COLLABORATIVE RESEARCH: Resolving Ambiguous Exposure-Age Chronologies of Antarctic Deglaciation with Measurements of In-Situ-Produced Cosmogenic Carbon-14

合作研究：通过测量原位产生的宇宙成因碳 14 来解决南极冰川消融的模糊暴露年龄年表

• 批准号: 1542976
• 负责人: Gregory Balco
• 金额: $ 5.06万
• 依托单位: Berkeley Geochronology Center
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-05-01 至 2021-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1542976&HistoricalAwards=false
• 关键词: COLLABORATIVE; RESEARCH; Resolving; Ambiguous; Exposure

The overall goal of this project is to determine the effect of past changes in the size of the Antarctic Ice Sheet on global sea level. At the peak of the last ice age 25,000 years ago, sea level was 120 meters (400 feet) lower than it is at present because water that is now part of the ocean was instead part of expanded glaciers and ice sheets in North America, Eurasia, and Antarctica. Between then and now, melting and retreat of this land ice caused sea level to rise. In this project, we aim to improve our understanding of how changes in the size of the Antarctic Ice Sheet contributed to this process. The overall strategy to accomplish this involves (i) visiting areas in Antarctica that are not now covered by ice; (ii) looking for geological evidence, specifically rock surface and sediment deposits, that indicates that these areas were covered by thicker ice in the past; and (iii) determining the age of these geological surfaces and deposits. This project addresses the final part of this strategy -- determining the age of Antarctic glacial rock surfaces or sediment deposits -- using a relatively new technique that involves measuring trace elements in rock surfaces that are produced by cosmic-ray bombardment after the rock surfaces are exposed by ice retreat. By applying this method to rock samples collected in previous visits to Antarctica, the timing of past expansion and contraction of the ice sheet can be determined. The main scientific outcomes expected from this project are (i) improved understanding of how Antarctic Ice Sheet changes contributed to past global sea level rise; and (ii) improved understanding of modern observed Antarctic Ice Sheet changes in a longer-term context. This second outcome will potentially improve predictions of future ice sheet behavior. Other outcomes of the project include training of individual undergraduate and graduate students, as well as the development of a new course on sea level change to be taught at Tulane University in New Orleans, a city that is being affected by sea level change today.This project will use measurements of in-situ-produced cosmogenic carbon-14 in quartz from existing samples collected at several sites in Antarctica to resolve major ambiguities in existing Last Glacial Maximum to present ice sheet reconstructions. This project is important because of the critical nature of accurate reconstructions of ice sheet change in constraining reconstructions of past sea level change. Although carbon-14 is most commonly exploited as a geochronometer through its production in the upper atmosphere and incorporation into organic materials, it is also produced within the crystal lattice of rocks and minerals that are exposed to the cosmic-ray flux at the Earth's surface. In this latter case, its concentration is proportional to the duration of surface exposure, and measurements of in-situ-produced carbon-14 can be used to date geological events that form or expose rock surfaces, for example, ice sheet expansion and retreat. Although carbon-14 is one of several trace radionuclides that can be used for this purpose, it is unique among them in that its half-life is short relative to the time scale of glacial-interglacial variations. Thus, in cases where rock surfaces in polar regions have been repeatedly covered and uncovered by ice sheet change during many glacial-interglacial cycles, carbon-14 measurements are uniquely suited to accurately dating the most recent episode of ice sheet advance and retreat. We aim to use this property to improve our understanding of Antarctic Ice Sheet change at a number of critically located sites at which other surface exposure dating methods have yielded ambiguous results. Geographically, these are focused in the Weddell Sea embayment of Antarctica, which is an area where the geometry of the Antarctic continent potentially permits large glacial-interglacial changes in ice volume but where existing geologic records of ice sheet change are particularly ambiguous. In addition, in-situ carbon-14 measurements, applied where independently constrained deglaciation chronologies already exist, can potentially allow us to date the last period of ice sheet advance as well as the most recent retreat.

该项目的总体目标是确定南极冰盖大小的过去变化对全球海平面的影响。在25，000年前的最后一个冰河时代的顶峰上，海平面比目前低120米（400英尺），因为现在已经是海洋的水是北美，欧亚大陆和南极洲扩张的冰川和冰盖的一部分。从那时到现在，熔化和撤退导致海平面上升。在这个项目中，我们旨在提高人们对南极冰盖大小的变化如何有助于这一过程的理解。实现此目的的总体策略涉及（i）访问南极的访问区，这些地区现在尚未被冰覆盖； （ii）寻找地质证据，特别是岩石表面和沉积物沉积物，表明这些地区过去被较厚的冰覆盖； （iii）确定这些地质表面和沉积物的年龄。该项目使用相对较新的技术解决了该策略的最后一部分 - 确定南极冰川岩石表面或沉积物沉积物的年龄，涉及在岩石表面暴露于冰层冰层后，涉及测量岩石表面中的微量元素。通过将此方法应用于先前访问南极的岩石样品，可以确定冰盖过去膨胀和收缩的时机。该项目预期的主要科学成果是（i）对南极冰盖变化如何促进过去的全球海平面上升的理解提高； （ii）在长期的背景下，对现代观察到的南极冰盖的变化有了改进的理解。 第二个结果将有可能改善对未来冰盖行为的预测。 Other outcomes of the project include training of individual undergraduate and graduate students, as well as the development of a new course on sea level change to be taught at Tulane University in New Orleans, a city that is being affected by sea level change today.This project will use measurements of in-situ-produced cosmogenic carbon-14 in quartz from existing samples collected at several sites in Antarctica to resolve major ambiguities in existing Last冰川最大以呈现冰盖重建。该项目很重要，因为在约束过去海平面变化的重建中，准确重建冰盖变化的批判性质。尽管碳-14最常见的是通过其在上层大气中的生产并掺入有机材料中作为地球运动仪，但在岩石和矿物质的晶格中也生产，这些岩石和矿物质暴露于地球表面的宇宙射线磁通量。在后一种情况下，它的浓度与表面暴露的持续时间成正比，而原位生产的碳14的测量可用于约会形成或暴露岩石表面的地质事件，例如，冰盖膨胀和撤退。尽管碳14是可用于此目的的几种痕量放射性核素之一，但它在它们之间是独一无二的，因为它的半衰期相对于冰川间 - 冰川变化的时间尺度短。因此，如果在许多冰川间冰期循环中反复覆盖并被冰盖变化覆盖和发现的情况下，碳14的测量非常适合准确地与最近的冰盖前进和撤退的最新一集。 我们的目的是利用这种特性来提高我们对南极冰盖变化的理解，在许多批判地点的地点，在其他地面暴露约会方法中产生了模棱两可的结果。从地理上讲，它们集中在南极洲的Weddell Sea Embayment上，南极洲的几何形状有可能允许冰量的大冰期间 - 冰期变化，但现有的冰盖变化地质记录尤其含糊不清。 此外，在已经存在独立约束脱气表的地方应用的原位碳-14测量值可能使我们能够约会冰盖的最后一个阶段，以及最新的撤退。