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The Glaciology Program is concerned with the history and dynamics of the antarctic ice sheet; this includes research on near-surface snow and firn, floating glacier ice (ice shelves), glaciers, ice streams and continental and marine ice sheets. These species of ice facilitate studies on ice dynamics, paleoenvironments (deduced from ice cores), numerical modeling, glacial geology, and remote sensing. Some current program objectives include:
• correlating antarctic climatic fluctuations (from ice core analysis) with data from arctic and lower-latitude ice cores;
• integrating the ice record with the terrestrial and marine records;
• investigating the physics of fast glacier flow with emphasis on processes at glacier beds;
• investigating ice-shelf stability; and
• identifying and quantifying the relationship between ice dynamics and climate change.
These topics come together in the multidisciplinary West Antarctic Ice Sheet program (WAIS), a major initiative of the Office of Polar Programs. The WAIS program – by developing an understanding of its history, current state, internal dynamics and its coupling to the current global climate – is hoping to perfect models to predict the ice sheet's future behavior. The Antarctic Glaciology Program also supports much of the land-based glacial geology undertaken by the U.S. Antarctic Program, especially more geologically recent events during the last 3 million years (between the Pliocene and Recent epochs).
Initial examination of the 500,000-year climate record at Mt. Moulton,
Geologists crave opportunities to examine the vertical face of any significant structure, since moving down through the horizontal layers exposes clues to the history of the region. One such opportunity presents itself at Mt. Moulton in West Antarctica, where a summit crater presents 600 meters of exposed ice, in which can be seen intercalated layers of tephra, the solid material (especially ash) that is ejected into the air during a volcanic eruption.
Using the Argon-40/Argon-39 technique, scientists provisionally believe the tephra layers range in age from 15,000 to 480,000 years; they appear to have originated in a nearby volcano, Mt. Berlin. In this 2-year project, we will revisit the Mt. Moulton blue ice site for detailed sampling of the ice section and associated tephra layers, which will be subjected to geochemical analysis to further refine the dates. Examination of the ice should help to determine climatic variations in West Antarctica over the last 500,000 years.
Our data should supplement that to be gleaned from the proposed west antarctic deep ice core, though ours could potentially yield a much longer climatic record. (IO-151-O)
Ice dynamics, the flow law, and vertical strain at Siple Dome.
Iceflow near a divide such as Siple Dome is unique because it is predominantly vertical. As ice is deformed vertically, the vertical strain rate dominates, and must be known in order to calibrate dynamic models of iceflow. This 3-year project – a collaboration between the Universities of Alaska, Washington and UC-San Diego – will measure the vertical strain rate (as a function of depth) at two sites on Siple Dome, Antarctica. We hope to develop a better analysis of the ice core than was possible from recent coring sites in central Greenland.
We plan to use two relatively new, high-resolution systems for measuring the core in hot-water drilled holes. These data, coupled with a determination of the flow-law, will be used to interpret the shapes of radar internal layering as indicators of the accumulation patterns and dynamic history of Siple Dome over the past 10,000 years; an improved model should emerge. This model will then provide a context in which to interpret the ice core drilled at Siple Dome: Both the thicknesses of the annual layers (as indicative of annual accumulation rates) and the borehole temperatures. (IO-164-O)
West Antarctic Ice Sheet surface melting: Recognition controls and
Glaciologists work to discover the history of dynamic processes, such as ice melting and climate. For example, surface melting on polar ice sheets can be said to occur when the temperature increases above some threshold. With data on these parameters, scientists try to link observed patterns to detectable changes in the macro glacial terrain, in hopes of developing models that may predict the future of antarctic ice.
This project focuses on the critical Ross Ice Shelf and Siple Dome regions of West Antarctica. There are currently in use several different procedures to measure melting:
• space-based microwave sensors record the occurrence of liquid water or refrozen ice layers in the near surface;
• Automatic Weather Stations (AWS) record the high temperatures that are linked to development of liquid water; and
• snow-pit and ice-core studies show layers where re-freezing of sufficient liquid water has caused a visibly distinct layer to form.
Each approach is different, and they are presently not well calibrated to one another. We hope to determine how the different measures of melting may be correlated, using a combination of techniques: Snow-pit, ice-core, AWS, remotely sensed data, and experiments on melt generation. By looking at a variety of records of past surface melting events in Antarctica, we hope to develop a context that will pinpoint especially high temperatures. With all of this data, we hope to develop a model for a seasonally resolved paleothermometry, based on a joint approach to measuring ice melt, as well as complementary paleothermometers such as borehole temperature, and isotopes. (IO-168-O)
Stress transmission at ice-stream shear margins.
Shear margins are areas of particular interest to glaciologists, providing evidence of how the slow accumulation of forces over time can create cataclysmic features. Three such ice stream shear margins are the object of this 3-year project aimed at elucidating the transmission of stress. From measurements of the strain rate, we hope to deduce the net force per unit of ice-stream length transmitted between ridge ice and ice-stream ice. We hope to:
• determine how much of the motion of the ice streams is controlled from the inter-stream ridges;
• correlate the magnitude of this lateral drag with the driving stress on the ice stream, and with ice stream width; and
• determine whether lateral drag support can be associated with the margin moving laterally.
For field work, we will use ski-equipped Twin Otters to install two remote camps that will each be occupied for about 6 days. The Support Office for Aerogeophysical Research in Antarctica (SOAR) facility will conduct aerial surveys to determine the ice thickness on the inter-stream ridges, as well as the ice thickness and surface slope on the ice streams. The field measurements will be complemented by repeat images of Ice Stream E adjacent to the field site [taken by the french SPOT satellite], to allow velocities in the ice-stream side of the margin to be determined. Comparing these velocities to those obtained from the strain-grid surveys will provide an estimate of the amount of softening of the ice in the margins. (IO-169-O)
West Antarctic glaciology.
The West Antarctic Ice Sheet (WAIS) shows patterns of iceflow that are not fully understood. One so-called surge hypothesis has been put forth to explain the basis of these patterns; to test it, two critical questions must be answered:
• Are ice streams B, D, and E currently surging?
• What has been the buttressing effect of an enlarging Crary Ice Rise on the flow of ice stream B?
This 3-year project is addressing these questions by collecting data from the air, from space and from the surface. Many of the studies of change in West Antarctica have been based on interpolations and calculations with large uncertainties. We hope to take advantage of global positioning system data to minimize field logistic requirements and develop sharper data. Specifically, we plan to obtain direct measures of (expected) thinning in the upper portion of ice stream D; as well as repeated satellite image measurements at the heads of ice streams B, D, and E. If these reveal inland migration of the onset area, sustained surging may be verified and the hypothesis strengthened.
We will also take new measurements of the thickness, surface elevation, and velocity of the ice, in order to compare the buttressing impact (of Crary Ice Rise) on ice stream B's flow with data collected during the 1950s, 1970s, and 1980s. This part of the study should yield a time series of change in the WAIS over the last half century. (IO-173-O)
High-resolution chronology of millennial-scale lake-level fluctuations
in the Dry Valleys (Antarctica) from uranium-thorium and radiocarbon dating.
Virtually all research science enhances the wisdom and experience of the investigator, but some programs are actually designed around that concept, and targeted at specific groups of scientists. The Professional Opportunities for Women in Research and Engineering (POWRE) program affords new research and educational enhancement opportunities for women scientists.
After a program of study and apprenticeship designed around specific scientific skills, the principal investigator (PI) will undertake a study of the fluctuations (on a millennial scale) of lake levels in the Dry Valleys of Antarctica, looking for basic causes of climate change. The primary activity will be testing the reservoir effect in order to ensure that the chronology of lake-level fluctuations is accurate. With this data in hand, she will make a comparison study of millennial-scale fluctuations in other lakes around the world.
The project was specifically designed to increase the educational and research skills of the principal investigator. She will learn the following new information/skills:
• thermal ionization mass spectrometry (TIMS) uranium/thorium (U/TH) dating with Dr. G. Henderson at Lamont-Doherty Earth Observatory (LDEO) and Oxford University;
• millennial-scale climate change with Drs. W. Broecker and G. Bond, LDEO, and with Drs. D. Oppo and L. Keigwin, Woods Hole Oceanographic Institution;
• antarctic limnology with Dr. C. Hendy, University of Waikato; and
• regional climate modeling with Dr. K. Maasch, University of Maine.
In gathering data from the Dry Valleys, the PI will use TIMS, U/TH and accelerator mass spectrometric (AMS) radiocarbon dating of lacustrine carbonates. Her knowledge of limnology will help not only to assess the lake reservoir effect, but provides a foundation to inquire into the causes 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. (IO-196-O)
SOAR laser: Calibration and first measurement for ice-sheet change
The Support Office for Aerogeophysical Research in Antarctica (SOAR) facility provides equipment and analysis for a number of Antarctic projects and researchers. Thus, its data are ramified through numerous studies, and must be verifiably valid. This 3-year project will evaluate some of SOAR's capability; especially the use of its laser, to generate precise and accurate measurements of the elevation of the antarctic ice sheet, and to track ongoing changes.
Tests will be made in two modes: While the aircraft is parked, as well as during flights over ground-surveyed sites near the aircraft base camp. Once the laser and other equipment has been validated and calibrated, we will begin a limited program to measure changes over time in the surface elevation of glaciologically interesting sites. The goal is to run a "test case" to demonstrate SOAR's ability to accurately and precisely determine – and track change in – surface elevation. Thus "vetted," SOAR will become an asset to all investigators involved in precisely mapping and detecting change in the antarctic ice sheet. (IS-166-O)
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