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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2020-293
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-293
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  09 Sep 2020

09 Sep 2020

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A revised version of this preprint is currently under review for the journal BG.

Nitrate assimilation and regeneration in the Barents Sea: insights from nitrogen isotopes

Robyn E. Tuerena1, Joanne Hopkins2, Raja S. Ganeshram1, Louisa Norman3, Camille de la Vega3, Rachel Jeffreys3, and Claire Mahaffey3 Robyn E. Tuerena et al.
  • 1School of GeoSciences, University of Edinburgh, James Hutton Rd, Edinburgh, EH9 3FE, UK
  • 2National Oceanography Centre, 6 Brownlow Street, Liverpool, L3 5DA, UK
  • 3School of Environmental Sciences, University of Liverpool, 4 Brownlow St, Liverpool, L69 3GP, UK

Abstract. While the entire Arctic Ocean is warming rapidly, the Barents Sea in particular is experiencing significant warming and sea ice retreat. An increase in ocean heat transport from the Atlantic is causing the Barents Sea to be transformed from a cold, salinity stratified system into a warmer, less-stratified Atlantic-dominated climate regime. Productivity in the Barents Sea shelf is fuelled by waters of Atlantic origin (AW), which are ultimately exported to the Arctic basin. The consequences of this current regime shift on the nutrient characteristics of the Barents Sea are poorly defined. Here we use the stable isotopic ratios of nitrate (δ15N-NO3, δ18O-NO3), to determine the uptake and modification of AW nutrients in the Barents Sea. In summer months, phytoplankton consume nitrate, surface waters become nitrate depleted, and particulate nitrogen (δ15N-PN) reflects the AW nitrate source. The ammonification of organic matter in shallow sediments resupplies N to the water column through the season. Low δ18O-NO3 in the northern Barents Sea reveals that the nitrate in lower temperature Arctic Waters is > 80 % regenerated through seasonal nitrification. During on shelf nutrient uptake and regeneration, there is no significant change to δ15N-NO3 or N*, suggesting benthic denitrification does not impart an isotopic imprint on pelagic nitrate. Our results demonstrate that the Barents Sea is distinct from other Arctic shelves, where coupled partial nitrification-denitrification enriches δ15N-NO3 and decreases N*. Our results suggest that any current or future changes to productivity on the Barents Sea shelf are unlikely to alter the magnitude or isotopic signature of nutrient supply exported to the central Arctic basin. However, we suggest that the AW nutrient source ultimately determines Barents Sea productivity and changes to this supply may alter Barents Sea primary production and subsequent nutrient supply to the central Arctic Ocean.

Robyn E. Tuerena et al.

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Robyn E. Tuerena et al.

Robyn E. Tuerena et al.

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Short summary
The Barents Sea is a rapidly changing, shallow sea within the Arctic. Here, we found that over the growing season, nitrate, an essential nutrient, is fully consumed and likely to be the main limiting nutrient to algae. We found no evidence for nitrogen loss in the Barents Sea sediments, which may be because this region is dominated by energetic ocean currents. We suggest that future nutrient availability in the Barents Sea will depend on the source waters supplied from the Atlantic.
The Barents Sea is a rapidly changing, shallow sea within the Arctic. Here, we found that over...
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