Pavel Talalay¹, Laurent Augustin², Ryan Bay³, Gary Clow^4,5, Jialin Hong¹, Roger LeB.  Hooke⁶, Eric Lefebvre⁷, Alexey Markov¹, Hideaki Motoyama⁸, P. Buford Price³, Catherine Ritz⁷, Herbert Ueda⁹

¹Polar Research Center, Jilin University, Changchun, China, ²Division Technique de l’INSU, CNRS, La Seyne sur Mer, France, ³Department of Physics, University of California, Berkeley, USA, ⁴U.S. Geological Survey, Lakewood, USA, ⁵Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, USA, ⁶School of Earth and Climate Sciences and Climate Change Institute, Bryand Global Sciences Center, University of Maine, Orono, USA, ⁷Université Grenoble Alpes, CNRS, IGE, Grenoble, France, ⁸National Institute of Polar Research, Tokyo, Japan, ⁹U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, USA

The temperature of the Antarctic ice sheet and the temperature gradient at its base have been directly measured only a few times, although extensive thermodynamic modeling has been used to interpolate among measurements. During the last five decades, deep drilling projects at seven sites – Byrd, Dome C, South Pole, Kohnen, Dome F, Vostok, WAIS Divide – have succeeded in reaching to, or nearly to, the bedrock in inland locations in Antarctica. The Byrd and Kohnen holes encountered water at the base of the ice sheet and water welled up into the holes. The borehole at Vostok penetrated to subglacial Lake Vostok at 3769.3 m, and here water rose from the lake to a height of more than 340 m. Measured temperature profiles in five of the boreholes (Vostok, Dome C, Kohnen, Dome F, South Pole) increase nearly linearly with depth as expected in locations with minimal accumulation and hence small vertical velocities. Vertical advection is much greater at the locations of the Byrd and WAIS Divide boreholes in West Antarctica and there the upper part of the ice sheet is nearly isothermal, but at depth the temperature gradient is nearly the same as at the other sites. Temperature gradients at the bed are 2.2-2.5 C/100 m at Dome C, Dome F and Vostok, and significantly higher – 3.04 C/100 m – at Kohnen. Measured temperature gradients at Dome C, Kohnen, and Dome F correspond to conductive heat fluxes between 51.1–62.7 mW m-2, while at Vostok, at the boundary between the ice and the lake water, the flux is only 46.1 mW m-2. To estimate the geothermal flux from the sub-ice temperature gradients, however, one also needs to account energy used to melt ice at the base.