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

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-stra...

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Published in:Biogeosciences
Main Authors: Tuerena, Robyn E., Hopkins, Joanne, Ganeshram, Raja S., Norman, Louisa, Vega, Camille, Jeffreys, Rachel, Mahaffey, Claire
Format: Text
Language:English
Published: 2021
Subjects:
Online Access:https://doi.org/10.5194/bg-18-637-2021
https://bg.copernicus.org/articles/18/637/2021/
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spelling ftcopernicus:oai:publications.copernicus.org:bg87502 2023-05-15T14:29:11+02:00 Nitrate assimilation and regeneration in the Barents Sea: insights from nitrate isotopes Tuerena, Robyn E. Hopkins, Joanne Ganeshram, Raja S. Norman, Louisa Vega, Camille Jeffreys, Rachel Mahaffey, Claire 2021-01-28 application/pdf https://doi.org/10.5194/bg-18-637-2021 https://bg.copernicus.org/articles/18/637/2021/ eng eng doi:10.5194/bg-18-637-2021 https://bg.copernicus.org/articles/18/637/2021/ eISSN: 1726-4189 Text 2021 ftcopernicus https://doi.org/10.5194/bg-18-637-2021 2021-02-01T17:21:47Z 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 ( δ 15 N- NO 3 , δ 18 O- NO 3 ) 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 ( δ 15 N-PN) reflects the AW nitrate source. The ammonification of organic matter in shallow sediments resupplies N to the water column and replenishes the nitrate inventory for the following season. Low δ 18 O- NO 3 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 δ 15 N- NO 3 or N * , suggesting that 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 benthic denitrification enriches δ 15 N- NO 3 and decreases N * . As nutrients are efficiently recycled in the Barents Sea and there is no significant loss of N through benthic denitrification, changes to Barents Sea productivity are unlikely to alter N availability on shelf or the magnitude of N advected to the central Arctic Basin. However, we suggest that the AW nutrient source ultimately determines Barents Sea productivity and that changes to AW delivery have the potential to alter Barents Sea primary production and subsequent nutrient supply to the central Arctic Ocean. Text Arctic Basin Arctic Arctic Ocean Barents Sea Phytoplankton Sea ice Copernicus Publications: E-Journals Arctic Arctic Ocean Barents Sea Biogeosciences 18 2 637 653
institution Open Polar
collection Copernicus Publications: E-Journals
op_collection_id ftcopernicus
language English
description 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 ( δ 15 N- NO 3 , δ 18 O- NO 3 ) 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 ( δ 15 N-PN) reflects the AW nitrate source. The ammonification of organic matter in shallow sediments resupplies N to the water column and replenishes the nitrate inventory for the following season. Low δ 18 O- NO 3 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 δ 15 N- NO 3 or N * , suggesting that 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 benthic denitrification enriches δ 15 N- NO 3 and decreases N * . As nutrients are efficiently recycled in the Barents Sea and there is no significant loss of N through benthic denitrification, changes to Barents Sea productivity are unlikely to alter N availability on shelf or the magnitude of N advected to the central Arctic Basin. However, we suggest that the AW nutrient source ultimately determines Barents Sea productivity and that changes to AW delivery have the potential to alter Barents Sea primary production and subsequent nutrient supply to the central Arctic Ocean.
format Text
author Tuerena, Robyn E.
Hopkins, Joanne
Ganeshram, Raja S.
Norman, Louisa
Vega, Camille
Jeffreys, Rachel
Mahaffey, Claire
spellingShingle Tuerena, Robyn E.
Hopkins, Joanne
Ganeshram, Raja S.
Norman, Louisa
Vega, Camille
Jeffreys, Rachel
Mahaffey, Claire
Nitrate assimilation and regeneration in the Barents Sea: insights from nitrate isotopes
author_facet Tuerena, Robyn E.
Hopkins, Joanne
Ganeshram, Raja S.
Norman, Louisa
Vega, Camille
Jeffreys, Rachel
Mahaffey, Claire
author_sort Tuerena, Robyn E.
title Nitrate assimilation and regeneration in the Barents Sea: insights from nitrate isotopes
title_short Nitrate assimilation and regeneration in the Barents Sea: insights from nitrate isotopes
title_full Nitrate assimilation and regeneration in the Barents Sea: insights from nitrate isotopes
title_fullStr Nitrate assimilation and regeneration in the Barents Sea: insights from nitrate isotopes
title_full_unstemmed Nitrate assimilation and regeneration in the Barents Sea: insights from nitrate isotopes
title_sort nitrate assimilation and regeneration in the barents sea: insights from nitrate isotopes
publishDate 2021
url https://doi.org/10.5194/bg-18-637-2021
https://bg.copernicus.org/articles/18/637/2021/
geographic Arctic
Arctic Ocean
Barents Sea
geographic_facet Arctic
Arctic Ocean
Barents Sea
genre Arctic Basin
Arctic
Arctic Ocean
Barents Sea
Phytoplankton
Sea ice
genre_facet Arctic Basin
Arctic
Arctic Ocean
Barents Sea
Phytoplankton
Sea ice
op_source eISSN: 1726-4189
op_relation doi:10.5194/bg-18-637-2021
https://bg.copernicus.org/articles/18/637/2021/
op_doi https://doi.org/10.5194/bg-18-637-2021
container_title Biogeosciences
container_volume 18
container_issue 2
container_start_page 637
op_container_end_page 653
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