Bremerhaven, 28 February 2013. Atmospheric carbon dioxide and the Antarctic temperature increased synchronously during the last deglacial warming 20,000 to 10,000 years ago. A European team of researchers comes to this conclusion after having re-analysed the age of the enclosed air bubbles in the Antarctic ice core EPICA Dome C. The study, in which the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, was involved, appeared now in the scientific journal Science.
Changes in the chemical composition of the atmosphere in the past can be reconstructed from air bubbles enclosed in Antarctic ice. In this way it has been possible to determine the natural variability of the greenhouse gas carbon dioxide over the past 800,000 years from ice cores. Over the same time window and on the same ice core changes in Antarctic temperature were also reconstructed. How quickly air bubbles were deposited in ice cores at which depth has now been recalculated under the lead of the French Laboratoire de Glaciologie et Geophysique de l’Environnement. With the assistance of the nitrogen isotope 15 N they were able to show that the enclosed air in the EPICA Dome C ice core during the transition from the last glacial to the current interglacial period is older than hitherto assumed. This ice core was obtained in the EPICA project (European Project for Ice Coring in Antarctica).
“We have discovered that previous age calculations of the enclosed gases are too inaccurate based on what we know today,” says Dr. Peter Köhler, physicist at the Alfred Wegener Institute (AWI), Helmholtz Centre for Polar and Marine Research and co-author of the Science study. Temperature and greenhouse gas measurements of the ice cores are made at different depths. Every depth is then assigned an age. The necessary age models for temperature and greenhouse gases differ here. Temperature changes are reconstructed indirectly via the isotopy of the water molecules of the ice. Concentrations of greenhouse gases are measured directly from the antique air bubbles which must have been completely separated from the atmosphere when they were formed. This happens at the lower end of the firn during the so-called bubble close-off at a lock-in depth of around 100 meters where snow compacts to form ice.
During a re-analysis of the lock-in depth in the EPICA Dome C ice core the researchers have now recalculated the thickness of the firn layer by using the nitrogen isotope 15 N . What they found was that the carbon dioxide content of the atmosphere increased “synchronously” with the Antarctic temperature during the transition from the last glacial to the interglacial period 20,000 to 10,000 years ago. “Synchronously” is defined by the scientists in this study as time differences of less than 200 years during the four known abrupt changes between both climate variables in the period examined.
“We describe the synchronous rise in the Antarctic temperature and the global atmospheric carbon dioxide content during the last transition from a glacial cold stage to an interglacial warm period. This synchronicity suggests that there are probably strong feedback mechanisms which link the two climate variables. It is important to note here that our study only shows details about the synchronicity of these two variables. If we wish to completely understand how the end of the last glacial period occurred, we also need to incorporate data on temperature changes from other parts of the Earth. Furthermore, we must be able to set our results and those of other time series into the correct temporal context. For this final interpretation also the application of state-of-the-art climate models will be necessary”, explains AWI physicist Köhler.
Notes for Editors
Original publication:
F. Parrenin, V. Masson-Delmotte, P. Köhler, D. Raynaud, D. Paillard, J. Schwander, C. Barbante, A. Landais, A. Wegner, J. Jouzel: Synchronous Change of Atmospheric CO2 and Antarctic Temperature During the Last Deglacial Warming. Science XX (2013); DOI: 10.1126/science.1226368
Institutions involved:
Laboratoire de Glaciologie et Géophysique de l'Environnement (CNRS/UJF), Grenoble, France
Laboratoire des Sciences du Climat et de l'Environnement (CEA/CNRS/UVSQ-IPSL), Gif-sur-Yvette, France
Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
Physics Institute, University of Bern, Bern, Switzerland
Department of Environmental Sciences, University of Venice, Venice, Italy
Institute for the Dynamics of Environmental Processes–CNR, University of Venice, Venice, Italy
Your scientific contact partner is Dr. Peter Köhler (Tel.: +49 471 4831-1687, e-mail: Peter.Koehler(at)awi.de). Your contact partner in the Communications and Media Department of the Alfred Wegener Institute is Dr. Folke Mehrtens (Tel. +49 471 4831-2007, e-mail: Folke.Mehrtens(at)awi.de).
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The Alfred Wegener Institute conducts research in the Arctic and Antarctic and in the high and mid-latitude oceans. The Institute coordinates German polar research and provides important infrastructure such as the research icebreaker Polarstern and stations in the Arctic and Antarctic to the international scientific world. The Alfred Wegener Institute is one of the 18 research centres of the Helmholtz Association, the largest scientific organisation in Germany.
