Introduction


The European Project for Ice Coring in Antarctica (EPICA) is a consortium of laboratories and Antarctic logistics operators from ten nations. Its goal is to recover two deep ice cores in East Antarctica. The study of one core (EDML) from Kohnen Station in the Dronning Maud Land sector of Antarctica is aimed at producing a high-resolution record of at least one glacial–interglacial cycle in the sector of Antarctica facing the Atlantic Ocean, for comparison with Greenland records. The second core (EDC) from Dome C, discussed here, is aimed at producing a record of the longest time period possible.

Observations


The Dome C site has an ice thickness of 3,309 meters. The first core was recovered with a drilling depth of 3,190 m, of which 3,139 m had been analyzed at the time of this paper for several constituents including deuterium excess, delta-oxygen-18, and atmospheric CO2 and CH4. This ice core provides a climate record for the past 740,000 years.

EPICA DOME C ice cores
EPICA DOME C ice cores
EPICA Dome C ice core record
(a) Calculated insolation. Upper blue curve (left axis), mid-July insolation at 65° N; lower black curve (right axis), annual mean insolation at 75°S (the latitude of Dome C).
(b) delta-deuterium from EPICA Dome C (3,000-yr averages). Vostok delta-Deuterium (red) is shown for comparison and some MIS stage numbers are indicated.
(c) Marine delta-oxygen-18 isotope record - solid blue line and dashed red line
(d) Dust from EPICA Dome C.

For the four most recent glacial cycles, the data agree well with the record from Vostok. The earlier period, between 740,000 and 430,000 years ago, was characterized by lower temperatures in interglacial periods in Antarctica, but the interglacial was a greater proportion of each glacial/interglacial cycle.

Antarctic Vostok and EPICA Dome C ice cores have provided a composite record of atmospheric carbon dioxide levels over the past 650,000 years. Results of the lowest 200 meters of the Dome C ice core extend the record of atmospheric carbon dioxide concentration by two complete glacial cycles to 800,000 years before present. It analysis reveals that atmospheric carbon dioxide is strongly correlated with Antarctic temperature throughout eight glacial cycles. Between 650,000 and 750,000 yr before present CO2 concentrations were significantly lower than in the more recent cycles.

Temperature and CO2 over 800,000 years
Temperature and CO2 over 800,000 years
Comparison of temperature and CO2
Temperature from Dome C with respect to the mean temperature of the last millennium (black curve)
CO2 from Dome C (solid circles in purple, blue, black; red open circles), Taylor Dome (brown) and Vostok (green).
Horizontal lines are mean values of temperature and CO2 for the time periods 799–650, 650–450, 450–270 and 270–50 kyr bp.
Glacial terminations are indicated using Roman numerals in subscript; Marine Isotope Stages (MIS) are given in italic Arabic numerals. Source Lüthi et al. 2007

Analysis of an interglacial similar to present


The transition from glacial to interglacial conditions about 430,000 years ago (Termination V) resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases, but there are significant differences in the patterns of change.
Observations for Termination V
Observations for Termination V

Observations for Termination V.
CO2 (circles); CH4 (diamonds) ; delta-deuterium (black line); dust (line with crosses).
Event 1, CO2 peak/delta-D peak; Event 2, CO2 early increase/delta-D early increase.

The interglacial stage following Termination V was exceptionally long—28,000 years compared to, for example, the 12,000 years recorded so far in the present interglacial period. Given the similarities between this earlier warm period and today, the results may imply that without human intervention, a climate similar to the present one would extend well into the future.

Editor's comments


This paper reports the results of analyses of ice cores drilled 3,139 m deep at the Dome C station in eastern Antarctica. From the ice cores it is possible to determine CO2, CH4 and dust concentrations and isotopic composition which can be used to estimate air temperature. The record extends over eight glacial-interglacial cycles. The results for the most recent four glacial-interglacial cycles show a strong correlation with Vostok. The authors draw attention to the fifth termination which has some important interglacial to the current interglacial. The fifth interglacial was also the longest, lasting about 28,000 years.

Sources


Eight glacial cycles from an Antarctic ice core, EPICA community members, Nature 429, 623-628 (10 June 2004)

High-resolution carbon dioxide concentration record 650,000–800,000 years before present, Dieter Lüthi, Martine Le Floch, Bernhard Bereiter, Thomas Blunier, Jean-Marc Barnola, Urs Siegenthaler, Dominique Raynaud, Jean Jouzel, Hubertus Fischer, Kenji Kawamura & Thomas F. Stocker, Nature 453, 379-382 (15 May 2008) doi:10.1038/nature06949