The proposed work will investigate changes in the compositional variation of glacial tills over time across two concentric sequences of Pleistocene moraines located adjacent to the heads of East Antarctic outlet glaciers in the Transantarctic Mountains (TAM). The chronologic framework for this work will be generated from cosmogenic exposure ages of boulders on prominent morainal ridges. The PIs hypothesize that variations in till composition may indicate a change in ice flow direction or a change in the composition of the original source area, while ages of the moraines provide a long-term terrestrial perspective on ice sheet dynamics. Both results are vital for modeling experiments that aim to reconstruct the East Antarctic Ice Sheet and assess its role in the global climate system and its potential impact on global sea level rise. The variation of till compositions through time also allows for a more accurate interpretation of sediment cores from the Ross Sea and the Southern Ocean. Additionally, till exposures at the head of some East Antarctic outlet glaciers have been shown to contain subglacial material derived from East Antarctic bedrock, providing a window through the ice to view East Antarctica?s inaccessible bedrock. Till samples will be collected from two well-preserved sequences of moraine crests at Mt. Howe (head of Scott Glacier) and Mt. Achernar (between Beardmore and Nimrod Glaciers). Each size fraction in glacial till provides potentially valuable information, and the PIs will measure the petrography of the clast and sand fractions, quantitative X-ray diffraction on the crushed <2mm fraction, elemental abundance of the silt/clay fraction, and U/Pb of detrital zircons in the sand fraction. Data collection will rely on established methods previously used in this region and the PIs will also explore new methods to assess their efficacy. On the same moraines crests sampled for provenance studies, the PIs will sample for cosmogenic surface exposure analyses to provide a chronologic framework at the sites for provenance changes through time.
Broader Impact The proposed research involves graduate and undergraduate training in a diverse array of laboratory methods. Students and PIs will be make presentations to community and campus groups, as well as conduct interviews with local news outlets. The proposed work also establishes a new, potentially long-term, collaboration between scientists at IUPUI and LDEO and brings a new PI (Kaplan) into the field of Antarctic Earth Sciences.
The aim of our project is to study how the East Antarctic Ice Sheet has changed in the past, where it comes through the Transantarctic Mountains. The spine of the mountain range pokes through the ice sheet surface in places, and causes deposits of sediment, such as moraines, to accumulate on the glacier surface. Over time, as the ice surface has gone up and down, it has left series of sediment deposits in places. The intellectual merit of the project stems from the fact that such sediment deposits, which are not common in the interior of Antarctica, offer unique insight and teach us about the present and past behavior of the ice sheet. Over the life of the project, we carried out a twofold approach to study the deposits in the central part of the Transantarctic Mountains. First, our colleagues at the Indiana University-Purdue University Indianapolis focused primarily on the composition and nature of the sediment that has accumulated around the mountains above the present ice sheet surface. Variations in the sediment composition may indicate changes in how the ice sheet flowed or eroded its bed, because of changes in its dynamic. The second approach, primarily carried out by the group at Lamont-Doherty Earth Observatory, has been to determine the ages of the sediment deposits (moraines) that the two groups are collaboratively studying together. The ages of the sediments or moraines provide the temporal framework for when they were deposited on the ice sheet surface in the past, as the thickness changed. In general, the ages provide a long-term perspective on the dynamics of the East Antarctic ice sheet and its relative stability. In particular, a specific goal was to document whether the sediments at two field sites could teach us about ice sheet history prior to the last Ice Age, before about 30,000 years ago. There are several important outcomes of the project. First, we indeed found glacial deposits at least several hundred thousand years old still preserved above the present ice sheet surface, within the central Transantarctic Mountains. At two field sites, our study will provide insight into former ice sheet behavior on relatively long timescales, including both cold glacial-age and warm non-glacial age climates. Second, we are able to provide age ranges for changes in the former East Antarctic ice surface (for example, when it was higher and lower), which was not possible in prior studies, despite decades of research on such deposits. A third important finding is that the interior of the East Antarctic Ice Sheet - which contains the largest volume of ice on Earth - has been relatively stable for hundreds of thousands of years. We find only tens of meters of change over the last half a million years or so, including during warm as well as cold periods. This includes a period when some hypothesize the West Antarctic Ice Sheet collapsed, about 110,000 to 130,000 years ago, when climate was slightly warmer than present. In terms of broader impacts, one of the most important of the project was the establishment and growth of a collaboration between scientists at Indiana University-Purdue University Indianapolis and Lamont-Doherty Earth Observatory, including graduate students. To our knowledge, this study was the first to combine the two different approaches discussed above in the same project, to achieve the same aim; that is, to study the composition and age of the deposits left behind by the former East Antarctic Ice Sheet. The project has now provided several researchers at different stages of their careers, including undergraduates and graduate students (at IUPUI), with new research experience and expertise in working in various aspects of Antarctic science and associated training. The success of the collaboration, including student exchange, will obviously have broader impacts beyond just the life of this award. This includes ongoing and future projects between the groups. In terms of scientific broader impacts, the project's findings and outcomes are relevant, overall, for all disciplines interested in the history of the interior of the East Antarctic Ice Sheet and the geologic archives recorded in the central Transantarctic Mountains. This work also has relevance for researchers who model present and future ice sheet scenarios; these researchers require observations of past configurations of the ice sheet to test the robustness of their models. On a final note, one of the most important scientific broader impacts concerns our conclusion that little change (tens of meters) appears to have occurred in the interior of the East Antarctic Ice Sheet for hundreds of thousands of years and it has been relatively stable. Such relative stability, of the bulk of ice on the Antarctic continent, is of relevance to researchers interested in how the ice sheet may have changed over time and it possible effect on sea level.
