Late Neogene to Quaternary climate and ice sheet history of West Antarctica

西南极冰盖(WAIS)拥有220万千米3的冰量，占南极冰量的10%左右。在最近的过去，WAIS的质量损失速度急剧加快，目前WAIS是南极大陆融化最快的区域。目前的估计表明，在过去20年里，WAIS对南极洲冰块总质量的减少贡献了约86%，如果以目前的速度融化，可能会导致全球海平面上升一米，直到本世纪末。WAIS的完全崩溃可能导致全球海平面上升高达6米。模型预测表明，这种崩溃可能自中新世晚期以来反复发生，并在地质上相对较短的时间内展开，只有几百年的时间。这样的模型模拟还表明，可能已经越过了导致WAIS崩溃的门槛，即使在相对温和的温室气体排放情景下，大部分冰盖也可能消失。然而，这些模型的预测在冰盖消失的时间和绝对量方面显示出很大的不确定性。代理记录提供了关于WAIS过去兴衰的信息，这可能有助于我们更好地了解这个非常脆弱但具有全球重要性的地区未来的行为。这种代理记录可以专门用于约束和测试冰盖模型，这些模型旨在预测WAIS未来的行为和WAIS对全球海平面上升的潜在贡献。然而，目前很大程度上缺乏定义WAIS深部冰盖历史的代理记录。IODP考察期间从阿蒙森海大陆隆起获得的沉积物379：“阿蒙森海西南极冰盖历史”提供了WAIS自6.8 Ma以来的气候和冰盖动力学的第一个连续记录，并将能够以前所未有的分辨率重建冰盖范围的时空变化。在这里提出的项目中，我们计划采用多代理方法，结合大宗地球化学、同位素和脂肪生物标记物技术，调查WAIS对不断变化的环境条件的响应，并确定WAIS以前在多大程度上发生过部分或完全崩溃，以及在什么时间尺度上发生过。特别是，我们的目标是为这一全球海洋区域产生第一个连续的晚中新世至第四纪古温度记录，并检验冰盖的退缩直接受相对温暖的绕极深水侵入西南极大陆架控制的假设。此外，我们计划确定水生和陆地生态系统对冰块进退的反应，并探索这些系统在未来全球变暖的情景下是作为碳源还是碳汇。

The West Antarctic Ice Sheet (WAIS) holds an ice volume of 2.2 million km3 and thereby contributes ~10% to the ice volume of Antarctica. Rates of mass loss from the WAIS have dramatically accelerated in the recent past and at present the WAIS is the fastest melting region of the Antarctic continent. Current estimates suggest that the WAIS contributed about 86% to the total ice mass loss of Antarctica over the last two decades and if melting continues at its present pace, it may lead to a global sea level rise by up to one meter until the end of this century. A complete collapse of the WAIS may result in a global sea level rise of up to 6 m. Model predictions indicate that such collapses may have occurred repeatedly since the late Miocene and unfold within a geologically relative short timespan of only several hundreds of years. Such model simulations also suggest that a threshold leading to the collapse of the WAIS may have been crossed already and that much of the ice sheet could be lost even under relatively moderate greenhouse gas emission scenarios. These model predictions, however, show large uncertainties in terms of timing and absolute volume of ice sheet loss. Proxy records that yield information on the past waxing and waning of the WAIS may help in improving our understanding on the future behaviour of this very vulnerable but globally important region of our planet. Such proxy records may specifically be used for constraining and testing ice sheet models that aim to predict future WAIS behaviour and the potential contribution of the WAIS to global sea level rise. Yet proxy records defining the deep time ice sheet history of the WAIS are largely lacking at present. Sediments obtained from the continental rise of the Amundsen Sea during IODP Expedition 379: “Amundsen Sea West Antarctic Ice Sheet History” provide the first continuous records of climate and ice sheet dynamics of the WAIS that date back to ~6.8 Ma and will allow reconstructing spatiotemporal variations of the ice sheet extent in an as yet unprecedented resolution. In the project proposed here, we plan to employ a multi-proxy approach, combining bulk-geochemical, isotope and lipid biomarker techniques, to investigate the response of the WAIS to changing environmental conditions and determine to which extent partial to full collapses of the WAIS have occurred previously and on which time scales. In particular, we aim to generate the first continuous late Miocene to Quaternary paleotemperature record for this region of the global oceans and test the hypothesis that the retreat of the ice sheet is directly controlled by incursions of relatively warm circumpolar deep water onto the West Antarctic shelf. In addition, we plan to determine the response of the aquatic and terrestrial ecosystems to advances and retreats of ice masses and explore whether these systems will act as sources or sinks of carbon under future scenarios of global warming.