Subglacial Chemical Weathering under East Antarctica

Indiana University, Bloomington IN

Investigators

Abstract

Nontechnical Description Chemical weathering is the process by which rocks and minerals are turned to clay, oxides, and chemical nutrients. Most of these weathering reactions consume atmospheric gases, such as oxygen and carbon dioxide, and therefore chemical weathering can drive natural, long-term changes in atmosphere chemistry. The nutrients released from rocks by chemical weathering are transported to the oceans and are necessary for the maintenance of life on Earth. The principal aim of this project is to assess how much chemical weathering occurs beneath Antarctica's largest ice sheet. Elsewhere in the world, chemical weathering is assessed by analyzing the outflow of rivers, but such direct measurements of chemical outflow are not possible because nearly all of Antarctica is covered by ice. In Antarctica investigators use samples from the Transantarctic Mountains where the interaction of flowing ice with mountain peaks causes rock and mineral material to emerge from the glacier base. This project will assess the degree to which this emerging mineral material has been chemically weathered compared to the underlying rock and the time scale at which such weathering occurs. Technical Description Preliminary data from a Transantarctic Mountain site strongly suggests that the mineral products of chemical weathering (clays and oxides) are more abundant in the emerging material than in the underlying rocks. However, the chemical alteration of this material could have occurred recently or prior to glaciers forming in Antarctica. To constrain the timeline of weathering and thereby assess modern rates of weathering in Antarctica, this p[project will analyze two rare, radioactive isotopes within the weathered minerals. Because these isotopes are lost through radioactive decay, they act as clocks that can time the formation of the clays and oxides that form during chemical weathering. Minerals that pre-date the ice will have these isotopes clinging to their surface but not in their crystal structure. By first chemically removing the elements on the surface on the clays and oxides and then analyzing the minerals themselves, the project investigators will determine whether the minerals formed recently under the ice or beforehand in an ice-free environment. By calculating how recently these minerals formed and by analyzing the rate at which ice transports them off the continent, they will be able to calculate chemical weathering rates at locations up and down the Transantarctic Mountains. The result will be an estimate the impact of weathering under the East Antarctic ice sheet on the chemistry of the Earth's ocean nutrients. This research will provide valuable training for the next generation of polar scientists. 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.