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SPRI Review 2001: Glacier Hydrology and Dynamics Group

Glacier Hydrology and Dynamics Group

Dr N. Arnold

Dr I. Willis, D. Rippin, A. Fox

The arrival of 'modern' humans in Europe around 30,000 years ago, followed by the extinction of the Neanderthals, may seem an odd motivation for research by glaciologists based in the Institute. However, the first papers from the Stage 3 Project, an international, multidisciplinary research effort, in which members of the GHD Group have been involved from the outset, have recently been published. The Stage 3 Project aims to improve our understanding of this momentous event by providing more detailed, and hopefully more realistic, information about the climate in Europe during Oxygen Isotope Stage 3 (OIS3), between around 45,000 and 30,000 years ago. Ice cores from the Greenland Ice Sheet have shown that the climate during this period was quite unstable, and the project goals are to evaluate if this variability played a significant role in early human history.

OIS3 spanned the period in the middle of the last 'Ice Age,' known in Europe as the Weichselian. The popular view of this time period is of 'vast ice sheets and an unrelenting, bitterly cold climate, fit neither for human nor beast, that lasted up to 100,000 years' (Van Andel 2002: 2). However, recent advances in our understanding of ice-age climates have shown that this is not necessarily true. Ice cores have provided amazingly detailed information about past climates, and have shown that such extreme conditions are actually quite rare, even during a so-called 'ice age.' These cores suggest that OIS3, in particular, formed a relatively warm interlude during the Weichselian, albeit with a rather unstable climate. During this time, warm events, with temperatures sometimes only 2°C below present-day European values, lasted a few millennia, but these were punctuated by cold events, lasting a few centuries, that were almost as cold as the last glacial maximum.

In order to build a better picture of the European climate during this time, a key factor is the extent of the European ice sheets during OIS3. The 'conventional wisdom' for the history of European ice sheets is of large, relatively stable ice sheets covering most, if not all, of Scandinavia for the bulk of the Weichselian, expanding from these areas into northern Germany, and possibly across the North Sea, some time after 30,000 years ago. However, there is some controversial evidence that during OIS3, large areas of Scandinavia may have been ice-free, given the warm climate that prevailed for at least part of OIS3. Members of the GHD Group became involved with the project to evaluate the possibility of such smaller ice sheets from a glaciological perspective, using ice-sheet models to evaluate if such a smaller ice sheet was glacio-logically 'plausible.' If it were, this lack of ice could mean that the climate in northern Europe might have been much milder than previously supposed; the modelled ice sheet extent would also provide a key boundary condition for General Circulation Model experiments, linked to a Regional Climate Model for Europe, which aim to evaluate the European climate during OIS3, and which form a key component of the work for the Stage 3 Project. This work has now been undertaken by a team led by Professor Eric Barron of Pennsylvania State University.

The ice-sheet model developed by the GHD Group specifically included the effect of glacier hydrology on ice-sheet dynamics. Hydrology is believed to play a key role in explaining the dynamics of present-day glaciers and ice sheets, and it seems very likely to have played a key role in the past. The model developed sought to investigate this possible impact, and the idea that during a period of warmer climate, more meltwater would be available beneath the ice, which could enable the hydrology to have more impact on ice flow. The modelling work showed that this seems to be the case; during warm periods, the ice flows faster, due to lubrication of the base of the ice by water. This transports ice more rapidly from the cold interior of the ice sheet to the melting margin, leading to a rapid shrinking of the ice sheet. During the shorter cold spells, the lack of water means the ice sheet can only move slowly, and so cannot advance rapidly across the landscape. These results have now been published (Arnold and Sharp 2002; Arnold and others 2002), and form the boundary condition for the climate modelling work.

Other research highlights during the year have been the recent award of the PhD to Dave Rippin, for his research on the dynamics of Midre Lovenbreen, Svalbard; the successful conclusion of the NERC funded project obtained by Dr Arnold, which investigated the small-scale variability of glacier surface characteristics and their impact on glacier energy balance, in collaboration with Dr Gareth Rees and the Remote Sensing Group; and Andy Fox's success in developing a distributed model for snow hydrology on glacier surfaces, the initial results of which are to be presented at the forthcoming European Geophysical Union Conference.

References

Arnold, N.S., and M.J. Sharp. 2002. Flow variability in the Scandinavian ice sheet: modelling the coupling between ice sheet flow and hydrology. Quaternary Science Reviews 21: 485-502.

Arnold, N.S., T.H. Van Andel, and V. Valen. 2002. Extent and dynamics of the Scandinavian Ice Sheet during Oxygen Isotope Stage 3 (65,000-25,000 yr BP). Quaternary Research 57: 38-48.

Van Andel, T.H. 2002. The climate and landscape of the middle part of the Weichselian glaciation in Europe: the Stage 3 Project. Quaternary Research 57: 2-8.