The Nitrogen Isotopic Composition of Tissue and Shell‐Bound Organic Matter of Planktic Foraminifera in Southern Ocean Surface Waters
Abstract We present the first nitrogen isotope (δ15N) measurements of planktic foraminifera, paleoceanographically important zooplankton, from the nutrient‐rich waters of the modern Southern Ocean. Foraminifera were collected from net tows in the Subantarctic and Polar Frontal Zones (SAZ and PFZ, re...
Published in: | Geochemistry, Geophysics, Geosystems |
---|---|
Main Authors: | , , , , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
Wiley
2020
|
Subjects: | |
Online Access: | https://doi.org/10.1029/2019GC008440 https://doaj.org/article/50a2c5dc35c04ee89c42ca163c88d5e4 |
id |
ftdoajarticles:oai:doaj.org/article:50a2c5dc35c04ee89c42ca163c88d5e4 |
---|---|
record_format |
openpolar |
spelling |
ftdoajarticles:oai:doaj.org/article:50a2c5dc35c04ee89c42ca163c88d5e4 2023-12-03T10:30:31+01:00 The Nitrogen Isotopic Composition of Tissue and Shell‐Bound Organic Matter of Planktic Foraminifera in Southern Ocean Surface Waters Sandi M. Smart Sarah E. Fawcett Haojia Ren Ralf Schiebel Emily M. Tompkins Alfredo Martínez‐García Luca Stirnimann Alakendra Roychoudhury Gerald H. Haug Daniel M. Sigman 2020-02-01T00:00:00Z https://doi.org/10.1029/2019GC008440 https://doaj.org/article/50a2c5dc35c04ee89c42ca163c88d5e4 EN eng Wiley https://doi.org/10.1029/2019GC008440 https://doaj.org/toc/1525-2027 1525-2027 doi:10.1029/2019GC008440 https://doaj.org/article/50a2c5dc35c04ee89c42ca163c88d5e4 Geochemistry, Geophysics, Geosystems, Vol 21, Iss 2, Pp n/a-n/a (2020) planktic foraminifera nitrogen isotopes paleo‐proxy Southern Ocean Geophysics. Cosmic physics QC801-809 Geology QE1-996.5 article 2020 ftdoajarticles https://doi.org/10.1029/2019GC008440 2023-11-05T01:35:59Z Abstract We present the first nitrogen isotope (δ15N) measurements of planktic foraminifera, paleoceanographically important zooplankton, from the nutrient‐rich waters of the modern Southern Ocean. Foraminifera were collected from net tows in the Subantarctic and Polar Frontal Zones (SAZ and PFZ, respectively) south of Africa during winter 2015 and late summer 2016. In late summer, consistent with preferential uptake of 14N‐nitrate and the progressive, northward depletion of nitrate by phytoplankton across the Southern Ocean, foraminifer tissue and shell‐bound δ15N rise equatorward along with nitrate δ15N. However, foraminifer δ15N is ~3‰ lower than expected for heterotrophs relying on photosynthetic biomass generated directly from nitrate. This discrepancy appears to originate with the particulate organic N (PON) in late‐summer surface waters, the δ15N of which is lowered by ammonium recycling. In winter, when overall productivity and foraminifer production are reduced, foraminifer δ15N is higher (by 4.6 ± 0.8‰ for tissue and by 4.0 ± 1.5‰ for shell‐bound N compared to late summer) and exhibits no clear north‐south trend. These characteristics can also be explained by the feeding‐driven connection of foraminifera to PON, which is elevated in δ15N by net degradation in winter. Therefore, foraminifer δ15N is more closely tied to PON δ15N than to nitrate δ15N in the Southern Ocean mixed layer. Combining our isotope data with previously reported sediment trap fluxes from the western Pacific SAZ/PFZ suggests that, under modern conditions, the late‐summer ammonium recycling signal outweighs that of wintertime decomposition on the annually integrated δ15N of sinking foraminifera. Article in Journal/Newspaper Southern Ocean Directory of Open Access Journals: DOAJ Articles Pacific Southern Ocean Geochemistry, Geophysics, Geosystems 21 2 |
institution |
Open Polar |
collection |
Directory of Open Access Journals: DOAJ Articles |
op_collection_id |
ftdoajarticles |
language |
English |
topic |
planktic foraminifera nitrogen isotopes paleo‐proxy Southern Ocean Geophysics. Cosmic physics QC801-809 Geology QE1-996.5 |
spellingShingle |
planktic foraminifera nitrogen isotopes paleo‐proxy Southern Ocean Geophysics. Cosmic physics QC801-809 Geology QE1-996.5 Sandi M. Smart Sarah E. Fawcett Haojia Ren Ralf Schiebel Emily M. Tompkins Alfredo Martínez‐García Luca Stirnimann Alakendra Roychoudhury Gerald H. Haug Daniel M. Sigman The Nitrogen Isotopic Composition of Tissue and Shell‐Bound Organic Matter of Planktic Foraminifera in Southern Ocean Surface Waters |
topic_facet |
planktic foraminifera nitrogen isotopes paleo‐proxy Southern Ocean Geophysics. Cosmic physics QC801-809 Geology QE1-996.5 |
description |
Abstract We present the first nitrogen isotope (δ15N) measurements of planktic foraminifera, paleoceanographically important zooplankton, from the nutrient‐rich waters of the modern Southern Ocean. Foraminifera were collected from net tows in the Subantarctic and Polar Frontal Zones (SAZ and PFZ, respectively) south of Africa during winter 2015 and late summer 2016. In late summer, consistent with preferential uptake of 14N‐nitrate and the progressive, northward depletion of nitrate by phytoplankton across the Southern Ocean, foraminifer tissue and shell‐bound δ15N rise equatorward along with nitrate δ15N. However, foraminifer δ15N is ~3‰ lower than expected for heterotrophs relying on photosynthetic biomass generated directly from nitrate. This discrepancy appears to originate with the particulate organic N (PON) in late‐summer surface waters, the δ15N of which is lowered by ammonium recycling. In winter, when overall productivity and foraminifer production are reduced, foraminifer δ15N is higher (by 4.6 ± 0.8‰ for tissue and by 4.0 ± 1.5‰ for shell‐bound N compared to late summer) and exhibits no clear north‐south trend. These characteristics can also be explained by the feeding‐driven connection of foraminifera to PON, which is elevated in δ15N by net degradation in winter. Therefore, foraminifer δ15N is more closely tied to PON δ15N than to nitrate δ15N in the Southern Ocean mixed layer. Combining our isotope data with previously reported sediment trap fluxes from the western Pacific SAZ/PFZ suggests that, under modern conditions, the late‐summer ammonium recycling signal outweighs that of wintertime decomposition on the annually integrated δ15N of sinking foraminifera. |
format |
Article in Journal/Newspaper |
author |
Sandi M. Smart Sarah E. Fawcett Haojia Ren Ralf Schiebel Emily M. Tompkins Alfredo Martínez‐García Luca Stirnimann Alakendra Roychoudhury Gerald H. Haug Daniel M. Sigman |
author_facet |
Sandi M. Smart Sarah E. Fawcett Haojia Ren Ralf Schiebel Emily M. Tompkins Alfredo Martínez‐García Luca Stirnimann Alakendra Roychoudhury Gerald H. Haug Daniel M. Sigman |
author_sort |
Sandi M. Smart |
title |
The Nitrogen Isotopic Composition of Tissue and Shell‐Bound Organic Matter of Planktic Foraminifera in Southern Ocean Surface Waters |
title_short |
The Nitrogen Isotopic Composition of Tissue and Shell‐Bound Organic Matter of Planktic Foraminifera in Southern Ocean Surface Waters |
title_full |
The Nitrogen Isotopic Composition of Tissue and Shell‐Bound Organic Matter of Planktic Foraminifera in Southern Ocean Surface Waters |
title_fullStr |
The Nitrogen Isotopic Composition of Tissue and Shell‐Bound Organic Matter of Planktic Foraminifera in Southern Ocean Surface Waters |
title_full_unstemmed |
The Nitrogen Isotopic Composition of Tissue and Shell‐Bound Organic Matter of Planktic Foraminifera in Southern Ocean Surface Waters |
title_sort |
nitrogen isotopic composition of tissue and shell‐bound organic matter of planktic foraminifera in southern ocean surface waters |
publisher |
Wiley |
publishDate |
2020 |
url |
https://doi.org/10.1029/2019GC008440 https://doaj.org/article/50a2c5dc35c04ee89c42ca163c88d5e4 |
geographic |
Pacific Southern Ocean |
geographic_facet |
Pacific Southern Ocean |
genre |
Southern Ocean |
genre_facet |
Southern Ocean |
op_source |
Geochemistry, Geophysics, Geosystems, Vol 21, Iss 2, Pp n/a-n/a (2020) |
op_relation |
https://doi.org/10.1029/2019GC008440 https://doaj.org/toc/1525-2027 1525-2027 doi:10.1029/2019GC008440 https://doaj.org/article/50a2c5dc35c04ee89c42ca163c88d5e4 |
op_doi |
https://doi.org/10.1029/2019GC008440 |
container_title |
Geochemistry, Geophysics, Geosystems |
container_volume |
21 |
container_issue |
2 |
_version_ |
1784256396574851072 |