scholarly journals Effects of uncertainties in the geothermal heat flux distribution on the Greenland Ice Sheet: An assessment of existing heat flow models

2012 ◽  
Vol 117 (F2) ◽  
pp. n/a-n/a ◽  
Author(s):  
I. Rogozhina ◽  
J. M. Hagedoorn ◽  
Z. Martinec ◽  
K. Fleming ◽  
O. Soucek ◽  
...  
Keyword(s):  
Heat Flux ◽  
Heat Flow ◽  
Flux Distribution ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Heat Flux Distribution ◽  
Geothermal Heat ◽  
Flow Models

The effect of geothermal heat flux on the deglacial evolution of the Greenland ice sheet

2021 ◽  
Author(s):  
Parviz Ajourlou ◽  
François PH Lapointe ◽  
Glenn A Milne ◽  
Yasmina Martos
Keyword(s):  
Boundary Condition ◽  
Heat Flux ◽  
Thermal State ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Sampling Procedure ◽  
Geophysical Research ◽  
Geothermal Heat ◽  
Input Field ◽  
Uncertainty Estimates

<p>Geothermal heat flux (GHF) is known to be an important control on the basal thermal state of an ice sheet which, in turn, is a key factor in governing how the ice sheet will evolve in response to a given climate forcing. In recent years, several studies have estimated GHF beneath the Greenland ice sheet using different approaches (e.g. Rezvanbehbahani et al., Geophysical Research Letters, 2017; Martos et al., Geophysical Research Letters, 2018; Greve, Polar Data Journal, 2019). Comparing these different estimates indicates poor agreement and thus large uncertainty in our knowledge of this important boundary condition for modelling the ice sheet. The primary aim of this study is to quantify the influence of this uncertainty on modelling the past evolution of the ice sheet with a focus on the most recent deglaciation. We build on past work that considered three GHF models (Rogozhina et al., 2011) by considering over 100 different realizations of this input field. We use the uncertainty estimates from Martos et al. (Geophysical Research Letters, 2018) to generate GHF realisations via a statistical sampling procedure. A sensitivity analysis using these realisations and the Parallel Ice Sheet Model (PISM, Bueler and Brown, Journal of Geophysical Research, 2009) indicates that uncertainty in GHF has a dramatic impact on both the volume and spatial distribution of ice since the last glacial maximum, indicating that more precise constraints on this boundary condition are required to improve our understanding of past ice sheet evolution and, consequently, reduce uncertainty in future projections.</p>

Implications for the lithospheric structure of Greenland by applying different heat flow models

2021 ◽  
Author(s):  
Agnes Wansing ◽  
Jörg Ebbing ◽  
Mareen Lösing ◽  
Sergei Lebedev ◽  
Nicolas Celli ◽  
...  
Keyword(s):  
Heat Flow ◽  
Heat Dissipation ◽  
Ice Sheet ◽  
Magnetic Data ◽  
Similarity Function ◽  
Lithospheric Structure ◽  
Temperature Structure ◽  
Geothermal Heat ◽  
Flow Models ◽  
Ice Sheet Dynamics

<p>The lithospheric structure of Greenland is still poorly known due to its thick ice sheet, the sparseness of seismological stations, and the limitation of geological outcrops near coastal areas. As only a few geothermal measurements are available for Greenland, one must rely on geophysical models. Such models of Moho and LAB depths and sub-ice geothermal heat-flow vary largely.</p><p>Our approach is to model the lithospheric architecture by geophysical-petrological modelling with LitMod3D. The model is built to reproduce gravity observations, the observed elevation with isostasy assumptions and the velocities from a tomography model. Furthermore, we adjust the thermal parameters and the temperature structure of the model to agree with different geothermal heat flow models. We use three different heat flow models, one from machine learning, one from a spectral analysis of magnetic data and another one which is compiled from a similarity study with tomography data.</p><p>For the latter, a new shear wave tomography model of Greenland is used. Vs-depth profiles from Greenland are compared with velocity profiles from the US Array, where a statistical link between Vs profiles and surface heat flow has been established. A similarity function determines the most similar areas in the U.S. and assigns the mean heat-flow from these areas to the corresponding area in Greenland.</p><p>The geothermal heat flow models will be further used to discuss the influence on ice sheet dynamics by comparison to friction heat and viscous heat dissipation from surface meltwater.</p>

scholarly journals Sensitivity of the frozen/melted basal boundary to perturbations of basal traction and geothermal heat flux: Isunnguata Sermia, western Greenland

2011 ◽  
Vol 52 (59) ◽  
pp. 43-50 ◽  
Author(s):  
Douglas J. Brinkerhoff ◽  
Toby W. Meierbachtol ◽  
Jesse V. Johnson ◽  
Joel T. Harper
Keyword(s):  
Heat Flux ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Thermal Conditions ◽  
Two Dimensional ◽  
Adjoint Model ◽  
The West ◽  
Geothermal Heat ◽  
Coupled Numerical Model ◽  
The Difference

AbstractA full-stress, thermomechanically coupled, numerical model is used to explore the interaction between basal thermal conditions and motion of a terrestrially terminating section of the west Greenland ice sheet. The model domain is a two-dimensional flowline profile extending from the ice divide to the margin. We use data-assimilation techniques based on the adjoint model in order to optimize the basal traction field, minimizing the difference between modeled and observed surface velocities. We monitor the sensitivity of the frozen/melted boundary (FMB) to changes in prescribed geothermal heat flux and sliding speed by applying perturbations to each of these parameters. The FMB shows sensitivity to the prescribed geothermal heat flux below an upper threshold where a maximum portion of the bed is already melted. The position of the FMB is insensitive to perturbations applied to the basal traction field. This insensitivity is due to the short distances over which longitudinal stresses act in an ice sheet.

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 Heat Flux Distribution Near a Crevasse

1963 ◽  
Vol 4 (34) ◽  
pp. 461-465
Author(s):  
C. J. Pings
Keyword(s):  
Heat Flux ◽  
Heat Flow ◽  
Flux Distribution ◽  
Temperature Data ◽  
Flux Vector ◽  
Heat Flux Distribution ◽  
Flow Lines ◽  
Heat Flux Vector ◽  
Graphical Differentiation ◽  
Improved Accuracy

AbstractPreviously reported experimental temperature data were used to compute the two components of the heat flux vector in the ice body adjacent to a crevasse in a glacier of the ice sheet of northern Greenland. Graphical differentiation techniques were employed. The computed components were used to synthesize values of the beat flux vector, including magnitude and direction. Improved accuracy was achieved over the previously reported technique of sketching heat flow lines orthogonal to the isotherms.

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 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 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 Subglacial topography and geothermal heat flux: Potential interactions with drainage of the Greenland ice sheet

2007 ◽  
Vol 34 (12) ◽  
Author(s):  
C. J. van der Veen ◽  
T. Leftwich ◽  
R. von Frese ◽  
B. M. Csatho ◽  
J. Li
Keyword(s):  
Heat Flux ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Geothermal Heat ◽  
Subglacial Topography ◽  
Potential Interactions

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.

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