Fine reactive sediments produced by glacial erosion sustain microbial habitats in subglacial, ice marginal and other sedimentary environments. Therefore, it is not surprising that microbially- mediated rock-water interactions dominate the anionic composition of glacial meltwaters and acquire nutrients with the capacity to fertilise downstream ecosystems.

 

However, those processes are difficult to detect when glacier surface melting strongly reduces the signal to noise ratio found in runoff samples. Therefore, to identify those processes, evaluate microbially mediated production but also to classify microbial communities, we have been sampling subglacial waters and icings from Svalbard’s multiple glaciers during the pre-melt and the end of ablation season. In so doing, we have also developed redox-sensitive, groundwater sampling techniques suitable for air temperatures as low as -30oC.

 

Our results reveal weathering environments characterised by low redox weathering processes (iron and sulphate reduction, methanogenesis) that are barely detectable in summer runoff. We have also found that the icings formed when these springs discharge into the proglacial environment during winter are active ecosystems regardless the season. Furthermore, heterogeneity in microbial communities existing on and within the icings was discovered.

 

Greater abundance of microorganisms was observed in the upper and lowermost parts of the icings, yet not all icings were the same. Major variations in the microbial community structure were therefore found from one icing to another. In some cases a significant autotrophic community were fertilised by high concentrations of iron and ammonium, resulting in the development of distinct microbial mats.