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储量，总共足以使海平面上升近200英尺。即使是冰量的微小调整，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，3000万年前，当南极洲从温暖的环境转变为冰盖的南部大陆时，冰是如何生长到覆盖这块大陆的？普里兹湾是东南极冰盖(EAIS)的一个主要水系盆地，其海底以前曾被钻探过，以恢复南极大陆冰盖形成之前和整个时间段数百万年前的沉积物。在海洋沉积物中发现的最后一批植物物质作为生物标记物，记录了雨雪的化学特征，这些化学特征滋养了植物，后来又滋养了不断扩大的冰川。冰川携带的沉积物也被沉积在海底，可以进行分析，以发现冰川是如何流过地形的。在这里，研究人员将确定由冰盖增长引起并推动的降水变化。这项研究将从国际海洋发现计划(IODP)核心储存库的海底沉积物档案中收集数据并进一步分析样本。最终，这些发现可以帮助了解气候和冰盖模型中的温度-降水-冰之间的联系。该项目将支持三名女性早期职业科学家(博士生和研究技术员)的培训，私人投资机构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计划；促进美洲原住民社会的地方分会和科学和其他机会计划中的奇卡诺人)，从校园和当地社区学院中代表性较低的少数族裔招募本科生参与者。南极地球科学教育材料将得到开放获取的专业插图的协助，并用于公共教育和传播工作，以吸引洛杉矶、加利福尼亚州和哥伦比亚特区当地社区的参与。南加州大学和南卡罗来纳大学的研究人员将共同研究早新生代温室气候状态的倒数第二时刻：大约400万年的全球变冷，最终达到始新世/渐新世过渡(~34 Ma)。在对南极洲冰层扩张之前的条件的了解方面，仍然存在重大差距。特别是，冰盖的原材料供应(即水分)以及前驱冰川的时间、频率和持续时间受到的限制很小。这项合作方案结合了有机和无机的替代物，研究了从温室到冰库过渡期间南极水文气候是如何变化的。中心假设是，随着降温的进行，水文循环减弱。成岩和含氢沉积物的植物蜡氢和碳同位素(水文气候指标)和Hf-ND同位素(机械风化指标)对降水和冰川推进作出强烈而快速的响应。这种详细和敏感的组合方法将测试是否存在打断前冰库间隔的隐藏冰川(和/或温暖事件)。将在一个沉积区的普里兹湾海洋沉积物岩心上进行研究，以寻找风化和侵蚀的产物，这些产物是通过Lambert Graben从南极洲中心运输过来的。该项目将产生有关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，预计将显示与降温和冰盖生长相关的干燥。这种双重方法将从植物生物标志物的河流侵蚀和冰川侵蚀的变化中解开气候信号。这一建议具有潜在的变革性，因为有机和无机替代品的组合可以揭示干旱和冰川膨胀的快速转变，而反应较慢的替代品和更远端的档案可能遗漏了这一点。这项研究意义重大，因为水气候似乎是温度-冰冻圈滞后的关键因素。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.