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We elucidated the effects of snow and remineralization processes on nutrient distributions in multi-year landfast sea ice (fast ice) in Lutzow-Holm Bay, East Antarctica. Based on sea-ice salinity, oxygen isotopic ratios, and thin section analyses, we found that the multi-year fast ice grew upward due to the year-by-year accumulation of snow. Compared to ice of seawater origin, nutrient concentrations in shallow fast ice were low due to replacement by clean and fresh snow. In deeper ice of seawater origin (the lower half of the multi-year fast ice column), remineralization was dominated by the degradation of organic matter. By comparison between first- and muti-year ice, the biological uptake and the remineralization were dominated in relatively young ice and older ice, respectively, under the physical process of brine drainage.

The full length of Parker Ice Tongue on the Victoria Land Coast, Antarctica, calved in March 2020. Calving of this magnitude (18 km) is not previously seen for this location. The mean growth rate (...

The aim of the present study is to assess a conservation priority area (CPA) network proposed for the Russian Arctic seas (47 areas) with regard to underlying oceanographical features and to discuss further development of marine conservation planning. The oceanographical features included in the analysis were obtained from the literature or inferred from schemes of climatic oceanography. The most frequent oceanographic feature associated with a particular CPA is constant advection of a particular water mass, followed by local water mass transformation, seasonal ice zones, flaw polynyas, and external sources of nutrients. Particularly important are major frontal zones, and coastal phenomena such as coastal/offshore waters transition zones, massifs of fast ice and specific regimes of semi-isolated fjords and bays. Each Arctic sea in the study area or its large part (in the Barents Sea) is characterized by a distinct combination of oceanographical features associated with the respective CPAs. Although most oceanographical features were not involved in the process of developing the CPA network directly, the resulting CPAs are shown to have a solid oceanographical background. While this oceanographical background needs further understanding, it provides the possibility to refine the MPA boundaries and plan future studies. Furthermore it allows evaluation of potential resistance and resilience of CPAs to climate change by focusing on relevant oceanographical processes and the adaptive potential of biota on an area by area basis.

This is the peer reviewed version of the following article: Ruther, D.C., Winsborrow, M., Andreassen, K. & Forwick, M. (2017). Grounding line proximal sediment characteristics at a marine-based, late-stage ice stream margin. Journal of Quaternary Science, 32(4), 463-474. https://doi.org/10.1002/jqs.2939, which has been published in final form at https://doi.org/10.1002/jqs.2939 . This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.

The Gulf of Bothnia hosted a variety of palaeo-glaciodynamic environments throughout the growth and decay of the last Fennoscandian Ice Sheet, from the main ice-sheet divide to a major corridor of ...

The distribution and drainage of meltwater at the base of glaciers sensitively affects fast ice flow. Classical studies suggest that thin meltwater films between the overlying ice and a hard-rock b...

This study investigates the impact of wind-induced sea ice drift on sea ice cover over the Indian Ocean sector of the Southern Ocean (IOS) in the contrasting Southern Annular Mode (SAM) years during a summer (February) and a winter (July) month. Analysis of reanalysis wind shows that during positive SAM events, westerlies show stronger and more zonal flow over the west IOS (west of 45°E), while a stronger northerly component is seen over the east IOS, to the south of 55°S during both February and July. This is attributed to the zonally asymmetric feature of sea level pressure over the IOS. A coupled ocean–sea ice model was forced with dynamical wind forcing for positive and negative SAM events during above months. The zonal contrast as seen in wind and surface current is transferred to the sea ice drift. A stronger zonal eastward sea ice drift is apparent over the west IOS, suggesting increased transport of sea ice from the Weddell Sea region in July. The eastward advection of sea ice results in piling of sea ice over west IOS and causes an increase in sea ice concentration and thickness. Over east IOS, the sea ice drift shows a strong southeastward anomaly from the sea ice edge towards the coast. This results in a piling of sea ice near the coast and a divergence of sea ice near the edge. This results in a negative anomaly in sea ice concentration and sea ice thickness over east IOS. Thus, the dynamical SAM forcing leads to a non-annular response in sea ice cover over the IOS.

Ground counts during 1959–1968 compared with counts using high resolution (0.6 m2) satellite imagery during 2008–2012 indicated many fewer Weddell seals (Leptonychotes weddellii) at two major molting areas in the western Ross Sea: Edisto Inlet-Moubray Bay, northern Victoria Land, and McMurdo Sound, southern Victoria Land. Breeding seals have largely disappeared from Edisto-Moubray, though the breeding population in McMurdo Sound appears to have recovered from harvest in the 1960s. The timing of decline, or perhaps spreading (lower numbers of seals in more places), is unknown but appears unrelated to changes in sea ice conditions. We analyzed both historic and satellite-derived ice data confirming a large expansion of pack ice mostly offshore of the Ross Sea, and not over the continental shelf (main Weddell seal habitat), and a thinning of fast ice along Victoria Land (conceivably beneficial to seals). Timing of fast ice presence and extent in coves and bays along Victoria Land, remains the same. The reduction in numbers is consistent with an altered food web, the reasons for which are complex. In the context of a recent industrial fishery targeting a seal prey species, a large-scale seal monitoring program is required to increase understanding of seal population changes.

Climate-forced ice losses are increasing potential for iceberg-seabed collisions, termed ice scour. At Ryder Bay, West Antarctic Peninsula (WAP) sea ice, oceanography, phytoplankton and encrusting zoobenthos have been monitored since 1998. In 2003, grids of seabed markers, covering 225 m2, were established, surveyed and replaced annually to measure ice scour frequency. Disturbance history has been recorded for each m2 of seabed monitored at 5–25 m for ~13 years. Encrusting fauna, collected from impacted and nonimpacted metres each year, show coincident benthos responses in growth, mortality and mass of benthic immobilized carbon. Encrusting benthic growth was mainly determined by microalgal bloom duration; each day, nanophytoplankton exceeded 200 μg L−1 produced ~0.05 mm radial growth of bryozoans, and sea temperature >0 °C added 0.002 mm day−1. Mortality and persistence of growth, as benthic carbon immobilization, were mainly influenced by ice scour. Nearly 30% of monitored seabed was hit each year, and just 7% of shallows were not hit. Hits in deeper water were more deadly, but less frequent, so mortality decreased with depth. Five-year recovery time doubled benthic carbon stocks. Scour-driven mortality varied annually, with two-thirds of all monitored fauna killed in a single year (2009). Reduced fast ice after 2006 ramped iceberg scouring, killing half the encrusting benthos each year in following years. Ice scour coupled with low phytoplankton biomass drove a phase shift to high mortality and depressed zoobenthic immobilized carbon stocks, which has persevered for 10 years since. Stocks of immobilized benthic carbon averaged nearly 15 g m−2. WAP ice scouring may be recycling 80 000 tonnes of carbon yr−1. Without scouring, such carbon would remain immobilized and the 2.3% of shelf which are shallows could be as productive as all the remaining continental shelf. The region's future, when glaciers reach grounding lines and iceberg production diminishes, is as a major global sink of carbon storage.

Amplitude analysis of reflection seismic data reveals the presence of highly variable bed conditions under the main sticky spot and adjacent regions of the Kamb Ice Stream (KIS—formerly ice stream C). The sticky spot, which is a zone of bed that imparts high basal resistance to ice flow, is situated on a local topographic high composed of consolidated sediments or sedimentary rock. Any meltwater draining from upglacier along the base of the ice is routed around the sticky spot. The ice over the sticky spot includes, in at least some places, a seismically detectable basal layer containing a low concentration of debris, which locally thickens to 40 m over a topographic low in the bed. The ice-contact basal material ranges from dilated and highly porous to more-compacted and stiff, and perhaps locally frozen. The softer material is preferentially in topographic lows, but there is not a one-to-one correspondence between basal character and basal topography. We speculate that the 40-m-thick frozen-on debris layer formed by glaciohydraulic supercooling of lake-drainage events along a basal channel during the former, active phase of the ice stream. We also speculate that loss of lubricating water, perhaps from piracy upstream, contributed to the slowdown of the ice stream, with drag from the sticky spot playing an important role, and with the basal heterogeneity greatly increasing after the slowdown of the ice stream.

Aeolian sand and dust in polar regions are transported offshore over sea ice and released to the ocean during summer melt. This process has long been considered an important contributor to polar sea floor sedimentation and as a source of bioavailable iron that triggers vast phytoplankton blooms. Reported here are aeolian sediment dispersal patterns and accumulation rates varying between 0·2 g m−2 yr−1 and 55 g m−2 yr−1 over 3000 km2 of sea ice in McMurdo Sound, south-west Ross Sea, adjacent to the largest ice free area in Antarctica. Sediment distribution and the abundance of southern McMurdo Volcanic Group-derived glass, show that most sediment originates from the McMurdo Ice Shelf and nearby coastal outcrops. Almost no sediment is derived from the extensive ice free areas of the McMurdo Dry Valleys due to winnowed surficial layers shielding sand-sized and silt-sized material from wind erosion and because of the imposing topographic barrier of the north-south aligned piedmont glaciers. Southerly winds of intermediate strength (ca 20 m sec−1) are primarily responsible for transporting sediment northwards and offshore. The results presented here indicate that sand-sized sediment does not travel more than ca 5 km offshore, but very-fine sand and silt grains can travel >100 km from source. For sites >10 km from the coast, the mass accumulation rate is relatively uniform (1·14 ± 0·57 g m−2 yr−1), three orders of magnitude above estimated global atmospheric dust values for the region. This uniformity represents a sea floor sedimentation rate of only 0·2 cm kyr−1, well below the rates of >9 cm kyr−1 reported for biogenic-dominated sedimentation measured over much of the Ross Sea. These results show that, even for this region of high-windblown sediment flux, aeolian processes are only a minor contributor to sea floor sedimentation, excepting areas proximal to coastal sources.

The distribution of basal drag zones (sticky spots) underneath palaeo-ice streams or lobes is largely unknown. We investigated the centre of the large (300 km long and up to 400 km wide) deglacial Hayes Lobe in NE Manitoba, Canada, by focusing on surficial till and its composition to get insights into dispersal patterns and their potential relationships to areas of basal drag. Subglacial bed roughness is a good criterion to identify areas of basal drag, but till composition may provide important insights across smoother beds. The onset zone of the Hayes Lobe overlies Palaeozoic Carbonate Platform rocks, whereas the majority of the lobe overlies the low-lying Canadian Shield. We show that, within a 3500-km2 central area of this lobe, calcareous detritus within the till has been transported over 100 km within subglacial environments of reduced ice-bed coupling and fast ice flow. Six per cent of samples (n = 782), however, outline 0.2 to 4 km wide spots with a dominantly local composition. The glacial history and composition indicate that the till within these spots contains high inheritance from a pre-Late Wisconsinan ice-flow phase, which we suggest was protected beneath sticky spots (low erosion, high strength) during transport of substantial calcareous detritus to the area. Furthermore, our findings show that local till spots are present within streamlined landforms, as well as till blankets or veneers over bedrock. This diverse geomorphology indicates that the process of drumlinization within the deglacial Hayes Lobe does not appear to have been responsible for significant sediment transport or deposition across the study area. The overall record thus indicates potentially complex spatiotemporal shifts between calcareous till deposition, sticky conditions, erosion and drumlinization – which supports the subglacial bed mosaic model.

Ringed seal (Pusa hispida) breeding distribution has been extensively studied across near-shore habitats, but has received limited attention at a seascape scale due to the difficulty in accessing offshore sea ice environments. Employing highly visible predation attempts by polar bears (Ursus maritimus) on ringed seals in subnivean lairs observed by helicopter, the spatial relationship between predatory behaviour and ringed seal breeding habitat was examined. Resource selection functions were used to determine the relative probability of predation attempts on ringed seals in lairs as a function of habitat during a period of low ringed seal natality (2004–2006). Ringed seal pup kill locations were compared between years of low (2003–2006) and high (2007–2011) natality to assess the effect of reproductive output on habitat use. During years of low natality, polar bear hunting attempts were more likely in near-shore fast ice, and pup kills were observed predominately in fast ice (fast = 65 %, pack = 29 %, P = 0.002) at a median distance of 36 km from shore. In years of high natality, pup kills were observed farther from shore (median = 46 km, P = 0.03), and there was no difference in the proportion of observations in fast ice and pack ice (fast = 43 %, pack = 52 %, P = 0.29). These results suggest that the facultative use of adjacent offshore pack ice by breeding ringed seals may be influenced by natality. This study illustrates how documenting the behaviour of a predator can facilitate insight into the distribution of a cryptic prey.

We present an 8000-year history spanning 650km of ice margin retreat for the largest marine- terminating ice stream draining the former British-Irish Ice Sheet. Bayesian modelling of the geochronological data shows the ISIS expanded 34.0-25.3ka, accelerating into the Celtic Sea to reach maximum limits 25.3-24.5ka before a collapse with rapid marginal retreat to the northern Irish Sea Basin (ISB). This retreat was rapid and driven by climatic warming, sea-level rise, mega-tidal amplitudes and reactivation of meridional circulation in the North Atlantic. The retreat, though rapid, is uneven, with the stepped retreat pattern possibly a function of the passage of the ice stream between normal and adverse ice bed gradients and changing ice stream geometry. Initially, wide calving margins and adverse slopes encouraged rapid retreat (! 550m a " 1 ) that slowed (! 100m a " 1 ) at the topographic constriction and bathymetric high between southern Ireland and Wales before rates increased (! 200m a " 1 ) across adverse bed slopes and wider and deeper basin configuration in the northern ISB. These data point to the importance of the ice bed slope and lateral extent in predicting the longer-term (>1000 a) patterns and rates of ice-marginal retreat during phases of rapid collapse, which has implications for the modelling of projected rapid retreat of present-day ice streams. Copyright # 2013 John Wiley & Sons, Ltd.

The extent of multi-year sea ice impacts climate processes worldwide, such as ocean–atmosphere carbon dioxide exchange and deep ocean current formation. Reconstructing these processes in the past, and assessing the distribution of ecologically and climatically significant features, such as polynas, requires recognition of sediments deposited under multi-year sea ice, but little is known about their characteristics. Textural analysis of subaerial and sea floor sediment in Explorers Cove, McMurdo Sound, at the mouth of Taylor Valley, Antarctica, augmented with observations of sedimentary structures and faunal components, elucidates how sediment is transported to the sea floor and allows characterization of the deposits. Comparison of grain-size characteristics of subaerial (moraine, delta and sea-ice surface) sediment and sea floor sediment from short cores taken at depths of 7 to 25 m indicates that the likely source of the moderately to poorly sorted sea floor sand is deltaic sediment; small glacial meltwater streams have built deltas since Taylor Valley became ice-free ca 7000 years ago. Windblown sediment accumulating on the multi-year sea ice close to the coast typically is coarser grained than sediment on the sea floor; this suggests that the transport of sediment through the ice to the sea floor is not the predominant mode of sediment transfer. However, supra-sea-ice sediment does move to the sea floor through local fractures. The rate of sedimentation under multi-year sea ice is low because of limited stream flow and biogenic sedimentation; the ice cover inhibits primary productivity and dampens waves, precluding physical re-suspension. The upper centimetres of sea floor sediment are churned by epifaunal scallops and brittle stars that leave no telltale biogenic structures and whose calcite ossicles and shells may be poorly preserved. The resulting deposits under multi-year sea ice are poorly sorted, massive sand that provides little evidence of the bioturbators that have masked the indicators of the original physical depositional processes.

We report analyses of a dataset spanning 38 years of near-annual fishing for Antarctic toothfish Dissostichus mawsoni, using a vertical setline through the fast ice of McMurdo Sound, Antarctica, 1972-2010. This constitutes one of the longest biological time series in the Southern Ocean, and certainly the longest for any fish. Fish total length, condition and catch per unit effort (CPUE) were derived from the more than 5500 fish caught. Contrary to expectation, length-frequency was dominated by fish in the upper half of the industrial catch. The discrepancy may be due to biases in the sampling capabilities of vertical (this study) versus benthic (horizontal) fishing gear (industry long lines), related to the fact that only large Antarctic toothfish (more than 100 cm TL) are neutrally buoyant and occur in the water column. Fish length and condition increased from the early 1970s to the early 1990s and then decreased, related to sea ice cover, with lags of 8 months to 5 years, and may ultimately be related to the fishery (which targets large fish) and changes in the Southern Annular Mode through effects on toothfish main prey, Antarctic silverfish Pleuragramma antarcticum. CPUE was constant through 2001 and then decreased dramatically, likely related to the industrial fishery, which began in 1996 and which concentrates effort over the Ross Sea slope, where tagged McMurdo fish have been found. Due to limited prey choices and, therefore, close coupling among mesopredators of the Ross Sea, Antarctic toothfish included, the fishery may be altering the trophic structure of the Ross Sea.

Saks, T., Kalvans, A. & Zelcs, V. 2012 (January): Subglacial bed deformation and dynamics of the Apriķi glacial tongue, W Latvia. Boreas, Vol. 41, pp. 124–140. 10.1111/j.1502-3885.2011.00222.x. ISSN 0300-9483. We evaluate the glacial dynamics and subglacial processes of the Apriķi glacial tongue in western Latvia during the Northern Lithuanian (Linkuva) oscillation of the last Scandinavian glaciation. The spatial arrangement of glacial bedforms and deformation structures are used to reconstruct the ice dynamics in the study area. The relationship between geological structures at the glacier bed and the spatial distribution of drumlins and glacigenic diapirs, on the one hand, and the permeability of sediment and bedrock, on the other, is ascertained. Drumlins are found in the upper part of the Apriķi glacial tongue area and are composed of soft deformable sediments overlying highly permeable Devonian dolomite. The soft deformable clayey silty bed with low hydraulic conductivity is conducive to the development of diapirs. The occurrence of diapirs and drumlins is controlled by the fluctuation of pore-water pressure at the glacier bed and is considered to be an indicator of fast ice flow of the Apriķi glacial tongue during its reactivation at the end of the Oldest Dryas (18–15 ka BP).

This paper reviews isotopic research on the characterisation and identification of various types of ground ice throughout the Canadian Arctic, including buried glacier ice, massive segregated ice, segregated ice lenses and offshore ice-rich permafrost, as well as ice related to other cold-region phenomena such as ice wedges, icings (aufeis), frost blisters and pingos. The formational age of ground ice bodies ranges from recent (seasonal ice in the active layer) to tens of thousands of years, when the region experienced widespread continental-scale glaciation. Modern ice lenses generally have 18O/16O ratios of -18 to -22‰, while modern ice wedges usually range from -22 to -25‰. δ18O values as high as -14‰ are representative of the Hypsithermal period (4000 to 8000 years BP), while glacial-age ice has been measured with 18O/16O ratios as low as -36‰. Buried glacier ice often preserves climatic variations from the time of snow deposition. Other massive ground ice bodies contain isotopic signatures (18O and 2H) that indicate variable fractionation of the isotopes during freezing of the source water at stationary freezing fronts in either open or closed systems. Placing the ice bodies into a time frame can be accomplished either through age dating of the enclosing sediments and encased organics, or by direct dating of the ice utilising tritium (3H) for relatively young ice and radiocarbon (14C) analysis of contained gas bubbles for older ice. Copyright © 2011 John Wiley & Sons, Ltd.

Anchor ice rafting (transport of sediment by released anchor ice) occurs regularly on many ice-affected rivers. However, rafting is poorly understood and there is scant quantitative information about it. This paper describes anchor ice formation and ice rafting observations made in the Laramie River, a small river in Wyoming. Anchor ice forms on cobble, gravel and sand substrates in the Laramie River. When released from the bed, anchor ice rafts sediment from all of these size classes. Observations suggest that anchor ice plays a substantial role transporting coarse fluvial sediment because anchor readily envelops large particles extending above the bed. A comparison of anchor-ice rafted sediment with peak-discharge bedload sediment shows that the largest sediment is transported downstream during the winter when flows are at a minimum. The largest ice-rafted cobble identified in this study weighed 9.5 kg; peak floods are capable of moving sediment only about a hundredth of the cobble's weight. There is overlap in ice-rafted and bedload sediment transport; both processes move significant amounts of sand-sized material. The average sediment concentration in released, floating anchor ice samples was 22 g l−1. Copyright © 2010 John Wiley & Sons, Ltd.

Ross, M., Lajeunesse, P. & Kosar, K. G. A. 2010: The subglacial record of northern Hudson Bay: insights into the Hudson Strait Ice Stream catchment. Boreas, 10.1111/j.1502-3885.2010.00176.x. ISSN 0300-9483. In this paper, we present new insights into the glacial dynamics and potential configuration of the Hudson Strait Ice Stream catchment in the northern Hudson Bay–western Hudson Strait region. Our reconstruction is based on new field observations and till compositional data from Southampton Island, remote sensing imagery and multibeam bathymetric data from the Hudson Bay sea floor, as well as on a re-examination of previously published data from this vast region. Our findings suggest that, during the late Quaternary, the HSIS catchment consisted of a number of ice-stream tributaries feeding a curvilinear trunk that potentially extended into western Hudson Bay. In contrast to previous interpretations, the occurrence of fluted bedrock hills, over-deepened basins, Dubawnt erratics and carbonaceous till on the islands at the head of Hudson Strait is taken to imply that cold-based conditions did not prevail on these islands. The upland area of Southampton Island and the surrounding channels played an important role in controlling the location of the main tributaries, with the higher central terrain forming a large inter-ice-stream zone lacking carbonate detritus. Coats Island contains abundant evidence of vigorous ice flow, such as mega-scale glacial lineations (MSGLs). MSGLs also occur on the sea floor southwest of Coats Island but the sea-floor imprint is highly discontinuous. Observations on the western Hudson Bay mainland show evidence of southeastward fast ice flow that is spatially consistent with the Dubawnt dispersal train. Despite the geomorphological discontinuities, this may indicate that the HSIS onset zone extended far inside the Laurentide Ice Sheet and across contrasting geological domains.

Interannual changes in seasonal ground freezing and near-surface heat flow beneath zones of bottom-fast ice (BFI) were examined over the winters of 2005‐06 and 2006‐07 within the near-shore zone of the Mackenzie Delta, Canada. Winter variability in ground thermal conditions was determined at three monitoring sites. Ground-penetrating radar surveys were conducted in late winter to determine spatial variability in landfast ice conditions and the extent of ice-bonded sediments. Shallow water sites ( 1m of water) experienced prolonged periods of floating ice, which limited the duration of ice contact with the sediment bed and the depth of seasonal frost, and resulted in warmer winter ground temperatures (between � 0.58 Ca nd� 2.68C). Under similar water depths, interannual changes in ice growth altered the timing of BFI and winter heat loss from the ground. When comparing conditions over the twowinters, 2005‐06 was characterised by a decrease in ice thickness that limited the extent of BFI and seasonal cooling of the ground. These changes in ice conditions had a greater effect on the thermal conditions at sites where water depths were close to the maximum ice thickness. The short ice contact times at these sites are important to the thermal state of permafrost, as only minimal heat exchange contributing to permafrost cooling occurs prior to freezeback of the active layer. Copyright # 2010 John Wiley & Sons, Ltd.

The drainage system beneath ice sheets is poorly understood, even though it is a major determinant of their basal boundary condition, with implications for their form, flow and stability, and particularly of the ice streams that are crucial dynamic components. Understanding can be enhanced by evidence from the beds of former ice sheets. Glaciological principles are applied to geological evidence in the Vale of York that demonstrate occupancy by a major ice stream of the British ice sheet, with deduced gravitational shear stresses in the range 4-24 kPa, compared with a typical glacier shear stress of about 80-100 kPa, and horizontal velocities in the terminal zone in the range of 400-950 ma 1 . It is shown that the ice stream was in an almost buoyant state, with effective pressures in the range 50- 100 kPa forarange of ice pressures between 2000and 5000kPa. Similar deductions are madefor other ice streams on the southern flank of the British ice sheet. The esker system in the area of the ice stream represents locations of subglacial drainage tunnels that are suggested to be the key drainage elements in ice sheets where excess surface water penetrates to the bed. A theory of channel-groundwater coupling which self-organises in response to the rate of water recharge and the transmissivity of the subglacial bed is applied to the sub-ice stream esker system. When matched to local geological evidence, the theory predicts the distribution of basal water pressures, the rate of recharge of surface water to the glacier bed, local shear stresses, the areal pattern of sedimentary processes including bed deformation, and their seasonal fluctuations. Predictions of the annual recharge rate of 950 mm are consistent with the modern values of modern mean annual rainfall in the Ouse (Vale of York) catchment of 906mm. The calculated mean annual discharge of the four major subglacial rivers in 55 m 3 s � 1 , compared with a mean flow of the modern Ouse of 49 m 3 s 1 . A transient analysis shows the response time of water pressures in the underlying aquifer to changes in surface recharge to be of the order 10-100 days, suggesting the possibility of instabilities at the ice-bed interface. It is not possible, however, to determine whether the Vale of York ice stream was characterized by stable or instable (surging) flow. Copyright # 2010 John Wiley & Sons, Ltd.

The article of record as published may be located at http://dx.doi.org/10.1002/qj.618 The surface of the Arctic Ocean in summer is a mix of sea ice and water in both leads and melt ponds. Here we use data collected at multiple sites during the year-long experiment to study the SurfaceHeatBudget of the Arctic Ocean (SHEBA)to develop a bulk turbulent flux algorithm for predicting the surface fluxes of momentum and sensible and latent heat over the Arctic Ocean during summer from readily measured or modelled quantities. The distinctive aerodynamic feature of summer sea ice is that the leads andmelt ponds create vertical ice faces that the wind can push against; momentum transfer to the surface is thus enhanced through form drag. In effect, summer sea ice behaves aerodynamically like themarginal ice zone, which is another surface that consists of sea ice and water. In our bulk flux algorithm, we therefore combine our SHEBA measurements of the neutral-stability drag coefficient at a reference height of 10 m, CDN10, with similar measurements from marginal ice zones that have been reported in the literature to create a unified parametrization for CDN10 for summer sea ice and for anymarginal ice zone. This parametrization predicts CDN10 from a second-order polynomial in ice concentration. Our bulk flux algorithm also includes expressions for the roughness lengths for temperature and humidity, introduces new profile stratification corrections for stable stratification, and effectively eliminates the singularities that often occur initerativeflux algorithms for very light winds. In summary, this new algorithm seems capable of estimating the friction velocity u∗ (a surrogate for the momentum flux) over summer sea ice with an absolute accuracy of 0.02–0.03 m s−1; the sensible heat flux, with an accuracy of about 6Wm−2; and the latent heat flux, with an accuracy of 3.5Wm−2. Both NSF (award 06-11942) and the National Aeronautics and Space Administration (award NNX07AL77G) supported ELA at NorthWest Research Associates during the preparation of this manuscript, and NSF also supported POGP with award 06-12428.

This paper investigates the processes governing bedrock bedform evolution in ice sheet and ice stream areas in central West Greenland, and explores the evidence for a cross-shelf ice stream at the Last Glacial Maximum (LGM). To the east of Sisimiut the formation of streamlined bedforms with high elongation ratios and high bedform density has been controlled by geological structure and topography in slow-flowing ice sheet areas. At the coast, the effects of regional flow convergence, caused by coastal fjord orientation, routed ice into the Sisimiut/Itilleq area where it formed an ice stream onset zone. This funnelled ice into an offshore trough (Holsteinsborg Dyb), resulting in a southwesterly regional ice flow direction and the formation of a topographically routed ice stream (Holsteinsborg Isbrae). To the south of this, striae and bedform evidence show that local valley glaciers initially flowed east to west across the coast, but were later redirected by the Itilleq Fjord ice which turned southwestward due to diffluent flow and deflection by Holsteinsborg Isbrae. Roches moutonnees in this area have low elongation ratios and high bedform density, but do not provide unequivocal support for ice streaming, as they are a product of both bedrock structure and changes in ice flow direction, rather than enhanced flow velocities. Cosmogenic surface exposure ages limit maximum ice sheet surface elevation to ca. 755–810 m above sea level in this region. Such ice thickness enabled Holsteinsborg Isbrae to reach the mid/outer continental shelf during the LGM, and to contribute to the formation of a trough mouth fan and the Outer Hellefisk moraines. Initial deglaciation across this region was driven by rising sea level and increasing air temperatures prior to the Bolling Interstadial at ca. 14.5 cal. ka BP. Between 12 and 10 cal. ka BP both increased air and ocean temperatures post the Younger Dryas, and peak sea-level rise up to the marine limit, caused accelerated thinning and marginal retreat through calving, although dating evidence suggests ice streams remained along the inner shelf/coast boundary until at least ca. 10 cal. ka BP, their longevity maintained by increased ice thickness and ice discharge. Copyright © 2009 John Wiley & Sons, Ltd.

The outline and trend of 6566 subglacial bedforms in the New York Drumlin Field have been digitized from digital elevation data. A spatial predictive model has been used to extend values of bedform elongation over an area measuring 200 km × 110 km. The resulting surface is used in conjunction with depth-to-bedrock data and an assumed duration of ice residence to test three proposed controls on bedform elongation. Upon comparison, the resulting display of morphometry is best explained by differences in ice velocity across the field of study. The existence of multiple zones of fast-moving ice located along the southern margin of the Laurentide Ice Sheet is implied by the observed patterns of bedform elongation and orientation. We present two interpretations that are consistent with the observations. First, enhanced basal sliding caused by decreasing effective pressure near a calving margin is suggested as a possible mechanism by which localized fast ice flow is initiated and maintained. Second, topographically controlled ice streams likely occupied the fjord-like troughs of the Appalachian Upland northern rim. Contrary to previous understanding of the Laurentide southern margin in New York State, the resulting palaeoglaciological reconstruction illustrates a dynamic mosaic of ice stream and/or outlet glacier activity. Copyright © 2009 John Wiley & Sons, Ltd.

Numerical experiments suggest that the last glaciation severely affected the upper lithosphere groundwater system in NW Poland: primarily its flow pattern, velocities and fluxes. We have simulated subglacial groundwater flow in two and three spatial dimensions using finite difference codes for steady-state and transient conditions. The results show how profoundly the ice sheet modifies groundwater pressure heads beneath and some distance beyond the ice margin. All model runs show water discharge at the ice forefield driven by ice-sheet-thickness-modulated, down-ice-decreasing hydraulic heads. In relation to non-glacial times, the transient 3D model shows significant changes in the groundwater flow directions in a regionally extensive aquifer ca. 90 m below the ice–bed interface and up to 40 km in front of the glacier. Comparison with empirical data suggests that, depending on the model run, only between 5 and 24% of the meltwater formed at the ice sole drained through the bed as groundwater. This is consistent with field observations documenting abundant occurrence of tunnel valleys, indicating that the remaining portion of basal meltwater was evacuated through a channelized subglacial drainage system. Groundwater flow simulation suggests that in areas of very low hydraulic conductivity and adverse subglacial slopes water ponding at the ice sole was likely. In these areas the relief shows distinct palaeo-ice lobes, indicating fast ice flow, possibly triggered by the undrained water at the ice–bed interface. Owing to the abundance of low-permeability strata in the bed, the simulated groundwater flow depth is less than ca. 200 m. Copyright © 2009 John Wiley & Sons, Ltd.

This study investigates the marginal subglacial bedrock bedforms of Jakobshavns Isbrae, West Greenland, in order to examine the processes governing bedform evolution in ice stream and ice sheet areas, and to reconstruct the interplay between ice stream and ice sheet dynamics. Differences in bedform morphology (roche moutonnee or whaleback) are used to explore contrasts in basal conditions between fast and slow ice flow. Bedform density is higher in ice stream areas and whalebacks are common. We interpret that this is related to higher ice velocities and thicker ice which suppress bed separation. However, modification of whalebacks by plucking occurs during deglaciation due to ice thinning, flow deceleration, crevassing and fluctuations in basal water pressure. The bedform evidence points to widespread basal sliding during past advances of Jakobshavns Isbrae. This was encouraged by increased basal temperatures and melting at depth, as well as the steep marginal gradients of Jakobshavns Isfjord which allowed rapid downslope evacuation of meltwater leading to strong ice/bedrock coupling and scouring. In contrast to soft-bedded ice stream bedforms, the occurrence of fixed basal perturbations and higher bed roughness in rigid bed settings prevents the basal ice subsole from maintaining a stable form which, coupled with secondary plucking, counteracts the development of bedforms with high elongation ratios. Cross-cutting striae and double-plucked, rectilinear bedforms suggest that Jakobshavns Isbrae became partially unconfined during growth phases, causing localised diffluent flow and changes in ice sheet dynamics around Disko Bugt. It is likely that Disko Bugt harboured a convergent ice flow system during repeated glacial cycles, resulting in the formation of a large coalesced ice stream which reached the continental shelf edge.

A considerable discussion concerning the extent of the last Scandinavian and Scottish ice sheets has continued for several years. In contrast to earlier models based on an ice sheet extending to the edge of the continental shelf, recent proposals favor a limited geographical and vertical extent and imply that the Scandinavian and British ice sheets did not coalesce in the North Sea. These models indicate an ice-free, open embayment in the northern North Sea and areas of dry land in the southern North Sea region during the Late Weichselian/Devensian glacial maximum. Late Weichselian ice-sheet profiles from the North Sea to the adjacent land areas of southern Norway have been tentatively reconstructed. Low-gradient profiles in the present shelf areas are explained by unconsolidated, deformable sediments on the continental shelf inducing subglacial water pressure and low basal shear stress beneath marginal parts of the Scandinavian ice sheet. Combined with higher basal shear stress conditions in the present mainland areas, this explains the slightly concave and convex shape of the reconstructed ice-sheet profiles in the present coastal and inland areas of western Norway, respectively.

A numerical ice-sheet model was run in order to produce reconstructions of the Late Weichselian ice coverage of Franz Josef Land, Russian High Arctic. The model grid covers the archipelago and surrounding shelf, but does not include the whole Barents-Kara region or the extensive ice cover that may have built up there. One experiment, where rates of iceberg calving at the grounded margin were curtailed because of the assumed presence of permanent thick sea ice, yielded a single I.8 km-thick ice dome which covered the entire archipelago and surrounding sea. If, however, iceberg calving were included in the model's environmental input, the extent of the ice sheet would be limited to the periphery of the archipelago. If a large ice sheet existed over Franz Josef Land, the deglaciation of the islands may have been linked to the decay of the adjacent Barents-Kara Sea Ice Sheet, permitting iceberg calving (enhanced by relative sea-level rise) to occur. The introduction of a water-depth-related iceberg calving function at 15 000 yr ago forced an initial rapid rate of ice-sheet decay of 30 000 km3 1000 yr'. However, as the ice sheet thinned, and isostatic rebound began, the calculated rate of iceberg calving was reduced such that ice remained over the archipelago at 8000 yr ago. The model's failure to simulate complete ice-sheet decay by 8000 yr ago is at variance with radiocarbon-dated raised terraces on Franz Josef Land, which indicates the complete deglaciation of the islands at this time.

On the basis of glacial landforms interpreted by means of Landsat satellite imagery and ice-flow data obtained by other methods, the Scandinavian ice sheet has been observed to have divided at the deglaciation stage into several ice lobes. The ice lobes were more active parts of the uniform ice sheet. They represent parts that had bordered on each other in different directions or on more passive portions of the ice. The reasons for the appearance of separate ice lobes were evidently the Fennoscandian topography, the location of accumulation areas, and regional differences in the amounts of ice generated. In the boundary zones of the different ice lobes, there occur exceptionally large glaciofluvial forms and moraines (interlobate complexes). An area of passive ice was often between ice lobes, and in such areas there occur no noteworthy eskers, marginal formations or streamlined forms. In the part of Finland located on the southern side of the Arctic Circle, six different ice lobes and four major areas of passive ice are interpreted to have existed.

The sediments and landforms preserved on palaeo-ice-stream beds can provide important information about their subglacial conditions and flow mechanisms, and the processes accompanying their shutdown. In this paper, detailed observations of an intriguing subglacial landform assemblage of ribbed moraines superimposed on glacial lineations on the Dubawnt Lake Ice Stream bed (north-west Canadian Shield) are presented, including their morphometry, internal structure (from ground penetrating radar (GPR) surveys and from glaciogeological analysis) and sedimentological characteristics (from sediment architecture and lithofacies analysis). The observations suggest an abrupt change in ice dynamics that correlates with two phases of glacial landform development. This hypothesis is based on evidence from a deformed lodgement till, which subsequently underwent brittle deformation and developed prominent thrust (shear) structures and tension fractures. Tension fractures are observed in a sediment exposure and thrust structures are observed in GPR surveys, where they occur most prominently in the ribbed moraine ridge crests. The presence of the fractures, and their association with a population of clasts in the till that are orientated with their a-axes transverse to the inferred ice flow direction, suggests a compressional flow regime. It is therefore inferred that the glacial lineations were formed under an extensional flow regime during ice stream activity, but that at some point patches of till under the ice stream stiffened through dewatering. The subsequent increase in basal shear stress resulted in compressional flow and the development of subglacial thrusting and the building of ribbed moraines. We therefore suggest that ribbed moraines may form in areas of compressional flow under ice streams, i.e. sticky spots, and/or at the transition between slow and fast ice flow along parts of an ice stream. The general absence of ribbed moraines on most other palaeo-ice-stream beds suggests that either these ice streams continued operating during deglaciation or processes other than the development of localized compressional flow (sticky spots) led to their shutdown (e.g. ice depletion).

Deglaciation of northern Baffin Island involved several large ice streams with contrasting histories. Three north-flowing, marine-based ice streams were in place during the Last Glacial Maximum, but they retreated at widely varying rates during the early and middle Holocene. The Steensby Inlet Ice Stream formed in response to over-steepening of the ice front during deglaciation of Foxe Basin. It caused an abrupt change, in places a general reversal, of flow about 6 ka BP and operated across its full width for only about 500 years. Nevertheless, it left a distinct subglacial footprint, including an hourglass shaped bedform set. A dense network of till samples from the region of the ice stream reveals a sharp-sided, pluglike dispersal of carbonate debris that was sustained by erosion in the source area of about 5 mm a−1. The ice stream devolved into valley-controlled ice streams separated by cold-based ice over interfluves. The former evacuated debris along valleys and left erosional till scarps along the sides of sliding ice. Post-ice-stream end moraines, including the large Gifford Moraine, require later cold-based flow across the drumlins formed by the ice stream. Copyright © 2008 John Wiley & Sons, Ltd.

High-resolution bathymetric mapping of the fjords and continental shelf around the Svalbard archipelago shows an extensive pattern of large- and medium-scale submarine landforms formed by differences in ice-flow regimes. Mega-scale glacial lineations, lateral moraines, transverse ridges and glaciotectonic features are superimposed on the large-scale fjord, shelf and cross-shelf trough morphology of the margin. From these landforms we have inferred the flow and dynamics of the last ice sheet on Svalbard. Major fjords and their adjacent cross-shelf troughs have been identified as the main routes for ice streams draining the ice sheet. On the west coast of Svalbard major pathways existed along Bellsund, Isfjorden and Kongsfjorden. Along the northern Svalbard margin most of the ice drained through the Woodfjorden cross-shelf trough and Wijdefjorden-Hinlopen strait. Extensive areas with trough-parallel glacial lineations in the cross-shelf troughs suggest fast ice flow by palaeo-ice streams. Lateral ice-stream moraines, several tens of kilometres in length, have been mapped along the margins of some of the cross-shelf troughs, identifying the border zone between fast ice flow and stagnant or slow-flowing ice on intervening banks. Several general implications can be drawn from the interpretation of the glacier-derived submarine landforms around Svalbard. Firstly, the Late Weichselian ice sheet was partitioned into fast-flowing ice streams separated by slower moving ice. Secondly, our submarine morphological evidence supports earlier sedimentological, stratigraphical and chronological studies in implying that a large ice sheet reached the shelf edge around almost all of western and northern Svalbard in the Late Weichselian. The idea of a relatively restricted ice sheet over Svalbard, with ice-free conditions in some areas of the west coast at the Last Glacial Maximum, is therefore unlikely to be correct. Thirdly, the ice sheet appears to have retreated more rapidly from the cross-shelf troughs and outer fjords, although sometimes this occurred in a punctuated pattern indicated by grounding-zone wedges, and more slowly from the intervening shallower banks. In addition, a grounding zone for the ice sheet has been mapped at the shelf edge 10–20 km off the northwest coast of Svalbard, suggesting that ice did not reach the adjacent Yermak Plateau during the Late Weichselian.

Underwater vocalization monitoring and surveys, both on ice and underwater, were used to determine ifWeddell seals (Leptonychotes weddellii) near Mawson Station, Antarctica, remain under the fast ice during winter within close range of breeding sites. Daytime and nighttime underwater calling rates were examined at seven breeding sites during austral winter and spring to identify seasonal and diel patterns. Seals rarely hauled out at any of the sites during winter, although all cohorts (adult males, females, and juveniles) were observed underwater and surfacing at breathing holes throughout winter (June-September) and spring (October-December). Seal vocalizations were recorded during each sampling session throughout the study (n = 102 daytime at seven sites collectively, and n = 5 24-h samples at each of two sites). Mean daytime calling rate was low in mid-winter (July) (mean = 18.9 ± 7.1 calls/min) but increased monthly, reaching a peak during the breeding season (November) (mean = 62.6 ± 15.7 calls/min). Mean nighttime calling rate was high throughout the winter and early spring (July-October) with mean nocturnal calling rate in July (mean = 61.8 ± 35.1 calls/min) nearly equal to mean daytime calling rate in November (during 24-h daylight). Reduced vocal behavior during winter daylight periods may result from animals utilizing the limited daylight hours for nonvocal activities, possibly feeding.

Late Devensian glacial sediments and landforms of the Isle of Man record the advance and deglacial signature of the central sector of the British-Irish Ice Sheet. Evidence from the area, gathered from striae, erratic trains and drift limits, show ice was routed over and around the island in two flow phases post-36 kyr BP. In the south of the island, streamlined depositional bedforms with low elongation ratios suggest low ice-flow velocities resulting from one or more of (i) the up-ice location of the island within a regional onset zone, (ii) flow retardation of ice interacting with the margins of the island and (iii) localized drainage of the deforming bed. The deglacial landform assemblage of lateral marginal sandurs and drainage diversions, coupled with a lack of dead-ice features, suggests ice did not downwaste in situ but retreated intact along the coastal margins as Manx Upland ice thinned. In the north of the island, however, the Bride Moraine complex indicates a change in deglacial ice-sheet dynamics, with temporary re-advance and marginal oscillation causing proglacial tectonism and thrusting of the glacial sediment pile, possibly during the Killard Point Stadial event (18.8-16.4 cal. kyr BP). From a basin-wide perspective, the Irish Sea Basin sector of the British-Irish Ice Sheet had many of the characteristics of an ice stream, such as a zone of flow convergence up-ice, a grounding line in the southern Celtic Sea and recessional limits characterized by proglacially tectonized and thrust dead-ice landscapes indicative of a rapidly oscillating ice margin.

Although drumlins and other subglacial bedforms are well-studied features, controls on their formation and morphometry have remained elusive. Of current interest is the hypothesis that elongate bedforms (length:width ratios≥ 10) indicate fast ice flow, and perhaps the location of past ice streams. This hypothesis is explored by analysing drumlins from the New York State drumlin field. A subset of 548 drumlins between Oneida Lake and Lake Ontario was digitized using 10-m grid cell digital elevation data. Because bedform elongation is greatest along the axis of a reconstructed lobe and increases down flowline, elongate bedforms are best explained by fast ice flow. The swath of elongate bedforms between lakes Ontario and Oneida, the boundaries of which do not coincide with topography, may signify the location of an ice stream during deglaciation.

This study describes the distribution of Weddell seals Leptonychotes weddelli in winter (May-September 1999) at the Vestfold Hills, in Prydz Bay, East Antarctica. Specifically, we describe the spatial extent of haul-out sites in shore-fast sea-ice, commonly referred to as fast-ice. As winter progressed, and the fast-ice grew thick (ca 2 m), most of the inshore holes closed over, and the seals' distribution became restricted to ocean areas beyond land and islands. Using observations from the end of winter only, we fitted Generalised Additive Models (GAMs) to generate resource selection functions, which are models that yield values proportional to the probability of use. The models showed that seal distribution was defined mainly by distance to ice-edge and distance to land. Distance to ice-bergs was also selected for models of some regions. We present the results as maps of the fitted probability of seal presence, predicted by the binomial GAM for offshore regions, both with and without autocorrelation terms. The maps illustrate the expected distribution encompassing most of the observed distribution. On this basis, we hypothesise that propensity for the fast-ice to crack is the major determinant of Weddell seal distribution in winter. Proximity to open water and pack-ice habitats could also influence the distribution of haul-out sites in fast-ice areas. This is the first quantitative study of Weddell seal distribution in winter. Potential for regional variation is discussed. Copyright © Ecography 2005.

Glacially deformed permafrost at North Head, in the Tuktoyaktuk Coastlands of western Arctic Canada, contains a complex ground-ice stratigraphy that formed during the course of the last glacial–interglacial cycle. Two generations of ground ice are distinguished within a single stratigraphic sequence. Pre-deformation ice has been glacially deformed or eroded beneath the cold-based margin of the Laurentide Ice Sheet (LIS) during Marine Isotope Stage 2. Such ice comprises (1) buried basal ice, (2) massive segregated ice and (3) ice clasts subglacially eroded from pre-existing ground ice. In contrast, post-deformation ice has not been glacially disturbed because it formed during or after deglaciation; it includes (4) dykes and sills of intrusive ice, (5) massive segregated-intrusive ice, (6) ice wedges and composite wedges, (7) segregated ice and (8) pool ice. The superimposition of post-deformation intrusive ice and massive segregated-intrusive ice into permafrost containing pre-deformation ground ice indicates that substantial quantities of overpressurized water were injected into ice-marginal permafrost during or after deglaciation. The required external water source for the post-deformation intrusive ice was probably overpressurized subpermafrost groundwater in front of the retreating margin of the LIS. Injection of this water into proglacial permafrost hydraulically fractured the permafrost and formed ice dykes, ice sills and massive segregated-intrusive ice. A two-stage model of massive-ice development can be reconciled with known permafrost and glacial conditions in the ice-marginal context of the Late Wisconsinan LIS. The model probably applies to some other glaciated terrains of the western Canadian Arctic.

A distinct vertical zonation was observed among diatoms in a bottom congelation ice community at McMurdo Sound, Antarctica during the 1981 spring bloom. The bottom 20 cm of ice collected in December from four stations with variable snow cover was subdivided into 5 cm sections for analysis of algal distribution. Algal abundance was inversely related to the depth of snow cover, and generally decreased with increasing distance above the ice-water interface. Most diatoms, including the dominant species Nitzschia stellata Manguin, Amphiprora kufferathii Manguin and Fragilaria islandica var. adeliae Manguin showed peak abundance in the bottom 10 cm of the ice, where the proportion of living to empty cells was also highest. Two species, however, an Auricula Castracane sp. and Navicula glaciei van Heurck, reached highest concentrations at depths 10–20 cm above the ice-water interface. We considered two factors as contributing to the observed vertical zonation: (1) successive blooms at the ice-water interface become spatially stratified within the ice by further accretion below; (2) a differential growth of species occurs along physicochemical gradients within the ice column. A comparison of early versus late season profiles suggests the latter mechanism may prevail once ice accretion has ceased.

Polarella glacialis (Montresor et al.) was identified in Davis Station sea ice by morphological and DNA sequence comparison of cultures with those of the authentic strain P. glacialis CCMP 1383 isolated from McMurdo Sound. Cells and cysts of the Davis isolate (FL1B) were morphologically indistinguishable from P. glacialis, and comparison of the large subunit rDNA of both cultures demonstrated only 0.2% sequence divergence over 1366 base pairs. The photosynthetic pigments of P. glacialis (strains FL1B and CCMP 1383) were typical of dinoflagellates, with peridinin (contributing up to 31%) as the major accessory pigment. Extremely high levels of polyunsaturated fatty acids (PUFA, up to 76.3%) were characteristic of P. glacialis isolate FL1B. The high PUFA concentration of this species is thought to be an adaptation to survive the cold temperatures of the upper fast ice. The sterol profile of FL1B was atypical of dinoflagellates, with 4-desmethylsterols (up to 79%) in greater abundance than 4α-methyl sterols (up to 24%). 27-Nor-24-methylcholest-5,22E-dien-3β-ol was identified as the principle sterol in P. glacialis, contributing up to 64% of the total sterol composition.

The glacial geomorphology of the Waterville Plateau (ca. 55 km 2 ) provides information on the dynamics of the Okanogan Lobe, southern sector of the Cordilleran Ice Sheet in north-central Washington. The Okanogan Lobe had a profound influence on the landscape. It diverted meltwater and floodwater along the ice front contributing to the Channeled Scabland features during the late Wisconsin (Fraser Glaciation). The glacial imprint may record surge behaviour of the former Okanogan Lobe based on a comparison with other glacial landsystems. Conditions that may have promoted instability include regional topographic constraints, ice marginal lakes and dynamics of the subglacial hydrological system, which probably included a subglacial reservoir. The ice-surface morphology and estimated driving stresses (17-26 kPa) implied from ice thickness and surface slope reconstructed in the terminal area also suggest fast basal flow characteristics. This work identifies the location of a fast flowing ice corridor and this probably affected the stability and mass balance of the south-central portion of the Cordilleran Ice Sheet. Evidence for fast ice flow is lacking in the main Okanogan River Valley, probably because it was destroyed during deglaciation by various glacial and fluvial processes. The only signature of fast ice flow left is the imprint on the Waterville Plateau. Copyright 2004 John Wiley & Sons, Ltd.

Subglacial bed conditions are key to understanding ice stream behaviour and evolution, with bed roughness reflecting substrate composition and flow resistance. Here we present an analysis of bed roughness in the Siple Coast region of West Antarctica from airborne radio-echo sounding data. The ice streams are associated generally with low bed roughness values, which decrease downstream. The bed of the slow-flowing Ice Stream C (∼10 000 km2) is also characterized by being smooth at all scales (wavelengths ranging from 5 km to in excess of 40 km). Furthermore, the bed is smooth either side of Ice Stream C. This suggests the location of the ice stream is controlled by internal ice sheet dynamics rather than by bed morphology. If the ice stream were encouraged to migrate laterally, when active, there would be little resistance offered by the subglacial morphology. Other inter-ice stream regions are rough, however, indicating a subglacial topographic influence on ice stream position. Bed roughness increases up-flow of ice streams, which, unless the bed is modified, may limit the inland migration of these systems. Copyright © 2004 John Wiley & Sons, Ltd.

The Norwegian Channel between Skagerrak, in the southeast, and the continental margin of the northern North Sea, in the northwest, is the result of processes related to repeated ice stream activity through the last 1.1 m yr. In such periods the Skagerrak Trough (700 m deep) has acted as a confluence area for glacial ice from southeastern Norway, southern Sweden and parts of the Baltic. Possibly related to the threshold in the Norwegian Channel off Jaeren (250 m deep), the ice stream, on a number of occasions over the last 400 ka, inundated the coastal lowlands and left an imprint of NW-oriented ice directional features (drumlins, stone orientations in tills and striations). Marine interstadial sediments found up to 200 m a.s.l. on Jaeren have been suggested to reflect glacial isostasy related to the Norwegian Channel Ice Stream (NCIS). In the channel itself, the ice stream activity is evidenced by mega-scale glacial lineations on till surfaces. As a result of subsidence, the most complete sedimentary records of early phases of the NCIS are preserved close to the continental margin in the North Sea Fan region. The strongest evidence for ice stream erosion during the last glacial phase is found in the Skagerrak. On the continental slope the ice stream activity is evidenced by the large North Sea Fan, which is mainly a result of deposition of glacial-fed debris flows. Northwards of the North Sea Fan, rapid deposition of meltwater plume deposits, possibly related to the NCIS, is detected as far north as the Voring Plateau. The NCIS system offers a unique possibility to study ice stream related processes and the impact the ice stream development had on open ocean sedimentation and circulation.

Ice streams are major dynamic elements of modern ice sheets, and are believed to have significantly influenced the behaviour of past ice sheets. Funen Island exhibits a number of geomorphological and geological features indicative of a Late Weichselian ice stream, a land-based, terminal branch of the major Baltic Ice Stream that drained the Scandinavian Ice Sheet along the Baltic Sea depression. The ice stream in the study area operated during the Young Baltic Advance. Its track on Funen is characterized by a prominent drumlin field with long, attenuated drumlins consisting of till. The field has an arcuate shape indicating ice-flow deflection around the island's interior. Beneath the drumlin-forming till is a major erosional surface with a boulder pavement, the stones of which have heavily faceted and striated upper surfaces. Ploughing marks are found around the boulders. Exact correspondence of striations, till fabric and drumlin orientation indicates a remarkably consistent flow direction during ice streaming. We infer that fast ice flow was facilitated by basal water pressure elevated to the vicinity of the flotation point. The ice movement was by basal sliding and bed deformation under water pressure at the flotation level or slightly below it, respectively. Subglacial channels and eskers post-dating the drumlins mark a drainage phase that terminated the ice-stream activity close to the deglaciation. Identification of other ice streams in the Peribaltic area is essential for better understanding the dynamics of the land-based part of the Scandinavian Ice Sheet during the last glaciation.

With the aid of three case studies we summarize sedimentological and structural evidence in Wisconsinan subglacial till and its substrate that can be used to infer the presence of former fast-moving ice. We compare sedimentological characteristics of till with its stone fabric, stone surface erosional features and orientations of fractures, faults and folds in till and substrate, in order to interpret the processes that formed the till. In the cases we studied, stones in tills that experienced ductile deformation (inferred to be associated with fast-moving ice) show variable alignment of latest surface striae. Moreover, striae are inconsistent with the orientations of lee ends and chattermarks on the same stones, and with the dip directions of shallow shear planes and (or) steeper tension fractures in the till matrix. These observations indicate that stones were rotating in a flowing till matrix prior to their final emplacement. Ductile shear of fine-textured, water-saturated till and Jeffrey-like rotation of stones are invoked where most of the following occur together: (i) delicate striae follow the curvature of stone surfaces; (ii) a-axis fabrics are multimodal to girdle-like; (iii) stone a axis eigenvectors, striae orientation and stone lee end alignments fall between the modes of stone fabrics; (iv) stone pavements are uneven with vertically oriented and inverted bullet-shaped stones; (v) soft sediment clasts and (or) fragile fossils are preserved.

The Cairngorm Mountain area of Scotland is a classic example of a landscape of selective linear glacial erosion, with sharp contrasts in the intensity of glacial erosion between the deeply incised troughs and valleys and the undulating high plateau. This article examines the Quaternary development of Glen Avon, a 200 m deep glacial trough set within the high plateau of the mountains. Evidence concerning the aggregate basal thermal regimes of the topographically controlled ice streams that formerly developed in this area is reconstructed from the geomorphological record, including bedforms indicative of wet-based, sliding ice and of dry-based ice frozen to its bed. This mapping indicates that basal sliding was not confined exclusively to the troughs but extended towards valley heads and on to parts of the plateau adjacent to troughs. The extent of basal sliding appears to have been greatest beneath pre-Late Devensian ice sheets. Basal ice temperatures are modelled under steady-state conditions for the last ice sheet at c. 18 ka BP. Basal thermal regimes are predicted using a reconstruction of the preglacial relief and for the current topography of the area. Convergent flow of ice through the preglacial valley system appears to have been sufficient to induce basal melting and therefore to initiate valley deepening. This effect is enhanced when the model is run across the present topography. Comparison of results of the geomorphological mapping and the modelling reveals significant differences between the actual and predicted extent of basal sliding outside the main ice stream. The overall conclusion is that many ice streams in mountainous terrain are inherited from the locations of preglacial valleys, which serve to accelerate ice flow and promote frictional heating beneath ice sheets.

Geologic evidence such as subglacial troughs and grounding zone wedges indicate that soft-bedded, West Antarctic ice streams are capable of eroding, transporting and depositing large volumes of debris at high rates (˜100 m3 yr-1 per meter width). In order to understand the dynamics of ice streams and the geologic effects of their activity, it is important to understand the physical mechanisms that control these high rates of sub-ice-stream sediment generation and transport. Here, we use a numerical model of Ice Stream C run over c. 8500 model years to quantify the effects of a recently proposed, till-ploughing mechanism of till formation and redistribution beneath ice streams (Tulaczyk et al. 2001; Clark et al. in press). Our results show that this ‘transport-limited’ mechanism, in which till transport rates scale with ice velocity and erosion rates with spatial gradients of velocity, is consistent with existing constraints. For instance, our model results predict significantly higher (˜0.6 mm yr-1) average erosion rates beneath ice-stream tributaries, which are underlain by deep subglacial troughs, than beneath ice-stream trunks (˜0.2mm yr-1), whose subglacial troughs have a significantly smaller relief. We would not obtain this satisfactory result if subglacial erosion was parametrized in the model using the more traditional approach of scaling erosion rates with ice velocity (what we call the ‘production-limited’ parametrization). Because of the requirement of ice continuity, the magnitude of ice velocity generally increases downstream in polar ice streams, and so do the production-limited erosion rates. Pending further investigations, we propose that geologic and geomorphic effects of soft-bedded ice streams should be quantified using some form of a ‘transport-limited’ parametrization of subglacial erosion rates, e.g. the till-ploughing mechanism.

We report evidence for a major ice stream that operated over the northwestern Canadian Shield in the Keewatin Sector of the Laurentide Ice Sheet during the last deglaciation 9000-8200 (uncalibrated) yr BP. It is reconstructed at 450rkm in length, 140rkm in width, and had an estimated catchment area of 190 000rkm². Mapping from satellite imagery reveals a suite of bedforms ('flow-set') characterized by a highly convergent onset zone, abrupt lateral margins, and where flow was presumed to have been fastest, a remarkably coherent pattern of mega-scale glacial lineations with lengths approaching 13rkm and elongation ratios in excess of 40:1. Spatial variations in bedform elongation within the flow-set match the expected velocity field of a terrestrial ice stream. The flow pattern does not appear to be steered by topography and its location on the hard bedrock of the Canadian Shield is surprising. A soft sedimentary basin may have influenced ice-stream activity by lubricating the bed over the downstream crystalline bedrock, but it is unlikely that it operated over a pervasively deforming till layer. The location of the ice stream challenges the view that they only arise in deep bedrock troughs or over thick deposits of 'soft' fine-grained sediments. We speculate that fast ice flow may have been triggered when a steep ice sheet surface gradient with high driving stresses contacted a proglacial lake. An increase in velocity through calving could have propagated fast ice flow upstream (in the vicinity of the Keewatin Ice Divide) through a series of thermomechanical feedback mechanisms. It exerted a considerable impact on the Laurentide Ice Sheet, forcing the demise of one of the last major ice centres.

It has been suggested that extremely long subglacial bedforms (e.g. attenuated drumlins and mega-scale glacial lineations) record former areas of fast-flowing ice and that bedform elongation ratio is a useful proxy for ice velocity. Despite the availability of much data pertaining to the measurement and analysis of subglacial bedforms, these assumptions have rarely been explicitly addressed in detail. In this paper, we demonstrate that long subglacial bedforms (length:width ratios ge10:1) are indicative of fast ice flow. Using satellite imagery, we mapped over 8000 lineaments associated with a highly convergent flow pattern near Dubawnt Lake, District of Keewatin, Canada. This flow pattern is unusual in that it displays a large zone of convergence feeding into a main 'trunk' and then diverging towards the inferred ice margin. The 'bottleneck' pattern is taken to record an increase and subsequent decrease in ice velocity and we analysed transverse and longitudinal variations in bedform morphometry. The main trunk of the flow pattern (down-ice of the convergent zone) is characterized by mega-scale glacial lineations of great length (up to 13 km) and high elongation ratios (up to 43:1). The down-ice variations in elongation ratio reflect exactly what we would expect from a terrestrial ice stream whose velocity increases in the onset zone passes through a maximum in the main trunk and slows down as the ice diverges at the terminus. It is suggested that any unifying theory of drumlin formation must be able to account for the association between long subglacial bedforms and fast ice flow, although it is not assumed that fast ice flow always produces attenuated bedforms. A further implication of this work is that many more ice streams may be identified on the basis of attenuated subglacial bedforms, radically altering our views on the flow dynamics of former ice sheets.