Impacts of Ice-Ocean Stress on the Subpolar Southern Ocean: Role of the Ocean Surface Current

Abstract

The mechanical influences involved in the interaction between the Antarctic sea ice and ocean surface current (OSC) on the subpolar Southern Ocean have been systematically investigated for the first time by conducting two simulations that include and exclude the OSC in the calculation of the ice-ocean stress (IOS), using an eddy-permitting coupled ocean-sea ice global model. By comparing the results of these two experiments, significant increases of 5%, 27%, and 24%, were found in the subpolar Southern Ocean when excluding the OSC in the IOS calculation for the ocean surface stress, upwelling, and downwelling, respectively. Excluding the OSC in the IOS calculation also visibly strengthens the total mechanical energy input to the OSC by about 16%, and increases the eddy kinetic energy and mean kinetic energy by about 38% and 12%, respectively. Moreover, the response of the meridional overturning circulation in the Southern Ocean yields respective increases of about 16% and 15% for the upper and lower branches; and the subpolar gyres are also found to considerably intensify, by about 12%, 11%, and 11% in the Weddell Gyre, the Ross Gyre, and the Australian-Antarctic Gyre, respectively. The strengthened ocean circulations and Ekman pumping result in a warmer sea surface temperature (SST), and hence an incremental surface heat loss. The increased sea ice drift and warm SST lead to an expansion of the sea ice area and a reduction of sea ice volume. These results emphasize the importance of OSCs in the air-sea-ice interactions on the global ocean circulations and the mass balance of Antarctic ice shelves, and this component may become more significant as the rapid change of Antarctic sea ice.

摘要

本文利用一个冰-海耦合的全球高分辨率模式研究了海洋表层流速在冰海耦合过程中的作用及其对南大洋亚极地海洋和南极海冰的影响。通过对比冰海应力计算过程中包含和不包含海洋表层流速的实验结果发现,不考虑海洋表层流速时区域平均的海表面应力、向上和向下的埃克曼抽吸分别增强了5%,27%和24%;同时风场输入到亚极地南大洋中的动能增长了16%,该动能输入的增强分别引起了38%和12%的涡动能和平均动能的增加。另外,南大洋翻转环流的上层和底层分支分别加强了16%和15%;威德尔海环流、罗斯海环流和澳大利亚-南极大陆环流分别增强了12%,11%和11%;增强的海洋环流和埃克曼抽吸导致了海表面温度的升高从而引起了显著的亚极地南大洋失热。海冰运动的增强和较暖的海表面温度共同导致了南极海冰面积增加和体积的减少。本研究结果指明了海洋表层流速在海-冰-气相互作用过程中的重要性及其对全球冰架质量平衡的潜在重要影响,随着南极海冰面积的快速变化该冰海耦合过程的重要性将进一步加强。