Nitrogen cycling in the Southern Ocean Kerguelen Plateau area: evidence for significant surface nitrification from nitrate isotopic compositions
This paper presents whole water column data for nitrate N, O isotopic composition for the Kerguelen Plateau area and the basin extending east of Heard Island, aiming at understanding the N-cycling in this naturally iron fertilized area that is characterized by large re-current phytoplankton blooms....
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ftdoajarticles:oai:doaj.org/article:91e07c796f424137b737dd9039a085de 2023-05-15T16:33:56+02:00 Nitrogen cycling in the Southern Ocean Kerguelen Plateau area: evidence for significant surface nitrification from nitrate isotopic compositions F. Dehairs F. Fripiat A.-J. Cavagna T. W. Trull C. Fernandez D. Davies A. Roukaerts D. Fonseca Batista F. Planchon M. Elskens 2015-03-01T00:00:00Z https://doi.org/10.5194/bg-12-1459-2015 https://doaj.org/article/91e07c796f424137b737dd9039a085de EN eng Copernicus Publications http://www.biogeosciences.net/12/1459/2015/bg-12-1459-2015.pdf https://doaj.org/toc/1726-4170 https://doaj.org/toc/1726-4189 1726-4170 1726-4189 doi:10.5194/bg-12-1459-2015 https://doaj.org/article/91e07c796f424137b737dd9039a085de Biogeosciences, Vol 12, Iss 5, Pp 1459-1482 (2015) Ecology QH540-549.5 Life QH501-531 Geology QE1-996.5 article 2015 ftdoajarticles https://doi.org/10.5194/bg-12-1459-2015 2022-12-31T15:49:03Z This paper presents whole water column data for nitrate N, O isotopic composition for the Kerguelen Plateau area and the basin extending east of Heard Island, aiming at understanding the N-cycling in this naturally iron fertilized area that is characterized by large re-current phytoplankton blooms. The KEOPS 2 expedition (October–November 2011) took place in spring season and complements knowledge gathered during an earlier summer expedition to the same area (KEOPS 1, February–March 2005). As noted by others a remarkable condition of the system is the moderate consumption of nitrate over the season (nitrate remains >20 μM) while silicic acid becomes depleted, suggesting significant recycling of nitrogen. Nitrate isotopic signatures in the upper water column do mimic this condition, with surprising overlap of spring and summer regressions of δ 18 O NO 3 vs. δ 15 N NO 3 isotopic compositions. These regressions obey rather closely the 18 ε/ 15 ε discrimination expected for nitrate uptake ( 18 ε/ 15 ε = 1), but regression slopes as large as 1.6 were observed for the mixed layer above the Kerguelen Plateau. A preliminarily mass balance calculation for the early bloom period points toward significant nitrification occurring in the mixed layer and which may be equivalent to up to 47% of nitrate uptake above the Kerguelen Plateau. A further finding concerns deep ocean low δ 18 O NO 3 values (<2‰) underlying high chlorophyll waters at the Polar Front Zone and which cannot be explained by remineralization and nitrification of the local particulate nitrogen flux, which is too small in magnitude. However, the studied area is characterized by a complex recirculation pattern that would keep deep waters in the area and could impose a seasonally integrated signature of surface water processes on the deep waters. Article in Journal/Newspaper Heard Island Southern Ocean Directory of Open Access Journals: DOAJ Articles Southern Ocean Kerguelen Heard Island Biogeosciences 12 5 1459 1482 |
institution |
Open Polar |
collection |
Directory of Open Access Journals: DOAJ Articles |
op_collection_id |
ftdoajarticles |
language |
English |
topic |
Ecology QH540-549.5 Life QH501-531 Geology QE1-996.5 |
spellingShingle |
Ecology QH540-549.5 Life QH501-531 Geology QE1-996.5 F. Dehairs F. Fripiat A.-J. Cavagna T. W. Trull C. Fernandez D. Davies A. Roukaerts D. Fonseca Batista F. Planchon M. Elskens Nitrogen cycling in the Southern Ocean Kerguelen Plateau area: evidence for significant surface nitrification from nitrate isotopic compositions |
topic_facet |
Ecology QH540-549.5 Life QH501-531 Geology QE1-996.5 |
description |
This paper presents whole water column data for nitrate N, O isotopic composition for the Kerguelen Plateau area and the basin extending east of Heard Island, aiming at understanding the N-cycling in this naturally iron fertilized area that is characterized by large re-current phytoplankton blooms. The KEOPS 2 expedition (October–November 2011) took place in spring season and complements knowledge gathered during an earlier summer expedition to the same area (KEOPS 1, February–March 2005). As noted by others a remarkable condition of the system is the moderate consumption of nitrate over the season (nitrate remains >20 μM) while silicic acid becomes depleted, suggesting significant recycling of nitrogen. Nitrate isotopic signatures in the upper water column do mimic this condition, with surprising overlap of spring and summer regressions of δ 18 O NO 3 vs. δ 15 N NO 3 isotopic compositions. These regressions obey rather closely the 18 ε/ 15 ε discrimination expected for nitrate uptake ( 18 ε/ 15 ε = 1), but regression slopes as large as 1.6 were observed for the mixed layer above the Kerguelen Plateau. A preliminarily mass balance calculation for the early bloom period points toward significant nitrification occurring in the mixed layer and which may be equivalent to up to 47% of nitrate uptake above the Kerguelen Plateau. A further finding concerns deep ocean low δ 18 O NO 3 values (<2‰) underlying high chlorophyll waters at the Polar Front Zone and which cannot be explained by remineralization and nitrification of the local particulate nitrogen flux, which is too small in magnitude. However, the studied area is characterized by a complex recirculation pattern that would keep deep waters in the area and could impose a seasonally integrated signature of surface water processes on the deep waters. |
format |
Article in Journal/Newspaper |
author |
F. Dehairs F. Fripiat A.-J. Cavagna T. W. Trull C. Fernandez D. Davies A. Roukaerts D. Fonseca Batista F. Planchon M. Elskens |
author_facet |
F. Dehairs F. Fripiat A.-J. Cavagna T. W. Trull C. Fernandez D. Davies A. Roukaerts D. Fonseca Batista F. Planchon M. Elskens |
author_sort |
F. Dehairs |
title |
Nitrogen cycling in the Southern Ocean Kerguelen Plateau area: evidence for significant surface nitrification from nitrate isotopic compositions |
title_short |
Nitrogen cycling in the Southern Ocean Kerguelen Plateau area: evidence for significant surface nitrification from nitrate isotopic compositions |
title_full |
Nitrogen cycling in the Southern Ocean Kerguelen Plateau area: evidence for significant surface nitrification from nitrate isotopic compositions |
title_fullStr |
Nitrogen cycling in the Southern Ocean Kerguelen Plateau area: evidence for significant surface nitrification from nitrate isotopic compositions |
title_full_unstemmed |
Nitrogen cycling in the Southern Ocean Kerguelen Plateau area: evidence for significant surface nitrification from nitrate isotopic compositions |
title_sort |
nitrogen cycling in the southern ocean kerguelen plateau area: evidence for significant surface nitrification from nitrate isotopic compositions |
publisher |
Copernicus Publications |
publishDate |
2015 |
url |
https://doi.org/10.5194/bg-12-1459-2015 https://doaj.org/article/91e07c796f424137b737dd9039a085de |
geographic |
Southern Ocean Kerguelen Heard Island |
geographic_facet |
Southern Ocean Kerguelen Heard Island |
genre |
Heard Island Southern Ocean |
genre_facet |
Heard Island Southern Ocean |
op_source |
Biogeosciences, Vol 12, Iss 5, Pp 1459-1482 (2015) |
op_relation |
http://www.biogeosciences.net/12/1459/2015/bg-12-1459-2015.pdf https://doaj.org/toc/1726-4170 https://doaj.org/toc/1726-4189 1726-4170 1726-4189 doi:10.5194/bg-12-1459-2015 https://doaj.org/article/91e07c796f424137b737dd9039a085de |
op_doi |
https://doi.org/10.5194/bg-12-1459-2015 |
container_title |
Biogeosciences |
container_volume |
12 |
container_issue |
5 |
container_start_page |
1459 |
op_container_end_page |
1482 |
_version_ |
1766023685176557568 |