Collaborative Research: Window into the World with 40,000-year Glacial Cycles from Climate Records in Million Year-old Ice from the Allan Hills Blue Ice Area

合作研究：通过艾伦山蓝冰区百万年冰层的气候记录了解 40,000 年冰川循环的世界之窗

• 批准号: 1443306
• 负责人: Paul Mayewski
• 金额: $ 15.15万
• 依托单位: University of Maine
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1443306&HistoricalAwards=false
• 关键词: Collaborative; Research; Window; into; World

Bubbles of ancient air trapped in ice cores permit the direct reconstruction of atmospheric composition and allow us to link greenhouse gases and global climate over the last 800,000 years. Previous field expeditions to the Allan Hills blue ice area, Antarctica, have recovered ice cores that date to one million years, the oldest ice cores yet recovered from Antarctica. These records have revealed that interglacial CO2 concentrations decreased by 800,000 years ago and that, in the warmer world 1 million years ago, CO2 and Antarctic temperature were linked as during the last 800,000 years. This project will return to the Allan Hills blue ice area to recover additional ice cores that date to 1 million years or older. The climate records developed from the drilled ice cores will provide new insights into the chemical composition of the atmosphere and Antarctic climate during times of comparable or even greater warmth than the present day. Our results will help answer questions about issues associated with anthropogenic change. These include the relationship between temperature change and the mass balance of Antarctic ice; precipitation and aridity variations associated with radiatively forced climate change; and the climate significance of sea ice extent. The project will entrain two graduate students and a postdoctoral scholar, and will conduct outreach including workshops to engage teachers in carbon science and ice cores.Between about 2.8-0.9 million years ago, Earth's climate was characterized by 40,000-year cycles, driven or paced by changes in the tilt of Earth's spin axis. Much is known about the "40,000-year" world from studies of deep-sea sediments, but our understanding of climate change during this period is incomplete because we lack records of Antarctic climate and direct records of atmospheric greenhouse gas concentrations. We propose to address these issues by building on our recent studies of ancient ice from the Main Ice Field, Allan Hills, Antarctica. During previous field seasons we recovered ice extending, discontinuously, from 0.1-1.0 million years old. Ice was dated by measuring the 40Ar/38Ar (Argon) ratio of the trapped gases. Our discovery of million year-old ice demonstrates that there is gas-record-quality ice from the 40,000-year world in the Allan Hills Main Ice Field. We have identified two different sites, each overlying bedrock at ~ 200 m depth, that are attractive targets for coring ice dating to 1 million years and older. This project aims to core the ice at these two sites, re-occupy a previous site with million year-old ice and drill it down to the bedrock, and generate 10-20 short (~10-meter) cores in areas where our previous work and terrestrial meteorite ages suggest ancient surface ice. We plan to date the ice using the 40Ar/38Ar ages of trapped Argon. We also plan to characterize the continuity of our cores by measuring the deuterium and oxygen isotope ratios in the ice, methane, ratios of Oxygen and Argon to Nitrogen in trapped gas, the Nitrogen-15 isotope (d15N) of Nitrogen, and the Oxygen-18 isotope (d18O) of Oxygen. As the ice may be stratigraphically disturbed, these measurements will provide diagnostic properties for assessing the continuity of the ice-core records. Successful retrieval of ice older than one million years will provide the opportunity for follow-up work to measure the CO2 concentration and other properties within the ice to inform on the temperature history of the Allan Hills region, dust sources and source-area aridity, moisture sources, densification conditions, global average ocean temperature, and greenhouse gas concentrations. We will analyze the data in the context of leading hypotheses of the 40,000-year world and the Mid-Pleistocene Transition to the 100,000-year world. We expect to advance understanding of climate dynamics during these periods.

冰芯中的古代空气气泡可以直接重建大气成分，并使我们能够将过去 80 万年的温室气体和全球气候联系起来。此前对南极洲艾伦山蓝冰区的实地考察已经发现了距今一百万年的冰芯，这是迄今为止在南极洲发现的最古老的冰芯。 这些记录表明，间冰期二氧化碳浓度在 80 万年前减少，并且在 100 万年前的温暖世界中，二氧化碳和南极温度在过去 80 万年中是相关的。 该项目将返回艾伦山蓝冰区，以回收更多 100 万年前或更早的冰芯。 从钻取的冰芯中得出的气候记录将为了解与现在相当甚至更高的温暖时期的大气化学成分和南极气候提供新的见解。 我们的结果将有助于回答与人为变化相关的问题。其中包括温度变化与南极冰的质量平衡之间的关系；与辐射强迫气候变化有关的降水和干旱变化；以及海冰范围的气候意义。 该项目将招收两名研究生和一名博士后学者，并将开展外展活动，包括举办讲习班，让碳科学和冰芯领域的教师参与其中。在大约 2.8 至 90 万年前，地球气候的特点是 4 万年的循环，无论是驱动还是节奏通过地球自转轴倾斜度的变化。通过对深海沉积物的研究，我们对“四万年”的世界有了很多了解，但我们对这一时期气候变化的了解并不完整，因为我们缺乏南极气候的记录和大气温室气体浓度的直接记录。 我们建议通过最近对南极洲艾伦山主冰原古代冰的研究来解决这些问题。在之前的野外季节中，我们断断续续地恢复了年龄从 0.1 到 100 万年的冰。通过测量捕获气体的 40Ar/38Ar（氩）比率来测定冰的年代。我们对百万年冰的发现表明，艾伦山主冰原中存在着来自四万年世界的气体记录质量的冰。我们已经确定了两个不同的地点，每个地点都覆盖在约 200 m 深度的基岩上，对于可追溯至 100 万年或更早的冰芯来说，这些地点都是有吸引力的目标。该项目的目的是对这两个地点的冰进行取芯，重新占据之前有百万年历史的冰的地点，并将其钻到基岩，并在我们之前的区域生成 10-20 个短（约 10 米）的冰芯。工作和陆地陨石年龄表明古老的表面冰。 我们计划使用被困氩的 40Ar/38Ar 年龄来测定冰的年代。 我们还计划通过测量冰中的氘和氧同位素比率、甲烷、捕获气体中氧和氩与氮的比率、氮的氮 15 同位素 (d15N) 和氧同位素来表征堆芯的连续性。氧的 18 同位素 (d18O)。 由于冰可能受到地层扰动，这些测量将为评估冰芯记录的连续性提供诊断特性。 成功检索超过一百万年的冰将为后续工作提供机会，测量冰内的二氧化碳浓度和其他特性，以了解艾伦山地区的温度历史、灰尘源和源区的干燥度、湿度来源、致密化条件、全球平均海洋温度和温室气体浓度。 我们将在 40,000 年世界和中更新世过渡到 100,000 年世界的主要假设的背景下分析数据。我们希望加深对这些时期气候动态的了解。