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Geology and Geophysics

Antarctica is not only one of the world's seven continents, but also comprises most of one of its dozen major crustal plates, accounting for about nine percent of the Earth's continental (lithospheric) crust. Very little of this land is visible however, covered as it is by the vast East Antarctic Ice Sheet and the smaller West Antarctic Ice Sheet. The ice sheets average some 3 kilometers deep a virtual vault, 90 percent of the ice on Earth is here. And it is heavy, depressing the crust beneath it some 600 meters. These physical characteristics, while not static, are current. Yet thanks to the sciences of geology and geophysics, powered by modern instruments and informed by the paradigm of plate tectonics/continental drift, Antarctica is also a time machine.

Geologists have found evidence that there was once a forested supercontinent in the Southern Hemisphere, which they call Gondwanaland. Before the Earth's constantly shifting plate movement began to break it up 150 million years ago, Antarctica was a core piece of this assembly; its adjoining land has since become Africa, Madagascar, India, Australia and South America. The Antarctic Plate drifted south at little more than a centimeter each year, but geologic time eventually yields cataclysmic results: The journey moved it into ever colder, high-latitude climates, at a rate of about 4ºC for each million years; eventually life conditions had changed dramatically, and Antarctica arrived at a near polar position. This astounding history of rock and life on Earth has left a stratigraphic and fossil record, locked in and beneath the ice, the sea, and in the bedrock below both.

As the ice sheets developed, they assumed what has become a key role in modulating global climate, through their interaction with oceanic and atmospheric circulation. As a bonus, the South Pole also presents a strategic point to monitor the Earth's current seismic activity. Antarctica is the highest continent on Earth (about 2,150 m above sea level), with its fair share of mountains and volcanoes; thus many generic questions of interest to earth scientists worldwide also apply to this region. Some specific issues focused on by the Geology and Geophysics program include:

determining the tectonic evolution of Antarctica and its relationship to the evolution of the continents from Precambrian time (600 million years ago) to the present;

determining Antarctica's crustal structure;

determining how the dispersal of antarctic continental fragments may have affected the paleocirculation of the world oceans, the evolution of life, and the global climate (from prehistoric times to the present);

reconstructing a more detailed history of the ice sheets, identifying geological controls to ice sheet behavior, and defining geological responses to the ice sheets on regional and global scales; and

determining the evolution of sedimentary basins within the continent and along continental margins.

All of these problems will be simplified as scientists improve their models of where, when, and how crustal plate movement wrought Antarctica and its surrounding ocean basins. The program funds investigation into the relationships between the geological evolution of the antarctic plate and the life and processes that can be deduced to accompany it: Paleocirculation of the world ocean, paleoclimate of the Earth, and the evolution of high-latitude biota. A current emphasis is the West Antarctic Ice Sheet Program (WAIS), research on the smaller of the continent's two ice sheets, conducted also under the aegis of the Glaciology program. Several important research support activities are also underway:

Meteorites: In a partnership with NASA and the Smithsonian Institution, the program supports meteorite collection through ANSMET, the Antarctic Search for Meteorites, and chairs an interagency committee, responsible for curating and distributing samples of the antarctic meteorites.

Mapping and geodesy: In partnership with the U.S. Geological Survey, the program supports mapping and geodetic activities as an investment for future research in earth sciences. The U.S. Antarctic Resources Center (US-ARC) constitutes the USAP contribution to the Scientific Committee on Antarctic Research (SCAR) library system for earth sciences information; housed here is the largest collection of antarctic aerial photographs in the world, as well as many maps, satellite images, and a storehouse of geodetic information.

Marine sediment and geological drill cores: In a partnership with the Antarctic Marine Geology Research Facilty at Florida State University, the program manages and disseminates marine sediment and geological drill cores mined in Antarctica. The collection includes an array of sediment cores as well as geological drill cores from the Dry Valley Drilling Project, the CIROS drilling program, and the Cape Roberts Drilling Project. The facility fills requests for samples from researchers worldwide, and also accommodates visiting researchers working on site.

Global positioning system measurement of isostatic rebound and tectonic deformation in Marie Byrd Land, West Antarctica.
Bruce Luyendyk, University of California at Santa Barbara.

The Ross embayment and western Marie Byrd Land are part of the west antarctic rift system. Most scientists agree that this region is undergoing active deformation, but the rates and causes of deformation remain essentially unknown. Tectonic extension may be occurring in the Ross embayment as West and East Antarctica continue to separate. Crustal uplift could be occurring in western Marie Byrd Land due to isostatic rebound following the last glacial age.

If tectonic extension is occurring in the embayment - depending on its magnitude - it could greatly influence global plate circuit calculations. It could also constrain our understanding of the history of extension in the embayment and the consequent uplift history of the Transantarctic Mountains. Postglacial rebound in western Marie Byrd Land would depend on when and how the ice sheet was configured during the Last Glacial Maximum. The big question is whether the ice sheet collapsed in mid-Holocene time.

This study will install three continuous and autonomous global positioning system (GPS) stations on outcrops in western Marie Byrd Land, on baselines of around 100 kilometers. These stations will gather data over a 4-year period and operate in concert with GPS stations being installed in the Transantarctic Mountains in a separate project; the result will be a baseline array deployed all across the Ross embayment. The array will also detect strain gradients in western Marie Byrd Land. This system should determine crustal strain rates to an accuracy of 1 millimeter per year for horizontal, and 2 millimeters per year for vertical. The strain data from western Marie Byrd Land and the Transantarctic Mountains should enable us to construct both tectonic extension and glacial rebound models.

This is a joint project between the University of California at Santa Barbara scientists and a team at the Jet Propulsion Laboratory at the California Institute of Technology. (GF-121-O)

(GO-052-M, GO-052-P & GO-052-S)
Antarctic Mapping and Geodesy.
Jerry L Mullins and Richard E Witmer, U.S. Geological Survey.

Geodetic surveying, aerial photography, remote sensing (principally using several varieties of satellite imagery), and mapping are all activities necessary for the successful operation of a multifaceted scientific and exploration effort in Antarctica. The U.S. Geological Survey provides these support activities to the U.S. Antarctic Research Program.

Year-round data acquisition, cataloging, and data dissemination activities will continue in the U.S. Antarctic Resource Center for geospatial information. Field surveys will be conducted in support of specific research projects, and as part of a continuing program to collect the ground-control data necessary to transform existing geodetic data to an earth-centered system suitable for future satellite mapping programs.

LandSat data will be collected as part of satellite image mapping activities; this will permit continued publication of additional 1:50,000 scale topographic maps in the McMurdo Dry Valleys region. Such topographic studies provide a uniform base map on which to ensure that scientific information (from geology, glaciology, biology and other areas) is spatially accurate. These, as well as the satellite image maps, are used by scientists to plan and execute future research work. Spatially-referenced, digital cartographic data will be produced in tandem with the published maps. (GO-052-M, GO-052-P & GO-052-S)

Stability of land surfaces in the McMurdo Dry Valleys: Insights based on the dynamics of subsurface ice and sand-wedge polygons. Bernard Hallet, University of Washington.

The dynamic nature of climate has received growing public attention because of growing concerns about warming and the recent occurrence of seemingly extreme weather events. In this context, understanding the inherent variability of Earth's climate and how humans can affect Earth's environment is becoming increasingly more important. We are studying features of the landscape and soils of the dry valley region of Antarctica to provide a more complete understanding of past climatic and environmental conditions.

One important means of improving our understanding of the planetary climate system is to treat the Earth as a natural laboratory and examine its past behavior. One of the most extreme changes in the climate system during the last few million years was the transition from a warm period in the Pliocene to an ice-age world. Scientists believe that during this interval relatively mild conditions in Antarctica gave way rapidly to intense glacial conditions that catalyzed the growth of what has become the largest ice sheet on Earth. This inference is based on geologic indicators of past climate, from which some scientists suggest that East Antarctica was relatively warm and largely free of glaciers about 3 to 4 million years ago (during parts of the Pliocene). The mild conditions ended abruptly, with rapid ice-sheet growth and development of the very cold, dry climate that now characterizes this region. A contrasting view, based on substantial geologic evidence, suggests that East Antarctica has been cold and the ice sheet stable for at least 8 million years, and perhaps considerably longer. These views lead to drastically different interpretations of the stability of Earth's climate.

We hope our research will help resolve this important dilemma by introducing independent new evidence and insights derived from studies of the stability of ground ice and land surfaces in the McMurdo Dry Valleys of Antarctica. We will study modern-day processes that have important implications for understanding the occurrence of buried ice found recently in Beacon Valley. This ice may be the oldest ice on Earth, and, if so, will provide strong evidence of long-term stability of the East Antarctic Ice Sheet, and may also provide a rare glimpse into atmospheric conditions millions of years ago.

Specific processes to be investigated include

exchange at the ground surface that affects ground temperature;

water-vapor transport and other processes leading to the formation or loss of ice in the soil; and

frost cracking due to contraction during rapid cooling of the frozen ground in the winter, and its resulting disruptions of the soil. (GO-053-O)

Response of the East Antarctic Ice Sheet to Middle Miocene global change.
David R Marchant, Boston University.

As evidence of global climate change continues to accumulate, scientists concentrate on models that might indicate what impacts such change could have. Among the most important questions: What could happen to the East Antarctic Ice Sheet- One of the largest known global climate shifts occurred in Middle Miocene time (between about 15.6 and 12.5 million years ago). As the isotopic composition of oxygen in the oceans shifted, dramatic global cooling and reorganization of ocean circulation patterns can be seen. This significant and irreversible shift set the stage for modern oceanic and atmospheric circulation, and for the bipolar ice ages that have dominated climate records for the last 12.5 million years. How did Antarctica respond to this great climate shift? Could growth of the antarctic ice sheet have initiated this shift? If so, how might future fluctuations in the volume of ice on East Antarctica influence atmospheric and oceanic circulation?

Recently there was an unexpected breakthrough in antarctic geology - discovery of Miocene-age volcanic ashes interbedded with surficial sediments in southern Victoria Land. These terrestrial deposits provide unambiguous data from which to generate precise climatic and glaciological reconstructions of how the global climate changed and the ice sheet evolved. This site appears to be the only place in Antarctica where pristine, Miocene-age, unconsolidated deposits are preserved at the ground surface.

These data also permit scientists to address key questions, such as -

What contributing factors in Antarctica led to the abrupt global cooling about 14 million years ago?

Does the Middle Miocene shift in the isotopic composition of the oceans signify a major expansion of east antarctic ice?

Or rather, does this isotopic shift instead reflect a change in ocean temperature or circulation?

And a related question: When did cold, hyper-arid, polar-desert conditions (signifying the development of a polar East Antarctic Ice Sheet) first evolve in Antarctica? In analyzing these deposits, we expect to obtain a precise chronological sequence, based on 50 laser-fusion isotopic analyses of in-situ volcanic ashes and 20 cosmogenic, exposure-age analyses of ancient deposits. We also expect to develop a coeval record of the Miocene paleoclimate, based on textural changes in alpine drifts, the areal distribution of ice-marginal lakes, the abundance of dated, patterned ground and ventifact pavements, and the geochemistry of buried soils and volcanic-ash deposits. (GO-054-O)

ANSMET (the Antarctic Search for Meteorites).
Ralph Harvey, Case Western Reserve University.

Since 1976, ANSMET (the Antarctic Search for Meteorites program) has recovered more than 10,000 meteorite specimens from locations along the Transantarctic Mountains. Antarctica is the world's premier meteorite hunting ground for two reasons. First, although meteorites fall all over the globe at random, the likelihood of finding a meteorite is enhanced if the background material is plain and the accumulation rate of terrestrial sediment is low; this makes the East Antarctic Ice Sheet the perfect medium.

Second, along the margins of the sheet, ice flow is sometimes blocked by mountains, nunataks, and other obstructions; this exposes slow-moving or stagnant ice to the fierce katabatic winds, which can diminish the ice and expose what is known as a "lag deposit" of meteorites (a representative portion of those that were sprinkled throughout the volume of ice lost to the wind). When such a process continues for millenia, the concentration of meteorites unveiled can be spectacular.

It is important to continue recovering antarctic meteorites because they are the only currently available source of new, non-microscopic extraterrestrial material. As such, they provide essential "ground truth" (existence proof) about the composition of asteroids, planets, and other bodies of our solar system. ANSMET recovers samples from the asteroids, the Moon and Mars for a tiny fraction of the cost of a sample return mission.

During the 2000-2001 field season, ANSMET will visit the Meteorite Hills region at the headwaters of the Darwin Glacier. This site has been visited twice previously for reconnaissance purposes, yielding about 60 meteorites during a few days searching. Systematically searching this important icefield will be the primary focus of the upcoming season. Other nearby targets will be explored during extended helicopter-supported reconnaissance; we anticipate visiting Bates Nunataks, Butcher Ridge, and other nearby icefields. (GO-058-O)

Tracking the west antarctic rift flank.
Paul Fitzgerald and Suzanne L. Baldwin, University of Arizona.

Reconstructing the motion of the Earth's crustal plates in prehistory is rarely as simple as looking at a blueprint. Geological evidence may suggest conflicting narratives, and newly developing techniques are often the key to resolving the puzzle. The rift system in West Antarctica is an example.

Scientists believe that the uplifted Cenozoic rift shoulder of the west antarctic rift system extends along the Transantarctic Mountains and the northwestern flank of the Ellsworth-Whitmore Mountains crustal block. Fission track data drawn from the block indicate that although most of the erosion exposing the rock strata (denudation) occurred there in Late Jurassic/Early Cretaceous times, a significant component of denudation is permissible in the Cenozoic. In contrast, most of the rock uplift and denudation in the Transantarctic Mountains occurred in the Cenozoic. We hope to shed some light on this controversy and on the timing of uplift and denudation at key localities, as well as on the patterns of uplift and denudation along the west antarctic rift shoulder, through a series of thermochronologic studies.

Our objectives are:

to determine the extent and timing of denudation of the west antarctic rift flank;

to further delineate patterns of uplift and denudation along the length of the Transantarctic Mountains;

to document the thermal history of basement rocks from different crustal blocks; and

to compare and contrast the thermal histories of East Antarctica (Transantarctic Mountains) and West Antarctica (Ellsworth-Whitmore Mountains crustal block).

We will address these objectives using thermochronologic techniques, specifically apatite fission track thermochronology and argon-40/argon-39 (40Ar/39Ar) thermochronology. All laboratory work will be undertaken at the Center for Thermochronology and Noble Gas Studies at the University of Arizona. The application of low-temperature thermochronologic methods has made fundamental contributions to our understanding of the uplift and denudation history of the Transantarctic Mountains and the Ellsworth Mountains.

Data that integrates both fission track and 40Ar/39Ar thermochronology will lead to a better understanding of the geological evolution of a continent with a number of mountain ranges and two large crustal plates. We know that the west antarctic rift created the Transantarctic Mountains during the Cenozoic. But did that same event curve into West Antarctica along the northwest flank of the Ellsworth-Whitmore Mountains? Or were the plates aligned such that, instead, it ripped eastward across most of Antarctica? Of such scientific distinctions is the history of the Earth constructed. (GO-059-O)

Global climate change and evolutionary ecology of antarctic mollusks in the Late Eocene.
Richard B. Aronson, Dauphin Island Sea Lab

The Eocene epoch ran from about 65 to 55 million years ago, when evidence suggests that global climate change had an important influence in Antarctica. Formerly cool-temperate conditions in the region began to shift to the polar climate that has persisted until now. As temperatures dropped, shallow-water, antarctic marine communities began to change, and these effects are still evident in the peculiar ecological relationships observed among species living in modern antarctic communities.

In particular this Late Eocene cooling reduced the abundance of fish and crabs, which in turn reduced skeleton-crushing predation on invertebrates. Thus dense populations of ophiuroids (brittlestars) and crinoids (sea lilies) began to appear in shallow-water settings. These low-predation communities appear as dense fossil echinoderm assemblages in the upper portion of the Late Eocene La Meseta Formation on Seymour Island, off the Antarctic Peninsula. Dense ophiuroid and crinoid populations remain common in shallow-water habitats in Antarctica today, but at temperate and tropical latitudes they have generally been eliminated by predators. The persistence in Antarctica of these populations is an important ecological legacy of climatic cooling in the Eocene.

For the antarctic ophiuroids and crinoids, the influence of declining predation is now well documented; but the effects of cooling on the more abundant mollusks have not been investigated. Our project will examine the evolutionary ecology of gastropods (snails) and bivalves (clams) in this same Late Eocene time frame. Based on the predicted responses of mollusks to declining temperature and changing levels of predation, we will test a series of hypotheses in the La Meseta Formation on Seymour Island. The shapes of gastropod shells, the activities of gastropods that prey on other mollusks by drilling holes in their shells, and the effects of predation on the thickness of mollusk shells, should have changed significantly through late Eocene time.

Since Seymour Island contains the only antarctic fossil outcrops readily accessible from this crucial period in Earth's history, such investigations provide a unique opportunity to learn how climate change may have affected antarctic marine communities. In practical terms, models suggest that global climate change - over the next few decades to centuries - is predicted to increase upwelling in some temperate coastal regions, which would lower water temperatures. Recent ecological evidence suggests this could lower predation in those areas. Our model of the La Meseta faunas' response to global cooling in the late Eocene should enhance understanding of the dynamic structure of modern benthic communities. (GO-065-O)

Formation of the Dry Valleys, Antarctica: Linking thermochronometric (U-Th/He) and cosmogenic constraints on landscape development.
Martha House and Kenneth Farley, California Institute of Technology, and John Encarnacion, St. Louis University.

The formation of mountains (known as orogenesis) occurs over time. Pinpointing the age of sequential episodes helps to elucidate how the Earth's crust was deformed, and to shed light on the dynamics between climate and forming mountains. But accurate dating, especially of older events, remains elusive, because erosion over time changes and compromises the geomorphologic expressions and the sedimentation record. The higher the elevation, the older the originating event, but the more likely there is to have been erosion. Other geochemical tools - such as surface-exposure dating - have been developed for tracking erosion and landform development, but these also provide information on only the most recent history (less than 1 million years). Thus the much greater age of many mountain belts, and their complex internal geometry, present a challenge to scientists trying to understand their temporal and physiographic/tectonic evolution.

One technique for closing this gap of knowledge - apatite fission track thermochronometry - rests on a basic scientific assumption. As rock moves upward away from the Earth's internal molten processes, it cools. Scientists use cooling data to measure both exhumation (movement of a rock upward with respect to the earth's surface) and bedrock uplift (movement of the rock upward with respect to the geoid, or sea-level). These data provide input for landscape-evolution models, with episodes of rapid cooling attributed to the topographic rise of mountain belts (even though some scientists have shown that such a correlation does not always hold).

Such models should be improved by combining low-temperature thermochronometry with surface-exposure dating. The McMurdo Dry Valleys region of the Transantarctic Mountains is an ideal place for such an exercise; many of the modern land surfaces in the region appear to be upwards of 15 million years old, which means there has been comparably little erosion since the mid-Miocene. The apatite fission tracks indicate some rocks in the McMurdo Dry Valleys cooled through approximately 105C as recently as about 45 million years. This leaves a gap of about 30 million years where our knowledge of the evolution of this mountain range must be inferred very roughly.

This project will focus on this gap by employing a combination of recently developed methods. The newly developed apatite-helium (U-Th/He) thermochronometer (which improves temperature sensitivity to 70C) can constrain events during this period and will also provide a more fine-grained r ecord of the time sequence when topographic relief occurred. By combining these thermochronometric indications of river valley incision with cosmic-ray exposure ages, we can develop more details of the geomorphologic evolution of the McMurdo Dry Valleys region. In particular, a more accurate formation age for the McMurdo Dry Valleys will constrain the period for the orogenesis of the Transantarctic Mountains. More generally, our work should have implications for the geodynamic evolution of the region and will contribute to the debate over Cenozoic changes due to paleoclimate that would have influenced the growth and stability of the East Antarctic Ice Sheet. (GO-066-O)

Late Cretaceous and Cenozoic reconstructions of the southwest Pacific.
Steven C. Cande, Scripps Institution of Oceanography.

Crustal plate motion is never as predictable as earth scientists would like - witness the devastation wrought by unpredicted earthquakes. In Antarctica, there is controversy regarding a possible missing plate boundary, as well as tectonic uncertainties in the motion between East and West Antarctica; in particular, questions about the relative drift between major hotspot groups. The plates of the Southwest Pacific region are rotational, so that earthquakes are relatively rare. Still, the models that describe the motion of the Pacific, Antarctic, and Australian plates - and the continental fragments of New Zealand, West Antarctica, Iselin Bank, East Antarctica, and Australia - could be improved. This research focuses on these models.

Previous work has documented mid-Tertiary seafloor spreading in a NNW-striking direction, producing magnetic anomalies between East and West Antarctica. This would explain the approximate 150 kilometer-opening of the Adare Trough, north of the Ross Sea. The hypothesized motion, however, is insufficient to resolve the apparent discrepancy between the actual plate motions and those that would follow from the assumption that the hotspots were fixed.

The motion between East and West Antarctica indicates a very small rotation. Thus, scientists would like to develop models of finite plate rotation in this area to a high degree of accuracy, particularly for older times. This goal is now attainable - using data sets compiled by Japanese and Italian scientists on recent cruises in the region - if our project is able to develop and confirm certain crucial data. By collecting new marine geophysical data on selected transits of the R/V Nathaniel B. Palmer, we hope to

o improve the rotation model for mid-Tertiary extension between East and West Antarctica by directly considering the plate boundary between the Pacific and Australia plates in the calculation of Australia-West Antarctica motion;

improve the reconstructions for Late Cretaceous and Early Tertiary times by including new constraints on several boundaries not previously used in the reconstructions;

address the issue of the fixed position of global hotspots through the implications of new rotation models; and,

re-examine the geophysical data from the Western Ross Sea embayment, in light of a model for substantial mid-Cenozoic extension. (GO-071-O)

Quarternary glacial history and paleoenvironments of the East Antarctic margin.
Amy Leventer, Colgate University.

What was Antarctica like long ago? Geologists refer to the last 11,000 years as the Holocene epoch and have found sedimentary records in the Antarctic Peninsula and Ross Sea (West Antarctica) that suggest a pattern throughout much of this time. Primary biological production, as well as the extent of sea-ice, are seen to vary, on scales of hundreds and thousands of years. How far into the Southern Ocean the antarctic ice sheet extends - as sea-ice forms and retreats seasonally - is to some extent a function of solar energy. Scientists also know that the ice sheet has a central role in global oceanic and atmospheric systems.

This set of theories about Antarctica rest primarily on the study of deposits taken from the west antarctic ridge. In this project, we will focus on a 500 km stretch of the east antarctic margin, including Prydz Bay and the MacRobertson Shelf. Glacial marine sediments present a challenge to researchers trying to reconstruct Holocene paleoenvironments. Scientists from Australia and the United States will use detailed sedimentologic, geochemical, micropaleontological, and paleomagnetic techniques; a multi-faceted approach necessary to extracting reliable paleoenvironmental data. Operating from the research ship Nathaniel B. Palmer, we will conduct high-resolution seismic mapping and coring of sediments deposited in inner shelf depressions. Chronological work performed on the data extracted from these samples should determine the timing and duration of previous periods of glacial marine sedimentation on the east antarctic margin during the late Pleistocene.

These high-resolution Holocene records from the east antarctic margin, supplemented with the data already developed from West Antarctica, will permit us to develop a circum-antarctic suite of data regarding the response of southern glacial and oceanographic systems to Late Quaternary climate change. These results are expected to significantly advance our understanding of the behavior of the antarctic ice-sheet and ocean system in the recent geologic past. (G-O73-O)

Bio-optical properties of Southern Ocean waters.
Kevin Arrigo, Stanford University.

In recent years, more ocean-color satellites have come on line, but these instrument systems function amidst a complex set of operating assumptions. High-quality bio-optical data is needed to calibrate the sensors in this equipment, and algorithms must be developed and validated to make the systems efficiently operational. Unfortunately, the waters in such high-latitude, remote and often inaccessible regions of the Earth present challenges to the gathering of good bio-optical data.

During a 60-day cruise on the R/V Nathaniel B. Palmer (the same cruise as project GO-073-O), we will cover a large area in the Southern Ocean, from Australia to Prydz Bay to South Africa. We expect to encounter many different water types and masses with different bio-optical properties. By deploying multi-wavelength radiometers at each daylight station and additionally at one-degree latitudes, we expect to collect a grid of baseline data to develop a useful profile of the water column. (GO-073-A)

Dry valleys seismograph project.
Kent Anderson and Carl Mulcahy, U.S. Geological Survey.

One recurrent issue in seismography is noise; that is, background phenomena that can interfere with clear and precise readings. The Dry Valleys Seismograph Project - a cooperative undertaking with the New Zealand Antarctic Program - was established to record broadband, high-dynamic-range, digital seismic data from the remote Wright Valley, a site removed from the environmental and anthropogenic noise ubiquitous on Ross Island.

The Wright Valley site provides one of the few locations on the continent with direct access to bedrock. The station there consists of a triaxial broadband borehole seismometer (100 meters deep) and a vertical short-period instrument at 30 meters. The seismological data are digitized at the remote location, telemetered by repeaters on Mount Newell and Crater Hill, and received eventually by the recording computer at the Hatherton Laboratory at Scott Base, where a backup archive is created.

These data will eventually reach the international seismological community; from Hatheton they pass along a point-to-point protocol link to the Internet at McMurdo Station and thence to the Albuquerque Seismological Laboratory for general distribution. This data set has beautifully complemented the data from other seismic stations operated by the Albuquerque Seismological Laboratory at Amundsen-Scott South Pole Station, Palmer Station, and Casey, an Australian base. (GO-078-O)

Mount Erebus Volcano Observatory: Gas emissions and seismic studies.
Philip R. Kyle and Richard C. Aster, New Mexico Institute of Mining & Technology.

Mount Erebus on Ross Island is Antarctica's most active volcano; also the only one with a persistent convecting lake of molten, alkali-rich phonolitic magma in its summit crater. This makes Erebus one of the few volcanoes on Earth with nearly continuous, small explosive activity and continuous internal earthquake (seismic) activity. As such, it provides the ideal natural laboratory to study these phenomena: How gas is given off by magma, and the seismic activity that results from a convecting magma conduit.

This project entails a combination of seismic studies and gas emission rate measurements, designed to elucidate the nature and dynamics of the magmatic plumbing system, as well as eruptions and degassing from the lava lake.

The gas studies will provide some of the first data available on carbon-dioxide degassing from a highly alkalic magma system. They should also help to evaluate how much lead from Mount Erebus (relative to lead released by marine aerosols) gets into the snow on the East Antarctic Ice Sheet, and thus shed light on hypotheses about the anthropogenic origins of lead. Further goals of the gas studies are to

examine the role of Erebus as a source of gas and aerosols to the antarctic environment;

understand the role of volcanism as a source of carbon-dioxide emissions to the atmosphere, especially for a highly alkalic magma;

understand the evolution of the main volatile substances (water vapor, carbon-dioxide, total sulfur, fluorine and chlorine) in the Erebus magmatic system, as well as their role in the eruptive behavior of Erebus; and

correlate the nature of the gas emissions with the observed seismic activity.

The seismic studies of the volcano will add a permanent broadband seismic station to the array and update the present data acquisition system. We also plan to expand development of the current software to register automatic and precise timing of when and where earthquakes occur.

Deformation studies to monitor the movement of magma inside the volcano will be made using GPS campaign-style geodetic measurements, supplemented by an array of permanent continuous operating GPS stations. Two new stations in the 2000-2001 field season will make the array a set of 3, single frequency, L1 stations and a dual frequency station. The latter station and its associated meteorological package will become part of the global SuomiNet array, providing real-time, atmospheric, precipitable water vapor measurements and other geodetic and meteorological information.

The resultant data should enhance the collection of earthquakes that we are using in a computer model of the interior of the volcano, as well as provide a tool scientists can use for volcano surveillance, eruption monitoring, and for detecting subtle changes in the internal behavior of volcanoes. The broadband data will support a detailed study of the explosion mechanism, especially the very-long-period signals they emit. It should also help us detect temporal and spatial variability in earthquake mechanisms, which in turn might provide more insights into how variations in gas emissions may be implicated. (GO-081-O)

Global positioning system measurements of crustal motion in Antarctica.
Carol Raymond, Jet Propulsion Laboratory.

Geodesy is the mathematically-grounded science of using measurements to map the positions and shapes of the Earth's surface features. The satellite-based global positioning system (GPS) has revolutionized the techniques and enhanced the accuracy of geodetic work. Work on this project has established a geodetic network in the Transantarctic Mountains of Antarctica to measure both vertical and horizontal crustal velocities.

The vertical crustal velocities measured by GPS reflect the viscoelastic response of the solid Earth to antarctic deglaciation. That data will enable us to evaluate discrepancies between models that describe when antarctic deglaciation probably occurred - either in Late Pleistocene/Early Holocene (about 10,000 years ago) or more recently, in the Late Holocene. These data will also constrain the length of time over which the antarctic ice sheet disintegrated and should provide a reconstruction of its changes. If antarcitc deglaciation occurred later (in the mid-Holocene) we would expect this new, high-precision GPS geodetic system to detect a specific pattern of uplift, near the Transantarctic Mountains.

Horizontal deformation induced by rebound can also be measured; these data help constrain models of present-day changes in antarctic ice mass by tracking how the lithosphere is deformed by ongoing glacial loading and unloading. We are predicting that horizontal component (the lithospheric response to ongoing ice-mass changes) to be an order of magnitude smaller than the vertical (the viscoelastic response to late Pleistocene/Holocene deglaciation). Conversely, that predicted rebound signal should be much larger than the associated tectonic uplift rates. Also, our baseline measurements will cross known fault lines in the Transantarctic Mountains, and may capture co-seismic motion, should an aseismic slip or an earthquake occur.

This autonomous GPS station (AGS) network sends daily data reports to McMurdo Station, and has been designed as a permanent installation that will continue to monitor motion in the region. Advanced processing techniques - such as orbit modeling, troposphere correction, ionosphere correction, and extraction of annual and seasonal solid Earth and ocean tidal signals - have been developed to refine the accuracy of these crustal velocity measurements, especially for the vertical component. (GO-082-O)

TAMSEIS: A broadband seismic experiment to investigate deep continental structure across the east-west antarctic boundary.
Douglas Wiens, Washington University.

Antarctica in shape looks generally like Australia, though half again as large; but beneath its enormous ice sheet lies evidence of its origin. East Antarctica has a bedrock continent-like foundation, while the ice sheet over West Antarctica - a third the area - in fact covers a series of "islands." West Antarctica shares a geologic history with the South American Andes Mountains, the result of plates colliding and subducting. East Antarctica is more like a large coherent chunk that broke free of the supercontinent Gondwanaland and drifted to a new position at the bottom of the world. The boundary between these two regions (with their disparate geologic pedigrees) is called the east-west antarctic boundary, and the crust and upper mantle here reveals many important and interesting distinctions, which tell the basic story of the tectonic development of Antarctica.

This project will collect 3 years worth of seismic measurements - using three different arrays and a total of 44 seismic stations - all geared to evaluating geodynamic models of the evolution of Antarctica that rely on data about the crust and upper mantle. To analyze the data, we will use a variety of proven modeling techniques, including body- and surface-wave tomography, receiver function inversion, and shear-wave splitting analysis.

One basic question is, How were the Transantarctic Mountains formed? Though widely considered a classic example of rift-flank uplift, there is little consensus about the exact uplift mechanism. Many theories, ranging from delayed phase changes to transform-flank uplift, have been proposed. All of these make various assumptions about upper mantle structure beneath and adjacent to the rift-side of the mountain front.

Another focus will be the structure of the east antarctic craton, the highest ice block in the world. Was this anomalous elevation a prime driver in the onset of glaciation there? More to the point, how did it arise? Proposed models include isostatic uplift from thickened crust, anomalously depleted upper mantle, and thermally modified upper mantle, as well as dynamic uplift. How far the old continental lithosphere extends is also uncertain. In particular, it is unknown whether the old lithosphere extends to the western edge of East Antarctica beneath the crustal rocks deformed during the Ross Orogeny (formation).

When completed and analyzed, this comprehensive set of data and theory testing will enable new maps of the variation in crustal thickness, upper mantle structure, anisotropy, and mantle discontinuity topography across the boundary of East and West Antarctica, providing a much enhanced foundation for understanding the geodynamics of the antarctic. (GO-089-O)

(GO-090-P and GO-090-S)
Logistics support for global seismographic network stations at the South Pole and Palmer Stations.
Rhett Butler, Incorporated Research Institution for Seismology.

Seismology, perhaps as much as any other science, is a global enterprise. Seismic waves resulting from earthquakes and other events can only be interpreted through simultaneous measurements at strategic points all over the planet. The measurement and analysis of these seismic waves are not only fundamental for the study of the earthquakes, but also serve as the primary data source for the study of the Earth's interior. To help establish the facilities required for this crucial scientific mission, IRIS (the Incorporated Research Institution for Seismology) was created in 1985.

IRIS is a consortium of universities with research and educational programs in seismology. Ninety-seven universities are currently members, including nearly all U.S. universities that run seismological research programs. Since 1986, IRIS (through a cooperative agreement with the National Science Foundation and in cooperation with the U.S. Geological Survey) has developed and installed the Global Seismographic Network (GSN). The GSN now has about about 135 broadband, digital, high-dynamic-range, seismographic stations around the world, all with real-time communications.

The GSN seismic equipment at Amundsen-Scott South Pole Station and at Palmer Station, Antarctica, were installed jointly by IRIS and ISGS, who together continue to operate and maintain them. The GSN sites in Antarctica are vital to seismic studies of Antarctica and the Southern Hemisphere. The state-of-the-art seismic instrumentation is an intrinsic component of the National Science Foundation effort to advance seismology and Earth science globally. (GO-090-P and GO-091-S)

Paleoceanography of Eocene decapod-rich rocks in Antarctica and southern South America.
Rodney A. Feldman, Kent State University.

Climate is intimately associated with many of the variations found in life on Earth, and nowhere is this more evident than at the extreme high latitudes. Thus fossils often contain clues to paleoclimate and, in turn, to other aspects of peleoecology. Certain fossil mollusks known to contain decapod crustaceans (crabs and lobsters) can be found in Eocene rocks in Antarctica and southern South America. In this project we are targeting the sites rich with these rocks, because the decapods provide a unique, diverse database on biogeographic distribution throughout the high southern latitudes. These mollusk fossils permit us to estimate proxy seasonal temperature at the time - and in the precise habitat - in which the decapods lived, by determining their oxygen isotopic compositions (del-18-O values).

We also hope to refine global paleoceanographic models, and to run a series of oceanic and atmospheric circulation models. The water temperature data derived from analysis of fossil material will be used to select the most reasonable atmospheric and oceanic circulation models, and to evaluate the effects of various gateways to circulation in the antarctic region. Our work should therefore provide two important results. First, detailed information on seasonal variation in water temperature in near-shore environments of the high southern latitudes. Second, refinements on the paleoecological interpretations of the decapods that will be essential for comparing related fossil and extant species. This kind of study provides a unique opportunity for modelers to develop efficient ways to use specified seasonal sea-surface temperature data developed by paleontology. During this project, we will collaborate not only with colleagues at Woods Hole Oceanographic Institution, but also with scientists from the Instituto Antartico Argentino. (GO-093-O)

Permian-Triassic basin history of southern Victoria Land and the Darwin Mountains.
John Isbell, University of Wisconsin.

The Earth is believed to have once consisted of a single land mass, a supercontinent called Pangea, composed of all the continental crust that now makes up the various continental and island surfaces. As tectonic forces began to break up the land mass about 150 million years ago, Gondwanaland was born (as was Laurasia); its southern portion would eventually become Antarctica. Before this split, around 250 million years ago, geologic features extended across what would become separate continents. One of the largest depositional basins was the "Gondwanide foredeep," more than 10,000 kilometers long, extending across the land that would become southern South America, South Africa, the Falkland Islands, Antarctica, and Australia.

Antarctica's central location in this ancient assemblage, between South Africa and Australia, make southern Victoria Land and the Darwin Mountains key areas for testing paleogeographic and paleoclimatic models. Such work will further constrain the paleoenvironmental, tectonic, biotic, and paleogeographic histories of southern Pangea, and provide a unique polar view of the world during an icehouse to greenhouse transition.

Our project is a collaborative sedimentological, palynological, and paleomagnetic study of Permian and Lower Triassic strata in these areas. We will recover paleomagnetic signatures from Permian and Triassic petrified wood, silicified peat, and coal, which were cemented during early diagenesis (the process of undergoing chemical, bioilogical and physical change until metamorphism is reached). Paleopalynological analyses - the study of fossilized microscopic organisms - will provide time control for the succession.

We hope to be able to

determine a Late Paleozoic (as Gondwanaland drifted over the South pole) glacial/deglaciation history for southern Victoria Land and the Darwin Mountains,

document Permian strata to better understand the environments of high-latitude fluvial coal-bearing deposits,

document Triassic lithofacies to better understand high-latitude conditions during the Early-to-Middle Triassic "coal gap" interval,

provide a well-constrained stratigraphic framework for the Permian-to-Lower Triassic succession,

test the diachronous and inversion tectonic models for the Panthalassan Margin of southwestern Pangea, and

construct better paleogeographic models for Gondwanaland by obtaining new Gondwanaland reference poles for the Permian and Triassic. (GO-094-O)

Acquisition and operation of broadband seismograph equipment at Chilean bases in the Antarctic Peninsula region
Douglas Wiens and Gideon P Smith, Washington University.

The present-day tectonics and seismological structure of the Antarctic Peninsula and Scotia Plate region are among the most poorly understood of any location in the world. This region offers a unique and complex geodynamic setting, as illustrated by recent changes in the pattern of volcanism and other tectonic activity. We constitute the U.S. component of an international effort, using a large-scale deployment of broadband seismographs to study the seismotectonics and seismic structure of these regions.

During the 1996-97 field season, broadband seismographs were installed at strategic locations; one on the tip of South America and three more in the South Shetland Islands and on the Antarctic Peninsula. In succeeding years, seven more were added to the network, which has yielded excellent data and some suggestive early results. As the project continues, cumulative data should enhance understanding of the seismicity of the South Shetland Trench, an unusual subduction zone where young lithosphere is subducting very slowly.

The continuing collaboration between Washington University and the Universidad de Chile will contribute important seismological data to the IRIS data center, as well as to other international seismological collaborators. Such mutual exchanges with other national antarctic seismology research programs will accumulate data from a variety of other proprietary broadband stations in the region.

These data will support seismic studies of the upper mantle velocity structure of several complicated tectonic regions in the area, including the South Shetland subduction zone, the Bransfield backarc rift, and diffuse plate boundaries in the areas around Patagonia, the Drake Passage, and along the South Scotia Ridge. Such studies should provide important constraints on the crustal structure beneath the stations; in turn improved structural models will help to pinpoint better locations for future instruments. (GO-97-O)

Neogene-Quaternary volcanic alignments in the Transantarctic Mountains-Ross Sea region.
Terry J. Wilson, Ohio State University.

Plate tectonics has become the reigning paradigm to explain both the evolution and the current dynamics of the Earth. But in addition to the more dramatic movement of the Earth's crustal plates, the crust also contains buoyancy forces that contribute to basic calculations, and distinguishing between these and plate boundary forces is important. The "Antarctic Stress Map Project" (ASMAP) initially will obtain data on these forces from Neogene/Quaternary volcanic vent alignments within the Transantarctic Mountains and adjacent West Antarctic rift system in the Ross Sea region.

We will map the distribution, alignments, and morphologies of volcanic cones and other volcanic features using high-resolution satellite imagery (SPOT, SAR) and aerial photographs. Field tests will assess any structural associations that we can find between faults and volcanic vent alignments. These data will be coupled with existing chronological and petrological information on the volcanic rocks, as well as other dike and fault data, to interpret alignments and to define neotectonic stress states throughout this sector of Antarctica.

We will be able to analyze the stress regime in the context of other ongoing studies of contemporary tectonics and paleo-kinematics of the Transantarctic Mountains rift flank and adjacent rift system. This new stress field data, derived from the unique antarctic setting, will help to constrain the role of plate-boundary and crustal buoyancy forces in actively deforming intraplate regions. (GO-099-O)

Geology and geochronology of the Byrd Glacier discontinuity, Antarctica-A pilot study.
Edmund Stump, Arizona State University.

The East Antarctic Ice Sheet breaches the Transantarctic Mountains by way of a handful outlet glaciers; Byrd Glacier is the largest of these, contributing about a quarter of all the ice moving from there to the Ross Ice Shelf. A major geological discontinuity in the Ross orogen of the Transantarctic Mountains has been discovered here, located beneath Byrd Glacier.

This project continues the probe into this area and structure, by mapping the Byrd Group (Early Cambrian Shackleton Limestone and younger Douglas Conglomerate) for structure, and trying to develop the basis for understanding its kinematic evolution. Another target of interest is Mt. Madison; its geochronology and structural and metamorphic history should be revealed from samples of outcropping, amphibolite-grade metamorphic rocks (Selbourne Marble).

Using snowmobiles and supported by helicopters, we will also collect igneous and high-grade metamorphic rocks (Horney Formation) in the Britannia Range, and will investigate Shackleton Limestone. We hope to determine the thermochronology of the Selbourne Marble, and to further constrain the provenance age of the Douglas Conglomerate.

All rock samples will be returned to for further study. Structural data will be reduced at Arizona State University; metamorphic studies of the Selbourne Marble will be conducted at the University of Siena; and isotopic studies at both the Ohio State University (40Ar/39Ar, Sm-Nd) and the University of Kansas (U-Pb). (GO-116-O)

Antarctic network of unattended broadband integrated seismometers (ANUBIS).
Sridhar Anandakrishnan, University of Alabama.

Despite much attention in recent years, the structure and dynamics of the antarctic crust and the composition and geometry of the mantle are still poorly understood. Seismology remains the primary method for studying these structures, as well as processes in the Earth's deeper asthenosphere, but Antarctica lags behind in the effort to improve global seismic imaging and tomography. On this huge continent, there are only eight broadband seismic observatories. Except for the installation at South Pole, those stations are along the margins of the continent and none are in West Antarctica. By contrast, there are 200 permanent stations worldwide in the Federation of Digital Seismograph Networks (FDSN), and some 1,000 more, in national networks not yet integrated into the FDSN.

We have developed a passive seismic network of 11 long-term broadband seismic stations on the continent itself. Because 98 percent of the continent is ice covered, these stations will be installed at the surface of the ice sheet. The body-wave data thus recorded from regional and teleseismic earthquakes can be analyzed at each station for local crustal thickness, lamination, Poisson's ratio (a measure of crustal composition), crust and mantle anisotropy (a measure of current and former stress regimes), and identification of rift zones and crustal block boundaries. In addition, the data from all stations (including the existing peripheral ones) can be used for seismic tomographic analysis to detail lateral variations in these properties. Four of the stations will be installed at existing automatic geophysical observatory sites (in East Antarctica), which will provide heat and power for the data loggers. The remaining seven stations will be established in West Antarctica and will be powered and heated by wind turbines during the austral winter. (GO-180-O)

High precision GPS survey support.
Bjorn Johns, University NAVSTAR Consortium (UNAVCO).

UNAVCO provides year-round support for scientific applications of the Global Positioning System (GPS) to the National Science Foundation's Office of Polar Programs (NSF/OPP) Antarctic Program. This support includes pre-season planning, field support, and post-season follow-up, as well as development work for supporting new applications. UNAVCO maintains a "satellite" facility at McMurdo Station during the austral summer research season, providing a full range of support services including geodetic GPS equipment, training, project planning, field support, technical consultation, data processing, and data archiving.

UNAVCO also operates a community differential GPS (DGPS) base station that covers McMurdo Sound and Taylor Valley, provides maintenance support to the MCM4 continuous GPS station as contractual support to the NASA GPS Global Network (GGN), and supports remote continuous GPS stations for scientific investigations.

Using GPS, vector baselines between receivers separated by 100 kilometers or more are routinely measured to within 1 centimeter (that is, 100 parts per billion). UNAVCO is also able to support researchers who are investigating global, regional, and local crustal motions where maximum accuracy (in the millimeter range) of baseline measurement is required. GPS measurements using portable equipment can be completed in a few hours or less. Such expediency lends itself to research applications in global plate tectonics, earthquake mechanics, volcano monitoring, and regional tectonics. (GO-295-O)

The young marginal basin as a key to understanding the rift-drift transition and andean orogenesis: OBS refraction profiling for crustal structure in Bransfield Strait.
James A Austin, Gail L Christeson, Ian W Dalziel, and Yosio Nakamura; U. of Texas Austin.

Bransfield Strait (in the northern Antarctic Peninsula) is one of a small number of modern basins that may be critical for understanding ancient mountain-building processes. The Strait is an actively-extending marginal basin in the far southeast Pacific, situated in an inactive volcanic arc between the Antarctic Peninsula and the South Shetland Islands. Widespread crustal extension, accompanied by volcanism along the Strait's axis, may be associated with slow underthrusting of oceanic crust at the South Shetland Trench.

Some 140 million years ago (during the Jurassic/Early Cretaceous), similar "back-arc" extension is known to have occurred along the entire Pacific margin of the supercontinent known as Gondwanaland. This area has become western South America and West Antarctica. Then, some 100 million years ago, mid-Cretaceous deformation of these basins initiated the uplift that produced the Andes. Thus, scientists believe that elucidating the deep structure and evolution of Bransfield rift could provide a model of crustal precursor activity that will more fully describe the early evolution of this globally important mountain chain.

Years of international earth sciences research in Bransfield Strait have produced consensus on important aspects of its geologic environment. It is a young rift (probably about 4 million years old) in pre-existing Antarctic Peninsula crust; continued stretching of this crust results in complex fault patterns and associated volcanism. The volcanism, high heat flow, and mapped crustal trends are all consistent with the basin's continuing evolution as a rift. The volcanism occurring there is recent and continues to occur along a "neovolcanic" zone centralized along the basin's axis (another point of consensus). Multichannel seismic data collected aboard R/V Maurice Ewing in 1991 illustrate the following basin-wide characteristics of Bransfield Strait -

widespread extension and faulting,

the rise of crustal diapirs or domes associated with flower-shaped normal-fault structures, and

a complicated system of fault-bounded segments across the strike.

The geophysical evidence also suggests northeast-to-southwest propagation of the rift, with initial crustal inflation/doming followed by deflation/subsidence, volcanism, and extension along normal faults.

Although Bransfield Strait exhibits geophysical and geologic evidence for extension and volcanism, continental crust fragmentation in this "back-arc" basin is still underway and has yet to generate ocean crust. Instead, the Bransfield rift lies near the critical area that marks the transition from intracontinental rifting to seafloor-spreading. Because the basin is asymmetric and appears to manifest shallow intracrustal detachment faulting, it is near the edge of the spectrum of models that explain how continents break up. As such, the region is an excellent "natural lab" for studying the diverse processes that form continental margins. Thus a couple of significant questions arise: What stage of evolution is the Bransfield rift experiencing? Does it provide a basis for constructing models of Andean mountain-building? The answers are to be found by defining Bransfield rift's deep crustal structure. Our project begins this task by collecting and analyzing high-quality, high-density, ocean-bottom seismometer (OBS) profiles, both along and across the Strait's strike. The scientific objectives are to

develop a detailed seismic velocity model for this rift;

calibrate velocity structure and crustal thickness changes associated with presumed northeast-to-southwest rift propagation, as deduced from the multichannel seismic interpretations;

document the degree to which deep velocity structure corresponds to along- and across-strike crustal segmentation; and

assess structural relationships between the South Shetland Islands "arc" and Bransfield rift.

The OBS data we expect to collect will also be integrated with other geophysical explorations of the region (such as both Ewing profiles). This piece of the puzzle will complement ongoing deep seismic analysis of Antarctic Peninsula crust to the southwest, as well as additional OBS monitoring for deep earthquakes. Ultimately, the complex plate tectonic evolution of this region may be clarified. (GO-306-O)

Understanding the boundary conditions of the Lake Vostok evnironmen: A site survey for future work.
Robin Bell, Lamont-Doherty Earth Observatory.

Antarctica is often referred to as a hostile environment, but many scientists welcome the unusual and extreme conditions to be found there as a pathway to key insights into the development of Earth and other bodies in the solar system. Looking beneath the ice, for example, can reveal lakes with oligotrophic environments - ecosystems deficient in plant nutrients, and which have extremely high levels of dissolved oxygen. Study of such subglacial systems could reveal:

the processes associated with rapid evolutionary radiation after the extensive Neoproterozoic glaciations;

the overall carbon cycle through glacial and interglacial periods; and

the possible adaptations organisms may require to thrive in environments like Europa, the ice- covered moon of Jupiter.

Antarctica's ice sheets, several kilometers thick, sit atop many of these subglacial lakes - over 70 have been identified thus far. Of these, Lake Vostok is large enough to be clearly seen from space with satellite altimetry. Though about the area of Lake Ontario, Vostok has much more water, with depths up to 600 meters. The overlying ice sheet is a kind of conveyer belt, continually delivering new water, nutrients, gas hydrates, sediments, and microbes as it flows across the lake. These lakes are not abiotic and sterile as might be presumed but generally support mosses, algae and bacteria.

This project undertakes a kind of frontier exploration by air of Lake Vostok; we hope to determine the fundamental boundary conditions for this subglacial lake as an essential first step toward understanding the physical processes to be found within its waters. We will conduct an aerogeophysical survey, with gravity, magnetic, laser-altimetry, and ice-penetrating radar studies, refining and testing methods first in other lakes. Then we expect to compile a basic set of ice-surface elevation, subglacial topography, gravity and magnetic anomaly maps for the water cavity; and also to estimate the thickness of the sediments beneath the lake from magnetic data.

These maps will become tools to distinguish between two competing models for the geologic origin of the lake - either, the lake is an active tectonic rift, like Lake Baikal; or the lake is the result of glacial scouring. Any extensional rift can be easily identified with our aerogeophysical survey.

When we interpret the airborne geophysical survey with geologic models, we should have the first geological constraints of the interior of the east antarctic continent based on modern data. And biology will come into play as well, since the underlying geology will influence the ecosystem within the lake. For example, one of the critical issues for the subglacial ecosystem of Lake Vostok will be the flux of nutrients. Based on the distance between distinctive internal layers observed on the radar data, we should be able to estimate regions of freezing and melting. Such basic boundary conditions are crucial as a guide for any future international effort to explore the lake in situ. And these results will also improve our understanding of east antarctic geologic structures more generally. (GS-098-A)

Support Office for Aerogeophysical Research (SOAR).
D.D. Blankenship, D.L. Morse, I.W.D. Dalziel and J.W. Holt. University of Texas at Austin.

Since 1994, the Support Office for Aerogeophysical Research (SOAR) has operated and maintained an aerogeophysical instrument package (aboard a de Havilland Twin Otter aircraft) that consists of an ice-penetrating radar sounder, a laser altimeter, a gravimeter and a magnetometer. All are tightly integrated with one another, as well as with the aircraft's avionics and power packages. In addition, we maintain an array of aircraft and ground-based GPS receivers to support kinematic differential positioning using carrier-phase observations. SOAR activities have included

developing aerogeophysical research projects with NSF/OPP investigators;

upgrading the aerogeophysical instrumentation package to accommodate new science projects and advances in technology;

fielding this instrument package to accomplish SOAR-developed projects; and

managing, reducing, and analyzing the acquired aerogeophysical data.

Since its inception, SOAR has flown 377 missions during six field campaigns over a six-year period, and surveyed approximately 200,000 line-kilometers over both East and West Antarctica. During the 2000-2001 austral summer the University of Texas at Austin will conduct an aerogeophysical campaign to accomplish surveys for two SOAR-developed projects -

"Understanding the boundary conditions of the Lake Vostok environment: A site survey for future studies" (Bell and Studinger, LDEO, GS-098-A); and

"Seismic investivation of the deep continental structure across the east-west antarctic boundary" (Weins, Washington University, and Anandakrishnan, University of Alabama, GO-089-O).

We will configure and test the survey aircraft in McMurdo, conduct survey flights from an NSF-supported base adjacent to the Lake Vostok drilling camp, and briefly occupy one or two remote bases on the East Antarctic Ice Sheet. We will reduce and distill these aerogeophysical data to produce profiles and maps of surface elevation, bed elevation, gravity and magnetic field intensity; these images will be used not only by these investigators, but will be published and released to national geophysical and glaciological data centers. (GS-098-O)

Pagodroma Group stratigraphy and paleontology: Participation in ANARE 2000- 2001.
David Harwood, University of Nebraska.

The East Antarctic Ice Sheet covers an enormous area, and contains Lambert Glacier, the largest glacier in the world. Over 40 kilometers wide and some 2500 meters deep in places, Lambert Glacier makes a 400-kilometer journey across East Antarctica past the Prince Charles Mountains. A part of this range, the Padroma Group, bears strata with marine fossils left behind in ancient times as the ice sheet drains into Prydz Bay some 300 kilometers away.

Russian and Australian scientists have been exploring this formation, and this investigator teams up with the Australian National Antarctic Research Expedition (ANARE) to try to use sedimentary deposits and other geological evidence to reconstruct how the ice sheet may have varied, especially over the last 20 million years (the Upper Tertiary epochs of the Miocene and the Pliocene are often referred to collectively as Neogene time). Ice sheet history is largely a record of advances and retreats. Marine microfossil data indicates open water at some point and therefore a relative retreat; advance of the ice sheet can be deduced from erosional and ice-grounding features evident in the strata.

Recent scientific debate about the Neogene history of antarctic glaciation use the age of the Sirius Group as a baseline, deduced from marine diatoms found in these strata. Preliminary results from coeval strata of the Pagodroma Group suggest there may have been significant variation in the volume of the East Antarctic Ice Sheet during the Late Neogene. Some have held that these marine microfossils could have been driven and delivered by the wind, but the abundance of diatoms in some intervals of the Pagodroma Group (up to 3.5 percent biogenic silica) that we expect to verify, and the stratigraphic position of in situ marine diatomaceous laminites should reaffirm the ice sheet retreat hypothesis.

Documenting such stratigraphy in the field and verifying the paleontological content in the laboratory are essential for placing the disparate deposits into a temporal and stratigraphic framework. Once done, this area's ice sheet history can then be correlated with other regions in the Prince Charles Mountains and also with other areas of Antarctica.

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