NSFGEO-NERC Paleoclimate signatures of the climate response to West Antarctic ice sheet collapse

在古气候和冰川学研究中一个悬而未决的主要问题是，西南极冰盖(WAIS)是否在最后一次间冰期--海洋同位素阶段5E-130ka至116ka之间崩塌。有确凿的证据表明WAIS在过去70万年内的某个时候崩溃(Scherer等人，1998年)，但WAIS在特定时间崩溃的证据要么是间接的(和模棱两可的)，要么不足以限制时间和规模(Joughin和Alley，2011)。对过去WAIS崩溃的时间和速度缺乏了解，这阻碍了我们验证未来WAIS可能崩溃的模型的能力。美国国家科学院最近的一份报告将这个问题--以前WAIS崩溃的速度和时间，特别是MIS5e期间是否发生崩溃--列为极地研究战略投资的重中之重(极地研究委员会，2015)。它可能通过气候系统对崩溃的反应的证据来限制过去WAIS崩溃的速度和时间。这一想法与寻找以前冰川形态的冰川地质证据(例如，Naish等人，2009年)或根据海平面记录推断冰盖大小的想法不同。相反，这里的想法是，冰盖大小的显著变化将导致大气和海洋循环的变化，这些变化记录在古气候档案中，如冰芯、洞穴或海洋和湖泊沉积物。最近的模拟工作表明，对WAIS崩溃的气候反应可能包括以下内容(Justino等人，2015年；Steig等人，2015年；Singh等人，正在出版；Holloway等人，在回顾中)：-AMOC(大西洋经向翻转环流)--热带辐合带(ITCZ)向北移动--南极洲上空，包括崩溃区域以外地区上空温度和18O比的变化--这些气候反应不是融水强迫的结果(尽管这也可能是重要的)，而是由于南极冰盖形态的重大变化导致的大气环流变化。冰盖形态影响大气环流并不是一个新概念；对于劳伦蒂德和芬诺斯坎迪亚冰盖，已经有许多研究证明了这一点(例如，Kutzbach和Guetter，1986年；Roe和Lindzen，2001年)。但是，南极冰盖可能在以前的间冰期发生的相对较小的变化(以及未来可能发生的对人为气候强迫的反应)的想法是新颖的，值得进一步探讨。这是这里提出的工作的基础。

A major unanswered question in paleoclimate and glaciological research is whether the West Antarctic ice sheet (WAIS) collapsed during the last interglacial period, Marine Isotope Stage (MIS) 5e, between ~130 and ~116 ka. There is solid evidence for WAIS collapse at some point within the last 700,000 years (Scherer et al., 1998), but the evidence for WAIS collapses at specific times is either indirect (and equivocal) or is insufficient to constrain the timing and magnitude (Joughin and Alley, 2011). Lack of knowledge of both the timing and rate of WAIS collapse in the past hampers our ability to validate models of potential WAIS collapse in the future. A recent report of the U.S. National Academy of Sciences identified this question - the rate and timing of previous WAIS collapses, and particularly whether collapse occurred during MIS 5e - as a top priority for strategic investments in polar research (Polar Research Board, 2015).It may be possible to constrain both the rate and timing of WAIS collapse in the past through evidence of the response of the climate system to that collapse. This idea is distinct from that of looking for glacial-geological evidence of former ice configurations (e.g., Naish et al., 2009), or inferring ice sheet size from sea level records. Instead, the idea here is that significant changes in ice sheet size will cause changes in atmospheric and ocean circulation that are recorded in paleoclimate archives such as ice cores, speleothems, or marine and lake sediments. Recent modeling work shows that the climate responses to WAIS collapse likely include the following (Justino et al., 2015; Steig et al., 2015; Singh et al., in press; Holloway et al., in review): - changes in AMOC (Atlantic meridional overturning circulation) - a northward shift in the ITCZ (intertropical convergence zone) - changes in temperature and 18O ratios in precipitation over Antarctica, including areas outside the region of collapseThese climate responses are not the consequences of meltwater forcing (though this may also be important), but instead are owing to changes in atmospheric circulation resulting from the significant changes in the morphology of the Antarctic ice sheet. That ice sheet morphology affects atmospheric circulation is not a new concept; there have been many studies demonstrating this for the Laurentide and Fennoscandian ice sheets (e.g., Kutzbach and Guetter, 1986; Roe and Lindzen, 2001). But the idea that the comparatively small changes in the Antarctic ice sheet that may have occurred during previous interglacial periods (and that may occur in the future in response to anthropogenic climate forcing) is novel, and deserves further exploration. This is the basis of the work proposed here.