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

被困在冰芯中的古代空气气泡使我们能够直接重建大气成分，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色冰区的实地考察已经发现了距今100万年的冰芯，这是迄今为止在南极洲发现的最古老的冰芯。这些记录揭示了80万年前间冰期二氧化碳浓度的下降，并且在100万年前较暖的世界中，二氧化碳和南极温度在过去80万年中是有联系的。该项目将返回艾伦山蓝冰区，以恢复可追溯到100万年或更早的其他冰芯。从钻探的冰芯中得到的气候记录将为大气的化学成分和南极气候提供新的见解，在与现在相当甚至更温暖的时期。我们的研究结果将有助于回答与人为变化有关的问题。其中包括温度变化与南极冰的物质平衡之间的关系；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，并将开展外联活动，包括让教师参与碳科学和冰芯的研讨会。在大约280万至90万年前，地球的气候以4万年的周期为特征，由地球自转轴倾斜的变化所驱动或调节。通过对深海沉积物的研究，我们对“4万年”世界的了解很多，但我们对这一时期气候变化的理解是不完整的，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。我们建议以我们最近对南极洲艾伦山主要冰原的古代冰的研究为基础来解决这些问题。在之前的野外季节，我们恢复了从10万到100万年不等的冰延伸。通过测量捕获气体的40Ar/38Ar（氩气）比率来确定冰的年代。我们发现的数百万年前的冰表明，在艾伦山主要冰原中，有来自4万年世界的气体质量冰。我们已经确定了两个不同的地点，每个地点都位于约200米深的基岩上，这是对100万年或更古老的冰进行取样的有吸引力的目标。这个项目的目的是在这两个地点取冰芯，重新占据之前的一个有数百万年历史的冰的地点，并将其钻到基岩上，并在我们之前的工作和陆地陨石年龄表明古代表面冰的区域产生10-20个短（~10米）的岩芯。我们计划用捕获氩的40Ar/38Ar年龄来确定冰的年代。我们还计划通过测量冰、甲烷中的氘和氧同位素比值、捕获气体中氧和氩与氮的比值、氮的氮-15同位素（d15N）和氧的氧-18同位素（d18O）来表征我们岩心的连续性。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性质。成功回收超过100万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、尘埃源和源区干旱、水分来源、致密化条件、全球平均海洋温度和温室气体浓度。我们将在4万年世界和中更新世过渡到10万年世界的主要假设的背景下分析数据。我们期望在这些时期推进对气候动力学的理解。

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.