The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
Soren Rysgaard - One of the best experts on this subject based on the ideXlab platform.
-
local coastal water masses control heat levels in a west greenland tidewater outlet glacier Fjord
Journal of Geophysical Research, 2018Co-Authors: John Mortensen, Jørgen Bendtsen, Soren Rysgaard, Kristine Engel Arendt, Thomas Juulpedersen, D H Sogaard, Lorenz MeireAbstract:Fjords form the gateway between the open ocean and the Greenland Ice Sheet (GIS) and consequently play a crucial role for the stability of the Ice Sheet. Hydrographic observations, especially with seasonal resolution, from these Fjords are limited making it difficult to assess linkages between the Fjord, coastal water masses, and freshwater discharge from GIS. Here we present a decade‐long monthly hydrographic time series from a southwest Greenland Fjord in direct contact with GIS. Our observations reveal significant temporal and spatial water mass variations related to coastal, glacial, and atmospheric dynamics. During winter, the Fjord circulation is dominated by seasonal dense coastal inflows and the timing of these inflows determines intermediate and deepwater temperatures. During summer, runoff from GIS leads to a pronounced freshening of the Fjord. In general, the Fjord's seasonal circulation system damps the seasonal variation in temperature in the Fjord. This leads to a seasonal temperature range in the intermediate layer in the inner part of the Fjord that is half the observed range at the Fjord entrance. Changes in mean water temperatures in the intermediate layer seem predominantly linked to local coastal water masses, where cold winter/warm summer events decrease/increase the mean water temperatures. Consequently, these events play an important role in heat transport toward glacier termini.
-
seasonal variability of the circulation system in a west greenland tidewater outlet glacier Fjord godthabsFjord 64 n
Journal of Geophysical Research, 2014Co-Authors: John Mortensen, Jørgen Bendtsen, Soren Rysgaard, Kunuk LennertAbstract:Many tidewater outlet glacier Fjords surround the coast of Greenland, and their dynamics and circulation are of great importance for understanding the heat transport toward glaciers from the ice sheet. Thus, Fjord circulation is a critical aspect for assessing the threat of global sea level rise due to melting of the ice sheet. However, very few observational studies describe the seasonal dynamics of Fjord circulation. Here we present the first continuous current measurements (April–November) from a deep mooring deployed in a west Greenland tidewater outlet glacier Fjord. Four distinct circulation phases are identified during the period, and they are related to exchange processes with coastal waters, tidal mixing, and melt processes on the Greenland Ice Sheet. During early summer, warm intermediate water is transported toward the glacier at an average velocity of about 7 cm s−1. In late summer, the average velocity decreases to 3 cm s−1 during a period with significant subglacial freshwater discharges. During this period, a large variability in current velocities is also observed. The associated average heat transport in an intermediate-depth range corresponds to 568 GW in early summer and is reduced to 287 GW in late summer. These heat fluxes are at the higher end of previously reported fluxes. Our measurements show that the intermediate heat transport varies over time and during summer provides a major contribution to the heat budget and, thereby, potentially to glacial melt. We suggest that intermediate heat transport may play a similar important role in other Fjords around Greenland.
-
seasonal surface layer dynamics and sensitivity to runoff in a high arctic Fjord young sound tyrolerFjord 74 n
Journal of Geophysical Research, 2014Co-Authors: Jørgen Bendtsen, John Mortensen, Soren RysgaardAbstract:Runoff from the Greenland Ice Sheet, local glaciers, and snowmelt along the northeastern Greenland coastline has a significant impact on coastal water masses flowing south toward Denmark Strait. Very few direct measurements of runoff currently exist in this large area, and the water masses near the coast are also difficult to measure due to the presence of icebergs and sea ice. Measurements from the Zackenberg Research station, located in Young Sound/TyrolerFjord in northeast Greenland (74°N), provide some of the few observations of hydrographic, hydrologic, and atmospheric parameters from this remote area. Here we analyze measurements from the Fjord and also measurements in the ambient water masses, which are found in the outer Fjord and between the Fjord and the East Greenland Current and validate and apply a numerical model of the Fjord. A model sensitivity study allows us to constrain runoff estimates for the area. We also show that a total runoff between 0.9 and 1.4 km3 in 2006 is in accordance with observed surface salinities and calculated freshwater content in the Fjord. This indicates that earlier reported runoff to the area is significantly underestimated and that melt from glaciers and the Greenland Ice Sheet in this region may be up to 50% larger than the current estimate. Model simulations indicate the presence of a cold low-saline coastal water mass formed by runoff from Fjords north of the Young Sound/TyrolerFjord system. Simulations of passive and age tracers show that residence time of river water during the summer period is about 1 month in the inner part of the Fjord.
Jørgen Bendtsen - One of the best experts on this subject based on the ideXlab platform.
-
local coastal water masses control heat levels in a west greenland tidewater outlet glacier Fjord
Journal of Geophysical Research, 2018Co-Authors: John Mortensen, Jørgen Bendtsen, Soren Rysgaard, Kristine Engel Arendt, Thomas Juulpedersen, D H Sogaard, Lorenz MeireAbstract:Fjords form the gateway between the open ocean and the Greenland Ice Sheet (GIS) and consequently play a crucial role for the stability of the Ice Sheet. Hydrographic observations, especially with seasonal resolution, from these Fjords are limited making it difficult to assess linkages between the Fjord, coastal water masses, and freshwater discharge from GIS. Here we present a decade‐long monthly hydrographic time series from a southwest Greenland Fjord in direct contact with GIS. Our observations reveal significant temporal and spatial water mass variations related to coastal, glacial, and atmospheric dynamics. During winter, the Fjord circulation is dominated by seasonal dense coastal inflows and the timing of these inflows determines intermediate and deepwater temperatures. During summer, runoff from GIS leads to a pronounced freshening of the Fjord. In general, the Fjord's seasonal circulation system damps the seasonal variation in temperature in the Fjord. This leads to a seasonal temperature range in the intermediate layer in the inner part of the Fjord that is half the observed range at the Fjord entrance. Changes in mean water temperatures in the intermediate layer seem predominantly linked to local coastal water masses, where cold winter/warm summer events decrease/increase the mean water temperatures. Consequently, these events play an important role in heat transport toward glacier termini.
-
Multibeam bathymetry and CTD measurements in two Fjord systems in southeastern Greenland
Earth System Science Data, 2017Co-Authors: Kristian K. Kjeldsen, Reimer Wilhelm Weinrebe, Jørgen Bendtsen, Anders A. Bjørk, Kurt H. KjærAbstract:Abstract. We present bathymetry and hydrological observations collected in the summer of 2014 from two Fjord systems in southeastern Greenland with a multibeam sonar system. Our results provide a detailed bathymetric map of the Fjord complex around the island of Skjoldungen in Skjoldungen Fjord and the outer part of Timmiarmiut Fjord and show far greater depths compared to the International Bathymetric Chart of the Arctic Ocean. The hydrography collected shows different properties in the Fjords with the bottom water masses below 240 m in Timmiarmiut Fjord being 1–2 °C warmer than in the two Fjords around Skjoldungen, but data also illustrate the influence of sills on the exchange of deeper water masses within Fjords. Moreover, evidence of subglacial discharge in Timmiarmiut Fjord, which is consistent with satellite observations of ice melange set into motion, adds to our increasing understanding of the distribution of subglacial meltwater. Data are available through the PANGAEA website at https://doi.pangaea.de/10.1594/PANGAEA.860627 .
-
Multibeam Bathymetry and CTD-Measurements in two Fjord systems in Southeast Greenland
2017Co-Authors: Kristian K. Kjeldsen, Jørgen Bendtsen, Anders A. Bjørk, Wilhelm Weinrebe, Kurt H. KjærAbstract:Abstract. We present bathymetry and hydrological observations collected in the summer of 2014 from two Fjord systems in Southeast Greenland, using SS Activ with a multibeam system temporally installed over the side of the ship. Our results provide a detailed bathymetric map of the Fjord complex around Skjoldungen Island and the outer part of Timmiarmiut Fjord and show far greater depths compared to the International Bathymetric Chart of the Arctic Ocean. The hydrography collected show different properties in the Fjords with the bottom water masses below 240 m in Timmiarmiut Fjord being 1–2 °C warmer than in the two Fjords around Skjoldungen Island, but data also illustrate the influence of sills on the exchange of deeper water masses within Fjords. Moreover, evidence of subglacial discharge in Timmiarmiut Fjord, consistent with satellite observations of ice mélange set into motion, adds to our increasing understanding of the distribution of subglacial meltwater. Data is available through the PANGAEA website https://doi.pangaea.de/10.1594/PANGAEA.860627.
-
seasonal variability of the circulation system in a west greenland tidewater outlet glacier Fjord godthabsFjord 64 n
Journal of Geophysical Research, 2014Co-Authors: John Mortensen, Jørgen Bendtsen, Soren Rysgaard, Kunuk LennertAbstract:Many tidewater outlet glacier Fjords surround the coast of Greenland, and their dynamics and circulation are of great importance for understanding the heat transport toward glaciers from the ice sheet. Thus, Fjord circulation is a critical aspect for assessing the threat of global sea level rise due to melting of the ice sheet. However, very few observational studies describe the seasonal dynamics of Fjord circulation. Here we present the first continuous current measurements (April–November) from a deep mooring deployed in a west Greenland tidewater outlet glacier Fjord. Four distinct circulation phases are identified during the period, and they are related to exchange processes with coastal waters, tidal mixing, and melt processes on the Greenland Ice Sheet. During early summer, warm intermediate water is transported toward the glacier at an average velocity of about 7 cm s−1. In late summer, the average velocity decreases to 3 cm s−1 during a period with significant subglacial freshwater discharges. During this period, a large variability in current velocities is also observed. The associated average heat transport in an intermediate-depth range corresponds to 568 GW in early summer and is reduced to 287 GW in late summer. These heat fluxes are at the higher end of previously reported fluxes. Our measurements show that the intermediate heat transport varies over time and during summer provides a major contribution to the heat budget and, thereby, potentially to glacial melt. We suggest that intermediate heat transport may play a similar important role in other Fjords around Greenland.
-
seasonal surface layer dynamics and sensitivity to runoff in a high arctic Fjord young sound tyrolerFjord 74 n
Journal of Geophysical Research, 2014Co-Authors: Jørgen Bendtsen, John Mortensen, Soren RysgaardAbstract:Runoff from the Greenland Ice Sheet, local glaciers, and snowmelt along the northeastern Greenland coastline has a significant impact on coastal water masses flowing south toward Denmark Strait. Very few direct measurements of runoff currently exist in this large area, and the water masses near the coast are also difficult to measure due to the presence of icebergs and sea ice. Measurements from the Zackenberg Research station, located in Young Sound/TyrolerFjord in northeast Greenland (74°N), provide some of the few observations of hydrographic, hydrologic, and atmospheric parameters from this remote area. Here we analyze measurements from the Fjord and also measurements in the ambient water masses, which are found in the outer Fjord and between the Fjord and the East Greenland Current and validate and apply a numerical model of the Fjord. A model sensitivity study allows us to constrain runoff estimates for the area. We also show that a total runoff between 0.9 and 1.4 km3 in 2006 is in accordance with observed surface salinities and calculated freshwater content in the Fjord. This indicates that earlier reported runoff to the area is significantly underestimated and that melt from glaciers and the Greenland Ice Sheet in this region may be up to 50% larger than the current estimate. Model simulations indicate the presence of a cold low-saline coastal water mass formed by runoff from Fjords north of the Young Sound/TyrolerFjord system. Simulations of passive and age tracers show that residence time of river water during the summer period is about 1 month in the inner part of the Fjord.
John Mortensen - One of the best experts on this subject based on the ideXlab platform.
-
local coastal water masses control heat levels in a west greenland tidewater outlet glacier Fjord
Journal of Geophysical Research, 2018Co-Authors: John Mortensen, Jørgen Bendtsen, Soren Rysgaard, Kristine Engel Arendt, Thomas Juulpedersen, D H Sogaard, Lorenz MeireAbstract:Fjords form the gateway between the open ocean and the Greenland Ice Sheet (GIS) and consequently play a crucial role for the stability of the Ice Sheet. Hydrographic observations, especially with seasonal resolution, from these Fjords are limited making it difficult to assess linkages between the Fjord, coastal water masses, and freshwater discharge from GIS. Here we present a decade‐long monthly hydrographic time series from a southwest Greenland Fjord in direct contact with GIS. Our observations reveal significant temporal and spatial water mass variations related to coastal, glacial, and atmospheric dynamics. During winter, the Fjord circulation is dominated by seasonal dense coastal inflows and the timing of these inflows determines intermediate and deepwater temperatures. During summer, runoff from GIS leads to a pronounced freshening of the Fjord. In general, the Fjord's seasonal circulation system damps the seasonal variation in temperature in the Fjord. This leads to a seasonal temperature range in the intermediate layer in the inner part of the Fjord that is half the observed range at the Fjord entrance. Changes in mean water temperatures in the intermediate layer seem predominantly linked to local coastal water masses, where cold winter/warm summer events decrease/increase the mean water temperatures. Consequently, these events play an important role in heat transport toward glacier termini.
-
seasonal variability of the circulation system in a west greenland tidewater outlet glacier Fjord godthabsFjord 64 n
Journal of Geophysical Research, 2014Co-Authors: John Mortensen, Jørgen Bendtsen, Soren Rysgaard, Kunuk LennertAbstract:Many tidewater outlet glacier Fjords surround the coast of Greenland, and their dynamics and circulation are of great importance for understanding the heat transport toward glaciers from the ice sheet. Thus, Fjord circulation is a critical aspect for assessing the threat of global sea level rise due to melting of the ice sheet. However, very few observational studies describe the seasonal dynamics of Fjord circulation. Here we present the first continuous current measurements (April–November) from a deep mooring deployed in a west Greenland tidewater outlet glacier Fjord. Four distinct circulation phases are identified during the period, and they are related to exchange processes with coastal waters, tidal mixing, and melt processes on the Greenland Ice Sheet. During early summer, warm intermediate water is transported toward the glacier at an average velocity of about 7 cm s−1. In late summer, the average velocity decreases to 3 cm s−1 during a period with significant subglacial freshwater discharges. During this period, a large variability in current velocities is also observed. The associated average heat transport in an intermediate-depth range corresponds to 568 GW in early summer and is reduced to 287 GW in late summer. These heat fluxes are at the higher end of previously reported fluxes. Our measurements show that the intermediate heat transport varies over time and during summer provides a major contribution to the heat budget and, thereby, potentially to glacial melt. We suggest that intermediate heat transport may play a similar important role in other Fjords around Greenland.
-
seasonal surface layer dynamics and sensitivity to runoff in a high arctic Fjord young sound tyrolerFjord 74 n
Journal of Geophysical Research, 2014Co-Authors: Jørgen Bendtsen, John Mortensen, Soren RysgaardAbstract:Runoff from the Greenland Ice Sheet, local glaciers, and snowmelt along the northeastern Greenland coastline has a significant impact on coastal water masses flowing south toward Denmark Strait. Very few direct measurements of runoff currently exist in this large area, and the water masses near the coast are also difficult to measure due to the presence of icebergs and sea ice. Measurements from the Zackenberg Research station, located in Young Sound/TyrolerFjord in northeast Greenland (74°N), provide some of the few observations of hydrographic, hydrologic, and atmospheric parameters from this remote area. Here we analyze measurements from the Fjord and also measurements in the ambient water masses, which are found in the outer Fjord and between the Fjord and the East Greenland Current and validate and apply a numerical model of the Fjord. A model sensitivity study allows us to constrain runoff estimates for the area. We also show that a total runoff between 0.9 and 1.4 km3 in 2006 is in accordance with observed surface salinities and calculated freshwater content in the Fjord. This indicates that earlier reported runoff to the area is significantly underestimated and that melt from glaciers and the Greenland Ice Sheet in this region may be up to 50% larger than the current estimate. Model simulations indicate the presence of a cold low-saline coastal water mass formed by runoff from Fjords north of the Young Sound/TyrolerFjord system. Simulations of passive and age tracers show that residence time of river water during the summer period is about 1 month in the inner part of the Fjord.
Julian A. Dowdeswell - One of the best experts on this subject based on the ideXlab platform.
-
Generating synthetic Fjord bathymetry for coastal Greenland
The Cryosphere, 2017Co-Authors: Christopher Williams, Stephen Cornford, Thomas M. Jordan, Julian A. Dowdeswell, Martin J. Siegert, Chris D. Clark, Darrel A. Swift, Andrew Sole, Ian Fenty, Jonathan L. BamberAbstract:Abstract. Bed topography is a critical boundary for the numerical modelling of ice sheets and ice–ocean interactions. A persistent issue with existing topography products for the bed of the Greenland Ice Sheet and surrounding sea floor is the poor representation of coastal bathymetry, especially in regions of floating ice and near the grounding line. Sparse data coverage, and the resultant coarse resolution at the ice–ocean boundary, poses issues in our ability to model ice flow advance and retreat from the present position. In addition, as Fjord bathymetry is known to exert strong control on ocean circulation and ice–ocean forcing, the lack of bed data leads to an inability to model these processes adequately. Since the release of the last complete Greenland bed topography–bathymetry product, new observational bathymetry data have become available. These data can be used to constrain bathymetry, but many Fjords remain completely unsampled and therefore poorly resolved. Here, as part of the development of the next generation of Greenland bed topography products, we present a new method for constraining the bathymetry of Fjord systems in regions where data coverage is sparse. For these cases, we generate synthetic Fjord geometries using a method conditioned by surveys of terrestrial glacial valleys as well as existing sinuous feature interpolation schemes. Our approach enables the capture of the general bathymetry profile of a Fjord in north-west Greenland close to Cape York, when compared to observational data. We validate our synthetic approach by demonstrating reduced overestimation of depths compared to past attempts to constrain Fjord bathymetry. We also present an analysis of the spectral characteristics of Fjord centrelines using recently acquired bathymetric observations, demonstrating how a stochastic model of Fjord bathymetry could be parameterised and used to create different realisations.
-
Submarine gullies and an axial channel in glacier-influenced Courtauld Fjord, East Greenland
Geological Society London Memoirs, 2016Co-Authors: Jeffrey Evans, Julian A. DowdeswellAbstract: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 Fjords. Gullies vary in distribution and dimensions depending on formation mechanisms, including 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 Kangerlugssuaq Fjord (68° N) 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). Fig. 1. Multibeam bathymetry and cross-profiles of submarine gullies in Courtauld Fjord, East Greenland. ( a ) Submarine gullies in the outer Fjord and subglacial bedforms in the inner Fjord. Courtauld Glacier drains into the head of the Fjord and several glaciers are also present along the east flank of the Fjord. Dashed white line and white arrows mark the lateral moraine on the western Fjord wall produced when Courtauld Glacier last advanced to the outer Fjord sill during the Little Ice …
-
Terminal and recessional moraines in the Fjords of southern Chile
Geological Society London Memoirs, 2016Co-Authors: Galderic Lastras, Julian A. DowdeswellAbstract:Moraine ridges marking the outermost limit of a glacier advance are known as terminal moraines; recessional moraines indicate stillstands or minor readvances during overall glacier retreat. At the Last Glacial Maximum, the Patagonian Ice Cap advanced to fill the complex Fjord system of southern Chile. Since then, ice has retreated producing recessional moraines, although tidewater glacier readvance during the cool period known as the Little Ice Age also deposited terminal moraines in the Fjords. At present, the remaining smaller ice caps of northern and southern Patagonia feed just a few tidewater glaciers, which are the lowest-latitude glaciers reaching the sea at Fjord heads today (Dowdeswell & Vasquez 2013). In southern Chile, a number of large sedimentary ridges have been mapped across Fjord axes (Fig. 1a–e) (Boyd et al. 2008; Dowdeswell & Vasquez 2013). Iceberg Fjord at 48° 43.5′ S is an arm of Messier Fjord, located immediately west of the northern part of the 13 000 km2 Southern Patagonian Ice Cap. A prominent submarine ridge is present across the 2 km wide Fjord about 3 km from the current terminus of the tidewater Tempano Glacier which drains west from the ice …
Lorenz Meire - One of the best experts on this subject based on the ideXlab platform.
-
local coastal water masses control heat levels in a west greenland tidewater outlet glacier Fjord
Journal of Geophysical Research, 2018Co-Authors: John Mortensen, Jørgen Bendtsen, Soren Rysgaard, Kristine Engel Arendt, Thomas Juulpedersen, D H Sogaard, Lorenz MeireAbstract:Fjords form the gateway between the open ocean and the Greenland Ice Sheet (GIS) and consequently play a crucial role for the stability of the Ice Sheet. Hydrographic observations, especially with seasonal resolution, from these Fjords are limited making it difficult to assess linkages between the Fjord, coastal water masses, and freshwater discharge from GIS. Here we present a decade‐long monthly hydrographic time series from a southwest Greenland Fjord in direct contact with GIS. Our observations reveal significant temporal and spatial water mass variations related to coastal, glacial, and atmospheric dynamics. During winter, the Fjord circulation is dominated by seasonal dense coastal inflows and the timing of these inflows determines intermediate and deepwater temperatures. During summer, runoff from GIS leads to a pronounced freshening of the Fjord. In general, the Fjord's seasonal circulation system damps the seasonal variation in temperature in the Fjord. This leads to a seasonal temperature range in the intermediate layer in the inner part of the Fjord that is half the observed range at the Fjord entrance. Changes in mean water temperatures in the intermediate layer seem predominantly linked to local coastal water masses, where cold winter/warm summer events decrease/increase the mean water temperatures. Consequently, these events play an important role in heat transport toward glacier termini.
-
Seasonal changes in Fe along a glaciated Greenlandic Fjord.
Frontiers in Earth Science, 2016Co-Authors: Mark J. Hopwood, Kristine Engel Arendt, Lorenz Meire, Douglas P. Connelly, Thomas Juul-pedersen, Mark C. Stinchcombe, Mario Esposito, Ram KrishnaAbstract:Greenland’s ice sheet is the second largest on Earth, and is under threat from a warming Arctic climate. An increase in freshwater discharge from Greenland has the potential to strongly influence the composition of adjacent water masses with the largest impact on marine ecosystems likely to be found within the glaciated Fjords. Here we demonstrate that physical and chemical estuarine processes within a large Greenlandic Fjord are critical factors in determining the fate of meltwater derived nutrients and particles, especially for non-conservative elements such as Fe. Concentrations of Fe and macronutrients in surface waters along GodthabsFjord, a southwest Greenlandic Fjord with freshwater input from 6 glaciers, changed markedly between the onset and peak of the meltwater season due to the development of a thin (