scholarly journals The effect of the north-east ice stream on the Greenland ice sheet in changing climates

2007 ◽  
Vol 1 (1) ◽  
pp. 41-76 ◽  
Author(s):  
R. Greve ◽  
S. Otsu
Keyword(s):  
Large Scale ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Simulation Code ◽  
North East ◽  
The North ◽  
Ice Stream ◽  
Basal Sliding ◽  
Speed Up ◽  
Fast Flow

Abstract. The north-east Greenland ice stream (NEGIS) was discovered as a large fast-flow feature of the Greenland ice sheet by synthetic aperture radar (SAR) imaginary of the ERS-1 satellite. In this study, the NEGIS is implemented in the dynamic/thermodynamic, large-scale ice-sheet model SICOPOLIS (Simulation Code for POLythermal Ice Sheets). In the first step, we simulate the evolution of the ice sheet on a 10-km grid for the period from 250 ka ago until today, driven by a climatology reconstructed from a combination of present-day observations and GCM results for the past. We assume that the NEGIS area is characterized by enhanced basal sliding compared to the "normal", slowly-flowing areas of the ice sheet, and find that the misfit between simulated and observed ice thicknesses and surface velocities is minimized for a sliding enhancement by the factor three. In the second step, the consequences of the NEGIS, and also of surface-meltwater-induced acceleration of basal sliding, for the possible decay of the Greenland ice sheet in future warming climates are investigated. It is demonstrated that the ice sheet is generally very susceptible to global warming on time-scales of centuries and that surface-meltwater-induced acceleration of basal sliding can speed up the decay significantly, whereas the NEGIS is not likely to dynamically destabilize the ice sheet as a whole.

scholarly journals Simulations of the Greenland ice sheet 100 years into the future with the full Stokes model Elmer/Ice

2012 ◽  
Vol 58 (209) ◽  
pp. 427-440 ◽  
Author(s):  
Hakime Seddik ◽  
Ralf Greve ◽  
Thomas Zwinger ◽  
Fabien Gillet-Chaulet ◽  
Olivier Gagliardini
Keyword(s):  
Global Warming ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Streams ◽  
Simulation Code ◽  
Dynamic Scenario ◽  
The Future ◽  
Basal Sliding

AbstractIt is likely that climate change will have a significant impact on the mass balance of the Greenland ice sheet, contributing to future sea-level rise. Here we present the implementation of the full Stokes model Elmer/Ice for the Greenland ice sheet, which includes a mesh refinement technique in order to resolve fast-flowing ice streams and outlet glaciers. We discuss simulations 100 years into the future, forced by scenarios defined by the SeaRISE (Sea-level Response to Ice Sheet Evolution) community effort. For comparison, the same experiments are also run with the shallow-ice model SICOPOLIS (SImulation COde for POLythermal Ice Sheets). We find that Elmer/Ice is ~43% more sensitive (exhibits a larger loss of ice-sheet volume relative to the control run) than SICOPOLIS for the ice-dynamic scenario (doubled basal sliding), but ~61 % less sensitive for the direct global warming scenario (based on the A1 B moderate-emission scenario for greenhouse gases). The scenario with combined A1B global warming and doubled basal sliding forcing produces a Greenland contribution to sea-level rise of ~15cm for Elmer/Ice and ~12cm for SICOPOLIS over the next 100 years.

Marine geophysical evidence for former expansion and flow of the Greenland Ice Sheet across the north-east Greenland continental shelf

2009 ◽  
Vol 24 (3) ◽  
pp. 279-293 ◽  
Author(s):  
Jeffrey Evans ◽  
Colm Ó Cofaigh ◽  
Julian A. Dowdeswell ◽  
Peter Wadhams
Keyword(s):  
Continental Shelf ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
East Greenland ◽  
North East ◽  
The North

scholarly journals The 8.2 ka cooling event related to extensive melting of the Greenland Ice Sheet

2008 ◽  
Vol 4 (5) ◽  
pp. 1219-1235 ◽  
Author(s):  
H. Ebbesen ◽  
A. Kuijpers ◽  
M. Moros ◽  
J. Lloyd ◽  
M.-S. Seidenkrantz ◽  
...  
Keyword(s):  
Large Scale ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Arctic Region ◽  
Trace Element Composition ◽  
Sedimentary Records ◽  
The North ◽  
Driving Mechanisms ◽  
Melt Water ◽  
Water Outflow

Abstract. The North Atlantic cooling event at 8200 calibrated (cal) yr BP has been attributed to effects of an extensive freshwater discharge from the Hudson Strait (Barber et al., 1999; Leverington et al., 2002). Here we present sedimentary records from 5 cores collected from the Greenland shelf. These document high magnetic susceptibility (MS) values related to massive silt deposition, which is ascribed to large-scale melt water outflow from the Greenland Ice Sheet (GIS) spanning the centuries before 8200 cal yr BP and ending after 8000 cal yr BP. XRF trace element composition and foraminiferal fauna's provide additional evidence for excessive melt-water production, which can be related to early Holocene warming of the circum-Arctic region including Greenland. Planktonic foraminiferal fauna data from the southern Davis Strait indicate the widespread presence of negative salinity anomalies reaching far offshore Greenland. Significant freshening of surface waters around Greenland prior to 8200 cal yr BP must have led to a slowdown of the deep-water formation which thus implies that significant melting of the GIS should be taken into account when discussing driving mechanisms behind the 8200 cal yr BP cooling event.

scholarly journals Calculated Patterns of Accumulation on the Greenland Ice Sheet

1967 ◽  
Vol 6 (48) ◽  
pp. 795-803 ◽  
Author(s):  
Steven J. Mock
Keyword(s):  
Mass Balance ◽  
Transition Zone ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
East Greenland ◽  
North East ◽  
The North ◽  
Regression Techniques ◽  
Independent Parameters ◽  
North Greenland

All available mean annual accumulation data on the Greenland ice sheet (excluding the Thule peninsula) have been collected and analyzed using multiple regression techniques to develop equations capable of predicting mean annual accumulation. The analysis was carried out for north Greenland, south Greenland, and for the transition zone between the two major regions. The resulting equations show that mean annual accumulation can be predicted from the independent parameters latitude, longitude and elevation. The patterns of accumulation are shown in a series of isohyetal (contours of accumulation in terms of water) maps. The major feature shown is a well defined asymmetry in accumulation; a pronounced east-slope maximum in south Greenland and an equally pronounced west-slope maximum in north Greenland. Poleward of lat. 69° N., isohyets decrease in elevation to the north. Mean annual accumulation ranges from >90 g./cm.2in south-east Greenland to <15 g./cm.2in north-east Greenland. A brief discussion of mass balance estimates of the Greenland ice sheet and of the relevance of this study to them is included.

scholarly journals Greenland ice-sheet volume sensitivity to basal, surface and initial conditions derived from an adjoint model

2009 ◽  
Vol 50 (52) ◽  
pp. 67-80 ◽  
Author(s):  
Patrick Heimbach ◽  
Véronique Bugnion
Keyword(s):  
Code Generation ◽  
Automatic Differentiation ◽  
Initial Conditions ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Adjoint Model ◽  
Control Variables ◽  
Simulation Code ◽  
Basal Sliding

AbstractWe extend the application of control methods to a comprehensive three-dimensional thermomechanical ice-sheet model, SICOPOLIS (SImulation COde for POLythermal Ice Sheets). Lagrange multipliers, i.e. sensitivities, are computed with an exact, efficient adjoint model that has been generated from SICOPOLIS by rigorous application of automatic differentiation. The case study uses the adjoint model to determine the sensitivity of the total Greenland ice volume to various control variables over a 100 year period. The control space has of the order 1.2 × 106 elements, consisting of spatial fields of basal flow parameters, surface and basal forcings and initial conditions. Reliability of the adjoint model was tested through finite-difference perturbation calculations for various control variables and perturbation regions, ascertaining quantitative inferences of the adjoint model. As well as confirming qualitative aspects of ice-sheet sensitivities (e.g. expected regional variations), we detect regions where model sensitivities are seemingly unexpected or counter-intuitive, albeit ‘real’ in the sense of actual model behavior. An example is inferred regions where sensitivities of ice-sheet volume to basal sliding coefficient are positive, i.e. where a local increase in basal sliding parameter increases the ice-sheet volume. Similarly, positive (generally negative) ice temperature sensitivities in certain parts of the ice sheet are found, the detection of which seems highly unlikely if only conventional perturbation experiments had been used. The object of this paper is largely a proof of concept. Available adjoint-code generation tools now open up a variety of novel model applications, notably with regard to sensitivity and uncertainty analyses and ice-sheet state estimation or data assimilation.

scholarly journals Heat flux and the North East Greenland Ice Stream

2021 ◽  
Author(s):  
Paul D. Bons ◽  
Tamara de Riese ◽  
Steven Franke ◽  
Maria-Gema Llorens ◽  
Till Sachau ◽  
...  
Keyword(s):  
Heat Flux ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Geothermal Heat ◽  
Radiogenic Heat ◽  
East Greenland ◽  
North East ◽  
Ice Stream

<p>The prominent North East Greenland Ice Stream (NEGIS) is an exceptionally large ice stream in the Greenland Ice sheet. It is over 500 km long, originates almost at the central ice divide, and contributes significantly to overall ice drainage from the Greenland Ice sheet. Surface velocities in the inland part of the ice stream are several times higher inside NEGIS than in the adjacent ice sheet. Modelling NEGIS is still a challenge as it remains unclear what actually causes and controls the ice stream.</p><p>An elevated geothermal heat flux is one of the factors that are being considered to trigger or drive the fast flow inside NEGIS. Unfortunately, the geothermal heat flux below NEGIS and its upstream area is poorly constrained and estimates vary from close to the global average for continental crust (ca. 60 mW/m<sup>2</sup>) to values as high as almost 1000 mW/m<sup>2</sup>. The latter would cause about 10 cm/yr of melting at the base of the ice sheet.</p><p>We present a brief survey of global geothermal heat flux data, especially from known hotspots, such as Iceland and Yellowstone. Heat fluxes in these areas that are known to be among the hottest on Earth rarely, if ever, exceed 300 mW/m<sup>2</sup>. A plume hotspot or its trail can therefore not cause heat fluxes at the high end of the suggested range. Other potential factors, such as hydrothermal fluid flow and radiogenic heat, also cannot raise the heat flux significantly. We conclude that the heat flux at NEGIS is very unlikely to exceed 100-150 mW/m<sup>2</sup>, and future modelling studies on NEGIS should thus be mindful of implementing realistic geothermal heat flux values. If NEGIS is not the result of an exceptionally high heat flux, we are left with the exciting challenge to find the true trigger of this fascinating structure.</p>

scholarly journals Recent North Greenland temperature warming and accumulation

2021 ◽  
Author(s):  
Helle Astrid Kjær ◽  
Patrick Zens ◽  
Ross Edwards ◽  
Martin Olesen ◽  
Ruth Mottram ◽  
...  
Keyword(s):  
Mass Balance ◽  
Climate Model ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Topographic Effects ◽  
North East ◽  
The North ◽  
North Greenland

Abstract. In a warming climate concise knowledge of the mass balance of the Greenland ice sheet is of utter importance. Speculations that current warming will increase the snow accumulation and mitigate mass balance losses are unconstrained as accumulation data across large regions of the northern ice sheet are scarce. We reconstructed the accumulation from six north Greenland shallow firn cores (~10 m) and eight snow cores (~2 m) to constrain recent accumulation patterns in northern Greenland and calculated recent warming in the same area using borehole temperature measurements. We find an increase in temperatures in the north Greenland interior of 0.9 to 2.5 °C (method and site dependent) per decade over the past two decades in line with an Arctic amplified anthropogenic warming. We compare annual reconstructed accumulation from the firn cores (1966–2015) to radar estimates and to annual re-analysis data (1980–2016) of precipitation subtracted evaporation from the regional climate model HIRHAM5, operated by the Danish Meteorological Institute. The spatial variability resembles that observed in earlier estimates with a clear increase west of the topographic divide and a low accumulation area across the north-eastern ice sheet. Our accumulation results are comparable to earlier firn core estimates, despite being larger in the east. We only find a positive significant trend in the accumulation for the period 2000–2010 to the northwest. In the vicinity of the EGRIP deep ice core drilling site, we find variable accumulation patterns for two 15 km apart firn cores likely owing to local topographic effects as a result of the North East Greenland Ice Stream dynamics.

scholarly journals Calculated Patterns of Accumulation on the Greenland Ice Sheet

1967 ◽  
Vol 6 (48) ◽  
pp. 795-803 ◽  
Author(s):  
Steven J. Mock
Keyword(s):  
Mass Balance ◽  
Transition Zone ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
East Greenland ◽  
North East ◽  
The North ◽  
Regression Techniques ◽  
Independent Parameters ◽  
North Greenland

All available mean annual accumulation data on the Greenland ice sheet (excluding the Thule peninsula) have been collected and analyzed using multiple regression techniques to develop equations capable of predicting mean annual accumulation. The analysis was carried out for north Greenland, south Greenland, and for the transition zone between the two major regions. The resulting equations show that mean annual accumulation can be predicted from the independent parameters latitude, longitude and elevation. The patterns of accumulation are shown in a series of isohyetal (contours of accumulation in terms of water) maps. The major feature shown is a well defined asymmetry in accumulation; a pronounced east-slope maximum in south Greenland and an equally pronounced west-slope maximum in north Greenland. Poleward of lat. 69° N., isohyets decrease in elevation to the north. Mean annual accumulation ranges from >90 g./cm.2 in south-east Greenland to <15 g./cm.2 in north-east Greenland. A brief discussion of mass balance estimates of the Greenland ice sheet and of the relevance of this study to them is included.

scholarly journals A confined–unconfined aquifer model for subglacial hydrology and its application to the North East Greenland Ice Stream

2017 ◽  
Author(s):  
Sebastian Beyer ◽  
Thomas Kleiner ◽  
Vadym Aizinger ◽  
Martin Rückamp ◽  
Angelika Humbert
Keyword(s):  
Computational Cost ◽  
Ice Sheet ◽  
Unconfined Aquifer ◽  
Ocean Modeling ◽  
Model Parameters ◽  
Efficient System ◽  
East Greenland ◽  
North East ◽  
The North ◽  
Ice Stream

Abstract. Subglacial hydrology plays an important role in the ice sheet dynamics as it determines the sliding velocity of ice sheets and also drives freshwater into the ocean. Modeling subglacial water has been a challenge for decades, and only recently new approaches have been developed such as representing subglacial channels and thin water sheets by separate layers of variable permeability. We extend this concept by modeling a confined and unconfined aquifer system (CUAS) in a single layer. The advantage of this formulation is that it prevents unphysical values of pressure at reasonable computational cost. We also performed sensitivity tests to investigate the effect of different model parameters. The strongest influence of model parameters was detected in terms governing the opening and closure of channels. Furthermore, we applied the model to the North East Greenland Ice Stream, where an efficient system independent of seasonal input was identified about 500 km downstream from the ice divide. Using the effective pressure from the hydrology model in the Ice Sheet System Model (ISSM) shows considerable improvements of modeled velocities in the coastal region.

scholarly journals Initial results of the SeaRISE numerical experiments with the models SICOPOLIS and IcIES for the Greenland ice sheet

2011 ◽  
Vol 52 (58) ◽  
pp. 23-30 ◽  
Author(s):  
Ralf Greve ◽  
Fuyuki Saito ◽  
Ayako Abe-Ouchi
Keyword(s):  
Mass Loss ◽  
Sea Level ◽  
Climate Warming ◽  
Large Scale ◽  
Initial Conditions ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Mass ◽  
Temperature And Precipitation ◽  
Basal Sliding

AbstarctSeaRISE (Sea-level Response to Ice Sheet Evolution) is a US-led multi-model community effort to predict the likely range of the contribution of the Greenland and Antarctic ice sheets to sea-level rise over the next few hundred years under global warming conditions. The Japanese ice-sheet modelling community is contributing to SeaRISE with two large-scale, dynamic/thermodynamic models: SICOPOLIS and IcIES. Here we discuss results for the Greenland ice sheet, obtained using both models under the forcings (surface temperature and precipitation scenarios) defined by the SeaRISE effort. A crucial point for meaningful simulations into the future is to obtain initial conditions that are close to the observed state of the present-day ice sheet. This is achieved by proper tuning during model spin-up from the last glacial/interglacial cycle to today. Experiments over 500 years indicate that both models are more sensitive (exhibit a larger rate of ice-sheet mass loss) to future climate warming (based on the A1B emission scenario) than to a doubling in the basal sliding speed. Ice-sheet mass loss varies between the two models by a factor of ~2 for sliding experiments and a factor of ~3 for climate-warming experiments, highlighting the importance of improved constraints on the parameterization of basal sliding and surface mass balance in ice-sheet models.

Sign in / Sign up

Export Citation Format

Share Document