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Kelly A Hogan - One of the best experts on this subject based on the ideXlab platform.
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Glacial Sedimentation fluxes and erosion rates associated with ice retreat in petermann fjord and nares strait north west greenland
The Cryosphere, 2020Co-Authors: Kelly A Hogan, Martin Jakobsson, Larry A Mayer, Brendan T Reilly, Anne E Jennings, Joseph S Stoner, Tove Nielsen, Katrine Juul Andresen, Egon NormarkAbstract:Abstract. Petermann Fjord is a deep ( >1000 m) fjord that incises the coastline of north-west Greenland and was carved by an expanded Petermann Glacier, one of the six largest outlet glaciers draining the modern Greenland Ice Sheet (GrIS). Between 5 and 70 m of unconsolidated glacigenic material infills in the fjord and adjacent Nares Strait, deposited as the Petermann and Nares Strait ice streams retreated through the area after the Last Glacial Maximum. We have investigated the deGlacial deposits using seismic stratigraphic techniques and have correlated our results with high-resolution bathymetric data and core lithofacies. We identify six seismo-acoustic facies in more than 3500 line kilometres of sub-bottom and seismic-reflection profiles throughout the fjord, Hall Basin and Kennedy Channel. Seismo-acoustic facies relate to bedrock or till surfaces (Facies I), subGlacial deposition (Facies II), deposition from meltwater plumes and icebergs in quiescent glacimarine conditions (Facies III, IV), deposition at grounded ice margins during stillstands in retreat (grounding-zone wedges; Facies V) and the redeposition of material downslope (Facies IV). These sediment units represent the total volume of Glacial sediment delivered to the mapped marine environment during retreat. We calculate a Glacial sediment flux for the former Petermann ice stream as 1080–1420 m 3 a −1 per metre of ice stream width and an average deGlacial erosion rate for the basin of 0.29–0.34 mm a −1 . Our deGlacial erosion rates are consistent with results from Antarctic Peninsula fjord systems but are several times lower than values for other modern GrIS catchments. This difference is attributed to fact that large volumes of surface water do not access the bed in the Petermann system, and we conclude that Glacial erosion is limited to areas overridden by streaming ice in this large outlet glacier setting. Erosion rates are also presented for two phases of ice retreat and confirm that there is significant variation in rates over a Glacial–deGlacial transition. Our new Glacial sediment fluxes and erosion rates show that the Petermann ice stream was approximately as efficient as the palaeo-Jakobshavn Isbrae at eroding, transporting and delivering sediment to its margin during early deglaciation.
Julian A. Dowdeswell - One of the best experts on this subject based on the ideXlab platform.
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New insights into the formation of submarine Glacial landforms from high-resolution Autonomous Underwater Vehicle data
Geomorphology, 2020Co-Authors: Christine Batchelor, Aleksandr Montelli, Dag Ottesen, Jeffrey Evans, E. K. Dowdeswell, Frazer Christie, Julian A. DowdeswellAbstract:Abstract Autonomous Underwater Vehicles (AUVs) deployed close to the seafloor can acquire high-resolution geophysical data about the topography and shallow stratigraphy of the seabed, yet have had limited application within the fields of Glacial geomorphology and ice sheet reconstruction. Here, we present multibeam echo-sounding, side-scan sonar, sub-bottom profiler and High-Resolution Synthetic Aperture Sonar (HISAS) data acquired during three AUV dives on the northeast Antarctic Peninsula continental shelf. These data enable Glacial landforms, including mega-scale Glacial lineations (MSGLs), grounding-zone wedges (GZWs) and iceberg ploughmarks, to be imaged at a horizontal resolution of a few tens of centimetres, allowing for the identification of subtle morphological features. We map tidal ridges that are interpreted as having been formed 1) along the ice-sheet grounding line by the squeezing up of soft seafloor sediments by vertical motion of the grounding line during tidal cycles, and 2) by the tidally driven motion of grounded or near-grounded icebergs. These data also enable the mapping of small GZWs that show the location of short-term still-stands or re-advances of the ice-sheet grounding zone. No meltwater channels are identified from our data, suggesting that free-flowing meltwater may not be essential for the formation of GZWs or MSGLs. The examples presented here show how high-resolution AUV-derived geophysical data provide a step-change in our ability to image seafloor Glacial landforms, enabling new interpretations about past ice dynamics and Glacial Sedimentation at fine temporal and spatial scales.
Egon Normark - One of the best experts on this subject based on the ideXlab platform.
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Glacial Sedimentation fluxes and erosion rates associated with ice retreat in petermann fjord and nares strait north west greenland
The Cryosphere, 2020Co-Authors: Kelly A Hogan, Martin Jakobsson, Larry A Mayer, Brendan T Reilly, Anne E Jennings, Joseph S Stoner, Tove Nielsen, Katrine Juul Andresen, Egon NormarkAbstract:Abstract. Petermann Fjord is a deep ( >1000 m) fjord that incises the coastline of north-west Greenland and was carved by an expanded Petermann Glacier, one of the six largest outlet glaciers draining the modern Greenland Ice Sheet (GrIS). Between 5 and 70 m of unconsolidated glacigenic material infills in the fjord and adjacent Nares Strait, deposited as the Petermann and Nares Strait ice streams retreated through the area after the Last Glacial Maximum. We have investigated the deGlacial deposits using seismic stratigraphic techniques and have correlated our results with high-resolution bathymetric data and core lithofacies. We identify six seismo-acoustic facies in more than 3500 line kilometres of sub-bottom and seismic-reflection profiles throughout the fjord, Hall Basin and Kennedy Channel. Seismo-acoustic facies relate to bedrock or till surfaces (Facies I), subGlacial deposition (Facies II), deposition from meltwater plumes and icebergs in quiescent glacimarine conditions (Facies III, IV), deposition at grounded ice margins during stillstands in retreat (grounding-zone wedges; Facies V) and the redeposition of material downslope (Facies IV). These sediment units represent the total volume of Glacial sediment delivered to the mapped marine environment during retreat. We calculate a Glacial sediment flux for the former Petermann ice stream as 1080–1420 m 3 a −1 per metre of ice stream width and an average deGlacial erosion rate for the basin of 0.29–0.34 mm a −1 . Our deGlacial erosion rates are consistent with results from Antarctic Peninsula fjord systems but are several times lower than values for other modern GrIS catchments. This difference is attributed to fact that large volumes of surface water do not access the bed in the Petermann system, and we conclude that Glacial erosion is limited to areas overridden by streaming ice in this large outlet glacier setting. Erosion rates are also presented for two phases of ice retreat and confirm that there is significant variation in rates over a Glacial–deGlacial transition. Our new Glacial sediment fluxes and erosion rates show that the Petermann ice stream was approximately as efficient as the palaeo-Jakobshavn Isbrae at eroding, transporting and delivering sediment to its margin during early deglaciation.
Christine Batchelor - One of the best experts on this subject based on the ideXlab platform.
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New insights into the formation of submarine Glacial landforms from high-resolution Autonomous Underwater Vehicle data
Geomorphology, 2020Co-Authors: Christine Batchelor, Aleksandr Montelli, Dag Ottesen, Jeffrey Evans, E. K. Dowdeswell, Frazer Christie, Julian A. DowdeswellAbstract:Abstract Autonomous Underwater Vehicles (AUVs) deployed close to the seafloor can acquire high-resolution geophysical data about the topography and shallow stratigraphy of the seabed, yet have had limited application within the fields of Glacial geomorphology and ice sheet reconstruction. Here, we present multibeam echo-sounding, side-scan sonar, sub-bottom profiler and High-Resolution Synthetic Aperture Sonar (HISAS) data acquired during three AUV dives on the northeast Antarctic Peninsula continental shelf. These data enable Glacial landforms, including mega-scale Glacial lineations (MSGLs), grounding-zone wedges (GZWs) and iceberg ploughmarks, to be imaged at a horizontal resolution of a few tens of centimetres, allowing for the identification of subtle morphological features. We map tidal ridges that are interpreted as having been formed 1) along the ice-sheet grounding line by the squeezing up of soft seafloor sediments by vertical motion of the grounding line during tidal cycles, and 2) by the tidally driven motion of grounded or near-grounded icebergs. These data also enable the mapping of small GZWs that show the location of short-term still-stands or re-advances of the ice-sheet grounding zone. No meltwater channels are identified from our data, suggesting that free-flowing meltwater may not be essential for the formation of GZWs or MSGLs. The examples presented here show how high-resolution AUV-derived geophysical data provide a step-change in our ability to image seafloor Glacial landforms, enabling new interpretations about past ice dynamics and Glacial Sedimentation at fine temporal and spatial scales.
Jeremy Evans - One of the best experts on this subject based on the ideXlab platform.
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continental margin Sedimentation with special reference to the north east atlantic margin
Sedimentology, 2000Co-Authors: P P E Weaver, Russell B Wynn, N H Kenyon, Jeremy EvansAbstract:The north-east Atlantic continental margin displays a wide range of sediment transport systems with both along-slope and down-slope processes. Off most of the north-west African margin, south of 26°N, upwelling produces elevated accumulation rates, although there is little fluvial input. This area is subject to infrequent but large-scale mass movements, giving rise to debris flows and turbidity currents. The turbidity currents traverse the slope and deposit thick layers on the abyssal plains, while debris flows deposit on the continental slope and rise. From the Atlas Mountains northwards to 56°N, the margin is less prone to mass movements, but is cut by a large number of canyons, which also funnel turbidity currents to the abyssal plains. The presence of a lithospheric plate boundary off SW Iberia is believed to have led to high rates of sediment transport to the deep sea. Even larger quantities of coarse sediments have fed the canyons and abyssal plains in the Bay of Biscay as a result of drainage from melting icecaps. Bottom currents have built sediment waves off the African and Iberian margins, and created erosional furrows south of the Canaries. The Mediterranean outflow is a particularly strong bottom current near the Straits of Gibraltar, depositing sand waves and mud waves in the Gulf of Cadiz. North of 56°N, the margin is heavily influenced by Glacial and glaciomarine processes active during Glacial times, which built Glacial trough-mouth fans, such as the North Sea Fan, and left iceberg scour marks on the upper slope and shelf. Over a long period, especially during interGlacials, this part of the margin has been greatly affected by along-slope currents, with less effect by turbidity currents than on the lower latitude margins. Large-scale mass movements are again a prominent feature, particularly off Norway and the Faeroes. Some of these mass movements have occurred during the Holocene, although high Glacial Sedimentation rates may have contributed to the instability.