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Thermal structure of Svalbard glaciers and implications for thermal switch models of glacier surging
Journal of Geophysical Research: Earth Surface
Abstract
Switches between cold- and warm-based conditions have long been invoked to explain surges of High Arctic glaciers. Here, we compile existing and new data on the thermal regime of six glaciers in Svalbard to test the applicability of thermal switch models. Two of the large glaciers of our sample are water-terminating while one is land-terminating. All three have a well-known surge history. They have a thick basal layer of temperate ice, superimposed by cold ice. A cold terminus forms during quiescence, but is mechanically removed by calving on tidewater glaciers. The other three glaciers are relatively small, and are either entirely cold or have a diminishing warm core. All three bear evidence of former warm-based thermal regimes and, in two cases, surge-like behavior during the Little Ice Age. In Svalbard, therefore, three types of glaciers have switched from slow to fast flow: (1) small glaciers that underwent thermal cycles during and following the LIA (switches between cold- and warm-based conditions), (2) large terrestrial glaciers which remain warm-based throughout the entire surge cycle but develop cold termini during quiescence, and (3) large tidewater glaciers that remain warm-based throughout the surge cycle. Our results demonstrate that thermal switching cannot explain the surges of large glaciers in Svalbard. We apply the concept of enthalpy cycling to the spectrum of surge and surge-like behavior displayed by these glaciers and demonstrate that all Svalbard surge-type glaciers can be understood within a single conceptual framework.
... Commonly, in situ ice thickness and thermal structure of a glacier is investigated by GPR surveys (e.g., Baelum & Benn, 2011;Björnsson et al., 1996;Irvine-Fynn et al., 2011;Karušs et al., 2019;Karušs, Lamsters, Sobota, Ješkins, & Džeriņš, 2022;Karušs, Lamsters, Sobota, Ješkins, Džeriņš, & Hodson, 2022;Lamsters et al., 2020aLamsters et al., , 2020bRippin et al., 2011;Sevestre et al., 2015). The possible polythermal structure of High Arctic glaciers is complex and difficult to reproduce by numerical simulations as studies show great differences between numerical modelling and in situ observations (e.g., Tsutaki et al., 2017). ...
... The highly variable thermal structure of Arctic glaciers is shown in numerous studies (e.g., Björnsson et al., 1996;Irvine-Fynn et al., 2011). The thermal structure of such glaciers is often not in a phase with a current warming climate usually leading to changes from polythermal structure to even entirely cold (Carrivick et al., 2023;Karušs, Lamsters, Sobota, Ješkins, Džeriņš, & Hodson, 2022;Rippin et al., 2011;Sevestre et al., 2015). The glacier thermal structure is related to and dependent on many factors including ice thickness, snow and firn layer thickness, presence of crevasses, surface meltwater percolation and freezing leading to cryo-hydrological warming, glacier geometry and dynamics including ice flow velocity, englacial strain distribution and frictional heating and glacier history (e.g., Carrivick et al., 2023;Forte et al., 2021;Gillespie et al., 2023;Irvine-Fynn et al., 2011;Karušs, Lamsters, Sobota, Ješkins, Džerin¸š, & Hodson, 2022;Murray et al., 2000;Rippin et al., 2011). ...
... Scattering facies can be interpreted in different ways as temperate ice, water percolation zones, zones with dense crevasses, shear zones or debris, rich ice (Björnsson et al., 1996;Forte et al., 2021;Karušs, Lamsters, Sobota, Ješkins, & Džeriņš, 2022;Karušs, Lamsters, Sobota, Ješkins, Džeriņš, & Hodson, 2022;Lamsters et al., 2020aLamsters et al., , 2020bPettersson et al., 2003;Santin et al., 2023;Sevestre et al., 2015). In our case, high scattering zones do not possess a distinct boundary with radar transparent facies as usually reported from polythermal glaciers where the cold/temperate ice transition is wellpronounced due to swift change in water content (e.g., Björnsson et al., 1996;Karušs, Lamsters, Sobota, Ješkins, & Džeriņš, 2022;Karušs, Lamsters, Sobota, Ješkins, Džeriņš, & Hodson, 2022;Pettersson et al., 2003;Sevestre et al., 2015). ...
Glaciers and ice caps surrounding the Greenland Ice Sheet are found to be sensitive to warming climate thus the knowledge of their thickness and internal structure is substantial to determine their future impact on sea level and local environment. Still, in situ glaciological measurements of such glaciers are very scarce. Here, we present the results of ground penetrating radar (GPR) and uncrewed aerial vehicle surveys conducted on the two southern outlet glaciers of Qaanaaq Ice Cap in NW Greenland.
GPR measurements reveal up to 170 m thick ice and the lack of englacial hyperbolae indicating no developed en/subglacial drainage system. The glaciers consist mainly of radar transparent facies characteristic for cold ice, while limited scattering facies appear closer to the glacier’s terminus beneath the thinnest ice and are attributed to debris inside the ice. Results show that the glaciers flow into narrow V-shaped valleys suggesting spatiotemporally limited subglacial erosion and restricted possible distribution of temperate ice in the past. The comparison of the ice thickness measurement data with global ice thickness model estimates shows considerable discrepancies emphasising the need of modelling improvements in the case of narrow valley and outlet glaciers.
... It is especially crucial to determine glacier volume as precisely as possible, especially when small glaciers are considered [2,3]. Despite the long history of glacier studies in Svalbard, measurements of ice thickness of individual glaciers with geophysical methods or drillings are still scarce [4][5][6][7], etc., due to the remote location of the archipelago. The same can be stated about the determination of the distribution of cold and temperate ice [5][6][7], etc. ...
... Despite the long history of glacier studies in Svalbard, measurements of ice thickness of individual glaciers with geophysical methods or drillings are still scarce [4][5][6][7], etc., due to the remote location of the archipelago. The same can be stated about the determination of the distribution of cold and temperate ice [5][6][7], etc. ...
... Since the first attempts to apply GPR to glacier studies [24] (pp. [4][5][6], a range of its application has been found [3,4,7,14,[25][26][27]. Observing that water inclusions in temperate ice causes intense scattering of GPR signal [5,6,28] provided a powerful tool for detailed mapping of thermal structure of glaciers. ...
Although measurements of thickness and internal structure of glaciers are substantial for
the understanding of their evolution and response to climate change, detailed data about polythermal glaciers, are scarce. Here, we present the first ground-penetrating radar (GPR) measurement data of Irenebreen, and high-resolution DEM and orthomosaic, obtained from unmanned aerial vehicle (UAV) photogrammetry. A combination of GPR and UAV data allowed for the reconstruction of the glacier geometry including thermal structure. We compare different methods of GPR signal propagation speed determination and argue that a common midpoint method (CMP) should be used if possible. Our observations reveal that Irenebreen is a polythermal glacier with a basal temperate ice layer, the volume of which volume reaches only 12% of the total glacier volume. We also observe the intense GPR signal scattering in two small zones in the ablation area and suggest that intense water percolation occurs in these places creating local areas of temperate ice. This finding emphasizes the possible formation of localised temperate ice zones in polythermal glaciers due to the coincidence of several factors. Our study demonstrates that a combination of UAV photogrammetry and GPR can be successfully applied and should be used for the high-resolution reconstruction of 3D geometries of small glaciers.
... N and 17°43.27 E) is a polythermal glacier (Sevestre et al., 2015) located in the Tempelfjorden region of Svalbard. It is approximately 15 km in length and has an area of 168 km 2 (König et al., 2014). ...
... Bamber (1987) applied a reflection coefficient-based analysis of the uppermost internal scattering horizon on similar glaciers across Svalbard from the same surveys, and concluded that it represents a layer of temperate ice with a water content of approximately 3%. In 2012 and 2015, Sevestre et al. (2015) undertook an extensive GPR campaign at 100 MHz, successfully mapping the distribution of temperate ice within the glacier, but encountering strong scattering throughout the deepest ice, precluding the ability to pick the bed confidently throughout. ...
... With the assumption of a constant velocity field, Stolt (Hambrey et al., 2005;Murray et al., 1997;Navarro et al., 2014;Saintenoy et al., 2013) or Kirchhoff migrations (Arcone et al., 1995;Schannwell et al., 2014;Sevestre et al., 2015) have been commonly applied to similar glacier GPR surveys on polythermal glaciers. In exploration seismic imaging, depth migration or reverse time migration (RTM) is undertaken when there are lateral variations in interval velocity due to the effect of energy refraction with depth (Yilmaz, 2001). ...
Ground‐penetrating radar (GPR) is widely used on polythermal glaciers to image bed topography and detect internal scatter due to water inclusions in temperate ice. The glaciological importance of this is twofold: bed topography is a primary component for modeling the long‐term evolution of glaciers and ice sheets, and the presence of temperate ice and associated englacial water significantly reduces overall ice viscosity. Englacial water has a direct influence on radar velocity, which can result in incorrect observations of bed topography due to errors in depth conversion. Assessment of radar velocities often requires multi‐offset surveys, yet these are logistically challenging and time consuming to acquire, hence techniques to extract velocity from common‐offset data are required. We calculate englacial radar velocity from common offset GPR data collected on Von Postbreen, a polythermal glacier in Svalbard. We first separate and enhance the diffracted wavefield by systematically assessing data coherence. We then use the focusing metric of negative entropy to deduce a migration velocity field and produce a velocity model which varies spatially across the glacier. We show that this velocity field successfully differentiates between areas of cold and temperate ice and can detect lateral variations in radar velocity close to the glacier bed. This velocity field results in consistently lower ice depths relative to those derived from a commonly assumed constant velocity, with an average difference of 4.9 ± 2.5% of local ice depth. This indicates that diffraction focusing and velocity estimation are crucial in retrieving correct bed topography in the presence of temperate ice.
... Before the primary processing, each raw data profile was initialized at the preprocessing stage to ensure the correct positioning from the GPS data, to reset the time to zero and to remove repeated traces (see Table 6) (Sevestre et al., 2015). After that, the primary data processing was undertaken as follows : ...
... The thermal regime and internal structure of glaciers are the dominant factors to determine the flow speed, deformation and glaciers' characteristics (Sevestre et al., 2015). The GPR measurement is a reputable direct approach to examine glacier thermal regime, and Svalbard glaciers have been widely surveyed using this method. ...
... The presence or absence of scattering in the radargrams provides a way to interpret the glacier ice as being either temperate or cold, or a mixture of the two (Navarro and Eisen, 2010), allowing inference of the hydrothermal structure of the glaciers under study. Cold and pure ice is relatively transparent to electromagnetic waves, whereas temperate ice creates scatter as the result of diffractions from water-filled voids (Bamber, 1987;Sevestre et al., 2015). In this study, three types of internal structure and thermal regime were revealed from the radar echo soundings data: a clean-ice, debris-free poly-thermal structure at lower Foxfonna; a debris-free, cold ice-bed structure at Foxfonna icecap, and a post-surge, debris-rich, cold ice-bed structure at Riperbreen. ...
The dwindling volume of Arctic small-size (<30km2) Unmanned Aerial Vehicles (UAVs) photogrammetric reconstructions (3,552 images in September 2020) and Ground-Penetrating Radar (GPR) profiles (40.31km in April 2021) of Foxfonna & Rieperbreen glacier on Svalbard reveal that the total glacier extent is 6.46 km and about 55.08% of the areal extent have been lost since 1936. Comparisons to elevation data obtained from historical aerial photography indicate total mean surface elevation change is -20.50 ± 11.31m from 1961 to 2020, with a constantly accelerating rate of negative elevation change per year. Besides, a total of 56.68% of the ice volume has been lost over 60 years between 1961 and 2020. The presence of scattering zone in the radargram of lower Foxfonna showed a possible area of temperate ice close to the head of the glacier, up to 20 m thick and beneath approximately 100 m of ice. In contrast, the rest of the glacier system was entirely cold. The temperate ice was found to have formed recently, which may be related to the heavily crevassed zone in the uppermost part of lower Foxfonna, and the introduction of surface meltwater during an extreme melt year on the Foxfonna icecap. Thrusting features in Rieperbreen’s radargram revealed a historical surge, which was also indicated by surrounding landforms and historical elevation change. Both Foxfonna and Rieperbreen accumulation areas are too low to take advantage of any positive mass change from the ongoing precipitation increase. The linear extrapolation of estimated ice volume per year suggests that Foxfonna and Rieperbreen will be almost non-existent by the 2050s. These invaluable sources of additional information may be critical in predicting the future prospects of the high Arctic small-size glaciers, which may not exist in the near future.
... Of these glaciers, ∼160 are marine-terminating, accounting for ∼60% of the total glacier area (Błaszczyk et al., 2009;Kochtitzky & Copland, 2022). Svalbard is also host to one of the largest concentrations of surge-type glaciers in the world (Sevestre et al., 2015), which exhibit cyclical flow instabilities with the potential to cause the rapid collapse of affected glaciers and ice caps (e.g. Dunse et al., 2015;Haga et al., 2020;Nuth et al., 2019;Willis et al., 2018). ...
... Dowdeswell et al., 1991) and the impacts of a warming climate on surge behaviour (e.g. Małecki et al., 2013;Sevestre et al., 2015). However, glacier surges are known to produce diagnostic suites of landforms (the surging glacier landsystem, Evans & Rea, 1999) that link the glacial geomorphology to surge mechanisms. ...
This paper presents a map of terrestrial glacial geomorphology of eleven surge-type and non-surge-type glacier forefields in southwest and west Spitsbergen, Svalbard. Glacier forefields were mapped using a combination of field surveys and the use of an uncrewed airborne vehicle in September 2022 and satellite imagery captured in 2020, with mapping performed in ArcGIS Pro at a 1:5000 scale. Maps were constructed for glaciers in Van Kuelenfjorden and Van Mijenfjorden (southwest Spitsbergen), and in Isfjorden, Billefjorden a fjord branch of Isfjorden and St. Jonsfjorden (west Spitsbergen), to obtain a breadth of glacier types and features representative of glacial landsystems on Svalbard. The detailed landform inventory was divided into: (i) ice marginal, (ii) subglacial, (iii) glaciofluvial and glaciolacustrine, (iv) supraglacial and (v) other non-glacial and contemporary features. These detailed maps provide a geomorphological insight into the past and present characteristics of glaciers on Svalbard. ARTICLE HISTORY
... Politermālie ledāji plaši izplatīti Svalbāras arhipelāgā (Björnsson et al., 1996). Mazākie ledāji Svalbārā var būt pārsvarā auksti, savukārt lielākie un aktīvākie -pārsvarā silti (Sevestre et al., 2015). Svalbāras ledāju termiskā režīma izmaiņām ir būtiska ietekme uz ledāju uzplūdiem. ...
... Galvenie faktori ir vairāki. Piemēram, liela loma bija uzpeldējušajai ledāja mēlei, kas ierobežoja tālāk iekšzemē esošā 71. att. ...
Monogrāfijas mērķis ir iepazīstināt Zemes zinātņu un citu dabaszinātņu studentus un plašāku sabiedrību ar jautājumiem par mūsdienu ledāju un ledus vairogu attīstību, klasifikāciju, plūsmas mehānismiem, deformāciju, hidroloģiju, termālo struktūru, izplatību, izmaiņām un aktuālākajiem zinātniskajiem pētījumiem, kā arī ar Latvijas Universitātes zinātnieku polāro ekspedīciju organizāciju, norisi un rezultātiem. Galvenā uzmanība grāmatā pievērsta mūsdienu ledāju, galvenokārt Arktikas un Antarktikas reģionu ledus vairogu, raksturojumam, jo šie ledāji ietver lielāko daļu pasaules ledāju ledus masas. Papildus aplūkota arī ledus un ledājiem līdzīgu formu izplatība Saules sistēmas debess ķermeņos. Vienlaikus ar izpratni par mūsdienu ledus vairogiem lasītājs gūs arī zināšanas par to, kā veidojušies, izzuduši pagātnes ledus vairogi, kas reiz klāja lielu daļu Ziemeļamerikas, Eirāzijas, iekļaujot Latviju, un kādi bijuši to dinamiskie procesi. Monogrāfiju bagātīgi ilustrē fotogrāfijas (tās galvenokārt uzņēmis grāmatas autors un viņa līdzgaitnieki), kā arī ekspedīcijās pētīto ledāju vizualizācijas, un šie materiāli nozīmīgi papildina tekstu, veicinot ar ledājiem saistīto procesu izpratni. Autors, pamatojoties uz savu pieredzi un novērojumiem mūsdienu ledājos, kā arī atspoguļoto jaunākajos zinātniskajos pētījumos, apskata nozīmīgākos pētniecības jautājumus un norises pasaules ledājos. Latvijas zinātnieku polāro ekspedīciju apraksts, cerams, kļūs par piemēru un iedvesmas avotu studentiem un pētniekiem, kas vēlas nākotnē turpināt attīstīt polāro pētījumu jomu Latvijā. Monogrāfijā apskatīta gan ekspedīciju organizācija un ikdiena, gan arī zinātniskie pētījumi un to rezultāti. Grāmata publicēta latviešu valodā, lai tā, kļūstot par vienu no retajiem uzziņu avotiem tiem latviešu lasītājiem, kuri vēlas izprast ledāju procesus un parādības dzimtajā valodā, veicinātu arī zinātnes terminoloģijas attīstību.
... signifies metres of water equivalent), for the period 2000-2019 (Schuler et al., 2020). The larger glaciers of SV are typically polythermal, with a temperate base and cold surface layer, whereas the small glaciers are predominantly cold, possibly with only patches of temperate bed (Hagen et al., 1993;Sevestre et al., 2015). Thus, mountain glaciers display low ice velocities, typically on the order of 1-15 m a −1 horizontally (e.g. ...
... However, glacier surges are common in SV (e.g. Jiskoot et al., 2000;Sevestre et al., 2015), but these have been seldom reported for local mountain glaciers over the past several decades. NZ comprises two main mountainous parts: Yuzhny Island and Severny Island. ...
Small land-terminating mountain glaciers are a widespread and important element of Arctic ecosystems, influencing local hydrology, microclimate, and ecology. Due to their relatively small ice volumes, this class of ice mass is particularly sensitive to the significant ongoing climate warming in the European sector of the Arctic, i.e. in the Barents Sea area. Archipelagos surrounding the Barents Sea, i.e. Svalbard (SV), Novaya Zemlya (NZ), and Franz Josef Land (FJ), host numerous populations of mountain glaciers, but their response to recent strong warming remains understudied in most locations. This paper aims to obtain a snapshot of their state by utilizing high-resolution elevation data (ArcticDEM) to investigate the recent (ca. 2011–2017) elevation and volume changes of 382 small glaciers across SV, NZ, and FJ. The study concludes that many mountain glacier sites across the Barents Sea have been in a critical imbalance with the recent climate and might melt away within the coming several decades. However, deviations from the general trend exist; e.g. a cluster of small glaciers in north SV has been experiencing thickening. The findings reveal that near-stagnant glaciers might exhibit contrasting behaviours (fast thinning vs. thickening) over relatively short distances, which is a challenge for glacier mass balance models but also an opportunity to test their reliability.
... The thermal regime of glaciers is important for several reasons. Warm-based ice can flow more quickly via basal flow or ice surging (e.g., Clarke, 1987;Sevestre et al., 2015), and also enables a range of subglacial hydrological processes that differ from cold-based ice (e.g., exchanges with the groundwater system; chemical weathering, erosion, and mobilisation of sediments in well-developed drainage systems; subglacial water storage). Warmer ice has a lower effective viscosity (Glen, 1955), with variations by a factor of ∼1,000 from temperatures of −50 to 0 • C (Marshall, 2005); hence, deformational velocities in temperate ice are much higher (e.g., Phillips et al., 2010;Bell et al., 2014). ...
... A transition from cold-to warm-based ice has been proposed as the trigger for deglaciation in the context of the 100-kyr glacial cycle (Marshall and Clark, 2002). The effects of basal flow have the potential to be dramatic, as observed in glacier surge cycles, since basal flow rates can greatly exceed those from internal ice deformation (e.g., Clarke, 1987;Sevestre et al., 2015). ...
Glaciers and ice sheets are experiencing dramatic changes in response to recent climate change. This is true in both mountain and polar regions, where the extreme sensitivity of the cryosphere to warming temperatures may be exacerbated by amplification of global climate change. For glaciers and ice sheets, this sensitivity is due to a number of non-linear and threshold processes within glacier mass balance and glacier dynamics. Some of this is simply tied to the freezing point of water; snow and ice are no longer viable above 0°C, so a gradual warming that crosses this threshold triggers the onset of melting or gives rise to an abrupt regime shift between snowfall and rainfall. Other non-linear, temperature-dependent processes are more subtle, such as the evolution from polythermal to temperate ice, which supports faster ice flow, a shift from meltwater retention to runoff in temperate or ice-rich (i.e., heavily melt-affected) firn, and transitions from sublimation to melting under warmer and more humid atmospheric conditions. As melt seasons lengthen, there is also a longer snow-free season and an expansion of glacier ablation area, with the increased exposure of low-albedo ice non-linearly increasing melt rates and meltwater runoff. This can be accentuated by increased concentration of particulate matter associated with algal activity, dust loading from adjacent deglaciated terrain, and deposition of impurities from industrial and wildfire activity. The loss of ice and darkening of glaciers represent an effective transition from white to grey in the world's mountain regions. This article discusses these transitions and regime shifts in the context of challenges to model and project glacier and ice sheet response to climate change.
... Near the terminus, mean annual surface velocities are persistently high (1.6-2.15 to m d −1 ) (Lefauconnier, 1987;Lefauconnier et al., 1994a;Kääb et al., 2005), and summer velocities peak up to 3.2 m d −1 . Such high velocities can only be achieved through basal sliding, which is consistent with the finding of widespread temperate basal conditions at several glaciers in the region (Björnsson et al., 1996;Sevestre et al., 2015). Kongsbreen has a more complex velocity pattern due to its split into two separate terminal branches: the northern, marine-terminating branch of the glacier is fast-flowing, with a maximal speed of 2.7 m d −1 (measured in 2012, Schellenberger et al., 2015), whereas the southern, partially land-terminating branch is slow-moving. ...
... Glaciers in Kongsfjord are polythermal, usually with basal temperatures at or close to the pressure melting point, meaning that water drains at their base all year through (Björnsson et al., 1996;Sevestre et al., 2015;Nuth et al., 2019). Glacial run-off is periodically released into the fjord, where it produces sediment-rich freshwater plumes that are of great importance for the glacio-marine dynamics and the ecosystem of Kongsfjorden (Svendsen et al., 2002;Everett et al., 2018). ...
By regulating the amount, the timing, and the location of meltwater supply to the glacier bed, supraglacial hydrology potentially exerts a major control on the evolution of the subglacial drainage system, which in turn modulates ice velocity. Yet the configuration of the supraglacial hydrological system has received only little attention in numerical models of subglacial hydrology so far. Here we apply the two-dimensional subglacial hydrology model GlaDS (Glacier Drainage System model) to a Svalbard glacier basin with the aim of investigating how the spatial distribution of meltwater recharge affects the characteristics of the basal drainage system. We design four experiments with various degrees of complexity in the way that meltwater is delivered to the subglacial drainage model. Our results show significant differences between experiments in the early summer transition from distributed to channelized drainage, with discrete recharge at moulins favouring channelization at higher elevations and driving overall lower water pressures. Otherwise, we find that water input configuration only poorly influences subglacial hydrology, which instead is controlled primarily by subglacial topography. All experiments fail to develop channels of sufficient efficiency to substantially reduce summertime water pressures, which we attribute to small surface gradients and short melt seasons. The findings of our study are potentially applicable to most Svalbard tidewater glaciers with similar topography and low meltwater recharge. The absence of efficient channelization implies that the dynamics of tidewater glaciers in the Svalbard archipelago may be sensitive to future long-term trends in meltwater supply.
... For example, the Longyearbreen Glacier is a cold-type glacier with supraglacial (on ice) and englacial (in ice) channels, and incisions in the ice (Gulley et al., 2009;Sevestre et al., 2015), which could promote accumulation of pollutants in microconduits of glacial ice. ...
Polar regions are relatively isolated from human activity and thus could offer insight into anthropogenic and ecological drivers of the spread of antibiotic resistance. Plasmids are of particular interest in this context given the central role that they are thought to play in the dissemination of antibiotic resistance genes (ARGs). However, plasmidomes are challenging to profile in environmental samples. The objective of this study was to compare various aspects of the plasmidome associated with glacial ice and adjacent aquatic environments across the high Arctic archipelago of Svalbard, representing a gradient of anthropogenic inputs and specific treated and untreated wastewater outflows to the sea. We accessed plasmidomes by applying enrichment cultures, plasmid isolation and shotgun Illumina sequencing of environmental samples. We examined the abundance and diversity of ARGs and other stress-response genes that might be co/cross-selected or co-transported in these environments, including biocide resistance genes (BRGs), metal resistance genes (MRGs), virulence genes (VGs) and integrons. We found striking differences between glacial ice and aquatic environments in terms of the ARGs carried by plasmids. We found a strong correlation between MRGs and ARGs in plasmids in the wastewaters and fjords. Alternatively, in glacial ice, VGs and BRGs genes were dominant , suggesting that glacial ice may be a repository of pathogenic strains. Moreover, ARGs were not found within the cassettes of integrons carried by the plasmids, which is suggestive of unique adaptive features of the microbial communities to their extreme environment. This study provides insight into the role of plasmids in facilitating bacterial adaptation to Arctic ecosystems as well as in shaping corresponding resistomes. Increasing human activity, warming of Arctic regions and associated increases in the meltwater runoff from glaciers could contribute to the release and spread of plasmid-related genes from Svalbard to the broader pool of ARGs in the Arctic Ocean.
K E Y W O R D S antibiotic resistance genes, Arctic, cryosphere, metal resistance genes, plasmids, virulence, wastewater
... Moreover, a complex glacier system can have both surge-type and non-surge-type parts, with different processes, such as surge initiation and re-initiation, occurring in different locations and at different times (Herzfeld, 1998;Herzfeld, McDonald, Stachura, et al., 2013). The BBGS shares this property of complexity with sections of the Greenland and Antarctic ice sheet margins, where surge-type glaciers are found neighboring non-surge-type glaciers and accelerating outlet glaciers (Herzfeld, 2004;Jiskoot, 1999;Sevestre et al., 2015). Thus, the study of the BBGS surge provides extra layers of insight into the complex glacier acceleration found along the ice sheet margins, compared to the more commonly studied surges of smaller mountain glaciers. ...
The Bering‐Bagley Glacier System (BBGS), Alaska, Earth's largest temperate surging glacier, surged in 2008–2013. We use numerical modeling and satellite observations to investigate how surging in a large and complex glacier system differs from surging in smaller glaciers for which our current understanding of the surge phenomenon is based. With numerical simulations of a long quiescent phase and a short surge phase in the BBGS, we show that surging is more spatiotemporally complex in larger glaciers with multiple reservoir areas forming during quiescence which interact in a cascading manner when ice accelerates during the surge phase. For each phase, we analyze the simulated elevation‐change and ice‐velocity pattern, infer information on the evolving basal drainage system through hydropotential analysis, and supplement these findings with observational data such as CryoSat‐2 digital elevation maps. During the quiescent simulation, water drainage paths become increasingly lateral and hydropotential wells form indicating an expanding storage capacity of subglacial water. These results are attributed to local bedrock topography characterized by large subglacial ridges that dam the down‐glacier flow of ice and water. In the surge simulation, we model surge evolution through Bering Glacier's trunk by imposing a basal friction representation that mimics a propagating surge wave. As the surge progresses, drainage efficiency further degrades in the active surging‐zone from its already inefficient, end‐of‐quiescence state. Results from this study improve our knowledge of surging in large and complex systems which generalizes to glacial accelerations observed in outlet glaciers of Greenland, thus reducing uncertainty in modeling sea‐level rise.
... For more information, see https://creativecommons.org/licenses/by/4.0/ of the ice base and the processes that cause the peculiar reflections near the ice base are diverse. They range from frozen basal water on the underside of the ice sheet [6], [7], [8], [9], englacial folding [10], [11], [12], entrained subglacial material [13] to cold-temperate transitions with liquid water inclusions [14], [15], [16], [17]. Other explanations include sharp transitions in crystal fabric, heterogeneous small-scale roughness, stagnant ice, or disrupted isochrones [18]. ...
Radio-echo sounding reveals patches of high backscatter in basal ice units, which represent distinct englacial features in the bottom parts of glaciers and ice sheets. Their material composition and physical properties are largely unknown due to their direct inaccessibility but could provide significant information on the physical state as well as on present and past processes at the ice-sheet base. Here, we investigate the material properties of basal ice units by comparing measured airborne radar data with synthetic radar responses generated using electromagnetic forward modelling. The observations were acquired at the onset of the Jutulstraumen Ice Stream in western Dronning Maud Land (East Antarctica) and show strong continuous near-basal reflections of up to 200m thickness in the normally echo-free zone. Based on our modelling, we suggest that these high-backscatter units are most likely composed of point reflectors with low-dielectric properties, suggesting thick packages of englacial entrained debris. We further investigate the effects of entrained particle size, and concentration in combination with different dielectric properties, which provide useful information to constrain the material composition of radar-detected units of high backscatter. The capability and application of radar wave modelling in complex englacial environments is therefore a valuable tool to further constrain the composition of basal ice and the physical conditions at the ice base.
... Additional sources of heat in the glacier body are dissipative heating due to ice deformation, glacier friction against the bed, flowing water friction in intraglacial channels, refreezing of water in snow and firn pores, and geothermal heat flow. These sources largely determine the distribution of cold and temperate ice and water in the body and at the bed of the glacier and they affect their hydrothermal structure and behavior [1][2][3][4]. The coexistence of cold and temperate ice in polythermal glaciers noticeably affects their mechanical and hydrological properties [5]. ...
... Our GPR survey confirmed the polythermal structure of Vestre Grønfjordbreen, which was first discovered in 2010 (Martín-Español et al. 2013). This structure, with a basal layer of temperate ice, superimposed by cold ice, and a cold terminus, is common for Svalbard polythermal glaciers (Sevestre et al. 2015). The outlines of an underlying temperate ice layer are presented in Figure 3. Since this layer is being identified on GPR sections by numerous bright local hyperbolic reflections (Figure 3d), the cold-temperate transition surface (CTS) was contoured along the line that envelops the topmost points (vertices) of these reflections. ...
The first seven years (2013/14–2019/20) of annual and seasonal mass-balance monitoring on the glacier Vestre Grønfjordbreen (16.4 km2), located south of the town of Barentsburg on Spitsbergen, Svalbard, are presented. This part of the archipelago is one of the least glaciated on Svalbard and at the same time it experiences the most prominent glacier retreat within the last few decades. The annual mass balance of Vestre Grønfjordbreen is negative, ranging from −0.60 ± 0.18 to −2.01 ± 0.26 m w.e. The results of direct observations are compared with the geodetic mass balance for the same period (July 2015 through end of summer 2019) to identify systematic bias in the record. As the mismatch between cumulative mass balances, defined by the glaciological method (−5.66 ± 0.47 m w.e.) and computed from geodetic differencing (−5.52 ± 0.40 m w.e.), lies within the uncertainty limits, no calibration of the mass-balance series is needed. From the results of a ground-penetrating radar (GPR) survey (spring 2019), which confirmed the polythermal glacier structure, a total glacier volume of 1.987 ± 0.139 km3 was found, meaning that the cumulative mass loss during the reported seven-year period equals 8 ± 1% of the total glacier mass. Observed annual ice-flow velocities, varying from 0.50 ± 0.10 to 4.50 ± 0.10 m year−1, are consistent with low mean bed and surface slopes (5° and 8°, respectively). Correlations of mass-balance values with meteorological observations at the Barentsburg weather station are mediocre, possibly due to anomalous values recorded for 2015/16: the negative mass-balance peak reported for the other land-terminating Svalbard glaciers was not observed at Vestre Grønfjordbreen.
... The sediment-bedrock boundary underneath the ice core of the terminal moraine was mapped this way, which was not possible using other geophysical methods. The potential use of antennas with higher frequencies (100 Mhz and higher) in the imaging of the active layer is high, but at the cost of depth resolution and the visualisation of moraine structures (Sevestre et al. 2015;Zhao et al. 2016). In addition, the scattering of GPR waves by loose rock, unconsolidated sediment and water in a partially or fully frozen state further limits the imaging potential. ...
This article presents the results of a geophysical survey from which detailed images of glacial and periglacial landforms and subsurface structures were obtained. Sediments and landforms on newly deglaciated terrain can be used to reconstruct the extent and character of glaciers in the past and add to the understanding of their response to climate and environmental changes. To derive spatial information from complex geomorphological terrain, joint interpretation of three non-intrusive geophysical methods were applied: Electrical Resistivity Tomography (ERT), Ground Penetrating Radar (GPR), and time-lapse Seismic Tomography. These were used to identify subsurface structures in the forefield of the retreating Hans Glacier in SW Spitsbergen, Svalbard. Three main zones were distinguished and described: outwash plain, terminal moraine from the last glacial maximum, and glacial forefield proximal to the glacier front. Geophysical profiles across these zones reveal information on glacio-fluvial sediment thickness and structure, ice thickness and structure, and bedrock topography. The freezing-thawing effect of the active layer has a strong and deep impact, as demonstrated by variations in P-wave velocity in the obtained outcomes. The results are discussed in the context of the current climate in Svalbard. This study provides a snapshot of ground parameters and the current state of the subsurface in southern Spitsbergen. The boundary between sediment-bedrock layers was estimated to be from 5 to 20 m in depth. It is the first such extensive description of periglacial structures in the forefield of the Hans Glacier, utilising the longest ERT profile (1500 m) in Svalbard together with deep GPR and precise seismic tomography.
... The distribution of warm and cold ice results in complex and still not fully understood thermal regime, which affects glaciers' hydrology and drainage system (Irvine-Fynn et al., 2011) and is responsible for surging events (Fowler et al., 2001). Thermal characterization of glaciers is a highly investigated issue, especially in Swiss Alps (Eisen et al., 2009;Rutishauser et al., 2016), Scandinavia (Pettersson et al., 2003;Gusmeroli et al., 2012;Reinardy et al., 2019), Svalbard (Sevestre et al., 2015), Canadian Arctic (Blatter and Hutter, 1991;Delcourt et al., 2013) and Chilean Andes (Gacitùa et al., 2015), among the other zones. In any case, it is essential to highlight that the number of scattering events depends not only on the water and/or debris content, but also on the frequency (or, better, on the spectral content) of the antennas used to perform the GPR survey (Björnsson et al., 1996). ...
In GPR profiles, ice is usually imaged as a mostly electromagnetic transparent facies. However, diffraction events, as well as internal layering, can be also observed. In some cases, the bedrock below glaciers is masked by dense diffractions usually interpreted as the effect of liquid water pockets inside the so-called warm ice. However, the actual physical meaning of such GPR facies is not always obvious, because it can be related also to mixed debris and ice deposits.
We adopted a strategy well known in medical sciences and referred as “differential diagnosis” in order to infer which is the actual meaning of a high scattering facies imaged within the Eastern Gran Zebrù glacier (Central Italian Alps) and, more generally, of all the internal glacier features. In fact, in many cases, there is no direct information to limit the subjectivity of geophysical interpretation; therefore, we provide all the discriminative hypotheses based on both independent and integrated criteria including GPR attribute analysis, imaging effects, reflection analysis, GPR frequency evaluations combined with geomorphological and remote sensing data obtained by two photogrammetric UAV and thermal infrared surveys.
On the basis of the differential diagnosis, we concluded that the high scattering zone embedded within the studied glacier is most likely related to a mixture of ice and debris probably formed during a past shrinking phase. Beside this case study, this approach could be helpful in other GPR glaciological surveys, in which the target is related not only to the bedrock detection, but also to a detailed analysis of the internal facies of a glacier.
... 4 For example, due to the low frequencies often used in ground-based glaciological radio-echo sounding (Scott et al., 2010;Sevestre et al., 2015;King et al., 2016), lengthy dipole antennas are often towed in-line to the survey direction and as such cannot be modeled accurately using 2D FDTD algorithms. ...
Finite-difference time-domain (FDTD) forward modeling is often used to gain a more quantitative understanding of the interactions between electromagnetic fields and targets. To undertake full 3D simulations the computational demands are challenging, so simulations are often undertaken in 2D where assumptions in the propagation of electromagnetic fields and source type can result in errors. We develop the concept of a sliced-3D simulation, wherein a thin slice of a 3D domain with strictly 2D geometry is used to minimize computational demands while obtaining synthetic waveforms that contain full 3D propagation effects. This approach requires optimization of perfectly matched layer (PML) boundary condition parameters so as to minimize the errors associated with the source being located close to the boundary, and as a result of grazing-incident angle wave conversion to evanescent energy. We explore the frequency dependence of PML parameters, and establish a relationship between complex frequency stretching parameters and effective wavelength. The resultant parameter choice is shown to minimize propagation errors in the context of a simple radioglaciological model, where 3D domains may be prohibitively large, and for a near-surface cross-borehole survey configuration, a case where full waveform inversion may typically be used.
... Overall, glaciers of SV are known to lose mass over many past decades, recently at -8 Gt a -1 , equivalent to ca. -0.23 m w.e. a -1 (2000( , Schuler et al., 2020. Larger glaciers of SV are typically polythermal, with a temperate base and cold surface layer, whereas small glaciers are predominantly cold, possibly with only patches of temperate bed (Hagen et al., 1993;Sevestre et al., 2015). Thus, mountain glaciers display low ice velocities, typically 90 on the order of 1-15 m a -1 horizontally (e.g. ...
Small land-terminating mountain glaciers are a widespread and important element of Arctic ecosystems, influencing local hydrology, microclimate, and ecology, among others. Due to little ice volumes, this class of ice masses is very sensitive to climate warming, the latter of which is extremely well manifested in the European sector of the Arctic, i.e. in the Barents Sea area. Archipelagos surrounding the Barents Sea, i.e. Svalbard (SV), Novaya Zemlya (NZ), and Franz Josef Land (FJ), host numerous populations of mountain glaciers, but their response to recent strong warming remains understudied in most locations. This paper aims to obtain a snapshot of their state by utilizing high-resolution elevation data (ArcticDEM) to investigate the recent (ca. 2011–2017) elevation and volume changes of 382 small glaciers across SV, NZ, and FJ. The study concludes that many mountain glacier sites across the Barents Sea have been in a critical imbalance with the recent climate and might melt away within the coming several decades. However, deviations from the general trend exist, e.g. a cluster of small glaciers in north SV experiencing thickening. The findings reveal that near-stagnant glaciers might exhibit contrasting behaviours (fast thinning vs. thickening) over relatively short distances, being a challenge for climate models, but also an opportunity to test their reliability.
... Дополнительные источники тепла в самой его толще -диссипативный разогрев изза деформации льда, трение ледника о ложе, трение текущей воды во внутриледниковых каналах, по вторное замерзание воды в порах снега и фирна, геотермический поток тепла. Эти источники во многом определяют распределение холодного и тёплого льда и воды в толще и у ложа ледника и влияют на их гидротермическую структуру и ди намику [1][2][3][4]. Сосуществование холодного и тёп лого льда в политермических ледниках заметно влияет на их механические и гидрологические свойства [5]. В частности, термический барьер из холодного льда на языке препятствует стоку под ледниковых вод, создавая угрозу их прорыва [4]. ...
... The GrIS has active subglacial hydrology with extensive regions of saturated sediments (Jordan et al., 2018;MacGregor et al., 2016), which allows for microbial activity and may contribute more aromatic DOM signatures at the onset of melt (Kellerman et al., 2020b;O'Donnell et al., 2016). Svalbard glaciers, on the other hand, are a mixture of cold-and polythermal-based glaciers (Sevestre et al., 2015). Outflow from cold-based glaciers originates from direct supraglacial inputs and ice-marginal flow, whereas the warm bases of polythermal glaciers allow for the interaction of supraglacial water with the basal environment as it is routed through subglacial channels to the outflow portal ( tential sources for each glacier may further explain the larger compositional variance in Svalbard rivers, compared to the similarity of outflow from Russell Glacier (Figures 4 and 5). ...
Glaciers and ice sheets cover over 10 % of Earth's land surface area and store a globally significant amount of dissolved organic matter (DOM), which is highly bioavailable when exported to proglacial environments. Recent rapid glacier mass loss is hypothesized to have increased fluxes of DOM from these environments, yet the molecular composition of glacially derived DOM has only been studied for a handful of glaciers. We determine DOM composition using ultrahigh resolution mass spectrometry from a diverse suite of Arctic glacial environments, including time series sampling from an ice sheet catchment in Greenland (Russell Glacier) and outflow from valley glaciers in catchments with varying degrees of glacial cover in Svalbard. Samples from the Greenland outflow time series exhibited a higher degree of similarity than glacier outflow between glaciers in Svalbard; however, supraglacial meltwater samples from Greenland and Svalbard were more similar to each other than corresponding glacial outflow. Outflow from Russell Glacier was enriched in polyphenolic formulae, potentially reflecting upstream inputs from plants and soils, or inputs from paleosols overridden by the ice sheet, whereas Svalbard rivers exhibited a high level of molecular richness and dissimilarity between sites. When comparing DOM compositional analyses from other aquatic systems, aliphatic, and peptide‐like formulae appear particularly abundant in supraglacial meltwater, suggesting the DOM quickly metabolized in previous incubations of glacial water originates from energy‐rich supraglacial sources. Therefore, as glaciers lose mass across the region, higher‐quality fuel for microbial degradation will increase heterotrophy in coastal systems with ramifications for carbon cycling.
Most small land-terminating glaciers in Svalbard have experienced large recession since the Little Ice Age (LIA) and today are thin, cold, and largely inactive. This likely contrasts to their LIA conditions, but the observational record from that time is sparse. We investigate the evolution of five small glaciers in central Nordenskiöld Land, Svalbard, from the LIA to 2019. Photogrammetric reconstructions and ground penetrating radar are used to reconstruct their geometric changes since 1936, and historical observation, photographs, and geomorphological mapping extend this history to before the 1900s. Our results show that from 1936 to 2019, the study glaciers on average lost 49.6% of their area and 77.4% ± 7.7% of their volume, with the greatest volume loss at Scott Turnerbreen of 91% ± 5%. Four out of these five glaciers strongly indicate a history of surge-like advances near the end of the LIA within one or two decades, and the rate of subsequent mass loss seems connected to their previous dynamics. This apparent switch to high activity during a period of rapid climatic change, could have implications for our understanding of past and future glacier evolution; climate change and highly dynamic glacier responses may be more connected than previously thought.
This paper presents geomorphological and historical records of the surge-type behaviour of Hansbreen, one of the most studied tidewater glaciers in Svalbard. The surge-type behaviour of the glacier has not been considered before due to the lack of evidence of this phenomenon. We integrate geomorphological mapping of the terrestrial and submarine forefields with historical data from the 19th and 20th centuries to reconstruct the glacier dynamics and identify the possible timing of surging. Landform assemblages are representative of the surging glacier land-system, including crevasse-squeeze ridges (CSRs) and submarine streamlined glacial lineations. Abundant CSRs in the outer part of the terrestrial forefield were also documented in the 1980s, but most have been obliterated since then. We suggest the identified surge landsystem was produced during a surge of Hansbreen detected from photographs taken during the Austro-Hungarian expedition in 1872. Historical photogrammetric photos from the Norwegian expedition in 1918 revealed surge-diagnostic features in the glacier surface, including a folded medial moraine and a dense, complex network of crevasses. A potential next surge remains questionable in the following decades due to the low-lying accumulation area of the main stream hindering the mass build-up, but potential surges of the tributary glaciers should not be excluded.
Study region: The northern region of the Karakoram Range. Study focus: Karakoram is a region in High Mountain Asia with many surge-type glaciers. This study employed over 200 high-temporal-resolution remote sensing images and investigated the variations in elevation and velocity of the Ghujerab River Head Glacier (GRHG) from 2019 to 2023. Furthermore, we elucidated the potential controlling mechanisms. New hydrological insights for the region: Our findings revealed that the GRHG, akin to typical surge-type glaciers in Karakoram, started to surge in the spring and finished surging in the summer, with a duration of less than two years. Throughout the surging process, the glacier transferred a mass of 0.11±0.003 km 3 from the reservoir area to the receiving area, resulting in a thickening of 91.59±1.04 m at the glacier terminus and thinning of 11.78±1.04 m in the upper glacier. By analysing the mass balance and glacier surface albedo during surging, we proposed that climatic disturbances in the glacier region provided essential material inputs for the surge. Additionally, based on the seasonal evolution pattern of glacier flow velocity, we inferred a close correlation between surging and variations in subglacial hydrology. The duration of acceleration and deceleration during glacier surging, as well as a comparison with existing studies, further support our conclusion. Future research integrating multi-source remote sensing and onsite observations can support numerical simulations to quantitatively reveal the key processes occurring beneath and within glaciers during surge events.
Svalbard has experienced a dramatic increase in air temperature and glacier retreat since the end of the Little Ice Age. In many cases, this retreat has resulted in glaciers transitioning from being marine-terminating to land-terminating. Nordenskiöldbreen is an excellent contemporary example of this transition. A set of historical observations of glacier front positions was used to assess Nordenskiöldbreen's retreat rate and we found that the southern portion of the glacier front retreated by ∼3500 m, since records began in 1896. The general retreat rate corresponds well with the air temperature trend during most of the 20th century. However, the average retreat rate has slowed since the 1990s despite increasing air temperatures. We show that this discrepancy between air temperature and retreat rate marks the transition from marine-terminating towards a land-terminating glacier, as the glacier's bedrock topography started to play an essential role in the glacier margin geometry, ice flow and retreat dynamics.
Observations remain sparse for peripheral glaciers and ice caps in Greenland. Here, we present the results of a multi-frequency radar survey of Lyngmarksbræen Ice Cap in West Greenland conducted in April 2017. Radar measurements show thick ice of up to ~120 m in subglacial valleys associated with the largest outlet glaciers, while relatively thin ice cover the upper plateau ice divides, suggesting future vulnerability to ice cap fragmentation. At the time of the radar survey, Lyngmarksbræen Ice Cap had a total volume of 0.82 ± 0.1 km ³ . Measurements show a 1.5–2 m thick end-of-winter snowpack, and that firn is largely absent, signifying a prolonged period of negative mass balance for most of the ice cap. The thermal regime of Lyngmarksbræen Ice Cap is investigated through analysis of scattering observed along radar profiles. Results show that the ice cap is largely below the pressure melting point, but that temperate ice exists both in deep basal pockets and in shallow zones that some places extend from ~15 m depth and to the ice base. The distribution of shallow temperate ice appears unrelated to variations in ice thickness; instead we find a strong correlation to the presence of nearby surface crevasses.
We present the first systematic inventory of surge-type glaciers for the whole of Greenland compiled from published datasets and multitemporal satellite images and digital elevation models. The inventory allows us to define the spatial and climatic distribution of surge-type glaciers and to analyse the timing of surges from 1985 to 2019. We identified 274 surge-type glaciers, an increase of 37% compared to previous work. Mapping surge-type glacier distribution by temperature and precipitation variables derived from ERA5-Land reanalysis data shows that the west and east clusters occur in well-defined climatic envelopes. Analysis of the timing of surge active phases during the periods ~1985 to 2000 (T1) and ~2000 to 2019 (T2) suggests that overall surge activity is similar in T1 and T2, but there appears to be a reduction in surging in the west cluster in T2. Our climate analysis shows a coincident increase in mean annual and mean winter air temperature between T1 and T2. We suggest that as glaciers thin under current warming, some surge-type glaciers in the west cluster may be being prevented from surging due to (1) their inability to build-up sufficient mass and (2) a switch from a polythermal to a largely cold-based thermal regime.
The rapid formation of glacial lakes is one of the most conspicuous landscape changes caused by
atmospheric warming in glacierised regions. However, relatively little is known about the history
and current state of glacial lakes in the High Arctic. This study aims to address this issue by providing the first inventory of glacial lakes in Svalbard, focusing in particular on the post-Little Ice
Age evolution of glacial lakes and their typology. To do so, we used aerial photographs and satellite imagery together with archival topographic data from 1936 to 2020. The inventory comprises the development of 566 glacial lakes (146 km2
) that were still in direct contact with
glaciers during the period 2008–2012. The results show a consistent increase in the total area
of glacial lakes from the 1930s to 2020 and suggest an apparent link between climatic and geological factors, and the formation of specific lake dam types: moraine, ice, or bedrock. We also
detected 134 glacial lake drainage events that have occurred since the 1930s. This study shows
that Svalbard has one of the highest rates of glacial lake development in the world, which is
an indicator of the overall dynamics of landscape change in the archipelago in response to climate
change
The centennial response of land-terminating glaciers in Greenland to climate change is largely unknown. Yet, such information is important to understand ongoing changes and for projecting the future evolution of Arctic subpolar glaciers, meltwater runoff, and sediment fluxes. This paper analyses the topography, geomorphology, and sedimentology of prominent moraine ridges and the proglacial areas of ice cap outlet glaciers on the Qaanaaq peninsula (Piulip Nunaa). We determine geometric changes of glaciers since the neoglacial maximum; the Little Ice Age (LIA), and we compare glacier behaviour during the LIA with that of the present day. There has been very little change in the rate of volume loss of each outlet glacier since the LIA compared with the rate between 2000 and 2019. However, the percentage of each glacier that is likely composed of cold-based ice has increased since the LIA, typically by 20%. The LIA moraines comprise subrounded, striated, and faceted clasts that evidence subglacial transport, and outwash plains, flutes, kames, and eskers that evidence subglacial motion and meltwater within temperate ice. Contrastingly, contemporary ice margins and their convex ice surfaces comprise pronounced primary foliation, ephemeral supraglacial drainage, sediment drapes from thrust plane fractures, and an absence of open crevasses and moulins. These calculations and observations together lead us to interpret that these outlet glaciers have transitioned towards an increasingly cold-based thermal regime despite a warming regional climate. Thermal regime transitions control glacier dynamics and therefore should be incorporated into glacier evolution models, especially where polythermal glaciers prevail and where climate is changing rapidly.
Surge-type glaciers in Svalbard are common and have been studied extensively. Whereas active phases of
surges were observed and thoroughly investigated recently, data on surges in the past are limited. They are
essential, however, to assess the duration of the surge cycle, to determine relation to climatic impulses, and
to better understand triggering factors and the mechanism of this phenomenon. Three glaciers located in
Recherchefjorden, NW Wedel Jarlsberg Land (Svalbard) were studied because they undergo the same
regional climate conditions but differ by the basin’s size and morphology front types. The article employed
different types of data, including geomorphological records, cartographic, graphic, and bibliographic sources.
These sources permitted the determination of the location of the termini of glaciers and the quantitative
and qualitative description of the rate of changes determined with computer analysis and statistical
compilation. Such analysis of other data sources enabled the reconstruction of glaciers’ behavior in the past.
Glacier surges in the study area correspond with this type of phenomenon in Svalbard. The results obtained
showed a certain synchronization of surges in the 1820s and 1830s, the 1880s, the first half of the twentieth
century, and particularly the last decade. Key Words: archival reconstruction, climate indication, DSAS GIS
application, surge-type glacier, Svalbard.
Many sediment-covered mountain areas affected by the growth of Pleistocene glaciers are over-consolidated. Palaeoglacial conditions are deduced from glacial consolidation and site investigations. Geomorphological evidence on the glacial extent and history is in this Thesis used as a framework for hydro-mechanical flow simulations in the valley glacier of Andorra and the lower Isère glaciated valley. From the effects observed within the fossil record of ancient glaciated valleys, a reliable reconstruction of palaeo-glaciers thickness is possible when former ice-tonges overlayed porous aquifers, because subglacial erosion was mitigated by the subglacial water pressure and limited subglacial till formation. Records of minimum preconsolidation values indicate a buoyant surging glacier. For palaeoglacier reconstruction, the glacial valley geomorphology is clue providing the palaeogeographical calibration for further hydrogeomechanical calculations, especially at successive glacial stages during the deglaciation. A modern analogue, the Hansbreen sub-polar glacier, helps to set up a conceptual model allowing a better understanding of the glaciology of the two studied former valley glaciers, comparable to a polythermal glacier type.
Tills and glaciolacustrine deposits from Andorra’s main valley and its principal tributary of La Massana allow for reliable local deglaciation patterns between GS-9 (40 ka b2k) and the Holocene Optimum (9.3–5.5 b2k). However, from the palaeoenvironmental data of the Pyrenees, deglaciation started sooner, and aridity affected the size of the glaciers from GS-10, resetting the valley glacier conditions ahead of GI-7. This affected the mainly prominent glacier-ice transfluence pass in the Pyrenees and the extension of the ice tongues on both sides of the mountain belt between GI-9 and GI-7, also during GS-5.2 and GI-5.1. During and posteriorly Heinrich event H4, aridity did not favour the development of valley glaciers in Andorra until stadial GS-7; however, glaciers in the Pyrenees progressed during the following Heinrich event (H3).
Using geochemical data (Al, Ti, Ca, K, P), a basic limnological study permits a palaeoenvironmental interpretation in Andorra by adding data from stable carbon isotope (δ13C) from bulk carbon samples and AMS dates. Results show four unreported inland δ13C cycles linked to low water levels in the ice-dammed lake of Andorra (La Massana palaeolake). At the beginning of each cycle, enhanced δ13C bulk carbon values are found (> -23‰), a proxy of abrupt shifting from Type-C3 to Type-C4 vegetation. The beginning of the LGM and Heinrich events H3 and H2 were marked by enhanced δ13C values interpreted as a product of strong climate change that boosted aridity. The retrieval period towards δ13C depleted values (< -23‰) spans 4,500±500 years.
In Andorra, the beginnings of H3 and H2 events were relatively dry, and the second half of the climate was moist. The first evidence of sediments coming from the motion of a temperate-base glacier in the Pyrenees was from stadial GI-3. Moist conditions suddenly stopped at the beginning of Heinrich event 2 and returned at the end of H2. This moisture behaviour during H2 on the southern slopes of the Pyrenees is the opposite of the wet-to-dry conditions described in NW Iberia. Conversely, the H1 event had a wet-to-dry structure coast to coast of Iberia, including in the SE Pyrenees (Andorra).
A transition from single-phase-like glacier advances (NW Iberia) to multiphase glacier advances (SE Pyrenees) was due to a change from cold- based glaciers to temperate-based glaciers. However, glacier sensibility to global changes increases through time toward NW Iberia. The Last Maximum Ice Extent and the Global LGM did not concur in places experiencing multiphase glacier advances. Indeed both extreme behaviours do not correspond to the same type of glaciers. Polar-type glaciers in NW Iberia are in this Thesis invoked, while tempered or polythermal were frequent in NE Iberia.
Abrupt glacier advances and quick glacier recession in Andorra are interpreted as surges from a mass-imbalanced glacier. Two kinds of surge events are distinguished from available data in the Pyrenees, those surges produced by overfed ice tongues fed by short-lived cold spells (in GS-2b and H1) and those surges produced by buoyant melting ice tongues within the glaciated valley (between stadials GS-5/GI-4, stadials GI-3/GS-3 and stadials GS-2.1b/GS-2.1a) by a warm moist climate. The winter solar rate increase (GI-3 and GS-5.1) and the evidence of polythermal-type glaciers matched. Conversely, summer insolation increases and wet-ice type oversaturated glaciers and surges at GS-2a concurred. In Andorra the snow- overfed glacier surges correlate with the decreasing winter insolation during GS-2b. In Iberia, the LGM would be placed between 23-17.5 ka and glaciers spread, linked to both wet westerlies from the North Atlantic and moisture supply of Mediterranean influence, reaching almost the eastern side of the Central Pyrenees, leading us to suppose an NW-NE seesaw climatic relationship across Iberia almost since GS-5.1. The oscillations of the oceanic thermal front promoted wet/dry westerly winds crossing over the Pyrenees, pushing back the Mediterranean influence towards the East.
By classifying glacial phases of the northern Iberian Peninsula fringe, four common glacial phases arise for the last glacial cycle:
A) An early LGC starting at MIS 5d having a recessional period during MIS 5c. Cold-type glaciers are expected to have existed in some of the extreme NW of the Iberian mountains until Termination 1.
B) The Last Maximum Ice Extent occurred mainly during MIS 5a – MIS 4. An asymmetrical glacier recession during MIS 3 was related to an increase in eastward aridity.
C) Significant glacier fluctuations during the MIS 3 – MIS 2 hinge, the appraisal of temperated-polythermal type of glaciers accompanied by a generalised moisture increase entailing valley glaciers to surge.
D) Side-to-side mountain range-scale deglaciation dissymmetry in MIS 2. The widespread expansion of tempered-polythermal type glaciers during the LGM period and Termination 1 had a proportional expansion to the available moisture.
The final deglaciation is characterised by relictual cirque glaciers disappearing during GS-1. In Andorra, a general rise in local river base levels occurred until the Holocene Optimum.
Unravelling the afore-cited glacial phases and unexpected research allows for a tesselated mapping of the SW continental Europe concerning part, or all of the LGC glacial phases outlined above:
1 – Areas where glaciers were prevalent during MIS 2, like the Iberian Central System, the NW and S French Massif Central, the NW Jura and the maritime Alps.
2 – Areas having a far-flung end moraine produced in a previous glacial phase (MIS 6 or posterior) showing stability until the MIS 2, as for ice caps/fields from the southern half of the Galicia mountains.
3 – Areas of pseudo-pleniglacial or apparent-pleniglacial condition, despite previous glacier recessions phases (albeit challenging to identify), as in most of the northern slope of the Pyrenees.
4 – Areas of multiphase glacier advances, like most of the southern slope of the Pyrenees, most of the Cantabrian Mountains, the half north of the Galicia mountains, the High Atlas, Sierra Nevada and the SW French Massif Central, the western Alps and the Vosges.
5 – Areas where glaciers were present from the LGM until Termination-I, like the northern Iberian range and Sanabria in Iberia. Nevertheless, other mountain ranges have a Type 5 glaciation scenario, like the southern Black Forest in Germany.
Keywords: Pyrenees, glaciations, glacial dynamics, Late Quaternary chronology, glacial valley deposits, over-consolidation, glaciolacustrine, palaeoenvironment, polythermal glaciers, sub-Milankovich cycles, glaciation types, SW Europe.
Keywords: Pyrenees, glaciations, glacial dynamics, Late Quaternary chronology, glacial valley deposits, over-consolidation, glaciolacustrine, palaeoenvironment, polythermal glaciers, sub-Milankovich cycles, glaciation types, SW Europe.
It is commonly asserted that there are two distinct classes of glacier surges: slow, long-duration ‘Svalbard-type’ surges, triggered by a transition from cold- to warm-based conditions (thermal switching), and fast, shorter-duration ‘Alaska-type’ surges triggered by a reorganisation of the basal drainage system (hydraulic switching). This classification, however, reflects neither the diversity of surges in Svalbard and Alaska (and other regions), nor the fundamental dynamic processes underlying all surges. We argue that enthalpy balance theory offers a framework for understanding the spectrum of glacier surging behaviours while emphasising their essential dynamic unity. In this paper, we summarise enthalpy balance theory, illustrate its potential to explain so-called ‘Svalbard-type’ and ‘Alaska-type’ surges using a single set of principles, and show examples of a much wider range of glacier surge behaviour than previously observed. We then identify some future directions for research, including strategies for testing predictions of the theory against field and remote sensing data, and priorities for numerical model development.
The widely used tool, Ground Penetrating Radar (GPR), has proven to be an excellent research method for glaciological studies. The total ice thickness and englacial structures can be studied, and the method can give information on the temperature regime within the ice. Good velocity profiles are needed to convert measured two‐way travel time to depth information. In addition, a good velocity analysis can be used to improve data processing. A number of methods can be used to find the GPR wave velocity, which are briefly described. This study used hyperbola fitting to estimate the velocity in a glaciological study. In addition, Kirchhoff's migration was used to finetune this velocity estimate. Within the Longyearbreen glacier, situated next to Longyearbyen on Spitsbergen, Svalbard archipelago, objects in the ice acts as scattering points that create hyperbolas. Using the hyperbola fitting method, a GPR wave velocity equal to 0.170 ± 0.005 m/ns was estimated. By doing Kirchhoff's migration and studying the collapse of hyperbolas with variations of the migration velocity, a more accurate velocity estimate can be achieved; 0.172 ± 0.002 m/ns. A more accurate velocity estimate like this opens possibilities for better characterisation of the ice body and ice thickness variations, as well as the variations of these as a function of time. In March 2022, the maximum ice thickness in the investigated area was calculated to be 88 ± 1 m. This article is protected by copyright. All rights reserved
Understanding fast ice flow is key to assessing the future of glaciers. Fast ice flow is controlled by sliding at the bed, yet that sliding is poorly understood. A growing number of studies show the relationship between sliding and basal shear stress transitions from an initially rate-strengthening behavior to a rate-independent or rate-weakening behavior. Studies that have tested a glacier sliding law with data remain rare. Surging glaciers, as we show in this study, can be used as a natural laboratory to inform sliding laws because a single glacier shows extreme velocity variations at a subannual timescale. The present study has two main goals: (1) we introduce a new workflow to produce velocity maps with a high spatiotemporal resolution from remote-sensing data, combining Sentinel-2 (S2) and Landsat 8 (L8) and using the results to describe the recent surge of Shisper Glacier, and (2) we present a generalized sliding law and substantiate the sliding-law behavior using the remote sensing dataset. The quality and spatiotemporal resolution of the velocity time series allow us to identify a gradual amplification of spring speed-up velocities in the 2 years leading up to the surge that started in November 2017. We also find that surface velocity patterns during the surge can be decomposed into three main phases, and each phase appears to be associated with hydraulic changes. Using this dataset, we are able to highlight the rate-independent and rate-weakening relationships between resistive stress and sliding during the surge. We then discuss the importance of the generalized sliding relationship to reconcile observations of fast ice flow, and in particular, different surge behaviors. The approach used in this study remains qualitative, but if coupled with better bed-elevation data and numerical modeling could lead to the widespread quantification of sliding-law parameters.
Understanding glacier drainage system behaviour and its response to increased meltwater production faces several challenges in the High Arctic because many glaciers are transitioning from polythermal to almost entirely cold thermal structures. We, therefore, used ground-penetrating radar data to investigate the thermal structure and drainage system of Waldemarbreen in Svalbard: a small High Arctic glacier believed to be undergoing thermal change. We found that Waldemarbreen retains up to 80 m of temperate ice in its upper reaches, but this thickness most likely is a relict from the Little Ice Age when greater ice volumes were insulated from winter cooling and caused greater driving stresses. Since then, negative mass balance and firn loss have prevented latent heat release and allowed near-surface ice temperatures to cool in winter, thus reducing the thickness of the temperate ice. Numerous reflectors that can be traced up-glacier are interpreted as englacial channels formed by hydrofracturing in the crevassed upper region of the glacier. The alternative cut and closure mechanism of conduit initiation only forms conduits in parts of the lower ablation area. Consequently, Waldemarbreen provides evidence that hydrofracturing at higher elevations can play a major role in englacial water drainage through cold ice.
Ice dammed glacial lake outburst floods (GLOFs) associated with surge glaciers are increasing in response to climate change. Predicting the phenomenon to protect downstream communities remains challenging around the globe. Surge-type glaciers are characterized by unsteady movements and frequent frontal advances, which cause natural hazards by obstructing river channels, forming ice-dammed lakes, which can cause GLOFs, posing threats downstream. The determination of the surge characteristics, timing and evolution of lakes and GLOFs is fundamental to flood control and disaster management. In this study, the case of the Khurdopin Glacier (Karakoram) is used to elucidate key behavioral characteristics of surging glaciers that usefully can be applied to understand the GLOF hazard from glaciers worldwide. Seven surge periodical cycles associated with the Khurdopin Glacier that occurred at intervals of 19–20 years between 1880 and 2020 were investigated using a GLOF dataset. The ice flow dynamics of three surge events that occurred between 1970 and 2020 were analyzed using high-resolution satellite imagery. The results indicate that the maximum and minimum surge velocities control the conduit development that drains lakes resulting in a number of GLOFs. A surge between 1998 and 2002 generated six GLOFs. A subglacial drainage model was developed to estimate the timing of the peak discharge in GLOF hydrographs. The results show that conduit melt enlargement becomes the dominant drainage process at one-third of the rising limb. These floods' high peak discharges and short durations are primarily due to the higher lake water temperature, which controls the conduit enlargement rate. Based on the current study results, the proposed model can be adopted worldwide for surge-type glaciers. The initiation of the main surge period, which leads to lake formation, can be anticipated, as the pre-surge period can be identified using remote-sensing analysis. The timing of ice-dammed lake formation and GLOFs can be estimated, providing residents and authorities time to take precautionary measures and thus limiting damage downstream.
Glacier hydrology describes water movement around, on, in and under glaciers. It plays an important role for glacier flow and thus ice transport into the sea and the associated sea level rise. It is further relevant for nutrient transport and release into ecosystems, for hydropower, and for drinking water supply in glaciated regions. Glacier related flood events are additionally a frequent geohazard, emphasizing the importance of accurate knowledge of glacier hydrology. This knowledge is, however, very limited due to general inaccessibility of glacial subsurface flows and thus lack of direct observations and technologies that could provide them. The present thesis therefore develops novel technologies, allowing to observe and study water flow inside glacial channels in detail, and applies them on Svalbard glaciers. For this, sensing drifters are proposed and their statistical repeatability tested. The instruments are then used to study water flow over glacier surfaces. Further, a method to reconstruct flow paths from drifter data is proposed and showcased with the example of a channel within a glacier. Additional speleological investigations provide permafrost temperatures under Svalbard glaciers and highlight the importance of meteorological glacier surface conditions for temperature and erosion of the glacier bed.
Although many convincing, diverse, and sometimes competing models of glacier surging have been proposed, the observed behavior of surging glaciers does not fit into distinct categories, and suggests the presence of a universal mechanism driving all surges. On the one hand, recent simulations of oscillatory flow behavior through the description of transient basal drag hint at a fundamental underlying process. On the other hand, the proposition of a unified model of oscillatory flow through the concept of enthalpy adopts a systems based view, in an attempt to rather unify different mechanisms through a single universal measure. While these two general approaches differ in perspective, they are not mutually exclusive, and seem likely to complement each other. A framework incorporating both approaches would see the mechanics of basal drag describing ice flow velocity and surge propagation as a function of forcing by conditions at the glacier bed, in turn modulated through the unified measure of enthalpy.
This study examines how longitudinal foliation develops in glaciers and ice sheets in a
wide range of topographic, climatic, and dynamic settings, at a variety of spatial scales.
Study locations include four valley glaciers in Svalbard (Austre Brøggerbreen, Midtre
Lovénbreen, Austre Lovénbreen, and Pedersenbreen), a valley glacier in Canada
(Sermilik Glacier), and seven outlet glaciers in Antarctica (Hatherton Glacier, Taylor
Glacier, Ferrar Glacier, Lambert Glacier, Recovery Glacier, Byrd Glacier, and Pine Island
Glacier). Detailed structural mapping of the valley glaciers from satellite imagery and
field-based measurements were used to document the formation of longitudinal
foliation in small-scale ice masses. These findings were ‘up-scaled’ and applied to much
larger glaciers and ice streams. Longitudinal foliation develops in concentrated bands
at flow unit boundaries as a result of enhanced simple shear. However, longitudinal
foliation is not directly observable from satellite imagery at the surface of larger-scale
valley glaciers. The longitudinal structures visible at the surface of larger-scale glaciers
form at flow-unit boundaries and are composed of bands of steeply dipping
longitudinal foliation; however, they appear as individual linear features on satellite
imagery as a result of the comparatively low spatial resolution of the imagery. The
persistence of flowlines in the Antarctic Ice Sheet through areas of crevassing and net
ablation (blue-ice areas) suggests that they are the surface representation of a three-dimensional structure. Flowlines are therefore inferred to be the surface expression of
flow-unit boundaries composed of bands of steeply dipping longitudinal foliation. The
survival and deformation of flowlines in areas of ice flow stagnation indicates that
flowlines form in their initiation zones and not along their entire length. Furthermore,
these ice stagnation areas indicate that flowlines record past ice dynamics and
switches in ice flow.
Glacier surges are cyclic oscillations of velocity and mass resulting from internal dynamic instabilities. For surge-type glaciers, cycles of advance and retreat are decoupled from climate forcing, so it is important to consider the possibility that former glaciers may have been surge-type when making climatic inferences from their dimensions and chronologies. In this paper, climatic and glacier geometric data are used to show that Scotland was likely the location of a surge cluster during the Loch Lomond Stade (∼12.9–11.7 ka), with high probabilities of surging for outlets of the West Highland Icefield and the larger glaciers in the Inner Hebrides and Northern Highlands. Terrestrial and marine landforms consistent with surging occur in all of these areas, and it is proposed that surge-type glaciers existed on the Islands of Skye and Mull, in the Northern Highlands, and in a ‘surging arc’ along the western, southern and south-eastern margins of the West Highland Icefield. The possibility that surge-type glaciers were widespread in Scotland during the Loch Lomond Stade offers a fresh perspective on some long-standing issues, including the relationship between style of deglaciation and climate change, the climatic significance of glacial chronologies, palaeoclimatic reconstructions, and the interpretation of numerical model results.
Understanding fast ice flow is key to assess the future of glaciers. Fast ice flow is controlled by sliding at the bed, yet that sliding is poorly understood. A growing number of studies show that the relationship between sliding and basal shear stress transitions from an initially rate-strengthening behavior to a rate-independent or rate-weakening behavior. Studies that have tested a glacier sliding law with data remain rare. Surging glaciers, as we show in this study, can be used as a natural laboratory 5 to inform sliding laws because a single glacier shows extreme velocity variations at a sub-annual timescale. The present study has two parts: (1) we introduce a new workflow to produce velocity maps with a high spatio-temporal resolution from remote sensing data combining Sentinel-2 and Landsat 8 and use the results to describe the recent surge of Shisper glacier, and (2) we present a generalized sliding law and provide a first-order assessment of the sliding-law parameters using the remote sensing dataset. The quality and spatio-temporal resolution of the velocity timeseries allow us to identify a gradual amplification of 10 spring speed-up velocities in the two years leading up to the surge that started by the end of 2017. We also find that surface velocity patterns during the surge can be decomposed in three main phases, and each phase appears to be associated with hydraulic changes. Using this dataset, we are able to constrain the sliding law parameter range necessary to encompass the sliding behavior of Shisper glacier, before and during the surge. We document a transition from rate-strengthening to rate-independent or rate-weakening behavior. A range of parameters is probably necessary to describe sliding at a single glacier. 15 The approach used in this study could be applied to many other sites in order to better constrain glacier sliding in various climatic and geographic settings.
The detachment of large parts of low-angle mountain glaciers resulting in massive ice–rock avalanches have so far been believed to be a unique type of event, made known to the global scientific community first for the 2002 Kolka Glacier detachment, Caucasus Mountains, and then for the 2016 collapses of two glaciers in the Aru range, Tibet. Since 2016, several so-far unrecognized low-angle glacier detachments have been recognized and described, and new ones have occurred. In the current contribution, we compile, compare, and discuss 20 actual or suspected large-volume detachments of low-angle mountain glaciers at 10 different sites in the Caucasus, the Pamirs, Tibet, Altai, the North American Cordillera, and the Southern Andes. Many of the detachments reached volumes in the order of 10–100 million m3. The similarities and differences between the presented cases indicate that glacier detachments often involve a coincidental combination of factors related to the lowering of basal friction, high or increasing driving stresses, concentration of shear stress, or low resistance to exceed stability thresholds. Particularly soft glacier beds seem to be a common condition among the observed events as they offer smooth contact areas between the glacier and the underlying substrate and are prone to till-strength weakening and eventually basal failure under high pore-water pressure. Partially or fully thawed glacier bed conditions and the presence of liquid water could thus play an important role in the detachments. Surface slopes of the detached glaciers range between around 10∘ and 20∘. This may be low enough to enable the development of thick and thus large-volume glaciers while also being steep enough to allow critical driving stresses to build up. We construct a simple slab model to estimate ranges of glacier slope and width above which a glacier may be able to detach when extensively losing basal resistance. From this model we estimate that all the detachments described in this study occurred due to a basal shear stress reduction of more than 50 %. Most of the ice–rock avalanches resulting from the detachments in this study have a particularly low angle of reach, down to around 5∘, likely due to their high ice content and connected liquefaction potential, the availability of soft basal slurries, and large amounts of basal water, as well as the smooth topographic setting typical for glacial valleys. Low-angle glacier detachments combine elements and likely also physical processes of glacier surges and ice break-offs from steep glaciers. The surge-like temporal evolution ahead of several detachments and their geographic proximity to other surge-type glaciers indicate the glacier detachments investigated can be interpreted as endmembers of the continuum of surge-like glacier instabilities. Though rare, glacier detachments appear to be more frequent than commonly thought and disclose, despite local differences in conditions and precursory evolutions, the fundamental and critical potential of low-angle soft glacier beds to fail catastrophically.
Over the last decades, glaciers on Svalbard were shrinking in response to the current climate change. Most of them decreased in size, area, and surface height with a stable negative or even accelerated changes in the mass balance. Many of them belong to the polythermal type, and as they shrink, their thermal regime can also change significantly depending on the climate and local parameters such as the ice facies distribution, the firn thickness, and others that affect the hydrology and movement of glaciers. Data from repeated GPR surveys in 1999 and 2018–2019 were used to identify changes in the thermal regime of the polythermal Aldegondabreen, Svalbard. The glacier has undergone a significant reduction of its temperate ice core, as a consequence of steadily negative mass balance, decreasing thickness, and the tongue retreat. The results show that over a 19‑year period, the total area of the glacier has decreased by 23.1% (from 6.94 to 5.34 km2), and the total volume of ice – by 36.4% (from 0.437 to 0.278 km3). At the same time, the area of its temperate core has decreased by 32.7% (from 1.196 to 0.804 km2), and the core volume – by 42.5% (from 0.035 to 0.02 km3). In this way, the relative rates of internal glacier changes associated with the warm core exceeded the external changes of the entire glacier. The share of temperate ice in the total volume of the glacier ice decreased from 8% to 7%. The glacier shrinking in response to rise of the air temperature was accompanied by its gradual internal «cooling». In the near future, this can result in a rapid transition of the glacier from a polythermal type into a cold one. Regular repeated geophysical surveys of the internal structure of the Svalbard polythermal glaciers can become an important element in the system of long-term monitoring of changes in climate and the natural environment of the archipelago, along with already existing observations of other sensitive natural indicators such as the size and mass balance.
We present a theoretical framework that integrates the dynamics of glaciers with and without the topographic confinement. This Part 1 paper concerns the former, which may exhibit surge cycles when subjected to thermal switches associated with the bed condition. With the topographic trough setting the glacier width and curbing the lateral drainage of the meltwater, the problem falls under the purview of the undrained plastic bed (UPB) formalism. Employing the UPB, we shall examine the external controls of the glacial behavior and test them against observations. Through our non-dimensionalization scheme, we construct a 2-D regime diagram, which allows a ready prognosis of the glacial properties over the full range of the external conditions, both climate- and size-related. We first discern the boundaries separating the glacial regimes of steady-creep, cyclic-surging and steady-sliding. We then apply the regime diagram to observed glaciers for quantitative comparisons. These include the Svalbard glaciers of both normal and surge types, Northeast Greenland Ice Stream characterized by steady-sliding, and Hudson Strait Ice Stream exhibiting cyclic surges. The quantitative validation of our model containing no free parameters suggests that the thermal switch may unify the dynamics of these diverse glaciers.
Proglacial icings accumulate in front of many High Arctic glaciers during the winter months, as water escapes from englacial or subglacial storage. Such icings have been interpreted as evidence for warm-based subglacial conditions, but several are now known to occur in front of cold-based glaciers. In this study, we investigate the drainage system of Tellbreen, a 3.5 km long glacier in central Spitsbergen, where a large proglacial icing develops each winter, to determine the location and geometry of storage elements. Digital elevation models (DEMs) of the glacier surface and bed were constructed using maps, differential GPS and ground penetrating radar (GPR). Rates of surface lowering indicate that the glacier has a long-term mass balance of −0.6 ± 0.2 m/year. Englacial and subglacial drainage channels were mapped using GPR, showing that Tellbreen has a diverse drainage system that is capable of storing, transporting and releasing water year round. In the upper part of the glacier, drainage is mainly via supraglacial channels. These transition downglacier into shallow englacial "cut and closure" channels, formed by the incision and roof closure of supraglacial channels. Below thin ice near the terminus, these channels reach the bed and contain stored water throughout the winter months. Even though no signs of temperate ice were detected and the bed is below pressure-melting point, Tellbreen has a surface-fed, channelized subglacial drainage system, which allows significant storage and delayed discharge.
Controls on the global distribution of surge-type glaciers hold the keys to a better understanding of surge mechanisms. We investigate correlations between the distribution of surge-type glaciers and climatic and glacier geometry variables, using a new global geodatabase of 2317 surge-type glaciers. The highest densities of surge-type glaciers occur within an optimal climatic envelope bounded by temperature and precipitation thresholds. Across all regions with both surge-type and normal glaciers, the former are larger, especially at the cold, dry end of the climatic spectrum. A species distribution model, Maxent, accurately predicts the major clusters of surge-type glaciers using a series of climatic and glacier geometry variables, but under-predicts clusters found outside the climatically optimal surge zone. We interpret the results in terms of a new enthalpy cycle model. Steady states require a balance between enthalpy gains generated by the balance flux and losses via heat conduction and meltwater discharge. This condition can be most easily satisfied in cold, dry environments (thin, low-flux glaciers, efficient conductive heat losses) and warm, humid environments (high meltwater discharges). Intermediate conditions correspond to the optimal surge zone, where neither heat conduction nor runoff can effectively discharge enthalpy gains, and dynamic cycling can result.
The tectonic effects of a glacier surge differ from those of steady state because flow is driven by longitudinal stresses rather than shear stresses. The orientations of recently formed crevasses, indicating the directions of the principal stresses, have been used to investigate tectonic processes in glacier surges recorded by repeat aerial photography. Long-term, large-magnitude shifts in stress regime are demonstrated, as are short-term propagation features. Two types of tide-water glacier advance are identified, depending on the position of the surge front relative to a low effective-pressure zone at the glacier terminus. -Authors
ABSTRACT. 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.
KEYWORDS: Arctic glaciology, basal ice, ice dynamics, structural glaciology, subglacial sediments
Controls on the global distribution of surge-type glaciers hold the keys to a better understanding of surge mechanisms. Our study represents the first investigation of the correlations between the global distribution of surge-type glaciers and climatic and geometric variables, using a new geodatabase inventorying all surge-type glaciers in the world. The highest densities of surge-type glaciers occur within an optimal climatic envelope bounded by temperature and precipitation. Across all regions with both surge-type and normal glaciers, the former are larger, especially at the cold, dry end of the climatic spectrum. Climate change can also alter the distribution of surge-type glaciers. A species distribution model, Maxent, accurately depicts the major clusters of surge-type glaciers using three variables: temperature, precipitation and glacier area, but under-predicts clusters found outside of the climatically optimal surge zone. We interpret the results in terms of a new enthalpy cycle model. Steady states require a balance between enthalpy gains generated by the balance flux and losses via heat conduction and meltwater discharge. This condition can be most easily satisfied in cold, dry environments (thin, low-flux glaciers, efficient conductive heat losses), and warm, humid environments (high meltwater discharges). Intermediate conditions correspond with the optimal surge zone, where neither heat conduction nor runoff can effectively discharge heat gains, and enthalpy cycling can result.
We present observations of a surge of the glaciers Skobreen-Paulabreen, Svalbard, during 2003-05, including a time-lapse movie of the frontal advance during 2005, Advanced Spaceborne Thermal Emission (ASTER) imagery and oblique aerial photographs. The surge initiated in Skobreen, and then propagated downglacier into the lower parts of Paulabreen. ASTER satellite images from different stages of the surge are used to evaluate the surge progression. Features on the glacier surface advanced 2800 m over 2.4 yr, averaging 3.2 m/day, while the front advanced less (ca. 1300 m) due to contemporaneous calving. The surge resulted in a lateral displacement of the medial moraines of Paulabreen of ca. 600 m at the glacier front. The time-lapse movie captured the advance of the frontal part of the glacier, and dramatically illustrates glacier dynamic processes in an accessible way. The movie documents a range of processes such as a plug-like flow of the glacier, proglacial thrusting, incorporation of old, dead ice at the margin, and calving into the fjord. The movie provides a useful resource for researchers, educators seeking to teach and inspire students, and those wishing to communicate the fascination of glacier science to a wider public.
We present ground-penetrating radar (GPR)–based volume calculations, with associated error estimates, for eight glaciers on Wedel Jarlsberg Land, southwestern Spitsbergen, Svalbard, and compare them with those obtained from volume-area scaling relationships. The volume estimates are based upon GPR ice-thickness data collected during the period 2004–2013. The total area and volume of the ensemble are 502.91 ± 18.60 km2 and 91.91 ± 2.75 km3, respectively. The individual areas, volumes, and average ice thickness lie within 0.37–140.99 km2, 0.01–31.98 km3, and 28–227 m, respectively, with a maximum recorded ice thickness of 619 ± 13 m on Austre Torellbreen. To estimate the ice volume of unsurveyed tributary glaciers, we combine polynomial cross-sections with a function providing the best fit to the measured ice thickness along the center line of a collection of 22 surveyed tributaries. For the time-to-depth conversion of GPR data, we test the use of a glacierwide constant radio-wave velocity chosen on the basis of local or regional common midpoint measurements, versus the use of distinct velocities for the firn, cold ice, and temperate ice layers, concluding that the corresponding volume calculations agree with each other within their error bounds.
Geometric changes on a sample of Svalbard glaciers were studied using subtraction of repeat digital terrain models to determine early surge-stage dynamics. Changes in surface features were also analyzed. A number of new surges were found for glaciers not known to have surged previously. The surge development could be followed through three stages, of which the first two had not been previously described in Svalbard. The first two stages are mainly identified from glacier thickness changes and showed little visual evidence. In stage 1, initial surface lowering was found in the upper part of the glacier, followed by a thickening further downglacier in stage 2. Stage 3 represents the period of well-developed surge dynamics that is usually reported. Some surges ceased at stage 2 as a partial surge and never developed into a fully active surge. These partial surges could be misinterpreted as rapid response to climate change. The results of this study further support previous findings that the majority of Svalbard glaciers are of surge type.
Nathorstbreen glacier system (NGS) recently experienced the largest surge in
Svalbard since 1936, and this was examined using spatial and temporal
observations from DEM differencing, time series of surface velocities from
satellite synthetic aperture radar (SAR) and other sources. The upper basins
with maximum accumulation during quiescence corresponded to regions of
initial lowering. Initial speed-up exceeded quiescent velocities by a factor
of several tens. This suggests that polythermal glacier surges are initiated
in the temperate area before mass is displaced downglacier. Subsequent
downglacier mass displacement coincided with areas where glacier velocity
increased by a factor of 100–200 times (stage 2). After more than 5 years,
the joint NGS terminus advanced abruptly into the fjord during winter,
increasing velocities even more. The advance was followed by up-glacier
propagation of crevasses, indicating the middle and subsequently the upper
part of the glaciers reacting to the mass displacement. NGS advanced
~15 km, while another ~3 km length was lost
due to calving. Surface lowering of ~50 m was observed in
some up-glacier areas, and in 5 years the total glacier area increased by 20%.
Maximum measured flow rates were at least 25 m d−1, 2500 times
quiescent velocity, while average velocities were about 10 m d−1. The
surges of Zawadzkibreen cycle with ca. 70-year periods.
Nathorstbreen glacier system (NGS) recently experienced the largest
surge in Svalbard since 1936, and is examined using spatial and temporal
observations from DEM differencing, time-series of surface velocities
from satellite synthetic aperture radar (SAR) and other sources. The
upper basins with maximum accumulation during quiescence correspond to
regions of initial lowering. Initial speed-up exceeds quiescent
velocities by a factor of several tens of times. This suggests that
polythermal glaciers surges are initiated in the temperate area before
mass is displaced downglacier. Subsequent downglacier mass displacement
coincides with areas of 100-200 times increased velocities (stage 2).
After > 5 yr the joint NGS terminus advanced abruptly into tidewater
during winter. The advance was followed by upglacier propagation of
crevasses, indicating a re-action following from the already displaced
mass and extending flow. NGS advanced ca. 15 km, while another ca. 3 km
length was lost due to calving. Surface lowering of ca. 50 m was
observed in some upglacier areas and during 5 yr the total area
increased by 20%. Maximum measured flow rates were at least 25 m
d-1, 2500 times quiescence, while average velocities were
about 10 m d-1. The surges of Zawadzkibreen cycle with ca. 70
yr periods.
Most polythermal glaciers in Svalbard, other than those of surge type,
have receded steadily since the early 20th century. Midre
Lovénbreen, a slow-moving, 4-km-long valley glacier terminating
on land, is a typical example, and its internal structures reflect
changing dynamics over this period. The three-dimensional structural
style of this glacier and the sequential development of structures have
been determined from surface mapping, ground-penetrating radar, and
numerical flow modeling. In order of formation the structures observed
today at the glacier surface are (1) primary stratification that has
become folded about flow-parallel axes; (2) axial plane longitudinal
foliation associated with this folding; (3) several sets of intersecting
crevasse traces; (4) arcuate upglacier-dipping fractures developed as
part of a thrust complex near the snout; and (5) longitudinal splaying
fractures in the snout area. The long-term evolution and dynamic
significance of these structures can be ascertained from historical
ground and aerial photographs. Modeling indicates that stratification
and foliation continue to evolve today as a result of internal
deformation, especially in zones of converging flow, where simple shear
is most pronounced, but within the tongue are carried passively toward
the snout. Crevasse traces appear to be no longer actively forming but
are interpreted as relict structures when the ice was more dynamic and
mostly wet based. The interpretation of arcuate fractures near the snout
as thrusts is supported by the matching orientations of modeled strain
ellipses, which illustrate the importance of longitudinal compression.
One of the few long instrumental records available for the Arctic is the Svalbard Airport composite series that hitherto began in 1911, with observations made on Spitsbergen, the largest island in the Svalbard Archipelago. This record has now been extended to 1898 with the inclusion of observations made by hunting and scientific expeditions. Temperature has been observed almost continuously in Svalbard since 1898, although at different sites. It has therefore been possible to create one composite series for Svalbard Airport covering the period 1898–2012, and this valuable new record is presented here. The series reveals large temperature variability on Spitsbergen, with the early 20th century warming as one striking feature: an abrupt change from the cold 1910s to the local maxima of the 1930s and 1950s. With the inclusion of the new data it is possible to show that the 1910s were colder than the years at the start of the series. From the 1960s, temperatures have increased, so the present temperature level is significantly higher than at any earlier period in the instrumental history. For the entire period, and for all seasons, there are positive, statistically significant trends. Regarding the annual mean, the total trend is 2.6°C/century, whereas the largest trend is in spring, at 3.9°C/century. In Europe, it is the Svalbard Archipelago that has experienced the greatest temperature increase during the latest three decades. The composite series may be downloaded from the home page of the Norwegian Meteorological Institute and should be used with reference to the present article.
[1] 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.
This paper presents the changes in the thermal structure of the polythermal glacier Storglaciären, northern Sweden, over the 20 year period 1989-2009 derived by comparing maps of the depth of the englacial transition between cold ice (permanently frozen) and temperate ice (which contains water inclusions). The maps are based on interpreted ice-penetrating radar surveys from 1989, 2001 and 2009.
Complex thinning of the cold layer, first identified between 1989 and 2001, is still ongoing. A volume calculation shows that Storglaciären has lost one-third of its cold surface layer volume in 20 years, with a mean thinning rate of 0.80 ± 0.24 m a ⁻¹ . We suggest that the thinning of the cold layer at Storglaciären is connected to the climatic warming experienced by sub-Arctic Scandinavia since the 1980s and we argue that repeated ice-penetrating radar surveys over the ablation area of polythermal glaciers offer a useful proxy for evaluating glacier responses to changes in climate.
Multiproxy analyses including hydrographical, geochemical, foraminferal, lithological and geophysical data reveal variable influences of the glaciers Tunabreen and von Postbreen as well as the river Sassenelva on the sedimentary environment in two Spitsbergen fjords during the Late Weichselian and the Holocene. Grounded ice covered the study area during the last glacial. The glacier fronts retreated stepwise during the latest Weichselian/earliest Holocene, and the glaciers were probably small during the early Holocene. A growth of Tunabreen occurred between 6 and 4 cal ka BP. Reduced input from Tunabreen from c. 3.7 cal ka BP was probably a result of suppressed iceberg rafting related to the enhanced formation of sea ice and/or reduced meltwater runoff. During the past two millennia, the glacier fronts advanced and retreated several times. The maximum Holocene glacier extent was reached at the end of a surge of von Postbreen in AD 1870. Characteristics of the modern glaciomarine environment include: (1) different colours and bulk-mineral assemblages of the turbid waters emanating from the main sediment sources; (2) variable locations of the turbid-water plumes as a consequence of wind forcing and the Coriolis effect; (3) stratified water masses during summers with interannual variations; (4) increasing productivity with increasing distance from the glacier fronts; (5) foraminifera-faunal assemblages typical for glacierproximal settings; and (6) periodical mass-transport activity.
Geodetic measurements indicate that a number of glaciers in western Svalbard ranging in size from 5-1000 km2 are losing mass at an accelerating rate. The average thinning rate for Midtre Lovénbreen, the glacier with the best data coverage, has increased steadily since 1936. Thinning rates for 2003-2005 are more than 4 times the average for the first measurement period 1936-1962 and are significantly greater than presented previously. On Slakbreen, thinning rates for the latest measurement period 1990-2003 are more than 4 times that of the period 1961-1977. Thinning of several glaciers along a previously measured airborne lidar profile in Wedel Jarls Land has also increased, doubling between the period 1990-1996 and 1996-2002. Our results imply an increased sea level contribution from Svalbard. In addition, the mass loss is an important influence on measured rates of rebound on western Svalbard and should be factored into analysis of GRACE results.
A deep-ice temperature measurement program has been conducted on Trapridge Glacier, Yukon Territory. Large regions of temperate ice are predicted at the base of the otherwise cold glacier, The glacier snout, frozen to bedrock, appears to act as an ice dam allowing the build up of an ice reservoir in the upper regions. Thermal regulation of the surges of Trapridge Glacier is suggested and the relevance of basal temperatures in large surging glaciers is discussed.
Radio echo soundings on Rusty Glacier, a small surge-type glacier in Yukon Territory reveal that the ice is considerably thicker than previously believed. A reinterpretation of deep ice-temperature measurements made in 1969 and 1970 suggests that a large zone of temperate basal ice exists. This result supports thermal instability as the surge mechanism for Rusty Glacier.
Surging outlet glaciers are important in draining large ice caps, but the mechanisms controlling surge periodicities are poorly known. We investigated a sediment sequence from the glacier-fed Lake Lögurinn in eastern Iceland, and our unique annually resolved data, based on sedimentary varves, imply that Eyjabakkajökull, an outlet glacier of Vatnajökull, began surging about 2200 cal a BP (before 1950 AD). Approximately 1700 cal a BP, the glacier started to surge at a uniform 34- to 38-year periodicity that prevailed until the coldest part of the Little Ice Age when the periodicity almost halved to 21–23 years. Since the late 1800 s the surge periodicity of Eyjabakkajökull has returned to a longer period of 35–40 years. We suggest that surge periodicities of Eyjabakkajökull are forced by climatically driven mass balance changes, which may be a common forcing factor for similar surge-type outlet glaciers. Copyright © 2011 John Wiley & Sons, Ltd.
A necessary condition for a glacier to surge by thermal instability is that the glacier be cold with basal ice at or near the melting point. Deep temperature measurements show that two small surge-type glaciers in the Yukon Territory meet this requirement, but shallow measurements in three other surge-type glaciers suggest a temperate regime. If the latter observations are accepted, not all surges are thermally controlled: if a single mechanism accounts for all surges it cannot be thermal instability.
In this paper it is argued that thermal instability remains a viable mechanism for explaining surges of many cold glaciers, and that regardless of the underlying mechanism, thermal processes must at least have a major influence on the surge behavior of cold glaciers.
Two numerical modelling experiments are described. The first involves a one-dimensional model which shows that thermal control can account for the remarkably constant surge cycle found in some glaciers. The second, a two-dimensional model of the time-dependent temperature structure of a surge-type glacier, shows that the relative amounts of temperate and cold basal ice can change considerably as the surge cycle progresses. This variation alone may be sufficient to explain surges, but even if this is not the case, thermal processes must affect the timing of surges in many cold glaciers.
A compelling feature of the thermal instability mechanism is that it offers an explanation of the factors controlling the non-random geographical distribution of surge-type glaciers. For a glacier to have a cold surface and near-temperate bed, the ice thickness, temperature, and geothermal flux must be fortuitously related.
Trapridge Glacier, Yukon, Canada, is a polythermal, soft-bedded surge-type glacier. As revealed by a 1951 aerial photograph, an important surge occurred in the 1940s, leaving the glacier heavily crevassed and at least 1 km downstream from the 1941 position. It is our conclusion that another surge, albeit far less dramatic, has been taking place over the last three decades and is now terminated. To quantify the changes in ice geometry, ground survey measurements were coupled with aerial photogrammetry to yield digital elevation models of the glacier from 1951 to present. For 1951, 1970, 1972, 1977 and 1981, years for which ground data are scarce or unavailable, DEMs were generated from stereographic analysis of aerial photographs. For the subsequent years, DEMs are obtained from ground survey data using our implementation of a Bayesian Kriging algorithm. For each year, the topography of the previous year is used as a background model and updated by the available survey data. This chain is initiated by the 1981 DEM obtained from aerial photogrammetry. Using exposed sections of the bed from the 1981 DEM and radar data, a map of the bed topography is obtained. Changes in the flow patterns are also investigated using an extended but variable array of flow markers. The results of this work indicate that the period from the previous surge to the present was characterized by two processes: 1) the deglaciation of the 1940s surge `receiving area' and 2) the slow advance of a mass wave from the upper reaches of the glacier. While it was previously believed that this mass reorganization was to precede a fast surge, it is now obvious that such a surge is not to happen. Ice velocity peaked at nearly 40 m/yr in the mid 1980s, fluctuated for the next 15 years and then dropped ca 2000 to reach ~10 m/yr in 2005. The bulge that formed in the 1980s at the transition between warm- and cold-based ice continued to propagate beyond the limits of the 1981 glacier. The glacier snout is currently ~200 m downstream from the 1981 terminus and not advancing. Together the DEMs and bed topography map enable us to characterize changes in the distribution and volume of ice, hydrological potential, and basal stress that accompanied the slow surge.
Changes in driving and resistive stresses play an essential role in governing the buoyancy forces that are important controls on the speed and irreversibility of tidewater glacier retreats. We describe changes in geometry, velocity and strain rate, and present a topdown force balance analysis performed over the lower reach of Columbia Glacier. Our analysis uses new measurements and estimates of basal topography and photogrammetric surface velocity measurements made between 1977 and 2001, while assuming depth-independent strain. Sensitivity tests show that the method is robust and insensitive to small changes in the calculation parameters. Spatial distributions of ice speed show little correspondence with driving stress. Instead, spatial patterns of ice speed exhibit a nonlinear correspondence with basal drag. Primary resistance to flow comes from basal drag, but lateral drag becomes increasingly more important throughout the retreat, which may account for observed increases in speed. Maximum basal drag is always located in a prominent constriction located ~12 km upstream from the pre-retreat terminus. Once the terminus retreated into deep water off the terminal moraine marking the modern maximum extent, the upstream location of this maximum basal drag helped to promote thinning and decrease effective pressure in the lower region by limiting replenishing ice flow from upstream. An increase in both ice velocity and calving resulted, initiating what appears to be an irreversible retreat.
The end of the Little Ice Age (LIA) in Svalbard (76-81°N), a climate-sensitive region at the northern extreme of strong poleward heat transfer, was marked by an abrupt increase in mean annual air temperature of up to 5°C around 1920. Glacier mass balance has been consistently negative since this time, and large cumulative net losses of mass have occurred at most glaciers. Energy-balance modelling confirms the sensitivity of Svalbard glaciers to climate change, predicting a negative shift in net mass balance of up to 0.8 m a-1 (water equivalent) per degree temperature rise. This climate-related shift in glacier mass balance has reduced the intensity of glacier surge activity in Svalbard. One glacier, known to have surged since the end of the LIA, has since failed to accumulate the mass required to re-initiate the surge cycle, and is also now cold at its base and incapable of rapid flow by basal sliding. Three overviews of the total number of actively-surging glaciers in Svalbard between 1936-90 show a decrease from 18 to 5. This is significant compared with the expected numbers of surges based on LIA conditions. Post-LIA climate change in Svalbard has therefore affected not only glacier extent, but also ice dynamics. This is trend will probably continue given CO2-induced climate-warming.
Trapridge Glacier, a polythermal surge-type glacier located in the St. Elias Mountains, Yukon Territory, Canada, passed through a complete surge cycle between 1951 and 2005. Air photos (1951–1981) and ground-based optical surveys (1969–2005) are used to quantify the modifications in flow and geometry that occurred over this period. Yearly averaged flow records suggest that the active phase began ∼1980, and lasted until ∼2000. The average velocity in the central area of the glacier went from 16 m yr−1 in 1974 to 39 m yr−1 in 1980; it peaked at 42 m yr−1 in 1984, and remained above 25 m yr−1 until 2001. Over that interval, the flow decelerated by steps, in 4-year pulses. After a particularly vigorous acceleration in 1997–1999, the glacier gradually slowed to presurge velocities. In 2005, the flow was less than 9 m yr−1. Digital elevation models are generated by stereographic analysis of air photos for 1951, 1970, 1972, 1977, and 1981. These models are updated annually using ground-based survey data and a novel implementation of Bayesian kriging. Over the course of the surge, the front of active ice advanced 450 m and the glacier area increased by 10%, with an associated thinning of the ice. The previous surge of Trapridge Glacier, starting before 1939 and ending before 1951, led to a terminus advance of ∼1 km. Comparison of the two surges suggests that the 1930s surge started with a slow progression similar to what we observed in the 1980s and 1990s, and switched to a faster flow mode after 1941. This second phase was never attained in the recent surge, probably owing to a lack of mass.
The ice masses of Svalbard cover an area of ca. 36 600 km2, and are thus among the largest glaciated areas in the Arctic. Annual mass balance measurements have been carried out on several Svalbard glaciers over up to 30 yr. However, these glaciers extend over only 0.5% of the total ice-covered area. The measured mean net balance has been negative and no changing trend has been observed. On some glaciers and larger ice caps, the mean net balance has also been measured at different altitudes by detecting radioactive reference layers from nuclear fallouts in 1963 and 1986 in shallow ice cores. The net balance/altitude curves have been estimated for thirteen different regions in Svalbard, and combined with digital elevation models of all Svalbard ice masses used to calculate the net balance in each 100-m altitude interval. The net loss of mass through iceberg calving was estimated and appears to be an important component of the net mass loss from Svalbard ice masses. The overall total net balance is slightly negative, � 4:5 6 1k m3 yr� 1; giving a specific net balance of ca. � 120 630 mm yr� 1 over the archipelago. The contribution of ice caps and glaciers on Svalbard to global sea-level change is, therefore, close to 0.01 mm yr� 1 as an average value over the last 30 years, which is less negative than former estimates.
Temperature measurements in a subpolar surge-type glacier reveal a distinctive thermal structure associated with the boundary between the ice reservoir and receiving areas. In the receiving area the glacier is cold based, but bottom temperature has increased as much as 0.5 °C between 1981 and 1982, and the basal heat flux is roughly 10 times the expected geothermal flux. Water percolation through permeable subglacial material is the probable energy source. Deformation of the substrate could destroy this drainage system and trigger a surge.
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, Uvérsbreen, Midre Lovénbreen and Austre Brøggerbreen. 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 Uvérsbreen 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 Uvérsbreen where meltwater accumulates during the summer (near the subglacial lake Setevatnet, 250 m a.s.l.). Lovénbreen 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 Brøggerbreen, 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.
A single pronounced internal reflecting horizon has been observed on radio echo-sounding from over 30 glaciers in Spitsbergen. They are often present along the entire length of the glacier, remaining at a fairly constant depth (100–200 m) below the ice surface. Echo-strength data from radio echo-sounding have been used to obtain reflection coefficients, for these horizons, of between -15 and -25 dB. Combined with results of ice-core studies, the possible causes of this internal layer are investigated. The presence of water is found to be the most likely explanation, indicating the existence, at depth, of a layer of temperate ice.
A necessary condition for a glacier to surge by thermal instability is that the glacier be cold with basal ice at or near the melting point. Deep temperature measurements show that two small surge-type glaciers in the Yukon Territory meet this requirement, but shallow measurements in three other surge-type glaciers suggest a temperate regime. If the latter observations are accepted, not all surges are thermally controlled: if a single mechanism accounts for all surges it cannot be thermal instability.
In this paper it is argued that thermal instability remains a viable mechanism for explaining surges of many cold glaciers, and that regardless of the underlying mechanism, thermal processes must at least have a major influence on the surge behavior of cold glaciers.
Two numerical modelling experiments are described. The first involves a one-dimensional model which shows that thermal control can account for the remarkably constant surge cycle found in some glaciers. The second, a two-dimensional model of the time-dependent temperature structure of a surge-type glacier, shows that the relative amounts of temperate and cold basal ice can change considerably as the surge cycle progresses. This variation alone may be sufficient to explain surges, but even if this is not the case, thermal processes must affect the timing of surges in many cold glaciers.
A compelling feature of the thermal instability mechanism is that it offers an explanation of the factors controlling the non-random geographical distribution of surge-type glaciers. For a glacier to have a cold surface and near-temperate bed, the ice thickness, temperature, and geothermal flux must be fortuitously related.
Radio echo soundings on Rusty Glacier, a small surge-type glacier in Yukon Territory reveal that the ice is considerably thicker than previously believed. A reinterpretation of deep ice-temperature measurements made in 1969 and 1970 suggests that a large zone of temperate basal ice exists. This result supports thermal instability as the surge mechanism for Rusty Glacier.
A deep-ice temperature measurement program has been conducted on Trapridge Glacier, Yukon Territory. Large regions of temperate ice are predicted at the base of the otherwise cold glacier, The glacier snout, frozen to bedrock, appears to act as an ice dam allowing the build up of an ice reservoir in the upper regions. Thermal regulation of the surges of Trapridge Glacier is suggested and the relevance of basal temperatures in large surging glaciers is discussed.
A single pronounced internal reflecting horizon has been observed on radio echo-sounding from over 30 glaciers in Spitsbergen. They are often present along the entire length of the glacier, remaining at a fairly constant depth (100–200 m) below the ice surface. Echo-strength data from radio echo-sounding have been used to obtain reflection coefficients, for these horizons, of between -15 and -25 dB. Combined with results of ice-core studies, the possible causes of this internal layer are investigated. The presence of water is found to be the most likely explanation, indicating the existence, at depth, of a layer of temperate ice.