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ASPI project

Antarctica phase VI (2006-2010)

ASPI - Antarctic Subglacial Processes and Interactions: Role of Transition Zones in Ice Sheet Stability

Subject and objectives

The aim of ASPI (Antarctic Subglacial Processes and Interactions) is
(i) to understand the interactions between the ice sheet and the subglacial environment and the processes that control the Antarctic ice sheet, and
(ii) to quantitatively determine the stability of the ice sheet in a changing climate and the impact of climatic variations on the coastal ice sheet.

A key factor in such quantification and impact assessment is the existence of transition zones within the ice sheet. Such transition zones are examples of specific boundary layers widely found in glaciology. Basically they are parts of the ice sheet which overlie basal transition zones where the flow is anomalous. Typical examples of such transition zones are the grounding lines, i.e. the interface between the ice sheet and an ice shelf, between an ice sheet and a subglacial lake, as well as between an ice shelf and its pinning points.

These transition zones are probably among the least understood elements of ice sheets, although they determine to a large extent the processes and dynamics of lateral expansion and retreat of ice sheets as well as the stability of marine ice sheets. Apart from their role in ice dynamics and ice sheet stability, processes and interactions within basal transition zones also hamper the interpretation of the paleoclimatic signal as recorded in deep ice cores. Basal deformation is responsible for disturbing this signal and understanding the processes at the base of ice sheets enables such signal recovery (Raynaud et al., 2005). The subglacial environment opens up new frontiers in Antarctic explorations, as this dynamic and extreme interface still needs to be explored in terms of glaciological, geological, geochemical and biological research efforts.

Together, the present Greenland and Antarctic ice sheets contain enough water to raise sea level by almost 70 m, so that only a small fractional change in their volume would already have a significant effect. Changes in ice discharge generally involve response times of the order of hundreds to thousands of years. The time-scales are determined by isostasy, the ratio of ice thickness to yearly mass turnover, processes affecting ice viscosity, and physical and thermal processes at the bed (IPCC, 2001). Based on satellite altimetry, Wingham et al. (1996) observed no surface elevation change in East Antarctica to within ± 5 mm/yr, but reported a negative trend in West Antarctica of -53 ± 9 mm/yr, largely located in the Pine Island and Thwaites Glacier basins. The measurements of Rignot (1998), showing a 1.2 ± 0.3 km/yr retreat of the grounding line of Pine Island Glacier between 1992 and 1996, suggest an ice-dynamic explanation for the observed thinning.

The West Antarctic Ice Sheet (WAIS) has received particular attention because it has been the most dynamic part of the Antarctic ice sheet in the recent geological past, and because most of it is grounded below sea level – a situation that, according to models proposed in the 1970s, could lead to flow instabilities and rapid ice discharge into the ocean when the surrounding ice shelves would weaken (Thomas, 1973). The potential of WAIS to collapse in response to future climate change is still a subject of debate and controversy. According to the IPCC estimate, major loss of grounded ice, and accelerated sea level rise, is very unlikely during the 21st century. Nonetheless, on a longer time-scale, changes in ice dynamics could result in significantly increased outflow of ice into the ice shelves and a grounding line retreat. However, processes governing such grounding line retreat still remain poorly understood.

Therefore, ASPI seeks to investigate (i) the processes responsible for grounding line migration in marine ice sheets (present and future behaviour), (ii) the effect of marine ice formation on the rheology and ice viscosity of the transition zone, hence the stability of ice shelves, (iii) the stability of subglacial lakes over longer time spans, and (iv) basal processes and interactions in order to unravel the paleoclimatic signal in deep ice cores.

Complementary resources about this scientific project

Partners and Contact information

Coordinator: Dr. Frank Pattyn
Université Libre de Bruxelles (ULB)
Department of Earth and Environmental Sciences (DSTE) - Polar Glaciology Unit CP 160/03
50, avenue F.D. Roosevelt
B-1050 Brussels
Tel: +32 (0)2 650 22 27
Fax: +32 (0)2 650 22 26
fpattyn@ulb.ac.be
www.ulb.ac.be/rech/inventaire/unites/ULB182.html

Partner 2: Dr. Jean-Louis Tison
Université Libre de Bruxelles (ULB)
Department of Earth and Environmental Sciences (DSTE) - Polar Glaciology Unit CP 160/03
50, avenue F.D. Roosevelt
B-1050 Brussels
Tel: +32 (0)2 650 22 27
Fax: +32 (0)2 650 22 26
jtison@ulb.ac.be
www.ulb.ac.be/rech/inventaire/unites/ULB182.html

Partner 3: Dr. Philippe Huybrechts
Vrije Universiteit Brussel,
Geography Department (VUB-DGGF)
Pleinlaan, 2
B-1050 Brussels
Belgium
Tel: +32-2-629.35.93
Fax:+32-2-629.33.78
phuybrec@vub.ac.be

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