Abstract
(Englisch)
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Background
Perennial snowbanks and glacierets frozen to the ground constitute virtually unexplored low-altitude ice archives of potentially important information on Holocene climatic variability. During the three project years such features have been investigated with the main goal of (1) describing their glaciological characteristics (thickness, temperature, structure, flow, age, ice accumulation) and (2) analysing the information contained within the ice (isotopes, impurities, organic matter, etc.) in view of climatic interpretations.
Extraordinarily important evidence about minimum glacierization has recently emerged from ice sites at low altitudes, the most spectacular one certainly being the finding of the Oetztal iceman. Special glaciological conditions explain the perfect conservation (cf. also Sjøvold, 1996) of this body which had been buried by snow and ice in a small topographic bedrock depression on a crest/saddle-site at Hauslabjoch (Austrian Alps; 3,200 m a.s.l.) more than 5,000 years ago and which thereafter remained in place until it melted free in 1991 (Baroni and Orombelli, 1996; Spindler, 1995). At a comparable saddle site (Lötschenpass, Swiss Alps) but at an even lower altitude (2,700 m a.s.l.), three well-preserved wooden bows and a number of other archaeological objects had been discovered as early as 1934 and 1944; recent 14C-AMS dating of the three bows gave dendro-chronologically corrected ages of around 4,000 calendar years (Bellwald, 1992). At Jungfraujoch and Titlis in the Swiss Alps, some basic glaciological information about cold ice on crests and summits is available from earlier consulting work (Haeberli and Iken, 1986; Haeberli et al., 1979, 1986; cf. also Haeberli et al., 1992). The summit ice-crest of Kebnekaise in northern Sweden sometimes exhibits distinct ice layers (Holmlund 1998) which are quite comparable to the ones seen at Chli Titlis, but indicate more pronounced lateral variations. Ice considerably older than a few centuries has been detected in perennial snow-banks of the Japanese Alps (Yamamoto and Yoshida 1987, Yoshida et al. 1990), and organic matter from caribou remains, dating back to 9300 yBP, was found within the surface layers of perennial ice patches in northern Canada (Bowyer et al., 1999). These latest findings seem to show that the extent of surface and near-surface ground ice may in places now be more reduced than ever before during even the entire Holocene.
Results of ALPCLIM studies
Since autumn 1998, investigations were initiated on several low-altitude ice patches and on a crest-type miniature ice cap at Piz Murtèl (all sites are located in the Engadin, Eastern Swiss Alps). Visual observation, shallow core drilling, borehole-temperature measurements, radio-echo sounding, temperature data-logging, geodetic surveying and finite-element modelling of basic 2-dimensional configurations were carried out (Frauenfelder et al., in preparation; Haeberli et al., in preparation) and provided first insights into a little studied phenomenon with considerable scientific-environmental research potential. Specific characteristics of the investigated sites - and probably of many other comparable mountain sites - can be summarised as follows: (1) their englacial temperatures are cold and the ice is (at least partly) frozen to the underlying bedrock, (2) ice formation is through refreezing of meltwater (superimposed ice development) rather than by firn compaction, (3) rates of annual movement are small, (4) at the base of the ice bodies (ice/bedrock-contact), movement may be close to zero and the age of basal ice layers may be considerable (historical, holocene?), and (5) direct access is possible to layers of old ages and to the ice/bedrock-contact.
Further investigations are planned and underway both at the Murtèl site and at additional locations, including the analysis of the ice cores, stake measurements at the ice crest, ongoing temperature measurements (bore-hole and minilogger) and observations with an automatic camera to gain more information about ice formation, movement, thermal conditions, permafrost relations, accumulation, and age distribution of the sites. Besides the potential interest of palaeoclimatic information from ice analysis, dating of basal layers and monitoring englacial temperatures as well as geometric changes are now of central interest in such crest- and cornice-type ice archives.
Cold miniature ice caps represent a newly detected ice archive with quite unique conditions of ice formation, flow and preservation. The scientific potential of such miniature ice caps is virtually unexplored and urgently needs systematic research. The existence of very old ice, direct access to ice/rock interface and basal ice, and possibilities of monitoring geometric and thermal changes belong to the most attractive aspects of such archives. Important steps to be undertaken now include the description of glaciological conditions of miniature ice-cap existence by a variety of advanced survey and drilling techniques, the definition of the palaeoclimatic significance of information contained within such still unexplored ice bodies, the establishment of bore-holes for long-term englacial temperature monitoring, comparison between the resulting evidence with evidence from Arctic and high-altitude ice cores and bore-holes, and reconstruction of recent temperature trends by inverse modelling of bore-hole temperatures. Corresponding results could be applied in view to retrospective considerations (historical and Holocene climate variability) as well as prospective assessments (signals of climate change in the coming decades as early detection-part of global climate-related programmes and strategies). In connection with the recently established European network of permafrost bore-holes, monitoring of both, permafrost and miniature ice caps, would constitute an important contribution at Tier 1-level (continental-scale transects along environmental gradients) in the Global Hierarchical Observation Strategy (GHOST) of the Global Terrestrial Observing System (GTOS; Cihlar et al., 1997).
Finally, it can be concluded that such low-altitude ice-archives deserve more interest and better systematic investigations in the near future, especially in view of the fact that the time remaining for their examination and survey might be passing by fast.
References
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