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Julian A. Dowdeswell - One of the best experts on this subject based on the ideXlab platform.
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Submarine Landforms on the Weddell Sea shelf imaged at high resolution using AUVs
2020Co-Authors: Julian A. Dowdeswell, Dag Ottesen, Christine Batchelor, Sasha Montelli, E. K. Dowdeswell, Jeffrey EvansAbstract:<p>Multibeam echo-sounders were deployed from Autonomous Underwater Vehicles (AUVs) flying close to the seafloor of the Weddell Sea shelf in order to investiagte the Glacial Landforms there with a view to understanding processes and patterns associated with deglaciation from the Last Glacial Maximum on the eastern side of the Antarctic Peninsula. A horizontal resolution of 0.5 m (using conventional mulitbeam systems), and in some cases 0.05 m (using interferometric multibeam equipment), allowed delicate seafloor Landforms to be mapped in several areas of the shelf beyond the Larsen C and former Larsen A and B ice shelves. A number of Glacial Landform assemblages were observed, including suites of delicate ridges associated with grounding-zone wedges and the grounding of icebergs on the shelf. These Landforms are probably related to the action of tides moving the ice up and down through a series of tidal cycles. At the highest spatial resolution, individual dropstones derived from rain-out during the melting of floating ice were imaged clearly. Imaging the seafloor at such high resolution allows both very detailed descriptions of submarine Landform morphology and also the complexity of such Landforms and Landform assemblages to be better understood, aiding the interpretation of the Glacial and related processes that led to their formation.</p>
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Glacial Landform assemblages in Spitsbergen fjords from the last full-Glacial, deglaciation and the late Holocene
Geological Society London Memoirs, 2016Co-Authors: Matthias Forwick, Julian A. Dowdeswell, Jan Sverre Laberg, Dag OttesenAbstract:Fjords are characteristic features of the western and northern coasts of Spitsbergen. They formed during repeated Glacial cycles when grounded glaciers drained large ice sheets occupying the Svalbard–Barents Sea region. Since grounded glaciers often erode and remove pre-existing deposits from fjord basins, depositional sequences in fjords are typically limited to the last Glacial–interGlacial cycle (e.g. Forwick & Vorren 2010). Holocene sediment drapes in Spitsbergen fjords are not usually thick enough to obscure Glacial Landforms and deposits from the last full-Glacial and deGlacial period. Glacier advances related to climatic cooling during the late Holocene, together with glacier surges, have led to the formation of complex Landform assemblages close to many fjord heads (e.g. Ottesen & Dowdeswell 2006; Ottesen et al. 2008; Streuff et al. 2015). The floors in the central and outer parts of several Spitsbergen fjords, including Kongsfjorden, Isfjorden, Billefjorden, Sassenfjorden and Tempelfjorden, reveal multiple streamlined sedimentary lineations orientated sub-parallel to fjord axes (Figs 1a, b, c, 2a; e.g. Ottesen et al. 2005; Baeten et al. 2010; Forwick et al. 2010). The ridges are≤5 km long, 15 m high and
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Glacial Landform assemblages in spitsbergen fjords from the last full Glacial deglaciation and the late holocene
Geological Society London Memoirs, 2016Co-Authors: Matthias Forwick, Julian A. Dowdeswell, Jan Sverre Laberg, Dag OttesenAbstract:Fjords are characteristic features of the western and northern coasts of Spitsbergen. They formed during repeated Glacial cycles when grounded glaciers drained large ice sheets occupying the Svalbard–Barents Sea region. Since grounded glaciers often erode and remove pre-existing deposits from fjord basins, depositional sequences in fjords are typically limited to the last Glacial–interGlacial cycle (e.g. Forwick & Vorren 2010). Holocene sediment drapes in Spitsbergen fjords are not usually thick enough to obscure Glacial Landforms and deposits from the last full-Glacial and deGlacial period. Glacier advances related to climatic cooling during the late Holocene, together with glacier surges, have led to the formation of complex Landform assemblages close to many fjord heads (e.g. Ottesen & Dowdeswell 2006; Ottesen et al. 2008; Streuff et al. 2015). The floors in the central and outer parts of several Spitsbergen fjords, including Kongsfjorden, Isfjorden, Billefjorden, Sassenfjorden and Tempelfjorden, reveal multiple streamlined sedimentary lineations orientated sub-parallel to fjord axes (Figs 1a, b, c, 2a; e.g. Ottesen et al. 2005; Baeten et al. 2010; Forwick et al. 2010). The ridges are≤5 km long, 15 m high and<500 m wide, with a spacing of up to 800 m; length-to-width ratios exceed 10:1. Elongate Landforms with length-to-width ratios smaller than 10:1 are also found in Kongsfjorden and Raudfjorden (e.g. Ottesen & Dowdeswell 2009; MacLachlan et al. 2010). Fig. 1. Examples of Glacial Landforms and sediments in Spitsbergen fjords. ( a ) Location of study areas (red boxes; map from IBCAO v. 3.0). Red boxes show locations of (b)–(d) and Figure 2. ( b ) Sun-illuminated multibeam-bathymetric image from Billefjorden (after Baeten et al. 2010). Acquisition system Kongsberg EM300. Frequency 30–34 kHz. Grid-cell size 5 m. ( c ) Sun-illuminated multibeam-bathymetric image from Kongsfjorden and southern Krossfjorden (courtesy of Boele Kuipers, Norwegian Hydrographic Service; for details see MacLachlan …
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submarine Glacial Landform distribution across the west greenland margin a fjord shelf slope transect through the uummannaq system 70 71 n
Geological Society London Memoirs, 2016Co-Authors: Julian A. Dowdeswell, K A Hogan, Colm O CofaighAbstract:Today, the Greenland Ice Sheet reaches the sea via a number of fast-flowing outlet glaciers that are fed by ice draining from huge interior basins (Rignot & Kanagaratnam 2006). At the Last Glacial Maximum (LGM), the ice sheet expanded to reach the continental shelf break around much of Greenland (O Cofaigh et al. 2013 a ). In the Uummannaq area at c. 70–71° N (Fig. 1a) there is now a 400 km distance between the terminus of Rink Glacier, which drains about 30 000 km2 of the ice sheet, and the shelf edge. This provides a transect from the modern glacier front, through a deep fjord system and adjacent cross-shelf trough, to the continental slope in Baffin Bay. The seafloor is now exposed along this transect and the Landforms produced by past Glacial activity can be examined using marine-geophysical methods. Deglaciation from the LGM was underway at the shelf edge in Uummannaq Trough by 14.8 kyr ago and from the mid-shelf by 10.9 kyr, and ice had probably retreated back into the fjord system by 9.3 kyr ago (O Cofaigh et al. 2013 a ; Roberts et al. 2013). Fig. 1. Regional bathymetry and shelf architecture of the Uummannaq fjord–shelf–slope system, West Greenland. The location of subsequent figures is also shown. ( a ) Multibeam-bathymetric coverage of the Uummannaq system (located as a red box on the inset location map of Greenland). UI, Ubekendt Island; RF, Rink Fjord. Regional bathymetry from IBCAO v. 3.0. ( b ) Dip-line seismic-reflection profile (130 km long) showing West Greenland continental shelf architecture comprising prograding sedimentary units. ( c ) 110 km long strike profile showing a Late Quaternary Glacial trough where erosion has truncated pre-existing reflectors (black arrows). The reflections marked bPP represent the lower boundary of Plio-Pleistocene erosion and glacier-influenced sediments; (b) and (c) are located in (a) …
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submarine Glacial Landform distribution along an antarctic peninsula palaeo ice stream a shelf slope transect through the marguerite trough system 66 70 s
Geological Society London Memoirs, 2016Co-Authors: Stephen J Livingstone, K A Hogan, Colm O Cofaigh, Julian A. DowdeswellAbstract:The Antarctic Peninsula comprises a thin spine of mountains and islands presently covered by an ice sheet up to 500 m thick that drains eastward and westward via outlet glaciers (Davies et al. 2012). The peninsula has undergone recent rapid warming, resulting in the collapse of fringing ice shelves and the retreat, thinning and acceleration of marine-terminating outlet glaciers (e.g. Pritchard & Vaughan 2007). At the Last Glacial Maximum (LGM), the ice sheet expanded to the continental shelf break around the peninsula, and was organized into a series of ice streams that drained along cross-shelf bathymetric troughs (O Cofaigh et al. 2014). Marguerite Bay is located on the west side of the Antarctic Peninsula, at about 66–70° S (Fig. 1). A 12–80 km wide and 370 km long trough extends across the bay from the northern terminus of George VI Ice Shelf to the continental shelf edge. Extensive marine-geophysical surveys of the trough reveal a suite of Glacial Landforms which record past flow of an ice stream which extended to the shelf edge at, or shortly after, the LGM. Subsequent retreat of the ice stream was underway by c. 14 ka ago and proceeded rapidly to the mid-shelf, where it slowed before accelerating once again to the inner shelf at c. 9 ka (Kilfeather et al. 2011). Fig. 1. Regional bathymetry and shelf architecture of the Marguerite Trough shelf–slope system, Antarctic Peninsula (AP). The location of subsequent figures is shown. ( a ) Multibeam-bathymetric coverage of the Marguerite Trough system. Light grey is grounded ice; dark grey is floating ice. Inset: location of study area on the Antarctic Peninsula (red box; map from IBCSO v. 1.0). Regional bathymetry from IBCAO v. 3.0. Arrows denote perspective of oblique views in Figures 2a and 3a. ( b ) 130 km along-dip seismic-reflection profile showing Antarctic …
Colm O Cofaigh - One of the best experts on this subject based on the ideXlab platform.
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the mixed bed Glacial Landform imprint of the north sea lobe in the western north sea
Earth Surface Processes and Landforms, 2019Co-Authors: David H Roberts, David J.a. Evans, Elena Grimoldi, Louise Callard, Chris D Clark, Heather Stewart, Dayton Dove, Margot Saher, Colm O Cofaigh, Richard C ChiverrellAbstract:© 2018 John Wiley & Sons, Ltd. During the last Glacial cycle an intriguing feature of the British-Irish Ice Sheet was the North Sea Lobe (NSL); fed from the Firth of Forth and which flowed south and parallel to the English east coast. The controls on the formation and behaviour of the NSL have long been debated, but in the southern North Sea recent work suggests the NSL formed a dynamic, oscillating terrestrial margin operating over a deforming bed. Further north, however, little is known of the behaviour of the NSL or under what conditions it operated. This paper analyses new acoustic, sedimentary and geomorphic data in order to evaluate the Glacial landsystem imprint and deGlacial history of the NSL offshore from NE England. SubGlacial tills (AF2/3) form a discontinuous mosaic interspersed with bedrock outcrops across the seafloor, with the partial excavation and advection of subGlacial sediment during both advance and retreat producing mega-scale Glacial lineations and grounding zone wedges. The resultant ‘mixed-bed’ Glacial landsystem is the product of a dynamic switch from a terrestrial piedmont-lobe margin with a net surplus of sediment to a partially erosive, quasi-stable, marine-terminating, ice stream lobe as the NSL withdrew northwards. Glaciomarine sediments (AF4) drape the underlying subGlacial mixed-bed imprint and point to a switch to tidewater conditions between 19.9 and 16.5 ka cal BP as the North Sea became inundated. The dominant controls on NSL recession during this period were changing ice flux through the Firth of Forth ice stream onset zone and water depths at the grounding line; the development of the mixed-bed landsystem being a response to grounding line instability. © 2018 John Wiley & Sons, Ltd.
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submarine Glacial Landform distribution across the west greenland margin a fjord shelf slope transect through the uummannaq system 70 71 n
Geological Society London Memoirs, 2016Co-Authors: Julian A. Dowdeswell, K A Hogan, Colm O CofaighAbstract:Today, the Greenland Ice Sheet reaches the sea via a number of fast-flowing outlet glaciers that are fed by ice draining from huge interior basins (Rignot & Kanagaratnam 2006). At the Last Glacial Maximum (LGM), the ice sheet expanded to reach the continental shelf break around much of Greenland (O Cofaigh et al. 2013 a ). In the Uummannaq area at c. 70–71° N (Fig. 1a) there is now a 400 km distance between the terminus of Rink Glacier, which drains about 30 000 km2 of the ice sheet, and the shelf edge. This provides a transect from the modern glacier front, through a deep fjord system and adjacent cross-shelf trough, to the continental slope in Baffin Bay. The seafloor is now exposed along this transect and the Landforms produced by past Glacial activity can be examined using marine-geophysical methods. Deglaciation from the LGM was underway at the shelf edge in Uummannaq Trough by 14.8 kyr ago and from the mid-shelf by 10.9 kyr, and ice had probably retreated back into the fjord system by 9.3 kyr ago (O Cofaigh et al. 2013 a ; Roberts et al. 2013). Fig. 1. Regional bathymetry and shelf architecture of the Uummannaq fjord–shelf–slope system, West Greenland. The location of subsequent figures is also shown. ( a ) Multibeam-bathymetric coverage of the Uummannaq system (located as a red box on the inset location map of Greenland). UI, Ubekendt Island; RF, Rink Fjord. Regional bathymetry from IBCAO v. 3.0. ( b ) Dip-line seismic-reflection profile (130 km long) showing West Greenland continental shelf architecture comprising prograding sedimentary units. ( c ) 110 km long strike profile showing a Late Quaternary Glacial trough where erosion has truncated pre-existing reflectors (black arrows). The reflections marked bPP represent the lower boundary of Plio-Pleistocene erosion and glacier-influenced sediments; (b) and (c) are located in (a) …
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submarine Glacial Landform distribution along an antarctic peninsula palaeo ice stream a shelf slope transect through the marguerite trough system 66 70 s
Geological Society London Memoirs, 2016Co-Authors: Stephen J Livingstone, K A Hogan, Colm O Cofaigh, Julian A. DowdeswellAbstract:The Antarctic Peninsula comprises a thin spine of mountains and islands presently covered by an ice sheet up to 500 m thick that drains eastward and westward via outlet glaciers (Davies et al. 2012). The peninsula has undergone recent rapid warming, resulting in the collapse of fringing ice shelves and the retreat, thinning and acceleration of marine-terminating outlet glaciers (e.g. Pritchard & Vaughan 2007). At the Last Glacial Maximum (LGM), the ice sheet expanded to the continental shelf break around the peninsula, and was organized into a series of ice streams that drained along cross-shelf bathymetric troughs (O Cofaigh et al. 2014). Marguerite Bay is located on the west side of the Antarctic Peninsula, at about 66–70° S (Fig. 1). A 12–80 km wide and 370 km long trough extends across the bay from the northern terminus of George VI Ice Shelf to the continental shelf edge. Extensive marine-geophysical surveys of the trough reveal a suite of Glacial Landforms which record past flow of an ice stream which extended to the shelf edge at, or shortly after, the LGM. Subsequent retreat of the ice stream was underway by c. 14 ka ago and proceeded rapidly to the mid-shelf, where it slowed before accelerating once again to the inner shelf at c. 9 ka (Kilfeather et al. 2011). Fig. 1. Regional bathymetry and shelf architecture of the Marguerite Trough shelf–slope system, Antarctic Peninsula (AP). The location of subsequent figures is shown. ( a ) Multibeam-bathymetric coverage of the Marguerite Trough system. Light grey is grounded ice; dark grey is floating ice. Inset: location of study area on the Antarctic Peninsula (red box; map from IBCSO v. 1.0). Regional bathymetry from IBCAO v. 3.0. Arrows denote perspective of oblique views in Figures 2a and 3a. ( b ) 130 km along-dip seismic-reflection profile showing Antarctic …
Dag Ottesen - One of the best experts on this subject based on the ideXlab platform.
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Submarine Landforms on the Weddell Sea shelf imaged at high resolution using AUVs
2020Co-Authors: Julian A. Dowdeswell, Dag Ottesen, Christine Batchelor, Sasha Montelli, E. K. Dowdeswell, Jeffrey EvansAbstract:<p>Multibeam echo-sounders were deployed from Autonomous Underwater Vehicles (AUVs) flying close to the seafloor of the Weddell Sea shelf in order to investiagte the Glacial Landforms there with a view to understanding processes and patterns associated with deglaciation from the Last Glacial Maximum on the eastern side of the Antarctic Peninsula. A horizontal resolution of 0.5 m (using conventional mulitbeam systems), and in some cases 0.05 m (using interferometric multibeam equipment), allowed delicate seafloor Landforms to be mapped in several areas of the shelf beyond the Larsen C and former Larsen A and B ice shelves. A number of Glacial Landform assemblages were observed, including suites of delicate ridges associated with grounding-zone wedges and the grounding of icebergs on the shelf. These Landforms are probably related to the action of tides moving the ice up and down through a series of tidal cycles. At the highest spatial resolution, individual dropstones derived from rain-out during the melting of floating ice were imaged clearly. Imaging the seafloor at such high resolution allows both very detailed descriptions of submarine Landform morphology and also the complexity of such Landforms and Landform assemblages to be better understood, aiding the interpretation of the Glacial and related processes that led to their formation.</p>
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Glacial Landform assemblages in Spitsbergen fjords from the last full-Glacial, deglaciation and the late Holocene
Geological Society London Memoirs, 2016Co-Authors: Matthias Forwick, Julian A. Dowdeswell, Jan Sverre Laberg, Dag OttesenAbstract:Fjords are characteristic features of the western and northern coasts of Spitsbergen. They formed during repeated Glacial cycles when grounded glaciers drained large ice sheets occupying the Svalbard–Barents Sea region. Since grounded glaciers often erode and remove pre-existing deposits from fjord basins, depositional sequences in fjords are typically limited to the last Glacial–interGlacial cycle (e.g. Forwick & Vorren 2010). Holocene sediment drapes in Spitsbergen fjords are not usually thick enough to obscure Glacial Landforms and deposits from the last full-Glacial and deGlacial period. Glacier advances related to climatic cooling during the late Holocene, together with glacier surges, have led to the formation of complex Landform assemblages close to many fjord heads (e.g. Ottesen & Dowdeswell 2006; Ottesen et al. 2008; Streuff et al. 2015). The floors in the central and outer parts of several Spitsbergen fjords, including Kongsfjorden, Isfjorden, Billefjorden, Sassenfjorden and Tempelfjorden, reveal multiple streamlined sedimentary lineations orientated sub-parallel to fjord axes (Figs 1a, b, c, 2a; e.g. Ottesen et al. 2005; Baeten et al. 2010; Forwick et al. 2010). The ridges are≤5 km long, 15 m high and
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Glacial Landform assemblages in spitsbergen fjords from the last full Glacial deglaciation and the late holocene
Geological Society London Memoirs, 2016Co-Authors: Matthias Forwick, Julian A. Dowdeswell, Jan Sverre Laberg, Dag OttesenAbstract:Fjords are characteristic features of the western and northern coasts of Spitsbergen. They formed during repeated Glacial cycles when grounded glaciers drained large ice sheets occupying the Svalbard–Barents Sea region. Since grounded glaciers often erode and remove pre-existing deposits from fjord basins, depositional sequences in fjords are typically limited to the last Glacial–interGlacial cycle (e.g. Forwick & Vorren 2010). Holocene sediment drapes in Spitsbergen fjords are not usually thick enough to obscure Glacial Landforms and deposits from the last full-Glacial and deGlacial period. Glacier advances related to climatic cooling during the late Holocene, together with glacier surges, have led to the formation of complex Landform assemblages close to many fjord heads (e.g. Ottesen & Dowdeswell 2006; Ottesen et al. 2008; Streuff et al. 2015). The floors in the central and outer parts of several Spitsbergen fjords, including Kongsfjorden, Isfjorden, Billefjorden, Sassenfjorden and Tempelfjorden, reveal multiple streamlined sedimentary lineations orientated sub-parallel to fjord axes (Figs 1a, b, c, 2a; e.g. Ottesen et al. 2005; Baeten et al. 2010; Forwick et al. 2010). The ridges are≤5 km long, 15 m high and<500 m wide, with a spacing of up to 800 m; length-to-width ratios exceed 10:1. Elongate Landforms with length-to-width ratios smaller than 10:1 are also found in Kongsfjorden and Raudfjorden (e.g. Ottesen & Dowdeswell 2009; MacLachlan et al. 2010). Fig. 1. Examples of Glacial Landforms and sediments in Spitsbergen fjords. ( a ) Location of study areas (red boxes; map from IBCAO v. 3.0). Red boxes show locations of (b)–(d) and Figure 2. ( b ) Sun-illuminated multibeam-bathymetric image from Billefjorden (after Baeten et al. 2010). Acquisition system Kongsberg EM300. Frequency 30–34 kHz. Grid-cell size 5 m. ( c ) Sun-illuminated multibeam-bathymetric image from Kongsfjorden and southern Krossfjorden (courtesy of Boele Kuipers, Norwegian Hydrographic Service; for details see MacLachlan …
K A Hogan - One of the best experts on this subject based on the ideXlab platform.
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submarine Glacial Landform distribution across the west greenland margin a fjord shelf slope transect through the uummannaq system 70 71 n
Geological Society London Memoirs, 2016Co-Authors: Julian A. Dowdeswell, K A Hogan, Colm O CofaighAbstract:Today, the Greenland Ice Sheet reaches the sea via a number of fast-flowing outlet glaciers that are fed by ice draining from huge interior basins (Rignot & Kanagaratnam 2006). At the Last Glacial Maximum (LGM), the ice sheet expanded to reach the continental shelf break around much of Greenland (O Cofaigh et al. 2013 a ). In the Uummannaq area at c. 70–71° N (Fig. 1a) there is now a 400 km distance between the terminus of Rink Glacier, which drains about 30 000 km2 of the ice sheet, and the shelf edge. This provides a transect from the modern glacier front, through a deep fjord system and adjacent cross-shelf trough, to the continental slope in Baffin Bay. The seafloor is now exposed along this transect and the Landforms produced by past Glacial activity can be examined using marine-geophysical methods. Deglaciation from the LGM was underway at the shelf edge in Uummannaq Trough by 14.8 kyr ago and from the mid-shelf by 10.9 kyr, and ice had probably retreated back into the fjord system by 9.3 kyr ago (O Cofaigh et al. 2013 a ; Roberts et al. 2013). Fig. 1. Regional bathymetry and shelf architecture of the Uummannaq fjord–shelf–slope system, West Greenland. The location of subsequent figures is also shown. ( a ) Multibeam-bathymetric coverage of the Uummannaq system (located as a red box on the inset location map of Greenland). UI, Ubekendt Island; RF, Rink Fjord. Regional bathymetry from IBCAO v. 3.0. ( b ) Dip-line seismic-reflection profile (130 km long) showing West Greenland continental shelf architecture comprising prograding sedimentary units. ( c ) 110 km long strike profile showing a Late Quaternary Glacial trough where erosion has truncated pre-existing reflectors (black arrows). The reflections marked bPP represent the lower boundary of Plio-Pleistocene erosion and glacier-influenced sediments; (b) and (c) are located in (a) …
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submarine Glacial Landform distribution along an antarctic peninsula palaeo ice stream a shelf slope transect through the marguerite trough system 66 70 s
Geological Society London Memoirs, 2016Co-Authors: Stephen J Livingstone, K A Hogan, Colm O Cofaigh, Julian A. DowdeswellAbstract:The Antarctic Peninsula comprises a thin spine of mountains and islands presently covered by an ice sheet up to 500 m thick that drains eastward and westward via outlet glaciers (Davies et al. 2012). The peninsula has undergone recent rapid warming, resulting in the collapse of fringing ice shelves and the retreat, thinning and acceleration of marine-terminating outlet glaciers (e.g. Pritchard & Vaughan 2007). At the Last Glacial Maximum (LGM), the ice sheet expanded to the continental shelf break around the peninsula, and was organized into a series of ice streams that drained along cross-shelf bathymetric troughs (O Cofaigh et al. 2014). Marguerite Bay is located on the west side of the Antarctic Peninsula, at about 66–70° S (Fig. 1). A 12–80 km wide and 370 km long trough extends across the bay from the northern terminus of George VI Ice Shelf to the continental shelf edge. Extensive marine-geophysical surveys of the trough reveal a suite of Glacial Landforms which record past flow of an ice stream which extended to the shelf edge at, or shortly after, the LGM. Subsequent retreat of the ice stream was underway by c. 14 ka ago and proceeded rapidly to the mid-shelf, where it slowed before accelerating once again to the inner shelf at c. 9 ka (Kilfeather et al. 2011). Fig. 1. Regional bathymetry and shelf architecture of the Marguerite Trough shelf–slope system, Antarctic Peninsula (AP). The location of subsequent figures is shown. ( a ) Multibeam-bathymetric coverage of the Marguerite Trough system. Light grey is grounded ice; dark grey is floating ice. Inset: location of study area on the Antarctic Peninsula (red box; map from IBCSO v. 1.0). Regional bathymetry from IBCAO v. 3.0. Arrows denote perspective of oblique views in Figures 2a and 3a. ( b ) 130 km along-dip seismic-reflection profile showing Antarctic …
Martin Jakobsson - One of the best experts on this subject based on the ideXlab platform.
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submarine Glacial Landform distribution in the central arctic ocean shelf slope basin system
Geological Society London Memoirs, 2016Co-Authors: Martin JakobssonAbstract:The central Arctic Ocean, including its surrounding seas, extends over an area of c. 9.5×106 km2 of which c. 53% comprises shallow continental shelves (Jakobsson 2002) (Fig. 1a). The surface of this nearly land-locked polar ocean is at present dominated by a perennial sea-ice cover with a maximum extent every year in late February to March and a minimum in early to mid-September (Fig. 1a) (Serreze et al. 2007). Outlet glaciers producing icebergs that drift in the central Arctic Ocean exist on northern Greenland, Ellesmere Island and on islands in the Barents and Kara seas (Diemand 2001) (Fig. 1a). Ice shelves, although substantially smaller than those found in Antarctica, presently exist in some of Greenland's fjords (Rignot & Kanagaratnam 2006), on Severnaya Zemlya (Williams & Dowdeswell 2001) and along the northern coast of Ellesmere Island (Jeffries 1992; Williams & Ferrigno 2012). Existing ice shelves around the Arctic Ocean are primarily formed through accretion of multiyear sea ice and gain their mass from snowfall and/or basal freezing. Fig. 1. ( a ) Bathymetric map of the Arctic Ocean and study areas (red boxes, map from IBCAO v. 3.0). Purple line is mean minimum sea-ice extent (September). Pink line is mean maximum sea-ice extent (March). AGT, Amundsen Gulf Trough; AP, Arlis Plateau; BS, Bering Strait; CP, Chukchi Plateau; CR, Chukchi Rise; FS, Fram Strait; HC, Herald Canyon; LR, Lomonosov Ridge; McT, M'Clure Trough; MJR, Morris Jesup Rise; MT, Mackenzie Trough; MR, Mendeleev Ridge; NS, Nares Strait; StT, St Anna Trough; YP, Yermak Plateau. ( b ) Ice-sheet extent during Last Glacial Maximum (LGM) (from Ehlers & Gibbard 2004; Svendsen et al. 2004; England et al. 2009). LGM topography is from ICE-5G (Peltier 2004). ( c ) Western section of the Canadian Arctic Archipelago with outlines of the main CSTs (black line) and …
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submarine Glacial Landform distribution across the west antarctic margin from grounding line to slope the pine island thwaites ice stream system
Geological Society London Memoirs, 2016Co-Authors: Alastair G C Graham, John B. Anderson, Martin Jakobsson, Johann Philipp Klages, Claus-dieter Hillenbrand, Robert D Larter, Karsten Gohl, Frank O Nitsche, James Smith, Adrian JenkinsAbstract:About 30% of ice draining the West Antarctic Ice Sheet discharges through several glacier systems into the Amundsen Sea Embayment (ASE) (Fig. 1a). Two major ice-stream outlets, Pine Island and Thwaites glaciers, have undergone significant twentieth century changes (e.g. Rignot et al. 2008) and much effort has focused upon understanding their late Quaternary Glacial history (Larter et al. 2014). At the Last Glacial Maximum (LGM), the ice sheet in the ASE expanded to reach the outer shelf and is postulated to have reached the shelf edge (Graham et al. 2010). The Pine Island and Thwaites glaciers combined regularly through Quaternary glaciations to carve out a >500 km long trough that extends from the shelf break back to the modern-day grounding line and beyond. Geophysical data exist for the breadth of this transect, including sub-ice-shelf bathymetry (Jenkins et al. 2010), making it one of the most complete palaeo-ice-stream landsystems known offshore of Antarctica. Deglaciation of the trough was underway by c. 20 cal. ka BP and was episodic, reaching a mid-shelf position by c. 13.5–12 cal. ka BP and retreating rapidly to the inner ASE by c. 11–9 cal. ka BP (Kirshner et al. 2012; Hillenbrand et al. 2013; Smith et al. 2014). Repeated pauses and several phases of ice-shelf break-up have been interpreted to have taken place during deglaciation based upon a well-preserved Landform and sediment record (Lowe & Anderson 2002; Graham et al. 2010; Jakobsson et al. 2011). Fig. 1. Bathymetry and seismic architecture of the Pine Island Trough region, West Antarctica. ( a ) Location of study area (red box; map from IBCSO v. 1.0). ( b ) Multibeam-bathymetric data for the eastern Amundsen Sea Embayment, collated from various published datasets (UK, German, Swedish and US). ( c ) Seismic line NBP9902-11 from the middle shelf of Pine Island Trough …