Partitioning the geothermal component of basal melting beneath ice-sheets: lessons from Greenland

Winnie Chu1, Tom Jordan1,2, Yasmina Martos4,5, Dustin Schroeder1,3, Jonathan Bamber2

1Department of Geophysics, Stanford University , Stanford, United States, 2School of Geographical Sciences, University of Bristol, Bristol, United Kingdom, 3Department of Electrical Engineering, Stanford University , Stanford , United States, 4NASA Goddard Space Flight Center, Greenbelt, United States, 5University of Maryland, College Park, United States

Geothermal heat flux impacts meltwater production and ice motion at the base of ice sheets. However, additional to geothermal heating, frictional and deformational heat sources also contribute to melt the ice base. Recent studies in Greenland Ice Sheet implicate that geothermal heating related to ancient hotspot activities influences the distribution of present-day subglacial hydrology. However, these studies mostly rely on qualitative comparisons between basal water and heat flux models. Presently, it is unclear how much of the observed basal water is produced by geothermal heating and how much is strain or friction related. Here we combine ice-sheet modeling, basal water predictions from radar sounding analysis, and the most advance geothermal heat flux distribution to provide a quantitative assessment of the role of geothermal heat flux on basal water production. We examine the sensitivity of basal melting to variations in geothermal heat flux using a thermal enthalpy scheme in the NASA Ice Sheet System Model (ISSM). By coupling the thermal and stress balance modeling components, we partition the relative contribution of geothermal, frictional, and deformational heating on basal melting for different regions across Greenland. We also use an ice-sheet-wide constraint for basal water derived from variability in radar bed reflectivity as an independent constraint to examine the model capabilities to produce basal melting. Together, our results reveal that the spatial distribution of elevated geothermal heat flux can explain the observed meltwater underneath vast regions of the Northern and Eastern ice-sheet interior. We discuss the implications of the presence of a stable melt production related to geothermal heating to the long-term dynamics and mass balance of the Greenland ice sheet. We also discuss how the approaches developed in Greenland could be adapted to further characterize the geothermal heat flux of the Antarctic Ice Sheet.

Spatial variability in geothermal heat flux in Antarctica: new measurements and ice dynamical implications

Carolyn Branecky Begeman1, Slawek Tulaczyk1, Andy Fisher1

1University Of California, Santa Cruz, Santa Cruz, United States

The difficulty of measuring geothermal heat flux (GHF) below ice sheets has directly hindered progress in understanding their role in ice sheet dynamics. We present a new GHF measurement from below the West Antarctic Ice Sheet, made in subglacial sediment near the grounding zone of the Whillans Ice Stream. The measured GHF is 88 ± 7 mW/m², a relatively high value compared to other continental settings and to other GHF measurements along the eastern Ross Sea of 55 mW/m² and 69 ± 21 mW/m², but within the range of regional values indicated by geophysical estimates. The new GHF measurement was made ~100 km from the only other direct GHF measurement below the ice sheet, which was considerably higher at 285 ± 80 mW/m², suggesting spatial variability that could be explained by shallow magmatic intrusions or the advection of heat by crustal fluids. Analytical calculations suggest that spatial variability in GHF exceeds spatial variability in the conductive heat flux through ice along the Siple Coast. Accurate GHF measurements and high-resolution GHF models may be necessary to reliably predict ice sheet evolution, including responses to ongoing and future climate change.

Evaluating the difference between geothermal flux and basal heat flux in the context of ice divide stability, Little Dome C, East Antarctica

Lucas H. Beem1, Jason L. Roberts2, Catherine Ritz3, Duncan A. Young1, Thomas G. Richter1, Donald D. Blankenship1

1University Of Texas – Institute For Geophysics, Austin, United States, 2Australian Antarctic Division, Kingston, Australia, 3University of Grenoble Alpes, Grenoble, France

Basal heat flux is the thermal energy that crosses the ice/bed interface and is geothermal flux modified by processes such as vertical advection of groundwater and local variability in geology. The basal conditions of Little Dome C are of particular interest due to the potential for the existence of 1.5 Myr old ice that is interpretable as a paleoclimate proxy. The stability of Dome C is a function of the basal interface character including basal heat flux and water distribution and each can be modified by groundwater, water flow in the subglacial sediment and bedrock.  Here we test the rate of heat flux from groundwater flow and its sensitivity to assumed subglacial geology and associated hydrological parameters. Multiple probable geological models are constructed for the Dome C region from radar derived geometry and interpretation of co-located gravity and magnetic field observations. The impact of groundwater on basal heat flux is sensitive to the chosen background geothermal gradient, but more so to the degree of assumed hydrological permeability. In certain configurations groundwater flow can modify local basal heat flux but a factor greater than 2.  Our interpretation is that the position of Dome C is above a region of lower hydrological permeability that decreases exposure of basal ice to heat and may play a stabilizing role, and therefore increase the likelihood of 1.5 Myr old ice survival. These result suggest the hypothesis that ice divide stability and old ice survivability are, in part, a function of the underlaying geology.

 

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