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bulletin 138

SCAR Bulletin No 138, July 2000

Summary Report of a Workshop, September 1999

Life under the Ice and the Climatic Evolution of Antarctica

The discovery of subglacial lakes has involved many scientists from several countries (Russia, United Kingdom, United States, France and Denmark) over a period of more than four decades. Observations of unusually flat areas atop the Antarctic ice sheet were compared to lakes in other settings by a Russian pilot, R V Robison, in 1961 (Siegert 1999). Prior to this it had been hypothesized from data obtained by the First Soviet Antarctic Expedition (SAE) in 1955-57 that lakes could exist under ice sheets (Kapitsa 1998). In 1963-64, a team led by A P Kapitsa of Moscow State University (the 9th SAE), studying the thickness of the ice sheet, collected seismic traces adjacent to Vostok station and serendipitously over Lake Vostok. These seismic traces would ultimately lead to the recognition of liquid bodies of water under the ice sheet. Confirmation of the existence of Lake Vostok came years later and took the collective efforts of the 9th SAE ice cover studies; radio-echo sounding of the ice sheet by an international team led by G de Q Robin during the 1973-75 airborne expeditions of the Scott Polar Research Institute (SPRI), the US National Science Foundation, and the Technical University of Denmark; and the results of ice sheet surface topographic studies using ERS-1 imagery at Mullard Space Science Laboratory (Ridley and others 1993). Oswald and Robin were the first to use airborne radar to detect several small subglacial lakes, reporting their conclusions in 1973 (Oswald and Robin 1973). Once ERS-1 information was available and a re-examination of the original Kapitsa seismic data had taken place, the true scale of the lake was apparent, its importance became clear, and an international workshop was convened in Cambridge in 1994. The discovery of Lake Vostok was first reported at the 23rd meeting of the Scientific Committee on Antarctic Research (SCAR) in Rome, Italy, August-September 1994 in a joint Russian-British report and the results were published in the journal Nature (Kapitsa and others 1996; Figure 1).

By 1996, speculation about the nature of the lake was far-reaching, including the suggestion that Lake Vostok water was most likely contained fresh water and that the lake would be expected to support a resident microbial population. The interest in the lakes continued to grow as an international drilling team came within a few hundred meters of the lake's liquid surface and encountered what appeared to be ice accreted from the lake water itself. The recognition of a substantial layer of sediments underlying the lake increased speculation on the forms of life that might exist in the lake. It also has become clear that many subglacial lakes occur under the East Antarctic ice sheet and that there may be a range of different types of lakes depending on their origins and evolution over geological time.

In the intervening years, interest in the exploration of these unusual and remote bodies of water led to additional workshops to develop a scientific rationale and plan for exploring subglacial lakes ('Lake Vostok: scientific objectives and technological requirements - an international workshop,' St Petersburg, Russia, 1998; and 'Lake Vostok: a curiosity or a focus for interdisciplinary study?' Washington, DC, November 1998). These workshops culminated with an 'International workshop on subglacial lake exploration' in Cambridge, United Kingdom, in September 1999, where the latest evidence about the nature of subglacial lakes was presented.

References

Kapitsa, A. 1998. Discovery and future exploration of Lake Vostok. Abstract volume for the international workshop 'Lake Vostok study: scientific objectives and technological requirements.' St Petersburg, Russia: Arctic and Antarctic Institute: 17-18. [Unpublished.]
 
Kapitsa, A., J.K. Ridley, G. de Q. Robin, M.J. Siegert, and I. Zotikov. 1996. Large deep freshwater lake beneath the ice of central East Antarctica. Nature 381: 684-686.
 
Oswald, G.K.A., and G. de Q. Robin. 1973. Lakes beneath the Antarctic Ice Sheet. Nature 245: 251-254.
 
Ridley, J.K., W. Cudlip, and S.W. Laxon. 1993. Identification of subglacial lakes using ERS-1 radar altimeter. Journal of Glaciology 39: 625-634.
 
Siegert, M.J. 1999. Antarctica's Lake Vostok. American Scientist 87: 510-517.

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Summary Report of a Workshop on
Subglacial Lake Exploration
Cambridge, United Kingdom, 26-29 September 1999

The vast East Antarctic Ice Sheet is now known to cover numerous lakes that may have existed for millions of years. The attention of the scientific community and the public has been captured by these lakes with interest in the nature of resident biota, the age of the lakes, the tectonic forces responsible for forming the lakes, and the record of Antarctic climatic history that is likely to be contained in the sediments beneath them. Prominent among these lakes is Lake Vostok, a remarkably large lake beneath about 4 km of ice in central East Antarctica. In September 1999, a workshop was held in Cambridge, UK, for the purpose of developing a science plan for the exploration of subglacial lakes with particular reference to Lake Vostok. In the course of these deliberations, it was concluded that the biology of the lakes is intrinsically intertwined with:

  1. the tectonic forces that have given rise to the lakes,
  2. the glaciological and geophysical processes that control the thermal and geochemical history of the lakes, and
  3. the climatic evolution of Antarctica.

Thus, the most fruitful scientific approach to the exploration of subglacial lakes is an integrated investigation of the lakes and their environs as closely coupled systems.

Scientific Goals

The principal scientific goals to be addressed by subglacial lake exploration are:

  1. to determine the form and distribution of life in the lake water, the sediment below, and the ice above;
  2. to recover climatic information contained in ice overlying the lakes and sediment underlying the lakes; and
  3. to understand the origins of subglacial lakes and its impact on the evolution of life under the ice.

To accomplish these goals, integrated studies addressing a comprehensive set of scientific objectives in glaciology, geology, microbiology, ecology, geochemistry, geophysics, and limnology are recommended.

Exploration Technologies

Significant technological developments will be required to enable the safe and timely study of subglacial lakes. Development needs include: technologies to reliably access subglacial lakes, in situ instrumentation to collect relevant information, devices for water and sediment return to the surface, and methodologies for deploying devices and acquiring samples from subglacial lakes without causing undue contamination or disturbance.

Stages of Exploration

Lake Vostok is the largest of the known subglacial lakes, and is a logical long-term target for subglacial exploration through in situ instrumentation and sample return. However, there are clear benefits to a staged, progressive scientific programme that includes:

Guiding Principles for Subglacial Lake Exploration

The following requirements are recognized as essential for the successful implementation of a subglacial lake exploration programme:

The best opportunity for attainment of important interdisciplinary scientific objectives is the study of larger lakes, such as Lake Vostok, and, therefore, Lake Vostok, or a lake its equivalent size, must be the ultimate target of a subglacial lake exploration programme.

Recommendations

To ensure continued progress toward the development and implementation of a subglacial exploration programme, the following actions are recommended.

  1. In recognition of the international setting of the lake and the ambitious scope of the scientific programme it is recommended:
  1. In recognition of the substantial resources and the wide range of skills required to accomplish a subglacial exploration programme, it is recommended:
  1. In recognition of the technological and logistical challenges to be overcome, it is recommended:

Fig. 1. A map of Antarctica showing the location of known subglacial lakes,
including Lake Vostok (courtesy of M J Siegert). Full size version (2919 by 2302 pixels)

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Interannual Variability in the Southern Ocean
Summary Report of a Workshop
Cambridge, United Kingdom, 2-7 August 1999

By Eileen E Hofmann
Center for Coastal Physical Oceanography, Crittenton Hall, Old Dominion University, Norfolk, VA 23529, USA
and
Julian Priddle
British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK

Over the last few years, it has become increasingly apparent that the Southern Ocean zone exhibits marked variability at interannual and longer time scales. This manifests itself in changes in patterns of sea-ice distribution, sea-surface temperature, and atmospheric pressure. It has clear consequences for the physical system, and this in turn impinges on the marine ecosystem. At present, it is unclear how much this variability arises from external forcing, and how much is generated by intrinsic variability.

To examine issues responsible for and related to Southern Ocean variability, a workshop was convened at the British Antarctic Survey in Cambridge, United Kingdom, 2-7 August 1999. The intent was to convene an interdisciplinary meeting, so that each scientist could benefit from as wide a range of information as possible. Therefore, the workshop attendees, more than 60 in number and representing 12 countries, included a range of specialists representing the disciplines of biological oceanography, physical oceanography, sea-ice dynamics, glaciology, climate research, and meteorology.

The workshop was structured around three themes that were chosen to provide a framework for developing a summary of the current state of knowledge on Southern Ocean variability. The first theme considered the nature of interannual and decadal change in the physical environment of the Southern Ocean. This section of the workshop drew upon the existing wide range of data sets that can be used to examine internannual to decadal change in the Southern Ocean and to define the character of large-scale variability. Although Southern Ocean variability can be described, there remains considerable uncertainty over the extent to which the variability is coherent around Antarctica, and how much is due to intrinsic behaviour or the Southern Ocean system as opposed to external forcing. Therefore, the second theme of the workshop focused on potential underlying mechanisms responsible for variability and the response of Southern Ocean variations to external forcing through teleconnections. The final workshop theme dealt with the implications of large-scale variability in the Southern Ocean because it is recognized that this has considerable importance in both physical and biological contexts. Issues, such as the determination of the coupling between the Southern Ocean and the global climate system, the interpretation of secular environmental change, possible variation in the biogeochemical role of the Southern Ocean, and the exploitation of marine living resources in the context of a comprehensive conservation framework, were the focus of this portion of the workshop.

The first day of the workshop consisted of plenary presentations related to the three themes. Theme one was overviewed in presentations which focused on interannual to subdecadal variation in: the Southern Hemisphere atmosphere (Ian Simmonds); Southern Ocean physical oceanography (John Church); and Southern Ocean sea ice (Steve Ackley). The issues of the variability mechanisms and teleconnections (theme 2) were treated in presentations on the El-Niño-Southern Oscillation (ENSO) and other atmospheric teleconnections in the Southern Hemisphere (Andrew Carleton) and teleconnections in ice and ocean variability (Doug Martinson). Implications of variability, encompassed in theme 3, were discussed in presentation on ecosystem impacts as seen in the Commission for Conservation of Antarctic Marine Living Resources (CCAMLR) study of the Southwest Atlantic&emdash;Antarctic Peninsula region (Roger Hewitt) and studies of the coupling between forcing and biological response (Steve Nicol). The final overview presentation considered the impacts of recent climate change on the cryosphere (David Vaughan). These informative presentations clearly showed the scientific advances that have been made in describing and understanding variability in the Southern Ocean. However, it was apparent that the research to date has only started to uncover tantalizing processes underlying Southern Ocean variability and that much remains to be done.

Following the plenary presentations was a series of shorter presentations by workshop participants, which gave more detail on specific aspects of Southern Ocean variability. Presentations relating to theme 1 focused on comparisons and analyses of different types of satellite observations (eg, sea-surface temperature, sea-ice concentration, and extent) and various long-term meteorological and oceanographical records. These studies showed that data sets exist for the Southern Ocean that are sufficient to study variability at time-scales that range from interannual to decadal and space-scales that range from regional to that of the entire Antarctic Circumpolar Current (ACC). Moreover, analyses of these data sets are yielding, for the first time, descriptions of Southern Ocean variability that can be related to global-scale atmospheric and oceanic variations.

Many of the presentations related to theme 2 provided different views of the Antarctic Circumpolar Wave (ACW). An Antarctic Circumpolar Wave in surface pressure, wind, temperature, and sea-ice extent is a recently described coupled atmospheric phenomenon that propagates around the Antarctic with a time-scale of four to six years. The ACW has been linked to interannual variations in Southern Ocean sea-ice extent and concentration. The causal mechanism underlying this correlation is under study, but it seems to be related to the atmospherically driven Ekman flux. Similarly, the coupling between the atmosphere and ocean that leads to triggering the ACW is a topic of current research interest, as is the relationship between the ACW and larger-scale ocean-atmosphere coupling, such as the ENSO. Current studies show weak correlations between the ACW and ENSO that, given the lively discussions at the workshop, are subject to more than one interpretation. Additional presentations showed that recent Global Circulation Models (GCMs) have been able to resolve the ACW. However, uncertainty remains over the wave number in both observations and models and the potential mechanism for reinforcing (or even triggering) or damping the ACW by links to quasi-stationary waves in the western Pacific and possibly in the Indian Ocean. Clearly, more research is needed to define better the ACW and its relationship to global-scale climate cycles.

Theme 3 was well-covered by presentations that attempted to link variations in physical forcing to variations in the Antarctic marine ecosystem. For example, one study showed, for the Antarctic Peninsula region, correlations between Antarctic krill (Euphausia superba) recruitment, wind strength, sea-ice cover, and ozone depletion parameters. The conclusion is that these variables are interlinked and that variability cascades throughout the environmental and biological system to produce unanticipated results. Similarly, interannual oscillations on the relative dominance of Antarctic krill and salps (a gelatinous zooplankton) in the Antarctic Peninsula region were suggested to be related to variations in the location of the southern boundary of the ACC, the ACW, or a combination of both. Alternative explanations for the observed shift in zooplankton community dominance were also put forward and discussed. Other presentations illustrated the potential coupling of Antarctic krill populations along the Antarctic Peninsula and those 1500 km across the Scotia Sea at South Georgia. These and the other presentations clearly showed that, for the first time, it is possible to view the Antarctic marine ecosystem in a holistic manner. Cause and effect relations between the physical and biological systems are beginning to emerge.

The ACW has also been linked to interannual variations in recruitment success of Antarctic krill and success of Southern Ocean top predator populations, such as Adélie penguins, seals, and whales. The linkages are indirect through the effect of the ACW on sea ice and the ascribed effects are often delayed in time, as well as location. Thus, strong mechanistic relationships between the ACW and biological productivity remain to be defined. However, the potential effect of the ACW on the Antarctic marine ecosystem is potentially large and deserving of continued study.

Following the presentations, the workshop participants subdivided into working groups that were charged with making recommendations that will stimulate continued and new research in the area of Southern Ocean variability. The first set of recommendations was directed at understanding the role of teleconnections in the Southern Ocean system. First and foremost, the role of the ACW needs better definition and the dynamics underlying this phenomenon need elucidation. Similarly, the ENSO signal, that is observed at high southern latitudes, needs to be defined in terms of its long-term variations, its connection with the ACW, and its connection with the Pacific-South American (PSA) pattern. The impact of other climate signals, such as the Semi-annual Oscillation, needs assessing in terms of effects on the Southern Ocean and the biology of the Antarctic ecosystem.

Variations in the hydrological cycle, due to changes in the rates of evaporation and precipitation, were thought to be important in that determining deep-water formation rates are perhaps related to the ACW, and may underlie multi-decadal atmospheric variations. Strong areas of oceanic divergence around the Antarctic may act as sources of heat and moisture to the atmosphere, which in turn will modify the evaporation-precipitation (E-P) balance. Also, the extent and thickness of sea ice and the formation of polynyas are sensitive to changes in E-P and the potential feedbacks between sea ice and E-P are numerous. These are all areas that need investigation.

An interesting conclusion from the workshop was identification of the need to understand better synoptic-scale atmospheric phenomena, such as the cyclones that develop from low atmospheric pressure systems. Changes in the number, size, intensity, and depth of these features have broad implications for oceanic and biological processes. These atmospheric features may provide a bridge for the exchange of 'information' between the subtropics and high southern latitudes.

Throughout the workshop presentations and discussions, the utility of numerical modelling for understanding atmospheric, oceanic, and biological processes and interactions was obvious. However, the models, while robust, still need development and require quality data sets for input, calibration, and verification. Thus, one recommendation is for continued and expanded atmospheric and oceanic monitoring networks, and also for re-analysis of existing data sets. Experiments in which coupled atmosphere-ocean GCMs are forced with observed increases in 'greenhouse' gas concentrations fail to reproduce the observed warming trend in the Antarctic Peninsula region. While this may indicate a lack of causal connection between the peninsula warming and (much smaller) global warming, firm conclusions cannot be drawn as current GCMs do not produce even the mean climate of the peninsula very well.

The workshop participants recognized that understanding sea-ice dynamics is an integral part of understanding Southern Ocean variability. In particular, the study of coastal and open-ocean polynyas in the Antarctic was considered to be an area where considerable scientific gains could be made in terms of understanding sea-ice variability, ocean-atmosphere coupling, and sea ice-climate interactions. Programmes, such as the polynya watch undertaken by the US National Ice Center, were regarded as being valuable resources in terms of defining where and when sea-ice anomalies occur. Rapid response programmes that provide repeated oceanographical, atmospheric, and biological measurements in polynyas were given a high priority. These discussions led to the recommendation for the establishment of programmes with the flexibility to mount rapid response sea-ice programmes.

Linking of variations in the Antarctic marine ecosystem with those in the physical environment was highlighted as a major research thrust for the next decade. Progress has been made in designing and implementing research programmes (eg Southern Ocean Global Ocean Ecosystems Dynamics programme) that will facilitate characterizing and understanding these interactions, but much is still to be done. Coupled circulation-biological models were recognized as powerful tools for integrating and synthesizing existing oceanographical and biological measurements to provide guidance for future field studies. However, advances in ocean circulation models, which will allow the circulation models to resolve frontal zones and boundaries that are of importance to biological populations, are needed.

Mechanistic links between sea ice and the distribution and productivity of biological populations and communities remain to be determined. Simple correlations with sea-ice extent and concentration, while useful, are not sufficient to determine these links. The workshop participants noted that proxy records, such as biological, geological, or palaeoecological time series, hold much promise for establishing some of these linkages.

Sea ice viewed from above is not the environment experienced by the biological communities that characterize this habitat. Thus, there is a pressing need for the development of instrumentation and techniques for measuring the under sea-ice communities. This may necessitate the involvement of a different community of scientists.

Many of the past studies of the Southern Ocean have focused on the open-ocean aspects of this system. However, the majority of the biological communities are found in continental shelf and coastal environments, which have received little attention. Thus, there is a need for studies of the physical oceanography, meteorology, and sea-ice dynamics of Antarctic coastal regions. The workshop discussions provided an opportunity to formulate research questions that are of interest to a range of disciplines and questions that are tractable, scientifically productive, and important.

Measurement and numerical model calculations suggest that the Southern Ocean is a major sink in the global carbon cycle; however, the magnitude of this sink and its variability in space and time are in question. The numerical models of global carbon cycling show clearly that accurate representations of ocean convection and overturning cells and marine primary productivity are critical to narrowing the range of carbon flux values and modelling the effects of future climate change on the ocean carbon cycle. Recent carbon cycling simulations for the Southern Ocean use atmospheric forcing fields that include interannual variability, such as the ACW. Correct simulation of interannual variability provides a strong validation check for the simulations, provided sufficient data are available for comparison to the model input. At present, data from the Southern Ocean that are adequate to provide this level of validation for the global carbon cycling models do not exist. Given the importance of understanding the role of the Southern Ocean in the global carbon cycle, the recommendation was made to undertake oceanographical sections, repeated at monthly intervals, at several places throughout the Southern Ocean. These sections must cross the extent of the ACC and be continued for several years. Such data sets were regarded as being critical to the development of models that accurately simulate the carbon balance of the Southern Ocean. Also, the workshop participants emphasized the need for development of autonomous instrumentation that can provide the needed real-time description of the Southern Ocean.

The breadth of the Variability Workshop made possible the discussion of a wide range of subjects that crossed traditional disciplinary boundaries, which is perhaps the most important result arising from the workshop. However, the diverse presentations and discussions converged to a few science highlights, suggesting that there are fundamental basic science issues that extend across all disciplines. There was consensus about the existence of the ACW, from both observationalists and modellers, although there are caveats about wave number, mechanisms, and intrinsic versus extrinsic forcing of this feature. The possibility of a mechanism for atmospheric tele-connection between ENSO and the ACW also grew in acceptance as the workshop progressed. The workshop attendees made an initial effort at identifying the causal linkages between variability of the Antarctic marine food web and interannual changes in the physical environment and emphasized that this is a system in which the parts can no longer be viewed separately from the whole. The importance of sea ice for all parts of the physical and biological system was obvious and understanding sea-ice effects is clearly an important area of research. The many results and future research ideas from the workshop will be available in a special section of the Journal of Geophysical Research, which is scheduled for publication in early 2001.

Acknowledgements

The workshop organizers gratefully acknowledge financial support from the International Council for Science through the UNESCO grant scheme, the Intergovernmental Oceanographic Commission, the Scientific Committee on Oceanic Research, the World Climate Research Programme, the Scientific Committee on Antarctic Research, and the British Antarctic Survey.