The continental ice sheet contains 90% of the world's fresh water, representing a potential sea level rise of approximately 60 meters. Major portions of the ice sheet grounded below sea level, such as the current West Antarctic ice sheet are potentially unstable on short time scales. Whether the ice sheet is currently growing or shrinking is unknown.
Seasonal sea ice coverage in the Southern Ocean increases from approximately 4 x 106 km^2 in summer to 20 x 106 km^2 in winter. During the austral summer the sea ice melts back almost to the edge of the Antarctic continent. During the last glacial maximum the sea ice in the Antarctic extended outward an additional 15 x 106 km^2 and its retreat in the summer was much reduced (CLIMAP 1981). These fluctuations in sea ice extent represent one of the most dramatic manifestations of climate change in the Southern Hemisphere. Recent paleoclimate studies have indicated that changes in atmospheric CO2 may be a major factor in regulating the sea ice extent in the Southern Ocean.
The timing and maximum extent of the sea ice in the Southern Ocean is forced to a large extent by the large-scale atmospheric processes. The same processes also influence the position of the major frontal systems and the strength of the various currents in the Southern Ocean. Since the type and abundance of species can differ on opposite sides of fronts (or in different water masses) a shift in the circulation or change in the intensity of a current can change the type and abundance of prey and predators.
The effect of atmospheric warming in the Southern Ocean may be to
reduce the areal extent of annual sea ice, which could reduce total
annual photosynthetic carbon fixation, destroy habitats, and disrupt
the life cycles of marine zooplankton and animals at higher trophic
levels, whose present-day biogeographic ranges are directly related to
the extent of sea ice coverage. Increased meltwater input from the
continental ice sheet might have a compensatory effect, further
extending the coastal
production zone.
1.2 The Antarctic marine ecosystem
The Antarctic marine food web is more complex than the simple linear
food chain (e.g. diatoms-krill-higher consumers) that has often been
described for this system. However, the links in the Antarctic food
web are often short and may be dominated by fewer than half a dozen
species. The shortness of these trophic connections arises because the
basic prey types (e.g. Euphausia superba) available to predators in
the Southern Ocean is limited and because among the basic prey types,
predators tend to concentrate on a core group of species, such as some
abundant euphausiids and fish near the base of the food chain. It has
been suggested that because of the apparent close coupling between
trophic levels, long-term studies focusing on these predator-prey
relationships and their environment will not only be critical to
understanding variability in Southern Ocean ecosystems in general, but
may ultimately form the basis for monitoring the effects of
man-induced perturbations on the system.
Long-term fluctations in the mesoscale abundance of the Antarctic krill are well documented, and although years of low krill biomass have been attributed to krill redistribution by physical forces, the mechanisms controlling abundance are not well understood. Recruitment to the krill population can be very localized, but the processes which determine recruitment success are not understood.
Even the immense spatial extent of the Antarctic marine ecosystem does
not provide sufficient buffer against departures caused by global
changes in environmental conditions, the stress of pollution, or
exploitation of renewable resources. if stress on any segment of the
ecosystem continues for long periods of time, the system may be
permanently altered. Documentation of natural population cycles and
the mechanisms underlying these cycles of natural variability is
important if we are to predict how changes in the environment due to
such things as global warming impact the biology of the Antarctic
ecosystem.
1.3 Site selection
A number of sites were discussed, all with relative merit. If a single
site had to be chosen, the Bellingshausen Sea, adjacent to the
Antarctic Peninsula coastal region, would be considered the primary
site. Although the circulation of the region is not well studied,
indications are that it contains an identifiable gyre which would
serve as a means to isolate definable populations, including those
which have pelagic or benthic larval stages. The Bellingshausen Sea
has several other advantages as a study site. First, it contains
relatively large populations of the key species recommended for study,
including krill, a variety of benthic species, and important species
of fishes, birds and seals. Second, the presence of sea ice, the
extent of which is anticipated to change in response to global climate
change, can be depended upon; this will assure studies of sea ice
dynamics in relation to population dynamics and habitat of key
species. Finally, this region is not only relatively easily accessible
by research vessel, but is near the highest concentration of
shore-based marine laboratories on the continent, which will provide
for high-quality scientific and logistic support. Secondary sites
recommended for study include the southeastern Weddell Sea, the
norhern part of the Atlantic Sector of the Southern Ocean, the Ross
Sea area, and the Indian Ocean Sector.
1.4 Zooplankton, including krill
Target species should emphasize the Antarctic krill (Euphausia
superba) and the salp (Salpa thompsoni) as the key target
species. Local populations should be defined by frequent surveys
carded out throughout the annual cycle, and molecular and biochemical
techniques, with a focus on locating key spawning sites, particularly
of krill. A key objective of population dynamics studies is to acquire
more data on populations in the winter, and particularly to identify
those demographic parameters which may be especially sensitive to
climate change, and to temperature increases in particular. Process
studies should focus on determining the environmental triggers for
metabolic and behavioral events, comparing metabolic responses between
environmental extremes, measuring physiological responses to
conditions outside the normal environmental range, and determining the
relative sensitivity of developmental stages to environmental
variables. Historical data should be exploited, particularly with
respect to site specific modeling activities. Modeling is required to
investigate the life cycles of zooplankton, to develop coupled
biological, physical, numerical models for krill and other zooplankton
populations, and to develop models regarding the formation,
maintenance and dissolution of patches of zooplankton. New technology
is particularly required to sample the upper 10 meters of the water
column, to sample the abundance and distribution of salps with minimal
disturbance to aggregates, to provide noninvasive techniques to
observe distributions of krill and other zooplankton, and to sample in
and immediately under sea ice.
1.5 Benthos
Target species should emphasize benthic forms with both pelagic and
benthic larval stages among the bivalves, echinoderms, and
crustaceans. Definable populations should be selected from regions in
both the high and low Antarctic, with a particular focus on the Ross
Sea, the southeast Weddell Sea, the Davis Sea in the high Antarctic,
and the South Orkney/South Shetland Islands and Antarctic Peninsula
regions in the low Antarctic. Population dynamics studies should focus
on colonization processes in areas exposed by recent calving of major
portions of ice shelf, species succession in areas with high iceberg
grounding frequency, and emphasize observations during winter. Process
studies should identify physical and biological forcing factors
including those delivering carbon to the benthos, ice conditions, flow
of local currents, temperature and salinity, light regimes, and redox
profiles in sediments. Measurements of the response of individuals and
populations should be assessed with regard to energy flow,
physiological response, population dynamics, and community
structure. A large body of historical data exists which should be
exploited, particularly from collections made near shore based
Antarctic field stations. Modeling studies should evaluate the
processes of aggregation, dispersal and settlement of meroplanktonic
larvae, and assess the role of climatic change on physiology and
population dynamics. New technology is required to quantitatively
assess distribution and abundance using video and camera technologies,
and to develop methods for determining the age of individuals.
1.6 Top predators
Target species should include a commercially harvested species
(e.g. Champsocephalus gunnari), a nonharvested holopelagic species
(e.g. Pleurogramma antarctica) and nonharvested near-shore
species (e.g. Notothenia neglecta). Other top predators should include
a variety of penguin species, the crabeater seal, and the Antarctic
fur seal. Population dynamics studies should focus on better
assessment of species distributions in time and space and should use
molecular techniques to distinguish populations. There is a need for
assessing growth and developmental rates of larval fishes, foraging
dynamics of birds and seals, and identification of populations of
birds and seals using marking and tracking studies. Process studies
should emphasize the effects of temperature on growth and development
of early life history stages of fishes, overwintering studies of top
predators, and the potential effects of ultraviolet radiation on fish
eggs and larvae. Historical data are readily available from a variety
of current and past programs; these should be made readily available
to principal investigators. Modeling studies should emphasize the
effects of the physical environment on the physiological rates and
demography of fishes, development of models for the population
dynamics of sea birds, models of the movement and dispersal of
foraging predators, and the effects of climate and fishing pressure on
harvested species. New technology is especially required in the areas
of improved acoustical hardware and software as applied to studying
fish populations, underwater visual systems for assessing
distributions of prey items, and improved satellite methods for
tracking other top predators.
1.7. International interactions
Under the terms of the Antarctic Treaty, Antarctica is not the
sovereign territory of any nation. Given the long-standing tradition
of international research, any scientific program carried out in the
Southern Ocean has an unusually high potential for international
cooperation. It is expected that a Southern Ocean GLOBEC study will
involve participation by many nations. Most countries maintain
research establishments devoted exclusively to Antarctic or polar
research; examples include the British Antarctic Survey, the Alfred
Wegener Institute für Polar- und Meeresforschung, and the National
Institute of Polar Research of Japan.
Numerous countries are interested in this region and international
groups such as the Convention for the Conservation of Antarctic Marine
Living Resources (CCAMLR) have an active interest in Antarctic marine
studies. Presently the U.S. has several agencies with strong interests
or ongoing programs in the Antarctic, including NSF-Division of Polar
Programs and NOAA (which holds the responsibility for carrying out US
CCAMLR activities). NASA has also been supporting scientific research
in this area. Other global geoscience initiatives such as World Ocean
Circulation Experiment (WOCE) and Joint Global Ocean Flux Study
(JGOFS) have planned, or are now planning, research components in the
Southern Ocean. It is expected that JGOFS field studies there will
begin in 1994, although the precise locations of the research have not
yet been finally agreed upon.
1.8. Field program logistics
Scientists endorsed a broad outline of a field program involving four
modes of studying the Bellingshausen Sea region:
The implementation process will require that an international committee be established to set forth a detailed research plan. This committee, convened under the aegis of SCAR or another appropriate international scientific body, will have to make decisions regarding (1) key elements of the scientific research plan and (2) timing and logistics. If an implementation committee is established in I992 it is conceivable that an international field research program could begin as early as 1996.