Glacier Margin Research Articles

Changes in glacier surface cover on Baltoro glacier, Karakoram, north Pakistan, 2001–2012

ABSTRACTThe presence of supraglacial debris on glaciers in the Himalaya-Karakoram affects the ablation rate of these glaciers and their response to climatic change. To understand how supraglacial debris distribution and associated surface features vary spatially and temporally, geomorphological mapping was undertaken on Baltoro Glacier, Karakoram, for three time-separated images between 2001–2012. Debris is supplied to the glacier system through frequent but small landslides at the glacier margin that form lateral and medial moraines and less frequent but higher volume rockfall events which are more lobate and often discontinuous in form. Debris on the glacier surface is identified as a series of distinct lithological units which merge downglacier of the convergence area between the Godwin-Austen and Baltoro South tributary glaciers. Debris distribution varies as a result of complex interaction between tributary glaciers and the main glacier tongue, complicated further by surge events on some tributary glaciers. Glacier flow dynamics mainly controls the evolution of a supraglacial debris layer. Identifying such spatial variability in debris rock type and temporal variability in debris distribution has implications for glacier ablation rate, affecting glacier surface energy balance. Accordingly, spatial and temporal variation in supraglacial debris should be considered when determining mass balance for these glaciers through time.

Geomorphology and sedimentology of the Caol Lairig valley, Scottish Highlands: evidence for local glacier margin advance and retreat during the Loch Lomond Stadial

A sedimentological investigation of new sections of Loch Lomond Stadial (LLS) age deposits is presented from Caol Lairig valley, located adjacent to Glen Roy, Lochaber, Scottish Highlands. The ice lobes in Caol Lairig and Glen Roy blocked local fluvial drainage systems forming lakes that cut shorelines, the ‘Parallel Roads of Glen Roy’ (Agassiz, 1840; Jamieson, 1863, 1892). Within Caol Lairig sediment sequences of proximal, distal and deltaic glaciolacustrine sediments and a subglacial till are reported. The till was deposited during ice advance into the valley and the different glaciolacustrine facies formed in the gap between the head of Caol Lairig and the receding ice margin. When the sediments are related to the shoreline and glacial geomorphological evidence, phases of ice advance and ice retreat and the concomitant changes in lake levels are identified. Initially ice retreat in Glen Roy and Caol Lairig was synchronous but after the fall to 325m the ice in Glen Roy retreated more quickly than in Caol Lairig. Differences in the ice thickness and the lake water depth in Glen Roy and Caol Lairig may have lead to preferential calving of the Glen Roy ice margin hastening ice retreat.

A major ice-calving event at Tasman Glacier terminus, Southern Alps, 22 February 2011

ABSTRACTTerminus calving of icebergs is a common mass-loss mechanism from water-terminating glaciers globally, including the lake-calving glaciers in New Zealand’s central Southern Alps. Calving rates can increase dramatically in response to increases in ice velocity and/or retreat of the glacier margin. Here, we describe a large calving event (c. 4.5 × 106 m3) observed at Tasman Glacier, which initiated around 30 min after the MW 6.2 Christchurch earthquake of 22 February 2011. The volume of this calving event was equalled or exceeded only once in a subsequent 13-month-long study. While the temporal association with the earthquake remains intriguing, the effects of any preconditioning factors remain unclear.

Geomorphic and shallow-acoustic investigation of an Antarctic Peninsula fjord system using high-resolution ROV and shipboard geophysical observations: Ice dynamics and behaviour since the Last Glacial Maximum

Detailed bathymetric and sub-bottom acoustic observations in Bourgeois Fjord (Marguerite Bay, Antarctic Peninsula) provide evidence on sedimentary processes and glacier dynamics during the last glacial cycle. Submarine landforms observed in the 50 km-long fjord, from the margins of modern tidewater glaciers to the now ice-distal Marguerite Bay, are described and interpreted. The landforms are grouped into four morpho-sedimentary systems: (i) glacial advance and full-glacial; (ii) subglacial and ice-marginal meltwater; (iii) glacial retreat and neoglaciation; and (iv) Holocene mass-wasting. These morpho-sedimentary systems have been integrated with morphological studies of the Marguerite Bay continental shelf and analysed in terms of the specific sedimentary processes and/or stages of the glacial cycle. They demonstrate the action of an ice-sheet outlet glacier that produced drumlins and crag-and-tail features in the main and outer fjord. Meltwater processes eroded bedrock channels and ponds infilled by fine-grained sediments. Following the last deglaciation of the fjord at about 9000 yr BP, subsequent Holocene neoglacial activity involved minor readvances of a tidewater glacier terminus in Blind Bay. Recent stillstands and/or minor readvances are inferred from the presence of a major transverse moraine that indicates grounded ice stabilization, probably during the Little Ice Age, and a series of smaller landforms that reveal intermittent minor readvances. Mass-wasting processes also affected the walls of the fjord and produced scars and fan-shaped deposits during the Holocene. Glacier-terminus changes during the last six decades, derived from satellite images and aerial photographs, reveal variable behaviour of adjacent tidewater glaciers. The smaller glaciers show the most marked recent retreat, influenced by regional physiography and catchment-area size.

Rapid glacial retreat on the Kamchatka Peninsula during the early 21st century

Abstract. Monitoring glacier fluctuations provides insights into changing glacial environments and recent climate change. The availability of satellite imagery offers the opportunity to view these changes for remote and inaccessible regions. Gaining an understanding of the ongoing changes in such regions is vital if a complete picture of glacial fluctuations globally is to be established. Here, satellite imagery (Landsat 7, 8 and ASTER) is used to conduct a multi-annual remote sensing survey of glacier fluctuations on the Kamchatka Peninsula (eastern Russia) over the 2000–2014 period. Glacier margins were digitised manually and reveal that, in 2000, the peninsula was occupied by 673 glaciers, with a total glacier surface area of 775.7 ± 27.9 km2. By 2014, the number of glaciers had increased to 738 (reflecting the fragmentation of larger glaciers), but their surface area had decreased to 592.9 ± 20.4 km2. This represents a ∼ 24 % decline in total glacier surface area between 2000 and 2014 and a notable acceleration in the rate of area loss since the late 20th century. Analysis of possible controls indicates that these glacier fluctuations were likely governed by variations in climate (particularly rising summer temperatures), though the response of individual glaciers was modulated by other (non-climatic) factors, principally glacier size, local shading and debris cover.

Multiple subglacial till deposition: A modern exemplar for Quaternary palaeoglaciology

The sedimentology of a vertical succession of alternating beds of massive and fissile diamictons on a þorisjökull plateau icefield outlet foreland is employed to assess the evolution of subglacial traction tills at the margins of active temperate glaciers with deformable substrates, where tills appear to form sub-marginal incrementally thickened wedges that display multiple till emplacement events, potentially of annual scale. Lodged boulders display strong A-axes and surface striae alignments which parallel surface flutings, indicating that fluting construction and till emplacement were related to moulding by consistent glacier flow from the SSW during the Little Ice Age. In contrast, clast macrofabrics at the sub-boulder size, not unlike those reported from other Icelandic tills, are not as strong as would be expected in a subglacially sheared medium, indicating shear strains too low for a steady state strain signature. This separation of fabric data has isolated the strain signatures of the lodgement and deformation components of subglacial traction till, whereby the orientations of the largest, lodged clasts record high cumulative shear strains and those of the sub-boulder sized clasts record greater susceptibility to deformation of their enclosing matrix. This is likely due to the effect of clast collisions in clast rich till and the perturbations set up by the numerous large boulders, consistent with observations on till fabrics in flutings and around lodged clasts. A/B plane macrofabric data display unusually high degrees of isotropy, reflective of the more variable orientations of A/B planes, which are thought to reflect A/B plane susceptibility to dip parallel or anastomosing shear planes. A wide range of clast angularity values reflects the localized input of freshly plucked and hence relatively highly angular blocks to the deforming layer, a characteristic of stepped bedrock profiles beneath the snouts of mountain glaciers. Finally, we hypothesize that the massive and fissile units may represent A and B horizons of subglacial deforming layer couplets, and that each couplet could record seasonal emplacement and partial inter-couplet modification near the ice margin. If the latter is the case, then less than 1 m of subglacial till is advected to the glacier margin per (annual?) deformation event.

Detailed subglacial topography and drumlins at the marginal zone of Múlajökull outlet glacier, central Iceland: Evidence from low frequency GPR data

New ground penetrating radar (GPR) observations on the Múlajökull surge-type outlet glacier, central Iceland, are presented. Overall 10.5 km of GPR profile lines were recorded parallel to the glacier margin in August, 2015. Detailed GPR investigations combined with high-accuracy GPS measurements allowed to build a high-resolution model of the subglacial topography. We provide new evidence of streamlined ridges beneath Múlajökull’s marginal zone interpreted as drumlins and show the location of the upper edge of the drumlin field. This discovery improves understanding of the location, morphology and development of drumlins as other geophysical observations of subglacial bedforms beneath modern outlet glaciers are quite rare. The location of drumlins corresponds with the position of the major sets of crevasses in the digital elevation model (2008) suggesting the presence of additional drumlins beneath such crevasses in the ice-marginal zone. We suggest this semi-circular pattern of crevasses to be formed due to the variable glacier strain rates created by the subglacial topography. Numerous hyperbolic diffractions representing reflections of englacial channels are found in radar profiles suggesting a well-developed channelized drainage system of a surge-type glacier in its quiescence phase. The calculated thinning of the ice surface in the investigated area (0.65 km2) is on average 17.9 m during 2008–2015.

Properties and processes of recently established soils from deglaciation of Cierva Point, Western Antarctic Peninsula

For more than sixty years the Antarctic Peninsula has experienced significant temperature increases that have accelerated glacial retreat. Glacial losses, along with the relatively warm and moist climatic conditions of the region, have increased the rate of soil development. The objective of this study is to study the properties and genesis of soils at Cierva Point, which is located in the zone of maximum warming along the western Antarctic Peninsula. Cierva Point is a terraced, steeply sloping, ice-free peninsula containing a small retreating glacier. The peninsula contains a large penguin rookery and significant areas of moss buildup. Twenty-seven soils were described; physical and chemical properties from each horizon were analyzed. Four categories of soil were identified: acidic (pH<5), neutral (pH>5), moss-dominated (high organic matter accumulations), and ornithogenic (high phosphorus accumulations). Neutral soils were newly formed soils which had undergone the least development and were located closest to the glacier margin. Acidic soils were located farthest from the glacier margin, allowing for a greater nutrient leaching to occur; these soils have extremely low pH values (as low as 3.5) but did not have the high phosphorus accumulations found in ornithogenic soils or the high soil carbon content found in moss-dominated soils. In a region with rapidly retreating glaciers, such as the Antarctic Peninsula, proximity to the glacier margin becomes an important factor determining soil properties. Soils farther from the glacier have had more time to be affected by leaching, penguin activity, and moss buildup.

Benthic foraminiferal faunas reveal transport dynamics and no-analog environments on a glaciated margin (Gulf of Alaska)

Paleoecological and faunal-based paleoenvironmental studies rely on fossil assemblages that have high fidelity to the once-living faunas and to the target environment. However, many sedimentary records contain multiple depositional facies, transported sediments with their associated fossils, and varying degrees of taphonomic alteration, which can confound interpretations. Here we combine measures of compositional fidelity, modern analog faunal methods, sedimentary analyses, and taphonomic scoring to examine the history of sediment transport and environmental change in a ~60,000year continental slope record from the Gulf of Alaska using benthic foraminiferal assemblages. These assemblages generally have good compositional fidelity to modern faunas in the Gulf of Alaska, but are not necessarily faithful to the modern continental slope. Fossil benthic foraminiferal assemblages with modern analogs from shelf and slope environments are intercalated downcore suggesting episodes of sedimentary transport to the slope site. Fossil assemblages without modern analogs in this record appear ecologically, rather than taphonomically, derived and thus suggest that the range of past environmental variation in the Gulf of Alaska is not captured by modern spatial variation. These no-analog fossil assemblages are allied with analog assemblages using similarity in taxonomic and sedimentary characteristics, permitting analysis of environmental change in shelf and slope settings from a single core. The faunal composition of the no-analog assemblages suggests the Gulf of Alaska slope experienced lower oxygen conditions in the past than observed in the modern gulf. Lower productivity is also suggested for some shelf samples, however geochemical proxy data are necessary to fully interpret the no-analog assemblages.

Controls on microalgal community structures in cryoconite holes upon high-Arctic glaciers, Svalbard

Abstract. Glaciers are known to harbor surprisingly complex ecosystems. On their surface, distinct cylindrical holes filled with meltwater and sediments are considered hot spots for microbial life. The present paper addresses possible biological interactions within the community of prokaryotic cyanobacteria and eukaryotic microalgae (microalgae) and relations to their potential grazers, such as tardigrades and rotifers, additional to their environmental controls. Svalbard glaciers with substantial allochthonous input of material from local sources reveal high microalgal densities. Small valley glaciers with high sediment coverages and high impact of birds show high biomasses and support a high biological diversity. Invertebrate grazer densities do not show any significant negative correlation with microalgal abundances but rather a positive correlation with eukaryotic microalgae. Shared environmental preferences and a positive effect of grazing are the proposed mechanisms to explain these correlations. Most microalgae found in this study form colonies (&lt; 10 cells, or &gt; 25 µm), which may protect them against invertebrate grazing. This finding rather indicates grazing as a positive control on eukaryotic microalgae by nutrient recycling. Density differences between the eukaryotic microalgae and prokaryotic cyanobacteria and their high distinction in redundancy (RDA) and principal component (PCA) analyses indicate that these two groups are in strong contrast. Eukaryotic microalgae occurred mainly in unstable cryoconite holes with high sediment loads, high N : P ratios, and a high impact of nutrient input by bird guano, as a proxy for nutrients. In these environments autochthonous nitrogen fixation appears to be negligible. Selective wind transport of Oscillatoriales via soil and dust particles is proposed to explain their dominance in cryoconites further away from the glacier margins. We propose that, for the studied glaciers, nutrient levels related to recycling of limiting nutrients are the main factor driving variation in the community structure of microalgae and grazers.

Delineation of Debris-Covered Glaciers Based on a Combination of Geomorphometric Parameters and a TIR/NIR/SWIR Band Ratio

Accurate mapping of glaciers is important for the management of water resources, studying glacier mass-balance, and monitoring glacier health. However, many glaciers are partially covered by debris of varying thicknesses, and these debris-covered glacier areas are difficult to distinguish clearly from the adjacent valley rock using optical remote sensing data due to their similar reflectance in the visible-to-near-infrared (VNIR) wavelength region. For better detection of the debris-covered glacier margin, a new method was proposed here which considers glacier terrain features (concave and convex landscapes) as well as VNIR reflectance, shortwave-infrared reflectance (SWIR), and thermal infrared (TIR) information. The proposed method uses several geomorphometric parameters (slope, plan, and profile curvature) and a Landsat Thematic Mapper (TM) band ratio image TM TIR/(TM NIR/TM SWIR) for mapping the Yengisogat glacier in the Shaksgam valley of China. The final debris-covered glacier boundary is generated by thresholding the band ratio image and overlaying it onto the result derived from cluster analysis performed using plan, profile curvature, and combined with mean of slope information. Evaluation of the final debris-covered glacier outline was carried out through comparison with GIS data from several reference data sets, and the final Yengisogat glacier outline had a difference of less than 1% in area compared to the reference data sets.

The lateglacial lakes of Glens Roy, Spean and vicinity (Lochaber district, Scottish Highlands)

This paper summarises the evidence for glacial ice advance into lower Glen Spean during the Loch Lomond Stadial which involved the blockage of westward-flowing drainage to form a series of ice-dammed lakes, the former surfaces of which are marked by prominent shorelines. Detailed mapping of glacigenic landforms and instrumental levelling of the shorelines reveals a dynamic interplay between the glacier margins and lake formation. Subsequent deglaciation led to lowering of the lake levels, at times by catastrophic drainage beneath the ice (jökulhlaup). The abandoned shorelines have been warped and dislocated in numerous places as a result of glacio-isostatic deformation, faulting and landslip activity. The pattern of retreat of the ice can be deduced from the mapped distributions of retreat moraines and the levelled altitudes of numerous kame and fluvial terrace fragments. The sequence of events outlined in this paper provides important context for understanding the evolution of the landscape of the Glen Roy area during the Loch Lomond Stadial, and a prelude to more recent studies reported in other contributions to this thematic issue.

Geodetic mass balance record with rigorous uncertainty estimates deduced from aerial photographs and lidar data – Case study from Drangajökull ice cap, NW Iceland

Abstract. In this paper we describe how recent high-resolution digital elevation models (DEMs) can be used to extract glacier surface DEMs from old aerial photographs and to evaluate the uncertainty of the mass balance record derived from the DEMs. We present a case study for Drangajökull ice cap, NW Iceland. This ice cap covered an area of 144 km2 when it was surveyed with airborne lidar in 2011. Aerial photographs spanning all or most of the ice cap are available from survey flights in 1946, 1960, 1975, 1985, 1994 and 2005. All ground control points used to constrain the orientation of the aerial photographs were obtained from the high-resolution lidar DEM. The lidar DEM was also used to estimate errors of the extracted photogrammetric DEMs in ice- and snow-free areas, at nunataks and outside the glacier margin. The derived errors of each DEM were used to constrain a spherical semivariogram model, which along with the derived errors in ice- and snow-free areas were used as inputs into 1000 sequential Gaussian simulations (SGSims). The simulations were used to estimate the possible bias in the entire glaciated part of the DEM and the 95 % confidence level of this bias. This results in bias correction varying in magnitude between 0.03 m (in 1975) and 1.66 m (in 1946) and uncertainty values between ±0.21 m (in 2005) and ±1.58 m (in 1946). Error estimation methods based on more simple proxies would typically yield 2–4 times larger error estimates. The aerial photographs used were acquired between late June and early October. An additional seasonal bias correction was therefore estimated using a degree-day model to obtain the volume change between the start of 2 glaciological years (1 October). This correction was largest for the 1960 DEM, corresponding to an average elevation change of −3.5 m or approx. three-quarters of the volume change between the 1960 and the 1975 DEMs. The total uncertainty of the derived mass balance record is dominated by uncertainty in the volume changes caused by uncertainties of the SGSim bias correction, the seasonal bias correction and the interpolation of glacier surface where data are lacking. The record shows a glacier-wide mass balance rate of Ḃ = −0.26 ± 0.04 m w.e. a−1 for the entire study period (1946–2011). We observe significant decadal variability including periods of mass gain, peaking in 1985–1994 with Ḃ = 0.27 ± 0.11 m w.e. a−1. There is a striking difference when Ḃ is calculated separately for the western and eastern halves of Drangajökull, with a reduction of eastern part on average ∼ 3 times faster than the western part. Our study emphasizes the need for applying rigorous geostatistical methods for obtaining uncertainty estimates of geodetic mass balance, the importance of seasonal corrections of DEMs from glaciers with high mass turnover and the risk of extrapolating mass balance record from one glacier to another even over short distances.

Bouldery debris mantle deposited by cold-based ice offshore of the Vestfold Hills, East Antarctica

Streamlined subglacial sediments are common in seafloor bathymetric images from many glaciated margins. Less common are seafloor features left by cold-based ice. The shallow waters around the now largely ice-free Vestfold Hills in East Antarctica (Fig. 1a, e) show few streamlined sedimentary features, even though the area has clearly been glaciated as implied by striated bedrock, moraine ridges and abundant erratic boulders on adjacent exposed land. A likely explanation for the absence of streamlined subglacial landforms is that the area was glaciated by ice frozen to its bed. Fig. 1. Multibeam swath bathymetry, outcrop photo and topographic profiles of boulder-rich debris mantle and sand ribbons from the Vestfold Hills coastal zone, East Antarctica. ( a ) Sun-illuminated bathymetric image of Airport Beach Embayment showing the debris mantle. Ice-keel ploughmarks are shown outside the embayment. Acquisition system Kongsberg EM3002. Frequency 300 kHz. Grid-cell size 2 m. ( b ) Close-up of debris mantle showing individual boulders. ( c ) Photograph of bouldery debris mantle above sea level. Large boulder is 4 m in diameter. ( d ) Multibeam image of sand ribbons and boulders. ( e ) Location of study area (red …

Cascades and plunge pools on the continental slope of the Gulf of Alaska

More than 321 400 km2 of seafloor in the Gulf of Alaska was mapped in 2005 (Gardner & Mayer 2005). Both bathymetry and high-resolution backscatter data were collected from the R/V Kilo Moana . The resulting digital terrain models and backscatter mosaics provide a remarkable view of the processes on a tectonically active, glaciated margin. In the course of these surveys several morphological features, similar to cascades and plunge pools found beneath terrestrial waterfalls, were identified on the continental slope. Although several cascade-like features are seen along the continental slope of the southeastern Alaskan margin, the most prominent is found SW of Yakutak Bay and south of the Malispina Glacier which emanates from the St Elias Mountain Range (Fig. 1a, b). The St Elias Range includes some of the highest mountains in North America with remarkable vertical relief, for example Mount St Elias rises to 5489 m above sea level in less than 16 km horizontal distance (Fig. 1a, b). Offshore of Yakutak Bay is the Yakutak Valley, a large, glacially excavated, submarine valley that cuts NE–SW across the continental shelf. Yakutak Valley originates in Yakutak Bay with a width of approximately 50 km and a depth of 120 m as it reaches the shelf break 90 km from the mouth of the bay (Fig. 1a). Fig. 1. Multibeam bathymetry and backscatter along the SE Alaskan margin. ( a …

About this title ‐ Atlas of Submarine Glacial Landforms: Modern, Quaternary and Ancient

New geophysical techniques (multibeam echo sounding and 3D seismics) have revolutionized high-resolution imaging of the modern seafloor and palaeo-shelf surfaces in Arctic and Antarctic waters, generating vast quantities of data and novel insights into sedimentary architecture and past environmental conditions. The Atlas of Submarine Glacial Landforms is a comprehensive and timely summary of the current state of knowledge of these high-latitude glacier-influenced systems. The Atlas presents over 180 contributions describing, illustrating and discussing the full variability of landforms found on the high-latitude glacier-influenced seafloor, from fjords and continental shelves to the continental slope, rise and deep-sea basins beyond. The distribution and geometry of these submarine landforms provide key information on past ice-sheet extent and the direction and nature of ice flow and dynamics. The papers discuss individual seafloor landforms, landform assemblages and entire landsystems from relatively mild to extreme glacimarine climatic settings and on timescales from the modern margins of tidewater glaciers, through Quaternary examples to ancient glaciations in the Late Ordovician.

Skjoldryggen terminal moraine on the mid-Norwegian shelf

Terminal moraines are relatively large ridges of diamictic glacial debris produced at the outermost margins of past glaciers and ice sheets. Their identification on land is important in mapping the maximum extent of Quaternary ice sheets (e.g. Svendsen et al. 2004; Benn & Evans 2010). In marine environments where fast-flowing ice streams reach the shelf edge during full-glacial intervals, moraine ridges are not usually present and the seafloor is characterized by parallel-to-flow streamlined sediments (Ottesen & Dowdeswell 2009). Submarine terminal moraine ridges, by contrast, appear more typical of slower-flowing marine ice margins (Dahlgren et al. 2002; Dowdeswell & Elverhoi 2002; Dowdeswell et al. 2016). A very large ridge, about 150 km long and up to approximately 200 m high relative to the adjacent shelf, is located on the outermost part of the mid-Norwegian continental shelf edge between about 65° and 66° N (Fig. 1a). It is known as Skjoldryggen (‘skjold’ means ‘shield’ and ‘ryggen’ means ‘the ridge’ in Norwegian). Along most of its length, the ridge has a steeper offshore slope relative to …

Debris-flow lobes on the distal flanks of terminal moraines in Spitsbergen fjords

Terminal and recessional moraines formed at the margins of tidewater glaciers are often asymmetrical, with relatively steep ice-distal sides and lower-gradient ice-proximal slopes (e.g. Benn & Evans 2010; Dowdeswell & Vasquez 2013). Their ice-distal slopes, in particular, may be the locations of slope failure and the generation of debris flows that produce elongate lobes of sediment that flow down the distal moraine-ridge flanks. Glacier-derived diamictic sediment forms the major component of most moraine ridges, and debris flows derived from such material would also be expected to produce debrites of heterogeneous particle size and with abrupt lateral margins and terminations. In several Spitsbergen fjords (Fig. 1g), well-defined elongate lobes of sediment are found on the relatively steep (but usually <2°) ice-distal slopes of terminal moraine ridges (Fig. 1) (e.g. Boulton et al. 1996; Plassen et al. 2004; Ottesen & Dowdeswell 2006). The submarine crests of the terminal moraines are typically too shallow to be traversed by survey vessels, so the ridge crests themselves occur just beyond the swath coverage at the left side of each image in Figure 1 at water …

A tidewater glacier landform assemblage in Belcher Inlet, Canadian Arctic

Belcher Glacier, a 35 km long tidewater outlet glacier of the 12 000 km2 ice cap on Devon Island (Dowdeswell et al. 2004), is one of the fastest-flowing glaciers in the Canadian Arctic (Van Wychen et al. 2014) (Fig. 1). Belcher Glacier and neighbouring Fitzroy Glacier to the southeast account for about 55% of the iceberg calving loss from the Devon Ice Cap (Van Wychen et al. 2014). The terminus of Belcher Glacier remained relatively stable between the 1960s (light blue dashed line in Fig. 1a) and 2000 (Landsat 7 satellite image in Fig. 1a). In contrast, the unnamed glacier immediately to the north retreated 2 km during this period (Fig. 1a). Belcher Glacier and the unnamed glacier retreated around 500 and 250 m, respectively, between 2000 and 2014 (dark blue dashed line in Fig. 1a). The bed topography of Belcher Glacier, which is around 250 m below sea level at the present-day glacier margin (Fig. 1c) and remains below sea level in the lower 11 km of the glacier, suggests that its terminus region may become unstable in the event of future retreat. Seafloor mapping of Belcher Inlet beyond the termini of Belcher Glacier and the unnamed glacier (Fig. 1a), together with sub-bottom profiling, provide information about the dynamic behaviour of tidewater glaciers. Fig. 1. ( a ) Swath bathymetry of Belcher Inlet, Arctic Canada (acquired in 2006), superimposed on 2000 Landsat 7 satellite imagery. Multibeam acquisition systems Kongsberg EM300 and Kongsberg EM3002S. Frequency 30 and 300 kHz, respectively. Grid-cell size 10 m. Light blue and dark blue dashed lines are terminus positions derived from 1960s and 2014 aerial photographs, respectively. ( b ) Multibeam-bathymetric image of the seafloor immediately in front of Belcher Glacier. ( c ) 2014 airborne radar profile of Belcher Glacier, showing the depth of the …

Annual moraine ridges in Tempelfjorden, Spitsbergen

Surging tidewater glaciers produce a characteristic landform assemblage with glacial lineations, networks of crevasse-fill ridges, large terminal moraine ridges and several recessional moraines, which often override glacial lineations (Solheim 1991; Ottesen et al. 2008). Submarine recessional moraines have also been mapped beyond several Svalbard tidewater glaciers and are interpreted to record an annual to semi-annual signal of glacial retreat during the quiescent phase of the surge cycle (Ottesen & Dowdeswell 2006; Ottesen et al. 2008). The moraine ridges probably form during winter stillstands or minor readvances of the glacier terminus (Boulton et al. 1996; Ottesen et al. 2008). Tunabreen is a tidewater glacier of surge type located in Tempelfjorden, Spitsbergen (Fig. 1e). It has surged three times since the Little Ice Age, in 1930, 1970 and between c. 2002 and 2005 (Forwick et al. 2010) producing large terminal moraines (Fig. 1a). During the latest surge, the glacier margin reached its maximum extent in 2004 and has since retreated about 1 km. Fig. 1. Multibeam-bathymetric images of Tempelfjorden, Svalbard. Image courtesy of the Norwegian Hydrographic Service (permission no. 13/G706). ( a ) Image of inner Tempelfjorden, superimposed on an aerial image from 2009 (Photo …