Preprints
https://doi.org/10.5194/tc-2020-326
https://doi.org/10.5194/tc-2020-326

  05 Nov 2020

05 Nov 2020

Review status: a revised version of this preprint is currently under review for the journal TC.

Subglacial upwelling in winter/spring increases under-ice primary production

Tobias Reiner Vonnahme1, Emma Persson1, Ulrike Dietrich1, Eva Hejdukova2, Christine Dybwad1, Josef Elster3, Melissa Chierici4,5, and Rolf Gradinger1 Tobias Reiner Vonnahme et al.
  • 1Department of Arctic and Marine Biology, UiT – The Arctic University of Norway, Tromsø, Norway
  • 2Department of Ecology, Faculty of Science, Charles University, Prague, Czech Republic
  • 3University of South Bohemia, České Budějovice, and Institute of Botany ASCR, Třeboň, Czech Republic
  • 4Institute of Marine Research, Tromsø, Norway
  • 5University Centre in Svalbard (UNIS), Longyearbyen, Svalbard, Norway

Abstract. Subglacial upwelling of nutrient rich bottom water is known to support high summer primary production in Arctic fjord systems. However, during the winter/spring season, the importance of subglacial upwelling has not been considered yet. We hypothesized that subglacial upwelling under sea ice is present in winter/spring and sufficient to increase phytoplankton primary productivity. We evaluated the effects of the subglacial upwelling on primary production in a seasonally fast ice covered Svalbard fjord (Billefjorden) influenced by a tidewater outlet glacier in April/May 2019. We found clear evidence for subglacial upwelling. Although the estimated entrainment factor (1.6) and total fluxes were lower than in summer studies, we observed substantial impact on the fjord ecosystem and primary production. The subglacial meltwater leads to a salinity stratified surface layer and sea ice formation with low bulk salinity and permeability. The combination of the stratified surface layer, a two-fold higher under-ice irradiance, and higher N and Si concentrations at the glacier front supported two orders of magnitude higher primary production (42.6 mg C m−2 d−1) compared to a marine reference site at the fast ice edge. The nutrient supply increased primary production by approximately 30 %. The brackish water sea ice at the glacier front with its low bulk salinity contained a reduced brine volume, limiting the inhabitable place and nutrient exchange with the underlying seawater compared to full marine sea ice. Microbial and algal communities were substantially different in subglacial influenced water and sea ice compared to the marine reference site, sharing taxa with the subglacial outflow water. We suggest that with climate change, the retreat of tidewater glaciers could lead to decreased under-ice phytoplankton primary production, while sea ice algae production and biomass may become increasingly important.

Tobias Reiner Vonnahme et al.

 
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Tobias Reiner Vonnahme et al.

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Replication data for: Subglacial upwelling in spring increases under-ice primary production Vonnahme, Tobias Reiner, Persson, Emma, Dietrich, Ulrike, Hejdukova, Eva, Dybwad, Christine, Chierci, Melissa, and Dubourg, Paul https://doi.org/10.18710/MTPR9E

Tobias Reiner Vonnahme et al.

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Short summary
We describe the impact of subglacial upwelling in winter/spring on a sea-ice covered fjord in Svalbard by comparing a glacier influenced and two reference sites. We suggest subglacial upwelling as the main source of fresh nutrients and freshwater to the surface, leading to increased phytoplankton primary production (two orders of magnitude), a strongly stratified surface layer, brackish sea ice with limited permeability and low sea ice algae biomass, and different microbial communities.