The International Geosphere-Biosphere Programme on Past Global Changes (IGBP-PAGES) and the Global Change and the Antarctic Programme (GLOCHANT) of the Scientific Committee on Antarctic Research (SCAR) are coordinating an investigation of the Late Quaternary sedimentary record of Antarctic Ice Margin Evolution (ANTIME). Much of the ANTIME sedimentary research is focused on the coastal region surrounding the Antarctic ice margin, and includes the inner continental shelf, coastal ice-free oases and mountain basins. The resolution of past fluctuations in the extent and volume of the Antarctic ice sheet will enable ANTIME researchers to determine the time-dependent contribution of the Antarctic ice sheet to fluctuating global sea-level, over the Last Glacial Cycle (last 130 kyr). Additional studies on coastal evolution, paleoecology, paleolimnology and paleohydrology are establishing a detailed history of climate and environmental events on a centennial to millennial-scale during the Holocene (last 10 kyr). A workshop was held during September 1998 at Lake Kawaguchi-ko, Japan, to develop an effective implementation plan for the coastal component of the ANTIME program. Coastal and glacial geomorphologists along with geochemists and paleoecologists attended the workshop, which was hosted by Japan's National Institute of Polar Research, with funding for participant support from the IGBP-PAGES, SCAR-ANTIME, US National Science Foundation, Fukutake Foundation and the Japan Polar Research Association.

Scientific presentations made at the workshop provided the basis for determining the priority research issues, which were summarised into the following three questions directed at resolving the complex history of climate and environmental change:

1) Does the Antarctic distribution of Holocene relative sea-level high-stands reflect regional differences in ice sheet extent at the Last Glacial Maximum (LGM) ?

In the last two decades there has been considerable debate on the size and extent of the Antarctic ice sheet and its sea-level contribution during the Last Glacial Cycle. One of the clues to resolve this issue may be the striking correspondence between the spatial distribution of modern ice accumulation rate and the spatial distribution of Holocene relative sea-level high-stands (marine limits) and isostatic rebound of the bedrock around East Antarctica. The ice accumulation rate is a primary determinant of how big the ice sheet can grow and expand onto the continental shelf. Following the glacial expansion during the Last Glacial Cycle, the ice sheet margin thinned and retreated to its present position. The mass of ice sheet removed from the coastal zone can be estimated from the amount of observed post-glacial isostatic rebound, which is often manifest in the emergence of islands and promontories along the present Antarctic coast. Hence, the regional differences in ice sheet growth during the Last Glacial Cycle may be determined from the examination of the spatial patterns of ice accumulation and isostatic rebound. Along the coast from Victoria Land to western Wilkes Land (170=B0 E to 100=B0 E), marine limits= are on the order of 30 m above present sea level, whereas they are usually less than half this elevation along the remainder of the explored East Antarctic coast. From isostatic relationships, this suggests that the East Antarctic ice sheet reached its maximum extent along the (170=B0 E to 100= =B0 E) sector, and that ice sheet growth around the remainder of East Antarctica may have been considerably smaller. The greatest area of ice sheet growth was in the Ross Sea and Weddell Sea embayments, into which the expanded West Antarctic ice sheet drained. This work, together with the research on resolving the timing of the post-glacial retreat has a strong bearing on our interpretation of the Antarctic contribution to sea-level. A recent synthesis study by Ingolfsson et al. (1998) indicates that the bulk of the Antarctic contribution to sea-level rise following the LGM occurred late, between 8 to 5 kyr BP, after the northern hemisphere deglaciation had been completed. However, the reasons for such a rapid and late deglaciation are unclear.

2) Have environmental changes in the circum-Antarctic coastal zone been largely synchronous during the Holocene?

Despite the fragmented nature of the sedimentary record in coastal Antarctica, there remains evidence for considerable climate and oceanic variability on centennial to millennial time-scales during the Holocene. Proxy records of changes in sea-ice extent and open water within the coastal zone, lacustrine water balance and glacial extent are providing an insight into climate variability. Geochemical analyses, principally stable oxygen and carbon isotopes, on modern and fossil calcareous marine species are providing data on oceanic conditions such as temperature, salinity and glacial meltwater input, which control their ecology. Circumpolar marine mollusc species are particularly suitable for these analyses since they have lifespans exceeding several decades with well-resolved sub-seasonal growth bands in their shells. The abundance of in situ marine molluscs in the isostatically uplifted coastal sediments which occur above the Antarctic shoreline, is enabling researchers to assemble a circum-Antarctic paleoecology and paleoenvironmental data set. These marine mollusc fossils generally date from 8 kyr BP which is consistent with the timing of ice-sheet retreat and associated isostatic uplift of the coastal areas. The subsequent environmental and climate events appear to have occurred synchronously around the circum-Antarctic. This will be tested through the use of multiple chronologies and the preparation of a circum-Antarctic stratigraphy. A circum-Antarctic history of seawater salinity and temperature will provide a basis for interpreting fluctuations in sea-ice concentration and glacial melting episodes, and for regional comparison with other Antarctic and other Southern Hemisphere proxy climate records.

3) Do marine fossils, dated as pre-Holocene by radiocarbon analyses, represent multiple marine events recorded around the Antarctic margin?

The ice core and deep-sea marine sediment records of proxy climate depict several warm periods known as interstadials during the Last Glacial Cycle. The sensitivity of the Antarctic ice sheet to these interstadial events is largely unknown, and would provide useful analogous data for predicting the response of the ice sheet to future abrupt and non-linear climate change. Some insight into the record of interstadial events has been determined from the collection and analysis of emerged marine macrofossils from both East and West Antarctica. Circum-Antarctic radiocarbon data measured on these macrofossils, forms a bimodal 14C-age distribution with peaks at 35-20 kyr and 8-0 kyr BP (Berkman et al. 1998). This may indicate that the coastline has experienced two periods of glacial retreat during the Last Glacial Cycle which may have been associated with climate warming. It is possible that during these intervals, the coastline may have experienced less fast sea-ice and more open water than present. In addition, glacial-geomorphological, landscape weathering and lacustrine sedimentary evidence from modern Antarctic glacial ice-free 'oases' in East Antarctica indicates that some regions were free of glacial ice or with a thin locally derived ice cover prior to (40 kyr BP) and during the LGM (20 kyr BP). ANTIME researchers are examining whether this reduction in glacial and sea ice defines the Antarctic response to the global climate oscillations (interstadial or warm events) or whether these coastal events primarily reflect the recession of the ice sheet due to its internal dynamics.

Whatever the cause of these events, their timing remains ambiguous. Amino acid racemisation (AAR) analyses made on calcareous macrofossils in raised marine deposits indicate that some of these species may be much older (Last Interglacial, 125 kyr BP or even earlier warm climate periods), and may have been subsequently reworked by glacial and coastal processes before being exposed in modern sediments. Consequently, the development of comparative geochronologies using thermoluminescence, optically stimulated luminescence (OSL), cosmogenic isotope and amino acid racemization analyses, is a high priority for ANTIME to resolve the sequence of events. Even within the range of radiocarbon dating (up to 30-50 kyr BP), such multi-chronometer approaches are vital because of the significant problems that remain with understanding the Antarctic radiocarbon variability in regions, species and time in both the marine and terrestrial systems. These radiocarbon questions will be the focus of the next ANTIME workshop to be held at the Woods Hole Oceanographic Institution in May 1999.

Process Studies

In addition to focusing on the above three questions, ANTIME research is also being applied to modern process studies, to enhance the interpretation of proxy records associated with analogous systems in the past. Continuous measurements of vertical land movements using global positioning systems (GPS) over periods of several years are being developed to provide direct measurements of modern isostatic rebound rates from ice-free coastal areas.

Data from submersible remotely operated vehicles (ROV) equipped with photographic and hydrographic instrumentation, are being used to interpret sedimentary features associated with the underwater dynamics and the glacial history of ice masses which extend into the ocean. Geochemical research on the carbon cycling in lacustrine systems has revealed a vertical radiocarbon zonation in Antarctic lakes (Doran et al. in press). In general, there is an upper zone which is mixed with atmospheric radiocarbon and has near modern ages. Underneath, radiocarbon ages are thousands of years old and largely influenced by glacial meltwater. This research has significant implications for the interpretation of lacustrine paleoecology and glacial landscape evolution.

The ANTIME Science and Implementation Plan is currently being drafted. The plan will be available from both the GLOCHANT and PAGES Project Offices in the first half of 1999. It will also be available on the ANTIME home page ( http://www.antcrc.utas.edu.au/scar/antime/antime.html).

For further information an overall state of the art synthesis of offshore and onshore research on ANTIME themes was recently published as a series of papers in a special issue of Antarctic Science (Volume 10, No. 3, September 1998, 223-366). Abstracts of papers presented at the workshop are available at (http://polarmet.mps.ohio-state.edu).

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