Subglacial Chemical Weathering under East Antarctica (NSF Grant)
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. We will accomplish this by comparing the relative abundance of minerals formed by chemical weathering in East Antarctic sediments to their abundance in the underlying rocks. We will measure meteoric 10Be and U series isotopes that date the age of mineral formation and allow us determine which minerals formed in the subglacial environment and which may pre-date glaciation. By performing these measurements on samples from sites that span the Trans-antarctic Mountains, we will assess the physical and spatial controls on East Antarctic chemical weathering rates.
East Antarctic Glacial Landscape Evolution (EAGLE): A Study using Combined Thermochronology, Geochronology and Provenance Analysis (NSF Grant)
The main objective of this project is to reconstruct a chronology of East Antarctic subglacial landscape evolution to understand the tectonic and climatic forcing behind landscape modification, and how it has influenced past ice sheet inception and dynamics. Our approach focuses on acquiring a record of the cooling and erosion history contained in East Antarctic-derived detrital mineral grains and clasts in offshore sediments deposited both before and after the onset of Antarctic glaciation. Samples will be taken from existing drill core and marine sediment core material from offshore Wilkes Land (100°E-160°E) and the Ross Sea. Multiple geo- and thermo-chronometers will be employed to reconstruct source region cooling history including U-Pb, fission-track, and (U-Th)/He dating of zircon and apatite, and 40Ar/39Ar dating of hornblende, mica, and feldspar. This offshore record will be augmented and tested by applying the same methods to onshore bedrock samples in the Transantarctic Mountains obtained from the US Polar Rock Repository and through fieldwork. The onshore work will additionally address the debated incision history of the large glacial troughs that cut the range, now occupied by glaciers draining the East Antarctic Ice Sheet. This includes collection of samples from several age-elevation transects, apatite 4He/3He thermochronometry, and Pecube thermo-kinematic modeling. Acquiring an extensive geo- and thermo-chronologic database will also provide valuable new information on the poorly known ice-hidden geology and tectonics of subglacial East Antarctica that has implications for improving supercontinent reconstructions and understanding continental break-up.
Evaluating a new tool to understand Indiana’s glacial history and patterns of contamination in groundwater
The primary goal of this project is to develop a classification system for determining the origins of till and associated, potential groundwater contaminants in Indiana to the Saginaw Lobe, Huron-Erie Lobe, or the Lake Michigan Lobe of the Laurentide Ice Sheet. We will use three data sets of zircon ages: distil detrital zircons, proximal detrital zircons, and in situ zircons. Till samples from the Mississinewa moraine of the Huron-Erie Lobe, the Valparaiso moraine of the Lake Michigan Lobe, and the Kalamazoo moraine of the Saginaw Lobe will be sieved to gather distil detrital zircons. Samples of sedimentary bedrock from Michigan will be crushed and sieved to gather proximal detrital zircons. Data from previous studies of zircon attributed to the Grenville and Superior Provinces of Canada will be the source of in situ zircons ages. We will determine the ages of both sets of detrital zircons by using U-Pb dating at the Arizona LaserChron Center. The distil detrital, proximal detrital, and in situ zircon ages will be correlated to one another in order to determine likely provenance and travel paths of both sets of detrital zircons. Once we have sufficient data points to credibly define our fingerprints for the three lobes, a model will be developed. The model will be based on a linear discriminate analysis in order to classify the origin of detrital zircons that do not have a clear origin at the time of sampling. This classification system will be usable in future studies to determine the origins and travel paths of contaminants that may have travelled with glacial till and infiltrated groundwater.
Multidisciplinary Analysis of Antarctic Blue Ice Moraine Formation and their Potential as Climate Archives over Multiple Glacial Cycles (NSF Grant)
Direct observations of ice sheet history from the margins of Antarctica’s polar plateau are essential for testing numerical ice sheet models, and the laterally extensive, blue-ice moraines of the Mt. Achernar Moraine complex in the central Transantarctic Mountains contain a unique and nearly untapped direct, quasi-continuous record of ice sheet change over multiple glacial cycles. The project objectives include improved understanding of processes and rates of blue ice moraine formation, as well as identifying the topographic, glaciological, and climatic controls on their evolution. Data to be collected with fieldwork in Antarctica include: imaging of internal ice structure with ground-penetrating radar, measurement of ice flow velocity and direction with a global positioning system (GPS) array, analysis of debris concentration and composition in glacier ice, state-of-the-art cosmogenic multi-nuclide analyses to determine exposure ages of moraine debris, mapping of trimlines and provenance analysis. Numerical model simulations, constrained by field data, will be used to evaluate the factors influencing changes in glacier flow that potentially impact the accumulation of the moraine debris. All together, the new data and modeling efforts will improve conceptual models of blue ice moraine formation, and thereby make them a more valuable proxy for developing a better understanding of the history of the ice sheet.
Deglacial Ice Dynamics in the Weddell Sea Embayment using Sediment Provenance (NSF Grant)
Drawdown of the Antarctic ice sheets under future warming is a critical topic for climate change and sea level rise. It is not well known which ice streams are most vulnerable, nor how fast and how far they retreat, but insight can be gained by reconstructing ice drawdowns in the Weddell Sea embayment under past warming conditions. The project will compare the patterns of the three most recent deglaciations, examine possible contributions to Meltwater Pulse 1A, and test the relative stability of ice streams draining from East and West Antarctica. Much of the West Antarctic ice may have melted during the Eemian (previous interglacial ~120,000 yrs ago), so it is an apt analogue for predicting future ice drawdown over the coming centuries. Our objectives are to: (1) define the provenance source areas by characterizing Ar, U-Pb, and Nd isotopic signatures, and heavy mineral and Fe-Ti oxide compositions of detritus from each major ice stream entering the Weddell Sea, using onshore tills transported by ice streams and existing shelf sediment cores from along the front of the Ronne and Filchner Ice Shelves and (2) document the stratigraphic changes in provenance of iceberg-rafted debris (IRD) and glacially-eroded material in two deep water sediment cores in the NW Weddell Sea. The provenance information identifies which groups of ice streams were actively eroding and exporting detritus to the ocean (via iceberg rafting and bottom currents), and the stratigraphy of the cores shows the relative sequence of ice stream activity through time.