Abstract

Antarctic cryoconite holes (CHs) are mostly perennially ice-lidded and sediment-filled depressions that constitute important features on glaciers and ice sheets. Once being hydrologically connected, these microbially dominated mini-ecosystems provide nutrients and biota for downstream environments. For example, the East Antarctic Anuchin Glacier gradually melts into the adjacent perennially ice-covered Lake Untersee, and CH biota from this glacier contribute up to one third of the community composition in benthic microbial mats within the lake. However, biogeochemical features of these CHs and associated spatial patterns across the glacier are still unknown. Here we hypothesized about the CH minerogenic composition between the different sources such as the medial moraine and other zones. Further, we intended to investigate if the depth of the CH mirrors the CH community composition, organic matter (OM) content and would support productivity. In this study we show that both microbial communities and biogeochemical parameters in CHs were significantly different between the zones medial moraine and the glacier terminus. Variations in microbial community composition are the result of factors such as depth, diameter, organic matter, total carbon, particle size, and mineral diversity. More than 90% of all ribosomal sequence variants (RSV) reads were classified as Proteobacteria, Cyanobacteria, Bacteroidetes, Actinobacteria, and Acidobacteria. Archaea were detected in 85% of all samples and exclusively belonged to the classes Halobacteria, Methanomicrobia, and Thermoplasmata. The most abundant genus was Halorubrum (Halobacteria) and was identified in nine RSVs. The core microbiome for bacteria comprised 30 RSVs that were affiliated with Cyanobacteria, Bacteroidetes, Actinobacteria, and Proteobacteria. The archaeal fraction of the core microbiome consisted of three RSVs belonging to unknown genera of Methanomicrobiales and Thermoplasmatales and the genus Rice_Cluster_I (Methanocellales). Further, mean bacterial carbon production in cryoconite was exceptionally low and similar rates have not been reported elsewhere. However, bacterial carbon production insignificantly trended toward higher rates in shallow CHs and did not seem to be supported by accumulation of OM and nutrients, respectively, in deeper holes. OM fractions were significantly different between shallower CHs along the medial moraine and deeper CHs at the glacier terminus. Overall, our findings suggest that wind-blown material originating south and southeast of the Anuchin Glacier and deposits from a nunatak are assumed to be local inoculation sources. High sequence similarities between samples from the Untersee Oasis and other Antarctic sites further indicate long-range atmospheric transport mechanisms that complement local inoculation sources.

Highlights

  • One typical characteristic of glaciers and ice sheets is the occurrence of cryoconite holes (CHs)

  • The average mineral diversity was higher along the medial moraine (AMH: 7.25 ± 1.26, AML: 7.25 ± 2.75) than at the glacier terminus (ANR: 5 ± 0, WIP: 4.67 ± 0.58) and inferred that the mineral composition differed between samples collected along the medial moraine (AMH, AML) and those from regions closer to Lake Untersee (ANR, WIP)

  • CHs at the Anuchin Glacier are considered as important biotic inoculum sources for adjacent Lake Untersee ecosystem (Weisleitner et al, 2019b)

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Summary

Introduction

One typical characteristic of glaciers and ice sheets is the occurrence of cryoconite holes (CHs). These small water bodies form when dark organic and inorganic debris attach to ice surfaces and decrease the albedo locally (Anesio et al, 2009). Solar irradiation promotes melting of the matter into deeper ice layers until the rates of downward movement and surface ice ablation enter a steady state equilibrium (Gribbon, 1979; Hodson et al, 2013). The basins are filled with sediments in the bottom and liquid water on the top (Takeuchi et al, 2001). E. Nordenskiöld recognized the ecological importance of these miniature lakes on the Greenland ice sheet (Leslie, 2011). About one hundred years later, CH research was pioneered in Antarctica by Wharton et al (1981) despite the gained knowledge and recent technological advances, they remain a “dark biological secret of the cryosphere” (Cook et al, 2016)

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