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Discussion papers | Copyright
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 08 Aug 2018

Research article | 08 Aug 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal The Cryosphere (TC).

Microbial processes in the weathering crust aquifer of a temperate glacier

Brent C. Christner1,2, Heather F. Lavender2, Christina L. Davis1, Erin E. Oliver2,a, Sarah U. Neuhaus3, Krista F. Myers4, Birgit Hagedorn5, Slawek M. Tulaczyk3, Peter T. Doran4, and William C. Stone6 Brent C. Christner et al.
  • 1University of Florida, Department of Microbiology and Cell Science, Biodiversity Institute, Gainesville, FL 32611 USA
  • 2Louisiana State University, Department of Biological Sciences, Baton Rouge, LA 70803 USA
  • 3University of California Santa Cruz, Department of Earth and Planetary Sciences, Santa Cruz, CA 95064 USA
  • 4Louisiana State University, Department of Geology and Geophysics, Baton Rouge, LA 70803 USA
  • 5Sustainable Earth Research LLC, Anchorage, AK 99508 USA
  • 6Stone Aerospace, Del Valle, TX 78617 USA
  • acurrent address: San Diego State University, Department of Biology, San Diego, CA 92182 USA

Abstract. Incident solar radiation absorbed within the ablation zone of glaciers generates a shallow perched aquifer and seasonal ice-bound microbial habitat. During the melt seasons of 2014 and 2015, borehole investigations were used to examine the physical, geochemical, and microbiological properties in the near-surface ice and aquifer of the temperate Matanuska Glacier (southcentral Alaska). Based on temperature, solar forcing, and ice optical properties, the dissipation of shortwave radiation promoted internal melting and the formation of a weathering crust with a maximum depth of ~2m. Boreholes into the weathering crust provided access to water percolating through the porous ice. The water had low ion concentrations (4–12µScm−1), was aerobic (12mgO2L−1), contained 200 to 8,300cellsmL−1, and harbored growing populations with estimated in situ generation times of 11 to 14 days. During the melt season, the upper 2m of ice experienced at least 3% of the surface photosynthetically active radiation flux and possessed a fractional water content as high as 10%. Photosynthetic subsistence of biogeochemical reactions in the weathering crust ecosystem was supported by ex situ metabolic experiments and the presence of phototrophic taxa (cyanobacteria, golden and green algae) in the aquifer samples. Melt water durations of ~7.5 months coupled with the growth estimates imply biomass may increase by four orders-of-magnitude each year. Our results provide insight on how seasonal dynamics affect habitability of near-surface ice and microbial processes in a portion of the glacial biome poised to expand in extent with increasing global temperature and ablation season duration.

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Short summary
Solar radiation that penetrates into the glacier heats the ice to produce nutrient-containing meltwater and provides light that fuels an ecosystem within the ice. Our analysis documents a near-surface photic zone in a glacier that functions as a liquid water oasis in the ice over half the annual cycle. Since microbial growth on glacier surfaces reduces the amount of solar radiation reflected, microbial processes at depths below the surface may also darken ice and accelerate meltwater production.
Solar radiation that penetrates into the glacier heats the ice to produce nutrient-containing...