- Past climate changes : general presentation and tools - Antarctic ice cores : from Byrd to Vostok - Byrd, old Dome C and Vostok - The last glacial-interglacial cycle - Isotope :temperature - Dating strategy - Two glacial cycles : oxygen 18 of atmospheric oxygen - The last four climatic cycles - The Vostok lake - Greenland ice cores : from Camp Century to GRIP/GISP2 - Ongoing projects : EPICA, North GRIP and others

Antarctic ice cores (the situation in 1997)

Deep (more than 2 km long) ice cores in Antarctica

© CNRS LGGE

VOSTOK deep drillings : Russia, France and USA

We get a deuterium profile with respect to depth We need a climate (temperature) profile wrt time Temperature interpretation, Dating ice cores

 D decreases by 6‰ when Ts decreases by 1°C ; spatial slope

Adapted from Hoffmann, Jouzel, Werner (in prep) Observed slope 0.75‰/°C Temporal Slope Spatial Slope (model)

Temperature interpretation Magnitude of isotope/temperature scaling for interpretation of central Antarctic ice cores JGR 2003 J. Jouzel, F. Vimeux, N. Caillon, G. Delaygue, G. Hoffmann, V. Masson-Delmotte and F. Parrenin The evidence presently available indicates that, unlike for Greenland, the present-day spatial-slope can probably be taken as a surrogate of the temporal slope to interpret glacial-interglacial isotopic changes at sites such as Vostok and EPICA Dome C. Corresponding temperature changes are within - 10 % to + 30% of those obtained from the conventional interpretation based on the use of the spatial slope.

Dating strategy To estimate the thickness of an annual layer,we combine : - an ice flow model : thinning function accounting for the origin of the ice upflow from Vostok (Ridge B area) - a model which gives the accumulation history based on the assumption that accumulation is linked with the derivative of the saturation pressure and thus depends on temperature only(derived from the deuterium profile)

We get a temperature profile wrt time LGM was 6± 1.5 ° C colder than present-day (9 °C at the surface Dating of the core : accuracy of ± 5000 years

Air oxygen 18 depends on on the oxygen 18 of the sea and on the ratio of continental (driven by the rythm of the monsoon dominated by the Precessional cycle, around 23 K) and of oceanic productivities. * Confirmation of the climate insolation link, chronology

Relationship with insolation stands both for temperature and oxygen 18 of air (which can be used for improving dating)

Lorius, Jouzel, Raynaud, Hansen, Le Treut, High correlation between Antarctic temperature and greenhouse gases R 2 =0.78 (CO 2 ) ; R 2 =0.78 (CH 4 ); 0.84 (greenhouse ; Dpresent-LGM = 2.3 W.m -2 ) - Multivariate analysis with - Greenhouse change - dust - sulfate - ice volume (albedo) - local insolation. - With various assumptions and datings, the GHG contribution is between 40 and 65 % - 80 % of the T vostok variance due to forcings of global significance (GHG, albedo). This suggests that at the global scale ~ 2 out of 4 to 5°C are due to GHG, e.g. amplification of a factor of 3 due to fast feedbacks (slow feedbacks are part of the response) and  T CO2 = °C

Petit et al., 1999

Illustration : J.R. Petit

More than 200 m of lake ice above subglacial lake Vostok, Antarctica Jouzel et al., Science, 1999

Un lac sous la glace Identifié en 1996 par des scientifiques russes et britanniques (Kapitsa et al., 1996) 250 km de long, 40 km de large et 400 m de profondeur moyenne RADARSAT image du Lac Vostok (NASA).

Temperature history of the last 4 climatic cycles from Vostok core We focus on the termination III (stage 7.5) recorded around 240,000 years BP in Vostok water isotopes. Petit et al., 1999 Caillon et al., Goldshmidt 2002

Comparison of CO 2 and argon records suggests that CO 2 concentration increases lagged Antarctica warming by 800  100 years. CO 2 and temperature

Caillon et al., Goldshmidt 2002 Sequence of events surrounding termination

What is the geographical significance of the Vostok temperature record ?

Deep (more than 2 km long) ice cores in Antarctica

Comparison of Dome F and Vostok profiles Watanabe et al., Nature

Comparison of the Dome F and Vostok temperature profiles

K.Pahnke, R.Zahn, H.Elderfield, M.Schulz, Science, August, ,000-year Centennial-Scale Marine Record of Southern Hemisphere Climatic Oscillation (45°S, East of New Zealand)