02368nas a2200229 4500008004100000245007900041210006900120260001200189520162900201653002401830653001301854653002101867653002001888653001401908653002501922100002401947700002501971700002201996700002302018700002402041856007302065 2020 eng d00aNutrient uptake in the supraglacial stream network of an Antarctic glacier0 aNutrient uptake in the supraglacial stream network of an Antarct c08/20203 a

In polar regions, where many glaciers are cold‐based (frozen to their beds), biological communities on the glacier surface can modulate and transform nutrients, controlling downstream delivery. However, it remains unclear whether supraglacial streams are nutrient sinks or sources and the rates of nutrient processing. In order to test this, we conducted tracer‐injections in three supraglacial streams (62 to 123 m long) on Canada Glacier in the Taylor Valley, of the McMurdo Dry Valleys, Antarctica. We conducted a series of additions including: nitrate (N), N + phosphate (P), N+ P + glucose (C), and N+C. In two reaches, N‐only additions resulted in N uptake. The third reach showed net N release during the N‐only addition, but high N uptake in the N+P addition, indicating P‐limitation or N+P co‐limitation. Co‐injecting C did not increase N‐uptake. Additionally, in these systems at low N concentrations the streams can be a net source of nitrogen. We confirmed these findings using laboratory‐based nutrient incubation experiments on sediment collected from stream channels on Canada Glacier and two other glaciers in the Taylor Valley. Together, these results suggest there is active biological processing of nutrients occurring in these supraglacial streams despite low sediment cover, high flow velocities and cold temperatures, modifying the input signals to proglacial streams. As glaciers world‐wide undergo rapid change, these findings further our understanding of how melt generated on glacier surfaces set the initial nutrient signature for subglacial and downstream environments.

10aMcMurdo Dry Valleys10anitrogen10anutrient tracers10anutrient uptake10asediments10asupraglacial streams1 aBergstrom, Anna, J.1 aGooseff, Michael, N.1 aSingley, Joel, G.1 aCohen, Matthew, J.1 aWelch, Kathleen, A. uhttps://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020JG00567902146nas a2200193 4500008004100000245011200041210006900153260001200222490000600234520149600240653001501736653002101751653002701772653002501799653001901824100001901843700001701862856007301879 2018 eng d00aDissolved Trace and Minor Elements in Cryoconite Holes and Supraglacial Streams, Canada Glacier, Antarctica0 aDissolved Trace and Minor Elements in Cryoconite Holes and Supra c04/20180 v63 a

 

We present a synthesis of the trace element chemistry in melt on the surface Canada Glacier, Taylor Valley, McMurdo Dry Valleys (MDV), Antarctica (∼78◦S). The MDV is largely ice-free. Low accumulation rates, strong winds, and proximity to the valley floor make these glaciers dusty in comparison to their inland counterparts. This study examines both supraglacial melt streams and cryoconite holes. Supraglacial streams on the lower Canada Glacier have median dissolved (<0.4 μm) concentrations of Fe, Mn, As, Cu, and V of 71.5, 75.5, 3.7, 4.6, and 4.3 nM. All dissolved Cd concentrations and the vast majority of Pb values are below our analytical detection (i.e., 0.4 and 0.06 nM). Chemical behavior did not follow similar trends for eastern and western draining waters. Heterogeneity likely reflects distinctions eolian deposition, rock:water ratios, and hydrologic connectivity. Future increases in wind-delivered sediment will likely drive dynamic responses in melt chemistry. For elements above detection limits, dissolved concentrations in glacier surface melt are within an order of magnitude of concentrations observed in proglacial streams (i.e., flowing on the valley floor). The Fe enrichment of cryoconite water relative to N, P, or Si exceeds enrichment observed in marine phytoplankton. This suggests that the glacier surface is an important source of Fe to downstream ecosystems.

 

10aAntarctica10acryoconite holes10aglacier melt chemistry10asupraglacial streams10atrace elements1 aFortner, Sarah1 aLyons, Berry uhttp://journal.frontiersin.org/article/10.3389/feart.2018.00031/full