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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-317
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-317
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 09 Sep 2019

Submitted as: research article | 09 Sep 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Basal thermal regime affects the biogeochemistry of subglacial systems

Ashley Dubnick1, Martin Sharp1, Brad Danielson1,2, Alireza Saidi-Mehrabad3, and Joel Barker4 Ashley Dubnick et al.
  • 1Department of Earth and Atmospheric Science, University of Alberta, Edmonton AB, T6G 2E3, Canada
  • 2Fiera Biological Consulting, Suite 301, 10359-82 Ave, Edmonton AB, T6E 1Z9
  • 3Department of Biological Sciences, University of Alberta, Edmonton AB, T6G 2E3, Canada
  • 4School of Earth Sciences, The Ohio State University, Marion 43302, USA

Abstract. Ice formed in the subglacial environment can contain some of the highest concentrations of solutes, nutrients, and microbes found in glacier systems. Upon glacial melt, these materials are released to downstream freshwater and marine ecosystems and glacier forefields. Despite the potential ecological importance of basal ice, our understanding of its biogeochemical characteristics, and their spatial and temporal variability, remains limited. We hypothesize that the basal thermal regime of glaciers is a dominant control on subglacial biogeochemistry because it influences the degree to which glaciers mobilize material from the underlying substrate and controls the nature and extent of biogeochemical activity that occurs at glacier beds. Here, we characterize the solutes, nutrients, and microbes found in the basal regions of a cold-based glacier and three polythermal glaciers and compare them to those found in overlying glacier ice. Compared to its parent glacier ice, basal ice from polythermal glaciers was consistently enriched in major ions, dissolved organic matter (including a specific fraction of humic-like fluorescent material), and microbes, and occasionally enriched in dissolved phosphorus and reduced nitrogen (NH4+) and in a second dissolved component of humic-like fluorescent material. In contrast, the biogeochemistry of basal ice from the cold-based glacier was remarkably similar to that of its parent glacier ice. Although basal ice from the cold-based glacier may have acquired some inorganic and organic nutrients from the underlying substrate, it did not appear to contain significant amounts of either solutes or microbes derived from the glacier bed. These findings suggest that a glacier's basal thermal regime can play an important role in determining the mix of solutes, nutrients, and microbes that are acquired from subglacial substrates and/or produced in situ.

Ashley Dubnick et al.
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Ashley Dubnick et al.
Ashley Dubnick et al.
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Short summary
We found that glaciers with basal temperatures near the melting point mobilize more solutes, nutrients and microbes from the underlying substrate and are more likely to promote in situ biogeochemical activity than glaciers with basal temperatures well below the melting point. The temperature at the base of glaciers is therefore an important control on the biogeochemistry of ice near glacier beds, and ultimately, the potential solutes, nutrients and microbes exported from glaciated watersheds.
We found that glaciers with basal temperatures near the melting point mobilize more solutes,...
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