Collaborative Research: Late Quaternary History of Reedy Glacier

The stability of the marine West Antarctic Ice Sheet (WAIS) remains an important, unresolved problem for predicting future sea level change. Recent studies indicate that the mass balance of the ice sheet today may be negative or positive. The apparent differences may stem in part from short-term fluctuations in flow. By comparison, geologic observations provide evidence of behavior over much longer time scales. Recent work involving glacial-geologic mapping, dating and ice-penetrating radar surveys suggests that deglaciation of both the Ross Sea Embayment and coastal Marie Byrd Land continued into the late Holocene, and leaves open the possibility of ongoing deglaciation and grounding-line retreat. However, previous work in the Ross Sea Embayment was based on data from just three locations that are all far to the north of the present grounding line. Additional data from farther south in the Ross Sea Embayment are needed to investigate whether recession has ended, or if the rate and pattern of deglaciation inferred from our previous study still apply to the present grounding line. This award provides support to reconstruct the evolution of Reedy Glacier, in the southern Transantarctic Mountains, since the Last Glacial Maximum (LGM). Because Reedy Glacier emerges from the mountains above the grounding line, its surface slope and elevation should record changes in thickness of grounded ice in the Ross Sea up to the present day. The deglaciation chronology of Reedy Glacier therefore can indicate whether Holocene retreat of the WAIS ended thousands of years ago, or is still continuing at present. This integrated glaciologic, glacial-geologic, and cosmogenic-isotope exposure- dating project will reconstruct past levels of Reedy Glacier. Over two field seasons, moraines will be mapped, dated and correlated at sites along the length of the glacier. Radar and GPS measurements will be made to supplement existing ice thickness and velocity data, which are needed as input for a model of glacier dynamics. The model will be used to relate geologic measurements to the grounding-line position downstream. Ultimately, the mapping, dating and ice-modeling components of the study will be integrated into a reconstruction that defines changes in ice thickness in the southern Ross Sea since the LGM, and relates these changes to the history of grounding-line retreat. This work directly addresses key goals of the West Antarctic Ice Sheet Initiative, which are to understand the dynamics, recent history and possible future behavior of the West Antarctic Ice Sheet

Deglacial Chronology of the Northern Scott Coast from Relative Sea-Level Curves

This award provides support for three years for a project to develop a radiocarbon chronology for recession of grounded ice from the northwestern Ross Sea Embayment (northern Scott Coast) since the Last Glacial Maximum (LGM). A key unresolved question in Antarctic glaciology concerns the stability of the marine-based West Antarctic ice sheet (WAIS). One way to gain insight into present and future stability is to examine its past behavior. In particular, the timing of deglaciation from the LGM position on the continental shelf is critical for isolating the mechanisms (sea level, climate, ocean temperature, and internal dynamics) that control WAIS dynamics. The northern Scott Coast was likely the first area to become free of grounded ice and hence is critical for isolating triggering mechanisms. Initial retreat from the Ross Sea Embayment was thought to have begun as early as 17,000 years ago; corresponding to the rise in sea level see in the Barbados coral record. In contrast, recent glacial geologic mapping and relative sea-level work from the southern Scott Coast suggests that deglaciation of the Ross Sea Embayment was a Holocene event, with southward grounding-line migration past Ross Island shortly before 6500 14C yr. B.P. This chronology suggests that rising sea level could not have driven grounding-line retreat to the Siple Coast, because deglacial sea-level rise essentially was accomplished by mid-Holocene. One deficiency in the southern Scott Coast work is that it cannot differentiate among the possible triggering mechanisms that initiated retreat because it is 450 km from the LGM grounding-line position. In this project, relative sea level (RSL) curves will be constructed on a transect along the northern Scott Coast from accelerator mass spectrometer 14C dates of seal skin and shells within raised beaches. These curves will provide information concerning the timing of the uploading of grounded ice from the northwestern Ross Sea Embayment. This study should help to evaluate those factors which could have triggered deglaciation and hence controlled the extent of the West Antarctic ice sheet (WAIS)

Collaborative Research: Constraints on the last Ross Ice Sheet from Glacial Deposits in the Southern Transantarctic Mountains

This award supports a project to study the former thickness and retreat history of Shackleton and Beardmore Glaciers which flow through the Transantarctic Mountains (TAMs) into the southern Ross Sea. Lateral moraine deposits along the lower reaches of these major outlet glaciers will be mapped and dated and the results will help to date the LGM and constrain the thickness of ice where it left the Transantarctic Mountains and flowed into the Ross Sea. The intellectual merit of the project is that the results will allow scientists to distinguish between models of ice retreat, which have important implications for former ice configuration and dynamics, and to constrain the contribution from Ross Sea deglaciation to global sea level through the late Holocene. In addition, this will make a significant contribution to a better understanding of the magnitude and timing of postglacial sea-level change and the potential contribution of Antarctica to sea-level rise in future. The broader impacts of the project are that the work will help quantify changes in grounded ice volume since the LGM, improve understanding of the ice dynamics responsible, and examine their implications for future sea level change. The project will train future scientists through participation of two graduate students and undergraduates who will develop self-contained research projects. As in previous Antarctic projects, there will be interaction with K-12 students through classroom visits, web-based expedition journals, letters from the field, and discussions with teachers and will allow the project to be shared with a wide audience. This award has field work in Antarctica

Collaborative Research: Sensitivity of Local Glaciers in Central East Greenland to Holocene Climate Change

This award will support an investigation of Holocene glacier fluctuations in the Scoresby Sund region of central East Greenland (~70-72¿N, 22-28¿W) along a transect from a coastal maritime setting to the continental conditions adjacent to the Greenland Ice Sheet. The \u27Intellectual Merit\u27 of the proposed study lies in the potential to affirm, or otherwise, the widely-held view that the scale of glacier and ice sheet change being observed today in Greenland is not unique in the Holocene. The current recession of glaciers in the Scoresby Sund region is exposing sub-fossil vegetation that grew at times when glaciers were smaller than at present. These emerging records yield a rare opportunity to examine both the biota of these warm times and, more critically, the response of the glaciers to temperatures as high as, or higher than, at present. Development of a chronology for a network of sites in the Scoresby Sund region, including a site adjacent to the Renland ice core, across an environmental gradient can provide insights into recent patterns of ice sheet distribution. However, to place these in context requires a longer temporal framework. Thus, two additional objectives emerge. First, compare late-Holocene glacier fluctuations in Greenland with glacier fluctuations in other mid-to-high Northern Hemisphere locations. This will assess whether glaciers in Greenland are more or less sensitive than their counterparts in other high-latitude locations. Second, document a continuous pattern of glacier fluctuations in Greenland during Holocene time. When contrasted with paleoclimate indicators, such as the GRIP borehole paleotemperature record, how Scoresby Sund glaciers responded to warmer-than-present times, such as the so-called Holocene Climatic Optimum (~5000-9000 years ago), can be assessed. The proposed study has numerous \u27Broader Impacts\u27. It will contribute to the educational development of graduate and undergraduate students at Dartmouth College, the University of Maine, and the University of Cincinnati, and tie in with the IGERT program at Dartmouth College. The PIs will also visit elementary schools and present public lectures on climate change. The results of the study will be added to an interactive, Web-based learning system and stand-alone kiosk deployed at Acadia National Park

AMS Radiocarbon Chronology of Glacier Fluctuations in the South Shetland Islands During the Last Glacial/Interglacial Hemicycle:Implications for Global Climate Change

This award supports a two year program to produce a new reconstruction of ice extent, elevation and thickness at the Last Glacial Maximum (LGM) for the South Shetland Islands in the Antarctic Peninsula. One field season on Livingston Island will involve mapping the areal extent and geomorphology of glacial drift and determining the elevation and distribution of trimlines. In addition, ice flow direction will be determined by mapping and measuring the elevation of erosional features and the position of erratic boulders. One of the main goals of this work will be to demonstrate whether or not organic material suitable for radiocarbon dating exists in the South Shetland Islands. If so, the age of the deposits will be determined by measuring the carbon-14 age of plant, algal, and fungal remains preserved at the base of the deposits, as well as incorporated marine shells, seal skin and other organic material that may be found in raised beach deposits. Another goal will be to concentrate on the development of relative sea-level curves from 2-3 key areas to show whether or not construction of such curves for the South Shetland Islands is possible. The new reconstruction of ice extent, elevation and thickness at the Last Glacial Maximum for the South Shetland Islands which will be produced by this work will be useful in studies of ocean circulation and ice dynamics in the vicinity of the Drake Passage. It will also contribute to the production of a deglacial chronology which will afford important clues about the mechanisms controlling ice retreat in this region of the southern hemisphere

POWRE: High-Resolution Chronology of Millennial-Scale Lake-Level Fluctuations in the Dry Valleys (Antarctica) From Uranium-Thorium and Radiocarbon Dating

The Professional Opportunities for Women in Research and Engineering (POWRE) program affords new research and educational enhancement opportunities for women scientists. This project, which addresses the fundamental problem of the cause of millennial-scale climate change, contains components specifically designed to increase the educational and research skills of the principal investigator. She will learn the following new information/skills: 1) thermal ionization mass spectrometry (TIMS) uranium/thorium (U/TH) dating with Dr. G. Henderson at Lamont-Doherty Earth Observatory (LDEO) and Oxford University, 2) millennial-scale climate change with Drs. W. Broecker and G. Bond, LDEO, and with Drs. D. Oppo and L. Keigwin, Woods Hole Oceanographic Institution, 3) Antarctic limnology with Dr. C. Hendy, University of Waikato, and 4) regional climate modeling with Dr. K. Maasch, University of Maine. She will then apply her new knowledge and skills to a study of millennial-scale fluctuations of lake levels in the Dry Valleys of Antarctica. The investigator will use TIMS, U/TH and accelerator mass spectrometric (AMS) radiocarbon dating of lacustrine carbonates to test the reservoir effect in order to ensure that the chronology of lake-level fluctuations in accurate. She will then use her knowledge of millennial-scale fluctuations to determine if the lake variations are similar to those seen elsewhere in the world. Knowledge of limnology will help not only to assess the lake reservoir effect, but also to begin to determine the cause of large-scale changes in lake level. Likewise, regional climate modeling will allow her to gain insight into the energy balance and wind patterns of the Dry Valleys region during the last glacial maximum. These new skills will benefit the P.I., not only in this particular project relating to Antarctic lakes, but also in her future Antarctic and Southern Hemisphere research in New Zealand and Patagonia

Collaborative Research: Timing and Structure of the Last Glacial Maximum and Termination in Southern Peru: Implications for the Role of the Tropics in Climate Change

The role of the tropics in climate change has important implications for understanding both orbital-scale and abrupt climate variations. Yet our ability to assess tropical behavior during major climate events, such as the last glacial maximum (LGM), is limited by poor spatial coverage and insufficient control on sample ages. This project will address this problem by developing well-dated records of glacial fluctuations from the LGM through the termination and late-glacial period at Nevados Coropuna and Allinccapac in southern Peru and use these data in numerical simulations of glacier mass balance and local climate. These sites allow an examination of glacier variations, as well as coeval snowline changes, along a transect from the arid (Coropuna) to the humid (Allinccapac) Andes and thus document how major climate events may have been expressed in areas with distinctly different environments. This work consists of detailed mapping of moraines; precise surface-exposure age dating (3He and 10Be) of carefully selected boulders from moraine crests and drift edges; basal 14C ages of bogs interspersed among moraines; calculation of former snowline depression; and modeling of the relationship between glacier mass-balance changes and climate. The work will be an important step towards understanding tropical behavior and will finally allow a thorough testing of the Milankovitch hypothesis of ice ages in the tropics.Broader Impacts: This research educates and trains students, a postdoc, and a recent female Ph.D. There is a lecture series on local geology and global climate change given to eco-tourism students at the University of Arequipa, as well as lectures to the Lima archaeology department. K-12 students benefit through a long-standing associations with classrooms in rural, commonly economically disadvantaged Maine. The project maintains a website and is exploring a learning module. In addition, the research is part of a joint initiative to understand land use and settlement patterns of the first Americans in the Peruvian highlands

Collaborative Research: Grounding-line Retreat in the Southern Ross Sea - Constraints from Scott Glacier

This award supports a project to investigate late Pleistocene and Holocene changes in Scott Glacier, a key outlet glacier that flows directly into the Ross Sea just west of the present-day West Antarctic Ice Sheet (WAIS) grounding line. The overarching goals are to understand changes in WAIS configuration in the Ross Sea sector at and since the last glacial maximum (LGM) and to determine whether Holocene retreat observed in the Ross Embayment has ended or if it is still ongoing. To address these goals, moraine and drift sequences associated with Scott Glacier will be mapped and dated and ice thickness, surface velocity and surface mass balance will be measured to constrain an ice-flow model of the glacier. This model will be used to help interpret the dated geologic sequences. The intellectual merit of the project relates to gaining a better understanding of the West Antarctic Ice Sheet and how changing activity of fast-flowing outlet glaciers and ice streams exerts strong control on the mass balance of the ice sheet. Previous work suggests that grounding-line retreat in the Ross Sea continued into the late Holocene and left open the possibility of ongoing deglaciation as part of a long-term trend. Results from Reedy Glacier, an outlet glacier just behind the grounding line, suggest that retreat may have slowed substantially over the past 2000 years and perhaps even stopped. By coupling the work on Scott Glacier with recent data from Reedy Glacier, the grounding-line position will be bracketed and it should be possible to establish whether the retreat has truly ended or if it is ongoing. The broader impacts of the work relate to the societal relevance of an improved understanding of the West Antarctic ice sheet to establish how it will respond to current and possible future environmental changes. The work addresses this key goal of the West Antarctic Ice Sheet Initiative, as well as the International Polar Year focus on ice sheet history and dynamics. The work will develop future scientists through the education and training of one undergraduate and two Ph.D. students, interaction with K-12 students through classroom visits, web-based \u27expedition\u27 journals, letters from the field, and discussions with teachers. Results from this project will be posted with previous exposure dating results from Antarctica, on the University of Washington Cosmogenic Nuclide Lab website, which also provides information about chemical procedures and calculation methods to other scientists working with cosmogenic nuclides

Collaborative Research: Abandoned Elephant Seal Colonies in Antarctica: Integration of Genetic, Isotopic, and Geologic Approaches toward Understanding Holocene Environmental Change

During previous NSF-sponsored research, the PI\u27s discovered that southern elephant seal colonies once existed along the Victoria Land coast (VLC) of Antarctica, a region where they are no longer observed. Molted seal skin and hair occur along 300 km of coastline, more than 1000 km from any extant colony. The last record of a seal at a former colony site is at ~A.D. 1600. Because abandonment occurred prior to subantarctic sealing, disappearance of the VLC colony probably was due to environmental factors, possibly cooling and encroachment of land-fast, perennial sea ice that made access to haul-out sites difficult. The record of seal inhabitation along the VLC, therefore, has potential as a proxy for climate change. Elephant seals are a predominantly subantarctic species with circumpolar distribution. Genetic studies have revealed significant differentiation among populations, particularly with regard to that at Macquarie I., which is the extant population nearest to the abandoned VLC colony. Not only is the Macquarie population unique genetically, but it is has undergone unexplained decline of 2%/yr over the last 50 years3. In a pilot study, genetic analyses showed a close relationship between the VLC seals and those at Macquarie I. An understanding of the relationship between the two populations, as well as of the environmental pressures that led to the demise of the VLC colonies, will provide a better understanding of present-day population genetic structure, the effect of environmental change on seal populations, and possibly the reasons underlying the modern decline at Macquarie Island.This project addresses several key research problems: (1) Why did elephant seals colonize and then abandon the VLC? (2) What does the elephant seal record reveal about Holocene climate change and sea-ice conditions? (3) What were the foraging strategies of the seals and did these strategies change over time as climate varied? (4) How does the genetic structure of the VLC seals relate to extant populations? (5) How did genetic diversity change over time and with colony decline? (6) Using ancient samples to estimate mtDNA mutation rates, what can be learned about VLC population dynamics over time? (7) What was the ecological relationship between elephant seals and Adelie penguins that occupied the same sites, but apparently at different times? The proposed work includes the professional training of young researchers and incorporation of data into graduate and undergraduate courses