Relationship of nitrogen isotope fractionation to phytoplankton size and iron availability during the Southern Ocean Iron Release Experiment (SOIREE)
The 15N composition of sediments has been used as a proxy for nitrate utilization in surface waters to assess the role of Southern Ocean export production in glacial/interglacial changes in atmospheric CO2 concentration. Interpretation has relied on a temporally constant isotope effect () associated...
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ftunivtasecite:oai:ecite.utas.edu.au:29155 2023-05-15T18:24:43+02:00 Relationship of nitrogen isotope fractionation to phytoplankton size and iron availability during the Southern Ocean Iron Release Experiment (SOIREE) Karsh, K Trull, T Lourey, MJ Sigman, DM 2003 https://doi.org/10.4319/lo.2003.48.3.1058 http://ecite.utas.edu.au/29155 en eng American Society of Limnology and Oceanography http://dx.doi.org/10.4319/lo.2003.48.3.1058 Karsh, K and Trull, T and Lourey, MJ and Sigman, DM, Relationship of nitrogen isotope fractionation to phytoplankton size and iron availability during the Southern Ocean Iron Release Experiment (SOIREE), Limnology and Oceanography, 48, (3) pp. 1058-1068. ISSN 0024-3590 (2003) [Refereed Article] http://ecite.utas.edu.au/29155 Physical Sciences Optical Physics Lasers and Quantum Electronics Refereed Article PeerReviewed 2003 ftunivtasecite https://doi.org/10.4319/lo.2003.48.3.1058 2019-12-13T21:09:21Z The 15N composition of sediments has been used as a proxy for nitrate utilization in surface waters to assess the role of Southern Ocean export production in glacial/interglacial changes in atmospheric CO2 concentration. Interpretation has relied on a temporally constant isotope effect () associated with uptake and assimilation of nitrate by phytoplankton. To investigate the reliability of this approach, we examined the relationships between the 15N compositions of dissolved nitrate, bulk and size-fractionated (200, 70, 20, 5, 1 m) suspended particulate organic nitrogen (PON), and sinking particles obtained from sediment traps during the Southern Ocean iron release experiment (SOIREE). We found variations in phytoplankton nitrogen isotopic compositions with both cell size and iron availability. 15NPON increased by <2 with increasing size, both within and outside the iron-enriched patch. In comparison to unfertilized waters, 15NPON within the iron-fertilized patch was a further 3-4 higher in those size fractions dominated by large diatoms (20-70, 70-200 m). We speculate that this iron response might result from (1) variation in of nitrate utilization or (2) an iron-stimulated shift from ammonium-based to nitrate-based production. Comparing the 15N of the large diatom-dominated size fractions to the 15N of nitrate suggests relatively low values of 4-5, in contrast to estimated values of 7-10 from seasonal nitrate depletion and export production. This suggests that higher glacial 15N in Southern Ocean sediments could, in part, reflect increases in iron availability, dominant cell size, and possibly growth rates, and these effects must be considered in any quantitative scaling of 15N variations, including those of diatom-bound 15N, to the extent of nitrate utilization. Article in Journal/Newspaper Southern Ocean eCite UTAS (University of Tasmania) Southern Ocean Limnology and Oceanography 48 3 1058 1068 |
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Open Polar |
collection |
eCite UTAS (University of Tasmania) |
op_collection_id |
ftunivtasecite |
language |
English |
topic |
Physical Sciences Optical Physics Lasers and Quantum Electronics |
spellingShingle |
Physical Sciences Optical Physics Lasers and Quantum Electronics Karsh, K Trull, T Lourey, MJ Sigman, DM Relationship of nitrogen isotope fractionation to phytoplankton size and iron availability during the Southern Ocean Iron Release Experiment (SOIREE) |
topic_facet |
Physical Sciences Optical Physics Lasers and Quantum Electronics |
description |
The 15N composition of sediments has been used as a proxy for nitrate utilization in surface waters to assess the role of Southern Ocean export production in glacial/interglacial changes in atmospheric CO2 concentration. Interpretation has relied on a temporally constant isotope effect () associated with uptake and assimilation of nitrate by phytoplankton. To investigate the reliability of this approach, we examined the relationships between the 15N compositions of dissolved nitrate, bulk and size-fractionated (200, 70, 20, 5, 1 m) suspended particulate organic nitrogen (PON), and sinking particles obtained from sediment traps during the Southern Ocean iron release experiment (SOIREE). We found variations in phytoplankton nitrogen isotopic compositions with both cell size and iron availability. 15NPON increased by <2 with increasing size, both within and outside the iron-enriched patch. In comparison to unfertilized waters, 15NPON within the iron-fertilized patch was a further 3-4 higher in those size fractions dominated by large diatoms (20-70, 70-200 m). We speculate that this iron response might result from (1) variation in of nitrate utilization or (2) an iron-stimulated shift from ammonium-based to nitrate-based production. Comparing the 15N of the large diatom-dominated size fractions to the 15N of nitrate suggests relatively low values of 4-5, in contrast to estimated values of 7-10 from seasonal nitrate depletion and export production. This suggests that higher glacial 15N in Southern Ocean sediments could, in part, reflect increases in iron availability, dominant cell size, and possibly growth rates, and these effects must be considered in any quantitative scaling of 15N variations, including those of diatom-bound 15N, to the extent of nitrate utilization. |
format |
Article in Journal/Newspaper |
author |
Karsh, K Trull, T Lourey, MJ Sigman, DM |
author_facet |
Karsh, K Trull, T Lourey, MJ Sigman, DM |
author_sort |
Karsh, K |
title |
Relationship of nitrogen isotope fractionation to phytoplankton size and iron availability during the Southern Ocean Iron Release Experiment (SOIREE) |
title_short |
Relationship of nitrogen isotope fractionation to phytoplankton size and iron availability during the Southern Ocean Iron Release Experiment (SOIREE) |
title_full |
Relationship of nitrogen isotope fractionation to phytoplankton size and iron availability during the Southern Ocean Iron Release Experiment (SOIREE) |
title_fullStr |
Relationship of nitrogen isotope fractionation to phytoplankton size and iron availability during the Southern Ocean Iron Release Experiment (SOIREE) |
title_full_unstemmed |
Relationship of nitrogen isotope fractionation to phytoplankton size and iron availability during the Southern Ocean Iron Release Experiment (SOIREE) |
title_sort |
relationship of nitrogen isotope fractionation to phytoplankton size and iron availability during the southern ocean iron release experiment (soiree) |
publisher |
American Society of Limnology and Oceanography |
publishDate |
2003 |
url |
https://doi.org/10.4319/lo.2003.48.3.1058 http://ecite.utas.edu.au/29155 |
geographic |
Southern Ocean |
geographic_facet |
Southern Ocean |
genre |
Southern Ocean |
genre_facet |
Southern Ocean |
op_relation |
http://dx.doi.org/10.4319/lo.2003.48.3.1058 Karsh, K and Trull, T and Lourey, MJ and Sigman, DM, Relationship of nitrogen isotope fractionation to phytoplankton size and iron availability during the Southern Ocean Iron Release Experiment (SOIREE), Limnology and Oceanography, 48, (3) pp. 1058-1068. ISSN 0024-3590 (2003) [Refereed Article] http://ecite.utas.edu.au/29155 |
op_doi |
https://doi.org/10.4319/lo.2003.48.3.1058 |
container_title |
Limnology and Oceanography |
container_volume |
48 |
container_issue |
3 |
container_start_page |
1058 |
op_container_end_page |
1068 |
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1766205528643469312 |