黑潮延伸体北部混合海域营养盐输运及其对表层叶绿素浓度的影响

北太平洋副极地和副热带环流交汇的混合海域不但是西北太平洋南向物质输送的主要通道，也是重要的渔业资源地。混合海域的营养盐浓度和表层叶绿素浓度都受到黑潮延伸体海洋动力环境变化影响。当黑潮延伸体流轴剧烈摆动、中尺度涡活动频繁时，虽然混合海域的表层营养盐浓度和叶绿素浓度异常呈现低值，但其混合层深度并不存在相应变化。基于以上事实，申请人提出该海域表层叶绿素浓度受控于水平营养盐输运的猜想，而后者与海洋动力环境变化密切相关。针对混合海域黑潮延伸体及亲潮边界随时间变化和边界两侧水团性质差异巨大的特点，拟使用海洋再分析数据确定混合海域范围，从西北太平洋长期水文观测数据中提取混合海域典型水文剖面，描述物理-生化参数垂向分布；构建箱式模型估算混合海域营养盐收支情况；最终阐明营养盐输送对混合海域表层叶绿素浓度的影响。本项目的顺利实施可望加深对混合海域海洋物理-生化过程及北太平洋南北方向物质交换的认识。

The mixed water region (MWR), where the subtropical and subarctic gyre encounters in the Northeast Pacific, is not only the main path way that account for the southward material transport between the two gyres, but also the important fishery. The surface nutrient concentration and chlorophyll concentration in the MWR are modulated by the dynamic state variation of the Kuroshio Extension. When the axis of Kuroshio Extension frequently meanders and the mesoscale eddy is active, these above biogeochemical parameters show negative anomaly, whereas the mixed layer depth is independent to this variation. However, the underlying dynamics is still not well understood. Based on the observational facts, we suppose that the surface chlorophyll concentration is affected by the dynamic state through the variation of lateral nutrient transport. Considering the large difference in water property between the two sides of the boundary of MWR, we planned to use the ocean reanalysis data to define the temporally varied boundaries of MWR, i.e., the northern boundary defined by the Oyashio and the southern boundary defined by the Kuroshio extension, and then abstract the typical profile of the temperature, salinity, and nutrient concentration from the long term hydrographic observation data, to depict the typical spatial distribution of the nutrient concentration; to evaluate the nutrient budget in the MWR by using a box model; and to shed light on how the nutrient transport affects the surface chlorophyll concentration. The achievement of this project will deepen the understanding of the physical-biogeochemical processes in the MWR and the meridional material exchange in the North Pacific.