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Title: A Numerical reassessment of the Gulf of Mexico carbon system in connection with the Mississippi River and global ocean
Abstract. 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 aspCO2, pH, aragonite saturation state (ΩArag), calcitesaturation state (ΩCalc), CO2 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 CO2flux with previous modeling and observational studies gives us confidencethat our model provides a robust and updated CO2 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 µatm yr−1 increase in sea surfacepCO2. The air–sea CO2 exchange estimation confirms in accordance with severalprevious models and ocean surface pCO2 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.  more » « less
Award ID(s):
1903340
PAR ID:
10438463
Author(s) / Creator(s):
;
Date Published:
Journal Name:
Biogeosciences
Volume:
19
Issue:
18
ISSN:
1726-4189
Page Range / eLocation ID:
4589 to 4618
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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