Microbial abundance in surface ice on the Greenland Ice Sheet

Abstract

Measuring microbial abundance in glacier ice and identifying its controls is essential for a better understanding and quantification of biogeochemical processes in glacial ecosystems. However, cell enumeration of glacier ice samples is challenging due to typically low cell numbers and the presence of interfering mineral particles. We quantified for the first time the abundance of microbial cells in surface ice from geographically distinct sites on the Greenland Ice Sheet (GrIS), using three enumeration methods: epifluorescence microscopy (EFM), flow cytometry (FCM), and quantitative polymerase chain reaction (qPCR). In addition, we reviewed published data on microbial abundance in glacier ice and tested the three methods on artificial ice samples of realistic cell (102–107 cells ml−1) and mineral particle (0.1–100 mg ml−1) concentrations, simulating a range of glacial ice types, from clean subsurface ice to surface ice to sediment-laden basal ice. We then used multivariate statistical analysis to identify factors responsible for the variation in microbial abundance on the ice sheet. EFM gave the most accurate and reproducible results of the tested methodologies, and was therefore selected as the most suitable technique for cell enumeration of ice containing dust. Cell numbers in surface ice samples, determined by EFM, ranged from ~ 2 × 103 to ~ 2 × 106 cells ml−1 while dust concentrations ranged from 0.01 to 2 mg ml−1. The lowest abundances were found in ice sampled from the accumulation area of the ice sheet and in samples affected by fresh snow; these samples may be considered as a reference point of the cell abundance of precipitants that are deposited on the ice sheet surface. Dust content was the most significant variable to explain the variation in the abundance data, which suggests a direct association between deposited dust particles and cells and/or by their provision of limited nutrients to microbial communities on the GrIS.

Quantifying bioalbedo: a new physically based model and discussion of empirical methods for characterising biological influence on ice and snow albedo

“…4.6). Cells can be counted in field samples using traditional microscopy or flow cytometry, although the two methods may produce different results (Stibal et al, 2015). The chlorophyll content of a sample has traditionally been used as a proxy for biomass; however, the amount of chlorophyll in an individual cell is species-specific and changes over time as a mechanism of photoacclimation (e.g.…”

Modelling Glaciers in the HARMONIE-AROME NWP model

“…The observations show however, that the albedo continues to decline throughout the melt season to around 0.2 on the 30 June and even lower by the end of the summer. These low values reflect the formation of cryoconite and the accumulation of dirt and impurities that melt out of the ice as well as microbial activity on the glacier surface (Stibal et al, 2015) but QAS_L lies in the lowest part of the ablation zone and has much lower albedo values than typical for most of the ablation zone in Greenland, (Ryan et al, 2017), as also shown in Fig. 10.…”

Ecological Modeling of the Supraglacial Ecosystem: A Process-based Perspective

“…Spatial variability in carbon and nutrient concentrations and microbial abundance and activity has been reported from the GrIS (e.g., Hodson et al, 2010;Stibal et al, 2010Stibal et al, , 2012bStibal et al, , 2015aTelling et al, 2012;Yallop et al, 2012). However, direct measurements exist from very few discreet locations, and upscaling from point measurements to the whole ice sheet may introduce large errors.…”

“…Microbial cells deposited with snow may remain on the ice surface after the snow has melted and become part of the surface ice community, or they can be flushed from the ice sheet surface with meltwater (Cameron et al, 2015). Bare ice is exposed seasonally around the margins of the ice sheet and hosts a high abundance of algae (Uetake et al, 2010;Yallop et al, 2012) and other microorganisms (Stibal et al, 2015a;Cameron et al, 2016). The algae are important primary producers in the ecosystem and may contribute to surface melting via darkening the ice due to pigment production Yallop et al, 2012).…”

“…The algae are important primary producers in the ecosystem and may contribute to surface melting via darkening the ice due to pigment production Yallop et al, 2012). Abundance of other, mostly heterotrophic, microbes in surface ice has been found to correlate with dust concentration (Stibal et al, 2015a). Cryoconite, usually concentrated in cryoconite holes , hosts diverse and highly active microbial communities that consist of photoautotrophic cyanobacteria and a range of heterotrophic bacteria (Cameron et al, 2012(Cameron et al, , 2016Stibal et al, 2012bStibal et al, , 2015bEdwards et al, 2014;Uetake et al, 2016).…”