USAP-DC

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.

Person	Role
Mayewski, Paul A.	Investigator and contact
Kurbatov, Andrei V.	Investigator and contact
Brook, Edward J.	Investigator
Severinghaus, Jeffrey P.	Investigator
Higgins, John	Investigator

Antarctic Glaciology	Award # 1745007
Antarctic Glaciology	Award # 1745006
Antarctic Glaciology	Award # 1744993
Antarctic Glaciology	Award # 1744832
Antarctic Glaciology	Award # 0838843	Previous Award Collaborative Research: Exploring A 2 Million + Year Ice Climate Archive-Allan Hills Blue Ice Area (2MBIA) Kurbatov/0838843 This award supports a project to generate an absolute timescale for the Allan Hills Blue Ice Area (BIA), and then to reconstruct details of past climate changes and greenhouse gas concentrations for certain time periods back to 2.5 Ma. Ice ages will be determined by applying emerging methods for absolute and relative dating of trapped air bubbles (based on Argon-40/Argon-38, delta-18O of O2, and the O2/N2 ratio). To demonstrate the potential of the Allan Hills BIAs as a paleoclimate archive trenches and ice cores will be collected for age intervals corresponding to 110-140 ka, 1 Ma, and 2.5 Ma. During the proposed two field seasons a total of 6x100 m and additional 15 m cores will be combined with trenching. The intellectual merit of the proposed activity is that the results of this work will extend the landmark work of EPICA and other deep ice coring efforts, which give records dating back to 0.8 Ma, and will complement work planned by IPICS to drill a continuous Antarctic ice core extending to 1.5 Ma. The results will help to advance understanding of major climate regimes and transitions that took place between 0-2.5 Ma, including the 40 kyr world and the mid-Pleistocene climate transition. A major long-term scientific goal is to provide a transformative approach to the collection of paleoclimate records by establishing an "International Climate Park" in the Allan Hills BIA that would enable sampling of large quantities of known age ice as old as 2.5 Ma, by any interested American or foreign investigator. The broader impacts resulting from the proposed activity include training students who are well versed in advanced field, laboratory and numerical modeling methods combining geochemistry, glaciology, and paleoclimatology. We will include material relevant to our proposed research in our ongoing efforts in local education and in our outreach efforts for media. The University of Maine already has cyberinfrastructure, using state of the art web-based technology, which can provide a wide community of scientists with fast access to the results of our research. The work will contribute to the broad array of climate change studies that is informing worldwide understanding of natural and anthropogenic forced climate change, and the options for responding. This award has field work in Antarctica.

USAP-1745007_1

None in the Database

Repository	Title (link)	Format(s)	Status
USAP-DC	Allan Hills CMC3 ice core d18Oatm, d15N, dO2/N2, dAr/N2, d40/36Ar, d40/38Ar 2021 & 2022	Excel	exists
USAP-DC	I-165-M GPR Field Report 2019-2020		exists
USAP-DC	Allan Hills 2022-23 Shallow Ice Core Field Report	PDF	exists
USAP-DC	Snapshot record of CO2 and CH4 from the Allan Hills, Antarctica, ranging from 400,000 to 3 million years old		exists
USAP-DC	Heavy noble gases (Ar/Xe/Kr) from ALHIC1901, 1902, and 1903	Open XML Spreadsheet	exists
USAP-DC	CO2 and CH4 from Allan Hills ice cores ALHIC1901, 1902, and 1903	Open XML Spreadsheet	exists
USAP-DC	MOT data (Xe/Kr) from Allan Hills ice cores ALHIC1901, 1902, and 1903	Open XML Spreadsheet	exists
USAP-DC	Allan Hills Stable Water Isotopes	ASCII	exist

1. Shackleton, S., Seltzer, A., Baggenstos, D., & Lisiecki, L. E. (2023). Benthic δ18O records Earth’s energy imbalance. Nature Geoscience. (doi:10.1038/s41561-023-01250-y)
2. Higgins, J.A., Kurbatov, A.V., Spaulding, N.E., Brook, E., Introne, D.S., Chimiak, L.M., Yan, Y., Mayewski, P.A. and Bender, M.L., 2015. Atmospheric composition 1 million years ago from blue ice in the Allan Hills, Antarctica. Proceedings of the National Academy of Sciences, 112(22), pp.6887-6891. (doi:10.1073/pnas.1420232112)