globec_sop_rn5_nov_1991

# Chapter 1 - EXECUTIVE SUMMARY

## 1.1 Relation of a Southern Ocean GLOBEC study to climate change

Global climate change is predicted to be greatest at high latitudes, with dominant effects anticipated in the form of increased concentrations of atmospheric CO2, increased temperature, and changes in ocean circulation. The Antarctic has a high negative radiation budget; its immense masses of both continental ice and annual sea ice act as a refrigerator, moderating global temperature on a seasonal and multiannual basis.

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:

1. Quasisynoptic survey cruises;
2. Process oriented cruises;
3. Remote sensing; and
4. Shore based laboratory studies.

The emphasis of such a plan would be on observing the entire annual cycle, with a particular emphasis on winter. Such a study would continue for a period of at least three years.

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.