A novel flow-through microparticle detector was deployed concurrently with continuous flow analyses of major ions during the North Greenland Icecore Project 2000 field season. the easy-handling detector performs continuous counting and sizing. In this deployment the lower size-detection limit was conservatively set to 1.0 μm equivalent spherical particle diameter, and a depth resolution of ≤1cm was achieved for microparticle concentrations. the dust concentration usually followed the Ca2+ variability. Here results are presented from an inspection of the Ca/dust mass ratio in 23 selected intervals, 1.65 m long each, covering different climatic periods including Holocene and Last Glacial Maximum (LGM). A (Ca2+)/(insoluble dust) mass ratio of 0.29 was found for the Holocene and 0.11 for LGM. Changes to the Ca/dust ratio occur on an annual to multi-annual time-scale exhibiting the same pattern, i.e. a lower Ca/dust ratio for higher crustal concentrations. Moreover, the Ca2+/dust ratio may increase significantly during episodic events such as volcanic horizons due to enhanced dissolution of CaCO3. This calls into question the notion of deploying Ca2+ as a quantitative mineral dust reference species and shows the importance of variable source properties or fractionating processes during transport and deposition.

We explore a mathematical model that couples together a thermomechanically evolving subglacial channel, distributed cavity drainage, and basal sliding along a subglacial flood path fed by a jökulhlaup lake. It allows water transfer between channel and cavities and a migrating subglacial water divide or ‘seal’ to form between floods. Notably, it accounts for full coupling between the lake and subglacial drainage in terms of both discharge and pressure, unlike models that neglect the pressure coupling by imposing a known history of lake discharge at the channel inlet. This means that flood hydrographic evolution and its impact on glacier motion are consistently determined by our model. Numerical simulations for a model alpine lake yield stable limit cycles simulating repeating jökulhlaups, with the channel drawing water from the cavities at a varying rate that modulates basal sliding during each flood. A wave of fast sliding propagates down-glacier at flood initiation, followed by deceleration as the growing channel sucks water from the cavities. These behaviours cannot be correctly simulated without the full coupling. We show that the flood’s peak discharge, its initiation threshold and the magnitude of the ‘fast sliding’ wave decrease with the background water supply to the cavities.

Most glaciers in the Northern Hemisphere reached their postglacial maximum in recent times, that is, after the medieval period. During the last 100 or 150 years a significant retreat has taken place, and there is little sign that this is coming to an end. The current worldwide shrinkage of glaciers is considered to be a strong indication of global warming. However, glacier retreat should be judged against the natural variability of glacier systems. Numerical glacier models can be used to quantify this variability. I have studied the natural variability of three glaciers for which long historic records of glacier length exist: Nigardsbreen, Norway; Rhonegletscher, Switzerland; and Franz Josef Glacier, New Zealand. Integrations for a 10 000 year period, driven by random forcing of a realistic strength, show that the current retreat cannot be explained from natural variability in glacier length and must be due to external forcing.

Supraglacial lakes are known to trigger Antarctic ice-shelf instability and break-up. However, to date, no study has focused on lakes on Greenland's floating termini. Here, we apply lake boundary/area and depth algorithms to Landsat 8 imagery to analyse the inter- and intraseasonal evolution of supraglacial lakes across Petermann Glacier's (81°N) floating tongue from 2014 to 2016, while also comparing these lakes to those on the grounded ice. Lakes start to fill in June and quickly peak in total number, volume and area in late June/early July in response to increases in air temperatures. However, through July and August, total lake number, volume and area all decline, despite sustained high temperatures. These observations may be explained by the transportation of meltwater into the ocean by a river, and by lake drainage events on the floating tongue. Further, as mean lake depth remains relatively constant during this time, we suggest that a large proportion of the lakes that drain, do so completely, likely by rapid hydrofracture. The mean areas of lakes on the tongue are only ~20% of those on the grounded ice and exhibit lower variability in maximum and mean depth, differences likely attributable to the contrasting formation processes of lakes in each environment.

Sea-ice drift fields were obtained from sequences of synthetic aperture radar (SAR) images using a method based on pattern recognition. the accuracy of the method was estimated for two image products of the Envisat Advanced SAR (ASAR) with 25 m and 150 m pixel size. For data from the winter season it was found that 99% of the south–north and west–east components of the determined displacement vector are within ±3–5 pixels of a manually derived reference dataset, independent of the image resolution. For an image pair with 25 m resolution acquired during summer, the corresponding value is 12 pixels. Using the same resolution cell dimensions for the displacement fields in both image types, the estimated displacement components differed by 150–300 m. the use of different texture parameters for predicting the performance of the algorithm dependent on ice conditions and image characteristics was studied. It was found that high entropy values indicate a good performance.

Glacier inventories provide the baseline data to perform climate-change impact assessment on a regional scale in a consistent and spatially representative manner. In particular, a more accurate calculation of the current and future contribution to global sea-level rise from heavily glacierized regions such as Alaska is much needed. We present a new glacier inventory for a large part of western Alaska (including Kenai Peninsula and the Tordrillo, Chigmit and Chugach mountains), derived from nine Landsat Thematic Mapper scenes acquired between 2005 and 2009 using well-established automated glacier-mapping techniques (band ratio). Because many glaciers are covered by optically thick debris or volcanic ash and partly calve intowater, outlineswere manually edited in these wrongly classified regions during post-processing. In total we mapped ~8830 glaciers (>0.02 km2) with a total area of ~16 250 km2. Large parts of the area (47%) are covered by a few (31) large (>100 km2) glaciers, while glaciers less than 1 km2 constitute only 7.5% of the total area but 86% of the total number. We found a strong dependence of mean glacier elevation on distance from the ocean and only a weak one on aspect. Glacier area changes were calculated for a subset of 347 selected glaciers by comparison with the Digital Line Graph outlines from the US Geological Survey. The overall shrinkage was ~23% between 1948–57 and 2005–09.

Quaternary deposits in six sediment cores from the Scotia Sea, Antarctica, were examined for the presence of volcanic ash layers. The cores were recovered from water depths of 3369-4025 m. Altogether, 23 ash layers were found, 18 of which have been investigated by electron-probe microanalysis. Deception Island is identified as the source of all the ash layers analyzed. The upper ash layer in each core can be correlated across all six cores, over a distance of -100 km, on the basis of its unusual bimodal composition, major oxide geochemistry and stratigraphie position. Two other ash layers can also be correlated between several of the cores.

The subglacial drainage in a pronounced overdeepening of Grosser Aletschgletscher, Switzerland was investigated by borehole water-level observations and dye-tracer injections. In August 1990 and 1991, tracer was injected at the bottom of a borehole (depth 904 m and 710 m, respectively), and simultaneously in a nearby moulin. The moulin and borehole injections identified two different flow systems coexisting within the overdeepening. The moulin injection yielded short-lived, highly peaked break-through curves with high velocities, indicating a hydraulically efficient channelized system. The borehole-tracer return occurred in broad multiple peaks characterized by a striking diurnal periodicity and, in general, correlated inversely with discharge. Water level in the borehole experienced high diurnal variations in phase with discharge at the snout indicating “closed channel flow” over large parts of the glacier. We infer that the boreholes drained subglacially and were connected to a drainage system with significant long-term storage capacity. Release of labelled water was triggered by daily water-pressure cycles.

This paper considers the state of the deep ice borehole 5G at the Russian Antarctic Vostok station after penetration to the surface water of Vostok Subglacial Lake. It discusses the peculiar features of drilling the ‘fresh frozen’ lake water that has risen in the borehole and the technology for subsequent study of the lake water layer via borehole 5G filled with a kerosene–Freon® mixture. The extremely high rise of lake water via the borehole is attributed to a hydraulic fracture at the side of the borehole, which diverted a large amount of drilling fluid. The proposed technology for the study of the water layer envisages minimal environmental impact and excludes penetration of any of the kerosene–Freon® mixture to the water layer. This technology has been presented several times at different international forums. There was no critical comment on the Environmental Impact Assessment of the technology at the 37th Antarctic Treaty Consultative Meeting in 2014 and it was adopted for implementation.

Since the austral summer of 1994-95 the Alfred Wegener Institute has carried out airborne radio-echo sounding (RES) measurements in Antarctica with its newly designed RES system. Since 1995-96 an ongoing pre-site survey for an ice-coring drill site in Dronning Maud Land has been carried out as part of the European Project for Ice Goring in Antarctica. The survey covers an area of 948 000 km2, with >49 500 km of airborne RES obtained from >200 hours of flight operation flown during the period 1994-97. In this paper, first results of the airborne RES survey are graphically summarized as newly derived maps of the ice thickness and subglacial topography, as well as a three-dimensional view of surface and subglacial bed and outcrop topography, revealing a total ice volume of 1.48 x 106 km3.

Bolivian glaciers are an essential source of fresh water for the Altiplano, and any changes they may undergo in the near future due to ongoing climate change are of particular concern. Glaciar Zongo, Bolivia, located near the administrative capital La Paz, has been extensively monitored by the GLACIOCLIM observatory in the last two decades. Here we model the glacier dynamics using the 3-D full-Stokes model Elmer/Ice. The model was calibrated and validated over a recent period (1997–2010) using four independent datasets: available observations of surface velocities and surface mass balance were used for calibration, and changes in surface elevation and retreat of the glacier front were used for validation. Over the validation period, model outputs are in good agreement with observations (differences less than a small percentage). The future surface mass balance is assumed to depend on the equilibrium-line altitude (ELA) and temperature changes through the sensitivity of ELA to temperature. The model was then forced for the 21st century using temperature changes projected by nine Coupled Model Intercomparison Project phase 5 (CMIP5) models. Here we give results for three different representative concentration pathways (RCPs). The intermediate scenario RCP6.0 led to 69 ± 7% volume loss by 2100, while the two extreme scenarios, RCP2.6 and RCP8.5, led to 40 ± 7% and 89 ± 4% loss of volume, respectively.

A physically based finite-element heat-transfer model with phase change is used to simulate ice growth and thickness variability on shallow, thaw lakes on the North Slope of Alaska during the period 1947–97. The basic inputs to the model are air temperature and snow depth as recorded at the U.S. National Weather Service station, Barrow, Alaska. The simulated long-term mean maximum ice thickness was 1.91 ±0.21 m with a range from 1.33 m (1962) to 2.47 m (1976). Variations in the seasonal snow cover played a much greater role than air temperatures in controlling ice-thickness variability during the 50 year simulation period. The sensitivity of lake-ice growth to extremes of snow depth, air temperature and snow bulk thermal conductivity is investigated. This study shows that lake-ice thickness has varied significantly from year to year in northern Alaska. Continued variability combined with potential climate change could affect the area of ice that freezes completely to the bottom of lakes each winter, resulting in changes in water storage and availability, permafrost thermal regime and talik dynamics beneath lakes, and methane efflux and energy fluxes to the atmosphere. It is concluded that quantification and a full understanding of these potential effects will require systematic and continuous field measurements that will provide better forcing and validation fields for improved models.

Avalanche hazard is a threat to many residential areas in Iceland. In 1995 two avalanche accidents, causing a total of 34 fatalities in areas thought to be safe, prompted research on avalanche hazard assessment. A new method was developed, and in 2000 a new regulation on avalanche hazard zoning was issued. The method and regulation are based on individual risk, or annual probability of death due to avalanches. The major components of the method are the estimation of avalanche frequency, run-out distribution and vulnerability. The frequency is estimated locally for each path under consideration, but the run-out distribution is based on data from many locations, employing the concept of transferring avalanches between slopes. Finally the vulnerability is estimated using data from the 1995 avalanches. Under the new regulation, new hazard maps have been prepared for six of the most vulnerable villages in Iceland. Hazard zones are delineated using risk levels of 0.2×10–4, 0.7×10–4 and 2×10–4 a–1, with risk less than 0.2×10–4 a–1 considered acceptable. When explaining the new zoning to the public, a measure of annual individual risk that allows comparison with other risks in society has proven advantageous.

Level-line surveys at a number of sites on the Antarctic Peninsula since the early 1970s have shown a lowering of the ice surface elevation in areas where the climate is warm enough for melting to occur during summer. Results are presented here from annual surveys on the ice ramp at Rothcra Point. Over an 8 year period, a large proportion of the ramp shows a generally steady reduction in surface elevation. The uppermost part of the ramp shows no clear trend. The ice ramp has suffered a mean rate ofsurfaee lowering of 0.32 ma−1 w.e. over the period of the surveys, which is similar to that seen at other sites on the Antarctic Peninsula. Measured ice velocities on the ramp are low, so the surface lowering can be attributed directly to changes in surface mass balance. The Surveys coincide with a period of long-term increase in temperature and ablation seen in meteorological records. Comparison of the observed surface lowering with temperature data shows a good agreement, and we conclude that increasing air temperatures in the region will raise ablation and increase the recession rate of the ice ramp.

The role of synoptic-scale cyclones in the trends and variability of Arctic sea ice conditions has remained uncertain. In recognition, we conduct a systematic investigation of how sea-ice concentration (SIC) changes with cyclone passage, including all individual storms that pass over any part of the region's ice pack. For all seasons, especially summer and autumn, we find a pattern of higher ice concentration after a region is influenced by a cyclone compared to when it is not, primarily due to thermodynamic effects. During warm months, cyclones appear to slow the general day-to-day decline in concentration; in cold months, cyclones augment the day-to-day increase. These relationships are changing over time, with cyclone-associated concentration changes becoming less distinct from overall changes. Cyclone effects on ice divergence are spatially variable; computed fields are noisy. In summer, these dynamic effects of cyclone passage generally decrease SIC, but are outweighed by the thermodynamic effects (e.g., reductions in air temperature, shortwave radiation). In autumn, cyclone-associated concentration changes are not as easily explained by observed cyclone conditions. Key questions remain regarding the extent to which our findings are influenced by artifacts of surface melt and weather effects on the passive microwave retrievals.

Surface roughness enhances the net ablation rate associated with direct solar radiation relative to smooth surfaces, because roughness allows solar energy reflected from one part of the surface to be absorbed by another part. In this study we examine the feedback between solar-radiation-driven ablation and growth of surface roughness on the Greenland ice sheet, using a numerical model of radiative transfer. Our experiments extend previous work by examining: (1) the effects of diurnal and seasonal variation of solar zenith angle and azimuth relative to incipient roughness features, (2) the evolution of roughness geometry in response to radiatively driven ablation and (3) the relative solar energy collection efficiencies of various roughness geometries and geographic locations and orientations. A notable result of this examination is that the time evolution of the aspect ratio of surface features under solar-driven ablation collapses onto a roughly universal curve that depends only on latitude, not the detailed shape of the feature. The total enhancement of surface melt relative to a smooth surface over a full ablation season varies with this ratio, and this dependence suggests a way to parameterize roughness effects in large-scale models that cannot treat individual roughness features. Overall, our model results suggest that surface roughness at the latitudes spanned by the Greenland ice sheet tends to dissipate as the ablation season progresses.

We have studied the accuracy of ice thickness (hi) retrieval based on night-time MODIS (Moderate Resolution Imaging Spectroradiometer) ice surface temperature (Ts) images and HIRLAM (High Resolution Limited Area Model) weather forcing data from the Arctic. The study area is the Kara Sea and eastern part of the Barents Sea, and the study period spans November-April 2008–11 with 199 hi charts. For cloud masking of the MODIS data we had to use manual methods in order to improve detection of thin clouds and ice fog. The accuracy analysis of the retrieved hi was conducted with different methods, taking into account the inaccuracy of the HIRLAM weather forcing data. Maximum reliable hi under different air-temperature and wind-speed ranges was 35–50 cm under typical weather conditions (air temperature <–20cC, wind speed <5ms–1) present in the MODIS data. The accuracy is best for the 15–30 cm thickness range, ∼38%. The largest hi uncertainty comes from air temperature data. Our ice-thickness limits are more conservative than those in previous studies where numerical weather prediction model data were not used in the hi retrieval. Our study gives new detailed insight into the capability of Ts-based hi retrieval in the Arctic marginal seas during freeze-up and wintertime, and should also benefit work where MODIS hi charts are used.

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.

Lakes are a major feature of Arctic and Antarctic landscapes and are likely to be sensitive indicators ofclimate change. New bio-optical technologies for in situ measurements (e.g. UV-profiling) and remote sensing (e.g. light detection and ranging) now offer a suite of options for long-term monitoring at these sites. Certain properties of high-latitude lakes are highly responsive to changes in climate forcing and could be targeted within a monitoring strategy based on optical properties; these include lake levels, lake-ice dynamics, phytoplankton biomass and chromophoric dissolved organic matter (CDOM). High-latitude lakes are optically sensitive to changes in CDOM export from their surrounding catchments that could result from climate effects on hydrology and vegetation. Using a new model based on biologically weighted transparency, we show that a 20% change in GDOM concentration (as measured by dissolved organic carbon) can have a much greater effect on UV inhibition of phytoplankton than a similar percentage change in stratospheric ozone. Much of this effect is due to UV-A, because the reduced photodamaging effect per unit energy (i.e. low biological weighting) in this waveband is offset by its higher incident flux at the lake surface relative to UV-B and its deeper penetration into the water column. These transparency calculations also show that small changes in CDOM in polar lakes will have a large effect on underwater light availability for photosynthesis. The spectral absorption and fluorescence properties of CDOM lend themselves to a variety of optical monitoring approaches. Future research on the paleo-optics of GDOM will allow the interpretation of current optical trends in high-latitude lakes relative to the scales of natural variability in the past.

The spatial variability in snow accumulation varies between different regions in Dronning Maud Land, East Antarctica. This pattern cannot easily be explained by the single action of parameters such as distance to open sea, surface elevation or slope. In 1996-97 we mapped snow-layer depths within the top 11 m of the snowpack with a ground-based radar along a 500 km traverse on the polar plateau in central Dronning Maud Land. The results showed that the general accumulation pattern could be described by three major characteristic sections: a pronounced trend of decreasing net accumulation with increasing altitude from 2400 to 2840 m a.s.l.; relatively high erosion rates and occurrence of areas with net erosion at 2840-3140 m a.s.l.; and a slight trend of decreasing net accumulation with increasing altitude from 3140 to 3450 m a.s.l. The spatial variability in snow-layer depths showed a marked change around 3080 m a.s.l., with high variability at lower elevations and low variability at higher elevations. We also determined the spatial representativeness of 11 firn cores drilled along the traverse. In general, the representativeness of the cores was high. However, the core with the lowest representativeness underestimated the mean accumulation rate around the coring site by 22%. This shows that snow-radar data on spatial snow distribution are important for the interpretation of accumulation rates obtained from firn and ice cores.