楚科奇海及其邻近海域碳循环年际变化和机制研究

Challenged by the enormous pressure to reduce the global carbon emission, it is expected that the Arctic Ocean could absorb additional atmospheric CO2 with the retreating of sea-ice. The Chukchi Sea and adjacent waters, characterized with the highest carbon fixation in the global ocean and large carbon flux into the deep-ocean for sequestration, make substantial contributions to carbon cycling in the entire Arctic Ocean. The response mechanism of carbon cycling in this region to the rapidly changing environment is the foundation for the prediction of carbon sink in the Arctic Ocean. Existing observations have not yet fully explained the complex interaction among various processes of the Arctic system, thus there is urgency to develop high-resolution coupled ocean-ice-carbon models. This project plans to focus on the following aspects: to analyze the characteristics of hydrology, biogeochemistry and carbon cycling as well as their influencing factors based on observational data from China’s summer Arctic expeditions; to develop a carbon cycling model including biogeochemical processes for ice-covered shelf water and couple it to the advanced ocean and sea-ice model developed by the Bedford Institute of Oceanography of Canada; to carry out 15-year simulations for the period of 2002-present based on the high-resolution coupled ocean-ice-carbon model; to study the inter-annual variations of carbon sink/source patterns, sea-ice and ocean currents; to analyze the influences of rapidly changing sea-ice and growing Pacific inflow on the absorption of atmospheric CO2 and the vertical sinking carbon fluxes; to estimate how the wind and river runoff affect the carbon sink; to discuss the response of deep-ocean carbon sequestration to the changing environment; and to evaluate the effectiveness of continental shelf pump in the Chukchi Sea as well as its role played in the global carbon sink.

目前全球碳减排任务艰巨，海冰消退后北冰洋碳汇增加被期待。楚科奇海及其邻近海域拥有全球海洋最高固碳率和碳深海封存量，在整个北冰洋碳循环中举足轻重。楚科奇海碳循环过程对环境快速变化的响应机制是北冰洋碳汇预测的基础。现场观测难以厘清极区复杂的多过程相互作用，亟需发展高分辨率海洋-海冰-碳循环耦合模型。本项目拟在中国北极夏季考察的基础上，分析海域水文、生物地球化学和碳循环特征与影响因素；研发冰区陆架海含生物地球化学过程的碳循环模型，耦合加拿大贝德弗海洋研究所的最新海洋-海冰模型，建立高分辨率海洋-海冰-碳循环模型，进行1999-至今15年后报模拟，分析该海域碳的源/汇格局以及海冰、环流等的年际变化规律，探讨海冰快速变化和太平洋入流增加对海面CO2吸收和碳垂直沉降通量的影响，分析风场、径流等变化对碳汇作用的影响，探讨碳的深海输运埋藏对环境变化的响应，认识楚科奇海陆架泵效率及其在全球碳汇中的作用。

对楚科奇海及邻近海域海-气CO2通量及碳循环过程、变化规律与机制的认识是准确预测整个北冰洋碳汇能力的前提和关键。观测与数值模式结合分析是研究机制、预测未来的主要手段之一。项目执行期间，参加了2017-2020年四次中国北极科考航次，获得水文数据及碳酸盐体系数据，同时整理和订正了前期7次北极科考数据和近30年的国际碳数据集。于国内率先完成北冰洋海洋-海冰-生态系统-碳循环耦合模式的构建及后报计算，获得20余年可靠的稳定输出。结合观测与模式结果首先解析了海洋-海冰环境演变规律，实现了北冰洋陆架边缘海海冰变化基于机制研究的统计预报；厘清太平洋入流水在北冰洋的扩展路径，以环流输运为背景，系统评估了太平洋入流物质输运对海洋碳汇的影响；认识了楚科奇海碳汇作用多时间尺度变化，发现初级生产和开阔水域面积增加主控楚科奇海年均总碳汇增加，受海冰面积和局地风速变化影响，结冰期（10-12月）楚科奇海碳汇能力年际变化最为显著，主控该区年均总碳汇的年际变化；揭示了白令海纳瓦林角附近陆架-陆坡营养盐交换对太平洋水向楚科奇海补充营养盐的调控作用，发现支撑楚科奇海南、北生物热点区持续较高初级生产的营养盐分别来自平流输运的白令夏季水和底层太平洋冬季存留水混合向上补充；发现颗粒有机碳的沉积埋藏通量与初级生产的年际变化密切相关并呈现增加趋势；阐明了楚科奇海陆架泵高效运转的机制，发现陆架泵主要由太平洋入流驱动，巴罗峡谷和100m等深线是溶解无机碳向海盆输运的主要通道且两者输出通量相当，指出海-气碳交换和生物泵作用的增强促进楚科奇海陆架泵碳输出效率，同时也进一步加剧楚科奇海次表层水体酸化。共计发表学术论文26篇。项目所取得的成果系统认识了楚科奇海陆架碳循环机制，为全面理解极地陆架边缘海碳循环对气候变化的响应及未来变化预测提供科学基础。