Collaborative Research: Organic and Inorganic Geochemical Investigation of Hydrologic Change in East Antarctica in the 4 Million Years Before Full Glaciation

东南极冰盖拥有地球上最大的淡水量，总量足以使海平面上升近200英尺。即使是对冰储存量的微小调整，也会对世界各地的海岸线和气候产生重大影响。激发这个项目的问题是，当南极洲从一个温暖的环境变成一个被冰覆盖的南部大陆时，3000万年前的冰是如何生长到覆盖大陆的？南极洲东部冰盖（EAIS）的一个主要排水盆地-普拉茨湾的海底以前曾进行过钻探，以恢复南极洲大陆冰盖形成之前数百万年的沉积物。在海洋沉积物中作为“生物标志物”发现的最后一批植物物质残留物记录了降雨和降雪的化学特征，这些降雨和降雪为植物提供了养分，后来又为不断扩张的冰川提供了养分。冰川携带的沉积物也沉积在海底，可以通过分析来发现冰川是如何流过地貌的。在这里，研究人员将确定由冰盖生长引起的降水变化。这项研究将收集数据，并进一步分析来自国际海洋发现计划（IODP）核心储存库的海底沉积物档案的样本。最终，这些发现可以帮助为气候和冰盖模型中的温度-降水-冰的联系提供信息。该项目将支持培训三名女性早期职业科学家（博士生和研究技术员），PI和博士生将继续参与扩大参与的努力（例如，妇女参与科学和工程方案;促进美洲原住民和奇卡诺人参与科学和其他机会方案协会的地方分会），从两个校园和当地社区学院的代表性不足的少数民族中招募本科生参与者。南极地球科学教育材料将辅之以专业插图，开放获取，并用于公共教育和交流工作，以吸引加利福尼亚州洛杉矶和南卡罗来纳州哥伦比亚的当地社区。南加州大学和南卡罗来纳州大学的研究人员将共同研究新生代早期温室气候状态的倒数第二个时刻：约400万年的全球变冷，在始新世/渐新世过渡期达到顶峰（约34 Ma）。在了解南极洲冰扩张之前的条件方面仍然存在重大差距。特别是，冰盖原材料的供应（即，湿度）和时间，频率和持续时间的前体冰川是缺乏约束。这项合作提案结合了有机和无机代理，以研究南极水文气候如何在温室到冰库的过渡。核心假设是，随着冷却的进行，水文循环减弱。植物蜡的氢、碳同位素（水文气候指标）和成岩和成水沉积物的Hf-Nd同位素（机械风化指标）对降水和冰川推进的响应强烈而迅速。这种详细而敏感的综合方法将测试是否有隐藏的冰川（和/或温暖的事件），打断了前冰库的间隔。将在沉积区的普里兹湾海洋沉积物岩心上进行研究，以了解从南极洲中心通过兰伯特地堑搬运的风化和侵蚀产物。该项目将产生关于南极洲植物存在和水文气候以及冰川推进时间的替代信息，预计将显示与冷却和冰盖生长有关的干燥。这种双重方法将从植物生物标志物的河流与冰川侵蚀的变化中解开气候信号。这一提议具有潜在的变革性，因为有机和无机代理的结合可以揭示干旱和冰川扩张的快速转变，这可能在反应较慢的代理和更远的档案中被遗漏。这项研究意义重大，因为水文气候似乎是温度-冰冻圈滞后的关键因素。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The East Antarctic Ice Sheet holds the largest volume of freshwater on the planet, in total enough to raise sea level by almost two hundred feet. Even minor adjustments in the volume of ice stored have major implications for coastlines and climates around the world. The question motivating this project is how did the ice grow to cover the continent over thirty million years ago when Antarctica changed from a warmer environment to an ice-covered southern continent? The seafloor of Prydz Bay, a major drainage basin of the East Antarctic Ice Sheet (EAIS), has been drilled previously to recover sediments dating from millions of years prior to and across the time when inception of continental ice sheets occurred in Antarctica. The last remnants of plant material found as 'biomarkers' in the ocean sediments record the chemical signatures of rain and snowfall that fed the plants and later the expanding glaciers. Sediment carried by glaciers was also deposited on the seafloor and can be analyzed to discover how glaciers flowed across the landscape. Here, the researchers will identify precipitation changes that result from, and drive, ice sheet growth. This study will gather data and further analyze samples from the seafloor sediment archives of the International Ocean Discovery Program's (IODP) core repositories. Ultimately these findings can help inform temperature-precipitation-ice linkages within climate and ice sheet models. The project will support the training of three female, early career scientists (PhD & MS students, and research technician) and both PIs and the PhD student will continue their engagement with broadening participation efforts (e.g., Women in Science and Engineering Program; local chapters of Society for the advancement of Native Americans and Chicanos in Science and other access programs) to recruit undergraduate student participants from underrepresented minorities at both campuses and from local community colleges. Antarctic earth science education materials will be assisted by professional illustrations to be open access and used in public education and communication efforts to engage local communities in Los Angeles CA and Columbia SC. The researchers at the University of Southern California and the University of South Carolina will together study the penultimate moment of the early Cenozoic greenhouse climate state: the ~4 million years of global cooling that culminated in the Eocene/Oligocene transition (~34 Ma). Significant gaps remain in the understanding of the conditions that preceded ice expansion on Antarctica. In particular, the supply of raw material for ice sheets (i.e., moisture) and the timing, frequency, and duration of precursor glaciations is poorly constrained. This collaborative proposal combines organic and inorganic proxies to examine how Antarctic hydroclimate changed during the greenhouse to icehouse transition. The central hypothesis is that the hydrological cycle weakened as cooling proceeded. Plant-wax hydrogen and carbon isotopes (hydroclimate proxies) and Hf-Nd isotopes of lithogenous and hydrogenous sediments (mechanical weathering proxies) respond strongly and rapidly to precipitation and glacial advance. This detailed and sensitive combined approach will test whether there were hidden glaciations (and/or warm events) that punctuated the pre-icehouse interval. Studies will be conducted on Prydz Bay marine sediment cores in a depositional area for products of weathering and erosion that were (and are) transported through Lambert Graben from the center of Antarctica. The project will yield proxy information about the presence of plants and the hydroclimate of Antarctica and the timing of glacial advance, and is expected to show drying associated with cooling and ice-sheet growth. The dual approach will untangle climate signals from changes in fluvial versus glacial erosion of plant biomarkers. This proposal is potentially transformative because the combination of organic and inorganic proxies can reveal rapid transitions in aridity and glacial expansion, that may have been missed in slower-response proxies and more distal archives. The research is significant as hydroclimate seems to be a key player in the temperature-cryosphere hysteresis.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.