Total Air Content of the South Pole ice core

Abstract:

Total air content (TAC) is a measure of the amount of air trapped in polar ice, which is of interest due to the potential to reconstruct atmospheric pressure and elevation at ice core sites. Recent work, however, has shown that TAC in ice cores is controlled by a variety of factors. In the SPICEcore TAC record, in particular, there are a number of key features, including, (1) a large decrease in TAC from 0.11 ml/g during the glacial period to an averaged value of 0.08 ml/g during the Holocene, (2) rapid variability in the glacial period, captured between 52 ka and 40 ka, and (3) a period of TAC stability from 35 ka to 25 ka. Large millennial scale variability during the last ice age is anti-correlated with d15N-N₂, a firn thickness indicator, and positively correlated with the stable oxygen isotope temperature proxy. Variations are too large to be controlled by direct effects of temperature, and appear to be too rapid to be tied to elevation changes. Changes in firn densification are a likely candidate to explain these changes. However, TAC may be dominated by another mechanism at certain points in the climate history, explaining the lack of features later in the record. Longer term trends in to TAC appear to follow trends of local integrated solar insolation. Future work aims to further understand the implications of the correlated millennial scale variations of TAC, d15N-N2, and temperature, and possibly discern changes in ice sheet elevation via comparison of TAC records from multiple ice cores.