Modeling pCO2 variability in the Gulf of Mexico Biogeosciences

A three-dimensional coupled physical–biogeochemical model was used to simulate and examine temporal and spatial variability of sea surface pCO2 in the Gulf of Mexico (GoM). The model was driven by realistic atmospheric forcing, open boundary conditions from a data-assimilative global ocean circulation model, and observed freshwater and terrestrial nutrient and carbon input from major rivers. A 7-year model hindcast (2004–2010) was performed and validated against ship measurements. Model results revealed clear seasonality in surface pCO2 and were used to estimate carbon budgets in the Gulf. Based on the average of model simulations, the GoM was a net CO2 sink with a flux of 1.11 ± 0.84  ×  1012 mol C yr−1, which, together with the enormous fluvial inorganic carbon input, was comparable to the inorganic carbon export through the Loop Current. Two model sensitivity experiments were performed: one without biological sources and sinks and the other using river input from the 1904–1910 period as simulated by the Dynamic Land Ecosystem Model (DLEM). It was found that biological uptake was the primary driver making GoM an overall CO2 sink and that the carbon flux in the northern GoM was very susceptible to changes in river forcing. Large uncertainties in model simulations warrant further process-based investigations. Grant no. NA11NOS0120033

本研究采用三维耦合物理-生物地球化学模型，模拟并探究了墨西哥湾（Gulf of Mexico, GoM）海面pCO₂的时空变化特征。该模型以真实大气强迫场、来自数据同化全球海洋环流模型的开放边界条件，以及实测的主要河流淡水输入、陆地营养盐与碳输入作为驱动项。本研究开展了2004–2010年共计7年的模型历史回算，并利用船舶实测数据对模型结果进行了验证。模型结果显示海面pCO₂存在显著的季节周期性，并据此估算了墨西哥湾的碳收支。基于模型模拟的平均结果，墨西哥湾整体为大气CO₂的净汇，其碳通量为1.11 ± 0.84 × 10¹² mol C yr⁻¹；该通量与巨量河流无机碳输入之和，与通过环洋流（Loop Current）输出的无机碳通量量级相当。本研究设置两组模型敏感性试验：一组移除了生物源与生物汇过程，另一组采用动态陆地生态系统模型（Dynamic Land Ecosystem Model, DLEM）模拟的1904–1910年河流输入数据。研究发现，生物吸收是使墨西哥湾成为整体碳汇的核心驱动因子，且墨西哥湾北部的碳通量对河流强迫的变化极为敏感。模型模拟存在较大不确定性，亟需开展更多基于过程的深入研究。资助编号：NA11NOS0120033