Introduction to Special Section on Microcosms in Ice: The Biogeochemistry of Cryoconite Holes

Cryoconite holes are small, water filled, cylindrical melt-holes on glacial ice surface. Cryoconite, \u27cold dust,\u27 refers to the thin layer of sediment at the hole bottom. The holes form from surficial sediment patches that absorbs more solar radiation than the surrounding ice and which preferentially melt into the glacier forming a cylindrical water-filled hole. These holes form on the ice-covered, as opposed to snow covered, parts of glaciers world-wide, wherever there is sufficient energy for melting. Biogeochemically, cryoconite holes are interesting because the sediment is inncoculated with biologic material, a fraction of which thrives in the cryoconite environment of near-freezing waters and limited nutrient supply. The holes are thus oases for microbial life and biologically mediated chemical reactions on otherwise relatively inert glacier surfaces. Examining the chemical evolution of waters in cryoconite holes, showing how biogeochemical processes in cryoconite holes lead to increasing concentrations of dissolved organic carbon over time, which in may enhance adsorption of solar radiation by the water, aiding the development of deeper holes. If this is true, it suggests that there are a number of complex interactions between the biology, chemistry and biology of cryoconite holes, which act in concert to maintain life on glacier surfaces

Stable microbial community composition on the Greenland Ice Sheet

The first molecular-based studies of microbes in snow and on glaciers have only recently been performed on the vast Greenland Ice Sheet (GrIS). Aeolian microbial seeding is hypothesized to impact on glacier surface community compositions. Localized melting of glacier debris (cryoconite) into the surface ice forms cryoconite holes, which are considered ‘hot spots’ for microbial activity on glaciers. To date, few studies have attempted to assess the origin and evolution of cryoconite and cryoconite hole communities throughout a melt season. In this study, a range of experimental approaches was used for the first time to study the inputs, temporal and structural transformations of GrIS microbial communities over the course of a whole ablation season. Small amounts of aeolian (wind and snow) microbes were potentially seeding the stable communities that were already present on the glacier (composed mainly of Proteobacteria, Cyanobacteria and Actinobacteria). However, the dominant bacterial taxa in the aeolian samples (Firmicutes) did not establish themselves in local glacier surface communities. Cryoconite and cryoconite hole community composition remained stable throughout the ablation season following the fast community turnover, which accompanied the initial snow melt. The presence of stable communities in cryoconite and cryoconite holes on the GrIS will allow future studies to assess glacier surface microbial diversity at individual study sites from sampling intervals of short duration only. Aeolian inputs also had significantly different organic δ13C values (-28.0 to -27.0‰) from the glacier surface values (-25.7 to -23.6‰), indicating that in situ microbial processes are important in fixing new organic matter and transforming aeolian organic carbon. The continuous productivity of stable communities over one melt season makes them important contributors to biogeochemical nutrient cycling on glaciers

Drainage-system development in consecutive melt seasons at a polythermal, Arctic glacier, evaluated by flow-recession analysis and linear-reservoir simulation

The drainage systems of polythermal glaciers play an important role in high latitude hydrology, and are determinants of ice flow rate. Flow-recession analysis and linear-reservoir simulation of runoff time series are here used to evaluate seasonal and inter-annual variability in the drainage system of the polythermal Finsterwalderbreen, Svalbard, in 1999 and 2000. Linear flow recessions are pervasive, with mean coefficients of a fast reservoir varying from 16 h (1999) to 41 h (2000), and mean coefficients of an intermittent, slow reservoir varying from 54 h (1999) to 114 h (2000). Drainage-system efficiency is greater overall in the first of the two seasons, the simplest explanation of which is more rapid depletion of the snow cover. Reservoir coefficients generally decline during each season (at 0.22 h d–1 in 1999 and 0.52 h d–1 in 2000), denoting an increase in drainage efficiency. However, coefficients do not exhibit a consistent relationship with discharge. Finsterwalderbreen therefore appears to behave as an intermediate case between temperate glaciers and other polythermal glaciers with smaller proportions of temperate ice. Linear-reservoir runoff simulations exhibit limited sensitivity to a relatively wide range of reservoir coefficients, although the use of fixed coefficients in a spatially-lumped model can generate significant sub-seasonal error. At Finsterwalderbreen, an ice-marginal channel with the characteristics of a fast reservoir, and a subglacial upwelling with the characteristics of a slow reservoir, both route meltwater to the terminus. This suggests that drainage-system components of significantly contrasting efficiencies can co-exist spatially and temporally at polythermal glaciers

The hydrology of the proglacial zone of a high-Arctic glacier (Finsterwalderbreen, Svalbard): Atmospheric and surface water fluxes

Proglacial areas are expanding globally as a consequence of sustained glacier retreat, but there are very few studies focusing on their hydrology. This paper examines the surface and atmospheric water fluxes over a complete annual cycle in the proglacial area of the Svalbard glacier Finsterwalderbreen (77 N), through a combination of field measurements, physical modelling and statistical estimation. Precipitation in winter (226 mm) exceeded that in summer (29 mm), and over the course of the annual cycle total precipitation exceeded total evaporation (141 mm), although evaporative outputs from the proglacial area exceeded precipitation inputs during the dry summer. Runoff was highly irregular in time, with much of the total annual flow being concentrated into two relatively brief, early-to-mid summer intervals, the greater of which was characterised by the release of subglacially-stored water. Water fluxes were dominated by meltwater supply from the glacier: the total annual glacial runoff (7.38 × 107 m3) was an order-of-magnitude greater than the precipitation flux delivered directly to the proglacial area, and two orders-of-magnitude greater than evaporative losses from it. Outputs of meltwater from the proglacial area were not significantly different from inputs over the duration of the melt season, so surface water storage does not appear to be important in the studied catchment, despite episodes of flooding over shorter timescales. A synthesised description of the seasonal hydrological cycle in Finsterwalderbreen’s proglacial area is presented, which can be viewed as a set of hydrological boundary conditions for comparable high-latitude locations. Further study of these conditions is required, because the challenging nature of hydrometry in the high-latitudes has the potential to limit progress in understanding environmental change there