5. SCIENCE PLAN
In this revised Science and Implementation Plan, the key scientific questions
identified in the original plan (NASA Conference Publication 3115, Volume
1) are reexamined. Within some disciplines, the questions have been revised
to reflect recent discoveries. As before, broad tasks required to answer
those key questions and specific investigations to carry out those tasks
The numerous feedbacks and interactions that are part of the Antarctic environment
will necessitate many multidisciplinary investigations. Assignment of such
investigations here to any single discipline is arbitrary and not intended
to preclude interdisciplinary collaborations. In some cases, joint investigations
are mentioned in more than one discipline.
5.1.1. Ice Dynamics
Ice flow determines the rate at which snow that falls on an ice sheet is
returned to the oceans. Major changes in mass balance can only occur by
changes in ice flow. Flow by internally deformed ice is reasonably well
understood, but flow complexities introduced by rapid basal sliding and
anisotropic crystal orientations are not. Both occur in West Antarctica
where numerous ice streams, whose flow is controlled by these factors, dominate
the dynamics of the ice sheet. Rapid ice flow makes ice-sheet collapse possible.
It also can complicate interpretation of ice-core paleoclimate records.
1) What is the present distribution of surface-elevation change, and what
is the net mass balance of the West Antarctic ice sheet?
Net mass balance, the difference between mass gain and mass loss, is the
most basic measure of ice-sheet health. Local net mass balances indicate
the pattern of mass redistribution and can assist in interpreting the cause
of any imbalances. There are two principal techniques used to measure mass
balance: direct measurement of elevation change, and calculation of thickness
change based on measured volume fluxes.
Very precise repeat measurements of elevation can be done at isolated points
with either GPS positioning or conventional surveying (where fixed points
are visible), while satellite altimetry provides the broad spatial coverage
necessary to assess the general behavior of large ice sheets. GPS control
sites have been established on the West Antarctic ice sheet at Byrd Station
and on ice stream B. Coverage of West Antarctica with a radar altimeter
began in 1992 with the ERS-1 satellite but data are limited to the area
north of 81.5¡S. Thus, only one control site is now in satellite view. Reduction
and analysis of the altimetry data in the U.S. will most probably be funded
by NASA. Because of the large footprint of the radar altimeter and failure
of the precise orbit determination system, it is expected that at least
a 10-year data set will be required before reliable indications of regional
elevation change are obtained. This means the first return from these data
will not arrive until well into the next century. Radar altimeter data will
be compared with thickness changes at Byrd Station and calculated in limited
regions by other methods (see below). In many areas of West Antarctica,
these data will provide new measurements and will be useful in directing
future WAIS research.
Laser altimeters provide the same capability to directly measure elevation
change, but their smaller footprint and expected greater precision in satellite
position offer a significant enhancement to this technique. Laser altimetry
has been accomplished in Antarctica from a Twin Otter. NSF/OPP has made
this facility (SOAR) available to USAP investigators. Precision of repeat
elevation measurements is limited until precise GPS positioning can be used
to navigate the aircraft in real-time. A scanning laser altimeter avoids
this limitation and has been successfully operated in Greenland, however
the aircraft is not suitable for Antarctic operation at this time. NASA's
Geoscience Laser Altimeter System (GLAS) is scheduled to be launched into
space in 2001, and will provide dense, continuous coverage to 87¡S. Acceleration
of the launch schedule could make GLAS data relevant for WAIS.
A precaution that must be observed with elevation measurements is that they
are not a direct measure of mass change. Changes in firn density, or changes
in bed elevation (due to either changing till thickness or tectonic motions)
also cause surface elevation change. Thus, geophysical, geological and glaciological
studies must accompany surface elevation measurements to interpret the degree
to which such changes represent changes in ice mass.
The second method for calculating net mass balance sums mass fluxes into
and out of any given region to calculate the rate of change of ice mass
contained within the region. This method avoids the difficulty with elevation
measurements just mentioned, but introduces other problems-primarily an
increased reliance on field data which often are difficult to collect. This
method has already been applied in many areas of West Antarctica and provides
the basis for all that we currently know about thickening and thinning of
its ice sheet.
The basic data required are ice thickness and velocity across vertical sections
in the ice, accumulation at the upper surface and melt or accretion at the
base. Each parameter is discussed below.
Velocity data can be obtained by a variety of approaches: conventional surveys;
satellite surveying techniques (e.g., GPS); aerial photogrammetry; and,
most recently, repeat satellite imagery. Each approach has limitations.
The first three require a surface field party. In addition, conventional
surveys require fixed points (which are rare) and photogrammetry requires
that a network of control photo-targets be established. Satellite imagery
techniques have proven to be as accurate as traditional methods and provide
detailed data sets in regions where surface features are plentiful. Fortuitously,
these tend to be the regions of active flow with crevasses that would hamper
the mobility of surface field groups. Thus, there is a complementary match
between regions requiring field work and regions where surface motion can
be measured from space. Landsat and SPOT have been the primary sources of
satellite imagery. Near the turn of the century, ASTER will also become
SAR interferometry holds the potential for remotely measuring surface motion
in any area. The technique produces a detailed field of relative motion
(in the direction to the satellite). Offsetting the power of this technique
are restrictions including satellite coverage and spatial and temporal phase
coherence of the radar backscatter. Currently, the coverage of the ERS-1
SAR is limited to north of 78¡S. Radarsat, scheduled for launch in late
1995, will extend routine coverage to 79.5¡S with a brief period when the
entire Antarctic will be viewed.
The major error source when applying the mass balance method to ice stream
B is the uncertainty in the accumulation rate. The majority of surface accumulation
data come from analysis of shallow surface cores where peaks in radioactivity
indicate stratigraphic horizons corresponding to the years 1955 and 1964,
when there was an increase in the testing of nuclear bombs in the atmosphere.
Even the sparse measurements of accumulation rates available reveal that
snow accumulation is highest along the coast, but important spatial variations
are missed by any in-situ sampling strategy. Accumulation rates in most
West Antarctic areas are known only roughly. Large local variations discovered
in the past make it imperative that improvements be made to this data set.
Renewed interest in the utility of passive microwave imagery, combined with
ground truth and satellite temperature data, may significantly reduce the
errors of accumulation rate determinations over most West Antarctic regions.
These analyses, however, must conform to the new meteorological understandings
of the interannual and spatial characteristics of storm patterns which determine
when, where, and how much moisture is delivered to the ice sheet. A fuller
discussion of this aspect appears in the Meteorology section (Section 5.2).
Ice thickness data are collected by radar soundings. Airborne surveys are
the most time- and cost-efficient means of collecting field data over large
areas, but often these rapid surveys are not capable of resolving internal
layers that are proving to be extremely valuable indicators of past dynamic
changes in ice flow. The utilization of smaller aircraft based remotely
in Antarctica has further increased the ability to cover remote areas. Recent
field seasons have seen a Twin Otter aircraft log over 25,000 flight kilometers
of radar sounding lines. No method of obtaining these data from satellites
seems feasible at this time.
The basal mass gain or loss is concentrated under the ice shelves, where
it can be substantially positive or negative. This is a primary concern
of the WAIS oceanographers and is discussed more in the Oceanography section
There is no single preferred method for determining the net mass balance
of the entire West Antarctic ice sheet. Remote sensing data can provide
many, but not all of the necessary parameters. A cross-checking strategy
employing both the elevation change method and the mass flux method should
be pursued. A few surface control points should be maintained with repeated
GPS measurements to confirm the satellite altimetry results. Landsat TM
images should be acquired as early as possible to determine velocities along
the entire perimeter of West Antarctica. The USGS already holds many of
the necessary visible images as part of an image acquisition and analysis
program of major Antarctic outlet glaciers. Additions to this archive may
be discovered from a pre-1972 collection of declassified photographs.
Ice thicknesses will need to be measured by airborne radar sounding at the
locations where velocities are measured and as close to the grounding lines
as possible. When measured inland of the grounding line, mass imbalance
converts directly to sea-level change. Grounding lines can be determined
from the imagery and are the most obvious place to measure discharge flux
because surface velocities approximate the depth-averaged velocity and basal
accumulation is minimal upstream of the grounding line. These radar sounding
flights would cover approximately 3000 km and be located predominantly along
the Amundsen and Bellingshausen coasts. Additional flights across the heads
of all ice streams would permit separate calculations of the mass balances
of the inland area and ice-stream area of West Antarctica. These flights
would add an additional 3000 km of flightlines.
Significant additions to field measurements of accumulation rates of the
West Antarctica ice sheet would require a major commitment of resources
and is not advisable. More prudent is pursuit of the passive microwave data
set meshed with meteorological studies. This approach may highlight specific
areas where field data would be particularly helpful. Additions to the accumulation-rate
data base along the highest ice divides of West Antarctica will come from
ITASE cores (see Section 6.2.4.). A new mass flux calculation will permit
a major improvement to the estimation of the net mass balance of West Antarctica.
Although WAIS is focused on the West Antarctic ice sheet, reconnaissance
of other marine ice-sheet regions should not be overlooked. Wilkes Land
in East Antarctica is such a region (see Map). Positioned farther north
than most of West Antarctica, it is an excellent region for a program of
monitoring surface elevation using satellite altimetry.
2) What are the physical controls on the motion and areal extent of ice
In order to answer this question, four distinct aspects of ice-stream mechanics
need to be understood:
- rapid basal motion and its effect on determining the positions of ice
- shear-margin mechanics and its effect on the lateral extent of ice streams;
- onset of stream flow and its effect on the slower moving inland ice; and
- ice-stream buttressing by ice shelves and its effect on grounding line
a) Basal Mechanics
Recent work has shown that physical conditions at the base of ice stream
B are favorable for the occurrence of rapid basal motion either by basal
sliding or by deformation of subsole till. The presence of deformable subsole
till in a layer a few meters thick has been demonstrated. This till layer
is spatially variable in thickness. The distribution of basal drag also
varies spatially from near zero in well lubricated areas to near the plastic
limit in other areas. Active till deformation accommodating ice-stream motion
is highly probable.
To formulate the mechanics of rapid basal motion so that a numerical model
can adequately predict ice-stream behavior, the following research tasks
need to be accomplished. (1) The basal till flow law, the basal sliding
law, and the individual contributions of basal till deformation and basal
sliding to ice-stream motion need to be determined observationally at several
representative locations in the ice-stream system. (2) The thickness of
the till layer needs to be measured and mapped throughout West Antarctica
to the extent feasible. (3) Hydraulic characteristics of the basal water
system under the ice streams and in the transition area at the ice-stream
head need to be determined and the physical control(s) on these characteristics
must be ascertained. (4) The results of (1) through (3) need to be integrated
into a quantitative model of the basal mechanics of ice streams.
Task (1) requires borehole geophysical work at the base of the ice streams,
combined with laboratory testing of till samples obtained by coring. Also
required at each site are measurements quantifying the current dynamics.
These measurements must include the surface topography and velocity fields
along with the internal layering. Task (2) requires high-resolution seismic
profiling, combined with spot checks of till thickness at borehole sites.
Task (3) addresses the key controlling variable in ice-stream mechanics,
the basal water pressure; because this parameter is not detectable by remote-sensing
methods, borehole geophysics is again required. Seismic monitoring of natural
basal events provides clues to Task (3) and points to key study areas for
Task (2). Task (4) is mainly interpretative and computational.
Tasks (1) and (3) have been essentially completed at one site. Remaining
sites can be completed at the rate of one per year, so that seven sites
can be completed by the end of the period discussed here. This should provide
an adequate sampling of different conditions. Task (2) is best done by running
seismic lines out from borehole sites. Additional geographic coverage can
be obtained using initial results to guide the selection of sites. Tasks
(1) through (3) require substantial LC-130 support. Once on-site, surface
transport can be used to move the drill rig distances of up to 20 kilometers,
as may be needed in the vicinity of some sites. Task (4) needs ongoing attention
throughout the program, as field data accumulate.
b) Shear Margin Mechanics
It is now recognized that the resistive drag at the ice-stream margins is
as important as the basal drag component. In areas with particularly well
lubricated beds, the side-drag completely determines the ice stream velocity.
Also, the mechanics of the marginal shear zones determines the positions
of the lateral edges of the ice stream and, therefore, the ice-stream width,
discharge and mass balance.
To get the information needed to quantify these aspects of shear zone mechanics
and to incorporate them into an overall model of ice-stream behavior, the
following investigations are needed: (1) mapping of shear zones by satellite
imagery, comparative studies of different shear zones based on the imagery,
and search for evidence of past or current changes in position of the zones;
(2) search for relations between location of margins and features of basal
topography; (3) ground-based study of selected shear margins to reveal detailed
flow patterns, the continuity of internal layers across the margins, and
whether the shear margins are currently migrating; (4) determination of
the flow law of ice in the shear zones, which is thought to differ from
the standard flow law (ice in the shear zone being weaker); (5) formulation
of detailed marginal-shear-zone mechanics, including the patterns of crevassing
and the physical mechanism by which the lateral position of the marginal
shear zones is controlled.
Task (1) will use satellite imagery collected by Landsat (north of 82.6¡S)
and SPOT, and eventually ASTER farther south. Lower resolution AVHRR imagery
also is useful. Task (2) requires radar sounding in addition to imagery.
Task (3) can be carried out with standard flow-velocity measuring techniques
using strain grids plus GPS surveying at selected points. Ground-based radio-echo
sounding is required to optimize the ability to follow internal layers into
areas of disturbed ice. Task (4) requires ice coring to retrieve deep ice
samples from the shear zones for mechanical testing (flow-law determination),
and for structural and fabric studies aimed at revealing the mechanism of
anomalous rheology. Task (5) involves computational interpretation and hopefully,
the development of a quantitative theory of marginal shear zones.
The imagery required for (1) will require only a modest number of SPOT images
(5-10) to augment the larger collection required for the net mass balance
and basal mechanics studies already mentioned. For (2), more detailed radio-echo
sounding data will be needed at locations where anomalous marginal features
appear on imagery. A number of locations on ice streams D and E have already
been identified and will be included in the radio-echo sounding flights
already described. Tasks (3) and (4) require dedicated field camps at the
margin. A minimum of two sites would be required-one site adjacent to ice
stream B has already been completed.
c) Onset Mechanics
The initiation zone of ice streams must, by continuity, experience intense
stretching due to the acceleration of ice as it makes a transition from
slow flow to rapid flow. Thinning and headward migration of the onset area
are probable. Understanding the conditions of this transition region are
central to the ability to model the dynamic behavior of marine ice sheets.
A basic challenge in studying this phenomenon is identifying its location.
Satellite images reveal a spectrum of onset signatures. At one end are gradual
transitions where flowbanding is well developed upstream of any tensile
crevassing. At the other extreme is a sudden onset with long tensile crevasses
extending across the entire stream width.
Specific tasks that must be undertaken to address the onset phenomenon are:
(1) surface velocity measurements to identify the specific areas of acceleration;
(2) characterization of the basal, lateral and internal ice upstream, within,
and downstream of onset; (3) direct sampling of bed and water regimes in
these areas; and (4) quantification of this process for numerical simulations.
Task (1) requires a broad-scale survey to determine the location(s) of maximum
stretching. Visible imagery can guide the positioning of such a survey.
Task (2) will begin with airborne radio-echo sounding, but must include
ground-based surveys (both passive and active seismic and radio-echo sounding)
once the critical onset areas are located. These studies will further refine
the location where basal conditions (e.g., till thickness and dilatancy)
occur. Drillers can then efficiently chose specific sites to undertake Task
(3). Incorporation of all these field data into a physical model will complete
Given the variety of onset areas seen in imagery, a "typical" site may not
exist-a minimum of two sites should be studied. Landsat imagery has been
used to plan the anticipated beginning of the first onset study on ice stream
D. Airborne radar flights are also planned. SAR interferometry would be
of particular advantage for determining the velocity field in a more crevassed
d) Buttressing Mechanics
The strength of the connection between the ocean and the ice sheet rests
on how effectively resistance to ice-shelf flow is transmitted upstream
to the grounded ice. For many years, the buttressing effect of ice shelves
has been held to be the primary resistance to ice-sheet collapse. Detailed
measurements now have been made that show that the mechanical effect of
Crary Ice Rise, one of the largest ice-shelf features, is felt for only
a relatively short distance up ice stream B. Nevertheless, the response
behavior of the grounding line area is strongly dependent upon ice-shelf
buttressing and it is in the grounding-line area that the marine-ice-sheet
instability occurs. Evidence that current growth of Crary Ice Rise is having
a large impact on the regional velocity field and may be reducing the discharge
of ice stream B, supports this view. Further, satellite imagery has revealed
contorted features that indicate strongly transient flow.
WAIS can accomplish an improved understanding of buttressing mechanics through
the following investigations: (1) monitoring the changing deformation in
this area; (2) developing mechanical models that adequately represent the
flow of ice shelves past ice rises and over ice rumples; (3) mapping the
full set of contorted flowbands providing a history of the flow on the ice
shelf; and (4) incorporating the models of (2) into simulations that adequately
describe the history indicated by (3).
Task (1) can be achieved primarily through periodic acquisition of SPOT
imagery in critical areas and through surface field teams remeasuring existing
stations left from previous years. Task (2) is an interpretative task building
on the data of (1). Task (3) again relies on satellite imagery and can make
good use of lower resolution AVHRR imagery, while (4) is computational in
Crary Ice Rise, Steershead Crevasses, Roosevelt Island and Minna Bluff/Cape
Crozier are the major sites of buttressing on the Ross Ice Shelf. Of these,
only Crary Ice Rise has received intensive study. As monitoring of this
location is continued, the other three sites, along with initial studies
along the coastlines of the Amundsen and Bellingshausen Seas should be undertaken.
SAR imagery might prove especially useful along the northern coasts, as
cloud cover is pervasive.
3) How has the configuration of West Antarctica changed and how will the
volume of grounded ice change over the next decades to several centuries?
The West Antarctic ice sheet is expected to change in the future because
it has changed in the past. Some signatures and remnant effects of past
behavior still exist in the ice. These features are seen in the imagery
and within the internal layering of the ice sheet. Once identified and understood,
they can be separated from the ice-mechanical investigations detailed above
and used to strengthen the development of time-dependent numerical models.
The goal of these models is to adequately incorporate the physical processes
and interactions identified by other WAIS investigations. Such models provide
the only means to predict future behavior of the West Antarctic. The models
should include heat flow to define material properties throughout the ice
column and subglacial stratum, and meteorological calculations to account
for varying accumulation rates as the ice-sheet configuration changes with
time. No such completely coupled models yet exist.
These models must be validated by demonstrating that they can represent
known past configurations as well as depict transient events identified
by the analyses of field data. These data, in combination with satellite
data will provide the initial conditions, the boundary conditions, and the
ice-sheet configurations for such validation experiments. Field work supports
the imagery-based hypothesis that older ice streams existed, following different
courses. This discovery increases the challenge to both data collection
and model performance. Appropriate input to the model might span the period
from the last glacial maximum to the present. To be credible, any model
must be able to accurately reproduce this period.
With a validated model, predictions about the future behavior of the ice
sheet and its effects on sea level will be made. Again, initial conditions
(the present configuration and net mass balance) and environmental data
(accumulation rate, oceanic circulation) will be required. In the absence
of a model capable of internally updating these environmental parameters,
a series of scenarios might be provided by the relevant experts to bracket
adequately the ranges of possible future situations. Model predictions for
these various scenarios will encompass the range of possible future ice-sheet
configurations and their effects on global sea level. Model runs that bracket
likely ice-sheet response are desirable to address socio-political concerns
centered on issues such as greenhouse warming, where even the best global
climate models can only indicate a range of probable future climates.
This task is predominantly computational. Satellite imagery and radio-echo
sounding provide the historical configurations. The development of suitably
dynamic models is complex and should not be postponed while awaiting data
collection and analysis. Enough is already known about possible ice dynamic
mechanisms that fruitful model development is possible. Also, because of
the eventual complexity of such a model and the variety of numerical methods
that might be employed within the model, it is advisable that this task
be undertaken by more than a single investigator or group.
5.1.2. Ice Cores
Ice cores provide unique records of climate and climate change. Long and
high-resolution records of atmospheric composition and chemical loadings
are key to understanding global climate change and biogeochemical cycles.
Local records of snow accumulation and temperature provide "weather stations"
for climate-change studies, as well as providing the boundary conditions
for ice-flow and ice-stability models. The physical properties of ice cores
and boreholes open a window into the mechanics of ice flow and the holes
provide access to the bed beneath, further constraining ice-flow models.
Ice coring can date internal layers detected by radio-echo sounding, providing
a chronology that further enhances the use of these natural markers to determine
the history of ice dynamics. In short, ice-dynamical studies and atmospheric
studies are critical to the interpretation of ice cores, just as ice cores
are critical to understanding atmospheric and ice-flow processes.
1) What is the history of ice-sheet forcing and response?
Occurrence of Eemian/Sangamonian/5e ice in the base of the ice core would
resolve the long-standing debate about whether the West Antarctic ice sheet
collapsed at that time and would be a major advance toward assessing the
potential for future West Antarctic ice- sheet collapse. (Unfortunately,
lack of such ice does not confirm collapse, as old ice may have been lost
to basal melting or near-basal mixing processes.) Dating can be accomplished
through counting annual layers, correlating isotopic or other records to
dated sub-ice, continental shelf and deep-sea sedimentary records, through
ice-flow modeling, or through newer methods utilizing cosmogenic isotopes.
Spatial extension of the stratigraphy at such a location, through radar
sounding of the surrounding area, would enlarge the region where ice could
be inferred to have existed during the Sangamon. The temperature profile
in the ice must be measured as well as the geothermal gradient and the thermal
properties of the underlying bed to determine the melting rate of basal
The ice core contains a record of snow accumulation (annual layer thicknesses,
corrected for ice-flow thinning), and of temperature (stable-isotopic ratios,
borehole temperature). Along with sea level, these are the major forcings
of ice-sheet changes, which must be known over the most recent glacial cycle
to allow modeling of the current and future ice-sheet behavior. The history
of temperature/accumulation-rate covariation may provide important information
on the likely accumulation-rate response to anthropogenic warming, and the
likely effect on sea level.
Measurements of the total gas content of the air trapped in the cores provide
a measure of atmospheric pressure that existed when the air cavities were
sealed. Assuming stable atmospheric circulation patterns, this pressure
can be converted to a surface elevation. Ambiguity associated with this
assumption can be reduced by sampling the ice sheet at a number of locations.
More sites provide a valuable measure of the pattern of elevation change
as well as less ambiguity for each measurement. Sampling is desired in central
regions and in more dynamic, marginal areas. A record of elevation since
the last glacial maximum can be obtained by drilling to only a few hundred
meters depth in some places, so it is feasible to collect several of these
cores without expending major logistic resources. The ice-core record of
former surface elevations will be compared with the geological record obtained
from nunataks and coastal mountains (see Section 5.4.1).
2) What is the history of regional climatic conditions?
The chemical and particulate records in ice cores provide a multi-dimensional
view of regional climate change. Variations in biogenic productivity in
adjacent oceans (MSA, iodine), atmospheric processes (nitrate), wind speed
(sea salt), continental aridity (crustal aerosol), etc. can be determined
from ice cores. High-resolution data are especially valuable. An accumulation-rate
record allows changes in atmospheric loading to be distinguished from changes
in dilution by water flux, thus increasing the value of the chemical and
particulate records. The regional and global record of volcanism is especially
interesting, both as a climatic forcing and as a potential high-resolution
tool for interhemispheric and ice-core/marine-core correlations. By identifying
and characterizing the surrounding particulate source regions, the patterns
and changes of atmospheric circulation can be inferred from the core analyses,
making them useful for testing the predictions of atmospheric numerical
3) What is the high-resolution history of globally mixed gases?
Questions remain about the effect of high calcium levels in Greenlandic
ice on the CO2 record recovered. The Antarctic record is not suspect, but
existing deep Antarctic cores lack the high resolution of the Greenlandic
records. A deep, high-resolution Antarctic core is needed to learn whether
rapid fluctuations have occurred in CO2. Such a core also will allow confirmation
of other Greenlandic measurements. The high-resolution records of CH4, delta18O
of O2, or other gases will allow accurate correlation of the gas records
of the cores between hemispheres.
4) What is the physical nature of the ice and its substrate and have variations
in these properties occurred?
Crystal size, fabric and temperature all influence the effective viscosity
of the ice and represent the integrated deformation and temperature history
of the ice. These data are useful in constraining flow models that attempt
to reproduce the history of the ice sheet. Electrical properties are perhaps
the best data to correlate with the existence of internal radar-reflecting
layers which are believed to represent isochrones. The ability to date internal
layers at a core site allows core dating to be extended to other regions
if continuous internal layers can be followed.
Many of the most important data at a core site are collected once the core
is removed, and many of these data will be directly relevant to other disciplines
working within WAIS. Basal debris-laden ice or subglacial unconsolidated
sediments may indicate greatly accelerated flow and also may provide key
historical data through identification of microfossils, exposure-age dating
of the rocks, or other indicators. Repeat inclinometry (for deformation
and mass-balance calculations), sonic logging (for ice fabrics), and basal
water pressure all should be measured. To assist the geologists, subglacial
coring should be undertaken. Geothermal flux, which must be measured in
the bed to obtain accurate results if the ice is wet-based or has been wet
recently, is one of the important controls on ice flow, although one that
is unlikely to change rapidly over time, except possibly close to volcanoes.
5) What is the history of solar-terrestrial and extraterrestrial interactions?
Cosmogenic isotopes including 14C, 10Be, in ice cores are largely controlled
by processes beyond the Earth's atmosphere. High-resolution records of cosmogenic
isotopic concentrations and snow accumulation allow calculation of fluxes,
and partitioning of variations between changes in production (extraterrestrial
controls) and deposition (Earth climate control). If time-series analyses
of various ice-core parameters recover solar periodicities, these indicate
the strength of solar-terrestrial interactions.
6) Precisely where should the drilling occur and what is the most cost-effective
Site-selection activities (aerogeophysics, ground glaciology and radio-echo
sounding, shallow coring, automatic weather-station observations) have been
started or are funded and will proceed soon. Vigorous pursuit of these activities
is warranted, with expansion to include automatic weather stations at the
likely deep-coring sites and initiation of long-term atmospheric-sampling
and surface-glaciology studies there. This should lead to recovery of two
deep cores, one inland and one on Siple Dome, beginning in 1997-98. These
sites have been chosen to optimize the ability to answer the above questions.
To conserve logistical capability, core processing should be concentrated
in the National Ice Core Laboratory in Denver. It is worth noting that this
is a much less expensive proposition than working in the field, but may
involve more science dollars. (A meal in McMurdo or at a field camp is paid
by logistics, but a meal in Denver comes from science dollars.) A full suite
of isotopic, chemical, particulate, electrical, and physical studies of
the core is warranted, as are borehole logging and sub-ice core recovery.
Better development of fingerprinting techniques for volcanic ash should
be pursued, to allow exceptionally high-resolution correlation with Northern
Hemisphere ice cores through identification of global fallout of large eruptions.
This must be tied to multi-parameter counting of annual layers, including
chemical as well as electrical, optical and isotopic techniques. Further
details are given in the WAISCORES document (U.S. Ice Core Working Group,
The major meteorological controls on the ice sheet are accumulation rate
and surface temperature. Thus, the broad goal of the meteorological component
of WAIS is to understand the spatial patterns and temporal variability of
precipitation (nearly equal to accumulation on large spatial scales) and
temperature over the West Antarctic ice sheet as consequences of the coupling
between the atmospheric circulation and the ice-sheet topography. These
key environmental upper boundary conditions on the ice sheet will be described
for both present and altered ice-sheet conditions for input into glaciological
ice-flow models. Atmospheric numerical models will be important for understanding
changes to the atmospheric circulation (and resulting accumulation and temperature
patterns) through the glacial-interglacial cycle as it will be reconstructed
by WAIS investigators, and for calculating future scenarios of atmospheric
circulation used in predicting future ice-sheet behavior.
Interpretation of ice-core records will both require and contribute to understanding
of temporal variations in snow accumulation. Annual oscillations in a number
of tracers can allow layer counting and development of extremely detailed
accumulation records. Longer term variations in these and other tracers
in the ice reflect modification of the global climate system (changes in
atmospheric circulation and their impact on biogeochemical cycles). Rigorous
reconstruction of past climate and atmospheric composition requires better
understanding of the links between the composition of the atmosphere and
glacial ice records. Atmosphere-to-snow transfer is one poorly understood
aspect of the overall transfer function between air and glacial ice. Improved
understanding of this question demands investigation of atmospheric dynamics
on smaller scales (e.g., boundary-layer/free troposphere exchange) in addition
to the synoptic and mesoscale analyses outlined below.
1) What is the magnitude and interannual variability of moisture transport
onto the West Antarctic ice sheet?
The atmospheric transport of water vapor across the coastline yields the
snowfall that nourishes the ice sheet. Knowledge of the moisture transport
in the West Antarctic sector is limited. Particular tasks that must be accomplished
to answer the above question are: 1) analysis of past regional radiosonde
records (particularly from Byrd Station) to extract moisture fluxes at the
limited number of sampling sites; 2) development of methods to derive moisture
fluxes from existing satellite remote-sensing data, particularly focusing
upon the difficulties associated with underlying pack-ice and ice-sheet
surfaces; 3) continuing analysis of broad-scale atmospheric numerical diagnoses
(e.g., from the European Centre for Medium-Range Weather Forecasting) to
ensure that all available observations are being incorporated; and 4) an
expansion of the in-situ data-collection network including automatic weather
stations (AWSs) on the ice sheet and offshore islands, and deployment of
free-drifting buoys in the oceans.
Only task (4) requires field work. It is proposed to deploy two new AWS
sites each year during the 5 years of Phase I, in addition to servicing
previously established sites. This should be sufficient to establish a synoptic-scale
array on the ice sheet. WAIS ice-coring activities could benefit significantly
from an AWS placed at each coring site for year-round atmospheric observations.
Collection of the traditional AWS variables could be augmented by measurements
of snow accumulation from an array of acoustic snow-height sensors, and
some simple, automated analyses of snow chemistry or at least automated
collection of snow samples. At sites where air-snow investigations are conducted,
networks of at least three AWS units are desirable to provide insight into
vorticity and subsidence of regional-scale air-masses. Measurements at these
sites should also include meteorological soundings (tethered and/or radiosondes)
plus soundings of chemical tracers (e.g., O3 instruments can fly with the
meteorological sensors) that would supplement the sparse regional sounding
network. In addition, tower-based measurements of fluxes of heat, momentum
and water vapor would provide local-scale information on vertical exchange
between the snow surface and the atmosphere.
It is assumed that the World Climate Research Program's International Antarctic
Drifting Buoy Project will succeed in monitoring the synoptic-scale atmospheric
circulation over the ocean areas surrounding Antarctica. Additionally, it
is anticipated that considerable assistance with the remote-sensing research
will be obtained from groups already active.
2) What are the important synoptic processes that affect the moisture flux
and what is the variability of each process?
Cyclonic activity controls the patterns and variability of moisture flux
across the edge of the ice sheet, but very little is known about the basic
processes. The long-term (15-20 year) climatology of synoptic systems (primarily
cyclones) over high latitudes of the South Pacific Ocean should be established
from synoptic analyses that have satisfactorily incorporated all available
observations (e.g., the satellite measurements routinely being recorded
at McMurdo and Palmer Stations). Particular emphasis should be placed upon
establishing the patterns of variability and the associations between the
sea-ice and cyclone occurrence. Satellite and available in-situ data need
to be evaluated for the frequency and characteristics of these synoptic
influences on the West Antarctic ice sheet.
It may be possible to supplement such investigations by tracing snow strata
to map the amounts and extents of snowfall produced by major storms over
the ice sheet. Continued investigations of mesoscale cyclone formation,
tracks, etc., are needed on seasonal and interannual time scales to resolve
their role in snowfall over the ice sheet. Once again, satellite and available
in-situ observations will provide the key data.
No additional field work is required beyond the expansion of the AWS and
ocean-buoy network described in the previous section. It is expected that
analyses of these data will mature as the data base expands.
3) What are the patterns of large-scale variability in the atmospheric circulation?
Synoptic processes express broader scale atmospheric, oceanic and ice-sheet
conditions. An understanding is needed of the dominant, large-scale patterns
of variability and how these processes interact. Examples of this variability
on weekly and seasonal time scales are atmospheric blocking, and links with
tropical convection and sea-ice variations. Emphasis is placed here on the
interannual, global-scale El Nio Southern Oscillation (ENSO) events, which,
as studies have indicated, may be strongly manifested in West Antarctica.
Synoptic analyses can interact effectively with ice-core studies of ENSO-related
depositional events. The South Pacific Cloud Band (SPCB) should be studied
as a possible major candidate for transmitting the ENSO and higher frequency
tropical impulses to high latitudes of the South Pacific Ocean.
Satellite and synoptic analyses are the primary sources of data. Analyses
of existing and new data are required but field work is not needed.
4) How would the important atmospheric processes change under altered boundary
This question must be answered to provide ice-flow models with scenarios
of past and future atmospheric forcings on the ice sheet. A coordinated
observational and modeling effort is required with the purpose of understanding
the relationship between the nature and variability of moisture fluxes and
extratropical cyclones. The modeling studies require as input the topography
of the ice sheet, the atmospheric composition and the oceanic surface conditions
(sea-surface temperature and sea-ice distributions), illustrating once again
the close links between the various disciplines.
Currently, two modeling strategies exist for simulating atmospheric processes.
Regional (or mesoscale) models use relatively short time integrations (a
few days to approximately 1 week) to understand fine-scale details of atmospheric
processes, such as the evolution of cyclones and related synoptic and mesoscale
processes. General Circulation Models (GCMs) are used for longer term integrations
of a month or so to applications involving geologic time scales. Both modeling
strategies must be employed in WAIS. Regional modeling efforts should be
focused on the synoptic-scale environment, assessing the patterns of moisture
transport on a case-study basis using data from available observational
networks. These case studies then will be used to refine the parameterization
schemes in GCM simulations.
In addition, physical processes not currently represented in the GCM simulations
need to be incorporated. As an example, existing GCMs resolve the katabatic
wind regime only crudely, yet recent studies have indicated that these winds
may play a critical role in the evolution of the circumpolar vortex which,
in turn, affects the flux of moisture onto the continent through the interaction
of the circumpolar vortex with extratropical cyclones.
No field work is required for the modeling activities. The work will depend
on refined GCMs with full coupling of atmospheric and oceanic simulations.
Substantial opportunities exist for interaction with other WAIS activities.
Predictive GCMs hold the promise of understanding the nature of the glacial-interglacial
5) What are the mechanisms by which the snow is actually generated?
This process is important in understanding how the atmosphere is affected
by the ice sheet, but has never been studied observationally. Investigation
of the detailed atmospheric dynamics associated with invasions of moist
air into West Antarctica is needed, along with an evaluation of the accompanying
cloud microphysical and chemical processes that govern cloud and precipitation
formation. These studies will feed into theoretical and modeling studies
of topographically forced snowfall.
Ice-core interpretation will be considerably enhanced by improved knowledge
of the physics governing the parameters measured in ice cores, particularly
stable isotopes and chemical constituents. Opportunities for cooperation
with the ice-core drilling should include simultaneous measurements in the
air and on the ice sheet. Air-snow exchange investigations were integrated
with the recent deep drilling programs at Summit, Greenland. This experience
has resulted in development of sampling, analytical and modeling approaches
that will allow early determination of the important processes at each new
polar coring site, so that these can be focused on in intensive field and
laboratory investigations. (See the WAISCORES science plan for a more detailed
discussion of air-snow exchange issues.)
A well-instrumented research aircraft, like the NCAR Electra or equivalent,
is needed for these investigations. To minimize the transit time from the
base airfield and to maximize the measurement time of the aircraft, it probably
will be necessary to establish a suitable airstrip in West Antarctica, and
to operate the aircraft from this remote location at least part of the time.
The success of using blue-ice runways for other aircraft elsewhere in Antarctica
may open the door for this logistic requirement. It is recommended that
these aircraft campaigns be conducted during the first three field seasons
The principal direct link between the ocean and the ice sheet rests with
the water that circulates under the large ice shelves of West Antarctica.
An increase in the amount of heat being transported beneath and transferred
to these ice shelves leading to a reduction in their ability to buttress
the inland ice is often suggested as the likely mechanism by which a climatic
warming could trigger an ice-sheet collapse. Assessing the validity of this
hypothesis requires a better understanding of how sub-ice water circulation
and heat transport work today, and an understanding of how warmer oceanic
waters would be incorporated into the sub-shelf circulation. The oceanographic
studies of WAIS will focus on these coupled questions and will provide numerous
opportunities for interdisciplinary investigations.
1) What are the connections between the waters of the open ocean and those
on the continental shelf?
It is through the exchange of water at the continental shelf break, and
its subsequent modification on the continental shelf, that the global ocean
directly influences the ice-sheet environment. The edge of the Antarctic
continental shelf is one of the primary ventilation sites in the world ocean.
There, deep water evolves into surface and shelf waters which interact with
the atmosphere and sea ice, as well as with the ice margin and the undersides
of the ice shelves. Heat and salt are vigorously exchanged in coastal polynyas
and by deep vertical convection near the continental shelf break. Bottom
waters formed near Antarctica account for more than half of the abyssal
To understand the transport of fresh water and salt across the continental
shelf requires oceanographic measurements of salinity, temperature, chemical
tracers, and currents on appropriate temporal and spatial scales at representative
locations. Time-series observations should extend over several annual cycles,
encompassing the probable residence time for waters on the continental shelf.
Satellite measurements of sea-ice distribution and movement will help oceanographers
to understand the forcings and interannual variability and to identify sites
where air-sea interactions are highest. Efforts to model the ocean circulation
on the continental shelf should be cognizant of regional differences in
and sensitivity to changing wind fields and fresh water, salt and temperature
2) What is the spatial pattern and temporal variability of ocean interaction
with the ice shelves of West Antarctica?
Most of the ice in West Antarctica feeds large ice shelves that float over
warmer sea water. An increase in sub-ice-shelf melting has long been believed
to be a likely trigger for marine ice-sheet collapse (see Section 3). Modeling
experiments have shown that changes in ocean thermohaline characteristics
could produce shifts in the strength of the sub-ice circulations, which
now appear to cause relatively high melt rates near the ice-shelf grounding
lines. Because the seawater freezing point falls with increasing pressure,
melting rates are highest where the ice-sheet drafts and grounding lines
are deepest. These melting rates could increase if the grounding lines retreated
into deeper basins, but basal sills that restrict the circulation, and ponding
of dense seawater could create negative feedbacks.
Order-of-magnitude differences have been reported between the basal melting
and freezing rates beneath different ice shelves. Where the sub-ice-shelf
circulation is dominated by cold, dense, high-salinity shelf water as in
the Ross and Weddell Seas, average basal melt rates appear to be in the
range of 20 - 60 cm/yr. Where "warm" circumpolar deep water floods the continental
shelf, as in the Bellingshausen and Amundsen Seas, basal melt rates can
exceed 200 cm/yr. It has yet to be determined how quickly future climate
change might alter the ocean characteristics or circulation near Antarctica,
possibly shifting the present distribution of high-melting and low-melting
Field measurements and modeling efforts should focus upon these two different
regimes, beginning in the Ross Sea which is better surveyed and has more
extensive oceanographic data bases. A transect along the axis of the major
Ice Shelf Water plume could extend from the ice-shelf grounding line to
the deep ocean. Along this transect, a series of holes drilled through the
Ross Ice Shelf would provide access to the sub-ice cavity in order to obtain
water samples and deploy instruments to record currents and basal melting
or accretion. These holes could also be used for collection of sub-ice sediments,
whose analysis can provide information on the history of the ice sheet (see
Section 5.4.2) and for biological studies of this unusual region.
Measurements near the grounding lines in both deep-water and shallow-water
environments should attempt to differentiate between meltwaters derived
from the ice shelf and from the grounded ice sheet. Coordinated time-series
measurements near the ice fronts would quantify the effects that cause high
melt rates in that region, and that affect the variability of Ice Shelf
Water (ISW) outflow. Present-generation oceanographic equipment must be
tested in the sub-ice environment, where the near-freezing temperatures
may present significant problems. Narrow ice-holes can be completed at lower
energy cost but that may, in turn, require miniaturization of standard oceanographic
equipment. Continued development of drilling technology should allow the
rapid retrieval of crystallographically and stratigraphically unaltered
ice cores from the basal regions of an ice shelf.
In the Amundsen-Bellingshausen Seas, relatively warm water floods the deeper
portions of the continental shelf. This region may be an area of recent
ice-shelf retreat, as marine geologists have identified sites where larger
ice shelves probably existed within the past few thousand years. A survey
of this region was carried out in early 1994 from the N.B. Palmer. Preliminary
results show relatively warm water beneath all the fringing ice shelves,
no well-developed oceanic front near the continental shelf break, major
uncharted topographic features on the shelf, myriads of icebergs, and a
highly diverse sea-ice cover.
3) What will be the spatial and temporal patterns of climatically induced
changes in the sea ice and ocean of the Southern Hemisphere?
If the ocean near Antarctica becomes warmer and fresher, this could lead
to decreased vertical heat flux from the deep water to the atmosphere and
increased heat transport onto the continental shelf. If sea-ice production
also decreases near Antarctica, then less-dense shelf water may be formed,
facilitating access of that warmer water to the ice shelves. Some General
Circulation Models yield less warming than earlier predicted in the Southern
Hemisphere atmosphere, but more warming in the Southern Hemisphere ocean
over the next several decades. Alternatively, a weaker thermohaline circulation,
resulting from less sea-ice formation, could slow shelf circulation and
reduce oceanic heat transport.
Investigating these questions will necessitate measuring, modeling and monitoring
the spatial and temporal variability of the continental margin sea-ice cover
and ocean circulation. Models that couple the deep-ocean, continental-shelf
and sub-ice-shelf circulations must be constrained by the observed ranges
of water properties, current velocities, sea-ice distributions and basal
mass balances. Oceanographic data bases and paleoclimatic indicators need
to be assembled and analyzed in the context of present-day seasonal, interannual
and regional variability. Methods developed for the Arctic to extract sea-ice
extent, thickness and motion from satellite data must be refined for Antarctic
use. These parameters can be verified by moored and drifting instruments,
sea-ice cores, and shipboard observations. Satellite and geochemical techniques
should aid in the identification of coastal regions of high salt or meltwater
flux or potentially high sensitivity to climatic perturbations.
4) What are the relationships between the northern limit of sea ice or between
the leads and polynyas in the sea ice and regional accumulation rates on
the ice sheet?
The ocean indirectly affects the ice sheet by providing the moisture which
the atmosphere delivers as snow. Much of this accumulation is apparently
delivered across hundreds of kilometers of sea ice, but the zonal range
of source areas is not well defined. Leads and polynyas in the otherwise-solid
sea-ice cover are also important local sources of moisture, increasing the
flux of heat and aerosols to the atmosphere, and potentially raising accumulation
rates over the ice sheet. Parameterization of this effect will be necessary
in full-scale numerical models of the West Antarctic environment.
To determine the seminal relationships between these interactions, data
of sea-ice concentrations, weather patterns, and accumulation rates are
required. Extended time series of sea-ice concentrations are now available
from satellite-based passive microwave sensors but the accuracy of concentration
estimates needs to be improved. Weather patterns can be derived from satellite
image data but supplemental data from automatic weather stations (AWSs)
installed near the locations of perennial coastal polynyas would provide
much-needed detail. These AWSs should be instrumented to measure accumulation
to augment a record of past accumulation rates and their spatial pattern
obtained from a set of shallow firn cores acquired at typical coastal sites.
The oceanographic projects that are essential to the realization of WAIS
objectives offer numerous opportunities for interdisciplinary cooperation.
These include interactions with: 1) modelers simulating the global-scale
coupled ocean-atmosphere circulations and the ice-sheet response to global
change; 2) meteorologists concerned with the sources of moisture to the
ice sheet, the annual cycles of ocean surface temperature and the siting
of AWSs; 3) remote-sensing specialists documenting spatial and temporal
changes in the ice-sheet perimeter or sea-ice distribution and movement;
4) glaciologists interested in regional variability in ice-shelf basal mass
balance and crevasse distribution; 5) geologists seeking environmental data
to interpret sediment cores, seismic data or bathymetric features; and 6)
biologists studying the dark and remote environments beneath ice shelves,
the impact of changing sea-ice cover on productivity, or the role of DMS
in the marine environment and in the atmosphere.
5.4. GEOLOGY AND GEOPHYSICS
The following three key questions are linked by the fact that the data to
answer them consist of dated marginal positions of the ice sheet-be they
on land, on the sea floor, or subglacial. Each topic is treated separately
1) What was the configuration of the West Antarctic ice sheet during and
following the last glacial maximum?
2) What is the configuration of the West Antarctic ice sheet during an extreme
3) Has the West Antarctic ice sheet undergone rapid, episodic mass loss
in the recent geologic past?
5.4.1. Terrestrial Geology
Drift sheets, including end moraines and erratic boulders, bedrock striae
and molded erosional forms, glacial fluvial and lacustrine features, trimlines
of weathering, and emerged marine strand features provide reliable evidence
upon which to reconstruct past configurations of the West Antarctic ice
sheet. From these features, the boundaries of the ice sheet, both areal
and vertical, and the flow direction can be determined. When tied to specific
times by relative and absolute dating methods (e.g., AMS and conventional
radiocarbon methods and cosmogenic surface exposure methods), these data
will allow the development of chronologies defining ice-sheet growth and
decay. In addition, they will provide bounds for the determination of rates
of advance and retreat. Time resolution of suitable numerical dating methods
for events since the last glacial maximum (LGM) is on the order of 50 to
The most promising geographic study areas for these investigations are:
the east flank of the Transantarctic Mountains; the nunataks and coastal
mountains of Marie Byrd Land and Ellsworth Land; and the Pensacola, Thiel,
Horlick and Whitmore Mountains. The Transantarctic Mountains have already
received a great deal of study, but gaps must be filled and the results
integrated with existing data. These gaps are included in the regions from
Cape Adare to Coulman Island, Coulman Island to McMurdo Sound, and McMurdo
Sound south to Darwin Glacier. Investigations should also be extended farther
southward into the Reedy Glacier area. In this area, the record can be directly
integrated with the past and present activity of ice stream A of the West
Antarctic ice sheet and its tributaries draining the East Antarctic ice
sheet. In addition, the former height of the ice sheet should be determined
on nunataks of the Thiel Mountains and in the area of the Foundation Ice
Stream. Foundation Ice Stream discharges into the Ronne Ice Shelf and is
similar to ice stream A in that its drainage is of predominantly West Antarctic
ice yet its tributary, Academy Glacier, drains a portion of the East Antarctic
ice sheet. Previous studies in the southern Transantarctic Mountains and
nunataks of west Antarctica until now have been hampered by lack of a reliable
dating method applicable for the time since the LGM. Continuing improvements
in the cosmogenic surface exposure dating method hold the promise of being
able to provide absolute chronologies of events.
The glacial history of the Antarctic Peninsula, although not physically
a part of the West Antarctic ice sheet, must also be determined. This record,
from the LGM to present, will form the connecting link between the record
of WAIS proper and the rapidly developing record south of 45¡S, in the Andes
of southern South America, and the Southern Alps of New Zealand. The record
from the peninsula will provide the basis for comparison of events both
north and south of the Antarctic Convergence and hence, a composite record
essential for documenting and understanding the role of Antarctica in global
climate and sea-level change.
The chronology of ice surface level and marginal position change, integrated
with data developed from marine geology studies of the glacial record preserved
on the continental shelf, will reveal whether episodes of rapid and episodic
ice wastage occurred during deglacial cycles. The data documenting such
episodes can then be compared with the global sea-level record. Ultimately,
these combined data will provide the critical historical record of the transient
behavior of the ice sheet essential for the control and calibration of ice-sheet
numerical models. In addition, the chronologies will be useful in testing
the consistency between interpretations derived from the ice core, ice dynamics,
and marine geology components of WAIS and with the expanding records from
southern South America and New Zealand just north of the Antarctic Convergence.
5.4.2. Marine Geology and Geophysics
The geologic record also extends to the ocean-covered areas of the continental
shelf where the ice sheets deposit material and rework this material when
they advance over it. The structure and stratigraphy of this sediment furnish
a record of glacial and glacial-marine conditions at the time of deposition
and possible clues to the roles that subglacial water, deforming till, bedrock
geology and heat flow may play in the dynamics of ice-stream motion. By
dating the core material using geochemical and paleontological techniques
and by evaluating the relative composition and character of the sediments,
the age of key units, and therefore the rates and patterns of ice-sheet
retreat, can be inferred. Furthermore, the stratigraphic progression on
the continental shelf may provide a direct record of the sequence of subglacial
events that led to ice-sheet retreat from the shelf.
Paleontological techniques also provide information on the bottom- water
characteristics (e.g., temperature, bathymetry, and proximity to grounded
ice), upper water mass characteristics (e.g., presence or absence of glacial
ice, salinity, light, mixing, and primary productivity), and terrestrial
palynology (e.g., vegetation characteristics, spores and pollen).
The specific tasks that must be accomplished to answer the above questions
are: 1) an analysis of existing high-resolution seismic data and piston
cores from the Ross Sea; 2) a mapping of the sea-floor stratigraphy using
multi-beam bottom imaging instruments; 3) a refinement of the location and
dating sequence of significant geologic features found in (2); and 4) an
overall synthesis of data and interpretation.
Task (1) will be undertaken initially to assess these existing data and
to define better those areas where field studies should be conducted. Seismic
analyses will concentrate on defining those areas where seismic facies and
morphological features imply former grounding-line positions.
Many piston cores have been acquired from the Ross Sea continental shelf,
mainly during Eltanin, Glacier and, most recently, R/V Palmer cruises. These
cores contain a valuable record of the late Pleistocene-Holocene glacial
setting on the shelf. Detailed sedimentological studies of these cores will
help to locate former grounding-line positions and the paleodrainage divides
of former ice sheets, and to study the nature of ice-sheet retreat from
the shelf. Studies are being conducted to evaluate methods of age-dating
these sediments so that the actual timing of ice-sheet retreat from the
continental shelf can be established and to extract information of water
mass characteristics and terrestrial palynology listed above. One or more
planned transects will extend from the continental slope to the ice-sheet
edge and along paleodrainage divides of specific ice streams (based on provenance
studies of tills conducted during the previous two years' studies). Age
dating of the contact between subglacial and glacial marine sediments in
these cores will rely on the most current radiometric dating methods (i.e.,
Tandem Accelerator Mass Spectrometry: TAMS) and may provide a record of
the timing and rate of ice-sheet retreat.
During the 1995 field season, mapping of the sea floor using multi-beam
bottom imaging instruments (task 2) will provide a wealth of information
about the subglacial environment during the last glacial maximum. This work,
done in conjunction with high-resolution seismic profiling, will result
in a three-dimensional reconstruction of the glacial sediments and the thin
veneer of Holocene sediments that blanket the Ross Sea continental shelf.
These sediments record the most recent expansion of the West Antarctic ice
sheet and its retreat from the shelf.
Information gained during the first 3 years of the project will be used
to reconstruct the geological setting (e.g., bedforms, subglacial meltwater
channels, sediment properties) associated with former grounding-line positions
on the shelf, and to examine the history of ice-sheet retreat from the shelf.
The fourth year will be devoted to task (4), which is exclusively interpretive.
If there have been problems in any of the prior data-collection seasons,
repeated field work in the above areas may be required.
Longer cores are required to test the hypothesis that bed deformation led
to rapid ice-sheet retreat. Marine geological and geophysical work accomplished
to date has shown that the sedimentary unit deposited during the last glacial
maximum is thicker than was anticipated. Piston cores from the continental
shelf penetrated diatomaceous muds, which reflect a glacial marine setting
similar to that of the present, with the ice sheet resting on glacial marine
sediments that were deposited in a position more proximate to the grounding
zone of the ice sheet. These cores bottom-out in the top of a unit that
has tentatively been interpreted as deformation till. Thus, the recovered
stratigraphic progression of bed deformation and ice-sheet retreat is incomplete.
Shallow drilling is needed to accomplish this objective.
The modern analog for the depositional environment of an extended West Antarctic
ice sheet is located underneath the Ross Ice Shelf at the grounding line
of the ice streams. Sediment cores recovered from beneath a series of access
holes drilled through the ice shelf will provide an unprecedented view of
how the sediment structures evolve. Seismic work at each drill site will
give the stratigraphic context of each core assisting in the generation
of a single, continuous record from the grounding line to the edge of the
continental shelf. This data set will enable a better interpretation of
the dynamics and history of the ice sheet, the depositional mechanism and
the role of water in the formation of these deposits. Logistic requirements
of this project will be reduced by coordination with WAIS oceanographic
investigators also working on the ice shelf.
Additional areas that must be studied include Pine Island Bay and the Wilkes
Land continental shelf. Pine Island Bay is an area of particular interest
due to the absence of ice shelves in the mouths of the two major outlet
ice streams. Marine geologic and geophysical studies of the bay combined
with the oceanographic studies recommended (see Section 5.3) should provide
insight into the history of ice-sheet advance and retreat in this unique
setting and possible causes. It is anticipated that one field season will
be sufficient to collect the seismic data and cores needed to address the
questions concerning the history of each area during and since the last
glacial maximum. The timing of this study would be coordinated with oceanographic
and meteorological interests in the region.
The continental shelf along portions of the Wilkes Land margin represents
the terminal drainage for two large marine-based ice drainage systems which
appear to be relatively stable. This contrast to the West Antarctic condition
would provide information on those factors which contribute to this stability.
The precise timing (within a few hundred years) of recession of the ice
sheet can be determined because of the presence of: a well-defined terminal
moraine system; a high-resolution post-glacial marine sequence; and a relict
subglacial morphology, fluted surfaces, etc. The age, composition, and distribution
of these features need to be evaluated through a program of high-resolution
seismic profiling, side-scan sonar surveys, and coring.
5.4.3. Subglacial Geology and Geophysics
To understand the minimum extent of the ice sheet (question 1b, above),
data must be collected from beneath the present-day ice sheet. Holes through
the ice can be drilled rapidly using hot-water systems, permitting frequent
access to the bed either underneath the ice shelf or underneath the grounded
ice sheet. Collected cores will be examined in detail for sediment physical
properties, composition and texture. Sedimentological, micropaleontological
and geochemical analyses will be performed to constrain the environment
of deposition, to establish the age of these deposits, and to help determine
the southernmost extent of the grounding line during past interglacials.
These data will be correlated with similar information derived from marine
sediments collected on the continental shelf or under the ice shelves to
provide a broader view of the history of the ice margin. Cores acquired
within the present zone of ice-sheet grounding will be used to test models
relating bed conditions to ice-sheet stability. The actual timing involved
in drilling at these sites will rely on coordination with glaciological
and oceanographic studies.
Subglacial geophysical investigations will also be directed at answering
a much different question than the trio of questions listed at the beginning
of this section.
4) What are the geologic controls on the flow of a marine ice sheet?
The answer to this question requires geophysical techniques to study the
geologic setting of the ice sheet. For this study, the subglacial lithology,
distribution of geothermal flux, and tectonic activity all must be considered.
There is evidence that the positions of the ice streams are controlled by
the subglacial lithology and perhaps by the thermal regime. If their rapid
motion is caused by a deforming subglacial till made weak by pressurized
subglacial water, then the ice streams must be located near a rapidly erodible
source of sediment as well as in a region characterized by basal melting.
It is known that the West Antarctic lithosphere is characterized by recent
volcanism and associated high geothermal flux, but few details exist on
the spatial pattern of these characteristics.
Most of the subglacial and englacial geophysical data of the West Antarctic
ice sheet and its underlying bed that are needed for WAIS will be collected
either by projects already planned, such as Antarctic Geophysical Initiative
(AGI) (see Section 6.1.2), or by collaborations with WAIS investigators
in ice dynamics, ice coring, or marine geology. This method of providing
ancillary data for glaciological studies in the Siple Coast Project (Section
6.1.1) proved effective and established the broad geophysical data base
upon which subsequent measurements during WAIS will be able to build.
Early in the WAIS program, a regional mapping of the ice-sheet configuration
and bed-type needs to be accomplished in the region of the catchments of
ice streams AÐE. Understanding the correlation of lithospheric boundaries
and subglacial morphology with changes in the dynamic regime between the
ice divide and the ice streams of this portion of the West Antarctic ice
sheet is critical to understanding its evolution, but insufficient data
exist. Airborne radar soundings combined with airborne gravity and magnetics
should be flown in cooperation with transects being undertaken by the AGI
A detailed aerogeophysical survey also will be required in the vicinity
of the proposed deep ice-drilling site on the divide between the Pine Island
and Ross Embayments. The surface, bed and internal-layer morphology supplied
by these studies are necessary boundary conditions for the ice-flow modeling
of the age-depth relation needed to understand the history of the West Antarctic
ice sheet and to date any ice cores from the ice sheet. Additionally, any
indications of lithospheric properties that might coincide with high geothermal
flux and a shortened core record can be evaluated before drilling begins.
These data can be obtained in conjunction with the aerogeophysical efforts
in support of ice dynamics and subglacial geology in the catchments of ice
streams D and E and over the Byrd subglacial basin.
Understanding the water and sediment budget as well as the ice rheology
in the region at the onset of ice streaming flow is critical to understanding
the dynamics of the ice sheet and our ability to model it. Because of this,
geophysical investigations of the bed character, bed morphology and ice
fabric using both ground radar and seismological techniques need to be undertaken
in the area near the onset of fast flow. These studies should begin immediately
after completion of the aerogeophysical program described above.
Determining the current state of the West Antarctic ice sheet will require
measuring the ice thickness of the outlet glaciers along the coast of Marie
Byrd Land. Satellite-image-derived velocities can be combined with these
data to determine the current mass outflow in these coastal areas to compare
with independently derived estimates of the iceberg calving rate. Reconnaissance
work of a similar nature in the marine portions of Wilkes Land is also advisable.
Biological phenomena in Antarctic terrestrial and marine systems are directly
influenced by ice-volume changes associated with the advance and retreat
of the West Antarctic ice sheet. Lakes in the Dry Valleys, for example,
have blue-green algae which have been used for dating paleo-shorelines and
sedimentary deposits that reflect changes in the local hydrology since the
Last Glacial Maximum (LGM). Marine fossils (including algae, invertebrates
and vertebrates) in emerged beaches and marine sediments, from the Ross
Sea to the Antarctic Peninsula, have been used for interpreting the regional
history of ice-sheet retreat. Emerged marine records also place constraints
on the extent of glacial isostatic uplift, which is a key to modeling Antarctic
ice-volume changes that have affected sea level since the LGM. While biological
phenomena may not directly influence the West Antarctic ice sheet, they
clearly are central to interpreting its complex dynamics.
1) How have WAIS margins and the coastal environmental features (such as
temperature, glacial-meltwater runoff or sea-ice extent) in the transition
zone between the WAIS and the ocean, changed since the LGM?
Biological phenomena that are impacted by the West Antarcitc ice sheet occur
within individual organisms as well as their populations and communities.
Individual organisms contain geochemical data (such as radiocarbon and stable
isotopes in shells) that reflect the hydrochemical conditions which existed
when they were alive. Over larger scales, changes in the ice-sheet margins
directly affect the distribution and abundance of species in adjacent populations
and communities. Together, these biological phenomena may provide sensitive
indicators of the climate/sea-level feedbacks which impact the stability
of the West Antarctic ice sheet. Specifically, biological phenomena address
the two following multidisciplinary questions which are related to the environmental
history and interactions associated with West Antarctic ice dynamics since
2) What are the modern analogs and experiments which are necessary to establish
baselines for interpreting biological phenomena in relation to WAIS dynamics
in the past?
General criteria for selecting the key biological phenomena should be based
on their fossil abundance, distribution and preservation. The first priority
should be given to bio-markers, such as diatoms and foraminifera or other
invertebrates, which complement ongoing glacial-geologic and oceanographic
studies. These bio-markers provide two relevant types of information: chronological
(based principally on their radiocarbon ages) and environmental (based on
species growth, geochemistry and assemblages). In addition to enhancing
the interdisciplinary framework of the WAIS program, coordination among
biological, glacio-geologic and oceanographic studies will minimize logistics.
Chronological information based on the radiocarbon ages of Antarctic marine
organisms is complicated by the upwelling of "old" deep water, which dominates
the radiocarbon reservoir in the Southern Ocean. Prior to the anthropogenic
impacts of nuclear bombs and fossil fuel combustion this century, the age
of the Antarctic marine radiocarbon reservoir was around 1300 years. However,
this radiocarbon reservoir may have been altered in the past by changes
in the flux of glacial meltwater and the transport of North Atlantic Deep
Water into the Southern Ocean. Unlike atmospheric radiocarbon variability,
which has been interpreted from tree-ring and coral records since the LGM,
variations in the radiocarbon reservoir of the Southern Ocean are unknown
during this period.
Assuming that the radiocarbon reservoir in the Southern Ocean has been constant
since the LGM is reasonable as a first approximation. However, additional
research on the radiocarbon reservoir in the Southern Ocean is necessary
for reconstructing the glacial history of the West Antarctic ice sheet to
interpret the relation between "rapid" climate and ice-sheet changes. This
research should be conducted across environmental gradients (such as meltwater
plumes) that represent hydrochemical changes that may have impacted the
Antarctic marine radiocarbon reservoir over time. In addition, the focus
of this radiocarbon research should be on calcareous species, which account
for the vast majority of Antarctic marine fossils.
Environmental information is recorded in the growth and geochemistry of
marine species' skeletons. Species growth records reflect seasonal, interannual
and decadal environmental variability - depending on the lifespans of the
species that are being studied. Growth records are complemented by geochemical
analyses (stable isotopes and trace elements), which can be used for interpreting
productivity, salinity and temperature variations in the Antarctic marine
environments. Together, the growth and geochemistry of modern marine species
provide experimental analogs for interpreting the environmental variability,
which is recorded in the skeletons of their fossils.
Environmental variability in the Southern Ocean also is reflected by the
distribution, abundance and composition of marine species assemblages. For
example, marine benthic species' diversities vary between eutrophic and
oligotrophic environments. Changes in the abundance of selected marine species
have been related to decadal oceanographic climate shifts in the Southern
Ocean. There also is an association between the composition of marine diatom
assemblages and sea-ice extent. To interpret the paleoecology of marine
fossil assemblages adjacent to the West Antarctic ice sheet, environmental
variations which affect their extant marine analogs should be experimentally
investigated across comparable habitat gradients (e.g., depth and latitude).
3) How have the distribution, abundance and geochemistry of West Antarctic
marine and terrestrial species been influenced by ice-sheet marginal phenomena
(e.g. ice shelves, ice tongues and piedmont glaciers) since the LGM?
To interpret "rapid" changes in the dynamics of the WAIS, those species
assemblages should be identified which have persisted over centuries and
millennia with the ability to respond to environmental changes over years
and decades. In this context, extreme environmental changes which eliminate
these species assemblages would be highlighted. Moreover, subtle environmental
changes that alter the dynamics of these assemblages could be calibrated
against long-term baselines. An additional criterion for identifying these
assemblages would be their relationships to phenomena which directly impact
WAIS dynamics, such as ice-shelf or meteorological processes.
Appropriate paleo-assemblages might include algal mats in the Dry Valley
lakes, benthic marine invertebrate populations in sheltered coves and harbors,
or seal and penguin rookeries. After being identified, the distribution,
abundance and geochemistry of the paleo-assemblages should be analyzed in
relation to their modern analogs.