Climate logging with a new rapid optical technique at Siple Dome

Abstract

The dust logger design is based on a decade of experience in the use of light sources to measure optical properties of deep Antarctic ice. Light is emitted at the top of the instrument by side‐directed LEDs, scattered or absorbed by dust in the ice surrounding the borehole, and collected in a downhole‐pointing photomultiplier tube (PMT) a meter below. With this method the ice is sampled at ambient pressure in a much larger volume than is the case in a core study, and the entire length can be logged in one day. In ice in which scattering is dominated by bubbles, the absorption from dust impurities is perceived as a drop in signal, whereas in bubble‐free ice the scattering from dust increases the light collected. We report on results obtained in Siple Dome Hole A in December 2000. The instrument measured increases in dust concentration extending over many meters during glacial maxima, as well as narrow spikes due to ∼ 1 cm thick ash and dust bands of volcanic origin. Monte Carlo simulation is employed to clarify data analysis and predict the capabilities of future designs.