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Nitrogen fixation under declining Arctic sea ice.

Lisa W von Friesen1,2, Hanna Farnelid3, Wilken-Jon von Appen4

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Summary
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Arctic nitrogen fixation by diazotrophs is crucial for primary productivity as sea ice declines. This study quantifies rates and identifies key microbial players in these changing polar waters.

Keywords:
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Area of Science:

  • Marine microbiology
  • Biogeochemistry
  • Arctic Oceanography

Background:

  • Climate change is driving significant sea ice decline in the Arctic.
  • Nitrogen availability is a key limiting factor for primary productivity in marine ecosystems.
  • Nitrogen fixation, performed by diazotrophs, converts atmospheric nitrogen into bioavailable forms.

Purpose of the Study:

  • To quantify nitrogen fixation rates in the Central Arctic Ocean and Eurasian Arctic marginal ice zone.
  • To determine the composition and activity of diazotrophs under varying sea ice conditions.
  • To understand the role of nitrogen fixation in supporting primary production in a changing Arctic.

Main Methods:

  • Field sampling across different sea ice regimes (multiyear ice and marginal ice zone).
  • Measurement of nitrogen fixation rates using incubation techniques.
  • Analysis of diazotroph community composition and gene expression.

Main Results:

  • Nitrogen fixation rates varied significantly, from below detection to 5.3 ± 3.65 nmol N L-1 d-1.
  • In the Central Arctic, nitrogen fixation positively correlated with primary production.
  • Active non-cyanobacterial diazotrophs were identified in sea ice-covered Arctic waters.

Conclusions:

  • Nitrogen fixation is an active process supporting primary production in sea ice-covered Arctic waters.
  • Diazotrophs, including non-cyanobacterial taxa, play a significant role in Arctic nitrogen cycling.
  • Understanding these processes is vital for predicting future Arctic marine ecosystem responses to climate change.