Retrieving the paleoclimatic signal from the deeper part of the EPICA Dome C ice core

J.-L Tison (1) , M de Angelis (2) , G Littot (3) , E Wolff (3) , H Fischer (4) , M Hansson (5) , M Bigler (4) , R Udisti (6) , A Wegner (7) , J Jouzel (8, 9) , B Stenni (10) , S Johnsen (11) , Valérie Masson-Delmotte (8, 9) , A. Landais (8, 9) , V Lipenkov (12) , L Loulergue (2) , J.-M Barnola (2) , J.-R Petit (2) , B Delmonte (13) , G Dreyfus (14) , D Dahl-Jensen (11) , G Durand (2) , B Bereiter (4) , A Schilt (4) , R Spahni (4) , K Pol (3) , R Lorrain (1) , R Souchez (1) , D Samyn (15)

1 Département des Sciences de la Terre et de l'Environnement
2 LGGE - Laboratoire de glaciologie et géophysique de l'environnement
3 BAS - British Antarctic Survey
4 CEP - Climate and Environmental Physics [Bern]
5 Stockholm University
6 Chemistry Department
7 Department of Bentho-pelagic processes
8 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
9 GLACCIOS - Glaces et Continents, Climats et Isotopes Stables
10 Dipartimento di Scienze Ambientali, Informatica e Statistica
11 NBI - Niels Bohr Institute [Copenhagen]
12 AARI - Arctic and Antarctic Research Institute
13 DISAT - Dipartimento di Scienze dell'Ambiente e del Territorio
14 Oak Ridge Institute for Science and Education Climate Change Policy and Technology Fellow with the US Department of Energy Office of Policy and International Affairs
15 Nagaoka University of Technology

An important share of paleoclimatic information is buried within the lowermost layers of deep ice cores. Because improving our records further back in time is one of the main challenges in the near future, it is essential to judge how deep these records remain unaltered, since the proximity of the bedrock is likely to interfere both with the recorded temporal sequence and the ice properties. In this paper, we present a multiparametric study (δD-δ18Oice , δ18Oatm , total air content, CO2 , CH4 , N2O, dust, high-resolution chemistry , ice texture) of the bottom 60 m of the EPICA (European Project for Ice Coring in Antarctica) Dome C ice core from central Antarctica. These bottom layers were subdivided into two distinct facies: the lower 12 m showing visible solid inclusions (basal dispersed ice facies) and the upper 48 m, which we will refer to as the " basal clean ice facies ". Some of the data are consistent with a pristine paleocli-matic signal, others show clear anomalies. It is demonstrated that neither large-scale bottom refreezing of subglacial water , nor mixing (be it internal or with a local basal end term from a previous/initial ice sheet configuration) can explain the observed bottom-ice properties. We focus on the high-resolution chemical profiles and on the available remote sensing data on the subglacial topography of the site to propose a mechanism by which relative stretching of the bottom-ice sheet layers is made possible, due to the progressively confining effect of subglacial valley sides.

Domaines: Sciences de l'environnement

J.-L Tison, M de Angelis, G Littot, E Wolff, H Fischer, et al.. Retrieving the paleoclimatic signal from the deeper part of the EPICA Dome C ice core. The Cryosphere, 2015, 9 (4), pp.1633-1648. ⟨10.5194/tc-9-1633-2015⟩. ⟨insu-01286552⟩