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

南极东部冰盖拥有地球上最大的淡水储量，总量足以使海平面上升近200英尺。即使储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。推动这个项目的问题是，3000万年前，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，冰是如何覆盖整个大陆的？Prydz湾是南极东部冰原（EAIS）的一个主要排水盆地，此前曾钻探过该地区的海底，以恢复数百万年前的沉积物，这些沉积物可以追溯到南极洲大陆冰原形成之前和跨越南极大陆冰原形成的时间。在海洋沉积物中发现的最后残留的植物物质作为“生物标志物”，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，后来又为不断扩大的冰川提供了养分。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经景观的。在这里，研究人员将确定由冰盖生长导致并驱动的降水变化。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）核心库海底沉积物档案的样本。最终，这些发现可以帮助在气候和冰盖模型中了解温度-降水-冰的联系。该项目将支持培训三名女性早期职业科学家（博士和硕士学生，以及研究技术人员），pi和博士生将继续参与扩大参与努力(例如，女性参与科学与工程计划；美国原住民和奇卡诺人科学促进会（Society for advancement for Native Americans and Chicanos in Science）的地方分会（以及其他准入项目），在两所大学和当地社区大学招募未被充分代表的少数族裔本科生。南极地球科学教育材料将在专业插图的帮助下开放获取，并用于公共教育和交流工作，以吸引洛杉矶和哥伦比亚南卡罗来纳州的当地社区。南加州大学和南卡罗莱纳大学的研究人员将共同研究早期新生代温室气候状态的倒数第二时刻：在始新世/渐新世过渡（~34 Ma）时达到顶峰的400万年全球变冷。在了解南极洲冰层膨胀之前的条件方面仍然存在重大差距。特别是，对冰原原料（即水分）的供应以及前冰期的时间、频率和持续时间的限制很少。这个合作方案结合了有机和无机指标来研究南极水文气候在温室到冰窖的转变过程中是如何变化的。核心假设是，随着降温的进行，水文循环减弱。植物蜡的氢和碳同位素（水文气候代用物）和岩质和氢质沉积物的Hf-Nd同位素（机械风化代用物）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/或温暖事件）在冰库之前的间隔中出现。将对一个沉积区的普里兹湾海洋沉积物岩心进行研究，以寻找从南极洲中心经过兰伯特地堑运送过来的风化和侵蚀产物。该项目将提供有关南极植物的存在和水文气候以及冰川推进时间的代理信息，并有望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和冰川侵蚀变化中理清气候信号。这一建议具有潜在的变革意义，因为有机和无机代用物的结合可以揭示干旱和冰川扩张的快速转变，这可能在响应较慢的代用物和更远的档案中被遗漏。该研究具有重要意义，因为水文气候似乎是温度-冰冻圈滞后的关键因素。该奖项反映了美国国家科学基金会的法定使命，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.