CO2 and CH4 from Allan Hills ice cores ALHIC1901, 1902, and 1903

Between about 2.8-0.9 Ma, Earth’s climate was characterized by 40 kyr cycles, driven or paced by changes in the tilt of Earth’s spin axis. Much is known about the 40k world from studies of deep-sea sediments, but our understanding of climate change during this period and the transition between the 40kyr glacial cycles from 2.8-0.9 Ma and the 100kyr glacial cycles of the last 0.9 Myr 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 >1 Ma ice discovered in shallow ice cores in the Allan Hills Blue Ice Area (BIA), Antarctica. During the 2015-2016 field season we recovered ice from two nearby drill cores that dates to > 2 million years in age using the 40Ar/38Ar ratio of the trapped gases. Our discovery of ice of this antiquity in two cores demonstrates that there is gas-record quality ice from the 40k world in the Allan Hills BIA. To further characterize the composition of Earth’s atmosphere and Antarctic climate during the 40k world we request support for two field seasons to drill new large-volume (4” or 9” diameter) ice cores at sites where we have previously identified >1 Ma ice and nearby sites where ground penetrating radar has identified bedrock features conducive to the preservation of old ice.
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约280万至90万年前，地球气候以4万年（kyr）周期为特征，该周期由地球自转轴倾角变化驱动或调控。尽管学界已通过深海沉积物研究对这一4万年周期时段有了较为充分的认知，但我们对该时段的气候变化，以及280万至90万年前的4万年冰期周期与近90万年以来的10万年冰期周期之间的转换机制的认知仍存在不足——这是因为我们尚未获取南极气候记录与大气温室气体浓度的直接观测记录。我们拟依托此前在南极艾伦山蓝冰区（Allan Hills Blue Ice Area, BIA）浅层冰芯中发现的距今超1百万年（Ma）冰体的研究成果，来解决上述问题。在2015-2016年野外作业季，我们借助捕获气体的40Ar/38Ar比值定年法，从两处邻近的钻探岩芯中获取了距今超200万年的冰体。我们在两处岩芯中发现如此古老的冰体，证明艾伦山蓝冰区内存在可获取高质量大气记录的、形成于4万年周期时段的冰体。为进一步解析该4万年周期时段的地球大气组成与南极气候，我们申请支持开展两个野外作业季的钻探工作：在先前已发现超1百万年冰体的点位，以及经探地雷达（ground penetrating radar）识别出利于古冰保存的基岩特征的邻近点位，钻取大体积（直径4英寸或9英寸）的新冰芯。