Glaciology and glacial geology

Recovery and science coordination of an ice core at Siple Dome, Antarctica. Kendrick Taylor, Desert Research Institute. This 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. This project provides the background for the Siple Dome drilling program, develops the opportunity for individual scientists to work on the ice core, and establishes 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). (S-152)

Near-surface processes affecting gas exchange: West antarctic ice sheet. Mary Albert, Cold Regions Research and Engineering Laboratory. This project will examine the physical processes that affect the manner in which 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. This project 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. (S-155)

The evolution of a polar ice sheet in East Antarctica. George Denton, University of Maine. This study seeks 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. The purpose of this project is to determine, 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). It is on this relict land surface that data will be collected which record Middle and Early Miocene glacial history and paleoclimate. The results should allow an identification of the transition from temperate to polar conditions. This work will involve landscape analysis, stratigraphy of glacial deposits, and argon-40/argon-39 dating of volcanic ashfalls. Denudation rates 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. (S-156)

Hot-water borehole drilling on Siple Dome to deploy vertical strain meters and to determine ice temperature and lateral continuity of climatic records at depth. Barclay Kamb, California Institute of Technology. The long-term objective of this project is to establish by direct observation in boreholes the physical mechanism of rapid motion of the West Antarctic ice streams, in relation to global climate change. In previous years, we have studied ice streams B and C and have developed techniques for rapid deep drilling with a hot-water jet and for obtaining ice cores by hot-water drilling. During the 1997-98 field season, we will apply the hot-water drilling technique to the problem of the vertical compression of ice at depth in the ice sheet at the Siple Dome deep-coring site and how this compression thins the annual layers of ice that accumulate each year on the surface of the ice sheet. Quantitative knowledge of this thinning process is necessary to evaluate an ice core's age at depth and the history of ice accumulation. Collaborating with investigators from the University of Alaska (S-164), we will drill 40 boreholes to various depths near the Siple Dome core site, while investigators from project S-164 install vertical strain meters in these holes to measure the vertical compression rate as a function of depth. Additional, this field season we will obtain a vertical profile of ice temperature near the strain-rate-measurement locations and drill a vertical sequence of ice cores near the main Siple Dome core site and at a location about 10 kilometers away. The temperature data are needed to interpret the strain-rate measurements in terms of an anisotropic flow for the ice at depth. The cores will be used to ascertain if the vertical profile of paleotemperatures and other climatic records is laterally continuous in the upper part and discontinuous at depth, as investigators found it to be in ice cores from Greenland (i.e., the GISP2 and GRIP cores). Lateral continuity of the records is important in demonstrating the reliability of climatic history inferred form the ice cores. (S-157)

Snow-atmosphere transfer function for reversibly deposited chemical species in West Antarctica. Roger Bales, University of Arizona. Measurements made by this project will help investigators improve their understanding of the relationship between formaldehyde (HCHO) and hydrogen peroxide (H2O2) in the atmosphere and the concentrations of the same species in antarctic snow, firn, and ice. This work aims to relate changes in concentrations in the snow, firn, and ice to corresponding changes in tropospheric chemistry. Atmospheric and firn sampling for formaldehyde and hydrogen peroxide at one or more of the WAIS (West Antarctic Ice Sheet) ice core drilling sites will be undertaken, and controlled laboratory studies to estimate thermodynamic and rate parameters will be performed. In addition, this work will involve modeling of atmosphere-snow exchange processes to infer the "transfer function" for reactive species at the sites and atmospheric photochemical modeling to relate changes in concentrations of formaldehyde and hydrogen peroxide in snow, firn, and ice to atmospheric oxidation capacity. This work will contribute to a better understanding of the relationship between atmospheric concentrations of various species and those same species measured in snow and ice samples. (S-158)

Passive microwave remote sensing for paleoclimate indicators at Siple Dome, Antarctica. Robert Bindschadler, National Aeronautics and Space Administration. Passive microwave data will be used in this project to validate key paleoclimate indicators used in glaciologic research. The specific contributions of this research are

The work will take place at Siple Dome, Antarctica, as part of the field activities associated with the ice-core drilling program there. (S-159)

Digital imaging for ice core analysis. Joan J. Fitzpatrick, U.S. Geological Survey, Denver. Over 2 years we will develop the technology and methodology for digitizing the photographs and analyzing the thin sections from ice cores and will investigate the application of digital technology for whole-core stratigraphy, using digital photography, image enhancement and image processing. The thin section analysis will be tested using samples already in hand from the Taylor Dome ice core. If we are successful, we will apply these techniques to samples from the Siple Dome ice core, in cooperation with the investigators funded to retrieve and examine these sections. The original digital images with all original data annotation files will be distributed to Siple Dome investigators so they can use these files to interpret 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.

Antarctic ice core records of oceanic emissions. Eric Saltzman, University of Miami. This project will develop long-term records of the atmospheric deposition of aerosolborne, marine-derived elements to the antarctic ice sheet. The project includes the sampling of antarctic ice-core samples from the Vostok ice core and the laboratory analysis of soluble ions in the ice. The analyses include methanesulfonate, non-sea-salt sulfate, and several additional ions derived from gaseous emissions from the sea surface, from seasalt, and associated with continental dust. The principal emphasis of this work is on sulfur, because of its role as a major aerosol-forming constituent of the atmosphere and because of its potential importance to climate. The main goal of the project is to complete analyses of the Vostok ice core. (S-161)

Ice dynamics, the flow law, and vertical strain at Siple Dome. William Harrison, University of Alaska at Fairbanks. This 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 to be drilled at Siple Dome during the 1997+1998 field season. 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. (S-164)

Physical and structural properties of the Siple Dome Core. Anthony Gow, Cold Regions Research and Engineering Laboratory. This project will investigate the visual stratigraphy, index physical properties, relaxation characteristics, and crystalline structure of ice cores from Siple Dome, West Antarctica. This investigation will include measurements of a time-priority nature 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. (S-165)

SOAR laser: Calibration and first measurement for ice-sheet change detection. Ian Whillans, Ohio State University. This 3-year study 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. This project 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. (S-166)

Reconstruction of paleotemperatures from precision borehole temperature logging: A Transantarctic Mountains transect from Taylor Dome to Ross Sea. Edwin Waddington, University of Washington. As a part of this study, we will gather data to provide a direct thermal measurement of any climate warming in the Ross Sea sector of Antarctica. When combined with existing McMurdo Dry Valleys climate records and indicators, these data should provide information about past relationships in the region among such climate factors as cloudiness, air temperature, and wind patterns. To obtain the data, we will log temperature as a function of depth in pre-existing boreholes on a transect from Taylor Dome through the McMurdo Dry Valleys to the Ross Sea. Paleotemperatures will be derived by applying formal inverse methods to the data. The oxygen-isotope proxy record from the Taylor Dome ice core will be compared with a true thermal record to calibrate the oxygen-isotope proxy record. Vertical strain rate will be measured in an existing 130-meter dry hole to allow correction for firn compaction and ice advection. (S-171)

West Antarctic Glaciology V. Robert Bindschadler, National Aeronautic and Space Administration. This 3-year project is designed to answer two questions of critical importance to understanding the iceflow of the west antarctic ice sheet:

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. (S-173)

Radar investigations of former shear margins: Roosevelt Island and ice stream C. Charles Bentley, University of Wisconsin at Madison. This 2-year project will perform radar investigations across former shear margins at Roosevelt Island and ice stream C to measure changes in the configuration and continuity of internal layers and the bed. The broad goal of these investigations is to gain an understanding of ice-stream flow and the timing and mechanisms of ice-stream shutdown. A high-resolution short-pulse radar system will be used for detailed examination of the uppermost 100 meters of the firn and ice, and a monopulse sounding-radar system will be used to image the rest of the ice column (including internal layers) and the bed. Changes in the shape and continuity of layers will be used to interpret mechanisms and modes of ice-stream flow including the possible migration of stagnation fronts and rates of shutdown. Variations in bed reflectivity will be used to deduce basal hydrology conditions across lineations. Accumulation rates deduced from snow pits and shallow cores will be used to estimate near-surface depth-age profiles. Improved understanding of ice-stream history opens the possibility of linking changes in the west antarctic ice sheet with the geologic evidence from northern Victoria Land and the ocean record of the retreat of the grounding line in the Ross Sea. (S-176)

Determining ice-sheet mass balance using global positioning system measurements. Gordon Hamilton, Ohio State University. Over the course of 3 years, we will measure the rate of thickening or thinning of the antarctic ice sheets at selected sites in East and West Antarctica. To do this, we will measure vertical velocities of markers anchored at several depths in the ice sheet and retrieve shallow firn cores to determine density and long-term average accumulation. Precise, absolute marker positions will be obtained using global positioning system surveys. The three existing sites will be revisited, and 13 new sites in nine locations will be established on the east and west antarctic ice sheets. Although we will use the measured thickening or thinning rates to test various glaciological hypotheses, the results of the work will also be useful for calibrating data from satellite and airborne altimetry of ice sheets. (S-178)

The quantitative assessment of the Mount Pinatubo signal in antarctic snow. Ellen Mosley-Thompson, Ohio State University. This study will sample surface snow in pits and drill shallow cores near South Pole to look for evidence of the June 1991 eruption of Mount Pinatubo in the Philippines. Extensive measurements and observations by satellite and by ground-based and airborne atmospheric instruments are available regarding the amount of sulfur dioxide emitted from the eruption, as well as the global distribution and decay of the stratospheric aerosols derived from the volcanic sulfur dioxide. Ground-based and airborne measurements in Antarctica clearly indicate that the stratospheric sulfate aerosols from this eruption reached high southern latitudes in late 1991 and persisted in the antarctic atmosphere through 1993. Preliminary results from snow pit samples recently taken in the South Pole area indicate that the Pinatubo signal exists and can be separated from the signal of another volcanic eruption (Cerro Hudson), which occurred in mid-August 1991. Combined with the known total sulfate aerosol production from Pinatubo, the proposed sampling and analyses will yield the quantitative information necessary to establish empirical relationships between the explosivity of a low-latitude eruption and the amplitude of its corresponding signals in antarctic snow. (S-185)

Measurements and model development of antarctic snow accumulation and transport dynamics. David Braaten, University of Kansas. A more thorough understanding of annual ice-sheet snow accumulation is important for interpreting paleoclimatic ice-core records, and assessing the role of wind on the mass transport of snow is important in understanding the redistribution of snow on the continent and mass transport off the continent. Our research continues to quantify the year-round snow accumulation dynamics and wind-blown mass transport of snow in remote katabatic wind areas, providing new insights into these complex nonlinear processes. Using instrumentation that disperses colored glass microspheres at 14-day intervals throughout the year and a sonic snow depth gauge that makes hourly measurements of snow-surface height, we can reconstruct in detail the complex accumulation and transport dynamics. The microspheres dispersed at fixed times throughout the year act as both time markers within the annual snow-accumulation profile and as tracers of snow mass transport by the wind. These insights are essential in developing and validating numerical models that are concurrently being developed to simulate these processes.

Snow-core and snow-pit sampling of the annual accumulation will be conducted at Ferrell automatic weather station (AWS) on the Ross Ice Shelf and AGO-2 on the polar plateau. At each site, we will take snow samples with a depth resolution of up to 1 centimeter and will analyze these to identify microsphere horizons within the annual accumulation profile. Snow cores will be obtained along a line in the prevailing wind direction and will be analyzed to identify microspheres transported by the wind. The instrumentation located at Ferrell AWS will be moved to Marilyn AWS on the Ross Ice Shelf, an area with very strong katabatic winds. (S-190)