Cryosphere: Antarctic ice growth and retreat

Antarctic Ice Sheet change during the last glacial cycle is unclear. The timing of moraine development in the Ross basin suggests that the ice sheet reached maximum thickness under the warming temperatures of the last termination

Grounding-zone wedges on the northern Larsen shelf, Antarctic Peninsula

Prominent quasi-linear or lobate wedge-shaped depositional sedimentary landforms, termed grounding-zone wedges (GZWs), are distributed widely on polar continental shelves. They are regarded as a product of the deposition of mainly subglacially-transported sediment at the grounding-zone of modern and palaeo ice sheets and ice streams (e.g. Shipp et al. 1999; Ottesen et al. 2005; Horgan et al. 2013). GZWs vary in shape, dimensions and regional distribution across the continental shelf, where they can form single or multiple and widely- or closely-spaced depositional features. The presence of these landforms is used to delimit the maximum and retreat positions of former ice-sheet margins on high-latitude continental shelves (e.g. Shipp et al. 1999; Ottesen et al. 2005). During the Late Glacial transition, retreat of the Antarctic Peninsula Ice Sheet that covered the shelf of the NE Antarctic Peninsula during the Last Glacial Maximum (LGM) produced several distinctive grounding-zone landforms (Evans et al. 2005)

Glacial lineations and recessional moraines on the continental shelf of Northeast Greenland

The Northeast Greenland continental shelf is only sparsely mapped due to its remoteness and harsh year-round sea-ice conditions. Mapping the distribution of submarine glacial landforms relies mainly on single track lines of multibeam echo sounder bathymetric data with only occasional systematic surveys. Ice streams drain the modern Greenland Ice Sheet [GrIS] to its northeastern margin in several fjords near the head of the Westwind Trough (Fig. 1a). The presence of glacial lineations and recessional moraines in the inner to middle trough indicates that the GrIS extended onto the continental shelf probably during the Last Glacial Maximum (Evans et al. 2009; Winkelmann et al. 2010)

Submarine gullies and an axial channel in glacier-influenced Courtauld Fjord, East Greenland

Submarine gullies have been observed widely in swath-bathymetric imagery of the shelf edge and upper slope on high-latitude margins (e.g. Noormets et al. 2009; Gales et al. 2013), but less frequently in glacier-influenced fjord settings. Gullies vary in distribution, morphology and dimensions depending on formation mechanisms; these include submarine mass wasting, subglacially or proglacially derived turbid underflows and dense bottom-water currents linked to brine rejection during sea-ice formation (e.g. Noormets et al. 2009). Since recession of the Greenland Ice Sheet through the Kangerlugssuaq Fjord system, at 68ºN in East Greenland, after the Last Glacial Maximum (Dowdeswell et al. 2010), significant seafloor erosion on the flanks of the inner tributary fjords has taken place to produce a series of submarine gullies and an axial channel (Fig. 1a-e)

Submarine landforms and shallow acoustic stratigraphy of a 400 km-long fjord-shelf-slope transect, Kangerlussuaq margin, East Greenland

Kangerlussuaq Fjord is a relatively uniform, steep-walled basin, whose floor has an almost smooth surface. Debris is supplied mainly from icebergs from the fast-flowing Kangerlussuaq Glacier. Sedimentation after iceberg release from multi-year sea ice is mainly by rain-out of fine-grained englacial debris. Streamlined glacial lineations and drumlins were produced at the sedimentary bed of an ice sheet that expanded into Kangerlussuaq Trough at the Last Glacial Maximum (LGM). Bedrock channels and crescentic overdeepenings indicate warm-based ice and free water beneath parts of the former ice sheet. Cross-cutting iceberg scour marks, which characterise outer Kangerlussuaq shelf, were produced not only during deglaciation, but also occasionally through the Holocene by deep-keeled icebergs from further north in East Greenland. The outward-convex contours of the shelf edge and slope beyond Kangerlussuaq Trough, and debris flows on the slope, suggest a glacier-influenced high-latitude fan. The distribution of streamlined subglacial landforms demonstrates that the Greenland Ice Sheet extended throughout Kangerlussuaq Fjord and reached at least 200 km across the shelf in Kangerlussuaq Trough at the LGM. Streamlined landform orientation indicates ice flow from the interior of Greenland down the axis of Kangerlussuaq Trough. There is little evidence for discrete sedimentary depocentres in the trough, implying that ice probably retreated rapidly from the outer and mid shelf during deglaciation

A new bathymetry of the Northeast Greenland continental shelf: constraints on glacial and 2 other processes

A new digital bathymetric model (DBM) for the Northeast Greenland (NEG) continental shelf (74°N–81°N) is presented. The DBM has a grid cell size of 250 m × 250 m and incorporates bathymetric data from 30 multibeam cruises, more than 20 single-beam cruises and first reflector depths from industrial seismic lines. The new DBM substantially improves the bathymetry compared to older models. The DBM not only allows a better delineation of previously known seafloor morphology but, in addition, reveals the presence of previously unmapped morphological features including glacially derived troughs, fjords, grounding-zone wedges, and lateral moraines. These submarine landforms are used to infer the past extent and ice-flow dynamics of the Greenland Ice Sheet during the last full-glacial period of the Quaternary and subsequent ice retreat across the continental shelf. The DBM reveals cross-shelf bathymetric troughs that may enable the inflow of warm Atlantic water masses across the shelf, driving enhanced basal melting of the marine-terminating outlet glaciers draining the ice sheet to the coast in Northeast Greenland. Knolls, sinks, and hummocky seafloor on the middle shelf are also suggested to be related to salt diapirism. North-south-orientated elongate depressions are identified that probably relate to ice-marginal processes in combination with erosion caused by the East Greenland Current. A single guyot-like peak has been discovered and is interpreted to have been produced during a volcanic event approximately 55 Ma ago

Using UAV acquired photography and structure from motion techniques for studying glacier landforms: application to the glacial flutes at Isfallsglaciären

Glacier and ice sheet retreat exposes freshly deglaciated terrain which often contains small-scale fragile geomorphological features which could provide insight into subglacial or submarginal processes. Subaerial exposure results in potentially rapid landscape modification or even disappearance of the minor-relief landforms as wind, weather, water and vegetation impact on the newly exposed surface. Ongoing retreat of many ice masses means there is a growing opportunity to obtain high resolution geospatial data from glacier forelands to aid in the understanding of recent subglacial and submarginal processes. Here we used an unmanned aerial vehicle to capture close-range aerial photography of the foreland of Isfallsglaciären, a small polythermal glacier situated in Swedish Lapland. An orthophoto and a digital elevation model with ~2cm horizontal resolution were created from this photography using structure from motion software. These geospatial data was used to create a geomorphological map of the foreland, documenting moraines, fans, channels and flutes. The unprecedented resolution of the data enabled us to derive morphological metrics (length, width and relief) of the smallest flutes, which is not possible with other data products normally used for glacial landform metrics mapping. The map and flute metrics compare well with previous studies, highlighting the potential of this technique for rapidly documenting glacier foreland geomorphology at an unprecedented scale and resolution. The vast majority of flutes were found to have an associated stoss-side boulder, with the remainder having a likely explanation for boulder absence (burial or erosion). Furthermore, the size of this boulder was found to strongly correlate with the width and relief of the lee-side flute. This is consistent with the lee-side cavity infill model of flute formation. Whether this model is applicable to all flutes, or multiple mechanisms are required, awaits further study

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

© 2016 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

Accelerated volume loss in glacier ablation zones of NE Greenland, Little Ice Age to present

Mountain glaciers at the periphery of the Greenland ice sheet are a crucial freshwater and sediment source to the North Atlantic and strongly impact Arctic terrestrial, fjord, and coastal biogeochemical cycles. In this study we mapped the extent of 1,848 mountain glaciers in NE Greenland at the Little Ice Age. We determined area and volume changes for the time periods Little Ice Age to 1980s and 1980s to 2014 and equilibrium line altitudes. There was at least 172.76 ± 34.55‐km3 volume lost between 1910 and 1980s, that is, a rate of 2.61 ± 0.52 km3/year. Between 1980s and 2014 the volume lost was 90.55 ± 18.11 km3, that is, a rate of 3.22 ± 0.64 km3/year, implying an increase of ~23% in the rate of ice volume loss. Overall, at least ~7% of mass loss from Greenland mountain glaciers and ice caps has come from the NE sector

Accelerated volume loss in glacier ablation zones of NE Greenland, Little Ice Age to present

Mountain glaciers at the periphery of the Greenland ice sheet are a crucial freshwater and sediment source to the North Atlantic and strongly impact Arctic terrestrial, fjord, and coastal biogeochemical cycles. In this study we mapped the extent of 1,848 mountain glaciers in NE Greenland at the Little Ice Age. We determined area and volume changes for the time periods Little Ice Age to 1980s and 1980s to 2014 and equilibrium line altitudes. There was at least 172.76 ± 34.55‐km3 volume lost between 1910 and 1980s, that is, a rate of 2.61 ± 0.52 km3/year. Between 1980s and 2014 the volume lost was 90.55 ± 18.11 km3, that is, a rate of 3.22 ± 0.64 km3/year, implying an increase of ~23% in the rate of ice volume loss. Overall, at least ~7% of mass loss from Greenland mountain glaciers and ice caps has come from the NE sector