Ice-flow Direction Research Articles

Unravelling the complex nature of the Upper Weichselian till section at Gdynia Babie Doły, northern Poland

Abstract The complexity of glacial sequences may increase when these formed underneath ice sheets despite subsequent changes in their extent that are accompanied by alterations in the direction of the ice flow. Our aim was to determine whether or not changes in ice sheet dynamics during the Late Weichselian are also recorded in sediments formed north of the area of its fluctuating margin (i.e., where the ice sheet prevailed independent of such fluctuations). It is shown that in these areas such a record could have occurred, as documented by results of till studies at Babie Doły. The examination was carried out using several analyses: lithofacies properties of sediments, petrographic till composition (fine gravel fraction, indicator erratics), till matrix CaCO3 content, till fabric, as well as orientation of striae on the top surfaces of large clasts. In parallel, datings of sub- and supra-till sediments using the TL method were carried out. The basal till at Babie Doły represents almost the entire Upper Weichselian, but it can be divided into subunits whose features indicate different ice flow directions and debris supply. The lower subunit developed as a result of the palaeo-ice stream along the main axis of the Baltic Sea (from the north), expanding to areas adjacent to the depression of the Gulf of Gdańsk. The upper subunit developed when the influence of the palaeo-ice stream in the study area decreased, the main role having been taken over by the ice flowing from the northwest. The till analysed also shows considerable lateral variation, indicative of the mosaic nature of subglacial sedimentation. We consider the diversity of permeability of deposits over which the ice sheet extended to be the prime factor that determined such a situation.

Crag-and-tail features: convergent ice flow through Eclipse Sound, Baffin Island, Arctic Canada

Elongate glacial landforms are typically orientated in the direction of ice flow (Benn & Evans 2010). They are often preserved in the submarine environment, providing information on past ice-sheet extent and flow pathways. The northeastern margin of the Laurentide Ice Sheet (LIS) covered much of eastern Baffin and Bylot islands during the Last Glacial Maximum (Dyke et al. 2002). Numerous elongate landforms on the seafloor of Eclipse Sound and Pond Inlet indicate the direction of ice flow around Bylot Island in the Canadian Arctic (Fig. 1b; Bennett et al. 2014). Fig. 1. Multibeam swath bathymetry, longitudinal profile, cross-section and sub-bottom acoustic profile of elongate submarine features in Eclipse Sound, Arctic Canada. ( a ) Location of study area (red box; map from IBCAO v. 3.0). ( b ) Sun-illuminated multibeam-bathymetric image of convergent crag-and-tails. Acquisition system Kongsberg Simrad EM300. Frequency 30 kHz. Grid-cell size 10 m. ( c ) Ice-flow lines inferred from crag-and-tails (white lines). Glacier flow is from SW to NE (white arrow). Crag-and-tails are roughly distributed in arcs of decreasing radius from SW to NE (red lines). ( d ) Longitudinal profile through a crag-and-tail (located in (b)). VE×4. ( e ) Cross-profile through crag-and-tails. Black arrows mark five sedimentary tails. VE×8. ( f ) Shallow sub-bottom profile across Eclipse Sound showing …

Landforms characteristic of inter-ice stream settings on the Norwegian and Svalbard continental margins

The suite of sedimentary landforms produced on continental shelves by fast-flowing ice streams is typified by features that are elongate and streamlined in the direction of past ice flow (e.g. Stokes & Clark 2001; Ottesen et al. 2005 a ; Livingstone et al. 2012). By contrast, the slower-flowing parts of an ice sheet, located between ice streams and fed by drainage basins that are often an order of magnitude or more smaller than the interior basins feeding the ice stream, have a very different set of characteristic submarine landforms; these are orientated predominantly transverse to the direction of past ice flow (Ottesen & Dowdeswell 2009; Klages et al. 2013, 2016). In addition, on many high-latitude shelf-banks glacial landforms produced beneath and at the margins of ice sheets are often reworked by the ploughing action of iceberg keels, sometimes to the point where these primary depositional landforms are almost obliterated (e.g. Dowdeswell et al. 1993, 2014). Submarine landforms from the western margin of the former Eurasian Ice Sheet, which extended across the shallow banks and deeper intervening troughs on the continental shelves of Norway and Svalbard at the Last Glacial Maximum (LGM) (Svendsen et al. 2004; Ottesen et al. 2005 a ), are used to illustrate this inter-ice stream palaeo-glacial setting (Fig. 1). In these locations, ice flux is limited by relatively small drainage-basin size and ice flow is likely to be slow relative to the 103–104 m a−1 velocities of adjacent ice streams (Dowdeswell & Siegert 1999). Fig. 1. ( a ) Location of study areas offshore of Norway and Svalbard (red boxes; map from IBCAO v. 3.0). Bathymetric data showing the pattern of shallow banks and intervening cross-shelf troughs offshore of ( b ) NW Norway and ( c ) NW Spitsbergen. WI, Wijdefjorden; KR, Krossfjorden. ### Description The …

Esker systems in the Gulf of Bothnia

Eskers, straight-to-sinuous ridges of waterlain sand and gravel, and their erosional meltwater channel counterparts are geomorphological imprints of the palaeo-glacial hydrological system. Esker networks hundreds of metres to hundreds of kilometres long are widespread features of Quaternary glaciations and are used to reconstruct regional and continental patterns of deglaciation. However, they have been less commonly reported from sedimentary marine environments. Esker systems from the southern Gulf of Bothnia are imaged with unprecedented clarity in new multibeam datasets which reveal a highly connected subglacial hydrological network and its relationship to an underlying drumlin field. Sinuous, elongate sediment ridges thread through a drumlin field which rises from about 80 to 50 m water depth in the southern Gulf of Bothnia (Fig. 1a–i). Individual ridge segments range from 4 km long and are c. 50–200 m wide and c. 2–20 m high. They connect into much longer esker chains over 15 km long, broken only by small gaps. The longer esker paths form a broadly dendritic network, with up to fourth-order ‘tributaries’, converging southward in the direction of ice-flow. Within tributary sections, localized braiding and anabranching occur; occasionally isolated distributaries do not reconnect to the main …

Buried mega-scale glacial lineations in the Norwegian Channel from 3D seismic imagery

The Norwegian Channel offshore of south and southwestern Norway, and the thick North Sea Fan beyond the shelf edge (Fig. 1d, f), are generally accepted to be mainly the result of repeated ice-stream erosion and subsequent deposition during the second half of the Quaternary (Rise & Rokoengen 1984; King et al. 1996; Nygard et al. 2002; Sejrup et al. 2003). Three-dimensional (3D) seismic imaging shows that buried lineations, probably produced about 0.5 million years ago (Sejrup et al. 1995), are preserved beneath the modern Norwegian Channel on the palaeo-shelf. The pattern of these lineations suggests a complex former ice-flow regime (Rise et al. 2004). Fig. 1. The imprint of ice streaming preserved at a buried surface in the northern Norwegian Channel. ( a ) Sun-illuminated image of seismic data showing lineations with amplitudes≤2 m. ( b ) Sketch of the lineations in (a) indicating ice-flow directions. ( c ) Enlarged 3D image of the palaeo-surface of unit C (located in (b)). ( d ) Proposed ice-flow model at the initial stage of a mid-Pleistocene glaciation …

Assemblages of submarine landforms in the glacial troughs of the northern Barents Sea, east of Svalbard

The Barents Sea is a wide, relatively deep epicontinental sea consisting of shallower banks ( c. 50–100 m depth) separated by broad, flat-bottomed troughs ( c. 200–400 m depth) that radiate out towards its western and northern margins (Fig. 1a). These troughs have been excavated by grounded ice during multiple glaciations through the Plio-Pleistocene (Jakobsson et al. 2014). During the Last Glacial Maximum (LGM) the Barents Sea Ice Sheet (BSIS) extended across the entire northern Barents Sea to the shelf break (Svendsen et al. 2004; Jakobsson et al. 2014). Fast-flowing ice drained the ice sheet through these troughs and produced a suite of seafloor landforms that preserves both a record of former ice-flow patterns and of how the ice sheet retreated during deglaciation (Dowdeswell et al. 2010; Hogan et al. 2010 a ). Fig. 1. Bathymetric images and sub-bottom profiles of landforms in glacial troughs east of Svalbard. Acquisition system Kongsberg EM120. Frequency 12 kHz. Grid-cell size 10–20 m. Acquisition system for profiles Kongsberg TOPAS PS018 parametric sub-bottom profiler (secondary beam frequency 0.5–6 kHz). ( a ) Location of study area (red boxes; map from IBCAO v. 3.0). KT, Kvitoya Trough; OT, Olga Trough; E, eastern Erik Eriksen Trough; W, western Erik Eriksen Trough; KKL, Kong Karls Land; No, Nordaustlandet; FVT, Franz Victoria Trough. ( b ) Glacial lineations (long dashes) overprinted in part by a debris-flow deposit (dotted) in western Erik Eriksen Trough; recessional moraine orientations shown by solid lines. Large black arrow indicates former ice-flow direction. ( c ) Saw-tooth-shaped recessional moraines in Olga Trough. ( d ) Hill–hole pairs and glacial lineations in eastern Olga Trough; same depth scale as (c). ( e ) Streamlined crag-and-tail landforms in Kvitoya Trough. ( f ) Sub-bottom profile over the till sheet and recessional moraines shown in (c). ( g ) Acoustic facies on the upper slope north of Kvitoya Trough. ( h ) Subglacial meltwater channels …

Stratified glacimarine basin-fills in West Greenland fjords

Acoustically stratified sediments that infill glacially eroded bedrock basins are common in fjords (Seramur et al. 1997; Gilbert et al. 1998; Hogan et al. 2012; Dowdeswell & Vasquez 2013). Internally, such stratified sediments are often characterized by relatively smooth reflections that parallel the seafloor. Sills between basins usually comprise bedrock, sometimes covered by a thin veneer of glacimarine sediment and/or till. Fjords in West Greenland, including Rink Fjord and Vaigat, contain bedrock basins infilled by acoustically stratified sediment (Fig. 1). The basin fills are a product of rain-out from turbid meltwater plumes, probably supplemented by iceberg-rafting and downslope resedimentation. Fig. 1. Multibeam bathymetry and acoustic sub-bottom profiles of submarine basins close to the coast of West Greenland. ( a ) Multibeam bathymetry from Rink Fjord, West Greenland, with water depths >1000 m. ( b ) 3.5 kHz sub-bottom profile from Rink Fjord showing stratified, conformable basin fill (Facies 2) between basement pinnacles (Facies 1). VE×96. ( c , d ) Multibeam bathymetry in Vaigat strait and a coastal basin, West Greenland, respectively; arrows indicate ice-flow directions during the last glacial based on the orientation of sculpted …

Drumlins in the Gulf of Bothnia

Drumlins are relatively small, elongate hills aligned with ice-flow direction (Menzies 1979). The name drumlin originates from the Irish word druim, which means rounded hill. They are among the most widespread glacial landforms. Drumlins are often likened to half-buried eggs or inverted spoons, with one slope blunter than the other. They belong to the group of ice-flow-parallel glacial landforms that includes glacial striae, flutes, crag-and-tails and mega-scale glacial lineations. Drumlins are very common in the landscape of central and northern Scandinavia (Hattestrand 1998), but their identification in the Baltic Sea and Gulf of Bothnia has been hindered by a lack of seafloor data. Here we show a drumlin field from the southern Gulf of Bothnia. The drumlin field shown in Figure 1 stretches for >85 km and probably continues northwards beyond the coverage of the high-resolution bathymetric data available for this study. The outlines of the drumlins are generally easy to distinguish (Fig. 1c), although their surfaces are frequently scarred by iceberg ploughmarks and pits (Fig. 1e, f). The drumlins are aligned NNW–SSE (169°) and their morphology changes progressively along the mapped section. The northern part is characterized by shorter, wider drumlins, whereas …

A set of grounding-zone wedges in Vestfjorden, North Norway

At the Last Glacial Maximum (LGM), a 400 km long fast-flowing ice stream drained an interior basin of the Scandinavian Ice Sheet of about 150 000 km2 through Vestfjorden and the adjacent cross-shelf trough of Traenadjupet further downstream (Fig. 1) (Ottesen et al. 2005 a ). Evidence for past ice-stream activity comes from a variety of submarine sedimentary landforms that are streamlined in the direction of past ice flow (Ottesen et al. 2005 b ). Superimposed on these streamlined landforms are several wedge-like sedimentary features orientated transverse to flow. These submarine landforms suggest that deglacial retreat was punctuated by stillstands that produced substantial depocentres known as grounding-zone wedges (GZWs) (e.g. Anderson 1999; Dowdeswell et al. 2008; Dowdeswell & Fugelli 2012; Batchelor & Dowdeswell 2015). Fig. 1. Grounding-zone wedges in Vestfjorden, North Norwegian margin. ( a ) Shaded-relief swath-bathymetric image of a 5500 km2 area of Vestfjorden showing two large GZWs which both override MSGLs and have further MSGLs on their surfaces. The shallowest parts of the GZWs have been affected by the ploughing action of iceberg keels. Acquisition system Kongsberg EM100. Frequency 97 kHz. Grid-cell size 50 m. ( b …

Grounding-zone wedges on the western Svalbard shelf

When ice sheets decay and retreat across continental shelves during regional deglaciation, the glacial landforms preserved on the seafloor provide evidence of the nature and rate of change. The presence of streamlined sedimentary landforms implies that fast-flowing ice streams drained a full-glacial ice sheet that extended across the continental shelf (e.g. Ottesen et al. 2005). By contrast, observations of sedimentary depocentres such as grounding-zone wedges (GZWs; Dowdeswell & Fugelli 2012; Batchelor & Dowdeswell 2015) in cross-shelf troughs are a clear indicator that halts in ice-sheet retreat, perhaps lasting centuries during which ice remained active delivering sediment to the grounding zone, took place between episodic phases of more rapid terminus retreat. The continental shelf west of Svalbard contains a number of sedimentary depocentres or wedges that are orientated across troughs, transverse to the direction of former ice flow (Fig. 1) (e.g. Ottesen et al. 2007; Forwick & Vorren 2010). Multibeam images of three sedimentary wedges are shown in Figure 1a–c. The wedges extend c. 5–20 km across the two fjords. Each …

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.

Introduction: an Atlas of Submarine Glacial Landforms

Glacial landforms and sediments exposed sub-aerially have been the subject of description, analysis and interpretation for more than a century (e.g. De Laski 1864; De Geer 1889). Indeed, such features provided important initial observations informing Louis Agassiz's ideas that ice was a key instrument in sculpting the landscape and that glaciers and ice sheets had extended to mid-latitudes during the past, implying that Earth's climate must have changed considerably through time (Agassiz 1840). It is only in the last few decades that attention has begun to focus on the marine evidence for the past growth and decay of ice sheets that is recorded in submarine landforms and sediments preserved on high-latitude continental margins. This interest has been driven, in part, by the recognition that sediments deposited below wave-base are often well preserved in the Quaternary geological record, and may be less subject to erosion and reworking than their terrestrial counterparts. In addition, new marine-geophysical technologies have enabled increasingly high-resolution imaging and penetration of the high-latitude seafloor, most notably using multibeam swath-bathymetric and three-dimensional (3D) seismic-reflection methods, and modern ice-strengthened and ice-breaking research vessels have allowed the effective deployment of these increasingly sophisticated instruments in the often ice-infested waters of the Arctic and Antarctic seas. The geological record from high-latitude continental margins is now recognized to provide key information on former ice-sheet extent, the direction and nature of past ice flow and dynamics, and a well-preserved window on the detailed form and composition of former ice-sheet beds (e.g. Ottesen et al. 2005; Anderson et al. 2014; Jakobsson et al. 2014). The geometry and distribution of submarine glacial landforms on the seafloor, and the underlying glacial-sedimentary stratigraphic record with which they are associated, is the topic of this volume. The aims and purpose of the Atlas are: (1) to …

Crag-and-tail landforms in outer Rijpfjorden, Nordaustlandet, Svalbard

Streamlined sedimentary and bedrock glacial landforms are widespread on high-latitude continental shelves and in fjords. It has been shown that they are orientated in the direction of past ice flow and are indicative of fast motion linked to basal processes (e.g. Clark 1994). Elongation ratios of these landforms have been suggested to reflect past ice velocity, with higher elongation ratios being characteristic of faster ice flow (e.g. Clark 1993). However, the subglacial substrate has a considerable influence on ice flow and on the resulting glacial landforms (e.g. Heroy & Anderson 2005). Using the character and distribution of streamlined, subglacially produced landforms, the extent and dynamics of former ice sheets and ice streams has been successfully reconstructed (e.g. Ottesen et al. 2005; Dowdeswell et al. 2010; Hogan et al. 2010 a , b ). The seafloor of Rijpfjorden on Nordaustlandet in eastern Svalbard (Fig. 1f) is dominated by crudely streamlined bedrock with south–north to SSW–NNE long-axis …

A subglacial landform assemblage on the outer shelf of M'Clure Strait, Canadian Arctic, ploughed by iceberg keels

M'Clure Strait in the Canadian Beaufort Sea (Fig. 1) is one of the largest cross-shelf troughs in the High Arctic, with a length of over 1000 km and a maximum cross-trough width of about 250 km (Batchelor & Dowdeswell 2014). It is thought to be the former location of a fast-flowing ice stream which drained the northwestern Laurentide Ice Sheet during the Late Wisconsinan, and probably a number of earlier Quaternary full-glacial periods (Stokes et al. 2006, 2009; Niessen et al. 2010; Batchelor et al. 2013). The Late Wisconsinan ice stream in M'Clure Strait is interpreted to have extended to the shelf break between 21–16 ka before undergoing rapid retreat (Stokes et al. 2009). Low rates of postglacial sedimentation have led to the preservation of an unusual assemblage of cross-cutting glacigenic landforms on the seafloor of outermost M'Clure Strait (Fig. 1). Fig. 1. ( a ) Swath bathymetry of the outer shelf of M'Clure Strait, Arctic Canada, superimposed on IBCAO v. 3.0 bathymetry (5 m contours). Multibeam acquisition system Kongsberg EM302. Frequency 30 kHz. Grid-cell size 10 m. Dashed line D indicates that the linear ridge-and-groove structures are probably continuous either side of the data gap. ( b ) Location of the study area (red box; map from IBCAO v. 3.0). MS, M'Clure Strait. ( c ) Schematic diagram showing the interpreted distribution of submarine landforms on the seafloor of M'Clure Strait which is described in the text. The probable direction of former ice flow is shown by a black arrow. The outer-shelf of M'Clure Strait contains several sets of landforms: linear ridge-and-groove structures, sinuous ridges, a wide trough-parallel ridge and three types of linear to curvilinear depressions. Multibeam imagery of the landforms is shown in Figure 1, together with a map of their distribution. Linear ridge-and-groove structures have an east–west orientation, parallel …

Mega-scale glacial lineations and grounding-zone wedges in Prydz Channel, East Antarctica

The Prydz Bay continental shelf was sculpted by the Lambert Glacier–Amery Ice Shelf system, a large outlet glacier that drains 16% of the East Antarctic Ice Sheet (Allison 1979; Fig. 1a). Prydz Channel (71–73° E; Fig. 1b) is a NW-trending cross-shelf trough (500–700 m deep) in western Prydz Bay that formed in the Pliocene, when the Lambert-Amery system first developed a fast-flowing ice stream (Fig. 1b; Cooper & O'Brien 2004). In Prydz Channel mega-scale glacial lineations (MSGLs) delineate the direction and orientation of past ice flow, and large grounding-zone wedges (GZWs; Batchelor & Dowdeswell 2015) in the inner channel mark the limit of the Last Glacial Maximum (LGM) ice advance about 250 km from the shelf edge (Fig. 1c, d, e). Fig. 1. Multibeam swath bathymetry and seismic-reflection profile of Prydz Channel, East Antarctica. ( a ) Location of study area (red box; map from IBCSO v. 1.0). ( b ) General bathymetry of Prydz Channel, delineated by the 500 m contour, and other relevant regional features. ( c ) Multibeam swath bathymetry of mega-scale glacial lineations (MSGLs) in Prydz Channel and grounding-zone …

Eskers in deglacial sediments of three Spitsbergen fjords

Eskers are elongate, straight to sinuous sedimentary ridges deposited in subglacial, englacial or supraglacial drainage networks (e.g. Warren & Ashley 1994). The following four basic esker types are distinguished (after Warren & Ashley 1994; Brennand 2000; Benn & Evans 2010): tunnel fills, formed in englacial and subglacial conduits and exposed by ice ablation; ice-channel fills, deposited in sub-aerial, ice-walled channels; segmented tunnel fills, deposited during stepwise glacier retreat; and beaded eskers, composed of subaqueous fans deposited during stepwise retreat of a water-terminating glacier. The planform of eskers can vary from uniform, simple ridges to complex, dendritic networks (Shilts et al. 1987; Warren & Ashley 1994). Eskers are usually aligned sub-parallel to the direction of former ice flow and the presence of subglacial eskers reveals the locations of conduits at the glacier bed. Furthermore, some tunnel-fill eskers may grade into ‘Nye’ channels cut into the substrate, reflecting a transition from deposition to erosion along the conduit axis (Benn & Evans 2010). Multiple elongate to sinuous ridges occur in a number of Spitsbergen fjords (Fig. 1). The ridges are several kilometres long and typically orientated sub-parallel to fjord axes. They occur at various water depths and in different parts of fjord …

Plesiosaurian fossils from Baltic glacial erratics: evidence of Early Jurassic marine amniotes from the southwestern margin of Fennoscandia

Abstract Early Jurassic plesiosaurian fossils are rare in the Scandinavian region, with a few isolated bones and teeth known from Bornholm, and anecdotal finds from East Greenland. The only other identifiable specimens derive from Toarcian-aged (based on ammonites) erratics deposited during Late Pleistocene glacial advances near the town of Ahrensburg, NE of Hamburg in northern Germany. The geographical source of these transported clasts is debated, but reconstructed ice-flow directions and lithofacies comparisons implicate either the offshore Baltic Sea between the Island of Bornholm and Mecklenburg–Vorpommern (Germany) or, less probably, south of the Danish Archipelago (Mecklenburg Bay). These regions collectively bordered the Fennoscandian landmass and adjacent Ringkøbing-Fyn Island in the late Early Jurassic, and were dominated by near-shore marine deltaic to basinal settings. The Ahrensburg plesiosaurian remains include postcranial elements reminiscent of both the microcleidid Seeleyosaurus and the rhomaelosaurid Meyerasaurus . These occur alongside other classic ‘Germanic province’ marine amniotes, such as the teleosaurid crocodyliform Steneosaurus and ichthyosaurian Stenopterygius cf. quadriscissus : thus, advocating faunal continuity between Scandinavia and southern Germany during the Toarcian, and a less pronounced marine reptile faunal provinciality than previously assumed.

Hill–hole pairs on the Norwegian continental shelf

Glacitectonic landforms and processes on the Norwegian continental shelf were first described by Saettem (1990). Over the past two decades, multibeam bathymetry has revealed a number of glacitectonic features. Three-dimensional (3D) seismic data have also shown that glacitectonic processes are more widespread than previously thought (Andreassen et al. 2004). Hill–hole pairs have been observed mainly on land (Moran et al. 1980; Aber & Ber 2007) and few examples are known from previously glaciated continental shelves (Fig. 1). Hill–hole pair sedimentology and structural geology have been examined at the terrestrial margin of the former North American Ice Sheet (Moran et al. 1980). The hills comprise thrust-block moraines apparently formed at former ice margins and the holes are source areas. Hill–hole axes are sub-parallel to inferred ice-flow direction. Compressive subglacial stresses, leading to tectonism, are thought to be induced by basal freezing close to thin ice-sheet margins (Moran et al. 1980). Fig. 1. Hill–hole pairs on the continental shelf off Norway. ( a ) Multibeam image of the Steinbitryggen–Sopphola hill–hole pair (S-S) and two less well-defined glacitectonic pairs (B, C) on Tromsoflaket bank. ( b ) Multibeam image of Hesteskoen hill–hole pair on easternmost Traenabanken. Acquisition system for (a) …

Surface velocity estimations of ice shelves in the northern Antarctic Peninsula derived from MODIS data

The ice shelves in the northern Antarctic Peninsula are highly sensitive to variations of temperature and have therefore served as indicators of global warming. In this study, we estimate the velocities of the ice shelves in the northern Antarctic Peninsula using co-registration of optically sensed images and correlation module (COSI-Corr) in the Environment for Visualizing Images (ENVI) based on Moderate Resolution Imaging Spectroradiometer (MODIS) images during 2000–2012, from which we conclude that the ice flow directions generally match the peninsulas pattern and the crevasse, ice flows mainly eastward into the Weddell Sea. The spatial pattern of velocity field exhibits an increasing trend from the western grounding line to the maximum at the middle part of the ice shelf front on Larsen C with a velocity of approximately 700 ma−1, and the velocity field shows relatively higher values in its southerly neighboring ice shelf (e.g. Smith Inlet). Additionally, ice flows are relatively quicker in the outer part of the ice shelf than in the inner parts. Temporal changes in surface velocities show a continuous increase from 2000 to 2012. It is worth noting that, the acceleration rate during 2000–2009 is relatively higher than that during 2009–2012, while the ice movement on the southern Larsen C and Smith Inlet shows a deceleration from 2009 to 2012.

An early to middle Miocene record of ice-sheet and landscape evolution from the Friis Hills, Antarctica

The Friis Hills (77°45′S, 161°30′E), in the McMurdo Dry Valleys region, Antarctica, is a 1-km-high inselberg with early to middle Miocene–aged glacial deposits preserved on its upper surface. Lithology, sedimentology, and ice-flow direction define three units within a 34-m-thick sequence: the Friis I, Friis II, and Cavendish drifts. Tills in Friis I drift were deposited from alpine glaciers flowing to the SW. An extensive tephra bed in the drift is 19.76 ± 0.11 Ma in age based on 40 Ar/ 39 Ar dating. Tills in Friis II drift were deposited from alpine glaciers flowing to the SE. Fossiliferous fluvial and lacustrine beds in the drift indicate that vegetation and insects repeatedly recolonized the Friis Hills during periods of reduced ice. The geographic distribution of modern descendants of the fossils specifies mean summer temperatures of 6–7 °C and precipitation as much as 3000 mm during these interglacial periods. The presence of fossils also indicates deposition of Friis II drift occurred before the mid-Miocene climate transition ca. 14.1 Ma. After this, eastward-flowing ice partially eroded the Friis I and II drifts. The ice also cut parallel troughs to the N and S, topographically isolating the Friis Hills. The Cavendish drift represents renewed deposition but from eastward-flowing outlet glaciers within the newly established troughs. Together, the Friis Hills drifts register multiple stages in the evolution of the East Antarctic cryosphere, including the general growth of the system, reorganizations of glacial drainage patterns, and periods of major downcutting. Importantly, they also provide constraints on terrestrial climate conditions during these stages. The Friis Hills record is the first that can be directly compared with shallow-marine records from the Ross Sea. The record also provides new constraints for paleoglaciological models of the early East Antarctic Ice Sheet. Based on lithologic and geomorphic arguments, the Friis Hills drifts are younger than nearby Sirius Group tillites, which predicates that the Sirius Group in the Dry Valleys region is at least early Miocene, or more probably, Oligocene in age.