scholarly journals Constraining the geothermal heat flux in Greenland at regions of radar-detected basal water

2019 ◽  
Vol 65 (254) ◽  
pp. 1023-1034 ◽  
Author(s):  
Soroush Rezvanbehbahani ◽  
Leigh A. Stearns ◽  
C. J. van der Veen ◽  
Gordon K. A. Oswald ◽  
Ralf Greve
Keyword(s):  
Heat Flux ◽  
Water Distribution ◽  
Ice Core ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Radar Data ◽  
Geothermal Heat ◽  
Community Effort ◽  
Pressure Melting

AbstractThe spatial distribution of basal water critically impacts the evolution of ice sheets. Current estimates of basal water distribution beneath the Greenland Ice Sheet (GrIS) contain large uncertainties due to poorly constrained boundary conditions, primarily from geothermal heat flux (GHF). The existing GHF models often contradict each other and implementing them in numerical ice-sheet models cannot reproduce the measured temperatures at ice core locations. Here we utilize two datasets of radar-detected basal water in Greenland to constrain the GHF at regions with a thawed bed. Using the three-dimensional ice-sheet model SICOPOLIS, we iteratively adjust the GHF to find the minimum GHF required to reach the bed to the pressure melting point, GHFpmp, at locations of radar-detected basal water. We identify parts of the central-east, south and northwest Greenland with significantly high GHFpmp. Conversely, we find that the majority of low-elevation regions of west Greenland and parts of northeast have very low GHFpmp. We compare the estimated constraints with the available GHF models for Greenland and show that GHF models often do not honor the estimated constraints. Our results highlight the need for community effort to reconcile the discrepancies between radar data, GHF models, and ice core information.

scholarly journals Relation of measured basal temperatures and the spatial distribution of the geothermal heat flux for the Greenland ice sheet

2005 ◽  
Vol 42 ◽  
pp. 424-432 ◽  
Author(s):  
Ralf Greve
Keyword(s):  
Heat Flux ◽  
Ice Core ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
High Heat ◽  
High Heat Flux ◽  
Climatic Forcing ◽  
Geothermal Heat ◽  
Direct Measurements

AbstractThe thermomechanical, three-dimensional ice-sheet model SICOPOLIS is applied to the Greenland ice sheet. Simulations over two glacial–interglacial cycles are carried out, driven by a climatic forcing interpolated between present conditions and Last Glacial Maximum anomalies. Based on the global heat-flow representation by Pollack and others (1993), we attempt to constrain the spatial pattern of the geothermal heat flux by comparing simulation results to direct measurements of basal temperatures at the GRIP, NorthGRIP, Camp Century and Dye 3 ice-core locations. The obtained heat-flux map shows an increasing trend from west to east, a high-heat-flux anomaly around NorthGRIP with values up to 135 mWm–2 and a low-heat-flux anomaly around Dye 3 with values down to 20 mW m–2. Validation is provided by the generally good fit between observed and measured ice thicknesses. Residual discrepancies are most likely due to deficiencies of the input precipitation rate and further variability of the geothermal heat flux not captured here.

scholarly journals Polythermal three-dimensional modelling of the Greenland ice sheet with varied geothermal heat flux

1995 ◽  
Vol 21 ◽  
pp. 8-12 ◽  
Author(s):  
R. Greve ◽  
K. Hutter
Keyword(s):  
Heat Flux ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Thermomechanical Coupling ◽  
Numerical Code ◽  
Maximum Height ◽  
Geothermal Heat ◽  
Input Surface ◽  
Sensitive Variable

Computations over 50 000 years into steady state with Greve’s polythermal ice-sheet model and its numerical code are performed for the Greenland ice sheet with today’s climatological input (surface temperature and accumulation function) and three values of the geothermal heat flux: (42, 54.6, 29.4) mW m−2. It is shown that through the thermomechanical coupling the geometry as well as the thermal regime, in particular that close to the bed, respond surprisingly strongly to the basal thermal heat input. The most sensitive variable is the basal temperature field, but the maximum height of the summit also varies by more than ±100m. Furthermore, some intercomparison of the model outputs with the real ice sheet is carried out, showing that the model provides reasonable results for the ice-sheet geometry as well as for the englacial temperatures.

scholarly journals Greenland under changing climates: sensitivity experiments with a new three-dimensional ice-sheet model

1995 ◽  
Vol 21 ◽  
pp. 1-7 ◽  
Author(s):  
Adeline Fabre ◽  
Anne Letréguilly ◽  
Catherine Ritz ◽  
Anne Mangeney
Keyword(s):  
Ice Core ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Velocity Fields ◽  
Geothermal Heat ◽  
Climate History ◽  
Isostatic Adjustment ◽  
Temperature And Velocity Fields ◽  
Different Climates

A new three-dimensional, time-dependent ice-sheet model, including the calculation of the coupled temperature and velocity fields, isostatic adjustment of the bedrock and a mass-balance parameterization, was used to reconstruct the evolution of the Greenland ice sheet in response to a climate history derived from the oxygen-18 measured in the GRIP ice core. Steady-state experiments were done to test the sensitivity of the model, first to variations of poorly known parameters, secondly to different climates. These experiments show that the modelled ice sheet is not very sensitive to variations in the geothermal heat flux, but very sensitive to changes in the accumulation.

scholarly journals Polythermal three-dimensional modelling of the Greenland ice sheet with varied geothermal heat flux

1995 ◽  
Vol 21 ◽  
pp. 8-12 ◽  
Author(s):  
R. Greve ◽  
K. Hutter
Keyword(s):  
Heat Flux ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Thermomechanical Coupling ◽  
Numerical Code ◽  
Maximum Height ◽  
Geothermal Heat ◽  
Input Surface ◽  
Sensitive Variable

Computations over 50 000 years into steady state with Greve’s polythermal ice-sheet model and its numerical code are performed for the Greenland ice sheet with today’s climatological input (surface temperature and accumulation function) and three values of the geothermal heat flux: (42, 54.6, 29.4) mW m−2. It is shown that through the thermomechanical coupling the geometry as well as the thermal regime, in particular that close to the bed, respond surprisingly strongly to the basal thermal heat input. The most sensitive variable is the basal temperature field, but the maximum height of the summit also varies by more than ±100m. Furthermore, some intercomparison of the model outputs with the real ice sheet is carried out, showing that the model provides reasonable results for the ice-sheet geometry as well as for the englacial temperatures.

scholarly journals Exceptionally High Geothermal Heat Flux Needed to Sustain the Northeast Greenland Ice Stream

2019 ◽  
Author(s):  
Silje Smith-Johnsen ◽  
Basile de Fleurian ◽  
Nicole Schlegel ◽  
Helene Seroussi ◽  
Kerim Nisanciolgu
Keyword(s):  
Heat Flux ◽  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Good Representation ◽  
Geothermal Heat ◽  
Ice Dynamics ◽  
Left Behind ◽  
Ice Stream ◽  
Using Data

Abstract. The Northeast Greenland Ice Stream (NEGIS) currently drains more than 10 % of the Greenland Ice Sheet area, and has recently undergone significant dynamic changes. It is therefore critical to accurately represent this feature when assessing the future contribution of Greenland to sea level rise. At present, NEGIS is reproduced in ice sheet models by inferring basal conditions using observed surface velocities. This approach helps estimate conditions at the base of the ice sheet, but cannot be used to estimate the evolution of basal drag in time, so it is not a good representation of the evolution of the ice sheet in future climate warming scenarios. NEGIS is suggested to be initiated by a geothermal heat flux anomaly close to the ice divide, left behind by the movement of Greenland over the Icelandic plume. However, the heat flux underneath the ice sheet is largely unknown, except for a few direct measurements from deep ice core drill sites. Using the Ice Sheet System Model (ISSM), with ice dynamics coupled to a subglacial hydrology model, we investigate the possibility of initiating NEGIS by inserting hotspots with various locations and intensities. We find that a minimum geothermal heat flux value of 970 mW/m2 located close to EastGRIP is required locally to reproduce the observed NEGIS velocities, consistent with previous estimates. By including high geothermal heat flux and the effect of water on sliding, we successfully reproduce the main characteristics of NEGIS in an ice sheet model without using data assimilation.

scholarly journals A constraint upon the basal water distribution and basal thermal state of the Greenland Ice Sheet from radar bed-echoes

2018 ◽  
Author(s):  
Thomas M. Jordan ◽  
Christopher N. Williams ◽  
Dustin M. Schroeder ◽  
Yasmina M. Martos ◽  
Michael A. Cooper ◽  
...  
Keyword(s):  
Heat Flux ◽  
Water Distribution ◽  
Thermal State ◽  
Numerical Models ◽  
Ice Sheet ◽  
Indirect Evidence ◽  
Greenland Ice Sheet ◽  
Large Area ◽  
Geothermal Heat ◽  
Radio Echo Sounding

Abstract. There is widespread, but often indirect, evidence that a significant fraction of the bed beneath the Greenland Ice Sheet is thawed (at or above the pressure melting point for ice). This includes the beds of major outlet glaciers and their tributaries and a large area around the NorthGRIP borehole in the ice-sheet interior. The ice-sheet scale distribution of basal water is, however, poorly constrained by existing observations. In principle, airborne radio-echo sounding (RES) enables the detection of basal water from bed-echo reflectivity, but unambiguous mapping is limited by uncertainty in signal attenuation. Here we introduce a new RES diagnostic for basal water that is associated with wet to dry transitions in bed material: bed-echo reflectivity variability. Importantly, this diagnostic is demonstrated to be attenuation-insensitive and the technique enables combined analysis of over a decade of Operation IceBridge survey data. The basal water predictions are compared with existing analyses for the basal thermal state (frozen and thawed beds) and geothermal heat flux. In addition to the outlet glaciers, we demonstrate widespread water storage in the northern and eastern interior. Notably, we observe a quasi-linear ‘corridor’ of basal water extending from NorthGRIP to Petermann glacier that spatially correlates with elevated heat flux predicted by a recent magnetic model. Finally, with a general aim to stimulate regional and process specific investigations, the basal water predictions are compared with bed topography, subglacial flow paths, and ice-sheet motion. The basal water distribution, and its relationship with the basal thermal state, provides a new constraint for numerical models.

scholarly journals Exceptionally high heat flux needed to sustain the Northeast Greenland Ice Stream

2020 ◽  
Vol 14 (3) ◽  
pp. 841-854 ◽  
Author(s):  
Silje Smith-Johnsen ◽  
Basile de Fleurian ◽  
Nicole Schlegel ◽  
Helene Seroussi ◽  
Kerim Nisancioglu
Keyword(s):  
Heat Flux ◽  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
High Heat ◽  
High Heat Flux ◽  
Good Representation ◽  
Geothermal Heat ◽  
Ice Dynamics ◽  
Ice Stream

Abstract. The Northeast Greenland Ice Stream (NEGIS) currently drains more than 10 % of the Greenland Ice Sheet area and has recently undergone significant dynamic changes. It is therefore critical to accurately represent this feature when assessing the future contribution of Greenland to sea level rise. At present, NEGIS is reproduced in ice sheet models by inferring basal conditions using observed surface velocities. This approach helps estimate conditions at the base of the ice sheet but cannot be used to estimate the evolution of basal drag in time, so it is not a good representation of the evolution of the ice sheet in future climate warming scenarios. NEGIS is suggested to be initiated by a geothermal heat flux anomaly close to the ice divide, left behind by the movement of Greenland over the Icelandic plume. However, the heat flux underneath the ice sheet is largely unknown, except for a few direct measurements from deep ice core drill sites. Using the Ice Sheet System Model (ISSM), with ice dynamics coupled to a subglacial hydrology model, we investigate the possibility of initiating NEGIS by inserting heat flux anomalies with various locations and intensities. In our model experiment, a minimum heat flux value of 970 mW m−2 located close to the East Greenland Ice-core Project (EGRIP) is required locally to reproduce the observed NEGIS velocities, giving basal melt rates consistent with previous estimates. The value cannot be attributed to geothermal heat flux alone and we suggest hydrothermal circulation as a potential explanation for the high local heat flux. By including high heat flux and the effect of water on sliding, we successfully reproduce the main characteristics of NEGIS in an ice sheet model without using data assimilation.

scholarly journals Greenland under changing climates: sensitivity experiments with a new three-dimensional ice-sheet model

1995 ◽  
Vol 21 ◽  
pp. 1-7 ◽  
Author(s):  
Adeline Fabre ◽  
Anne Letréguilly ◽  
Catherine Ritz ◽  
Anne Mangeney
Keyword(s):  
Ice Core ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Velocity Fields ◽  
Geothermal Heat ◽  
Climate History ◽  
Isostatic Adjustment ◽  
Temperature And Velocity Fields ◽  
Different Climates

A new three-dimensional, time-dependent ice-sheet model, including the calculation of the coupled temperature and velocity fields, isostatic adjustment of the bedrock and a mass-balance parameterization, was used to reconstruct the evolution of the Greenland ice sheet in response to a climate history derived from the oxygen-18 measured in the GRIP ice core. Steady-state experiments were done to test the sensitivity of the model, first to variations of poorly known parameters, secondly to different climates. These experiments show that the modelled ice sheet is not very sensitive to variations in the geothermal heat flux, but very sensitive to changes in the accumulation.

scholarly journals A constraint upon the basal water distribution and thermal state of the Greenland Ice Sheet from radar bed echoes

2018 ◽  
Vol 12 (9) ◽  
pp. 2831-2854 ◽  
Author(s):  
Thomas M. Jordan ◽  
Christopher N. Williams ◽  
Dustin M. Schroeder ◽  
Yasmina M. Martos ◽  
Michael A. Cooper ◽  
...  
Keyword(s):  
Heat Flux ◽  
Water Distribution ◽  
Thermal State ◽  
Numerical Models ◽  
Ice Sheet ◽  
Indirect Evidence ◽  
Greenland Ice Sheet ◽  
Large Area ◽  
Geothermal Heat ◽  
Radio Echo Sounding

Abstract. There is widespread, but often indirect, evidence that a significant fraction of the bed beneath the Greenland Ice Sheet is thawed (at or above the pressure melting point for ice). This includes the beds of major outlet glaciers and their tributaries and a large area around the NorthGRIP borehole in the ice-sheet interior. The ice-sheet-scale distribution of basal water is, however, poorly constrained by existing observations. In principle, airborne radio-echo sounding (RES) enables the detection of basal water from bed-echo reflectivity, but unambiguous mapping is limited by uncertainty in signal attenuation within the ice. Here we introduce a new, RES diagnostic for basal water that is associated with wet–dry transitions in bed material: bed-echo reflectivity variability. This technique acts as a form of edge detector and is a sufficient, but not necessary, criteria for basal water. However, the technique has the advantage of being attenuation insensitive and suited to combined analysis of over a decade of Operation IceBridge survey data.The basal water predictions are compared with existing analyses of the basal thermal state (frozen and thawed beds) and geothermal heat flux. In addition to the outlet glaciers, we demonstrate widespread water storage in the northern and eastern interior. Notably, we observe a quasilinear corridor of basal water extending from NorthGRIP to Petermann Glacier that spatially correlates with elevated heat flux predicted by a recent magnetic model. Finally, with a general aim to stimulate regional- and process-specific investigations, the basal water predictions are compared with bed topography, subglacial flow paths and ice-sheet motion. The basal water distribution, and its relationship with the thermal state, provides a new constraint for numerical models.

scholarly journals Where is the 1-million-year-old ice at Dome A?

2018 ◽  
Author(s):  
Liyun Zhao ◽  
John C. Moore ◽  
Bo Sun ◽  
Xueyuan Tang ◽  
Xiaoran Guo
Keyword(s):  
Heat Flux ◽  
Ice Core ◽  
Three Dimensional ◽  
Melting Rate ◽  
Dome A ◽  
Geothermal Heat ◽  
Pressure Melting ◽  
Kunlun Station ◽  
Ice Fabrics ◽  
Basal Melting

Abstract. Ice fabric influences the rheology of ice, and hence the age/depth profile at ice core drilling sites. We use the depth varying anisotropic fabric suggested by the recent polarimetric measurements around Dome A along with prescribed fabrics ranging from isotropic through girdle to single maximum in a three-dimensional, thermo-mechanically coupled full-Stokes model of a 70 × 70 km2 domain around Kunlun station. This model allows to simulate the near basal ice temperature and age, and ice flow around the location of the Chinese deep ice coring site. Ice fabrics and geothermal heat flux strongly affect the vertical advection and basal temperature which in consequence controls the age profile. Constraining modeled age-depth profiles with dated radar isochrones to 2/3 ice depth, the surface vertical velocity, and also the spatial variability of a radar isochrones dated to 153.3 kyr BP, limits the age of the deep ice at Kunlun to 649–831 kyr, a much smaller range than inferred previously. The simple interpretation of the polarmetric radar fabric data that we use produces best fits with a geothermal heat flux of 55 mWm−2. A heat flux of 50 mWm−2 is too low to fit the deeper radar layers, and a heat flux of 60 mWm−2 leads to unrealistic surface velocities. The modeled basal temperature at Kunlun reaches the pressure melting point with a basal melting rate of 2.2–2.7 mm yr−1. Using the spatial distribution of basal temperatures and the best fit fabric suggests that within 400 m of Kunlun station, 1 million-year old ice may be found 200 m above the bed, and there are large regions where even older ice is well above the bedrock within 1–2 km of the Kunlun station.

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