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.

在过去的一个世纪中，气候科学通过化学和同位素表征的各种地质​​档案（例如极地冰核，深胚层沉积物和洞穴洞穴）的化学和同位素表征来建立了地球冰河时代周期的广泛记录。这些集群档案提供了冰河时代周期以及这些重要的气候节奏引起的相关大型全球海平面波动的深刻见解。但是，此类记录仍然对过去温暖气候期间如何或哪个地球冰盖造成更高的海平面有限的见解。这对我们的现代世界尤为重要：南极冰盖目前是世界上最大的淡水水库，如果完全融化，它将将全球海平面提高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且难以获得，因为小于现代的冰盖几何形状的直接记录仍然埋在覆盖大陆的英里厚的冰下。因此，目前尚不清楚该冰盖在温暖的气候期间有多少贡献了过去的海平面上升，或者它将如何应对预期的近乎未来的气候变暖。在拟议的研究中，我们试图开发亚冰的化学沉淀物（在冰盖下发现的湖泊中形成的仪表）作为气候档案馆，它记录了南极冰盖对过去气候变化的反应。这些亚冰矿物形式在冰下积聚了十多年，记录了响应气候变化而发生的化学和同位素亚冰块特性的变化。最终，这些样品被冰盖侵蚀，并移至南极冰缘，并在那里收集并可以研究。这项研究将利用先进的地球化学，同位素和地质学技术来发展南极冰盖过去对温暖气候时期的反应，直接努力了解南极洲将如何应对未来的变暖。在变暖星球上提高海平面预测的努力致力于确定地球过去温暖时期的极地冰盖的温度，海平面和范围。然而，在过去和将来的海平面的重建中，大型不确定性是由于南极冰盖（AIS）的气候敏感性受到限制造成的。该研究项目旨在开发使用亚冰分沉淀物作为对气候变化的过去反应的档案。南极冰块下南极洲东部的冰山下沉淀物，这样做为AIS对气候变化的反应提供了全新的独特量度。在对这些沉淀物的初步检查中，我们确定了多个样品，这些样品由循环蛋白石和钙组成，这些样品跨越了数十万年的持续时间。我们对这些样品的初步地球化学表征表明，观察到的矿物学变化是由于同位素和化学上不同水之间的亚冰分水组成的循环变化所致。蛋白石形成的水被降低（Ce* 1和高铁/MN），并暴露于AIS外围发现的盐水地下水盐水相似的234U/238U组成。方解石形成的水是氧化和暴露的Δ18O组成，与耗尽的极性高原（-50‰）一致。 234U-230日期允许构建坚固的时间序列，该时间序列描述了这些矿物学和成分随着时间的变化。这些时间序列与其他南极攀岩记录（例如，冰核记录）的比较表明，钙的形成事件与当地温度或“南极同位素最大最高最大”的千禧一代变化一致，这代表了南半球温暖的时期，从而导致大量的子午线突出循环增加。最终，该项目旨在开发一个综合模型，以了解热盐周期的变化如何影响冰科反应，进而引起冰川水域组成的变化以及在珍贵档案中记录的矿物学阶段的变化。该奖项在法定的任务中反映了通过评估商标的支持，反映了NSF的法定任务，反映了诚实的支持。