Former dynamic behaviour of a cold-based valley glacier on Svalbard revealed by basal ice and structural glaciology investigations

Large numbers of small valley glaciers on Svalbard were thicker and more extensive during the Little Ice Age (LIA), demonstrated by prominent ice-cored moraines up to several kilometres beyond present-day margins. The majority of these glaciers have since experienced a long period of strongly negative mass balance during the 20th century and are now largely frozen to their beds, indicating they are likely to have undergone a thermal transition from a polythermal to a cold-based regime. We present evidence for such a switch by reconstructing the former flow dynamics and thermal regime of Tellbreen, a small cold-based valley glacier in central Spitsbergen, based on its basal sequence and glaciological structures. Within the basal sequence, the underlying matrix-supported diamict is interpreted as saturated subglacial traction till which has frozen at the bed, indicating that the thermal switch has resulted in a cessation of subglacial sediment deformation due to freezing of the former deforming layer. This is overlain by debris-poor dispersed facies ice, interpreted to have formed through strain-induced metamorphism of englacial ice. The sequential development of structures includes arcuate fracture traces, interpreted as shear planes formed in a compressive/transpressive stress regime; and fracture traces, interpreted as healed extensional crevasses. The formation of these sediment/ice facies and structures is indicative of dynamic, warm-based flow, most likely during the LIA when the glacier was significantly thicker.

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title: The Mass Balance of Circum-Arctic Glaciers and Recent Climate Change
abstract: The sum of winter accumulation and summer losses of mass from glaciers and ice sheets (net surface mass balance) varies with changing climate. In the Arctic, glaciers and ice caps, excluding the Greenland Ice Sheet, cover about 275,000 km2of both the widely glacierized archipelagos of the Canadian, Norwegian, and Russian High Arctic and the area north of about 60°N in Alaska, Iceland, and Scandinavia. Since the 1940s, surface mass balance time-series of varying length have been acquired from more than 40 Arctic ice caps and glaciers. Most Arctic glaciers have experienced predominantly negative net surface mass balance over the past few decades. There is no uniform recent trend in mass balance for the entire Arctic, although some regional trends occur. Examples are the increasingly negative mass balances for northern Alaska, due to higher summer temperatures, and increasingly positive mass balances for maritime Scandinavia and Iceland, due to increased winter precipitation. The negative mass balance of most Arctic glaciers may be a response to a step-like warming in the early twentieth century at the termination of the cold Little Ice Age. Arctic ice masses outside Greenland are at present contributing about 0.13 mm yr−1to global sea-level rise.

title: Controlled moraines: origins, characteristics and palaeoglaciological implications
abstract: Controlled moraines are supraglacial debris concentrations that become hummocky moraine upon de-icing and possess clear linearity due to the inheritance of the former pattern of debris-rich folia in the parent ice. Linearity is most striking wherever glacier ice cores still exist but it increasingly deteriorates with progressive melt-out. As a result, moraine linearity has a low preservation potential in deglaciated terrains but hummocky moraine tracts previously interpreted as evidence of areal stagnation may instead record receding polythermal glacier margins in which debris-rich ice was concentrated in frozen toe zones. Recent applications of modern glaciological analogues to palaeoglaciological reconstructions have implied that: (a) controlled moraine development can be ascribed to a specific process (e.g. englacial thrusting or supercooling); and (b) controlled moraine preservation potential is good enough to imply the occurrence of the specific process in former glacier snouts (e.g. ancient polythermal or supercooled snouts). These assumptions are tested using case studies of controlled moraine construction in which a wide range of debris entrainment and debris-rich ice thickening mechanisms are seen to produce the same geomorphic features. Polythermal conditions are crucial to the concentration of supraglacial debris and controlled moraines in glacier snouts via processes that are most effective at the glacier–permafrost interface. End moraines lie on a process–form continuum constrained by basal thermal regime. The morphological expression of englacial structures in controlled moraine ridges is most striking while the moraines retain ice cores, but the final deposits/landforms tend to consist of discontinuous transverse ridges with intervening hummocks, preserving only a weak impression of the former englacial structure. These are arranged in arcuate zones of hummocky moraine up to 2 km wide containing ice-walled lake plains and lying down flow of streamlined landforms produced by warm-based ice. A variety of debris entrainment mechanisms can produce the same geomorphic signature. Spatial and temporal variability in process–form relationships will lead to the sequential development of different types of end moraines during the recession of a glacier or ice sheet margin.

title: Apron Entrainment at the Margins of Sub-Polar Glaciers, North-West Ellesmere Island, Canadian High Arctic
abstract: From observations on the sub-polar glaciers of Phillips Inlet, north-west Ellesmere Island, neither complex basal thermal regimes nor internal thrusting need be invoked to explain all types of debris distribution in the basal ice of sub-polar glaciers. Debris is present in the terminal ice cliffs as: ( I) debris-poor folia expressing internal flow patterns; (2) debris-rich bands of various thickness; and (3) augens or clots. Debris-rich bands and augens are concentrated predominantly in the basal ice, contain a wide range of grain-s izes, cut across debris-poor folia, rarely extend > I m laterally, and are irregularly spaced. Obse rvations on patterns of entrainment and contemporary processes at ice margin s, together with clast-shape analyses, suggest that the recycling and re-incorporation of fluvi a l/ deltaic sediment, aprons, and pro-glacially thrusted blocks at th e ice face are an alternative process of debris entrainment to basa l plucking and large scale freeze-on a t the base of the glacier. The most active processes observed at the g lacier margins are fluvial, and the origins of so me debris-rich bands and augens are linked to thermal-eros ional niches and abandoned mea nders in the base of the glacier cliff face . Because the large-scale accumulation of ice-cored debris at glacier snouts represen ts periods of increased run-off and snout recession (spec ifically during the early Holocene) , basal and englacial debris concentrations resulting from glacial over-riding and re-incorporation have great palaeoclimatic s ignificance.

title: The basal ice layer of glaciers and ice sheets
abstract: In many glaciers and ice sheets there is a basal ice layer (BIL) in which the ice is conditioned primarily by processes operating at the bed. The BIL is chemically and physically distinctive, and is characterised by a component of basally derived sediment. The BIL is: a rheological control on ice-sheet dynamics; an indicator of subglacial conditions and processes; an agent of subglacial geologic processes; the source of a substantial proportion of glacial sediments; a limit to the downward extension of the climate record from deep ice cores. If debris characteristics of the BIL are preserved in glacial sediments, former glacier conditions can be inferred. Analysis of stable isotopes, gas and cation composition, ice crystallography, debris composition and structural glaciology has elucidated many mechanisms for BIL formation. Common elements can be identified from a range of locations. Key issues are entrainment of ice and debris from the bed, formation of new ice, metamorphism of existing ice in the BIL, and thickening of the BIL by deformation. A distinction can be made between basal ice formed by accretion of material from the bed (‘stratified facies’) and basal ice formed by metamorphic processes within the ice close to the bed (‘dispersed facies’).

title: Clast shape analysis and clast transport paths in glacial environments: A critical review of methods and the role of lithology
abstract: The reconstruction and tracing of transport paths in glaciated (and other) environments have a long tradition in the Earth Sciences. We here present a dataset of clast shape samples from a worldwide selection of glaciated mountain environments in order to assess the reliability of this approach overall and the role of lithology on the performance of clast shape measurements in particular. Our findings demonstrate that the widely-used RA-C40 co-variance approach is applicable to 63% of the 19 catchments investigated, while the alternative RWR-C40 approach is more widely applicable to 75% of these catchments. A systematic assessment of mixing of lithologies at the catchment scale demonstrates that such mixing leads to pronounced overlaps between different control envelopes that had previously been separated, thereby removing the discriminatory power of the method. Mixing of similar lithologies between different catchments shows an even more extreme loss of discriminatory power, which strongly suggests that lithology plays a primary role in determining clast shape, and that catchment-specific processes are superimposed. Systematic analysis of the dataset also shows that nearly all catchments (apart from two) can be grouped into two types. Type I relates to sites in lesser mountain ranges and is characterised by dominantly blocky forms in the subglacial realm, highlighting significant reworking processes. Type II sites are dominantly in high-mountain environments and characterised by a high similarity between subglacial and fluvial control envelopes. This indicates that, although reworking may be pronounced, it is not necessarily effective enough to remove the platy shape that most likely results from extraglacial and supraglacial inputs. Our study highlights the potential of clast shape analysis as a tool that allows generic processes to be identified between catchments, thereby enabling an understanding of debris cascades in glaciated mountain environments. We finish with recommendations for ensuring that future clast shape studies are robust, reproducible and comparable between different sites.

title: Application of borehole optical televiewing to investigating the 3-D structure of glaciers: implications for the formation of longitudinal debris ridges, midre Lovénbreen, Svalbard
abstract: Digital optical televiewing (OPTV) of hot-water-drilled boreholes is evaluated as a technique for the investigation of englacial ice and debris structures on the basis of six boreholes drilled in the terminus region of midre Lovénbreen, Svalbard. The resulting OPTV logs successfully reveal several visually distinctive englacial ice properties and deformation structures (e.g. oblique englacial fractures imaged here for the first time). Combining these OPTV logs with surface mapping has resulted in the identification of eight separate structural elements, several of which can be interpolated onto 3-D grids at a node spacing of 1 m vertically and 10 m horizontally. Basally derived englacial sediment layers are also found to be intercalated with primary stratification, elevated into near-vertical planes around a central fold axis by large-scale lateral folding. The analysis also allows supraglacial longitudinal debris ridges to be subclassified into two types: a previously described (type-I) form, which are the exposed fold axes of large-scale lateral folds, and a new (type-II) form experiencing secondary deformation by small-scale horizontal folding in association with vertical displacements across arcuate shear planes in response to longitudinally compressive stresses near the glacier terminus. Although using boreholes to investigate glacier structure is limited (e.g. by parallelism with vertical planes), applying OPTV to multiple boreholes at midre Lovénbreen has successfully revealed a range of 3-D structural elements at high spatial resolution. As such, interpolating between multiple OPTV logs overcomes many of the problems associated with interpretations made solely on the basis of surface-based structural mapping, and combining the two techniques represents a powerful glaciological tool.

title: Magnetic fabrics in the basal ice of a surge-type glacier
abstract: Anisotropy of magnetic susceptibility (AMS) has been shown to provide specific useful information regarding the kinematics of deformation within subglacially deformed sediments. Here we present results from debris-rich basal glacier ice to examine deformation associated with glacier motion. Basal ice samples were collected from Tunabreen, a polythermal surge-type glacier in Svalbard. The magnetic fabrics recorded show strong correlation with structures within the ice, such as sheath folds and macroscopic stretching lineations. Thermomagnetic, low-temperature susceptibility, varying field susceptibility, and isothermal remanent magnetism acquisition experiments reveal that the debris-rich basal ice samples have a susceptibility and anisotropy dominated by paramagnetic phases within the detrital sediment. Sediment grains entrained within the basal ice are inferred to have rotated into a preferential alignment during deformation associated with flow of the glacier. An up-glacier directed plunge of magnetic lineations and subtle deviation from bulk glacier flow at the margins highlight the importance of noncoaxial strain during surge propagation. The results suggest that AMS can be used as an ice petrofabric indicator for investigations of glacier deformation and interactions with the bed.

title: Graphical representation of particle shape using triangular diagrams: an Excel spreadsheet method
abstract: Analysis of the shape of sedimentary particles can provide information about their transport history and aid facies differentiation and the characterization of depositional environments. Triangular (Sneed and Folk) diagrams, employing ratios of the three orthogonal particle axes, have been advocated as the most appropriate method for unbiased presentation of primary particle shape data. A spreadsheet method for the production of these diagrams is described. Clast data-sets from a range of environments are presented using this method. An alternative use of the spreadsheet for the presentation of sedimentary fabric shape is suggested.

title: Glaciers and Glaciation
abstract: Glaciers and Glaciation is the classic textbook for all students of glaciation. Stimulating and accessible, it has established a reputation as a comprehensive and essential resource. 
 
In this new edition, the text, references, and illustrations have been thoroughly updated to give today's reader an up-to-the minute overview of the nature, origin, and behavior of glaciers and the geological and geomorphological evidence for their past history on earth. 
 
The first part of the book investigates the processes involved in forming glacier ice, the nature of glacier/climate relationships, the mechanisms of glacier flow, and the interactions of glaciers with other natural systems such as rivers, lakes, and oceans. 
 
In the second part, the emphasis moves to landforms and sediment, the interpretation of the earth's glacial legacy, and the reconstruction of glacial depositional environments and palaeoglaciology.

title: Weertman regelation, multiple refreezing events and the isotopic evolution of the basal ice layer
abstract: A simple model is developed to s imulate the isotopic fractionation which accompanies Weertman regelation at the bed of temperate-based glaciers. The fractionation equations of Jouzel and Souchez ( 1 982) are applied to multiple refreezing events over measured glacier-bed profiles, and mass balance is maintained as the basal ice and meltwater produced at one bedrock hummock enter the next. S imulation results indicate that undeformed regelation ice layers are on the order of millimetres to centimetres thick, often being completely melted at the stoss face of certain hummocks and exceptionally reaching a thickness in excess of 1 0 cm. Neither the internal morphology nor the isotopic composition of these layers is constant, but both vary down-glacier in accordance with bedrock configuration . A glacier-wide fractionation process is identified whereby heavy isotopes are preferentially removed fro m the basal meltwater film and incorporated into the basal ice. This process might go some way to explaining the anomalously "light" isotopic composition measured in base-flow waters leaving some glaciers. Vertical isotope profiles through undeformed basal ice layers are reconstructed and show that significant isotopic excursions can occur at a scale of millimeteres, while the range of isotopic compositions within such m ulti-layered regelation ice is greater than that which would occur in ice produced by a single refreezing event. In circumstances where the regelation system is disrupted by removal of film waters into a network of linked cavities, i t is found that the remaining basal ice may be significantly enriched in heavy isotopes relative to the composition of the initial mass inputs to the system. Heavy isotope enrichment of this m agnitude and consideration of the thickness of the basal ice layers concerned may explain the absence of recorded basal ice samples heavy enough to h ave been formed in equilibrium with subglacial precipitates sampled at one of the sites (Glacier de Tsanfleuron) and reported in an earlier paper.

title: Isotopic signature of debris-rich ice formed by regelation into a subglacial sediment bed
abstract: Among the processes that may entrain sediment in the bases of glaciers and ice sheets, basal ice may regelate downward into the pores of unlithified sediment. Laboratory studies suggest that this process leaves interstitial ice with a distribution of δ18O and δD that is distinct from that developed due to downward freezing of a semi-closed water reservoir. Although as a result of both processes these isotopes lie on a freezing slope in a δD-δ18O diagram, debris layers entrained by regelation past grains are both enriched in heavy isotopes with depth and display a downward decrease in deuterium excess, the converse of that due to downward freezing of a water reservoir. Moreover, the extent of enrichment can be significantly larger in the case of regelation into the bed. Reevaluated field data from West Greenland are consistent with regelation into the bed as an entrainment mechanism.

title: Basal Ice Facies and Their Formation in the Western Alps
abstract: Research at 11 glaciers in the western European Alps has resulted in the definition of 7 basal ice facies. The formation of each is investigated on the basis of its debris distribution, sedimentology, and stable isotope composition. Isotopic data are interpreted within an analytical framework that allows for variations in the isotopic composition of source waters. Ice facies formed by metamorphism are distinguished from those formed by open-system refreezing within basal cavities and from those formed by closed-system regelation. Individual basal ice facies are thereby linked to the subglacial physical conditions required for their formation. These associations allow inferences relating to bed type, basal temperature, and subglacial hydrology to be made on the basis of the presence of specific, diagnostic basal ice facies at any glacier where they may be observed.

title: Direct Observation of the Mechanism of Glacier Sliding over Bedrock
abstract: It has been demonstrated by direct observation in tunnels and by measurements of ice deformation in boreholes that an important mechanism in the flow of temperate glaciers is sliding of the ice over the bedrock at its base. Basal sliding or slip (R. P. Sharp, 1954, p. 826) normally accounts for the order of 50 per cent of the total surface velocity of typical valley glaciers in their thicker parts, the remainder being due to internal deformation within the ice (J. A. F. Gerrard, M. F. Perutz and A. Roch, 1952; J. G. McCall, 1952; W. H. Mathews, 1959; R. L. Shreve, 1961; J. C. Savage and W. S. B. Paterson, 1963).

title: Internal melting and ice accretion at the bottom of temperate glaciers
abstract: Temperate glacier ice is neither dry nor impermeable, as the standard theory of glacier sliding assumes. This fact leads to the already published concept of locally stress-controlled temperatures. Why the temperature is determined by the highest principal pressure, why the microscopic stress equals more or less the macroscopic one, and why water may flow in the capillary network even when water lenses at grain boundaries are freezing is explained. The new concept is applied to ice sliding on a hard bed having a sine profile, without cavitation

title: The Role of Folding and Foliation Development in the Genesis of Medial Moraines: Examples from Svalbard Glaciers
abstract: The structure and debris content of four glaciers in NW Spitsbergen (Svalbard) are described to test the hypothesis that medial moraines are the product of folding, accompanied by the development of longitudinal foliation. Using clast orientation, clast shape, and clast lithological data, combined with measurements of fold axes and foliation in ice, this hypothesis is shown to be applicable to small valley glaciers with multiple basins feeding a narrow tongue, a common situation in Svalbard. The glaciers examined show stratification (commonly incorporating angular rockfall‐derived debris) folded to varying degrees along flow‐parallel axes throughout the tongue. An axial plane foliation is commonly associated with this folding and attains its greatest strength at flow‐unit boundaries. The debris takes a medium‐level to high‐level transport path through the glacier, emerging at point sources defined by gently dipping fold hinges near the snout. As more of the folded debris layer melts out, downglacier‐widening medial moraines are formed. In a few locations, foliation containing basally derived debris also shows an axial planar relationship with folding; this debris typically melts out to produce diamicton with predominantly subrounded and subangular clasts. In this case, it is inferred that subglacial sediment and debris‐rich basal ice are folded within the body of the glacier and can reach the surface near the snout. The proglacial areas preserve evidence of medial moraines in the form of trains of coarse angular debris and foliation‐parallel ridges of diamicton, although the latter have a poor preservation potential. There is scope for applying these structural glaciological concepts to medial moraines wherever glaciers are fed by multiple basins.

title: Sedimentology of medial moraines on Berendon Glacier, British Columbia, Canada: Implications for debris transport in a glacierized basin
abstract: The character of sediments from medial moraines on Berendon Glacier, British Columbia, reflects periglacial processes rather than direct glacial erosion and transport. Sediments are passively transported as talus by the glacier, and a distinct sedimentology can be contrasted with lodgement tills. Medial morane sediment is derived from a number of sources and is transported on the glacier surface and at depth near the glacier bed — there is no evidence of either textural evolution with increasing distances of glacial transport or enhanced scour of the glacier bed in the vicinity of medial moraines. Particle-size distribution of both medial moraine debris (supraglacial morainic till) and lodgment tills is found to be independent of source rock. A bimodal grain-size distribution widely reported from the analysis of far-traveled Pleistocene tills from the mid-latitudes, reflecting the crushing characteristics of component minerals in the source rock, is not exhibited by tills from Berendon Glacier which have well-defined lithological sources. This reflects the short distances of debris transport by the glacier and is considered to be typical of other temperal valley glaciers.

title: Geomorphology and sedimentology of surging glaciers: a land-systems approach
abstract: The identification of surging glaciers and ice streams in glaciated landscapes is of major importance to the understanding of ice-sheet dynamics and for reconstructing ice sheets and climate. No single landform or diagnostic criterion has yet been found with which to identify surging glaciers. A surging-glacier land-system model is constructed using observations and measurements from contemporary surging-glacier snouts in Iceland, Svalbard, U.S.A. and Canada for differentiating ancient surging margins from other non-surging palaeoglaciers. This integrates the suite of landforms, sediments and stratigraphy produced at surging-glacier margins. Landforms produced during surging include thrust moraines, concertina eskers and subglacial crevasse-squeeze ridges. Sedimentary sequences are usually characterized by multiple stacked diamictons and stratified interbeds, which display severe glaciotectonic contortion and faulting. Hummocky moraine, comprising interbedded stratified sediments and mass-flow diamictons, has also been associated with surge margins where large quantities of supraglacial and englacial debris entrained during the surge event have melted out in situ. An example of the application of the land-system model is presented for east-central Alberta, Canada. A surging palaeo-ice stream is identified within this part of the southwestern Laurentide ice sheet, where thrust-block moraines, crevasse-squeeze ridges, flutings, hummocky moraine and glaciotectonized sediments are juxtaposed.

title: Response of subglacial sediments to basal freeze-on 1. Theory and comparison to observations from beneath the West Antarctic Ice Sheet
abstract: We have constructed a high-resolution numerical model of heat, water, and solute flows in sub-ice stream till subjected to basal freeze-on. The model builds on quantitative treatments of frost heave in permafrost soils.  The two latter effects can lead to supercooling of the ice base. This supercooling, in turn, induces hydraulic gradients that drive upward flow of pore water, which feeds the growth of segregation ice onto the freezing interface. This interface may progress into the till and form ice lenses if supercooling is sufficiently strong. Hence, the ice segregation process develops a stratified basal ice layer. In our model, a high basal temperature gradient (∼0.054°C m−1) triggers ice stream stoppage, and the loss of basal shear heating leads to relatively high basal freeze-on rates (∼3–5 mm a−1). In response, the subglacial till experiences comparatively rapid consolidation. Till porosity can decrease from 40% to 120 kPa, approximately within one century. Basal supercooling arising from redistribution of solutes and ice-water interfacial effects amounts to ca. −0.35°C below the pressure-melting point. Fine-grained till is in our model associated with widely spaced, thick ice lenses. Coarse-grained till yields thinner ice lenses that are more closely spaced. Our model results compare favorably, although not in all details, with available observational evidence from borehole studies of West Antarctic ice streams.

title: The thermal regime of sub-polar glaciers mapped by multi-frequency radio-echo sounding
abstract: Radio-echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale. Radar signals of 320-370 MHz penetrate ice at sub-freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water. Radar signals of 5-20 MHz, on the other hand, see through both the cold and the temperate ice down to the glacier bed. Radio-echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in Svalbard: Kongsvegen, Uversbreen. Midre Lovenbreen and Austre Broggerbreen. In the ablation area of Kongsvegen, a cold surface layer (50-160m) thick was underlain by a warm basal layer which is advected from the temperate accumulation area. The surface ablation of this cold layer may be compensated by freezing at its lower cold-temperate interface. This requires that the free water content in the ice at the freezing interface is about 1% of the volume. The cold surface layer is thicker beneath medial moraines and where cold-based hanging glaciers enter the main ice stream. On Uversbreen the thermal regime was similar to that of Kongsvegen. A temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between Kongsvegen and Uversbreen where meltwater accumulates during the summer (near the subglacial lake Setevatnet, 250 m a.s.l.). Lovenbreen was frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer (up to 50m) thick was fed by temperate ice from two cirques. On Austre Broggerbreen. a temperate basal layer was not detected by radio-echo soundings but the basal ice was observed to be at the melting point in two boreholes.

title: Mass balance and dynamics of a valley glacier measured by high-resolution LiDAR
abstract: The changing surface geometry of the glacier Midre Lovénbreen on Svalbard was investigated using LiDAR data acquired on 9 August 2003 and again on 5 July 2005. The data were processed to generate Digital Elevation Models (DEMs) of unprecedentedly high spatial resolution (2 m) and accuracy (better than 0.15 m). Comparison of the two DEMs allowed the mass balance of the glacier to be determined as more negative than −0.62 m yr−1 water equivalent, about twice as negative as the value estimated from in situ measurements. Comparison of the DEMs also showed that the area of the glacier decreased by around 0.3%, and the position of its margin retreated by around 14 m, from 2003 to 2005. It was also possible to track the motion of fine-scale features in the surface geometry such as meltwater channels, and hence to determine the glacier's surface velocity, in some areas. Typical average speeds were around 1–2 cm per day.

title: Changes in geometry and subglacial drainage of Midre Lovénbreen, Svalbard, determined from digital elevation models
abstract: Digital elevation models (DEMs) of the bed and surface of the polythermal Midre Lovenbreen, Svalbard, are used to identify changes in glacier geometry between 1977 and 1995. The calculated mean annual mass balance (−0·61 m water equivalent (w.e.) a−1) is more negative than that derived from field measurements (−0·35 m w.e. a−1), although the error associated with this value (±0·7 m a−1) suggests that the difference may be accounted for by errors. However, similar discrepancies between DEM-based and field-based measurements of mass balance have been reported elsewhere in Svalbard. Although errors may be responsible, patterns of surface elevation change may also be explained in terms of patterns of ablation, accumulation, and dynamics. The theoretical structure of the subglacial drainage system is modelled using different assumptions about subglacial water pressure, in 1977 and 1995. These reconstructions are compared with the observed positions of proglacial outlet streams. Decreasing subglacial water pressure results in a decrease in the influence of surface morphology and an increase in the role of the bed topography on drainage routing, which generally leads to more dispersed drainage. Long-term changes in the position of proglacial outlet streams occur as a result of changes in glacier geometry, but short-term changes may also occur in response to early season water pressures, controlled by meteorological and hydrological conditions.

title: Radiocarbon-dated Mytilus edulis and Modiolus modiolus from northern Svalbard: Climatic implications
abstract: Eighteen new age determinations on Mytilus edulis shells from northern Svalbard and two new age determinations on Modiolus modiolus shells are presented. Mytilus edulis appeared on the northern coast of Spitsbergen c . 9400 yr BP. Its maximum extension there seems to have been c . 7250 yr BP, which is also indicative of a climatic optimum. The first finding of Modiolus modiolus shells from northern Spitsbergen is reported, and revealed the age of c . 8300 yr BP, which is also indicative of marine climatic optimum conditions. Mytilus lived at the head of Woodfjorden until at least 5300 yr BP, but it is not possible to date its final disappearance from the northern coast. Mytilus has been absent from large parts of the coasts of Svalbard during the entire Holocene, indicating limited influence of warm Atlantic water there. Recent reports of living Mytilus edulis on Bjørnøya indicate a probable new occurrence there, and the question about a further immigration to Spitsbergen should be kept in mind. Such a faunistic change may provide data about a more general climatic warming in this part of the Arctic.

title: Holocene mass-transport activity and climate in outer Isfjorden, Spitsbergen: marine and subsurface evidence
abstract: The analyses of high-resolution seismic data, swath bathymetry data and sediment cores from the basin Svensksunddjupet in Isfjorden, Spitsbergen, reveal the deposits of repeated slope failures. Most of the slope failures occurred during three periods at c. 9650 cal. BP, 8350—8200 cal. BP and 3000 cal. BP. Suggested factors causing instability of the slopes include earthquake activity resulting from rapid isostatic uplift, excess pore pressure caused by relative sea-level fall and/or the presence of gas as well as climatic changes. Mass-transport deposits at the mouth of an incision at the southern slope of Svensksunddjupet are suggested to mainly relate to runoff from the land-based glacier Vardebreen. The increase of the mass-transport activity may indicate that Vardebreen either formed or increased in size at c. 7000 cal. BP.

title: Younger Dryas cirque glaciers in western Spitsbergen: smaller than during the Little Ice Age
abstract: The outermost moraines in front of the Scottbreen glacier in Spitsbergen date from c. AD 1900. These moraines rest on top of a marine shoreline radiocarbon-dated to about 11 200 14C yr BP and demonstrate that the AD-1900 moraines show the maximum glacier extent since late Allerod time. This means that Scottbreen was smaller during the Younger Dryas than at AD 1900, in contrast with glaciers on mainland western Europe, which were all much larger during the Younger Dryas. The explanation is probably starvation of precipitation on western Spitsbergen during the Younger Dryas. In contrast, ice sheets and glaciers in Spitsbergen reacted more or less in concert with glaciers in western Europe, during the global Last Glacial Maximum and the Little Ice Age.

title: Sensitivity to long-term climate change of subpermafrost groundwater systems in Svalbard
abstract: Deep subpermafrost aquifers are highly climate-dependent, with the permafrost as an aquitard preventing groundwater recharge and discharge. A study from the high-arctic island of Spitsbergen, Svalbard, shows that during a glacial to interglacial phase, both the permafrost and the glacier regime will respond to climatic changes, and a glacier-fed groundwater flow system will vary accordingly. A full glaciation results in the melting of permafrost, and groundwater can flow through pores and fracture systems in the rocks and sediments below the temperate zones of glaciers. These groundwater flow systems will mainly be localized to fjords and valleys and form low-lying terrestrial springs when the relative sea level drops during deglaciation due to glacio-isostatic rise. During an interglaciation, permafrost develops and thickens and the groundwater recharge and discharge areas will thereby be gradually reduced to a minimum reached at the warmest part of an interglaciation. An already frozen spring system cannot reopen before the permafrost melts. Only groundwater springs related to permanently warm-based glacial ice will persist into the next glaciation. During a new glaciation, flow systems that terminated during the previous interglaciation may become revitalized if overridden by warm-based ice causing permafrost thawing.