IngentaConnect Incorporation of particulates into accreted ice above subglacial ...

Authors: Royston-Bishop, George; Priscu, John C.; Tranter, Martyn; Christner, Brent; Siegert, Martin J.; Lee, Victoria

Source: Annals of Glaciology, Volume 40, Number 1, January 2005 , pp. 145-150(6)

Publisher: International Glaciological Society

Abstract:

The nature of microscopic particulates in meteoric and accreted ice from the Vostok (Antarctica) ice core is assessed in conjunction with existing ice-core data to investigate the mechanism by which particulates are incorporated into refrozen lake water. Melted ice samples from a range of icecore depths were filtered through 0.2 μm polycarbonate membranes, and secondary electron images were collected at ×500 magnification using a scanning electron microscope. Image analysis software was used to characterize the size and shape of particulates. Similar distributions of major-axis lengths, surface areas and shape factors (aspect ratio and compactness) for particulates in all accreted ice samples suggest that a single process may be responsible for incorporating the vast majority of particulates for all depths. Calculation of Stokes settling velocities for particulates of various sizes implies that 98% of particulates observed could 'float' to the ice-water interface with upward water velocities of 0.0003 m s⁻¹ where they could be incorporated by growing ice crystals, or by rising frazil ice crystals. The presence of particulates that are expected to sink in the water column (2%) and the uneven distribution of particulates in the ice core further implies that periodic perturbations to the lake's circulation, involving increased velocities, may have occurred in the past.

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Incorporation of particulates into accreted ice above subglacial Vostok lake, Antarctica