A Numerical reassessment of the Gulf of Mexico carbon system in connection with the Mississippi River and global ocean
A Numerical reassessment of the Gulf of Mexico carbon system in connection with the Mississippi River and global ocean
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DOI：
10.5194/bg-19-4589-2022
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发表时间：
2022-09
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影响因子：
4.9
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摘要。物理-生物地球化学耦合模型可以填补海洋碳观测的时空空白。在区域海洋应用物理-生物地球化学耦合模型面临的挑战包括碳模型边界条件的合理规定、缺乏现场观测以及某些生物地球化学过程的过度简化。在这项研究中，我们将一个耦合的物理-生物地球化学模型（区域海洋模拟系统，ROMS）应用于墨西哥湾（GoM），并在2000年至2019年期间实现了前所未有的20年高分辨率（5公里，1/22°）后播。生物地球化学模型考虑了溶解有机碳（DOC）池的动力学和碳酸盐矿物的形成和溶解。利用NCAR的CESM2-WACCM-FV2溶液对17种gcm在墨西哥湾水域的表现进行了评价，插值得到了生物地球化学边界。模型输出包括广泛关注的碳系统变量，如二氧化碳分压、pH值、文石饱和状态（ΩArag）、方解石饱和状态（ΩCalc）、二氧化碳海气通量和碳埋藏率。通过与浮标、基于遥感的机器学习（ML）产品和基于船舶的测量进行广泛的模型数据比较，评估了模型的鲁棒性。利用以前的模拟和观测研究对海气CO2通量的重新评估使我们相信，我们的模型提供了可靠的、更新的CO2通量估算，而NGoM是比以前报道的更强的碳汇。模式结果显示，在过去20年里，墨西哥湾水域的表面pH值下降了~ 0.0016 yr - 1，同时海面二氧化碳分压增加了~ 1.66 μ atm yr - 1。海气CO2交换估算根据以往的几种模式和海洋表面pCO2观测结果证实，河流主导的墨西哥湾北部（NGoM）是一个实质性的碳汇，而开放的墨西哥湾在夏季是一个碳源，在全年其余时间是一个碳汇。通过模型边界进行了敏感性试验，以评估河流输入和全球海洋的影响。NGoM碳系统被来自密西西比-阿恰法拉亚河水系（MARS）的大量碳输入（~ 15.5 Tg C yr−1 DIC和~ 2.3 Tg C yr−1 DOC）直接改变。此外，营养刺激的生物活动在NGoM沉积物中产生的颗粒有机质埋葬率比没有河流输送营养的情况高约105倍。公海碳系统状况受加勒比海经尤卡坦海峡的输入驱动，受热效应的影响大于生物因素。
Abstract. Coupled physical–biogeochemical models can fill the spatial and temporal gap in ocean carbon observations. Challenges of applying a coupled physical–biogeochemical model in the regional ocean include the reasonable prescription of carbon model boundary conditions, lack of in situ observations, and the oversimplification of certain biogeochemical processes. In this study, we applied a coupled physical–biogeochemical model (Regional Ocean Modelling System, ROMS) to the Gulf of Mexico (GoM) and achieved an unprecedented 20-year high-resolution (5 km, 1/22∘) hindcast covering the period of 2000 to 2019. The biogeochemical model incorporated the dynamics of dissolved organic carbon (DOC) pools and the formation and dissolution of carbonate minerals. The biogeochemical boundaries were interpolated from NCAR's CESM2-WACCM-FV2 solution after evaluating the performance of 17 GCMs in the GoM waters. Model outputs included carbon system variables of wide interest, such as pCO2, pH, aragonite saturation state (ΩArag), calcite saturation state (ΩCalc), CO2 air–sea flux, and carbon burial rate. The model's robustness is evaluated via extensive model–data comparison against buoys, remote-sensing-based machine learning (ML) products, and ship-based measurements. A reassessment of air–sea CO2 flux with previous modeling and observational studies gives us confidence that our model provides a robust and updated CO2 flux estimation, and NGoM is a stronger carbon sink than previously reported. Model results reveal 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 surface pCO2. The air–sea CO2 exchange estimation confirms in accordance with several previous models and ocean surface pCO2 observations that the river-dominated northern GoM (NGoM) is a substantial carbon sink, and the open GoM is a carbon source during summer and a carbon sink for the rest of the year. Sensitivity experiments are conducted to evaluate the impacts of river inputs and the global ocean via model boundaries. The NGoM carbon system is directly modified by the enormous carbon inputs (∼ 15.5 Tg C yr−1 DIC and ∼ 2.3 Tg C yr−1 DOC) from the Mississippi–Atchafalaya River System (MARS). Additionally, nutrient-stimulated biological activities create a ∼ 105 times higher particulate organic matter burial rate in NGoM sediment than in the case without river-delivered nutrients. The carbon system condition of the open ocean is driven by inputs from the Caribbean Sea via the Yucatan Channel and is affected more by thermal effects than biological factors.