Response of the East Antarctic Ice Sheet to Middle Miocene Global Change

摘要Marchant奖-9811877该奖项由极地计划办公室南极地质和地球物理计划提供，支持确定东南极冰盖对全球气候变化的响应的研究。最大的全球气候变化之一发生在大约1560万至1250万年前（中中新世时间）。在此期间，全球急剧降温和海洋环流模式的重组被记录为海洋中氧同位素组成的变化。这种戏剧性的永久性转变为现代海洋和大气环流奠定了基础，并迎来了在过去250万年中主导气候记录的两极冰河时代。南极洲如何应对大约1400万年前的气候大转变？南极冰盖的增长实际上引发了这种转变吗？如果是这样的话，未来东南极冰量的波动将如何影响大气和海洋环流？南极地质学最近（也是意想不到的）的突破使我们能够解决中新世中期全球气候变化和冰盖演变的根本问题，这是在维多利亚地南部发现的中新世火山灰与表层沉积物互层。这是第一次，现在有可能通过直接检查南极大陆上明确的中新世陆地沉积物来生成精确的气候和冰川重建。作为南极洲唯一一个在地表保存有原始中新世时期松散沉积物的地方，维多利亚地南部是无与伦比的中新世冰川地质资料的宝库。现在可以解决的关键问题包括：南极洲的哪些因素导致了大约1400万年前全球突然变冷？中新世中期海洋同位素组成的变化是否意味着东南极冰的主要扩张？或者，同位素的变化是否反映了海洋温度或环流的变化？一个相关的问题是，南极洲何时开始出现极端干旱、寒冷的极地沙漠条件（标志着南极洲东部极地冰盖的发展）？精确的年代控制将基于对现场火山灰的50次激光熔融同位素分析和对古代矿床的20次宇宙成因年代分析。中新世古气候的同时代记录将来自高山漂流物的结构变化、冰缘湖的区域分布、大量的过时图案地面和通风路面，以及埋藏土壤和火山灰沉积物的地球化学。

Abstract Marchant OPP-9811877This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports research to determine the response of the East Antarctic Ice Sheet to global climate change. One of the largest global climate shifts occurred between about 15.6 and 12.5 million years ago (Middle Miocene time). During this time, dramatic global cooling and reorganization of ocean circulation patterns were recorded as a shift in the isotopic composition of oxygen in the oceans. This dramatic and permanent shift set the stage for modern oceanic and atmospheric circulation and ushered in the bipolar ice ages that have dominated climate records for the last 2.5 million years. How did Antarctica respond to the great climate shift at about 14 million years ago? Did growth of the Antarctic Ice Sheet in fact initiate this shift? If so, how will future fluctuations in the volume of East Antarctic ice influence atmospheric and oceanic circulation?The recent (and unexpected) breakthrough in Antarctic geology that now allows us to address the fundamental problem of middle Miocene global climate change and ice sheet evolution is the discovery of Miocene-age volcanic ashes that are interbedded with surficial sediments in southern Victoria Land. For the first time, it is now possible to generate precise climate and glaciological reconstructions from direct examination of unambiguous, Miocene-age terrestrial deposits on the Antarctic continent. As the only place in Antarctica where pristine Miocene-age unconsolidated deposits are preserved at the ground surface, southern Victoria Land is unrivaled as a storehouse of Miocene glacial-geologic data. Key questions that now can be addressed include; What contributing factors on Antarctica led to abrupt global cooling at about 14 million years ago? Does the middle Miocene shift in the isotopic composition of the oceans signify a major expansion of East Antarctic ice? Or, does the isotopic shift instead reflect a change in ocean temperature or circulation? A related question is when did hyper-arid, cold polar-desert conditions (signifying the development of a polar East Antarctic ice sheet) first evolve in Antarctica?Precise chronological control will be based on 50 laser-fusion isotopic analyses of in-situ volcanic ashes and 20 cosmogenic exposure-age analyses of ancient deposits. A coeval record of Miocene paleoclimate will come from textural changes in alpine drifts, the areal distribution of ice-marginal lakes, the abundance of dated patterned ground and ventifact pavements, and the geochemistry of buried soils and volcanic-ash deposits.