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气泡使我们能够直接重建大气成分，并使我们能够将温室气体与过去80万年的全球气候联系起来。之前对南极洲艾伦山蓝色冰区的实地考察已经发现了可追溯到100万年前的冰芯，这是迄今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80万年前下降了，在100万年前变暖的世界中，二氧化碳和南极温度之间存在联系，就像过去80万年一样。该项目将返回到Allan Hills蓝色冰区，以回收更多可追溯到100万年或更早的冰芯。从钻探的冰芯产生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，这些时期的气温与现在相当，甚至更高。我们的结果将有助于回答与人为变化相关的问题。这些问题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。该项目将培养两名研究生和一名博士后学者，并将开展外联活动，包括举办研讨会，让教师参与碳科学和冰芯的研究。在大约280万年至90万年前之间，地球气候的特征是由地球自转轴倾斜的变化驱动或控制的4万年一周期。从对深海沉积物的研究中，我们已经了解了很多关于这4万年的世界，但我们对这段时间内的气候变化的了解是不完整的，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。我们建议在我们最近对南极洲艾伦山主冰场古冰的研究的基础上来解决这些问题。在以前的野外季节，我们恢复了从10万到100万年前断断续续的冰层。冰的年代是通过测量捕获气体的40Ar/38Ar(Ar)比值来确定的。我们发现的百万年前的冰表明，在艾伦山主冰场有来自4万年前世界上创纪录的气体质量的冰。我们已经确定了两个不同的地点，每个地点都覆盖在大约200米深的基岩上，这两个地点是取芯100万年或更早的冰的有吸引力的目标。该项目旨在将这两个地点的冰芯取芯，重新占据先前具有百万年历史的冰块并将其钻探到基岩，并在我们之前的工作和陆地陨石年龄表明古代地表冰的地区产生10-20个短(~10米)的岩芯。我们计划使用被困的Ar的40Ar/38Ar年龄来确定冰层的年代。我们还计划通过测量冰、甲烷中的氢和氧同位素比率、被困气体中的氧和氩与氮的比率、氮的氮-15同位素(D15N)和氧的氧-18同位素(D18O)来表征我们的岩芯的连续性。由于冰层可能受到地层扰动，这些测量将为评估冰芯记录的连续性提供诊断属性。成功取回超过一百万年的冰将为后续工作提供机会，以测量冰中的二氧化碳浓度和其他性质，以了解阿伦山地区的温度历史、尘埃源和源-区干燥度、水分来源、致密条件、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向10万年世界过渡的主要假设的背景下分析这些数据。我们期望在这些时期推进对气候动态的理解。

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.