Articles | Volume 11, issue 5
The Cryosphere, 11, 2231–2246, 2017

Special issue: Oldest Ice: finding and interpreting climate proxies in ice...

The Cryosphere, 11, 2231–2246, 2017

Research article 20 Sep 2017

Research article | 20 Sep 2017

Geothermal flux and basal melt rate in the Dome C region inferred from radar reflectivity and heat modelling

Olivier Passalacqua1, Catherine Ritz1, Frédéric Parrenin1, Stefano Urbini2, and Massimo Frezzotti3 Olivier Passalacqua et al.
  • 1Univ. Grenoble Alpes, CNRS, IGE, 38000 Grenoble, France
  • 2Istituto Nazionale di Geofisica e Vulcanologia, 00143 Rome, Italy
  • 3ENEA, Centro Ricerche Casaccia, P.O. Box 2400, 00100 Rome, Italy

Abstract. Basal melt rate is the most important physical quantity to be evaluated when looking for an old-ice drilling site, and it depends to a great extent on the geothermal flux (GF), which is poorly known under the East Antarctic ice sheet. Given that wet bedrock has higher reflectivity than dry bedrock, the wetness of the ice–bed interface can be assessed using radar echoes from the bedrock. But, since basal conditions depend on heat transfer forced by climate but lagged by the thick ice, the basal ice may currently be frozen whereas in the past it was generally melting. For that reason, the risk of bias between present and past conditions has to be evaluated. The objective of this study is to assess which locations in the Dome C area could have been protected from basal melting at any time in the past, which requires evaluating GF. We used an inverse approach to retrieve GF from radar-inferred distribution of wet and dry beds. A 1-D heat model is run over the last 800 ka to constrain the value of GF by assessing a critical ice thickness, i.e. the minimum ice thickness that would allow the present local distribution of basal melting. A regional map of the GF was then inferred over a 80 km  ×  130 km area, with a N–S gradient and with values ranging from 48 to 60 mW m−2. The forward model was then emulated by a polynomial function to compute a time-averaged value of the spatially variable basal melt rate over the region. Three main subregions appear to be free of basal melting, two because of a thin overlying ice and one, north of Dome C, because of a low GF.

Short summary
As the Dome C region is a key area for oldest-ice research, we need to better constrain the geothermal flux (GF) so that past basal melt rates are well constrained. Our inverse heat model significantly reduces the confidence intervals of the GF regional field around Dome C, which ranges from 48 to 60 mW m−2. Radar echoes need to be interpreted knowing the time lag of the climate signal to reach the bed. Several old-ice targets are confirmed and a new one is suggested, in which the GF is very low.