北冰洋次表层暖水热量释放对结冰过程的响应和反馈

The Arctic Ocean is regarded as the "indicator" of global warming, its sea-ice interaction has great influence on global climate change. As a part of sea-ice interaction, near-surface temperature maximun (NSTM) in the Arctic Ocean has strong relationship with sea ice change. Former studies of NSTM indicate the ways of heat release from NSTM, but the controlling factors of NSTM heat release still remain unclear. And the response and feedback of NSTM heat release to sea ice freezing is not detailed either. Besides, in freezing season, present ice-ocean coupled models in Arctic Ocean generally only consider the latent heat flux in the ice-ocean interface, but ignoring the oceanic heat flux from NSTM heat release. Present project firstly tries to describe the response and feedback of NSTM heat release to sea ice freezing with simultaneous Arctic air-ice-ocean observation data, then analyze the controlling factors and figure out the mechanism behind. Next, add the NSTM heat release in the ice-ocean interface in a 1-D coupled ice-ocean model, and improve the modeling of sea ice and underlying ocean changes.

北冰洋是全球变暖的“指示器”，其冰海相互作用强烈影响着全球气候变化。北冰洋次表层暖水是冰海相互作用的重要组成部分，次表层暖水的形成和发展与海冰融冻变化密切相关。前人研究发现了次表层暖水热量的释放方式，但是对其释放过程的控制因素并不明确，且对海冰变化过程的响应和反馈刻画不够细致。此外，现有北冰洋冰海耦合模式中，结冰季节的冰海界面通常只考虑海冰冻结引起的潜热通量，而忽略来自次表层暖水热量释放产生的海洋热通量。因此，本项目首先利用北冰洋气-冰-海同步观测资料，分析冰下次表层暖水热量释放对海冰结冰过程的响应和反馈，研究其热量释放控制因素，探究其释放机制。然后在一维冰海耦合模式中加入次表层暖水热量释放效应，改进冰底热力学强迫，从而更准确合理地模拟海冰厚度和冰下海洋变化。

随着北极变暖，北冰洋上层海洋也经历了巨大变化，其中最显著的现象之一是次表层暖水。次表层暖水的生成和消亡与海冰冻结和融化过程密切相关。本项目利用海冰物质平衡浮标、冰基拖曳式海洋剖面浮标、现场水文观测、湍流观测等数据重点刻画了海冰底部冻融期的时空变化，分析了上层海洋变化和次表层暖水对海冰底部冻融期变化的影响，并利用一维海洋模式模拟了结冰季节次表层暖水热量释放现象。随着海冰减退，上层海洋增暖提前，使得海冰底部融化提前。次表层暖水热量使得海冰融冰期延长，加剧海冰融化，同时推迟海冰底部冻结开始时间，减缓冬季海冰结冰速率，从而减小海冰冻结。上层海洋的混合强度表现出明显的地形增强效应，但是受强盐跃层和逆温层限制，下层热量对次表层暖水热量的贡献几乎可以忽略不计。一维海洋模式模拟的次表层暖水热量可以通过结冰析盐过程导致的对流混合“侵蚀”季节性盐跃层而释放，从而起减缓海冰底部冻结速率的作用。