Measurement of Atmospheric CO2 Trapped in the Ice Core from Siple Dome, Antarctica

Martin Wahlen

We have measured the and are measuring CO2 concentrations in air occluded in the newly drilled Siple Dome ice core from Antarctica. We did this so far at moderate depth resolution through the Holocene to the deepest samples we have. Higher resolution measurements will follow. The general pattern is similar to the Taylor Dome core and (at less resolution to the Vostok core). The dating of the Siple Dome core is not yet established firmly. However, the deepest CO2 results indicate values of mid way of termination II. Features of CO2 variations between 20 and 60 thousand years before present (kyr BP) resemble those by Indermuehle et al. (2000), Higher resolution data have to be done. Across termination I, CO2 follows temperature. As in the Holocene in Taylor Dome, the Siple Dome CO2 record shows that the carbon cycle did not reach steady state after the termination I

We adopted the gas age scale by 18O2 atm. (M. Bender and P. Barnett, pers. comm.) which we extrapolated to the bottom of the core. This shows evidence that the last 10 m of the core might contain termination II and beyond. We eagerly await obtaining some samples from the bottom. In the mean time we work on 13CO2 where the success rate of obtaining good values is limited due to rather low ice quality. In many samples one can smell butyl acetate, and even after careful trimming there is the possibility that preexisting cracks have sealed upon storage and butyl acetate is in the ice which interferes with the isotopic measurements, as in the ion source organic fragments are formed.