In the framework of the Eurocore drilling project 1989 at Summit, Central Greenland, air samples were collected from a drill hole in the firn at several depth levels. The samples have been analyzed for 85Kr, CO2, CH4, CFC's (F-11 and F-12) contents and for the isotopic composition of nitrogen and oxygen. The measured data are compared with the results of a diffusion model. CO2, for example, takes 12 years (with a standard deviation of 7.5 years) to diffuse from the surface to the firn-ice transition under the present climatic conditions at Summit. The difference between the age of the ice and the mean age of the occluded air is approximately 210 years. An enrichment of the heavier isotopes due to separation by gravity has been observed. Molecular diffusion alone suffices to explain the observed concentration trends in the firn column. We can, however, not exclude the existence of a convective zone below the surface. We have also measured the density and closed porosity along the firn core that has been retrieved when drilling the hole. The porosity data reveal that the air is occluded into bubbles mainly between 65 and 80 m, corresponding to densities of 790 and 830 kg/m 3, respectively.

Ice-core records of climate from Greenland and Antarctica show asynchronous temperature variations on millennial timescales during the last glacial period. The warming during the transition from glacial to interglacial conditions was markedly different between the hemispheres, a pattern attributed to the thermal bipolar see-saw. However, a record from the Ross Sea sector of East Antarctica has been suggested to be synchronous with Northern Hemisphere climate change. Here we present a temperature record from the Talos Dome ice core, also located in the Ross Sea sector. We compare our record with ice-core analyses from Greenland, based on methane synchronization, and find clearly asynchronous temperature changes during the deglaciation. We also find distinct differences in Antarctic records, pointing to differences in the climate evolution of the Indo-Pacific and Atlantic sectors of Antarctica. In the Atlantic sector, we find that the rate of warming slowed between 16,000 and 14,500 years ago, parallel with the deceleration of the rise in atmospheric carbon dioxide concentrations and with a slight cooling over Greenland. In addition, our chronology supports the hypothesis that the cooling of the Antarctic Cold Reversal is synchronous with the Bølling–Allerød warming in the northern hemisphere 14,700 years ago

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Interpretation of the past CO2 variations recorded in polar ice during the large climatic transitions requires an accurate determination of the air‐ice age difference. For the Vostok core, the age differences resulting from different assumptions on the firn densification process are compared and a new procedure is proposed to date the air trapped in this core. The penultimate deglaciation is studied on the basis of this new air dating and new CO2 measurements. These measurements and results obtained on other ice cores indicate that at the beginning of the deglaciations, the CO2 increase is either in phase or lags by less than about 1000 years with respect to the Antarctic temperature, while it clearly lags the temperature at the onset of the last glaciation.

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In order to study in detail the pre‐industrial CO2 level (back to about 900 AD) and its temporal variations, several ice cores from Greenland and Antarctica were analysed in two laboratories, and compared with previous records. The agreement between the two laboratories and between the different cores of the same hemisphere is good. However, the comparison of the northern hemisphere (Greenland) and southern hemisphere (Antarctica) records shows values systematically higher in the north than in the south, ranging from 20 ppmv at the turn of this millennium to nearly zero around the 18th century. Based on our present knowledge of the carbon cycle, an inter‐hemispheric gradient of 20 ppmv is unrealistic. Thus, in the oldest part of the record, at least one profile should not represent the true atmospheric CO2 concentrations. A companion paper by Anklin et al. (submitted), discusses the possible processes which can alter the atmospheric CO2 once trapped in the ice. Due to the fact that the impurity content is one order of magnitude lower in the Antarctic than in the Greenland ice, we are much more confident in the Antarctic record. The new results from D47 and D57 (Adélie Land) presented in this paper, confirm the CO2 fluctuation of about 10 ppmv at the end of the 13th century, previously observed by Siegenthaler et al. (1988) on an ice core drilled at South Pole. This fluctuation corresponds to a small imbalance of the carbon cycle (∼ 0.3 GT C/ yr), but its duration led to a significant cumulative input into the atmosphere. The changes observed in the pre‐industrial level are discussed in terms of climatic noise and variability.

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[1] Methane is one of the important greenhouse gases accumulating in the atmosphere today. The increased loading over the past 2 centuries is thought to be the result of increased anthropogenic emissions. Here we present records of the d 13 C of CH 4 in firn air from the South Pole and in trapped bubbles in a short ice core from Siple Dome, Antarctica, that help constrain historical emissions of various sources throughout the last 2 centuries. Using two firn air samplings in 1995 and 2001 we calculate that d 13 CH 4 has increased by an average of 0.06 ± 0.02%/yr over the 6 years between samplings. Our ice core results suggest the d 13 C of atmospheric CH 4 has increased by 1.8 ± 0.2% between 1820 A.D. and 2001 AD. The d 13 CH 4 changes in both data sets are the result of an increase in the relative proportion of CH 4 sources with elevated 13 C/ 12 C isotope ratios. One explanation for observed trends involves a 16 Tg/yr increase in CH 4 emissions associated with biomass burning over the past 2 centuries.