the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Biogeochemical evolution of ponded meltwater in a High Arctic subglacial tunnel
Ashley J. Dubnick
Rachel L. Spietz
Brad D. Danielson
Mark L. Skidmore
Eric S. Boyd
Dave B. Burgess
Charvanaa Dhoonmoon
Martin Sharp
Abstract. Subglacial environments comprise ~10 % of Earth’s land surface, host active microbial ecosystems, and are important components of global biogeochemical cycles. However, the broadly inaccessible nature of subglacial systems has left them vastly understudied, and research to date has been limited to laboratory experiments or field measurements using basal ice or subglacial water accessed through boreholes or from the glacier margin. In this study, we extend our understanding of subglacial biogeochemistry and microbiology to include observations of a slushy pond of water that occupied a remnant meltwater channel beneath a polythermal glacier in the Canadian High Arctic over winter. The hydraulics and geochemistry of the system suggest that the pond water originated as late-season, ice-marginal runoff with less than ~15 % solute contribution from subglacial sources. Over the eight months of persistent sub-zero regional temperatures, the pond gradually froze, cryo-concentrating solutes in the residual water by up to seven times. Despite cryo-concentration and the likely influx of some subglacial solute, the pond was depleted in only the most labile and biogeochemically-relevant compounds, including ammonium, phosphate, and dissolved organic matter, including a potentially labile tyrosine-like component. DNA amplicon sequencing revealed decreasing microbial diversity with distance into the meltwater channel. The pond at the terminus of the channel hosted a microbial community inherited from late-season meltwater, which was dominated by only six taxa related to known psychrophilic/psychrotolerant heterotrophs that have high metabolic diversity and broad habitat ranges. Collectively, our findings suggest that generalist microbes from the extraglacial or supraglacial environments can become established in subglacial aquatic systems and deplete reservoirs of nutrients and dissolved organic carbon over a period of months. These findings extend our understanding of the microbial and biogeochemical evolution of subglacial aquatic ecosystems and the extent of their habitability.
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Ashley J. Dubnick et al.
Status: open (until 18 Apr 2023)
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RC1: 'Comment on tc-2022-240', Zac Cooper, 22 Mar 2023
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This manuscript is exceptionally well-written. The methods are employed appropriately and the findings are clear and concisely presented. This manuscript benefits from the obvious care taken to employ interdisciplinary methods to explain a complex setting which helps increase the accessibility of this study to scientists across disciplines interested in the cryosphere. In this study, the details of the geochemical, physical, and microbiological aspects of a subglacial meltpond are interpreted with care to explore the biogeochemical of alteration of the chemical composition of waters resulting from glacial melt. These data highlight the importance of understanding the biological influence on this geological system while also demonstrating the habitability of this rarely studied ecosystem. Given the rapid change in polar and alpine regions, this work is an excellent contribution to the field and our understanding of the past, present, and future of the cryosphere. I found no errors in the text and happily recommend accepting this manuscript for publication as is.
Citation: https://doi.org/10.5194/tc-2022-240-RC1 -
RC2: 'Comment on tc-2022-240', Anonymous Referee #2, 23 Mar 2023
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It was a joy to read the manuscript by Dubnick and colleagues. The paper describes in detail the geochemical transformation (evolution) of late-season glacial meltwater as it undergoes freezing subglacially over winter. To my knowledge this is the first study of the type that can provide empirical data on these processes in a very interesting field site that can act as a natural laboratory. Despite the particular nature of the study site, the results presented here are of broader relevance and can inform on a wider array of subglacial systems. They exemplify what microbial and biogeochemical processes can occur subglacially in the context of subglacial environments as being active microbial habitats. They do so in a quantitative way by combining geochemical models, geochemical and microbial observations and go beyond simple data reporting often the case in similar studies. The manuscript is extremely well written, with great context and explanation for both expert and non-expert readers, well within the relevant scopes of the Cryosphere journal.
However, before recommending the article for publication, there are some minor comments that I believe would need addressing or clarifying:
Ashley J. Dubnick et al.
Ashley J. Dubnick et al.
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