The Co2 Record in Ice Cores: A Reconstruction of the Atmospheric Evolution Between 18 ka BP and 1850 AD (Abstract)

Air bubbles trapped in glacial ice at the time of its formation provide a unique record of variations in past worldwide atmospheric C02 content. Published records, covering approximately the last 30 to 40 ka, indicate a minimum in the C02 concentrations during the latter part of the last ice age, around 18 ka BP, with values of the order of 200 ppmv (see, in particular, Delmas and others 1980, Neftel and others 1982). The ice records indicate also that during approximately the last 2 ka, before any significant anthropogenic influence on the atmospheric C02 content, the concentrations were of the order of 260 to 270 ppmv (Neftel and others 1982, Barnola and others 1983). By comparison the , present mean annual concentration in the atmosphere is about 340 ppmv. We present new results obtained on the Dome C and D 57 cores taken in East Antarctica, which will be published in detail elsewhere. The D 57 results indicate that before 1850 AD the C02 concentration was as low as 258 ppmv, with a significant fluctuation between 258 and 272 ppmv in the interval between approximately 1500 and 1850 AD. The D 57 record also indicates the initiation of a marked increase in the C02 concentration near the second part of the last century and the first part of the present one. The new Dome C results provide a detailed C02 record for the last 25 ka which is in general agreement with the previously published Dome C record (Delmas and others 1980). This new record confirms, in particular, the occurrence of a low C02 level of the order of 200 ppmv during the last glacial maximum, around 18 ka BP. It indicates, also, that (1) the increase in C02 concentration associated with the end of the last ice age began before or simultaneously with the important climatic change indicated by the large shift observed in the isotopic composition of the ice, (2) this C02 increase may have occurred in two steps, and (3) there is a large scatter in the C02 concentration near the end of the ice age-Holocene transition, with most of the values as high as about the present-day atmospheric concentration of 340 ppmv. , Our new results permit the following preliminary conclusions to be made. (i). The atmospheric C02 level during pre-industrial times may have been as