A Numerical reassessment of the Gulf of Mexico carbon system in connection with the Mississippi River and global ocean

[摘要] Coupled physical–biogeochemical models can fill thespatial and temporal gap in ocean carbon observations. Challenges ofapplying a coupled physical–biogeochemical model in the regional oceaninclude the reasonable prescription of carbon model boundary conditions,lack of in situ observations, and the oversimplification of certainbiogeochemical processes. In this study, we applied a coupledphysical–biogeochemical model (Regional Ocean Modelling System, ROMS) to theGulf of Mexico (GoM) and achieved an unprecedented 20-year high-resolution(5 km, 1 / 22 ∘ ) hindcast covering the period of 2000 to 2019. Thebiogeochemical model incorporated the dynamics of dissolved organic carbon(DOC) pools and the formation and dissolution of carbonate minerals. Thebiogeochemical boundaries were interpolated from NCAR's CESM2-WACCM-FV2solution after evaluating the performance of 17 GCMs in the GoM waters. Modeloutputs included carbon system variables of wide interest, such as p CO 2 , pH, aragonite saturation state ( Ω Arag ), calcitesaturation state ( Ω Calc ), CO 2 air–sea flux, and carbon burialrate. The model's robustness is evaluated via extensive model–datacomparison against buoys, remote-sensing-based machine learning (ML)products, and ship-based measurements. A reassessment of air–sea CO 2 flux with previous modeling and observational studies gives us confidencethat our model provides a robust and updated CO 2 flux estimation, andNGoM is a stronger carbon sink than previously reported. Model resultsreveal that the GoM water has been experiencing a ∼  0.0016 yr −1 decrease in surface pH over the past 2 decades, accompanied by a ∼  1.66  µ atm yr −1 increase in sea surface p CO 2 . The air–sea CO 2 exchange estimation confirms in accordance with severalprevious models and ocean surface p CO 2 observations that theriver-dominated northern GoM (NGoM) is a substantial carbon sink, and theopen GoM is a carbon source during summer and a carbon sink for the rest ofthe year. Sensitivity experiments are conducted to evaluate the impacts ofriver inputs and the global ocean via model boundaries. The NGoM carbonsystem is directly modified by the enormous carbon inputs ( ∼  15.5 Tg C yr −1 DIC and ∼  2.3 Tg C yr −1 DOC) from theMississippi–Atchafalaya River System (MARS). Additionally,nutrient-stimulated biological activities create a ∼  105 timeshigher particulate organic matter burial rate in NGoM sediment than in thecase without river-delivered nutrients. The carbon system condition of theopen ocean is driven by inputs from the Caribbean Sea via the Yucatan Channeland is affected more by thermal effects than biological factors.

[学科分类] 大气科学