Developing new magnetic tracers of ice sheet instability and ocean circulation in the northern North Atlantic

Oregon State University, Corvallis OR

Investigators

Abstract

The Greenland Ice Sheet would contribute up to 7 meters of sea-level rise if it were to melt completely. Thus, knowing how the ice sheet has responded to past climates, both warmer and cooler than present, provides a natural laboratory to help understand how and/or when the Greenland Ice Sheet may respond in the future. While the geological record from land provides great insights into ice-sheet advance and retreat, these records are generally restricted to the last retreat of the Greenland Ice Sheet. Marine sediments from around Greenland, on the other hand, provide a less detailed record, but one that can be well-dated through many glacial-interglacial cycles providing information on the Greenland Ice Sheet through a range of climate conditions. This project will use newly developed magnetic grain-size separation measurements that are faster and cheaper than traditional isotopic approaches to determine sediment source locations, in order to infer ice-sheet processes. The project will sample and measure the magnetic properties of sediment cores collected from several locations to control for and help assess changes in the sediment transport around Greenland for the last 150 kyrs providing a record of the last two glacial to interglacial transitions and the subsequent interglaciations, including one that is warmer than present. The objective is to obtain a better understanding of the stability of the Greenland Ice Sheet and the ocean currents that transport materials around it. The project supports an early career postdoc, a graduate student and a summer undergraduate student. Public exhibits and presentations will be developed for the Oregon State University Marine Geology Repository. An educational module and short course materials will be developed on the new magnetic unmixing techniques used in this project. This project explores the spatial consistency of the south Greenland Ice Sheet (sGIS) sediment source. The North Atlantic Deep Western Boundary Current (DWBC) sediment transport system and how fundamental change in sediment delivery associated with glacial/interglacial changes in the DWBC both influence and potentially enrich understanding of sGIS retreat and ocean circulation in the North Atlantic. The project will characterize sediment sources by making particle size specific magnetic measurements of core top sediments from the Greenland and Norwegian seas, Holocene age sediments from the Greenland and Iceland Shelf, and Pleistocene age sediments from the deep ocean off the southern Greenland margin. Work on terrestrial samples from Iceland and Greenland show that magnetic properties vary strongly with source and sediment grain size, and by targeting the silt fraction it will be possible to clearly separate materials from the two locations. Magnetic properties of the silt fraction from the deep Eirik Ridge, a marine sediment drift south of Greenland, will be used to track Greenlandic erosional products during glacial terminations and interglaciations allowing for periods of increased sGIS ablation to be inferred. These magnetic grain-size signatures are consistent with the much more difficult to measure radiogenic isotopes, allowing the easier/cheaper magnetic measurements to more completely constrain the system through larger scale sampling. Characterizing the spatial variability in magnetic properties along the Greenland margin and across the Eirik Ridge will inform on, and control for, changes in transport associated with changes in the DWBC that delivers sediment to these regions. End member data derived previously will establish the interpretive framework needed to quantitatively separate magnetic components, and sedimentary processes, with an aim toward addressing the fundamental question of how process drives magnetic variation.