Collaborative Research: Snapshots of Early and Mid-Pleistocene Climate and Atmospheric Composition from the Allan Hills Blue Ice Area

被困在冰芯中的古代空气气泡被用来直接重建过去80万年的大气成分，以及它与南极和全球气候的联系。此前对南极洲艾伦山蓝冰区的实地考察，已经发现了可以追溯到270万年前的冰芯，这是迄今为止发现的最古老的极地冰样本。这些冰芯将对大气二氧化碳和甲烷浓度的直接观测和南极气候的间接记录延伸到地球气候历史的一个时期，这一时期代表了对未来人为气候变化的合理地质模拟。结果表明，在100万至200万年前，气候和温室气体的冰期-间冰期变率较小，南极气候和大气二氧化碳之间存在持续的联系。通过这个项目，该团队将返回艾伦山蓝冰区，以恢复可追溯到200万年或更早的其他冰芯。从这些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。项目结果将有助于回答与人为变化有关的问题，包括温度变化与南极冰质量平衡之间的关系以及大气温室气体与全球气候变化之间的关系。在过去的5200万年里，地球一直在变冷，冰盖在扩大。地球气候系统的周期性变化叠加在这种冷却上，这种变化是由地球绕太阳轨道的离心率、岁差和倾角的变化所驱动的。基于有孔虫方解石氧同位素测量的气候重建表明，在距今约280万年至120万年（Ma）之间，地球气候系统每约4万年（“40k世界”）在冰期和间冰期状态之间振荡。从1.2 ~ 0.8 Ma持续到现在，冰期旋回幅度增大，延长至~10万年（“100k世界”）。冰芯保存了古代的空气，可以直接重建大气中的二氧化碳和甲烷。他们还存档了区域气候、平均海洋温度、全球氧循环和附近大陆干旱程度的代用记录。对距今80万年的地层连续冰芯的研究表明，大气中的二氧化碳与气候密切相关，将冰芯记录延伸到距今40万年的世界是非常有趣的。最近在南极洲Allan Hills Blue ice Area （BIA）钻探的冰芯中发现了保存完好的冰，其年代为1.0至2.7 Ma，证明了在浅深度（200米）恢复地层不连续的旧冰的潜力。该项目将继续这项工作，通过检索新的大容量冰芯，并测量来自艾伦山BIA的新冰和现有冰的古气候特征。实验目标是更全面地描述40k世界气候系统和碳循环的基本特性。项目结果将对更新世气候变化产生影响，并将对在地质时间尺度上调节大气二氧化碳、甲烷和氧气的过程提供新的约束。考虑到Allan Hills BIA的冰的年龄至少有200万年，研究小组将钻探更多的冰芯，以寻找在上新世-更新世过渡时期（~2.8 Ma）北半球冰川开始之前的冰。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Bubbles of ancient air trapped in ice cores have been used to directly reconstruct atmospheric composition, and its links to Antarctic 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 extend as far back as 2.7 million years, by far the oldest polar ice samples yet recovered. These ice cores extend direct observations of atmospheric carbon dioxide and methane concentrations and indirect records of Antarctic climate into a period of Earth's climate history that represents a plausible geologic analogue to future anthropogenic climate change. The results demonstrate a smaller glacial-interglacial variability of climate and greenhouse gases, and a persistent linkage between Antarctic climate and atmospheric carbon dioxide, between 1 and 2 million years ago. Through this project, the team will return to the Allan Hills Blue Ice Area to recover additional ice cores that date to 2 million years or older. The climate records developed from these 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. Project results will help answer questions about issues associated with anthropogenic change including the relationship between temperature change and the mass balance of Antarctic ice and the relationship between atmospheric greenhouse gases and global climate change. Earth has been cooling, and ice sheets expanding, over the past ~52 million years. Superimposed on this cooling are periodic changes in Earth's climate system driven by variations in the eccentricity, precession, and obliquity of Earth's orbit around the Sun. Climate reconstructions based on measurements of oxygen isotopes in foraminiferal calcite indicate that, from ~2.8 to 1.2 million years before present (Ma), Earth's climate system oscillated between glacial and interglacial states every ~40,000 years (the "40k world"). Between 1.2-0.8 Ma and continuing to the present, the period of glacial cycles increased in amplitude and lengthened to ~100,000 years (the "100k world"). Ice cores preserve ancient air that allows direct reconstructions of atmospheric carbon dioxide and methane. They also archive proxy records of regional climate, mean ocean temperature, global oxygen cycling, and the aridity of nearby continents. Studies of stratigraphically continuous ice cores, extending to 800,000 years before present, have demonstrated that atmospheric carbon dioxide is strongly linked to climate, and it is of great interest to extend the ice-core record into the 40k world. Recent discoveries of well-preserved ice dating from 1.0 to 2.7 Ma from ice cores drilled in the Allan Hills Blue Ice Area (BIA), Antarctica, demonstrate the potential to retrieve stratigraphically discontinuous old ice at shallow depths (200 meters). This project will continue this work by retrieving new large-volume ice cores and measuring paleoclimate properties in both new and existing ice from the Allan Hills BIA. The experimental objectives are to more fully characterize fundamental properties of the climate system and the carbon cycle during the 40k world. Project results will have implications for Pleistocene climate change, and will provide new constraints on the processes that regulate atmospheric carbon dioxide, methane, and oxygen on geologic timescales. Given a demonstrated age of the ice at the Allan Hills BIA of at least 2 million years, the team will drill additional cores to prospect for ice that predates the initiation of Northern Hemisphere glaciation at the Plio-Pleistocene transition (~2.8 Ma).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.