Simulated temperature changes as a result of Antarctic ice sheet growth and CO2 reduction

During the Middle Miocene climate transition about 14 million years ago, the Antarctic ice sheet expanded to near-modern volume. Surprisingly, this ice sheet growth was accompanied by a warming in the surface waters of the Southern Ocean, whereas a slight deep-water temperature increase was delayed by more than 200 thousand years. Here we use a coupled atmosphere-ocean model to assess the relative effects of changes in atmospheric CO2 concentration and ice sheet growth on regional and global temperatures. In the simulations, changes in the wind field associated with the growth of the ice sheet induce changes in ocean circulation, deep-water formation and sea-ice cover that result in sea surface warming and deep-water cooling in large swaths of the Atlantic and Indian ocean sectors of the Southern Ocean. We interpret these changes as the dominant ocean surface response to a 100-thousand-year phase of massive ice growth in Antarctica. A rise in global annual mean temperatures is also seen in response to increased Antarctic ice surface elevation. In contrast, the longer-term surface and deep-water temperature trends are dominated by changes in atmospheric CO2 concentration. We therefore conclude that the climatic and oceanographic impacts of the Miocene expansion of the Antarctic ice sheet are governed by a complex interplay between wind field, ocean circulation and the sea-ice system.约1400万年前的中新世中期气候转型期，南极冰盖（Antarctic ice sheet）扩张至接近现代的体积规模。令人意外的是，此次冰盖扩张竟伴随南大洋表层海水升温，而深层海水的小幅升温则滞后了超过20万年。本研究采用大气-海洋耦合模式（coupled atmosphere-ocean model），评估大气二氧化碳（CO₂）浓度变化与冰盖扩张对区域及全球气温的相对影响。数值模拟结果显示，与冰盖扩张相关的风场变化会引发海洋环流、深层水形成与海冰覆盖的改变，进而导致南大洋大西洋与印度洋海域大片区域出现海表升温、深层海水降温的现象。我们将此类变化解读为南极持续10万年的大规模冰生长阶段主导的海洋表层响应。同时，南极冰面高程升高也会引发全球年平均气温上升。与之相反，长期尺度的表层与深层海水温度变化趋势则主要受大气二氧化碳浓度变化调控。因此本研究得出结论：中新世南极冰盖扩张所带来的气候与海洋学影响，是风场、海洋环流与海冰系统之间复杂相互作用的结果。