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In this study, we compare equilibrium-line altitudes (ELAs) calculated using the area–altitude balance ratio (AABR) and the accumulation–area ratio (AAR) methods, with measured ELAs derived from direct field observations. We utilise a GIS toolbox to calculate the ELA for 64 extant glaciers by applying the AABR and AAR methods to DEMs and polygons of their geometry. The calculated ELAs (c-ELAs) are then compared to measured zero-net balance ELAs (znb-ELAs) obtained from mass-balance time series held by the WGMS for the same glaciers. The correlation between znb-ELAs and AABR (1.56)/AAR (0.58) c-ELAs is very strong, with an r2 = 0.99. The smallest median difference between znb-ELAs and c-ELAs (i.e. 65.5 m) is obtained when a globally representative AABR of 1.56 is used. When applied to palaeoglacier-climate applications, this difference translates to ~0.42°C, well within the uncertainty of palaeotemperature proxies used to determine mean summer temperature at the ELA. The more widely used mean AABR of 1.75 is shown to be statistically invalid due to the skewness of the dataset. On this basis, when calculating glacier ELAs, we recommend the use of a global AABR value of 1.56.

The concept of Quaternary average conditions has gained popularity over the past few decades, especially with studies of long-term landscape evolution. In this paper, we critically assess this concept by analyzing the marine isotope record (LR04 δ18O stack) relative to the Quaternary. This shows that the frequency and amplitude of climate glacial-interglacial cycles are not constant throughout the Quaternary, with a clear change during the Middle Pleistocene Transition (MPT), and that many minor oscillations exist within each cycle. For this reason, the identification of pre- and post-MPT most-frequent and, cumulatively, longest-lasting (rather than average) conditions is recommended. The most-frequent pre-MPT δ18O value of 3.725 ± 0.025‰ last occurred during 11.31–11.47 ka, while the most-frequent post-MPT δ18O value of 4.475 ± 0.025‰ last occurred during 14.81–15.04 ka. However, many other δ18O values were almost as frequent throughout the Quaternary and we present geomorphological reasons as to why it is unlikely that the present-day landscape reflects Quaternary average or, indeed, most-frequent conditions. Collectively, our results indicate that extreme caution should be taken when attempting to infer long-term landscape evolution processes (including the buzzsaw hypothesis) based on average Quaternary conditions.

The Greenland Ice Sheet (GrIS) is known to have experienced widespread retreat over the last century. Information on outlet glacier dynamics, prior to this, are limited due to both a lack of observations and a paucity of mapped or mappable deglacial evidence which restricts our understanding of centennial to millennial timescale dynamics of the GrIS. Here we present glacial geomorphological mapping, for upper Godthåbsfjord, covering 5800 km2 at a scale of 1:92,000, using a combination of ASTER GDEM V2, a medium-resolution DEM (error

The Younger Dryas (YD) was a period of rapid climate cooling that occurred at the end of the last glaciation. Here, we present the first palaeoglacier-derived reconstruction of YD precipitation across Europe, determined from 122 reconstructed glaciers and proxy atmospheric temperatures. Positive precipitation anomalies (YD versus modern) are found along much of the western seaboard of Europe and across the Mediterranean. Negative precipitation anomalies occur over the Fennoscandian ice sheet, the North European Plain, and as far south as the Alps. This is consistent with a more southerly and zonal storm track, which is linked to a concomitant southern location of the Polar Frontal Jet Stream, generating cold air outbreaks and enhanced cyclogenesis, especially over the eastern Mediterranean. This atmospheric configuration resembles the modern Scandinavian (SCAND) circulation over Europe (a blocking high pressure over Scandinavia pushing storm tracks south and east), and by analogy, a seasonally varying palaeoprecipitation pattern is interpreted., Science Advances, 6 (50), ISSN:2375-2548

Improving our understanding of the processes governing mass loss from the cryosphere is inhibited by a lack of data at high spatial and temporal resolution. Satellite sensors can provide regional to global scale coverage of glacier processes but fail to resolve processes that occur rapidly, for example glacier calving. To observe these processes, the glaciology community must invest in new techniques that can monitor these processes adequately and fill this major research gap. Here, we will discuss the implementation of an exciting new radar system that is capable of imaging glacial terrain at a high angular resolution and during most weather conditions. The system, named AVTIS2, operates at 94 GHz (~3 mm) and offers a compromise between imaging resolution and penetration through atmospheric obscurants. AVTIS2 scans mechanically across a scene of interest in defined increments of azimuth and elevation angles and generates a 3D data cube of backscattered power. We use a point to maximum power criterion to generate point clouds and construct Digital Elevation Models (DEMs) of the terrain. Because AVTIS2 is a real aperture radar it does not require the phase stability of interferometric radars and can acquire DEMs irrespective of local environmental conditions. In this work, we have used the AVTIS2 radar to map Rhône Glacier in the Swiss Alps, representing the first ever time a millimetre wave radar has been used in this way. To improve our understanding of the performance of AVTIS2 for mapping glaciers, we have characterised the scattering properties of glacial ice at 94 GHz by calculating its Radar Cross Section (RCS). This is key to understanding the performance of AVTIS2 for mapping glaciers. This study represents the first investigation into the reflectivity of ice at millimetre wavelengths and the utility of millimetre wave radar as a surveying tool. We will report on the future application of this instrument in glaciological studies and the unique perspective it can offer.

We map glacial cirques, and analyse spatial variability in their altitude and aspect to derive a long-term, time-integrated, perspective on climate patterns during former periods of mountain glaciation (likely spanning multiple Quaternary glaciations) in Britain and Ireland. The data reveal that, although air temperatures were important, exposure to moisture-bearing air masses was the key factor in regulating sites of former mountain glacier formation, and indicate that during such periods, moisture supply was largely controlled by North Atlantic westerlies, with notable inland precipitation gradients (precipitation decreasing inland), similar to present day. In places, trends in cirque altitude may also reflect regional differences in the extent of cirque deepening, controlled by the dimensions and dynamics of the glaciers that came to occupy them. Specifically, comparatively deep cirques in coastal locations may reflect the former presence of dynamic (fed by moisture from the North Atlantic), but comparatively small, glaciers (largely confined to their cirques). By contrast, decreasing cirque depth further inland, may reflect the former presence of larger and/or less dynamic ice masses, occupying comparatively continental climatic conditions.

The search for a gas source near to Apache9s Forties Field in the North Sea was motivated by the prediction of an ever-increasing fuel gas shortfall as the field oil rate declined. The Central North Sea is well known for a large number of shallow gas hazards in the Pleistocene section that have historically caused blowouts during exploration and development. These gas accumulations typically show up as small bright anomalies on seismic data. In 2009, a large gas anomaly was identified to the east of Forties, and the Aviat Field was discovered in 2010 when exploration well 22/7-5 was drilled. The Aviat Field reservoir is interpreted to be a subaqueous glacial outwash fan, consisting of silt-grade, rock flour material, deposited in front of a grounded ice sheet in some 400 m of water. Aviat sits on an overcompacted silty mudstone that was deformed by this ice sheet – the Crenulate Marker. The distribution of this horizon implies that the Early Pleistocene ice sheet covered at least the northern half of the UK North Sea. Although the Aviat reservoir is thin (2–9 m thick), the well tests, pressure profiles and geophysical response demonstrate that the reservoir is well connected, extensive (over 35 km 2 ) with high deliverability (up to 18 MMscfd achieved). Aviat was sanctioned in 2014 for development as a fuel gas supply for the Forties Field, with first gas achieved in July 2016.

Source at https://doi.org/10.1016/j.margeo.2019.05.001. Marine-based ice streams are responsible for a significant proportion of the ice mass loss from the present-day Greenland Ice Sheet, East Antarctic Ice Sheet (EAIS) and West Antarctic Ice Sheet (WAIS) but the processes controlling their initiation, evolution and shutdown remain elusive, hindering our understanding of how existing ice masses will respond to predicted future warming. The exposed beds of palaeo-ice streams offer a unique opportunity to study subglacial processes, which are largely inaccessible in contemporary settings. We use high resolution multibeam swath bathymetry data from the Barents Sea to map the geomorphology of a palaeo-ice stream bed, located in Olgastretet (Olga Trough), approximately 75 km southeast of Kong Karls Land and 200 km east of central Svalbard. This reveals evidence for shut down of a marine-based ice stream, followed by a phase of passive retreat or lift-off of the ice stream facilitating preservation of crevasse-squeeze ridges (CSRs). Subsequently, active retreat of the ice margin was re-established and is marked by recessional moraine ridges located upstream of the CSRs. Previously, CSRs have been mainly associated with surging land-terminating ice margins, however our work adds to recent observations of CSRs on the beds of marine-based ice streams, implying that they may be more common than previously thought. It also indicates that marine-based ice streams may switch on- and off in a surge-like manner which has important implications for our understanding of ice stream life cycles and the modelling of ice sheets.

Glacier reconstructions are widely used in palaeoclimatic studies and this paper presents a new semi-automated method for generating glacier reconstructions: GlaRe, is a toolbox coded in Python and operating in ArcGIS. This toolbox provides tools to generate the ice thickness from the bed topography along a palaeoglacier flowline applying the standard flow law for ice, and generates the 3D surface of the palaeoglacier using multiple interpolation methods. The toolbox performance has been evaluated using two extant glaciers, an icefield and a cirque/valley glacier from which the subglacial topography is known, using the basic reconstruction routine in GlaRe. Results in terms of ice surface, ice extent and equilibrium line altitude show excellent agreement that confirms the robustness of this procedure in the reconstruction of palaeoglaciers from glacial landforms such as frontal moraines. GlaRe is a tool for palaeoglacier 3D surface reconstruction from bed topography.GlaRe is coded in Python and runs in ArcGIS as a toolbox.The theory of perfect plasticity equilibrium glacier profile is considered.Interpolation methods for glacier 3D surface creation are described and discussed.GlaRe is tested with two extant glaciers, showing a small, acceptable error.

The equilibrium-line altitudes (ELAs) of reconstructed palaeoglaciers have been widely used to assess palaeoclimatic conditions, yet this concept has rarely been tested using modern glaciers. To address this shortcoming, correlations between the ELAs of 513 modern cirque glaciers and present-day climatic and topographic variables across Scandinavia, as well as regional trends in ELA and climate, are analysed. ELAs are calculated using the Area-Altitude-Balance-Ratio method, with a ratio of 1.5 ± 0.4. Results indicate that glacier ELAs are strongly correlated with distance from the coast. This reflects the present-day precipitation pattern of the region (characterised by high precipitation near the sea) and demonstrates a climate dominated by a maritime-continental transition. Temperature explains differences in glacier ELA regional trends as well as ELA changes with latitude. Following standard meteorological convention, Scandinavia is divided into two macro-climate regions and analyses are run within the macro-regions as well as the complete dataset. The strength of correlations between ELA and precipitation increases when the study is divided into northern and southern macro-regions. These results test long held assumptions about relationships between climate and cirque glacier ELA, which is of particular relevance to palaeoclimatic studies based on the reconstruction of former cirque glaciers.

The englacial entrainment of basal debris during surges presents an opportunity to investigate processes acting at the glacier bed. The subsequent melt-out of debris-rich englacial structures during the quiescent phase produces geometrical ridge networks on glacier forelands that are diagnostic of surge activity. We investigate the link between debris entrainment and proglacial geomorphology by analyzing basal ice, englacial structures, and ridge networks exposed at the margins of Tunabreen, a tidewater surge-type glacier in Svalbard. The basal ice facies display clear evidence for brittle and ductile tectonic deformation, resulting in overall thickening of the basal ice sequence. The formation of debris-poor dispersed facies ice is the result of strain-induced metamorphism of meteoric ice near the bed. Debris-rich englacial structures display a variety of characteristics and morphologies and are interpreted to represent the incorporation and elevation of subglacial till via the squeezing of till into basal crevasses and hydrofracture exploitation of thrust faults, reoriented crevasse squeezes, and preexisting fractures. These structures are observed to melt-out and form embryonic geometrical ridge networks at the base of a terrestrially grounded ice cliff. Ridge networks are also located at the terrestrial margins of Tunabreen, neighboring Von Postbreen, and in a submarine position within Tempelfjorden. Analysis of network characteristics allows these ridges to be linked to different formational mechanisms of their parent debris-rich englacial structures. This in turn provides an insight into variations in the dominant tectonic stress regimes acting across the glacier during surges.

This paper investigates the controls on the formation of subglacially eroded bedrock bedforms beneath the topographically confined region upstream of the Uummannaq Ice Stream (UIS). During the last glacial cycle, palaeoglaciological conditions are believed to have been similar for all sites in the study, characterised by thick, fast-flowing ice moving over a rigid bedrock bed. Classic bedrock bedforms indicative of glacially eroded terrain were mapped, including p-forms, roches moutonnees, and whalebacks. Bedform long axes and plucked face orientations display close correlation (parallel and perpendicular) to palaeo-ice flow directions inferred from striae measurements. Across all sites, elongation ratios (length to width) varied by an order of magnitude between 0.8:1 and 8.4:1. Bedform properties (length, height, width, and long axis orientation) from four subsample areas, form morphometrically distinct populations, despite their close proximity and hypothesised similarity in palaeoglaciological conditions. Variations in lithology and geological structures (e.g., joint frequency; joint dip; joint orientation; bedding plane thickness; and bedding plane dip) provide lines of geological weakness, which focus the glacial erosion, in turn controlling bedform geometries. Determining the relationship (s) between bedding plane dip relative to palaeo-ice flow and bedform shape, relative length, amplitude, and wavelength has important ramifications for understanding subglacial bed roughness, cavity formation, and likely erosion style (quarrying and/or abrasion) at the ice-bed interface. This paper demonstrates a direct link between bedrock bedform geometries and geological structure and emphasises the need to understand bedrock bedform characteristics when reconstructing palaeoglaciological conditions.

Regional scale studies of glacial cirque metrics provide key insights on the (palaeo) environment related to the formation of these erosional landforms. The growing availability of high resolution terrain models means that more glacial cirques can be identified and mapped in the future. However, the extraction of their metrics still largely relies on time consuming manual techniques or the combination of, more or less obsolete, GIS tools. In this paper, a newly coded toolbox is provided for the automated, and comparatively quick, extraction of 16 key glacial cirque metrics; including length, width, circularity, planar and 3D area, elevation, slope, aspect, plan closure and hypsometry. The set of tools, named ACME (Automated Cirque Metric Extraction), is coded in Python, runs in one of the most commonly used GIS packages (ArcGIS) and has a user friendly interface. A polygon layer of mapped cirques is required for all metrics, while a Digital Terrain Model and a point layer of cirque threshold midpoints are needed to run some of the tools. Results from ACME are comparable to those from other techniques and can be obtained rapidly, allowing large cirque datasets to be analysed and potentially important regional trends highlighted.

This paper presents the first assessment of the Uummannaq ice stream system (UISS) in West Greenland. The UISS drained ~6% of the Greenland ice sheet (GrIS) at the Last Glacial Maximum (LGM). The onset of the UISS is a function of a convergent network of fjords which feed a geologically controlled trough system running offshore to the shelf break. Mapping, cosmogenic radiogenic nuclide (CRN) dating, and model output reveal that glacially scoured surfaces up to 1266 m above sea level (asl) in fjord-head areas were produced by warm-based ice moving offshore during the LGM, with the elevation of warm-based ice dropping westwards to ~700 m asl as the ice stream trunk zone developed. Marginal plateaux with allochthonous blockfields suggest that warm-based ice produced till and erratics up to ~1200 m asl, but CRN ages and weathering pits suggest this was pre-LGM, with only cold-based ice operating during the LGM. Deglaciation began on the outer shelf at ~14.8 cal. kyrs B.P., with Ubekendt Ejland becoming ice free at ~12.4 ka. The UISS then collapsed with over 100 km of retreat by ~11.4 ka–10.8 cal. kyrs B.P., a rapid and complex response to bathymetric deepening, trough widening, and sea-level rise coinciding with rapidly increasing air temperatures and solar radiation, but which occurred prior to ocean warming at ~8.4 cal. kyrs B.P. Local fjord constriction temporarily stabilized the unzipped UISS margins at the start of the Holocene before ice retreat inland of the current margin at ~8.7 ka.

South Africa experiences a range of different climatic regimes and is thus an ideal region to investigate Late Pleistocene environmental and climate change. However, detailed quantifiable palaeoclimate data are sparse in the region. In particular, reliable palaeoclimatic data are essential to resolve ongoing controversies regarding temperature depression and moisture availability during glacial periods in the sub-continent. Small glaciers close to the glaciation threshold are highly sensitive to changes in temperature and precipitation and are therefore ideal indicators of past climatic conditions during their existence. This paper derives some of the first quantitative data on Last Glacial Maximum (LGM) palaeoprecipitation in southern Africa, based on glacier reconstruction and mass balance modelling for the Lesotho Highlands. The reconstruction of former glaciers and their dynamics enables the determination of glacier viability under specific climatic envelopes. Glacier reconstructions at five sites in the Lesotho Highlands yield palaeoglaciers with Equilibrium Line Altitudes (ELAs) ranging from 3095 to 3298 m a.s.l., and reconstructed steady-state mass balance and flow dynamics are comparable with modern analogues. Topoclimatic factors are investigated, with temperature-radiation-index modelling indicating that topographic shading was an important factor determining the existence of small glaciers in this region. The occurrence of glaciation in the Drakensberg during the LGM suggests a potential increase in precipitation and change in its seasonality. Such trends are likely associated with an increased frequency of westerly wave (cold front) disturbances due to the northward shift of pressure belts, which would also increase precipitation as snow at higher altitudes. The application of a high resolution climate model (HadAM3h) to test this, displays a change in the seasonal timing of precipitation during the Last Glacial cycle, with a decrease in precipitation evident during the summer months. This is likely to have had important implications for the mass balance and survival of small niche glaciers in the region, with more precipitation falling during the spring – winter – autumn months as snow.

Ice streams drain large portions of ice sheets and play a fundamental role in governing their response to atmospheric and oceanic forcing, with implications for sea-level change. The mechanisms that generate ice stream flow remain elusive. Basal sliding and/or bed deformation have been hypothesized, but ice stream beds are largely inaccessible. Here we present a comprehensive, multi-scale study of the internal structure of mega-scale glacial lineations (MSGLs) formed at the bed of a palaeo ice stream. Analyses were undertaken at macro- and microscales, using multiple techniques including X-ray tomography, thin sections and ground penetrating radar (GPR) acquisitions. Results reveal homogeneity in stratigraphy, kinematics, granulometry and petrography. The consistency of the physical and geological properties demonstrates a continuously accreting, shallow-deforming, bed and invariant basal conditions. This implies that ice stream basal motion on soft sediment beds during MSGL formation is accommodated by plastic deformation, facilitated by continuous sediment supply and an inefficient drainage system., Ice streams are fundamental to ice sheet dynamics, but the mechanisms controlling their flow remain elusive. Here, the authors perform macro- and microscale analyses of mega-scale glacial lineations, which indicate a continuously accreting, shallow-deforming bed during ice stream flow.

A 200-km-long and 10-km-wide linear assemblage of till-filled geometrical ridges on the bed of the Maskwa palaeo-ice stream of the late Wisconsinan southwest Laurentide Ice Sheet are interpreted as crevasse-squeeze ridges (CSR) developed during internal flow unit reorganization, immediately prior to ice stream shutdown. Ridge orientations are predominantly orientated WNW–ESE, with a subordinate WSW–ENE alignment, both indicative of ice fracture development transverse to former ice stream flow, as indicated by NNE–SSW aligned MSGL. Subglacial till injection into basal and/or full depth, mode I and II crevasses occurred at the approximate centreline of the ice stream, in response to extension and fracturing. Landform preservation indicates that this took place during the final stages of ice streaming, immediately prior to ice stream shutdown. This linear zone of ice fracturing therefore likely represents the narrowing of the fast-flowing trunk, similar to the plug flow identified in some surging valley glaciers. Lateral drag between the final active flow unit and the slower moving ice on either side is likely recorded by the up-ice bending of the CSR limbs. The resulting CSR corridor, here related to an individual ice stream flow unit, constitutes a previously unreported style of crevasse infilling and contrasts with two existing CSR patterns: (1) wide arcuate zones of CSRs related to widespread fracturing within glacier surge lobes; and (2) narrow concentric arcs of CSRs and recessional push moraines related to submarginal till deformation at active temperate glacier lobes.

The Uummannaq region is a mosaic of glacial landsystems, consistent with hypothesised landscape distribution resulting from variations in subglacial thermal regime. The region is dominated by selective linear erosion which has spatially and altitudinally partitioned the landscape. Low altitude areas are dominated by glacial scour, with higher elevations are dominated by plateaux or mountain valley and cirque glaciers. The appearance and nature of each landscape type varies locally with altitude and latitude, as a function of bedrock geology and average glacial conditions. Selective linear erosion has been a primary control on landscape distribution throughout Uummannaq, leading to plateau formation and the growth of a coalescent fjord system in the Uummannaq region. This has allowed the development of the Uummannaq ice stream’s (UIS) onset zone during glacial periods. Fjord development has been enhanced by a down-stream change in geology to less-resistant lithologies, increasing erosional efficiency and allowing a single glacial channel to develop, encouraging glacier convergence and the initiation of ice streaming. The landscape has been affected by several periods of regional uplift from 33 Ma to present, and has been subject to subsequent fluvial and glacial erosion. Uplift has removed surfaces from the impact of widespread warm-based glaciation, leaving them as relict landsurfaces. The result of this is a regional altitude-dependant continuum of glacial modification, with extreme differences in erosion between high and low elevation surfaces. This study indicates that processes of long-term uplift, glacial erosion/protection, and spatial variability in erosion intensity have produced a highly partitioned landscape.

The Buchan Gravels Formation (BGF) takes the form of a series of gravel deposits of intriguing age and origin in North-East Scotland. The BGF is divided into two geographically-distinct groups, the Windy Hills Gravel Member (WHGM) and the Buchan Ridge Gravel Member (BRGM). The WHGM occurs in central Buchan, and is predominantly composed of quartzite gravels considered to have been deposited by eastwardly-flowing rivers. In contrast the BRGM is found in eastern Buchan, and is composed largely of flint-rich gravels, the precise origins of which are still under debate. Both gravel members are of considerable age, judging by the number of rotted clasts they contain. In addition, both presently occupy high ground, despite seeming to have originated as water-lain deposits. Although of unknown age, the BGF members provide evidence of topographic inversion since their deposition, and quite possibly preglacial age.

With the increasing use of digital elevation models in palaeo-glacier reconstructions and the availability of freeware spreadsheets the Area-Altitude Balance Ratio (AABR) and Balance Ratio (BR) methods are becoming increasingly used in palaeo-glacier reconstruction for estimating Equilibrium Line Altitudes (ELA) and subsequently deriving quantitative estimates of palaeo-climate. While there are many data detailing contemporary Accumulation Area Ratios, there are still only a few studies that have established, from contemporary environments, AABR/BR ratios. Publicly available glacier mass balance (World Glacier Monitoring Service, US Geological Survey, and Norwegian Water Directorate) and spatial extent datasets provided the basis for this research. From a time series of mass balance, regressing specific net balance against ELA allows the zero net balance ELA to be identified. Once the zero balance ELA is established, the glacier hypsometry above and below the ELA is defined. The AABR/BR is calculated by using (the right hand side) the following: AABR = b n a b / b n a c = ( z ¯ a c A a c ) / ( z ¯ a b A a b ) , where, bnab and bnac are the net mass balance gradients in the ablation and accumulation zones respectively, z ¯ a c and z ¯ a b are the area-weighted mean altitudes of the accumulation and ablation areas respectively and Aac and Aab are the areas of the accumulation and ablation areas respectively. AABRs are calculated for a suite of glaciers located across a range of climatic zones and glacier types, with Antarctica being excluded. The following “representative” AABRs are found: a global AABR = 1.75 ± 0.71; Mid-latitude maritime = 1.9 ± 0.81; High-latitude = 2.24 ± 0.85; North America – West Coast = 2.09 ± 0.93; North America – Eastern Rockies = 1.11 ± 0.1; Canadian Arctic = 2.91 ± 0.35; Svalbard = 2.13 ± 0.52; Western Norway = 1.5 ± 0.4; European Alps = 1.59 ± 0.6; Central Asia = 1.75 ± 0.56; Kamchatka = 3.18 ± 0.16. This study provides an empirically derived dataset characterising AABR ratios which may be used for ELA estimation in palaeo-glacier reconstructions and for palaeo-climate quantification.

Please click here to download the map associated with this article. A1:30,000 scale map of the snout and proglacial landscape of the surging Icelandic glacier Tungnaarjokull, based upon aerial photography from 1995, immediately after a surge, allows an assessment of the spatial variability in landform-sediment imprints of catastrophic glacier advance across upland bedrock ridges. The ice-margin parallel alignment of the bedrock ridges locally strongly directs proglacial meltwater drainage and initiates strong compression in the ice during surging, resulting in the development of prominent ice-cored hummocky moraine composed of glacifluvial sediment. Diagnostic surge landforms elsewhere on the foreland include thrust block and push moraines, overridden ice-cored thrust block moraines, crevasse squeeze ridges, long flutings, hummocky moraine and ice-cored, pitted outwash.

Evidence for former fast glacier flow (ice streaming) in the southwest Laurentide Ice Sheet is identified on the basis of regional glacial geomorphology and sedimentology, highlighting the depositional processes associated with the margin of a terrestrial terminating ice stream. Preliminary mapping from a digital elevation model of Alberta identifies corridors of smoothed topography and corridor-parallel streamlined landforms (megaflutes to mega-lineations) that display high levels of spatial coherency. Ridges that lie transverse to the dominant streamlining patterns are interpreted as: (a) series of minor recessional push moraines; (b) thrust block moraines or composite ridges/hill–hole pairs constructed during readvances/surges; and (c) overridden moraines (cupola hills), apparently of thrust origin. Together these landforms demarcate the beds and margins of former fast ice flow trunks or ice streams that terminated as lobate forms. Localised cross-cutting and/or misalignment of flow sets indicates temporal separation and the overprinting of ice streams/lobes. The fast-flow tracks are separated by areas of interlobate or inter-stream terrain in which moraines have been constructed at the margins of neighbouring (competing) ice streams/outlet glaciers; this inter-stream terrain was covered by more sluggish, non-streaming ice during full glacial conditions. Thin tills at the centres of the fast-flow corridors, in many places unconformably overlying stratified sediments, suggest that widespread till deformation may have been subordinate to basal sliding in driving fast ice flow but the general thickening of tills towards the lobate terminal margins of ice streams/outlet glaciers is consistent with subglacial deformation theory. In this area of relatively low relief we speculate that fast glacier flow or streaming was highly dynamic and transitory, sometimes with fast-flowing trunks topographically fixed in their onset zones and with the terminus migrating laterally. The occurrence of minor push moraines and flutings and associated landforms, because of their similarity to modern active temperate glacial landsystems, are interpreted as indicative of ice lobe marginal oscillations, possibly in response to seasonal climatic forcing, in locations where meltwater was more effectively drained from the glacier bed. Further north, the occurrence of surging glacier landsystems suggests that persistent fast glacier flow gave way to more transitory surging, possibly in response to the decreasing size of ice reservoir areas in dispersal centres and also locally facilitated by ice-bed decoupling and drawdown initiated by the development of ice-dammed lakes. Copyright © 2008 John Wiley & Sons, Ltd.

Oksfjordjokelen is located at ∼ 70° N on the Troms–Finnmark border in North Norway. During the Younger Dryas, it was decoupled from and sat just beyond the margin of the Scandinavian Ice Sheet. At this time the major fjords in Troms and Finnmark were ice-free with outlet glaciers from the icefield filling a number of smaller side valleys. Only one outlet from the icefield, Sorfjorddalen, is temporally well-constrained by 14 C dating and association with the Main Shoreline (associated with a period of minimal crustal rebound dated to the Younger Dryas). Sorfjorddalen is reconstructed using a valley centre-line iterative model and assuming a no-slip basal boundary condition. This assumption of cold-based ice is supported by the geomorphological evidence of angular bouldery fronto-lateral moraines formed during the Younger Dryas. The equilibrium line altitude for the Sorfjorddalen is calculated using both the Balance Ratio and Accumulation Area Ratio methods, and this is used to constrain the snout positions (generally to mapped moraines) of the other outlets. This approach assumes similarity of mass balance gradients and geometries of the outlet glaciers which is supported by present-day symmetry of the icefield. This method is extremely useful in such environments where dateable material is often difficult, if not impossible, to find. Some margins terminated in deep water where bathymetry was lacking, making calving quantification problematic with subsequent impacts on equilibrium line altitudes poorly constrained. These deep-water terminating snouts were discounted from subsequent palaeo-climate reconstructions. An empirical equilibrium line altitude temperature-precipitation relationship was used to define limits of climate change required to sustain the reconstructed icefield. Palaeo-precipitation estimates were refined using a palaeo-temperature estimate for the Younger Dryas from Andoya. Calculations of ice flux through the equilibrium line altitude were used to further constrain the mass balance characteristics of the reconstructed icefield and these suggest similarities with ice masses found in the northern (Nordaustlandet) regions of Svalbard.

Please click here to download the map associated with this article. A 1:30,000 scale map poster of the snout and proglacial landscape of the surging Icelandic glacier Bruarjokull, provides a spatial and temporal assessment of the geomorphic impacts of surging in glaciated terrains. Based upon aerial photography from 1998, 1999 and 2000, the map identifies the major landforms that are regarded as diagnostic of glacier surging when viewed in a landsystem framework; specifically, thrust block and push moraines, overridden thrust block moraines, zig-zag eskers, crevasse squeeze ridges, long utings, hummocky moraine and ice-cored, pitted outwash. This landscape imprint, when identi_ed in ancient glaciated terrains, can therefore be used as indicative of surge activity in palaeoglaciological reconstructions.

A toolbox for the automated calculation of glacier equilibrium-line altitudes (ELAs) using the Accumulation Area Ratio, Area-Altitude Balance Ratio, Area-Altitude and Kurowski methods is presented. These are the most commonly-used methods of ELA calculation in palaeo-glacier reconstructions. The toolbox has been coded in Python and runs in ArcGIS requiring only the reconstructed surface of the palaeo-glacier (a DEM) as input. Through fast and automatic calculation this toolbox simplifies the process of ELA determination and can successfully work both for a single glacier and for large datasets of multiple glaciers. We describe Equilibrium Line Altitude calculation methods for palaeoglaciers.We examine suitability of each method for different glacier types.We present a toolbox for automatic ELA calculation on AAR and AABR methods.Toolbox is coded in Python and runs in ArcGIS.Toolbox use and operation are described.

Many tidewater glaciers in Greenland are known to have undergone significant retreat during the last century following their Little Ice Age maxima. Where it is possible to reconstruct glacier change over this period, they provide excellent records for comparison to climate records, as well as calibration/validation for numerical models. These glacier change records therefore allow for tests of numerical models that seek to simulate tidewater glacier behaviour over multi-decadal to centennial timescales. Here we present a detailed record of behaviour from Kangiata Nunaata Sermia (KNS), SW Greenland, between 1859 and 2012, and compare it against available oceanographic and atmospheric temperature data between 1871 and 2012. We also use these records to evaluate the ability of a well-established one-dimensional flow-band model to replicate behaviour for the observation period. The record of terminus change demonstrates that KNS has advanced/retreated in phase with atmosphere and ocean climate anomalies averaged over multi-annual to decadal timescales. Results from an ensemble of model runs demonstrate that observed dynamics can be replicated. Model runs that provide a reasonable match to observations always require a significant atmospheric forcing component, but do not necessarily require an oceanic forcing component. Although the importance of oceanic forcing cannot be discounted, these results demonstrate that changes in atmospheric forcing are likely to be a primary driver of the terminus fluctuations of KNS from 1859 to 2012. We propose that the detail and length of the record presented makes KNS an ideal site for model validation exercises investigating links between climate, calving rates, and tidewater glacier dynamics.

Ground-penetrating radar (GPR) is becoming a commonly applied technique in geomorphology. However, its use in the study of subglacial bedforms has yet to be fully explored and exploited. This paper presents the results of a GPR feasibility study conducted on a drumlinized terrain in Cumbria, UK, where five drumlins were investigated using multiple radar antenna frequencies. The site was selected for the presence of nearby bedrock outcrops, suggesting a shallow drumlinized diamict–bedrock contact and a permeable lithology. Despite the clayey sediment and unfavourable weather conditions, a considerable penetration depth of ~12 m was achieved when using a 50 MHz antenna, with a separation of 1 m, trace spacing of 1 m and 128-fold vertical stack. Results indicate that the drumlinized diamict is in direct erosional contact with the bedrock. While the internal drumlin geometry is generally chaotic on the stoss side, evidence of layering dipping downflow at an angle greater than the drumlin surface profile was found on the lee side. The inter-drumlin areas comprise ~4 m of infill sediment that masks part of the original drumlin profile. Overall, this study indicates that GPR can be deployed successfully in the study of glacial bedform sedimentary architecture.

The elevation and age of surveyed shorelines in St Jonsfjorden, western Spitsbergen, provide a chronology for Late Weichselian deglaciation and a proxy for former ice thickness. Support is provided for previous reports of two sets of shorelines on NW Spitsbergen, the oldest (at 60 m in St Jonsfjorden) dating to a pre‐late Weichselian glaciation and the youngest documenting postglacial rebound. The remarkable survival of the older shorelines suggests that a large area of NW Spitsbergen was either covered by protective, cold‐based ice or was subject to only local glaciation during the late Weichselian even though glacier ice extended to the shelf edge in the Isfjorden Trough. A marine limit of 46 m at the mouth of St Jonsfjorden is compatible with the regional late Weichselian marine limit (LWML) dated to ∼13 ka BP. A partial relative sea level curve and equidistant shoreline diagram are produced for St Jonsfjorden and used in conjunction with relative sea level curves based on data from previous s...

Basal ice samples were collected from ice exposures in a natural subglacial cavity beneath an outlet glacier of Oksfjordjokelen, North Norway. Sediment and cation (Ca 2+ , Mg 2+ , Na + , K + ) concentrations were then determined, and indicate stacking of basal ice units producing a repeat pattern of 'clean firnification ice' overlying sediment-rich ice. All measured cations show correlation with sediment concentration indicating weathering reactions to be the dominant contributor of cations. Regressions of specific sediment surface area per unit volume with cation concentration are performed and used to predict cation concentrations. These predicted values provide an indication of cation relocation within the basal ice sequence. The results suggest limited melting and refreezing resulting in the relocation of predominantly monovalent cations downward through the profile. Exchange of cations into solution during the melting of sediment-rich ice samples has previously been suggested as a source of error in such investigations. Analyses of sediment-free regelation ice spicules formed at the bed show cation concentrations above firnification ice levels and comparable, in many instances, to the basal ice samples.

In spite of a widespread distribution, the way in which plateau icefields affect the glaciation and deglaciation of adjacent terrains is not particularly well-known. This paper aims to identify how the deglaciation of the fjord and plateau terrain of north Norway has influenced the glacial geomorphology and relative sea-level history of both local and adjacent areas and so serve as a model for interpreting similar areas along the continental margins of northwest Europe and elsewhere. The identification of moraines and their relationships with the Main shoreline of northern Norway allows the margins of the Oksfjordjokelen, Svartfjelljokelen and Langfjordjokelen plateau icefields to be identified in the adjacent terrains. In locations where ice margins are uncertain, it is also possible to reconstruct ice limits by means of glacier models appropriately constrained by known local conditions and dates. Earlier glacier margins, characterised in north Norway by ice shelves floating in the local inlets of major fjords, also can be related to known regional shorelines. The distribution of high shoreline fragments, augmented by radiocarbon dates, helps show the extent to which inter-island channels and outermost parts of fjords can become deglaciated relatively early in comparison with published maps of regional deglaciation. Plateau-icefield-centred glaciation became important sometime after 14 000 14C yr BP and was characterised by glacier readvances up to, and in some locations beyond, earlier moraines and raised marine features. Although overlooked until recently, the identification of the influence of plateau icefields on local glaciation, and their interaction with local and regional marine limits, is of great importance in accurate palaeoenvironmental reconstruction. Copyright © 2002 John Wiley & Sons, Ltd.

Tidewater glaciers in Greenland experienced widespread retreat during the last century. Information on their behaviour prior to this is often poorly constrained due to lack of observations, while determining the drivers prior to instrumental records is also problematic. Here we present a record of the dynamics of Kangiata Nunaata Sermia (KNS), southwest Greenland, from its Little Ice Age maximum (LIAmax) to 1859 – the period before continuous air temperature observations began at Nuuk in 1866. Using glacial geomorphology, historical accounts, photographs and GIS analyses, we provide evidence KNS was at its LIAmax by 1761, had retreated by ~5 km by 1808 and a further 7 km by 1859. This predates retreat at Jakobshavn Isbræ by 43–113 years, demonstrating the asynchroneity of tidewater glacier terminus response following the LIA. We use a one-dimensional flowband model to determine the relative sensitivity of KNS to atmospheric and oceanic climate forcing. Results demonstrate that terminus forcing rather than surface mass balance drove the retreat. Modelled glacier sensitivity to submarine melt rates is also insufficient to explain the retreat observed. However, moderate increases in crevasse water depth, driving an increase in calving, are capable of causing terminus retreat of the observed magnitude and timing.

The Quaternary glacial history of the Tweedsmuir Hills, Central Southern Uplands, Scotland, has received little attention since the 1980s, with earlier studies focussing on single lines of geomorphic evidence in isolated valleys. This study presents the first systematic glacial geomorphological assessment of the region, covering approximately 300 km2 with the map designed to be presented at A0. Mapping from remotely sensed imagery and field investigation reveal a large number of moraines and meltwater channels, both within valleys and occasionally extending to the plateau, alongside a range of peri- and para-glacial features, including solifluction lobes, alluvial fans, debris cones, river terraces and rock slope failures. Aspects of the mapped geomorphology are consistent with plateau icefield landsystems mapped elsewhere in Britain and this will hopefully form the basis for palaeoglaciological reconstructions which will improve our understanding of the extent and dynamics of former ice masses in the region.

A detailed study of a proglacial bedrock site and a subglacial cavity of an outlet of Øksfjordjøkelen, Norway, is presented together with observations from the foreland of Konowbreen, Spitsbergen. Striation directions and subglacial observations indicate that local ice-flow paths were highly variable, deviating at angles of approximately 90° from the main ice-flow direction. Stepped bedrock topography appears conducive to the production of highly variable ice-flow paths, because the high bed roughness creates a locally variable stress regime within the ice, including low-pressure, lee-side areas into which ice can flow. If ice flow is sustained along a specific path and the ice contains debris, then abrasion should produce an erosional bedform. Models are proposed whereby locally variable ice-flow patterns could produce erosional bedforms, which would be described as p-forms, purely through mechanical abrasion.

Landform assemblages and associated stratigraphy, sedimentology and structure are used in the reconstruction of palaeo-ice-sheet dynamics in Alberta, western Canada. Interpretations are based upon the modern analogues from four outlet glaciers at the margins of Vatnajokull and Myrdalsjokull, Iceland. In the area between Lloydminster and Lac la Biche, central Alberta, an extensive landform assemblage of megaflutings, crevasse-squeeze ridges and thrust-block-moraine arcs document the former surging of part of the margin of the Laurentide Ice Sheet during later stages of recession. This landform assemblage, including numerous exposures of glacitectonised bedrock and Quaternary sediments, is comparable to the landsystem of the surging glaciers Eyjabakkajokull and Bruarjokull in Iceland. Near High River southern Alberta, the former existence of an ice lobe characterised by active recession is recorded by closely spaced, low-amplitude recessional push moraines that drape tunnel valleys. These are comparable in form and pattern to annual push moraines and fluted till surfaces produced by Breidamerkurjokull and Sandfellsjokull, Iceland, and also include rimmed depressions produced by the escape of artesian water during ice-marginal pushing. This study provides interpretations of the regional glacial geomorphology of Alberta based upon comparisons of form and stratigraphy with modern glacial analogues, and provides an alternative to recent models which invoke large floods of subglacial meltwater to explain many of these same features. Implications for ice dynamics and regional till stratigraphies are discussed. Copyright © 1999 John Wiley & Sons, Ltd.

Plateau icefields occur commonly in glacierized areas and not uncommonly in glaciated mountains. We report on a glacierized area of plateaux and valleys centred round the highest peak Jiehkkevárri (1833 m) in the maritime Lyngen Alps, North Norway. Some valley glaciers are fed by steep, narrow plateau glacier outlets and/or ice avalanching from the plateaux over precipitous cliffs. Plateaux must therefore be considered as “contributing areas”, if they supply ice to valley systems below. Equilibrium line altitudes (ELAs) are calculated for the valley glaciers during the Little Ice Age (LIA), accounting for both input and no input of ice from plateaux above. The results show that ELAs may be at significantly higher altitudes when plateau/x are contributing ice mass. The response of plateau glaciers to climate amelioration since the end of the LIA is somewhat different to that of valley glaciers, which appear to be retreating markedly. These findings have significant implications for the interpretation of moraine systems, glacier dynamics, the construction and reconstruction of present and former ELAs, and palaeoclimates in glacierized and glaciated mountain plateau areas.

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

It is known that regions of warm- and cold-based ice sheets modify and protect the Landscape, respectively. Investigations on a small plateau-top ice field, Øksfjordjøkelen (40 km2), in north Norway have indicated that this situation can exist at a small scale. Margins of the plateau, exposed by ice retreat since AD 1850, provide evidence of a complex basal thermal regime: in some localities blockfields with patterned ground and, in others, abraded and quarried bedrock forelands have been exposed. Exposed blockfields are interpreted as areas covered by cold-based, non-erosive ice. In areas of sliding ice, substantial quantities of erosion are evident. Locally, bedrock shows three joint sets intersecting which produce joint-bounded blocks. Removal of these blocks during the Little Ice Age has produced small rock steps about 5–10 m long and 1–3 m high. Present-day basal sliding velocities at the snout are low (15 m a–1) and ice thickness over the whole glacier is < 190 m. Simple modelling for block removal shows a direct relationship with glacier-sliding velocity and inverse relationship with ice thickness. Preglacial weathering is shown to influence the size of removable blocks.

Complex glacigenic sediment sequences arranged in large arcuate assemblages and demarcating the lobate termini of fast ice flow corridors in western Canada represent the terrestrial equivalents of the trough-mouth fans of the marine palaeo-ice stream record. Intensive sedimentological and stratigraphic investigations at a regional scale are employed in the interpretation of thick units or sequences of diamicton and two depositional scenarios are proposed. First, glacier-marginal till thickening and the stacking of till wedges takes place in areas where an ice stream margin was stationary for short periods of time. Stacks of subglacial traction tills potentially record annual sub-marginal incremental thickening at ice stream margins especially in areas where densely spaced recessional push moraines appear to record seasonal climatic forcing. Second, proglacial lake and valley infilling with glacilacustrine rhythmites and mass flow diamictons is associated with the advection of sub-marginal till into preglacial bedrock depressions and records ice stream marginal oscillations and debris influx into discontinuous proglacial lakes, which act as subaqueous sediment sinks for materials that would otherwise have been used to construct sub-marginal till wedges and moraines. Glacial overriding modifies the deposits produced in both scenarios through deformation and the dislocation and entrainment of bedrock and sediment rafts at the margins of bedrock valley walls, resulting in the widespread development of glacitectonites and megablocks. The occurrence of the thickest deposits as preglacial valley fills may be significant in groundwater siphoning away from subglacial deforming layers and the promotion of sticky spots.

[1] Evidence for extensive crevassing is preserved on the deglaciated forelands of many surging glaciers as crevasse squeeze ridges (CSRs). At some point these crevasses make direct connection with the bed in order to become sediment filled, and full-depth connections have been inferred from turbid water up-wellings in crevasses and the formation of concertina eskers. The dynamics of seven surging glaciers are assessed, using a linear elastic fracture mechanics approach, to determine the likely directions of fracture and controlling parameters for Mode I crevasses. Extensional surface strain rates are insufficient to promote top-down full-depth penetration. For small crevasse spacing (

The history of the Arctic Ocean during the Cenozoic era (0-65 million years ago) is largely unknown from direct evidence. Here we present a Cenozoic palaeoceanographic record constructed from400 m of sediment core from a recent drilling expedition to the Lomonosov ridge in the Arctic Ocean. Our record shows a palaeoenvironmental transition from a warm 'greenhouse' world, during the late Palaeocene and early Eocene epochs, to a colder 'icehouse' world influenced by sea ice and icebergs from the middle Eocene epoch to the present. For the most recent approximately 14 Myr, we find sedimentation rates of 1-2 cm per thousand years, in stark contrast to the substantially lower rates proposed in earlier studies; this record of the Neogene reveals cooling of the Arctic that was synchronous with the expansion of Greenland ice (approximately 3.2 Myr ago) and East Antarctic ice (approximately 14 Myr ago). We find evidence for the first occurrence of ice-rafted debris in the middle Eocene epoch (approximately 45 Myr ago), some 35 Myr earlier than previously thought; fresh surface waters were present at approximately 49 Myr ago, before the onset of ice-rafted debris. Also, the temperatures of surface waters during the Palaeocene/Eocene thermal maximum (approximately 55 Myr ago) appear to have been substantially warmer than previously estimated. The revised timing of the earliest Arctic cooling events coincides with those from Antarctica, supporting arguments for bipolar symmetry in climate change.

The first scientific drilling expedition to the central Arctic Ocean was completed in September 2004. Integrated Ocean Drilling Program Expedition 302, Arctic Coring Expedition (ACEX), recovered sediment cores to 428 meters below seafloor (mbsf) in water depths of ~1300 m, 250 km from the North Pole.Expedition 302's destination was the Lomonosov Ridge, hypothesized to be a sliver of continental crust that broke away from the Eurasian plate at ~56 Ma. As the ridge moved northward and subsided, marine sedimentation occurred and continues to the present, resulting in what was anticipated from seismic data to be a continuous paleoceanographic record. The elevation of the ridge above the surrounding abyssal plains (~3 km) ensured that sediments atop the ridge were free of turbidites. The primary scientific objective of Expedition 302 was to continuously recover this sediment record and to sample the underlying sedimentary bedrock by drilling and coring from a stationary drillship.The biggest challenge during Expedition 302 was maintaining the drillship's location while drilling and coring in 2–4 m thick sea ice that moved at speeds approaching 0.5 kt. Sea-ice cover over the Lomonosov Ridge moves with one of the two major Arctic sea-ice circulation systems, the Transpolar Drift, and responds locally to wind, tides, and currents. Until now, the high Arctic Ocean Basin, known as "mare incognitum" within the scientific community, had never before been deeply cored because of these challenging sea-ice conditions.Initial results reveal that biogenic carbonate is present only in the Holocene–Pleistocene interval. The upper 198 mbsf represents a relatively high sedimentation rate record of the past 18 m.y. and is composed of sediment with ice-rafted debris and dropstones, suggesting that ice-covered conditions extended at least this far back in time. Details of the ice type (e.g., iceberg versus sea ice), timing, and characteristics (e.g., perennial versus seasonal) await further study. A hiatus occurs at 193.13 mbsf, spanning a 25 m.y. interval from the early Miocene to the middle Eocene between ~18 Ma and 43 Ma. The sediment record during the middle Eocene is of dark, organic-rich biosiliceous composition. Isolated pebbles, interpreted as ice-rafted dropstones, are present down to 239 mbsf, well into this middle Eocene interval. Around the lower/middle Eocene boundary an abundance of Azolla spp. occurs, suggesting that a fresh and/or low-salinity surface water setting dominated the region during this time period. Although predrilling predictions based on geophysical data had placed the base of the sediment column at 50 Ma, drilling revealed that the uppermost Paleocene to lowermost Eocene boundary interval, well known as the Paleocene/Eocene Thermal Maximum (PETM), was recovered. During the PETM, the temperature of the Arctic Ocean surface waters exceeded 20°C.Drilling during Expedition 302 also penetrated into the underlying sedimentary bedrock, revealing a shallow-water depositional environment of Late Cretaceous age.

In preparation for IODP Expedition 302, Arctic Coring Expedition (ACEX), a site survey database comprising geophysical and geological data from the Lomonosov Ridge was compiled. The accumulated database includes data collected from ice islands, icebreakers, and submarines from 1961 to 2001. In addition, seismic reflection profiles were collected during Expedition 302 that complement the existing seismic reflection data and facilitate integration between the acoustic stratigraphy and the Expedition 302 drill cores. An overview of these data is presented in this chapter.It is well recognized that collecting geophysical data in ice-covered seas, in particular the Arctic Ocean, is a challenging endeavor. This is because much of the Arctic Ocean is continuously covered with ice thicknesses that vary from 1 to 6 m. Over the continental shelves, sea ice can be absent during summer months, but it is present year-round in the central basins. This ice cover is the most dominant feature of the Arctic Ocean environment. It circulates in the ocean basin in two main circulation patterns: the Transpolar Drift and the Beaufort Gyre (see the "Expedition 302 summary" chapter; Rudels et al., 1996).Expedition 302 sites are located within the less severe of these two ice circulation systems, the Transpolar Drift, which primarily moves sea ice from the shelves where it is formed (the Laptev and East Siberian Seas) across the basin and exits through the Fram Strait. During late summer, concentrations of Arctic sea ice can be Early Arctic Ocean geophysical exploration was performed from ice-drift stations (Weber and Roots, 1990). However, the tracks from these drifting ice stations were controlled "by the whims of nature" (Jackson et al., 1990), preventing detailed, systematic surveys of predetermined target areas. These ice-drift stations were set up on stable icebergs that were trapped in sea ice and moved generally with the large drift patterns, but locally they were erratic, so preselected locations could not be surveyed. In the late 1980s, single icebreakers began to be used for oceanographic survey work in the Arctic Ocean. Between 1991 and 2001, four scientific icebreaker expeditions to the Lomonosov Ridge took place. These cruises all experienced local sea-ice conditions varying between 8/10 and 10/10. During these expeditions, towed geophysical equipment was occasionally damaged or lost, either because of a rapidly closing wake caused by local ice pressure or because ice had cut the air gun array.Conventionally powered icebreakers reached as far as the North Pole for the first time during the 1991 Expedition (Andersen and Carlsonn, 1992; Fütterer, 1992). Geophysical results from this expedition collected two important reflection profiles, AWI-91090 and AWI-91091, that crossed the Lomonosov Ridge between 87° and 88°N. These profiles imaged a ~450 m thick, well-stratified and apparently undisturbed drape of sediments overlying a prominent acoustic unconformity (Jokat et al., 1992) that spawned the idea to conduct a paleoceanographic drilling expedition to this Ridge.The use of US Navy nuclear submarines for geophysical mapping was implemented through the Science Ice Exercise program (SCICEX) (Newton, 2000). The development of the Seafloor Characterization and Mapping Pods (SCAMP), which hold a Chirp subbottom profiler, swath bathymetric profiler, and side scan sonar, was an essential part of the SCICEX program (Chayes et al., 1996). In 1999, the Lomonosov Ridge geophysical database was augmented with acoustic data acquired during the SCICEX program using the SCAMP system mounted on the US nuclear submarine USS Hawkbill (Edwards and Coakley, 2003).

The existing subglacial megaflood explanation of glacial sediment deposition and landform production in south-central Alberta relies upon four sets of observations and associated interpretations: (1) a subglacial genesis for all glacilacustrine sediments lying stratigraphically below a local melt-out till or “ice stagnation facies”; (2) a melt-out genesis for the “ice stagnation facies”; (3) a syn-depositional status for the glacitectonic disturbance visible in most exposures due to periodic ice–bed re-coupling; and (4) a subglacial megaflood origin for a “truncation surface” and clast lag that occurs at the top of the sedimentary exposures and the carving of hummocky terrain and flutes in the area. We provide alternative interpretations of the sediment-landform assemblages of the area and demonstrate that alternative, simpler interpretations of the evidence can be proposed. Specifically, we propose: (1) a proglacial rather than subglacial origin of glacilacustrine sediments; (2) a glacilacustrine origin for the “melt-out till” and its subsequent glacitectonic disturbance by minor glacier readvances; (3) postdepositional rather than syn-depositional glacitectonic disturbance due to a significant advance by glacier ice after the accumulation of a thick sequence of glacilacustrine sediments; (4) that some linear chains of hummocks are the morphological expression of glacitectonic folding and thrusting; (5) that the use of the truncation surfaces to propose a subglacial fluvial origin for hummocky moraine is flawed logic, because they do not constitute the tops of hummocks but rather occur on the interfluves that separate the numerous small coulees incised into the valley sides during postglacial time. Truncation surfaces and clast lags occur locally on the beds of spillway tracts and can be explained as the products of erosion by subaerial spillway water. The mega-flood explanation of flutings and hummocky moraine in the region is also questioned because these landforms record a regional ice flow imprint of mis-aligned and cross-cutting flow sets terminating at series of inset and locally cross-cutting and lobate transverse ridges (moraines). These landform associations preclude a subglacial flood origin for the flutings and demonstrate that the transverse ridges are more appropriately interpreted as recessional push moraines. The similarity of the glacial landforms of this region to the active, temperate glacial landsystem produced by historical glacier recession in modern glacierized catchments, where sheetfloods have not been influential in subglacial landform production, allows us to apply a modern analogue to landscape interpretation that does not include subglacial sheetflooding.

Information assembled in this chapter will help the reader understand the basis for our preliminary conclusions and also enable the interested investigator to select samples for further analysis. This information concerns only shipboard operations and analyses described in the site reports in the Leg 199 Initial Reports volume of the Proceedings of the Ocean Drilling Program. Methods used by various investigators for shore-based analyses of Leg 199 data will be described in the individual contributions published in the Scientific Results volume and in publications in various professional journals.

Glen’s flow law is a well-established general law for steady-state glacier ice deformation, and many laboratory tests and field measurements have been undertaken which have shown the generality of the law to be correct. In Nature, ice deformation is the response of the glacier/ice sheet to the applied self-weight stress of the ice mass (i.e. ice thickness, gravity and ice density) which produces a stress gradient within the ice column. Detailed experimental analyses of ice samples in the laboratory have until now only been undertaken using uniform stress fields in uniaxial or triaxial tests. Obviously the best method for investigating ice in the laboratory would be if stress gradients similar to those found in Nature could be replicated. In the following paper we describe the physical modelling of two (laboratory-prepared) isotropic, polycrystalline ice models (0.75 × 0.25 × 0.18 m) at enhanced gravity levels (80g) in a geotechnical beam centrifuge. Steel plate was placed on top of the ice model, replicating an overburden of approximately 36 m of ice (at 80g). Thus we were able to model the deformation of the lower 14 m of an ice mass approximately 50 m thick. Models are confined laterally by the Perspex strongbox walls, preventing lateral extension within the sample during testing. Models are unconfined on their downslope ends, rendering longitudinal stresses negligible. Deformation can therefore be treated as simple shear. Samples are instrumented with displacement markers and thermocouples. Values for A and n in the flow law derived from the experiments are reasonable and indicate the potential of this method for ice-deformation studies.

The Uummannaq Ice Stream System (UISS) was a convergent cross-shelf ice stream system that operated in West Greenland during the Last Glacial Maximum (LGM). This paper presents new evidence constraining the geometry and evolution of the northern sector of the UISS and considers the factors controlling its dynamic behaviour. Geomorphological mapping, 21 new terrestrial cosmogenic nuclide (TCN) exposure ages, and radiocarbon dating constrain LGM warm-based ice stream activity in the north of the system up to 1400 m a.s.l. Intervening plateaux areas either remained ice free, or were covered by cold-based icefields. Beyond the inner fjords, topography and bathymetry forced ice flow southwards into the Uummannaq Trough, where it coalesced with ice from the south, and formed the trunk zone of the UISS. Deglaciation of the UISS began at 14.9 cal. ka BP. Rapid retreat from the LGM limit was forced by an increase in air temperatures and rising sea level, enhanced by the bathymetric over-deepening of the Uummannaq and Igdlorssuit Sund troughs. Ice reached the inner fjord confines in the northern Uummannaq area by 11.6 ka and experienced an ice marginal stabilisation in Rink–Karrat Fjord for up to 5 ka. This was a function of topographic constriction and bathymetric shallowing, and occurred despite continued climatic forcing. In the neighbouring Ingia Fjord this did not occur. Following this period of stability, ice within Rink–Karrat Fjord retreated, reaching the present ice margin or beyond after 5 ka. The presence of a major ice stream within a mid-fjord setting, during the mid-Holocene and the Holocene Thermal Maximum (∼11–5 ka) is in direct contrast to records of other ice streams throughout West Greenland, which suggest ice had retreated beyond its present margin by 9–7 ka. This demonstrates the potential importance of topographic control on calving margin stability, and its ability to override climatic forcing.