Abstract
ABSTRACTCryoconite holes can be important sources and stores of water and nutrients on cold and polythermal glaciers, and they provide a habitat for various forms of biota. Understanding the hydrological connectivity of cryoconite holes may be the key to understanding the transport of nutrients and biological material to the proglacial areas of such glaciers. This paper aims to characterize and explain spatial variability in the connectivity of ice-lidded cryoconite holes on a small, piedmont glacier in the McMurdo Dry Valleys through geochemical analysis of cryoconite hole waters. Solute concentrations in both surface and near-surface ice and cryoconite holes, vary greatly along the glacier centerline, and all sample types displayed similar spatial patterns of variability. Using chloride as a tracer, we estimated variations in cryoconite hole connectivity along the glacier centerline. We found that a previously used mass transfer method did not provide reliable estimates of the time period for which cryoconite hole waters had been isolated from the atmosphere. We attribute this to spatial variability in both the chloride content of the surface ice and surface ablation rates. The approach may, however, be used to qualitatively characterize spatial variations in the hydrological connectivity of the cryoconite holes. These results also suggest that ice-lidded cryoconite holes are never truly isolated from the near-surface drainage system.
Highlights
Drainage or storage of water on glacier surfaces is dictated by the structure of the hydrological network and the temporal variability of hydrological connections
Cryoconite holes form when differential ablation causes a water-filled depression to form within the surface ice layer
To assess the spatial patterns of hydrological connectivity of cryoconite holes, we used the method employed by Fountain and others (2004) to estimate cryoconite hole isolation at ten sites along the glacier centerline (Fig. 1)
Summary
Drainage or storage of water on glacier surfaces is dictated by the structure of the hydrological network and the temporal variability of hydrological connections. Cryoconite hole development is largely restricted to cold-based and polythermal glaciers in high latitude and high-altitude regions (Takeuchi, 2002; Fountain and others, 2004; Anesio and others, 2007), as well as some temperate glaciers (Anesio and others, 2010), where low melt rates generate insufficient runoff to wash sediment from the glacier surface. In arid regions, such as the McMurdo Dry Valleys, cryoconite holes are often ice covered. According to previous studies using changes in chloride mass as a proxy for isolation time, cryoconite holes in Antarctica can remain isolated from both the atmosphere and other holes for several years (Fountain and others, 2004; Bagshaw and others, 2007)
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