Collaborative Research: Reconstructing East Antarctica’s Past Response to Climate using Subglacial Precipitates

合作研究：利用冰下降水重建东南极洲过去对气候的响应

• 批准号: 2042495
• 负责人: Terrence Blackburn
• 金额: $ 67.93万
• 依托单位: University of California-Santa Cruz
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-06-01 至 2025-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2042495&HistoricalAwards=false
• 关键词: Collaborative; Research; Reconstructing; East; Antarctica

Over the past century, climate science has constructed an extensive record of Earth’s ice age cycles through the chemical and isotopic characterization of various geologic archives such as polar ice cores, deep-ocean sediments, and cave speleothems. These climatic archives provide an insightful picture of ice age cycles and of the related large global sea level fluctuations triggered by these significant climate rhythms. However, such records still provide limited insight as to how or which of Earth’s ice sheets contributed to higher sea levels during past warm climate periods. This is of particular importance for our modern world: the Antarctic ice sheet is currently the world’s largest freshwater reservoir, which, if completely melted, would raise the global sea level by over 60 meters (200 feet). Yet, geologic records of Antarctic ice sheet sensitivity to warm climates are particularly limited and difficult to obtain, because the direct records of ice sheet geometry smaller than the modern one are still buried beneath the mile-thick ice covering the continent. Therefore, it remains unclear how much this ice sheet contributed to past sea level rise during warm climate periods or how it will respond to the anticipated near-future climate warming. In the proposed research we seek to develop sub-ice chemical precipitates—minerals that form in lakes found beneath the ice sheet—as a climatic archive, one that records how the Antarctic ice sheet responded to past climatic change. These sub-ice mineral formations accumulated beneath the ice for over a hundred thousand years, recording the changes in chemical and isotopic subglacial properties that occur in response to climate change. Eventually these samples were eroded by the ice sheet and moved to the Antarctic ice margin where they were collected and made available to study. This research will utilize advanced geochemical, isotopic and geochronologic techniques to develop record of the Antarctica ice sheet’s past response to warm climate periods, directly informing efforts to understand how Antarctica will response to future warming. Efforts to improve sea level forecasting on a warming planet have focused on determining the temperature, sea level and extent of polar ice sheets during Earth’s past warm periods. Large uncertainties, however, in reconstructions of past and future sea levels, result from the poorly constrained climate sensitivity of the Antarctic Ice sheet (AIS). This research project aims to develop the use of subglacial precipitates as an archive the Antarctic ice sheet (AIS) past response to climate change. The subglacial precipitates from East Antarctica form in water bodies beneath Antarctic ice and in doing so provide an entirely new and unique measure of how the AIS responds to climate change. In preliminary examination of these precipitates, we identified multiple samples consisting of cyclic opal and calcite that spans hundreds of thousands of years in duration. Our preliminary geochemical characterization of these samples indicates that the observed mineralogic changes result from a cyclic change in subglacial water compositions between isotopically and chemically distinct waters. Opal-forming waters are reduced (Ce* 1 and high Fe/Mn) and exhibit elevated 234U/238U compositions similar to the saline groundwater brines found at the periphery of the AIS. Calcite-forming waters, are rather, oxidized and exhibit δ18O compositions consistent with derivation from the depleted polar plateau ( -50 ‰). 234U-230Th dates permit construction of a robust timeseries describing these mineralogic and compositional changes through time. Comparisons of these time series with other Antarctic climate records (e.g., ice core records) reveal that calcite forming events align with millennial scale changes in local temperature or “Antarctic isotopic maximums”, which represent Southern Hemisphere warm periods resulting in increased Atlantic Meridional overturing circulation. Ultimately, this project seeks to develop a comprehensive model as to how changes in the thermohaline cycle induce a glaciologic response which in turn induces a change in the composition of subglacial waters and the mineralogic phase recorded within the precipitate archive.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.

在过去的世纪里，气候科学通过对极地冰芯、深海沉积物和洞穴洞穴沉积物等各种地质档案的化学和同位素表征，构建了地球冰河时代周期的广泛记录。这些气候档案提供了一幅关于冰河时代周期和由这些重大气候节律引发的相关全球海平面大幅波动的深刻图景。然而，这些记录仍然提供了有限的见解，以了解在过去的温暖气候时期，地球的冰盖如何或哪些导致海平面上升。这对我们的现代世界特别重要：南极冰盖是目前世界上最大的淡水水库，如果完全融化，将使全球海平面上升60米（200英尺）。然而，南极冰盖对温暖气候的敏感性的地质记录特别有限，而且很难获得，因为比现代冰盖更小的冰盖几何形状的直接记录仍然埋在覆盖大陆的一英里厚的冰层下。因此，目前还不清楚这片冰盖在过去温暖气候时期对海平面上升的贡献有多大，也不清楚它将如何应对预期的近期气候变暖。 在拟议的研究中，我们寻求开发冰下化学沉淀物-在冰盖下发现的湖泊中形成的矿物质-作为气候档案，记录南极冰盖如何应对过去的气候变化。这些冰下矿物在冰下积累了十多万年，记录了气候变化引起的冰下化学和同位素性质的变化。最终，这些样本被冰盖侵蚀并转移到南极冰缘，在那里它们被收集并用于研究。这项研究将利用先进的地球化学、同位素和地质年代学技术，记录南极洲冰盖过去对温暖气候时期的反应，直接为了解南极洲将如何应对未来变暖提供信息。 在一个变暖的星球上改善海平面预测的努力集中在确定地球过去温暖时期的温度，海平面和极地冰盖的范围。然而，在过去和未来的海平面重建的大的不确定性，从约束不良的气候敏感性南极冰盖（AIS）。该研究项目旨在开发冰下沉淀物的使用，作为南极冰盖（AIS）过去对气候变化反应的档案。来自南极洲东部的冰下沉淀物在南极冰下的水体中形成，这样做为AIS如何应对气候变化提供了一个全新的独特措施。在对这些沉淀物的初步检查中，我们确定了多个由周期蛋白石和方解石组成的样本，这些样本的持续时间长达数十万年。我们对这些样品的初步地球化学表征表明，所观察到的矿物学变化是由冰下水成分在同位素和化学性质不同的沃茨之间的周期性变化引起的。蛋白石形成沃茨减少（Ce* 1和高Fe/Mn），并表现出类似于在AIS外围发现的含盐地下水卤水的234 U/238 U成分升高。 方解石形成的沃茨是氧化的，其δ 18 O组成与贫化的极地高原（-50 ‰）一致。234 U-230 Th测年数据可以构建一个强大的时间序列，描述这些矿物学和成分随时间的变化。 这些时间序列与其他南极气候记录的比较（例如，冰芯记录）揭示了方解石形成事件与千年尺度的局部温度变化或“南极同位素最大值”相一致，这代表了南半球温暖时期导致大西洋经向翻转环流增加。最终，该项目旨在开发一个全面的模型，以了解温盐循环的变化如何引起冰川学反应，进而引起冰下沃茨成分和沉淀物档案中记录的矿物相的变化。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。