Collaborative Research: EAGER: Development of a Method for Paired Potassium/Argon Geochronology and Strontium-Neodymium-Lead Radiogenic Isotope Geochemistry of Dust in Ice Cores

Lead PI: Sidney Rasbury Hemming

Unit Affiliation: Geochemistry, Lamont-Doherty Earth Observatory (LDEO)

August 2020 - July 2022
Antarctica ; Southern Ocean
Project Type: Research

DESCRIPTION: Atmospheric dust and sediment serve as valuable tracers of past Earth and ocean processes because their geochemical compositions reflect their bedrock parent material. Scientists use the compositions of sediments and dust as a "fingerprint", linking materials at downstream sites, such as ice and sediment cores, back to their sources. Through geochemical fingerprinting, scientists have gained insight into the causes and impacts of abrupt climate changes, the stability of ice sheets and their potential contributions to sea level rise, and the mechanisms by which ocean and atmospheric circulation patterns change. This project aims to harness the capabilities of two different techniques used to determine sediment provenance. The approach will allow the team to address critical questions regarding past wind patterns around Antarctica, the roles of different dust sources in supplying nutrients to the Southern Ocean, and the behavior of the West Antarctic Ice Sheet during the last interglacial warm period. In addition, the method has the potential to be applied to extraterrestrial materials such as from the Mars Mission and Moon rocks.

Geochemical tracing of dust and other sediment sources is a powerful approach that aids in reconstructing past atmosphere, ocean, and ice-sheet dynamics. However, in some regions such as the Southern Hemisphere, even multi-variate approaches such as those using strontium, neodymium, and lead isotopes yield ambiguous results due to overlapping source-area compositions. The team has found that lead isotopes add great value in distinguishing sources and that combining these with potassium/argon geochronology provides significant additional constraints on sediment provenance. The added value is due to the relative ease of resetting potassium/argon ages during subsequent geologic events such as crystallization of new minerals during diagenesis, or by heating, with resetting occurring at lower temperatures than other isotopic systems. The team will develop and test the proposed approach using rock and mineral standards and fine-grained sediments, then apply it to ice-core dust samples from deaccessioned ice cores and dust from the Last Glacial Maximum at key sites. Beyond the broader scientific impact of this new approach, the project will provide opportunities for Colby College undergraduates to experience complete immersion in the world of discovery, working both in Dr. Bess Koffman's geochemistry lab at Colby and at the Lamont-Doherty Earth Observatory of Columbia University, where they will engage with a wider cohort of students from around the country and have access to state-of-the-art analytical facilities.