Recovery and science coordination of an ice core at Siple Dome, Antarctica. Kendrick Taylor, Desert Research Institute. Our project, which will recover a 1,000-meter ice core from Siple Dome, Antarctica, and coordinate a science management office for the scientific program, is part of the West Antarctic Ice Sheet (WAIS) program, which seeks to understand the current behavior of the west antarctic ice sheet and to decipher its past climate history. Siple Dome is located between ice streams C and D and is well situated to investigate coastal climate conditions and the dynamics of the Siple Coast ice streams, which drain the west antarctic ice sheet. The annual accumulation at the site is 7 to 11 centimeters of ice per year, and it is anticipated that annual layers will be identifiable to an age of at least 6,000 years. The length of the usable climate record will extend to at least 80,000 years.

We provide the background for the Siple Dome drilling program, develop the opportunity for individual scientists to work on the ice core, and establish a science coordination office to coordinate the activities of the various organizations involved in the project, including the National Science Foundation (NSF), the Polar Ice Coring Office (PICO), Antarctic Support Associates (ASA), and the National Ice Core Laboratory (NICL). (II-152-O)

Near-surface processes affecting gas exchange: West antarctic ice sheet. Mary Albert, Cold Regions Research and Engineering Laboratory. We will examine the physical processes that affect how heat, vapor, and chemical species in air are incorporated into snow and polar firn. The processes include advection, diffusion, and the effects of solar radiation penetration into the snow. An understanding of these processes is important because they control the rate at which reactive and nonreactive chemical species in the atmosphere become incorporated into the snow, firn, and polar ice and, thus, will affect interpretation of polar ice-core data. Currently, the interpretation of polar ice-core data assumes that diffusion controls the rate at which chemical species are incorporated into firn. We will determine whether ventilation, or advection of the species by air movement in the firn, and radiation penetration processes have a significant effect.

Field studies at the two west antarctic ice sheet deep-drilling sites will be conducted to determine the spatial and temporal extent for key parameters and boundary conditions needed to model the advection, conduction, and radiation transmission/absorption processes. An existing multidimensional numerical model is being expanded to simulate the processes and to serve as the basis for ongoing and future work in transport and distribution of reactive chemical species. (II-155-O)

Physical and structural properties of the Siple Dome Core. Anthony Gow, Cold Regions Research and Engineering Laboratory. We will investigate the visual stratigraphy, index physical properties, relaxation characteristics, and crystalline structure of ice cores from Siple Dome, West Antarctica. Our investigation will include time-sensitive measurements that must be initiated at the drill site on freshly drilled cores. This need will be especially pressing for cores from the brittle ice zone, which is expected to constitute a significant fraction of the ice core. The brittle zone includes ice in which relaxation, resulting from the release of confining pressure, is maximized and leads to significant changes in the mechanical condition of the core that must be considered in relation to the processing and analysis of ice samples for entrapped gas and chemical studies. This relaxation will be monitored via precision density measurements made initially at the drill site and repeated at intervals back in the United States.

Other studies will include measurement of the annual layering in the core to as great a depth as visual stratigraphy can be deciphered, crystal size measurements as a function of depth and age, c-axis fabric studies, and analysis of the physical properties of any debris-bearing basal ice and its relationship to the underlying bedrock. Only through careful documentation and analysis of these key properties can we hope to assess accurately the dynamic state of the ice and the age-depth relationships essential to deciphering the paleoclimate record at this location. (II-165-O)

The evolution of a polar ice sheet in East Antarctica. George Denton, University of Maine at Orono. We hope to determine the sequence and chronology of events that led to the development of the antarctic ice sheet. A continental-scale ice sheet probably first developed in East Antarctica close to the Eocene-Oligocene boundary under temperate climatic conditions. We hope to learn, from landscape analysis (with a numerical chronology), when (and why) these early temperate conditions gave way to a polar environment in Antarctica.

From previous fieldwork and recent photographic analysis, an extensive relict landscape (older than 17 million years) with landforms and erosional features characteristic of temperate glaciation has been delineated. This relict landscape has been called the Sessrumnir erosion surface, and it extends over 3 degrees of latitude and covers almost 10,000 square kilometers in three fault blocks of the Transantarctic Mountains (Convoy, Dry Valleys, and Royal Society). From this relict land surface, we will collect data that record Middle and Early Miocene glacial history and paleoclimate. The results should allow an identification of the transition from temperate to polar conditions. Our work will involve landscape analysis, stratigraphy of glacial deposits, and argon-40/argon-39 dating of volcanic ashfalls. The rates at which erosion is exposing the rock strata (denudation) will come from fission-track analyses and from exposure-age analyses of bedrock surfaces and erratic boulders. The overall results will elucidate the origin and stability of the polar antarctic cryosphere. (IO-156-O)

Basal conditions of ice stream D and related borehole studies of antarctic ice stream mechanics. Barclay Kamb, California Institute of Technology. To obtain observational evidence of the cause of rapid flow of the great ice streams in the west antarctic ice sheet, we have drilled a number of boreholes through ice stream B and C for measurement of the physical conditions and sampling of materials at the base of the ice, where lubrication of the rapid flow is thought to take place. In the 1998–1999 season, the scope of our study will be widened to include ice stream D, situated some 100 kilometers north of C. Several boreholes will be drilled by the hot-water drilling method to measure the basal water pressure, basal water transport, basal melt rate, basal sliding velocity, deformation, and sedimentology including fossil content of subglacial till if present, basal shear strain rate in the ice, and ice temperature profile. Our objective is to find out if the physical conditions and materials observable by borehole geophysics at the base of ice stream D are consistent with those found in ice stream B and point to a common basal mechanism of ice streaming. We will obtain hot-water drilled ice cores to reveal the internal structure of the ice stream for evaluation of the basal shear stress and rock debris content of the ice and for comparison with B and C. (IO-157-O)

Digital imaging for ice core analysis. Joan J. Fitzpatrick, U.S. Geological Survey, National Ice Core Laboratory. Over 2 years we will develop the technology and methodology for digitizing photographs and analyzing thin sections from ice cores. Besides applying digital technology to whole-core stratigraphy, we will investigate the use of digital photography, image enhancement and image processing. The thin section analysis will be piloted with samples already in hand from the Taylor Dome ice core. During the 1998-1999 austral summer, we will identify visual characteristics of ice from the West Antarctic Ice Sheet near Siple Dome. As the deep core is recovered it will be cut, sectioned, photographed, and analyzed. The original digital images, along with the original annotated data files, will be distributed to Siple Dome principal investigators to use in interpreting their own data. All software and hardware acquired for this project will become part of the permanent equipment inventory at the U.S. National Ice Core Laboratory and will be available for use by clients at the facility. (II-160-O)

Internal stratigraphy and basal conditions at the margins of active ice streams of the Siple Coast, Antarctica. Charles F. Raymond, University of Washington. To examine the geometry of the internal layering and the presence or absence of thawed zones outside the margins of active ice streams B and E and across the flow band feeding ice stream D, we will use surface-based radio-echo sounding.

Melting in the marginal shear zone and/or on the bed outside an ice stream relates to the amount of support of the ice stream from the sides compared to the bed and the conditions that limit expansion of its width. Radar observations will be extended over the crest of adjacent inter-ice-stream ridges (B/C and D/E) and areas next to the flow band in the onset of D. The purpose is to examine internal layering indicative of the histories of these areas adjacent to ice streams and to determine whether, in the past, ice streams have expanded into these presently stable areas. These goals concerning the physical controls and history of ice-stream width relate to how the discharge of ice streams has changed in the past and could change in the future to affect sea level. (IO-163-O)

Ice dynamics, the flow law, and vertical strain at Siple Dome. William Harrison, University of Alaska Fairbanks. Our 3-year project will measure the vertical strain rate as a function of depth at two sites on Siple Dome, Antarctica. Iceflow near a divide such as Siple Dome is unique because it is predominantly vertical. As a consequence, the component of ice deformation in the vertical direction, the vertical strain rate, is dominant. Its measurement is, therefore, important for the calibration of dynamic models of iceflow. Two different, relatively new, high-resolution systems for its measurement in hot-water drilled holes will be employed. The iceflow model resulting from the measurements and flow-law determination will be used to interpret the shapes of radar internal layering in terms of the dynamic history and accumulation patterns of Siple Dome over the past 10,000 years. The resulting improved model will also be applied to the interpretation of the thicknesses of the annual layers (to produce annual accumulation rates) and borehole temperatures from the ice core drilled at Siple Dome. The results should permit an improved analysis of the ice core, relative to what was possible at recent coring sites in central Greenland. This is a collaborative project between the University of Alaska, the University of California at San Diego, and the University of Washington. (IO-164-O)

Stress transmission at ice-stream shear margins. Ian Whillans, Ohio State University. Our 3-year project will study stress transmission at three ice-stream shear margins. The objectives are

• to determine how much of the motion of the ice streams is controlled from the interstream ridges,
• to compare the magnitude of this lateral drag with the driving stress on the ice stream and with ice-stream width, and
• to determine whether lateral drag support is associated with lateral migration of the margin.

The net force per unit ice-stream length transmitted between ridge ice and ice-stream ice will be deduced from measurements of strain rate.

Fieldwork will entail Twin Otter installation of remote camps that will each be occupied for about 12 days during the first season and about 6 days during the second. The Support Office for Aerogeophysical Research in Antarctica (SOAR) facility will conduct aerial surveys to determine ice thickness on the interstream ridges, as well as the ice thickness and surface slope on the ice streams. The field measurements will be complemented by repeat SPOT imagery of ice stream E adjacent to the field site, 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 V. Robert Bindschadler, National Aeronautic and Space Administration. Our 3-year project is designed to answer two questions of critical importance to understanding the iceflow of the west antarctic ice sheet:

• Are the Ross 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?

Both questions will be answered based on a combination of data collected on the surface, from the air, and from space. Although many past indications of change in West Antarctica have been based on interpolations and calculations with large uncertainties, these measurements will be direct, making use of rapid and accurate global positioning system data to minimize field logistic requirements. Direct measurement of expected thinning in the upper portion of ice stream D and repeated satellite image measurements at the heads of ice streams B, D, and E to detect the inland migration of the onset area (as is required by sustained surging) will enable a test of a surge hypothesis developed by Bindschadler. The buttressing impact of Crary Ice Rise on ice stream B's flow will be studied by comparing new measurements of ice thickness, surface elevation, and velocity with data collected during the 1950s, 1970s, and 1980s, thus providing a multidecadal time series of change. (IO-173-O)

Late Pleistocene inland west antarctic ice sheet elevations at Mount Takahe. William C. McIntosh, Thomas I. Wilch, and Nelia W. Dunbar, New Mexico Institute of Mining and Technology. Our objective is to establish a detailed record of volcanism at Mount Takahe volcano in Marie Byrd Land and provide absolute age and elevation data on inland paleoice levels on the west antarctic ice sheet during the most recent glacial cycle.

Previous work at Mount Takahe documented volcanic deposits located on the lower flanks that were erupted beneath, at, or above the level of the west antarctic ice sheet. These deposits have been dated to between 104,000 and 7,000 years before present and suggest that the inland west antarctic ice sheet was much higher during the last glacial cycle than it is today.

The inland paleoice level can be used to test conflicting hypotheses about the configuration of the west antarctic ice sheet in the late Wisconsin and the role of ice-sheet retreat in global sea-level rise. Well-constrained limits on inland paleoice levels during the past 100,000 years can be compared with global records of climate change to assess the relationship between the west antarctic ice sheet and the climate system. Finally, precisely dated paleoice levels can be used as "hard" input data for numerical models of ice-sheet dynamics. (IO-277-O)

SOAR laser: Calibration and first measurement for ice-sheet change detection. Ian Whillans, Ohio State University. During a 3-year study, we will make precise and accurate measurements of the elevation of the antarctic ice sheet to detect ongoing changes in the surface of the ice sheet. The location and pattern of change discovered may be used to deduce the causes of the changes. Suitable equipment for these measurements are part of the Support Office for Aerogeophysical Research in Antarctica (SOAR) facility. We will evaluate the quality and calibrate the measurements to be made by SOAR. Tests will be made both while the aircraft is parked and during flights over ground-surveyed sites near the aircraft base camp. After the validation and calibration is complete, a limited measurement program to detect time changes in surface elevation of glaciologically interesting sites will be started. At the conclusion of the program, the capability of the SOAR facility to determine surface elevation accurately and precisely will be established. SOAR will then be useful to all investigators who are interested in precision mapping and detection of change in the antarctic ice sheet. (IS-166-O)