Abstract
Ultra-oligotrophic Lake Untersee is among the largest and deepest surface lakes of Central Queen Maud Land in East Antarctica. It is dammed at its north end by the Anuchin Glacier and the ice-cover dynamics are controlled by sublimation — not melt — as the dominating ablation process and therefore surface melt during austral summer does not provide significant amounts of water for recharge compared to subsurface melt of the Anuchin Glacier. Several studies have already described the structure and function of the microbial communities within the water column and benthic environments of Lake Untersee, however, thus far there have been no studies that examine the linkages between the lake ecosystem with that of the surrounding soils or the Anuchin Glacier. The glacier may also play an important role as a major contributor of nutrients and biota into the lake ecosystem. Based on microbial 16S rRNA amplicon sequencing, we showed that the dominant bacterial signatures in Lake Untersee, the Anuchin Glacier and its surrounding soils were affiliated with Actinobacteria, Bacteroidetes, Cyanobacteria, Firmicutes, and Proteobacteria. Aerosol and local soil depositions on the glacier surface resulted in distinct microbial communities developing in glacier ice and cryoconite holes. Based on a source tracking algorithm, we found that cryoconite microbial assemblages were a potential source of organisms, explaining up to 36% of benthic microbial mat communities in the lake. However, the major biotic sources for the lake ecosystem are still unknown, illustrating the possible importance of englacial and subglacial zones. The Anuchin Glacier may be considered as a vector in a biological sense for the bacterial colonization of the perennially ice-covered Lake Untersee. However, despite a thick perennial ice cover, observed “lift-off” microbial mats escaping the lake make a bidirectional transfer of biota plausible. Hence, there is an exchange of biota between Lake Untersee and connective habitats possible despite the apparent sealing by a perennial ice cover and the absence of moat areas during austral summer.
Highlights
The largest ice sheet on Earth covers more than 99.8% of continental Antarctica (Burton-Johnson et al, 2016)
We showed that the proportion of cryoconite holes as source for benthic microbial mats in Lake Untersee made up to 36% while all other sampled source habitats as such were negligible (Figure 11)
Based on the observed species and the Shannon index, we showed that both supraglacial habitats are significantly different from each other with respect to their microbial community
Summary
The largest ice sheet on Earth covers more than 99.8% of continental Antarctica (Burton-Johnson et al, 2016). In contrast to cryoconite holes in other regions, the majority of those in Antarctica are continuously ice-covered (Fountain et al, 2004; Cook et al, 2016) and solar-induced subsurface melt provides liquid water only for a mere fraction of the year. They are disconnected from the atmosphere for most of the time, leading to unique environmental conditions such as extremely limited light intensities due to the ice lid (Bagshaw et al, 2016) or unusual hydrochemistry (Fountain et al, 2004). Compared to cryoconite holes, microbial abundance (Boetius et al, 2015) and metabolic activity (Edwards et al, 2013a) in glacier ice are low
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