南极埃默里冰架—普里兹湾环流相互作用的数值模拟研究

Antarctic ice shelves are the extensions of Antarctic ice sheets to the ocean. There are extensive heat and mass exchanges between ice sheets and ocean through ice shelves. Substantial observational studies have confirmed that Antarctic ice shelves, especially in the West Antarctic, are frequently experiencing the retreat and collapse in a warming climate, which have marked impacts on the sea level rise, ocean circulation and global climate system. As one of the key issues, interactions between ice shelves and ocean have a very important scientific significance. Based on the high resolution MITgcm coupled with an ice shelf module, this proposal will carry out a series of numerical studies on the interactions between Amery Ice Shelf and Prydz Bay ocean circulation system. Firstly, the importance of including an ice shelf module for simulating Prydz Bay Circulation will be examined. Secondly, various influential processes such as frazil thermodynamic process, tidal mixing, and ice draft change will be considered successively in the coupled ice shelf-ocean model. Through comparisons between simulations and observed data, a 3D high resolution coupled ice shelf-ocean model will be developed for Amery Ice Shelf-Prydz Bay Circulation system that can be used to more realistically simulate water mass properties and circulation in and out of the ice shelf cavity. Finally, a series of sensitivity experiments under various westerly wind forcing will be carried out to study the effects of pathway changes of Circumpolar Deep Water on the Amery Ice Shelf basal meting and freezing pattern.

南极冰架是南极内陆冰盖向海的延伸，冰盖通过冰架与海洋发生大量的热量与物质交换。观测研究表明：因当前气候变暖，近年来尤其在西南极沿岸，南极冰架的消退崩塌频繁发生，进而影响海平面上升、海洋环流与全球气候系统。冰架—海洋相互作用作为其中的关键问题之一具有非常重要的科学意义。本项目基于嵌套冰架模块的高分辨MITgcm海洋环流模式，针对南极埃默里冰架—普里兹湾环流相互作用开展数值模拟研究。首先，通过不含与包含埃默里冰架的数值对照试验论证冰架的存在对于普里兹湾及其邻近海域物理海洋过程模拟的重要性；其次，开展包括冰晶热动力过程、潮流掺混作用与冰架底部形态演变多因素作用的数值对比试验，建立能真实反映埃默里冰腔内外水团性质与环流结构的三维高分辨率冰架—海洋耦合模式；最后，通过设计改变西风强迫场的气候变化敏感性试验，研究绕极深层水输送路径的变化及其对埃默里冰架底部融化与冻结形式改变的影响。

冰架是南极冰盖与海洋的交界地带。已有研究证实，由海洋主导的冰架底部融化正加剧冰架薄化，减弱冰架对内陆冰盖支撑，增大接地冰向海入流，最终导致海平面上升。位于普里兹湾内的埃默里冰架就存在变性绕极深层水（mCDW）在近冰架前缘与高盐陆架水（HSSW）在冰架接地线处引起的两种底部融化形式。因此，本项目主要围绕mCDW入侵普里兹湾陆架和发起于接地线处的“冰泵”现象开展研究工作，得到以下重要结果：.1. 基于MITgcm，发展了国内首个区域高分辨率海洋-海冰-冰架耦合模式，以此确定了mCDW跨普里兹湾陆架入侵路径以及入侵强度同南极陆坡流季节变化的关系。.2. 首次运用数值模拟手段反演了观测到的mCDW上涌四女士浅滩（FLB）过程，揭示了FLB西侧地形的阶梯状下降是引起mCDW上涌的直接原因，由此强调了使用准确的高精度地形数据的重要性。.3. 基于悬浮冰晶与悬沙动力特征的相似性，首次在现有挟冰晶的冰架水（ISW）羽流模式中引入了平衡冰晶浓度垂向分布，由此计算的海洋冰分布范围更广，产量更大，更接近于实际观测。.4. 首次将挟冰晶的ISW羽流改进模式应用到了麦克默多冰架前缘的海冰下发现，改进模式能够更好地反映当地ISW属性与冰下海洋冰的分布，通过大量敏感性数值实验，首次给出了当地ISW过冷温度同海洋冰厚增长率关系。.5. 鉴于未来要引入非平衡冰晶浓度垂向分布及更合理的冰晶沉淀通量表达，针对不平衡悬沙输运，亦即悬沙浓度恢复饱和过程，进行解析与数值研究发现，（1）沿垂向各水层悬沙浓度恢复快慢不同，越靠近底部恢复越快；（2）平衡悬沙剖面是非平衡剖面的零阶近似；（3）现有悬沙近底通量表达都有其不合理性。.以上基于本项目所取得的研究结果对于评估南极冰盖质量平衡，应对当前气候变化局势，预测未来海平面上升具有重要的研究意义与科学价值。