Glacier clear ice bands indicate englacial channel microbial distribution

Abstract

Distant glacial areas are interconnected by a complex system of fractures and water channels which run in the glacier interior and characterize the englacial realm. Water can slowly freeze in these channels where the slow freezing excludes air bubbles giving the ice a clear aspect. This ice is uplifted to the surface ablation zone by glacial movements and can therefore be observed in the form of clear surface ice bands. We employed an indirect method to sample englacial water by coring these ice bands. We were able, for the first time, to compare microbial communities sampled from clear (i.e. frozen englacial water bands) and cloudy ice (i.e. meteoric ice) through 16S rRNA gene sequencing. Although microbial communities were primarily shaped and structured by their spatial distribution on the glacier, ice type was a clear secondary factor. One area of the glacier, in particular, presented significant microbial community clear/cloudy ice differences. Although the clear ice and supraglacial communities showed typical cold-adapted glacial communities, the cloudy ice had a less defined glacial community and ubiquitous environmental organisms. These results highlight the role of englacial channels in the microbial dispersion within the glacier and, possibly, in the shaping of glacial microbial communities.

Microbial dynamics in rapidly transforming Arctic proglacial landscapes

“…Ice cores from Arctic glaciers and the Greenland Ice Sheet were found to consist of Cyanobacteria, Alphaproteobacteria, Actinobacteria, Bacteroidetes, WPS-2, Firmicutes, Acidobacteria, Gammaproteobacteria and Armatimonadetes [3,39]. However, detection of excess gases such as carbon dioxide, methane, and nitrous oxide in glacial ice cores has suggested the possibility of active microbial metabolism within the ice or recent microbial deposition through meltwater channels, implying that the microbiome composition may have changed from the initial deposited community [40][41][42]. This corroborates with the recovery of viable isolates from glacial ice cores, dated over 750,000 years old, in the Tibetan plateau [43].…”

“…Interestingly, a large proportion of supraglacial meltwater enters the englacial and subglacial regions which can cause altered temperatures [44] and potentially provide additional nutrients that stimulate microbial activity. Englacial meltwater channels present as cloudy ice when frozen and exhibit microbial communities less associated with glacial cold-adapted microbial taxa than communities from clear englacial ice, indicating the effect of local conditions on microbial diversity within the englacial zone [26,42].…”

Glacial Water: A Dynamic Microbial Medium

“…The englacial realm, with its network of water pathways, transfers cells and nutrients within the glacial system. It is unclear whether the englacial realm also has a role in nutrient and carbon transformation and is characterized by a microbial community specific to englacial pathways conditions [ 150 ]. Microbial nutrient cycling observed in fast-flowing supraglacial streams [ 49 ] suggests that microbial processes may be significant in fast-flowing englacial conduits.…”

“…Liquid flow in veins has long residence times, suggesting low oxygen concentrations and anaerobic metabolism [ 68 , 155 ], which can be mediated by methanogens such as Methanosphaerula and Methanococcus [ 156 ]. Despite the high nutrient concentrations and favorable conditions for active communities, microbial structure and function in the englacial realm are poorly understood [ 150 , 151 ].…”