QRC members lead and participate in a wide range of disciplinary and interdisciplinary research projects from the study of past earth climates and glaciations to shifts in the geographic distributions and evolution of vegetation and faunal communities, to the evolution and dispersals of the genus Homo and the increasing scales of human modification of earth environments through the Holocene. QRC provides a venue for meeting and collaborating with scholars across Quaternary disciplines. We are also fortunate to be able to provide seed funding and small grants for member research projects. We are especially happy to support grad student and junior scholar research activities, much of which leads to larger, external funding from agencies like the National Science Foundation.
Constraining ages of glacial deposits recorded in a Victoria Valley permafrost core
Abstract: The past stability of the East Antarctic Ice Sheet (EAIS) remains an important, yet unsettled question. Efforts to address this question focus on EAIS stability during the Pliocene (5.33-2.58 Mya), a period characterized by CO2 levels comparable to today’s levels and global mean temperature comparable to those predicted for the end of the century. While the marine record from the Antarctic Drilling Project (ANDRILL) and recent ice-sheet models suggest a dynamic EAIS during the Pliocene, there is not yet strong corresponding terrestrial evidence of a dynamic Pliocene EAIS. Stratigraphic and geomorphic evidence of glacial deposits from EAIS outlet glaciers in the Antarctic Dry Valleys may provide the much-needed terrestrial record of EAIS stability. Here, a 15-meter ice-cemented permafrost core collected in Victoria Valley is analyzed using cosmogenic nuclides to provide quantitative constraints on the timing of the EAIS glacial history in the Dry Valleys. Based on the presence of oxidized layers from apparent paleosols, the core appears to have recorded four depositional events that are believed to represent different periods of glaciation. Each depositional unit was deposited and exposed to cosmic rays at the surface until subsequently buried during the next glacial event that then shielded the sediment from further cosmic ray exposure. Sediment was subsampled in the core at the upper, middle, and lower limits of each depositional unit and analyzed for 10Be and 26Al, as well as texture, soluble salts, and other parameters. Several possible models of the burial history, accounting for exposure time, burial time, and inherited nuclides, are tested using inverse modeling techniques to provide a timeline for EAIS history in Victoria Valley. Preliminary results of the four units show ages of 30 Ka, 1.05 Ma, 2.4 Ma, and 3.9 Ma, suggesting the earliest expansion of the EAIS coincides with the warmer and wetter conditions during the Pliocene and corroborates the ANDRILL findings.
Constraining past Antarctic Ice Sheet thickness using cosmogenic 14C in bedrock
Abstract: During the last glaciation, a grounded ice sheet filled the Ross Sea of Antarctica, where the Ross Ice Shelf exists today. This ice sheet began to thin around 13 kyr BP, and the transition from grounded to floating ice retreated inland towards its present position. We have mapped and dated glacial deposits alongside Darwin and Hatherton Glaciers, which record this thinning. Our new exposure ages suggest that the ice sheet remained grounded here until <3 kyr BP, which changes our understanding past ice flow in this region. Unfortunately, there was no clear limit of deposition at the mouth of Darwin Glacier, so we were not able to determine the thickness of the ice sheet at this location. We therefore will use cosmogenic 14C in a bedrock elevation transect from the mouth of Darwin Glacier, adjacent to the former Ross Sea Ice Sheet, in order to constrain the ice thickness during the last deglaciation. Due to the short half-life of this isotope, the concentration of 14C in rock reaches saturation within 30 kyr. Burial by ice would shield the rock from cosmic rays, shutting down the production of 14C. Even just a few thousand years of past ice cover will drastically reduce the concentration. Thus, if a given rock is saturated with respect to 14C, it could not have been covered by ice for any considerable amount of time in the last 30 kyr. If a rock contains less than the saturation concentration of 14C, then this suggests it was buried by ice during the last glaciation. Therefore, the respective elevations of the highest unsaturated sample and the lowest saturated sample will constrain the former ice sheet surface. We will use these data along with our chronology from nearby glacial deposits as constraints on a numerical ice-flow model in order to investigate the time at which the ice sheet began to thin at the mouth of Darwin Glacier.
Could the West Antarctic Ice Sheet have Collapsed in the Previous Interglacial Warm Period? A Modeling Assessment based on Stable Isotopes in the Deep Ice from Siple Dome
Abstract: The Quaternary period is characterized by growth and decay of large ice sheets. Because its bed is far below sea level, the West Antarctic Ice Sheet (WAIS) is vulnerable to the Marine Ice-sheet instability. Octopus populations in the Ross and Weddell seas, but now isolated by WAIS, and marine diatoms recovered from beneath the WAIS indicate that the WAIS was not present at some unknown time in the Quaternary. Stable isotopes of water in the bottom 8 meters of the 1-km-deep Siple Dome ice core imply that the basal ice, which dates from Marine Isotope Stage 5e (130-90 ka) or older, originated at a much higher and colder location than Siple Dome. Prof. Richard Alley at Penn State has suggested that the WAIS collapsed to form a floating ice shelf at some time during Marine Isotope Stage 5e, bringing ice from an unknown high inland location such as the Whitmore Mountains, out into the Ross Embayment, where, as floating a few hundred meters thick, it then grounded on a submarine shoal to form the modern Siple Dome. Subsequent flow in Siple Dome has subsequently reduced its thickness to the current 8 meters.
In this project, ESS undergraduate student, Izzati Ahamad Fouzi, will extend her research on this question by exploring a much wider range of proposed scenarios in order to establish limits on the climate and ice-flow histories that are compatible with the ice-core data. She will also prepare a manuscript for publication on the work. The proposed end result of the project will be a manuscript with Ms Ahamad Fouzi as lead author, to be submitted to a peer-reviewed scientific journal such as Quaternary Research, Journal of Glaciology, or The Cryosphere.
Reconstruction of Holocene temperatures from Greenland lake sediment cores using a novel method: Clumped Isotopes
Abstract: This project investigates the Northern Hemisphere arctic temperatures during the Holocene. Previous research on lake sediments from Braya Sø and Limnaea Sø found abrupt, large shifts in the carbon isotopes (δ18O and δ13C) over the past ~8,000 years, thought to be driven by changes in evaporation and precipitation [Anderson and Leng, 2004]. Recent research using alkenones from Braya Sø has shown significant (~2-5˚C) temperature variations in West Greenland during similar time periods [D’Andrea et al., 2011]. Both of these paleothermometers depend on changes in the lakes, through changes either in the δ18O composition or in the biological alkenones in response to fluctuating water temperatures. It remains to be determined how much of the reconstructed temperature changes are directly in response to a temperature shift, rather than hydrologic changes. To address this issue, this project uses clumped isotopes to (1) determine if the temperature of lake carbonate formation corresponds to the alkenone data; (2) determine if the purported temperature excursions during the Holocene reflect actual temperature changes; and (3) correct previously published δ18Owater values for temperature dependent fractionation using the actual lake temperatures determined here. The advantage of using clumped isotope measurement is that they give a direct measurement of lake temperature; the amount of clumping during carbonate formation is dependent solely on the temperature.