A deep high-resolution optical log of dust, ash, and stratigraphy in South Pole glacial ice

We describe a new dust logger designed to operate in water-filled IceCube boreholes in South Pole ice, and we give examples of its performance. We recorded optical effects due to bubbles, dust, and volcanic ash in situ from similar to 70 to 2100 meters. Seasonal layering in bubble concentration could also be discerned. Below similar to 1300 m over the interval 25 ka to 70 ka, because of the conversion of all air bubbles to invisible hydrate crystals, and the close match between refractive indices of the surrounding ice and the water in the borehole, scattering from dust provided fine-structure in the depth-dependence of concentration with a resolution of < 1 cm. Thin, highly absorptive horizons in the data set confirm there is significant fallout at South Pole of ash from explosive volcanic events. By locating and dating volcanic ash layers in the South Pole dust record, it may be possible to match them to volcanic layers found across Antarctica and in Greenland.