N. Tvis Knudsen

Hydrochemical characteristics of bulk meltwater from an entire ablation season, Longyearbreen, Svalbard

The ionic and isotopic characteristics of bulk waters emanating from the cold-based Longyearbreen, central Svalbard, in 2004 are examined to determine lithological, hydrological and glaciological controls on water composition, solute provenance and chemical denudation. The geology consisted of reactive coal seams and associated sedimentary rocks. Acidity caused by microbial-mediated oxidation of sulfides and, to a lesser extent, nitrogen-bearing minerals was neutralized by congruent dissolution of dolomite and incongruent weathering of silicates in open-system subglacial drainage channels. The ablation season was divided into an early melt season, a peak-flow period and a late melt season. The runoff distribution during these periods was 1.7%, 89.7% and 8.6%, respectively, whereas the solute flux distribution was 1.9%, 82.1% and 16.0%, respectively. Comparisons between different annual solute flux estimation methods indicated that extrapolation of peak-flow period data significantly underestimated both the early- and late-melt-season solute fluxes. About 3.8% of the solutes derived from sea-salt spray, 0.7% from acid aerosol deposition and 95.5% from crustal/organic sources. The physical and chemical conditions resulted in diffusion of CO 2 rather than atmospheric drawdown. The cation-equivalent weathering rate and the crustal solute yield were 322 ΣmEq + m -2 a -1 and 22 tkm -2 a -1 , respectively, which are within the regional range of Svalbard. However, the chemical weathering intensity was as high as 940 ΣmEq + m -3 owing to the relatively low specific discharge of 0.34 ma -1 .

20th-century glacier fluctuations on Disko Island (Qeqertarsuaq), Greenland

Abstract This study assesses glacier fluctuations on Disko Island (Qeqertarsuaq), central West Greenland, during the 20th century. A total of 247 glaciers, of which 75 are classified as surge-type glaciers, are included, representing about 95% of the glacierized area. Based on expedition accounts and early maps, it is concluded that recession rates were highest during the first half of the century. Between 1953 and 2005, 70% of the glaciers showed recession, 28% remained stationary and 2% experienced overall advance due to glacier surging. The mean recession rate of quiescent surge-type glaciers was 20 ma–1 compared to 8ma–1 for normal glaciers. Identification of changes in glacier length controlled by climate changes is achieved by excluding surge-type glaciers from the dataset. The result indicates that glaciers with ablation areas facing in the arc south to northwest, covering an area above 5 km2 and having a terminus elevation below 800 m are the most climate-sensitive.

Isotopic and ionic variations in glacier river water during three contrasting ablation seasons

The significance of the baseflow component of glacier river discharge in summer varies with geographical location, altitude, glacier geometry and glacier size. Baseflow is maintained by meltwater generated above the transient equilibrium line and by water released from temporary storage on, in or beneath the glacier. At the Norwegian glacier Austre Okstindbreen, where precipitation is generally high throughout the year and the summers are cool and wet, observations in three successive, but contrasting, years have shown that Na+ ion concentrations in the glacier river water are influenced strongly by the amount of snowmelt. This itself depends on the preceding winter conditions, which determine the amount of accumulation, and on the current summers weather. The efficiency of the glaciers drainage systems depends on the general progress of summer ablation. The speed with which the systems develop influences ion provision from subglacial sources. Ca 2+ ion concentrations are largely determined by subglacial conditions. Oxygen isotope variations in glacier river water reflect the relative contributions made to total discharge by snow meltwater and other sources; the composition of the snow cover, which is a function of winter temperatures, has a strong influence. Ice meltwater has low isotopic variability, but the isotopic composition of rainfall varies markedly. A simple model of mixing of englacial and subglacial waters, each of a constant composition, cannot be applied to a high-latitude glacier of the size and altitudinal range of Austre Okstindbreen.

Recent marginal changes of the Mittivakkat Glacier, Southeast Greenland and the discovery of remains of reindeer (Rangifer tarandus), polar bear (Ursus maritimus) and peaty material

Abstract Geografisk Tidsskrift, Danish Journal of Geography 108(1):137–142, 2008 During field observations in August 2005 antler remains of a reindeer were found at a recently deglaciated site at about 500 m asl., and bones from a polar bear were found at about 300 m asl. along the margin of Mittivakkat Glacier, Southeast Greenland. Radio carbon dating determined the age of the samples to 720 14C years and 350 14C years, respectively. In August 2006 old surface vegetation covering peaty material became exposed due to ice recession close to the site where the antler was found. The radio carbon age of small roots from the material was determined to 1530 14C years, and is in agreement with dating of woody remains of Salix glauca found close by, at the top of a nearby nunatak in 1999. The antler indicates that reindeer lived in the area when the glacier began to advance from a position where it was close to or smaller than today. The vegetation surface and peaty material indicate that the climate was warmer before the onset of the Little Ice Age in Southeast Greenland than today.

Glaciological features in the initial quiescent phase of Kuannersuit Glacier, Greenland

Abstract This paper describes glaciological features observed on the surface of the large outlet glacier Kuannersuit Glacier on Disko Island, West Greenland, during its initial quiescent phase after a major surge event occurred in 1995–98 in order to classify the glaciomorphological surge system. Focus is on surge features either associated with active surging such as a propagating surge front and serac formation or formed as a consequence of surging such as looped medial moraines and potholes; and on hydrological features related to the evolution of the glacier drainage system such as the supraglacial routing, moulin types and chasms. A chronological glaciomorphological model of the initial quiescent phase of Kuannersuit Glacier, which can be regarded as representative for large outlet surge‐type glaciers with terrestrial terminal regime and long quiescent phase, is proposed.

The presence of thrust-block naled after a major surge event: Kuannersuit Glacier, West Greenland

Abstract Thrust-block naled in front of Kuannersuit Glacier, West Greenland, appears to have formed during the termination of a terrestrial surge event by a combination of enhanced winter runoff, rapid advance of the glacier terminus, and proglacial stress release by thrusting and stacking of naled blocks. This process is equivalent to the formation of thrust-block moraines. The thrust-block naled consists of at least seven thrust sheets, which are characterized by stratified ice with beds composed of a lower debris-rich lamina, an intermediate dispersed lamina and a top clean-ice lamina, and underlain by frozen outwash deposits. The thrust-block naled differs from basal stratified ice in the absence of internal deformation structures, a relatively low debris concentration, a clay-rich particle-size distribution and a preferential sorting of lighter minerals. The oxygen isotope composition of the thrust-block naled is indistinguishable from δ18O values from meteoric glacier ice and bulk meltwater, but different from basal stratified ice facies. The d–δD relationship indicates that thrust-block naled has been formed by freezing of successive thin layers of bulk waters with variable isotopic composition, whereas basal stratified ice has developed in a subglacial environment with regelation. This work shows that the association between proglacial naled and rapidly advancing glaciers may have significant consequences for the proglacial geomorphology and the interpretation of basal ice layers.

RECENT CHANGES OF NORDBOGLETSCHER AND NORDGLETSCHER, JOHAN DAHL LAND, SOUTH GREENLAND

Generally, outlet glaciers from the Inland lee in South Greenland have retreated and thinned considerably since the 19th century. A sector in Johan Dahl Land, comprising the glaciers Nordbogletscher, Nordgletscher, and Eqalorutsit kangigdlit sermiat, has no trim-line zones. These glaciers have probably reached their most advanced position in historical time and are advancing further. Marginal and surface changes of the glaciers, over the last 30 years, are determined, using topographic maps based on aerial photographs taken in 1953, 1977, and 1981 and compared with ablation and surface movement of ice measured at stakes, established in 1978 at Nordbogletscher. The conclusion, made on the basis of the observations, is that the advance is the result of a higher transport rate of ice from the accumulation area than can ablate during the summers in the ablation area, under prevailing climatic conditions.

Recent changes of some glaciers of east Svartisen, Norway.

Changes which have taken place during the last hundred years at the north-eastern glaciers of Svartisen are welldocumented. Although the period has been characterised predominantly by glacier retreat, the rates of retreat have varied, as have changes of ice thickness at different altitudes. Comparisons of photogrammetric maps from 1945, 1968, 1975 and 1981 illustrate the differences, both temporal and spatial, at the two largest glaciers. Since 1945, a gradual increase of surface slope of the lower part of Fingerbreen has accompanied a fairly uniform decrease of thickness (about 3 m a-1). Above 500 m, however, the surface slope has changed little and the rate of decrease of ice thickness has not exceeded 2 m a-~. Minor advances of Fingerbreen have interrupted its recession and formed low transverse till ridges. At Lappebreen, retreat almost ceased between 1975 and 1981; above 600 m, the glacier thickness increased. Future studies of glacier change will be a valuable contribution to water resource investigations.

Surface-velocity and strain-rate variations at the glacier Austre Okstindbreen, Okstindan, Norway, 1976-95

Long-term observations of surface velocities and strain rates at the Norwegian glacier Austre Okstindbreen revealed both temporal and spatial var iations. During a period of 6 years, the amount of ice passing through a cross-section slightly below the mean equilibrium-line altitude (1250 m ) was some 30% less than the amount which accumulated above the equilibrium line. The mean horizontal component of surface velocity at the centre of the cross-section was of the order of 4550 m a I, whilst the thinner marginal ice moved less rapid I y. At an altitude of about 12301200 m, surface velocities generally increased as the ice entered a steep icefall. In the lower part of the icefall , mean surface velocities again were of the order of 50 m a I. From there, a general decrease down-glacier was evident, and longitudinal compression along the curving centre line of flow was accompanied by lateral extension. The contribution of internal deform ation to surface flow at the lower part of the glacier, which was less than ISO m thick, is likely to have been relatively small, and between-year variations of the horizontal component of surface flow which a ffected a large area probably were a response to changes of basal sliding rates, reflecting variations of mass balance and water availabi lity.