Abstract
AbstractWe describe seasonal changes in the biogeochemistry, microbial community and ecosystem production of two glacial snowpacks in the maritime Antarctic during a cold summer. Frequent snowfall and low, intermittent melt on the glaciers suppressed surface photosynthesis and promoted net heterotrophy. Concentrations of autotrophic cells (algae and cyanobacteria) were therefore low (average: 150–500 cells mL−1), and short‐term estimates of primary production were almost negligible in early summer (<0.1 μg C L−1 d−1). However, order of magnitude increases in Chlorophyllaconcentrations occurred later, especially within the mid‐snowpack and ice layers below. Short‐term primary production increased to ca. 1 μg C L−1 d−1in mid‐summer, and reached 53.1 μg C L−1 d−1in a mid‐snow layer close to an active penguin colony. However, there were significantly more bacteria than autotrophs in the snow (typically 103cells mL−1, but >104cells mL−1in basal ice near the penguin colony). The ratio of bacteria to autotrophs also increased throughout the summer, and short‐term bacterial production rates (0.2–2000 μg C L−1 d−1) usually exceeded primary production, especially in basal ice (10–1400 μg C L−1 d−1). The basal ice represented the least diverse but most productive habitat, and a striking feature was its low pH (down to 3.3). Furthermore, all of the overlying snow cover became increasingly acidic as the summer season progressed, which is attributed to enhanced emissions from wet guano in the penguin colony. The study demonstrates that active microbial communities can be expected, even when snowmelt is intermittent in the Antarctic summer.
Highlights
IntroductionSnow and Glacier Surface Ecosystems of the Antarctic
The key attributes of our results that describe this ecosystem include: (a) marked changes in the biogeochemical conditions within the snow, revealing nitrogen enrichment from external sources and a strong acidification effect, (b) significant gains in autotrophic cells, resulting in an order of magnitude increase in Chlorophyll a loading; and (c) distinct shifts in bacterial community composition and an order of magnitude increase in bacterial cell abundance that out-paced autotrophic cell proliferation. We argue that these attributes are likely to have been heavily influenced by the cool, wet summer conditions, whose frequent snowfalls and high winds most likely suppressed photosynthesis and forced the bacterial community to respond to acidifying processes that
Microbial diversity and activity were distinct between the different vertical “zones” within the snowpack, which included a surface 20 cm layer subject to repeated erosion/deposition by strong winds and fresh snowfall, a more stable mid-snowpack layer beneath it and an underlying basal ice layer of refrozen snowmelt superimposed upon the glacier surface
Summary
Snow and Glacier Surface Ecosystems of the Antarctic. Snow and glacier ice represent the most expansive terrestrial habitat in Antarctica, yet biological and biogeochemical functioning upon their surface remain virtually unexplored. D'Andrilli et al, 2017; Martinez-Alonso et al, 2019) These habitats have a fundamental dependence upon either snow accumulation prior to its transition into englacial ice, or snow ablation/deflation, prior to the onset of significant biological activity in summer (Hodson et al, 2015). Biological activity, nutrient assimilation and carbon transfers in Antarctica's near-surface icy habitats are greatly facilitated by the presence of meltwater. Melting glacial snowpacks represent a significant, but largely unaccounted component of the terrestrial ecology of Antarctica (Gray et al, 2020). A paucity of data from this region means that we are poorly placed to consider the impact of the projected doubling of melt over the three decades (Lee et al, 2017; Trusel et al, 2015; Vaughan, 2006), which will be dominated by the ablation of glacial snow and firn
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