Collaborative Research: Testing the Linchpin of WAIS Collapse with Diatoms and IRD in Pleistocene and Late Pliocene Strata of the Resolution Drift, Amundsen Sea, Antarctica

第一部分，非技术摘要40多年前，由于气候变暖，全球海平面上升，巨大的冰山首次进入南大洋，人们担心西南极冰盖(WAIS)可能容易释放冰。为了更好地评估这一威胁，科学家们需要知道此类事件是否发生在地质上最近的过去，即过去冰川-间冰期周期的温暖时段。2019年，在WAIS最脆弱的区域附近进行的海洋钻探产生了海底地质记录，证明了冰山在阿蒙森海深水中掉落大量沙子和鹅卵石的时间，这些沙子和鹅卵石被称为冰筏碎屑(IRD)。与冰盖下基岩被侵蚀的IRD一起产出的是丰富的硅藻(浮游藻类)微化石，这表明公海具有很高的生物生产力。新的沉积物岩芯完整、不间断地记录了过去300万年来冰盖范围的剧烈波动。因此，它们提供了一种手段，可以清楚地回答过去是否发生过冰盖崩塌的问题，并为其潜在的未来提供线索。该项目将调查IRD与硅藻产量高的证据相吻合的沉积区间，以测试这两个标准是否表明冰盖迅速崩溃。对IRD鹅卵石的地球化学分析将有助于追踪冰山的来源，找到可能是陆地上的地点。通过分析深海沉积物中硅藻和IRD高度聚集的条件，在那里可以避免局部海岸影响，我们将评估与过去冰盖坍塌事件相关的海洋和气候条件。硅藻提供了过去温度和海洋生产力变化的有力证据，当与时间联系在一起时，可以转化为冰盖下降的速度。这些结果将为设计、约束和测试下一套计算机模型提供关键数据，这些模型可以确定未来冰盖在变暖的世界中崩溃的可能性和时间。该项目将包括对来自不同背景的本科生和研究生的培训，将向公众介绍南极科学，并通过几项不同的外展工作使公众参与进来。第二部分，技术摘要南极阿蒙森海的新钻探岩芯(IODP探险379)包含了过去500万年来海洋变化和冰山漂浮碎片的连续记录。本研究旨在通过对冰期-间冰期岩石地层转换过程中的硅藻和IRD记录进行详细的定量分析，以确定晚上新世和更新世WAIS崩塌事件的时间和频率，从而识别这些大陆边缘深海沉积物中的西南极冰盖(WAIS)的撤退/崩塌的特征。调查人员将利用硅藻组合的高分辨率微古生物学和对IRD沉积事件的微观地层学分析，确保对U1532和U1533地点选定的间冰期岩芯的海洋古环境条件进行年龄限制和诊断性观测，而冰山漂浮碎屑的岩石学、地质年代学和热年代学将提供冰山来源和路径的证据。沉积古温度将通过一种新的古温度替代指标进行评估，该指标基于对南大洋主要硅藻Fragilariopsis kerguelsis的形态变化的定量评估。他们的结果将有助于新的冰盖模型的参数化，这些模型试图重建和预测西南极冰盖的行为。该项目将直接促进一所仅面向本科生的学院和一所服务于以第一代大学生和代表性不足群体为代表的人群的公立大学的本科生教育。这项拟议的工作横跨地质学、地球化学、沉积学、古生物学和古海洋学，将允许本科生在一个致力于社会相关研究的合作团队中通过动手研究培养不同的技能。这两名研究生将进行原创研究，并与本科生一起工作/指导，创造全面的研究经验，为他们在未来的学术或就业领域取得成功做好准备。来自南极洲西部深海记录的发现将由学生和研究人员在国内和国际会议以及一系列公共科学外展活动中进行交流。这一奖项反映了NSF的法定使命，并通过使用基金会的学术价值和更广泛的影响审查标准进行评估，被认为值得支持。

Part I, Non-technical Abstract Concerns that the West Antarctic Ice Sheet (WAIS) might be susceptible to releasing its ice as giant icebergs into the Southern Ocean due to a warming climate, raising global sea level, were first expressed more than 40 years ago. To best-assess this threat, scientists need to know whether such events occurred in the geologically recent past, during warm intervals of past glacial-interglacial cycles. Ocean drilling near the most vulnerable sector of the WAIS, in 2019, yielded seafloor geologic records demonstrating times when icebergs dropped large volumes of sands and pebbles, called ice-rafted detritus (IRD) in deep water of the Amundsen Sea. Occurring together with IRD that was eroded from bedrock beneath the ice sheets, there are abundant microfossils of diatoms (algal plankton), which indicate high biological productivity in the open ocean. The new sediment cores provide a complete, uninterrupted record of a time of dramatic fluctuations of ice sheet extent that occurred over the last 3 million years. Therefore, they provide the means to obtain clear answers to the question whether ice sheet collapse occurred in the past and offering clues to its potential future. This project will investigate sediment intervals where IRD coincides with evidence of high diatom production, to test whether these two criteria indicate rapid ice sheet collapse. Geochemical analysis of IRD pebbles will help trace the source of the icebergs to likely on-land sites. By analyzing conditions of high diatom and IRD accumulation in deep ocean sediment, where local coastal influences can be avoided, we will assess oceanographic and climatic conditions associated with past ice sheet collapse events. Diatoms provide powerful evidence of temperature and ocean productivity changes in the past, that, when linked to time, can translate into rates of ice sheet drawdown. These results will provide critical data for designing, constraining and testing the next suite computer models that can determine the likelihood and timing of future ice sheet collapse in a warming world. The project will include training of undergraduate and graduate students from diverse backgrounds, and the public will be introduced to Antarctic science and engaged through several different outreach efforts.Part 2, Technical AbstractNew drillcores from the Amundsen Sea, Antarctica (IODP Expedition 379) contain a continuous record of oceanographic changes and iceberg rafted debris (IRD) spanning the last 5 million years. This study aims to identify the signature of retreat/collapse of the West Antarctic Ice Sheet (WAIS) in these continental margin, deep-sea sediments by quantitatively analyzing, in detail, diatom and IRD records across glacial-interglacial lithostratigraphic transitions to establish the timing and frequency of Late Pliocene and Pleistocene WAIS collapse events. The investigators will secure age constraints and diagnostic observations of marine paleoenvironmental conditions for selected interglacial intervals of cores from sites U1532 and U1533, using high resolution micropaleontology of diatom assemblages coupled with microstratigraphic analysis of IRD depositional events, while petrography, geochronology and thermochronology of iceberg rafted clasts will provide evidence of iceberg sources and pathways. Depositional paleotemperatures will be assessed via a new paleotemperature proxy based on quantitative assessment of morphologic changes in the dominant Southern Ocean diatom Fragilariopsis kerguelensis. Their results will contribute to parameterization of new ice sheet models that seek to reconstruct and forecast West Antarctic Ice Sheet behavior. This project will directly contribute to undergraduate education at an undergraduate-only college and at a public university that serves a demographic typified by first generation university students and underrepresented groups. Spanning geology, geochemistry, sedimentology, paleontology and paleoceanography, the proposed work will allow undergraduate students to develop diverse skills through hands-on research within a collaborative team that is dedicated to societally relevant research. The two graduate students will conduct original research and work alongside/mentor undergraduates, making for a well-rounded research experience that prepares them for success in future academic or employment sectors. The discoveries that come from this deep-sea record from West Antarctica will be communicated by students and investigators at national and international conferences and an array of public science outreach events.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.