Continuous measurements of air content: first results from the EDML ice core, Antarctica

Abstract

The air content in cold glacier ice depends on the pore space volume and on local air pressure and temperature at the time of pore close-off. A new method to measure the air content of glacier ice has been developed and will be presented. The measurement has been integrated into the Continuous Flow Analysis set-up which is used for chemical profiling of the EPICA ice cores. It allows the continuous determination of the air content at high depth resolution (<1cm). The air content has been measured continuously in the deep ice core from Dronning Maud Land, Antarctica from 700 m to 2560 m depth, which corresponds to approx. 10 ka to 200 ka before present. First results indicate that the smoothed profile is not dominated by the 100 ka cycle but instead by the 40 ka insolation cycle. The high resolution record exhibits considerable variability of the air content even on the cm scale.The correlation of the aircontent with insolation shows that local insolation has an influence on the sintering process of snow and firn, as local pressure and temperature are expected to have only a small influence. In particular it can be concluded, that the firn porosity at pore close-off is controlled in the top meters or top centimeters of the snow pack.The high resolution profiles show larger relative variability in the example with higher average air content. This may reflect that the effective pore close-off happens at a shallower depth in this case due to formation of lids in layers with high density, which can trap the air below.These tentative findings suggest that the air content may be controlled by the degree of small-scale density variations, and that these density variations in turn may be connected to local surface insolation