Abstract
ABSTRACT Cryoconite holes are the most active and diverse microbial habitats on glacier and ice-sheet surfaces. In this article the authors demonstrate that the shape of cryoconite holes varies depending on ice-surface topography and that this has implications for the carbon cycling regime within. Net ecosystem production is shown to be controlled primarily by sediment thickness within holes. The authors show that irregular hole shapes are indicative of hole migration away from topographic shade, which promotes carbon fixation at the mesoscale on ice surfaces. A cellular automaton is used in conjunction with sediment-delivery experiments to show that migration is the result of simple sediment transfer processes, implying a relationship between ice-surface evolution and cryoconite biogeochemistry that has not previously been examined.
Highlights
Melt features called cryoconite holes are ubiquitous on ablating glacial ice worldwide
We suggest that topographically controlled spatial patterns of irradiance cause hole floors to slope, promoting the formation of thick layers of granules against downslope walls driving hole migration away from shade toward more evenly illuminated areas of ice surfaces (Figure 7)
We find that random downslope movements of cryoconite can produce cryopool-like features in our cellular automata, we speculate that the microtopography and hydrology of the ice around real cryopools influences the local sediment dynamics
Summary
Melt features called cryoconite holes are ubiquitous on ablating glacial ice worldwide. In Arctic and lower latitude environments during summer these are usually water-filled depressions containing small (1–10 mm) granules of organic and inorganic matter on their floors (Hodson et al 2008). They form because cryoconite granules have sufficient density to resist removal by meltwater and settle in microtopographic lows on ice surfaces (Langford et al 2010). An “equilibrium depth” is attained when the melt rate at the hole floor is equal to the lowering of the wider ice surface This equilibrium depth varies according to the irradiance of the hole floor. The diameter of these holes is controlled primarily by sediment supply, since a process of “lateral equilibration” has been identified (Cook et al.2010), whereby thick layers of granules spread out to cover the maximum possible surface area and drive hole expansion
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