http://hdl.handle.net/2122/134 Tue, 21 May 2013 06:10:57 GMT 2013-05-21T06:10:57Z http://hdl.handle.net/2122/7786 Title: Toward a radiometric ice clock: uranium ages of the Dome C ice core Authors: Aciego, S.; Institute of Geochemistry and Petrology, ETH Zurich, Switzerland; Bourdon, B.; Department of Geological Sciences, University of Michigan, Ann Arbor, MI, USA; Schwander, J.; Climate and Environmental Physics, Physics Institute, University of Bern, Switzerland; Baur, H.; Institute of Geochemistry and Petrology, ETH Zurich, Switzerland; Forieri, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: Ice sheets and deep ice cores have yielded a wealth of paleoclimate information based on continuous dating methods while independent radiometric ages of ice have remained elusive. Here we demonstrate the application of (234U/238U) measurements to dating the EPICA Dome C ice core based on the accumulation of 234U in the ice matrix from recoil during 238U decay out of dust bound within the ice. Measured (234U/238U) activity ratios within the ice generally increase with depth while the surface areas of the dust grains are relatively constant. Using a newly designed device for measuring surface area for small samples, we were able to estimate reliably the recoil efficiency of nuclides from dust to ice. The resulting calculated radiometric ages range between 80 ka and 870 ka. Measured samples in the upper 3100 m fall on the previously published age-depth profile. Samples in the 3200–3255 m section show a marked change from 723–870 ka to 85 ka indicating homogenization of the deep ice prior to resetting of the (234U/238U) age in the basal layers. The mechanism for homogenization is likely enhanced lateral ice flow due to high basal melting and geothermal heat flux. Fri, 31 Dec 2010 23:00:00 GMT http://hdl.handle.net/2122/7786 2010-12-31T23:00:00Z http://hdl.handle.net/2122/7273 Title: Ice and Bedrock Characteristics Underneath Dome C (Antarctica) From Radio Echo Sounding Data Analysis Authors: Zirizzotti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Cafarella, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Urbini, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: The Radio Echo Sounding (RES) system is one of the most widely used active remote sensing techniques for polar ice sheet exploration, including bedrock morphology studies and subglacial lake investigations. Recently, bedrock characterization has been improved through the analysis of radar echo strength. The analysis of the RES signal amplitude has been used to highlight areas of high reflectivity variation, attributable to wet ice-bedrock interfaces. In a previous paper the authors described a method to distinguish a wet or dry bedrock-ice interface by analyzing RES data and introducing a linear model for internal ice absorption. In the following paper this subject is reconsidered in greater depth, taking into account important aspects not considered in the previous paper. In particular, a comparison between the ice absorption rate from RES measurements and from EPICA ice core conductivity data was proposed. Moreover, the signal amplitude contributions of internal ice layers and different kinds of rock interface were evaluated. Encouraged by these results, further data analysis produced a new version of the bedrock reflectivity variation map of the Dome C area. The map confirms a wide dispersion of wet/dry rock interfaces in the area studied, indicating the possibility of flowing water along both sides of the Concordia Trench. Sun, 31 Jul 2011 22:00:00 GMT http://hdl.handle.net/2122/7273 2011-07-31T22:00:00Z http://hdl.handle.net/2122/2110 Title: Location of a new ice core site at Talos Dome (East Antarctica) Authors: Urbini, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Cafarella, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zirizzotti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bianchi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Tabacco, I.; Dipartimento di Scienze della Terra «Ardito Desio», Sezione Geofisica, Università degli Studi di Milano, Italy; Frezzotti, M.; ENEA - CRE Casaccia, S. Maria di Galeria (RM), Italy Abstract: In the frame of glaciology and palaeoclimate research, Talos Dome (72°48lS; 159°06lE), an ice dome on the East Antarctic plateau, represents the new selected site for a new deep ice core drilling. The increasing interest in this region is due to the fact that the ice accumulation is higher here than in other domes in East Antarctica. A new deep drilling in this site could give important information about the climate changes near the coast. Previous papers showed that the dome summit is situated above a sloped bedrock. A new position on a relatively flat bedrock 5-6 km far from here in the SE direction was defined as a possible new ice core site for an European (Italy, France, Swiss and United Kingdom) drilling project named as TALDICE (TALos Dome Ice Core Project). This point, named as ID1 (159°11l00mE; 72°49l40mS), became the centre of the Radio Echo Sounding (RES) flight plan during the 2003 Italian Antarctic expedition, with the aim of confirming the new drilling site choice. In this paper 2001 and 2003 RES data sets have been used to draw a better resolution of ice thickness, bottom morphology and internal layering of a restricted area around the dome. Based on the final results, point ID1 has been confirmed as the new coring site. Finally, the preliminary operations about the installation of the summer ice core camp (TALDICE) at ID1 site carried out during the XX Italian Antarctic expedition (November 2004-December 2005) are briefly described. Mon, 31 Jul 2006 22:00:00 GMT http://hdl.handle.net/2122/2110 2006-07-31T22:00:00Z