Nutrient distribution and nitrogen and oxygen isotopic compositionof nitrate in water masses of the subtropical southern Indian Ocean
The Indian Ocean subtropical gyre (IOSG) is one of five extensive subtropical gyres in the world\'s ocean. In contrast to those of the Atlantic and Pacific oceans, the IOSG has been sparsely studied. We investigate the water mass distributions based on temperature, salinity and oxygen data, and...
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fthzgzmk:oai:publications.hereon.de:38377 2023-06-11T04:17:00+02:00 Nutrient distribution and nitrogen and oxygen isotopic compositionof nitrate in water masses of the subtropical southern Indian Ocean Harms, N. Lahajnar, N. Gaye, B. Rixen, T. Dähnke, K. Ankele, M. Schwarz-Schampera, U. Emeis, K. 2019 https://publications.hereon.de/id/38377 https://publications.hzg.de/id/38377 https://doi.org/10.5194/bg-16-2715-2019 en eng EGU - Copernicus Publication https://dx.doi.org/10.5194/bg-16-2715-2019 urn:issn:1726-4170 https://publications.hereon.de/id/38377 https://publications.hzg.de/id/38377 https://doi.org/10.5194/bg-16-2715-2019 info:eu-repo/semantics/openAccess open_access oa_gold issn:1726-4170 Harms, N.; Lahajnar, N.; Gaye, B.; Rixen, T.; Dähnke, K.; Ankele, M.; Schwarz-Schampera, U.; Emeis, K.: Nutrient distribution and nitrogen and oxygen isotopic compositionof nitrate in water masses of the subtropical southern Indian Ocean . In: Biogeosciences. Vol. 16 (2019) 13, 2715 - 2732. (DOI: /10.5194/bg-16-2715-2019) info:eu-repo/semantics/article Zeitschrift Artikel 2019 fthzgzmk https://doi.org/10.5194/bg-16-2715-2019 2023-05-28T23:24:56Z The Indian Ocean subtropical gyre (IOSG) is one of five extensive subtropical gyres in the world\'s ocean. In contrast to those of the Atlantic and Pacific oceans, the IOSG has been sparsely studied. We investigate the water mass distributions based on temperature, salinity and oxygen data, and the concentrations of water column nutrients and the stable isotope composition of nitrate, using water samples collected between ∼30∘ S and the Equator during two expeditions: MSM 59/2 in 2016 and SO 259 in 2017. Our results are the first from this oceanic region and provide new information on nitrogen sources and transformation processes. We identify the thick layer of nutrient-depleted surface waters of the oligotrophic IOSG with nitrate (NO−3) and phosphate (PO3−4) concentrations of < 3 and < 0.3 µmol kg−1, respectively (< 300 m; σ < 26.4 kg−1 m−3). Increased nutrient concentrations towards the Equator represent the northern limb of the gyre, which is characterized by typical strong horizontal gradients of the outcropping nutriclines. The influx of the Subantarctic Mode Water (SAMW) from the Southern Ocean injects oxygen-saturated waters with preformed nutrients, indicated by the increased N and O isotope composition of nitrate (δ15N > 7 ‰; δ18O > 4 ‰) at 400–500 m (26.6–26.7 kg−1 m−3), into the subtropical thermocline. These values reflect partial N assimilation in the Southern Ocean. Moreover, in the northern study area, a residue of nitrate affected by denitrification in the Arabian Sea is imported into intermediate and deep water masses (> 27.0 kg−1 m−3) of the gyre, indicated by an N deficit (N* ∼−1 to −4 µmol kg−1) and by elevated isotopic ratios of nitrate (δ15N > 7 ‰; δ18O > 3 ‰). Remineralization of partially assimilated organic matter, produced in the subantarctic, leads to a decoupling of N and O isotopes in nitrate and results in a relatively low Δ(15–18) value of < 3 ‰ within the SAMW. In contrast, remineralization of 15N-enriched organic matter from the Arabian Sea indicates ... Article in Journal/Newspaper Southern Ocean Hereon Publications (Helmholtz-Zentrum) Indian Pacific Southern Ocean Biogeosciences 16 13 2715 2732 |
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Open Polar |
collection |
Hereon Publications (Helmholtz-Zentrum) |
op_collection_id |
fthzgzmk |
language |
English |
description |
The Indian Ocean subtropical gyre (IOSG) is one of five extensive subtropical gyres in the world\'s ocean. In contrast to those of the Atlantic and Pacific oceans, the IOSG has been sparsely studied. We investigate the water mass distributions based on temperature, salinity and oxygen data, and the concentrations of water column nutrients and the stable isotope composition of nitrate, using water samples collected between ∼30∘ S and the Equator during two expeditions: MSM 59/2 in 2016 and SO 259 in 2017. Our results are the first from this oceanic region and provide new information on nitrogen sources and transformation processes. We identify the thick layer of nutrient-depleted surface waters of the oligotrophic IOSG with nitrate (NO−3) and phosphate (PO3−4) concentrations of < 3 and < 0.3 µmol kg−1, respectively (< 300 m; σ < 26.4 kg−1 m−3). Increased nutrient concentrations towards the Equator represent the northern limb of the gyre, which is characterized by typical strong horizontal gradients of the outcropping nutriclines. The influx of the Subantarctic Mode Water (SAMW) from the Southern Ocean injects oxygen-saturated waters with preformed nutrients, indicated by the increased N and O isotope composition of nitrate (δ15N > 7 ‰; δ18O > 4 ‰) at 400–500 m (26.6–26.7 kg−1 m−3), into the subtropical thermocline. These values reflect partial N assimilation in the Southern Ocean. Moreover, in the northern study area, a residue of nitrate affected by denitrification in the Arabian Sea is imported into intermediate and deep water masses (> 27.0 kg−1 m−3) of the gyre, indicated by an N deficit (N* ∼−1 to −4 µmol kg−1) and by elevated isotopic ratios of nitrate (δ15N > 7 ‰; δ18O > 3 ‰). Remineralization of partially assimilated organic matter, produced in the subantarctic, leads to a decoupling of N and O isotopes in nitrate and results in a relatively low Δ(15–18) value of < 3 ‰ within the SAMW. In contrast, remineralization of 15N-enriched organic matter from the Arabian Sea indicates ... |
format |
Article in Journal/Newspaper |
author |
Harms, N. Lahajnar, N. Gaye, B. Rixen, T. Dähnke, K. Ankele, M. Schwarz-Schampera, U. Emeis, K. |
spellingShingle |
Harms, N. Lahajnar, N. Gaye, B. Rixen, T. Dähnke, K. Ankele, M. Schwarz-Schampera, U. Emeis, K. Nutrient distribution and nitrogen and oxygen isotopic compositionof nitrate in water masses of the subtropical southern Indian Ocean |
author_facet |
Harms, N. Lahajnar, N. Gaye, B. Rixen, T. Dähnke, K. Ankele, M. Schwarz-Schampera, U. Emeis, K. |
author_sort |
Harms, N. |
title |
Nutrient distribution and nitrogen and oxygen isotopic compositionof nitrate in water masses of the subtropical southern Indian Ocean |
title_short |
Nutrient distribution and nitrogen and oxygen isotopic compositionof nitrate in water masses of the subtropical southern Indian Ocean |
title_full |
Nutrient distribution and nitrogen and oxygen isotopic compositionof nitrate in water masses of the subtropical southern Indian Ocean |
title_fullStr |
Nutrient distribution and nitrogen and oxygen isotopic compositionof nitrate in water masses of the subtropical southern Indian Ocean |
title_full_unstemmed |
Nutrient distribution and nitrogen and oxygen isotopic compositionof nitrate in water masses of the subtropical southern Indian Ocean |
title_sort |
nutrient distribution and nitrogen and oxygen isotopic compositionof nitrate in water masses of the subtropical southern indian ocean |
publisher |
EGU - Copernicus Publication |
publishDate |
2019 |
url |
https://publications.hereon.de/id/38377 https://publications.hzg.de/id/38377 https://doi.org/10.5194/bg-16-2715-2019 |
geographic |
Indian Pacific Southern Ocean |
geographic_facet |
Indian Pacific Southern Ocean |
genre |
Southern Ocean |
genre_facet |
Southern Ocean |
op_source |
issn:1726-4170 Harms, N.; Lahajnar, N.; Gaye, B.; Rixen, T.; Dähnke, K.; Ankele, M.; Schwarz-Schampera, U.; Emeis, K.: Nutrient distribution and nitrogen and oxygen isotopic compositionof nitrate in water masses of the subtropical southern Indian Ocean . In: Biogeosciences. Vol. 16 (2019) 13, 2715 - 2732. (DOI: /10.5194/bg-16-2715-2019) |
op_relation |
https://dx.doi.org/10.5194/bg-16-2715-2019 urn:issn:1726-4170 https://publications.hereon.de/id/38377 https://publications.hzg.de/id/38377 https://doi.org/10.5194/bg-16-2715-2019 |
op_rights |
info:eu-repo/semantics/openAccess open_access oa_gold |
op_doi |
https://doi.org/10.5194/bg-16-2715-2019 |
container_title |
Biogeosciences |
container_volume |
16 |
container_issue |
13 |
container_start_page |
2715 |
op_container_end_page |
2732 |
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1768375770018742272 |