bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment of combined glacier and tree-ring studies to constrain latitudinal climate forcing of Scandinavian glacier mass balances
Authors: Jansson Peter , Linderholm Hans W.
Published: November 2007

Assessing climate change and its effects on the cryosphere is important, and individual proxies are commonly used for such assessments. We have investigated the possibility of combining glacier mass balance and tree-ring data to better understand regional climate variability in Scandinavia. There are substantial differences between climate information in mass-balance and tree-ring data. Summer balance (bS) is strongly related to summer temperature, while winter balance (bW) is less readily interpreted in terms of a climate signal. Tree rings are good summer temperature proxies, but due to the complexity of tree growth factors (e.g. the effect of the previous winter’s climate) tree-ring records do not exclusively represent summer temperatures. Combining bS and tree-ring records will not likely yield additional summer climate information. The relationship of mass balance with the Arctic Oscillation is stronger than with the North Atlantic Oscillation, especially for northernmost Sweden, whereas no such correlations were found for tree-ring data. The agreement between bN records from both maritime south-central Norway and continental northernmost Sweden and tree-ring data from Jämtland, in a maritime/continental climate transition zone, suggests possibilities to combine mass-balance and tree-ring data to provide information about climate over the entire year on interannual timescales.
Fresh-water discharge from Greenland using regional climate simulations
Authors: Sood Abha
Published: November 2007

The annual mass budget of the Greenland ice sheet (1992) and the fresh-water flux from Greenland including the coasts is determined using high-resolution regional climate model (REMO) simulations. The climate model is modified to include processes such as lateral flow over Greenland using a newly developed routing scheme, the effect of sub-grid-scale surface heterogeneity (orography) on surface temperature and runoff and an improved snow and ice model for the Greenland ice sheet for surface processes on the ice sheet. The high-resolution (0.125˚ grid size) simulations of accumulation and runoff fields are also assessed compared to the lower-resolution (0.5˚ grid size) simulations.
Mass-balance characteristics of arctic glaciers
Authors: Braithwaite Roger J.
Published: November 2007

A survey of available mass-balance data shows that glaciers on arctic islands, i.e. mountain glaciers and ice caps in northern Canada, Greenland, Svalbard and the Eurasian islands, share mass-balance characteristics of low annual amplitude and small interannual variability. By contrast, glaciers around the Arctic (e.g. in Alaska, Iceland, mainland Scandinavia and northern Eurasia) can have exceptionally large annual amplitude and interannual variability but otherwise share characteristics with glaciers in lower latitudes. The arctic island glaciers occur in areas with low annual precipitation and high annual temperature variability, i.e. in dry-cold or continental regions. Most glaciers surrounding the Arctic (Alaska, Iceland and Scandinavia) occur in areas with high annual precipitation and low annual temperature variability, i.e. in wet-warm or maritime regions. Earlier mass-balance modelling showed that arctic island glaciers have low sensitivity to temperature changes consistent with their low mass-balance amplitude. However, very large changes in mass balance could occur on arctic island glaciers if the sea ice surrounding the arctic islands were reduced so that the climate of the arctic islands becomes more maritime.
The presence of thrust-block naled after a major surge event: Kuannersuit Glacier, West Greenland
Authors: Yde Jacob C. , Tvis Knudsen N. , Larsen Nicolaj K. , Kronborg Christian , Nielsen Ole B. , Heinemeier Jan , Olsen Jesper
Published: November 2007

Thrust-block naled in front of Kuannersuit Glacier, West Greenland, appears to have formed during the termination of a terrestrial surge event by a combination of enhanced winter runoff, rapid advance of the glacier terminus, and proglacial stress release by thrusting and stacking of naled blocks. This process is equivalent to the formation of thrust-block moraines. The thrust-block naled consists of at least seven thrust sheets, which are characterized by stratified ice with beds composed of a lower debris-rich lamina, an intermediate dispersed lamina and a top clean-ice lamina, and underlain by frozen outwash deposits. The thrust-block naled differs from basal stratified ice in the absence of internal deformation structures, a relatively low debris concentration, a clay-rich particle-size distribution and a preferential sorting of lighter minerals. The oxygen isotope composition of the thrust-block naled is indistinguishable from δ18O values from meteoric glacier ice and bulk meltwater, but different from basal stratified ice facies. The d–δD relationship indicates that thrust-block naled has been formed by freezing of successive thin layers of bulk waters with variable isotopic composition, whereas basal stratified ice has developed in a subglacial environment with regelation. This work shows that the association between proglacial naled and rapidly advancing glaciers may have significant consequences for the proglacial geomorphology and the interpretation of basal ice layers.
Flow field of Kronebreen, Svalbard, using repeated Landsat 7 and ASTER data
Authors: Kääb Andreas , Lefauconnier Bernard , Melvold Kjetil
Published: November 2007

Knowledge about the spatio-temporal distribution of fast-flowing Arctic glaciers is still limited. Kronebreen, Svalbard, in particular, includes the confluence − and the dynamic interplay − of the fast-flowing Kronebreen and the currently slow-flowing Kongsvegen. In this study, image-matching techniques on the basis of repeated Landsat 7 Enhanced Thematic Mapper Plus (ETM+) pan and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite data are applied in order to derive surface velocity fields of the lowermost 10 km of Kronebreen for the annual periods 1999/2000, 2000/01, 2001/02 and a 40 day period around July 2001. This work perfectly complements differential synthetic aperture radar interferometry (DInSAR) studies available for Kronebreen. A complete surface velocity field is now available from combining the DInSAR studies for the upper part of the glacier and the optical image-matching study presented here. The data obtained within this study are also compared to velocity data of 1964, 1986, 1990 and 1996. As also suggested by previous studies, a significant spatio-temporal variability of the spring/summer and annual ice speeds becomes evident.
Palaeo-ice streams in the northern Keewatin sector of the Laurentide ice sheet
Authors: Angelis Hernán De , Kleman Johan
Published: November 2007

Evidence for ice streams in the Laurentide ice sheet is widespread. In the region of northern Keewatin and the Boothia Peninsula, Nunavut, Canada, palaeo-ice streams have been recognized, but their location, size and potential role in ice-sheet dynamics are poorly constrained. Based on the interpretation of satellite imagery, we produce a palaeo-ice-stream map of this region. Glacial directional landforms, eskers and moraines were mapped and integrated into landform assemblages using a glacial geological inversion model. Palaeo-frozen bed areas were also identified. Relative age of the geomorphic swarms was assessed by cross-cutting relationships and radiocarbon ages where available. Using this information we obtained a glaciologically plausible picture of ice-stream evolution within the northernmost Laurentide ice sheet. On the M’Clintock Channel corridor, three generations of pure ice streams are found. On Baffin Island and the Gulf of Boothia, glaciation was dominated by frozen-bed zones located on high plateaus and ice streams running along the troughs, i.e. topographic ice streams. A massive convergent pattern at the head of Committee Bay drained ice from both the Keewatin and Foxe sectors and was probably one of the main deglaciation channels of the Laurentide ice sheet. Finally, our results indicate that streaming flow was present in the deep interior of the Laurentide ice sheet, as recently shown for the Greenland and Antarctic ice sheets.
Analyses of a surging outlet glacier of Vatnajökull ice cap, Iceland
Authors: Aðalgeirsdóttir Guðfinna , Björnsson Helgi , Pálsson Finnur , Magnússon Eyjolfur
Published: November 2007

Many of the large outlet glaciers of Vatnajökull ice cap, Iceland, have a history of regular surges. The mass transport during surges can be up to 25% of the total ice flux. This is a considerable amount that affects the whole ice cap, the location of the ice divides, the flow field and the size and shape of the ice cap. Data from the surging outlet Dyngjujökull, on the northern side of Vatnajökull, which surged during the period 1998-2000, are presented: surface elevation changes, displacement and total mass tr ansport. The total gain in ice volume in the receiving area, due to the surge, is considerably smaller than the loss in the reservoir area. The difference is mainly due to enhanced melting rates on the larger surface area of the crevassed glacier surface, and increased turbulent fluxes above the surface, but also due to increased frictional melting at the bed during the surge. A two-dimensional vertically integrated numerical flow model, of standard shallow-ice approximation type, is used to show that a modeled glacier that is similar in size to Dyngjujökull and subject to the same mass balance has three times higher velocities than the measured velocity during the quiescent phase. Adding surges in the numerical model, by periodically increasing the sliding velocity, causes the glacier to retreat and oscillate around a smaller state when subject to the same mass-balance regime. Lowering the equilibrium line by 50 m lets the modeled surging glacier oscillate around a size similar to that of the present glacier, indicating that surging is an efficient long-term ablation mechanism.
Volume change of McCall Glacier, Arctic Alaska, USA, 1956–2003
Authors: Nolan Matt , Arendt Anthony , Rabus Bernhard , Hinzman Larry
Published: November 2007

A long history of research documents that McCall Glacier, Arctic Alaska, USA, continues to lose mass at a rate that is likely increasing with time. We present a photo comparison (1958-2003) that visually documents these volume changes, along with survey measurements that quantify these losses. Measurements of longitudinal profiles initially acquired from airborne laser altimetry, and repeated by ground-based surveys, indicate that the areally averaged rate of thinning increased between 1956-93 and 1993-2002, from 0.35 ± 0.07 m a-1 to 0.47 ± 0.03 m a-1, respectively; total volume loss was (8.3 × 107) ± (1.7 × 107) m3 and (2.7 × 107) ± (0.2 × 107) m3 (all in water equivalent) for these two time periods. These profiles also indicate that a 1 km stretch of the mid-ablation area is behaving differently from this trend, with a rate of thinning that is not changing with time. Lastly we present a comparison of several methods for calculating volume change and assess their relative errors.
Geochemical properties of the water–snow–ice complexes in the area of Shokalsky glacier, Novaya Zemlya, in relation to tabular ground-ice formation
Authors: Leibman M.O. , Arkhipov S.M. , Perednya D.D. , Savvichev A.S. , Vanshtein B.G. , Hubberten H.-W.
Published: November 2007

Tabular (massive) ground ice in periglacial areas of the Russian Arctic (Barents and Kara Sea coasts) is considered to be a remnant of past glacial epochs and is thus used as proof of the glacial extent. In this paper, we argue that the origin of these tabular ice bodies, which can be used as archives of specific climatic conditions and periglacial environments, is intra-sedimentary (migration/intrusion). The objective of this study is to establish geochemical benchmarks describing the ice formation from atmospheric moisture and compare them with geochemical data of tabular ground ice. Shokalsky glacier on Novaya Zemlya (NZ), on the east coast of the Barents Sea, was chosen as a possible moisture source for the formation of tabular ground ice at the key section ‘Shpindler’ on Yugorsky peninsula, on the south coast of the Kara Sea. Tabular ice in the Shpindler section was compared to the Shokalsky glacier ice in both isotope/geochemical and structural aspects. In general, the hydrochemical properties of glacier ice at NZ and ground ice from Shpindler are closely correlated, while stable-isotope, microelemental and microbiological properties are substantially different. It was concluded that glacier ice most likely participated in the formation of tabular ground ice, but only as a source of refrozen meltwater.
Breaching of an ice dam at Qorlortossup tasia, south Greenland
Authors: Mayer Christoph , Schuler Thomas V.
Published: November 2007

In July 2003 an ice-dammed lake was suddenly drained in an outburst flood at Qorlortorssup tasia in south Greenland, the site of a projected hydropower station. The lake developed during the first decades of the 20th century as a result of the recession of the ice cap in this area. It used to drain over a shallow rock spillway towards Sermeq kangigdleq, the adjacent outlet glacier to the north. In order to assess the hazard potential and the additional water contribution from the enlarged catchment, the glacial lake and its surroundings were investigated. Based on the analysis of available historical data, field investigations and model results, the history of lake generation and the sudden outbreak were reconstructed. With the lake formation the ice dam lost its connection to the ice cap. The flood was initiated after the ice surface became low enough for the lake water to overflow the glacier towards Qorlortorssup tasia basin, creating a gully through the glacier which drained approximately 55 × 106 m3 of water over a period of 8-10 days. Thanks to the stability of the dam and the downstream damping of the flood, there was no serious threat to a farm that is situated close to the planned power-station site. In the future, we expect much smaller floods, as a result of partial closure of the gully by ice movement or snowdrift in the winter. The new drainage pattern into Qorlortorssup tasia basin, however, will be a permanent situation. The amount of this new water contribution can only be roughly estimated since the exact size of the drainage basin is not well known.
The role of atmospheric circulation in the growth of sea-ice extent in marginal seas around the Arctic Ocean
Authors: Rikiishi Kunio , Ohtake Hideaki , Katagiri Yurika
Published: November 2007

Satellite data of weekly sea-ice extent and monthly means of objectively analyzed upper-air observation for the years 1978–95 are analyzed in order to investigate the role of atmospheric circulation in the growth of sea-ice extent in five marginal seas around the Arctic Ocean. It has been found that in all the regions the sea ice advances when a cold wind blows from the land (or from the Arctic ice field) to the region, whereas it hardly advances (or it retreats) when a warm wind blows over the region. Whether the wind is favorable or unfavorable for sea-ice growth depends on the position and intensity of the Icelandic low in the Atlantic sector and of the Aleutian low in the Pacific sector. This leads to a negative correlation in ice growth between the western region (Labrador or Okhotsk Sea) and the eastern region (Barents or Bering Sea). Significant correlations are also found across the continents, that is, positive correlations between the Barents Sea and the Sea of Okhotsk, and between the Labrador and Bering Seas. These teleconnections of ice growth can be explained by taking into account an observed negative correlation between the activities of the Icelandic low and Aleutian low.
Mass-balance rates derived by mapping internal tephra layers in Mýrdalsjökull and Vatnajökull ice caps, Iceland
Authors: Brandt Ola , Björnsson Helgi , Gjessing Yngvar
Published: November 2007

Internal tephra layers of known age have been detected by radio-echo soundings within the Mýrdalsjökull and Vatnajökull ice caps in Iceland. Assuming steady state, the estimated strain rates since these isochrones were deposited on the glacier surface have been used to calculate past average specific net balance rates in the accumulation zones along three flowlines on Mýrdalsjökull and one on Vatnajökull. For the period 1918-91 the specific mass-balance rate has been estimated to 4.5 and 3.5 m a-1 at 1350 ma.s.l. on the southern and northern slopes of Mýrdalsjökull, respectively. At 1800 m elevation on the Bardarbunga ice dome in Vatnajökull, the specific net balance averaged over the last three centuries is estimated to be about 2.1 ma–1. Given this specific net balance, a revised age-depth timescale is presented for a 400 m deep ice core recovered in 1972 from Bardarbunga. The ice at the bottom is estimated to be from AD 1750.
Static mass-balance sensitivity of Arctic glaciers and ice caps using a degree-day approach
Authors: Woul Mattias De , Hock Regine
Published: November 2007

Future climate warming is predicted to be more pronounced in the Arctic where approximately two-thirds of all small glaciers on Earth are located. A simple mass-balance model was applied to 42 glaciers and ice caps north of 60° N to estimate mass-balance sensitivities to a hypothetical climate perturbation. The model is based on daily temperature and precipitation data from climate stations in the vicinity of each glacier and ice cap. A regression analysis was made using a degree-day approach where the annual sum of positive daily air temperatures was correlated to measured summer mass balance, and the total annual snow precipitation was correlated to measured winter mass balance. The net mass-balance sensitivity to a hypothetical temperature increase of +1 K ranged from -0.2 to -2.0 m a-1, and an assumed increase in precipitation of +10% changed the mass balance by <+0.1 to +0.4 m a-1, thus on average offsetting the effect of a temperature increase by approximately 20%. Maritime glaciers showed considerably higher mass-balance sensitivities than continental glaciers, in agreement with similar previous studies. The highest sensitivities were found in Iceland, exceeding those reported in previous studies. Extrapolating our results, glaciers and ice caps north of 60° N are estimated to contribute ∼0.6 mm a–1 K–1 to global sea-level rise. Our results highlight the value of long-term mass-balance records and meteorological records in remote areas.
The International Trans-Antarctic Scientific Expedition (ITASE): an overview
Authors: Mayewski Paul Andrew , Frezzotti Massimo , Bertler Nancy , Ommen Tas VAN , Hamilton Gordon , Jacka Tim H. , Welch Brian , Frey Markus , Dahe Qin , Jiawen Ren , Simões Jefferson , Fily Michel , Oerter Hans , Nishio Fumihiko , Isaksson Elisabeth , Mulvaney Robert , Holmund Per , Lipenkov Volodya , Goodwin Ian
Published: November 2007

From its original formulation in 1990 the International Trans-Antarctic Scientific Expedition (ITASE) has had as its primary aim the collection and interpretation of a continent-wide array of environmental parameters assembled through the coordinated efforts of scientists from several nations. ITASE offers the ground-based opportunities of traditional-style traverse travel coupled with the modern technology of GPS, crevasse detecting radar, satellite communications and multidisciplinary research. By operating predominantly in the mode of an oversnow traverse, ITASE offers scientists the opportunity to experience the dynamic range of the Antarctic environment. ITASE also offers an important interactive venue for research similar to that afforded by oceanographic research vessels and large polar field camps, without the cost of the former or the lack of mobility of the latter. More importantly, the combination of disciplines represented by ITASE provides a unique, multidimensional (space and time) view of the ice sheet and its history. ITASE has now collected >20 000km of snow radar, recovered more than 240 firn/ice cores (total length 7000 m), remotely penetrated to ~4000m into the ice sheet, and sampled the atmosphere to heights of >20 km.
Solar forcing recorded by aerosol concentrations in coastal
Authors: Bertler Nancy A.N. , Mayewski Paul A. , Sneed Sharon B. , Naish Tim R. , Morgenstern Uwe , Barrett Peter J.
Published: November 2007

Ice-core chemistry data from Victoria Lower Glacier, Antarctica, suggest, at least for the last 50 years, a direct influence of solar activity variations on the McMurdo Dry Valleys (MDV) climate system via controls on air-mass input from two competing environments: the East Antarctic ice sheet and the Ross Sea. During periods of increased solar activity, when total solar irradiance is relatively high, the MDV climate system appears to be dominated by air masses originating from the Ross Sea, leading to higher aerosol deposition. During reduced solar activity, the Antarctic interior seems to be the dominant air-mass source, leading to lower aerosol concentration in the ice-core record. We propose that the sensitivity of the MDV to variations in solar irradiance is caused by strong albedo differences between the ice-free MDV and the ice sheet.
Sources and transport pathways of marine aerosol species into West Antarctica
Authors: Kaspari S. , Dixon D.A. , Sneed S.B. , Handley M.J.
Published: November 2007

Sixteen high-resolution marine aerosol (Na+, SO42–) records from spatially distributed International Trans-Antarctic Scientific Expedition (ITASE) ice cores spanning the last ~200 years from the Pine Island–Thwaites and Ross drainage systems and the South Pole are used to examine sources (sea spray and frost flowers) and transport pathways of marine aerosols into West Antarctica. Factors contributing to the amount of marine aerosols transported inland include sea-ice extent, the presence of open-water features (polynyas, leads), wind strength and direction, and the strength and positioning of low-pressure systems. Analysis of SO42–/Na+ ratios indicates that frost flowers can contribute significantly (40%) to the Na+ budget of Antarctic ice cores. Higher Na+ concentrations in the Ross drainage system may result from greater production of marine aerosols related to frost flowers in the Ross Sea region in association with greater sea-ice extent and larger open-water areas. Significant positive correlations of sea-ice extent and the Na+ time series exist in some regions of West Antarctica. Higher wind speeds in winter and higher Na+ concentrations when sea-level pressure is lower indicate that intensified atmospheric circulation enhances transport and production of marine aerosols.
A time marker at 17.5 kyr BP detected throughout West Antarctica
Authors: Jacobel Robert W. , Welch Brian C.
Published: November 2007

Deep radar soundings as part of the International Trans-Antarctic Scientific Expedition (US-ITASE) traverses in West Antarctica have revealed a bright internal reflector that we have imaged throughout widespread locations across the ice sheet. The layer is seen in traverses emanating from Byrd Station in four directions and has been traced continuously for distances of 535km toward the Weddell Sea drainage, 500km toward South Pole, 150km toward the Executive Committee Range and 160km toward Kamb Ice Stream (former Ice Stream C). The approximate area encompassed by the layer identified in these studies is 250 000km2. If the layer identification can also be extended to Siple Dome where we have additional radar soundings (Jacobel and others, 2000), the approximate area covered would increase by 50%. In many locations echo strength from the layer rivals the bed echo in amplitude even though it generally lies at a depth greater than half the ice thickness. At Byrd Station, where the layer depth is 1260 m, an age of ~17.5 kyr BP has been assigned based on the Blunier and Brook (2001) chronology. Hammer and others (1997) note that the acidity at this depth is >20 times the amplitude of any other part of the core. The depiction of this strong and widespread dated isochrone provides a unique time marker for much of the ice in West Antarctica. We apply a layer-tracing technique to infer the depth–time scale at the inland West Antarctic ice sheet divide and use this in a simple model to estimate the average accumulation rate.
Spatial distribution of biogenic sulphur compounds (MSA, nssSO42–) in the northern Victoria Land–Dome C–Wilkes Land area, East Antarctica
Authors: Becagli Silvia , Proposito Marco , Benassai Silvia , Gragnani Roberto , Magand Olivier , Traversi Rita , Udisti Roberto
Published: November 2007

During the 1992–2002 Antarctic expeditions, in the framework of the International Trans-Antarctic Expedition (ITASE) project, about 600 sites were sampled (superficial snow, snow pits and firn cores) along traverses in the northern Victoria Land–Dome C–Wilkes Land region. The sites were characterized by different geographical (distance from the sea, altitude) and climatological (annual mean accumulation rate, temperature) conditions and were affected by air masses from different marine sectors (Ross Sea, Pacific Ocean). Mean anion and cation contents were calculated at each site, in order to evaluate the spatial distribution of chemical impurities in snow. Here we discuss the distribution of non-sea-salt sulphate (nssSO42–) and of methanesulphonic acid (MSA) mainly originating from atmospheric oxidation of biogenic dimethyl sulphide; these compounds play a key role in climate control processes by acting as cloud condensation nuclei. The spatial distribution of nssSO42– and MSA is discussed as a function of distance from the sea, altitude and accumulation rate. Depositional fluxes of nssSO42– and MSA decrease as a function of distance from the sea, with a higher gradient in the first 200km step. There is an analogous trend with the site altitude, and the first 1600m step is relevant in determining the nssSO42– and MSA content in snow. The nssSO42–/MSA ratio depends on the distance from the sea and the biogenic source strength. At coastal sites, where biogenic inputs are dominant, this ratio is ~2. As biogenic input decreases (low MSA content) inland, the ratio increases, indicating the presence of alternative sources of nssSO42– (crustal, volcanic background) or advection of low-latitude air masses. By plotting total flux as a function of accumulation rate, dry depositional contributions were evaluated for nssSO42– and MSA in the Ross Sea and Pacific Ocean sectors. Non-sea-salt sulphate wet deposition prevails at sites where the accumulation rate (expressed as water equivalent) is higher than 70 kgm–2 a–1 (Ross Sea sector) or 370 kgm–2 a–1 (Pacific Ocean sector). MSA threshold values in these sectors are respectively 90 and 220 kgm–2 a–1.
A new velocity map for Byrd Glacier, East Antarctica, from sequential ASTER satellite imagery
Authors: Stearns Leigh , Hamilton Gordon
Published: November 2007

New ice-velocity measurements are obtained for the main trunk of Byrd Glacier, East Antarctica, using recently acquired Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery. The velocities are derived from the application of a cross-correlation technique to sequential images acquired in 2000 and 2001. Images were co-registered and ortho-rectified with the aid of a digital elevation model (DEM) generated from ASTER stereo imagery. This paper outlines the process of DEM generation, image co-registration and correction, and the application of the cross-correlation technique to obtain ice velocities. Comparison of the new velocity map with earlier measurements of velocity from 1978 indicates that the glacier has undergone a substantial deceleration between observations. Portions of the glacier flowing at speeds of ~850ma–1 in 1978/79 were flowing at ~650ma–1 in 2000/01. The cause of this change in ice dynamics is not known, but the observation shows that East Antarctic outlet glaciers can undergo substantial changes on relatively short timescales.
The use of salt injection and conductivity monitoring to infer near-margin hydrological conditions on Vestari-Hagafellsjökull, Iceland
Authors: Eyre Natalie S. , Payne Antony J. , Baldwin Duncan J. , Björnsson Helgi
Published: November 2007

Vestari-Hagafellsjökull is a surge-type outlet glacier from the Langjökull ice cap, Iceland. Intensive hydrological investigations were carried out during non-surge conditions in the summers of 1999 and 2000, and 14 boreholes were drilled using pressurized hot water over an area 800 m from the margin and approximately 5000 m2 in size, where ice thickness ranged from 60 to 70 m. Initial investigations showed that a large fraction of the boreholes drilled to the bed did not drain and were assumed not to connect to the subglacial drainage system. Subsequently, we investigated the hypothesis that boreholes which remain full may do so as a consequence of a balance between englacial inflow and basal drainage rather than the standard assumption that such boreholes are simply unconnected. In testing this hypothesis, we developed a new technique for measuring water motion within the borehole by monitoring the passage of a saline solution down the borehole’s water column. The technique allows rates of motion to be established, as well as allowing the quantification of net addition and loss of water from the borehole. Observations based on the motion of saline plumes within the boreholes lead us to the conclusion that some boreholes do indeed remain full as a consequence of a balance between englacial inflow and subglacial drainage. The abrupt dilution that occurs at the top of these boreholes suggests inflow from a near-surface englacial water source, while the descent of the saline plumes implies that water is being lost at the base to the subglacial system. The system appears to be driven by excess water head in the boreholes over flotation and implies that the borehole/bedrock interface can be ‘leaky’.
Hydrometeorological relationships on Haig Glacier, Alberta, Canada
Authors: Shea J.M. , Anslow F.S. , Marshall S.J.
Published: November 2007

We investigate the relationships between meteorological, hydrological and glaciological data collected at Haig Glacier, Alberta, Canada, for the 2002 and 2003 ablation seasons. Correlation, lag cross-correlation and multivariate regression analyses are employed to assess the seasonal evolution of relationships between temperature, temperature residuals, total daily radiation, albedo, accumulation-area ratio (AAR) and total daily discharge (Qi). Early-season melt is temperature-dependent, when AAR remains high and the hydraulic properties of the snowpack limit both diurnal discharge variability and a rapid hydrologic response. As the melt season progresses, a decreasing AAR and ripening of the snowpack induce a glacier-wide decrease in albedo, and a structured radiation–discharge response is observed. Radiation-detrended temperature values offer modest improvements over physical temperature values in multivariate regression models estimating daily discharge values. Using a detrended-temperature indexed melt model, we assess the transport efficiency of the glacial hydrologic system through a comparison of total modelled daily melt and observed discharge. Transport efficiency values support the notion of a purge effect during freezing events and at the end of the ablation season, and suggest that it is the evolution of the supraglacial drainage system that controls diurnal discharge variability.
Access of surface meltwater to beds of sub-freezing glaciers: preliminary insights
Authors: Alley Richard B. , Dupont Todd K. , Parizek Byron R. , Anandakrishnan Sridhar
Published: November 2007

Sufficiently deep water-filled fractures can penetrate even cold ice-sheet ice, but glaciogenic stresses are typically smaller than needed to propagate water-filled fractures that are less than a few tens of meters deep, as shown by our simplified analytical treatment based on analogous models of magmatic processes. However, water-filled fractures are inferred to reach the bed of Greenland through >1 km of ice and then collapse to form moulins, which are observed. Supraglacial lakes appear especially important among possible crack ‘nucleation’ mechanisms, because lakes can warm ice, supply water, and increase the pressure driving water flow and ice cracking.
Temporal isotope changes in wet snow layers in association with mass exchange between snow particles and liquid water in between the particles
Authors: Hashimoto S. , Zhou S. , Nakawo M. , Shimizu M. , Ishikawa N.
Published: November 2007

We carried out snow-pit observations at Nagaoka, Niigata prefecture, Japan, where the snow layers were at the melting point. It was observed that the water content in the snowpack was nearly constant at approximately 10%, and the coarsening rate of snow particles was about 0.4×10–3mm3 h–1, which was in the range between the rate for dry snow and that for snow soaked in water. The isotope change of snow particles by melting and freezing in a closed system under isothermal conditions at 0˚C was modeled. The temporal change in isotope concentration was calculated for wet snow layers, based on the fractionation between snow particles and liquid water in between the particles, in association with the coarsening of snow particles. The results compared well with field observations. These results suggest that the isotope concentration of the pore water that flows downward from the surface contributed significantly to the isotope change of snow particles.
A temperature-index model of stream flow at below-freezing temperatures in Taylor Valley, Antarctica
Authors: Ebnet Amy F. , Fountain Andrew G. , Nylen Thomas H. , Mcknight Diane M. , Jaros Christopher L.
Published: November 2007

We model runoff from glaciers in the McMurdo Dry Valleys, Antarctica, with summer (December–January) average air temperatures from 1990 to 2002 for the purpose of estimating decades- to millennial-scale glacial runoff into Lakes Fryxell, Hoare and Bonney. The relationship between summer temperatures and melt is found to be exponential near the melting temperature. We propose a variety of simple models that are calibrated using measured discharge from a number of streams draining from ten glaciers in Taylor Valley. The surface melting rate is constrained by mass-balance measurements from four of the glaciers. A model based solely on temperature produced good results (coefficient of determination, r2 = 0.71) for the south-facing glaciers, but poor results for the north-facing glaciers (r2 < 0). The inclusion of a solar radiation index increased the modeled melt from the north-facing glaciers and thus improved the results (r2 = 0.73) for the north-facing glaciers, with little change from the south-facing glaciers. Including a wind index did not improve the correlation between modeled and measured runoff.
Changes in geometry and subglacial drainage derived from digital elevation models: Unteraargletscher, Switzerland, 1927–97
Authors: Fischer Urs H. , Braun André , Bauder Andreas , Flowers Gwenn E.
Published: November 2007

Digital elevation models of the bed and surface of Unteraargletscher, Switzerland, are used to reconstruct the theoretical pattern of basal water drainage for the years 1927, 1947, 1961 and 1997, during which period the glacier was thinning and receding. The theoretical drainage pattern for 1997 compares well, in a broad sense, with the locations of active moulins and the hydraulic connection status of boreholes drilled to the glacier bed. Changes in the basal water-flow pattern over the period 1927–97 that are revealed by the theoretical reconstructions of the subglacial drainage system structure are likely to have resulted from changes in glacier geometry. Concurrent with the retreat and thinning of the glacier, the height of medial moraines increased, probably due to the insulating effect of the debris cover reducing the melt of the underlying ice. This increase of moraine heights has led to the formation of hydraulic barriers at the glacier bed such that water flow has become channelized beneath the ice along drainage axes that parallel the course of the medial moraines on the glacier surface.
Englacial phase changes and intergranular flow above subglacial lakes
Authors: Rempel Alan
Published: November 2007

Glaciers are permeated by liquid veins that line the triple junctions between ice grains and act as conduits for material transport. The density difference between water and ice produces a hydraulic gradient that drives liquid flow down towards the glacier bed. We investigate how variations in this transport rate are manifest in the lower regions of a glacier that floats on a subglacial reservoir. When the temperature rises towards the glacier bed, the associated permeability increase leads to more rapid fluid transport; internal melting supplies the changing flow. A reduction in hydraulic gradient results from surface energy effects, and causes a decreasing transport rate near the base; hence, freezing occurs within the polycrystalline ice. For representative values of the heat flux, soluble impurity loading and grain-size, the downward flux peaks at approximately 1–100mma–1 several tens of centimeters above the glacier bed. Beneath this level, the effects of surface energy control the fluid transport and cause the flow to reverse directions, pulling liquid upwards into the polycrystalline ice so that the flow does not introduce glacial material into the underlying reservoir.
Evolution of subglacial water pressure along a glacier’s length
Authors: Harper Joel T. , Humphrey Neil F. , Pfeffer W. Tad , Fudge Tyler , O’Neel Shad
Published: November 2007

Observations from along the length of Bench Glacier, Alaska, USA, show that the subglacial water-pressure field undergoes a multiphase transition from a winter mode to a summer mode. Data were collected at the glacier surface, the outlet stream, and in a network of 47 boreholes spanning the length of the 7 km long glacier. The winter pressure field was near overburden, with low-magnitude (centimeter to meter scale) and long-period (days to weeks) variations. During a spring speed-up event, boreholes showed synchronous variations and a slight pressure drop from prior winter values. Diurnal pressure variations followed the speed-up, with their onset associated with a glacier-wide pressure drop and flood at the terminus stream. Diurnal variations with swings of up to 80% of overburden pressure were typical of mid-summer. Several characteristics of our observations contradict common conceptions about the seasonal development of the subglacial drainage system and the linkages between subglacial hydrology and basal sliding: (1) increased water pressure did not accompany high sliding rates; (2) the drainage system showed activity characteristic of the spring season long before abundant water was available on the glacier surface; (3) the onset of both spring activity and diurnal variations of the drainage system did not show a spatial progression along the length of the glacier.
Detailed spatially distributed geothermal heat-flow data for modeling of basal temperatures and meltwater production beneath the Fennoscandian ice sheet
Authors: Näslund Jens-Ove , Jansson Peter , Fastook James L. , Johnson Jesse , Andersson Leif
Published: November 2007

Accurate modeling of ice sheets requires proper information on boundary conditions, including the geothermal heat flow (or heat-flow density (HFD)). Traditionally, one uniform HFD value is adopted for the entire modeled domain. We have calculated a distributed, high-resolution HFD dataset for an approximate core area (Sweden and Finland) of the Scandinavian ice sheet, and imbedded this within lower-resolution data published for surrounding regions. Within the Last Glacial Maximum ice margin, HFD varies with a factor of as much as 2.8 (HFD values ranging between 30 and 83 mWm–2), with an average of 49 mWm–2. This average value is 17% higher than 42 mWm–2, a common uniform value used in ice-sheet modeling studies of Fennoscandia. Using this new distributed dataset on HFD, instead of a traditional uniform value of 42 mWm–2, yields a 1.4 times larger total basal meltwater production for the last glacial cycle. Furthermore, using the new dataset in high-resolution modeling results in increased spatial thermal gradients at the bed. This enhances and introduces new local and regional effects on basal ice temperatures and melt rates. We observed significant strengthening of local ‘ice streaming’, which in one case correlates to an ice-flow event previously interpreted from geomorphology. Regional to local variations in geothermal heat flow need to be considered for proper identification and treatment of thermal and hydraulic bed conditions, most likely also when studying Laurentide, Greenland and Antarctic ice sheets.
Groundwater seeps in Taylor Valley Antarctica: an example of a subsurface melt event
Authors: Lyons W. Berry , Welch Kathleen A. , Carey Anne E. , Doran Peter T. , Wall Diana H. , Virginia Ross A. , Fountain Andrew G. , Csathó Bea M. , Tremper Catherine M.
Published: November 2007

The 2001/02 austral summer was the warmest summer on record in Taylor Valley, Antarctica, (∼78° S) since continuous records of temperature began in 1985. The highest stream-flows ever recorded in the Onyx River, Wright Valley, were also recorded that year (the record goes back to the 1969/70 austral summer). In early January 2002, a groundwater seep was observed flowing in the southwest portion of Taylor Valley. This flow has been named ‘Wormherder Creek’ (WHC) and represents an unusual event, probably occurring on a decadal time-scale. The physical characteristics of this feature suggest that it may have flowed at other times in the past. Other groundwater seeps, emanating from the north-facing slope of Taylor Valley, were also observed. Little work has been done previously on these very ephemeral seeps, and the source of water is unknown. These features, resembling recently described features on Mars, represent the melting of subsurface ice. The Martian features have been interpreted as groundwater seeps. In this paper we compare the chemistry of the WHC groundwater seep to that of the surrounding streams that flow every austral summer. The total dissolved solids content of WHC was ∼6 times greater than that of some nearby streams. The Na : Cl and SO4 : Cl ratios of the seep waters are higher than those of the streams, but the Mg : Cl and HCO3 : Cl ratios are lower, indicating different sources of solutes to the seeps compared to the streams. The enrichment of Na and SO4 relative to Cl may suggest significant dissolution of mirabilite within the previously unwetted soil. The proposed occurrence of abundant mirabilite in higher-elevation soils of the dry valley region agrees with geochemical models developed, but not tested, in the late 1970s. The geochemical data demonstrate that these seeps could be important in ‘rinsing’ the soils by dissolving and redistributing the long-term accumulation of salts, and perhaps improving habitat suitability for soil biota. The H4SiO4 concentration is 2–3 times greater in WHC than in the surrounding streams, indicating a large silicate-weathering component in the seep waters.
Numerical modeling investigations of the subglacial conditions of the southern Laurentide ice sheet
Authors: Bauder Andreas , Mickelson David M. , Marshall Shawn J.
Published: November 2007

Sub- and proglacial bed conditions influence advance and retreat of an ice sheet. The existence and distribution of frozen ground is of major importance for better understanding of ice-flow dynamics and landform formation. The southern margin of the Laurentide ice sheet (LIS) was dominated by the presence of relatively thin ice lobes that seem to have been very sensitive to external and internal physical conditions. Their extent and dynamics were highly influenced by the interaction of subglacial and proglacial conditions. A three-dimensional thermomechanical ice-sheet model was coupled with a model for the thermal regime in the upper Earth crust. The model has been applied to the LIS in order to investigate the spatial distribution of thermal conditions at the bed. The evolution of the whole LIS was modeled for the last glacial cycle, with primary attention on correct reconstruction of the southern margin. Our results show extensive temporal and spatial frozen ground conditions. Only a slow degradation of permafrost under the ice was found. We conclude that there are significant interactions between the ice sheet and the underlying frozen ground and that these influence both ice dynamics and landform development.
Reconstruction of past temperatures for Arctic glaciers subjected to intense subsurface melting
Authors: Nagornov Oleg V. , Konovalov Yuri V. , Tchijov Vladimir
Published: November 2007

Many glaciers are subject to melting due to high summer air temperatures. Here, the presence of meltwater in the subsurface layers of the glacier bulk, and its subsequent percolation and refreezing are implemented in the calibration of a paleothermometer. Accounting for the melt feature index and the measured oxygen-isotope ratio allows for calibration of the paleothermometer and comparison of different climatic proxies. The results of reconstructions agree with previous reconstructions at the depth of attenuation of the seasonal climate signals, which supports the validity of the paleothermometer calibration. The sensitivity of the reconstruction to variations of the model parameters was also studied. It was found that most likely snow–firn sequence and temperature fields were subjected to significant change due to current warming. Temperature changes in the snow–firn thickness of Akademii Nauk (Severnaya Zemlya, Russian High Arctic) and Austfonna (Svalbard) ice caps exceed by ∼6˚C the average Arctic temperature anomalies for the last 150 years. The reconstruction of the past surface temperatures and the parameters of the subsurface heat source due to refreezing of meltwater lead to the conclusion that meltwater spreads inside two to four annual layers for Akademii Nauk and Austfonna ice caps, respectively.
Basal and thermal control mechanisms of the Ragnhild glaciers, East Antarctica
Authors: Pattyn Frank , De Brabander Sang , Huyghe Ann
Published: November 2007

The Ragnhild glaciers are three enhanced-flow features situated between the Sør Rondane and Yamato Mountains in eastern Dronning Maud Land, Antarctica. We investigate the glaciological mechanisms controlling their existence and behavior, using a three-dimensional numerical thermomechanical ice-sheet model including higher-order stress gradients. This model is further extended with a steady-state model of subglacial water flow, based on the hydraulic potential gradient. Both static and dynamic simulations are capable of reproducing the enhanced ice-flow features. Although basal topography is responsible for the existence of the flow pattern, thermomechanical effects and basal sliding seem to locally soften and lubricate the ice in the main trunks. Lateral drag is a contributing factor in balancing the driving stress, as shear margins can be traced over a distance of hundreds of kilometers along west Ragnhild glacier. Different basal sliding scenarios show that central Ragnhild glacier stagnates as west Ragnhild glacier accelerates and progressively drains the whole catchment area by ice and water piracy.