21 Feb 2023
 | 21 Feb 2023
Status: a revised version of this preprint is currently under review for the journal TC.

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, and 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.

Ashley J. Dubnick et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2022-240', Zac Cooper, 22 Mar 2023
    • AC1: 'Reply on RC1', Ashley Dubnick, 17 May 2023
  • RC2: 'Comment on tc-2022-240', Anonymous Referee #2, 23 Mar 2023
    • AC2: 'Reply on RC2', Ashley Dubnick, 17 May 2023

Ashley J. Dubnick et al.

Ashley J. Dubnick et al.


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Short summary
At the end of an Arctic winter, we found ponded water 500 m under a glacier. We explored the chemistry and microbiology of this unique, dark, cold aquatic habitat to better understand ecology beneath glaciers. The water was occupied by cold-loving/tolerant microbes, with versatile metabolisms and broad habitat ranges, and was depleted in compounds commonly used by microbes. These results show that microbes can become established beneath glaciers and deplete nutrients within months.