School of Geographical Sciences, University of Bristol, Bristol, UK
School of Geographical Sciences, University of Bristol, Bristol, UK.
Philos Trans A Math Phys Eng Sci. 2015 Nov 13;373(2054). doi: 10.1098/rsta.2014.0419.
The glaciation of Antarctica at the Eocene-Oligocene transition (approx. 34 million years ago) was a major shift in the Earth's climate system, but the mechanisms that caused the glaciation, and its effects, remain highly debated. A number of recent studies have used coupled atmosphere-ocean climate models to assess the climatic effects of Antarctic glacial inception, with often contrasting results. Here, using the HadCM3L model, we show that the global atmosphere and ocean response to growth of the Antarctic ice sheet is sensitive to subtle variations in palaeogeography, using two reconstructions representing Eocene and Oligocene geological stages. The earlier stage (Eocene; Priabonian), which has a relatively constricted Tasman Seaway, shows a major increase in sea surface temperature over the Pacific sector of the Southern Ocean in response to the ice sheet. This response does not occur for the later stage (Oligocene; Rupelian), which has a more open Tasman Seaway. This difference in temperature response is attributed to reorganization of ocean currents between the stages. Following ice sheet expansion in the earlier stage, the large Ross Sea gyre circulation decreases in size. Stronger zonal flow through the Tasman Seaway allows salinities to increase in the Ross Sea, deep-water formation initiates and multiple feedbacks then occur amplifying the temperature response. This is potentially a model-dependent result, but it highlights the sensitive nature of model simulations to subtle variations in palaeogeography, and highlights the need for coupled ice sheet-climate simulations to properly represent and investigate feedback processes acting on these time scales.
始新世-渐新世过渡期（约 3400 万年前）南极冰盖的形成是地球气候系统的一次重大转变，但导致冰盖形成的机制及其影响仍存在很大争议。最近的一些研究使用耦合大气-海洋气候模型来评估南极冰原起始的气候影响，其结果往往存在很大差异。在这里，我们使用 HadCM3L 模型表明，全球大气和海洋对南极冰盖增长的响应对古地理位置的细微变化很敏感，我们使用代表始新世和渐新世地质阶段的两种重建方法进行了研究。早期阶段（始新世；Priabonian），塔斯曼海通道相对狭窄，对冰盖的响应是南大洋太平洋扇区海面温度的大幅上升。而对于后期阶段（渐新世；Rupelian），塔斯曼海通道更加开阔，这种温度响应不会发生。这种温度响应的差异归因于两个阶段之间洋流的重新组织。在早期阶段冰盖扩张之后，罗斯海大环流的规模减小。塔斯曼海通道的更强纬向流允许罗斯海的盐度增加，深海水形成并引发多个反馈，从而放大了温度响应。这可能是一个依赖于模型的结果，但它突出了模型模拟对古地理位置细微变化的敏感性，并强调了需要进行耦合冰盖-气候模拟，以正确表示和研究这些时间尺度上的反馈过程。
