Microbial processes in the weathering crust aquifer of a temperate glacier

Brent C. Christner, Heather F. Lavender, Christina L. Davis, Erin E. Oliver, Sarah U. Neuhaus, Krista F. Myers, Birgit Hagedorn, Slawek M. Tulaczyk, Peter T. Doran, William C. Stone
2018 The Cryosphere Discussions  
<p><strong>Abstract.</strong> 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
more » ... f shortwave radiation promoted internal melting and the formation of a weathering crust with a maximum depth of ~<span class="thinspace"></span>2<span class="thinspace"></span>m. Boreholes into the weathering crust provided access to water percolating through the porous ice. The water had low ion concentrations (4&amp;ndash;12<span class="thinspace"></span>µS<span class="thinspace"></span>cm<sup>&amp;minus;1</sup>), was aerobic (12<span class="thinspace"></span>mg<span class="thinspace"></span>O<sub>2</sub><span class="thinspace"></span>L<sup>&amp;minus;1</sup>), contained 200 to 8,300<span class="thinspace"></span>cells<span class="thinspace"></span>mL<sup>&amp;minus;1</sup>, and harbored growing populations with estimated in situ generation times of 11 to 14 days. During the melt season, the upper 2<span class="thinspace"></span>m of ice experienced at least 3<span class="thinspace"></span>% of the surface photosynthetically active radiation flux and possessed a fractional water content as high as 10<span class="thinspace"></span>%. 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 ~<span class="thinspace"></span>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.</p>
doi:10.5194/tc-2018-138 fatcat:5ovucuy3tvdx7epfidmoqwwqaa