspondence; thus this study contributes to improved constraints of the carbon budget in the region.
Highlights
The global ocean is absorbing approximately one-third of the anthropogenic CO2 released into the atmosphere from fossil fuel burning (e.g., Sabine et al, 2004; Gruber et al 2019), resulting in a sustained decline in seawater pH and the saturation state of calcium carbonate (e.g., Orr et al, 2005)
This paper is structured such that we (1) describe the ocean biogeochemical model and dataset used for the study; (2) validate the model based on observations from a coastal buoy, the GOMECC-1 cruise, and ship of opportunity (SOOP); (3) describe surface inorganic carbon system variables; (4) describe sea–air CO2 fluxes in coastal and ocean domains; and (5) discuss the main model results in the context of previous observational and modeling studies
Model results indicated that river runoff- and wind-driven circulation significantly influence coastal dissolved inorganic carbon (DIC) and total alkalinity (TA) patterns in coastal regions, impacting Ar, pressure of CO2 (pCO2), and sea–air CO2 flux seasonality
Summary
The global ocean is absorbing approximately one-third of the anthropogenic CO2 released into the atmosphere from fossil fuel burning (e.g., Sabine et al, 2004; Gruber et al 2019), resulting in a sustained decline in seawater pH and the saturation state of calcium carbonate (e.g., Orr et al, 2005). The modeled sea–air CO2 flux in the northern GoM (−0.32 mol m−2 yr−1) was about onethird of the flux derived by Huang et al (2015) and Lohrenz et al (2018), while the modeled flux for the deep Gulf (−1.04 mol m−2 yr−1) was more than twice the flux derived by Robbins et al (2014) In another modeling study, Laurent et al (2017) examined near-bottom acidification driven by coastal eutrophication. Their model reproduced observed patterns in surface pCO2, sea–air CO2 fluxes, pH, alkalinity, and dissolved inorganic carbon (DIC), but the model domain was limited to the Louisiana–Texas shelf. This paper is structured such that we (1) describe the ocean biogeochemical model and dataset used for the study; (2) validate the model based on observations from a coastal buoy, the GOMECC-1 cruise, and SOOP; (3) describe surface inorganic carbon system variables; (4) describe sea–air CO2 fluxes in coastal and ocean domains; and (5) discuss the main model results in the context of previous observational and modeling studies
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