This review examines the current understanding of the global coastal ocean carbon cycle and provides a new quantitative synthesis of air-sea CO2 exchange. This reanalysis yields an estimate for the globally integrated coastal ocean CO2 flux of −0.25 ± 0.05 Pg C year−1, with polar and subpolar regions accounting for most of the CO2 removal (>90%). A framework that classifies river-dominated ocean margin (RiOMar) and ocean-dominated margin (OceMar) systems is used to conceptualizecoastal carbon cycle processes. The carbon dynamics in three contrasting case study regions, the Baltic Sea, the Mid-Atlantic Bight, and the South China Sea, are compared in terms of the spatio-temporal variability of surface pCO2. Ocean carbon models that range from box models to three-dimensional coupled circulation-biogeochemical models are reviewed in terms of the ability to simulate key processes and project future changes in different continental shelf regions. Common unresolved challenges remain for implementation of these models across RiOMar and OceMar systems. The long-term trends in coastal ocean carbon fluxes for different coastal systems under anthropogenic stress that are emerging in observations and numerical simulations are highlighted. Knowledge gaps in projecting future perturbations associated with before and after net-zero CO2 emissions in the context of concurrent changes in the land-ocean-atmosphere coupled system pose a key challenge. ▪ A new synthesis yields an estimate for a globally integrated coastal ocean carbon sink of −0.25 Pg C year−1, with greater than 90% of atmospheric CO2 removal occurring in polar and subpolar regions. ▪ The sustained coastal and open ocean carbon sink is vital in mitigating climate change and meeting the target set by the Paris Agreement. ▪ Uncertainties in the future coastal ocean carbon cycle are associated with concurrent trends and changes in the land-ocean-atmosphere coupled system. ▪ The major gaps and challenges identified for current coastal ocean carbon research have important implications for climate and sustainability policies.

中文翻译：

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沿海海洋碳通量：合成、边界过程和未来趋势

本综述探讨了目前对全球沿海海洋碳循环的认识，并提供了一种新的气海二氧化碳定量综合方法2交换。这项再分析得出了全球综合沿海海洋二氧化碳的估计值2年通量为−0.25 ± 0.05 Pg C−1，极地和次极地地区占 CO 的大部分2去除率（>90%）。对河流主导的海洋边缘 (RiOMar) 和海洋主导的边缘 (OceMar) 系统进行分类的框架用于概念化沿海碳循环过程。根据表面 pCO 的时空变化，比较了波罗的海、中大西洋湾和南海这三个对比案例研究区域的碳动态2。从模拟关键过程和预测不同大陆架区域未来变化的能力方面，对从盒模型到三维耦合循环-生物地球化学模型的海洋碳模型进行了综述。在 RiOMar 和 OceMar 系统中实施这些模型仍然存在常见的未解决的挑战。重点介绍了观测和数值模拟中出现的人为胁迫下不同沿海系统沿海海洋碳通量的长期趋势。预测与二氧化碳净零排放前后相关的未来扰动的知识差距2陆地-海洋-大气耦合系统同时变化背景下的排放构成了一项关键挑战。 ▪ 一项新的合成估计全球综合沿海海洋碳汇为-0.25 Pg C 年−1，大气中CO含量超过90%2去除发生在极地和次极地地区。 ▪ 持续的沿海和公海碳汇对于减缓气候变化和实现《巴黎协定》设定的目标至关重要。 ▪ 未来沿海海洋碳循环的不确定性与陆地-海洋-大气耦合系统的并发趋势和变化有关。 ▪ 当前沿海海洋碳研究发现的主要差距和挑战对气候和可持续发展政策具有重要影响。