ALBERT

Description: The recovery of a 1.5 million yr long ice core from Antarctica represents a keystone of our understanding of Quaternary climate, the progression of glaciation over this time period and the role of greenhouse gas cycles in this progression. Here we tackle the question of where such ice may still be found in the Antarctic ice sheet. We can show that such old ice is most likely to exist in the plateau area of the East Antarctic ice sheet (EAIS) without stratigraphic disturbance and should be able to be recovered after careful pre-site selection studies. Based on a simple ice and heat flow model and glaciological observations, we conclude that positions in the vicinity of major domes and saddle position on the East Antarctic Plateau will most likely have such old ice in store and represent the best study areas for dedicated reconnaissance studies in the near future. In contrast to previous ice core drill site selections, however, we strongly suggest significantly reduced ice thickness to avoid bottom melting. For example for the geothermal heat flux and accumulation conditions at Dome C, an ice thickness lower than but close to about 2500 m would be required to find 1.5 Myr old ice (i.e., more than 700 m less than at the current EPICA Dome C drill site). Within this constraint, the resolution of an Oldest-Ice record and the distance of such old ice to the bedrock should be maximized to avoid ice flow disturbances, for example, by finding locations with minimum geothermal heat flux. As the geothermal heat flux is largely unknown for the EAIS, this parameter has to be carefully determined beforehand. In addition, detailed bedrock topography and ice flow history has to be reconstructed for candidates of an Oldest-Ice ice coring site. Finally, we argue strongly for rapid access drilling before any full, deep ice coring activity commences to bring datable samples to the surface and to allow an age check of the oldest ice.

Description: In the Eurasian Arctic, the archipelago of Severnaya Zemlya is the most eastern one which is covered by a considerable ice cap, giving the opportunity to study regional climate signals from the Holocene period. The Academii Nauk ice cap (Komsomolets Island) was chosen for drilling a deep ice core because it is the thickest and coldest ice cap on Severnaya Zemlya. A suitable drilling site was found at 80°31'N 94°49'E by the help of airborne radio-echo sounding data and SAR interferometry. The ice thickness was 724 m at this location. Drilling was carried out between 1999 and 2001 reaching bedrock. It was a joint project of the Alfred Wegener Institute (Germany), the Arctic and Antarctic Research Institute, and the Mining Institute (Russia, St.Petersburg both). An electromechanical ice core drill (KEMS-112M) was used, the same type as at Vostok Station, Antarctica. The paper presents the results of electrical conductivity measurements (DEP) of the whole ice core. Several zones with high conductivity were assumed to be caused by major volcanic eruptions. By help of catalogues of historical volcanic events we used these signals for core dating of the upper 245 meters. The time scale developed this way is in good agreement with horizons of enriched radioactivity caused by nuclear weapon tests in the early 1960's and by the Chernobyl accident. The d180 record fits almost perfectly to values published earlier by Klementev et al. for Akademii Nauk, however, we have no evidence for the age model used in this Russian paper. We found annual accumulation rates in the isotope record and in the electrical data indicating none-steady state conditions of this glacier in the past. Hence, the core ages are overestimated by flow models. There seems to be an age discordance in the deepest part of the core. For Akademii Nauk ice cap the isotope data indicate a climate warming since app. 1860 which is much higher than found at central Greenland (GRIP/GISP2), Devon lsland or Hans Tausen ice cap. REFERENCE Klementev, O.L.; Potapenko, V. Yu.; Savatyugin, L.M. & Nikolaev, V.l.: Studies of the intemal structure and thennal-hydrodynarnic state of Vavilov Glacier, Archipelago Sevemaya Zernlya. IAHS Publ. 208, 1991, p.49-59