Geothermal heat flux from measured temperature profiles in deep ice boreholes in Antarctica

Abstract

Abstract. The temperature at the Antarctic Ice Sheet bed and the temperature gradient in subglacial rocks have been directly measured only a few times, although extensive thermodynamic modeling has been used to estimate the geothermal heat flux (GHF) under the ice sheet. During the last 5 decades, deep ice-core drilling projects at six sites – Byrd, WAIS Divide, Dome C, Kohnen, Dome F, and Vostok – have succeeded in reaching or nearly reaching the bed at inland locations in Antarctica. When temperature profiles in these boreholes and steady-state heat flow modeling are combined with estimates of vertical velocity, the heat flow at the ice-sheet base is translated to a geothermal heat flux of 57.9 ± 6.4 mW m−2 at Dome C, 78.9 ± 5.0 mW m−2 at Dome F, and 86.9 ± 16.6 mW m−2 at Kohnen, all higher than the predicted values at these sites. This warm base under the East Antarctic Ice Sheet (EAIS) could be caused by radiogenic heat effects or hydrothermal circulation not accounted for by the models. The GHF at the base of the ice sheet at Vostok has a negative value of −3.6 ± 5.3 mW m−2, indicating that water from Lake Vostok is freezing onto the ice-sheet base. Correlation analyses between modeled and measured depth–age scales at the EAIS sites indicate that all of them can be adequately approximated by a steady-state model. Horizontal velocities and their variation over ice-age cycles are much greater for the West Antarctic Ice Sheet than for the interior EAIS sites; a steady-state model cannot precisely describe the temperature distribution here. Even if the correlation factors for the best fitting age–depth curve are only moderate for the West Antarctic sites, the GHF values estimated here of 88.4 ± 7.6 mW m−2 at Byrd and 113.3 ± 16.9 mW m−2 at WAIS Divide can be used as references before more precise estimates are made on the subject.

Preserved landscapes underneath the Antarctic Ice Sheet reveal the geomorphological history of Jutulstraumen Basin

“…Based on the individual GHF datasets, their modelling reveals it to be likely that the ice base has reached the pressure melting point at least once over the last 1.5 million years. Moreover, it has been shown that measured GHF in eastern DML is locally much higher than predicted by geophysical methods (Talalay et al, 2020), consistent with evidence for temperate bed conditions from the recovery of refrozen subglacial water at the EPICA-DML drill site (Weikusat et al, 2017;Wilhelms et al, 2014 conditions affect processes at the glacier bed under slow flow velocities and near the ice divides. In view of the apparent preservation of fluvial landscapes in the basin, it can be suggested that erosion in such settings may be limited to subglacial fluvial action with relatively limited consequences for landscapes.…”

Deep ice as a geochemical reactor: insights from iron speciation and mineralogy of dust in the Talos Dome ice core (East Antarctica)

“…Talos Dome is near the coast and its climate is tempered by the ocean. When considering the same depth, ice temperature at Talos Dome is about 15-20°C warmer than at inner sites (Talalay et al, 2020).…”

Investigating the internal structure of the Antarctic ice sheet: the utility of isochrones for spatiotemporal ice-sheet model calibration

“…Geothermal heat flux is uncertain for most parts of the Antarctic ice sheet, and regional differences between published datasets (Fig. 8) can be substantial (Burton-Johnson et al, 2020;Talalay et al, 2020). Local basal melting occurs under forcing with the Shapiro and Ritzwoller (2004) dataset as well but is largely limited to 0-1 mm a −1 and lies between 0.25-0.5 mm a −1 around EDC.…”

“…Even a near-perfect match to present-day observables can conceal overfitting of the model due to weakly constrained boundary conditions, e.g. uncertainties in the climate forcing or geothermal heat flux (Burton-Johnson et al, 2020;Talalay et al, 2020). To counter the effects of overfitting, promising attempts to improve the initialisation of ice-sheet models have been made which involve transient inversions of multiple surface elevation observations over time (Goldberg et al, 2015), albeit only on the regional scale and limited to the extent of the satellite record.…”