Nitrogen and carbon cycling in the South Atlantic Ocean: A stable isotope study along a 40°S transect (UK GEOTRACES)
Fixed N (nitrate, nitrite, and ammonium) is a limiting nutrient for photosynthesis in the surface ocean. The rates and relative importance of N cycling processes, however, are temporally and spatially complex, which hamper their direct measurement and quantification. The South Atlantic subtropical f...
Main Author: | |
---|---|
Other Authors: | , , |
Format: | Doctoral or Postdoctoral Thesis |
Language: | English |
Published: |
The University of Edinburgh
2015
|
Subjects: | |
Online Access: | http://hdl.handle.net/1842/10443 |
id |
ftunivedinburgh:oai:era.ed.ac.uk:1842/10443 |
---|---|
record_format |
openpolar |
spelling |
ftunivedinburgh:oai:era.ed.ac.uk:1842/10443 2023-07-30T04:04:57+02:00 Nitrogen and carbon cycling in the South Atlantic Ocean: A stable isotope study along a 40°S transect (UK GEOTRACES) Tuerena, Robyn Elizabeth Ganeshram, Raja Geibert, Walter Natural Environment Research Council (NERC) 30/06/2015 application/msword application/pdf http://hdl.handle.net/1842/10443 en eng The University of Edinburgh http://hdl.handle.net/1842/10443 nitrogen isotope carbon South Atlantic Thesis or Dissertation Doctoral PhD Doctor of Philosophy 2015 ftunivedinburgh 2023-07-09T20:31:46Z Fixed N (nitrate, nitrite, and ammonium) is a limiting nutrient for photosynthesis in the surface ocean. The rates and relative importance of N cycling processes, however, are temporally and spatially complex, which hamper their direct measurement and quantification. The South Atlantic subtropical front separates the Atlantic Ocean and the subantarctic, an area which can elucidate information about water masses both entering and leaving the basin. Through the GEOTRACES programme, an oceanographic section across 40°S in the South Atlantic is used to investigate biogeochemical cycling of nitrogen and carbon in this region. Hydrographic data, in combination with the isotopic composition of nitrate (NO3-), particulate organic carbon and particulate nitrogen (δ15NNO3, δ18ONO3, δ13CPOC, δ15NPN), is used to provide integrative measurements for temporally and spatially variable processes of the marine N-cycle and C-cycle. A thorough examination of the stable isotope cycling of particulate and dissolved N across the subtropical front is used to quantify the supply of fixed N to the mixed layer. The relative importance of nitrate from the subsurface, N2 fixation, terrestrial input and atmospheric deposition in supplying production is determined. Typically, 30-50% of the export flux in the subtropical water masses is sourced from N2 fixers and up to 75% within the Brazil Current. This finding suggests that diazotrophs may be abundant in the South West Atlantic providing a source of new N to this region. To assess the basin scale N-cycling processes, the deep water masses were analysed to reveal the origin and history of NO3-. Intermediate waters formed in the subantarctic are enriched in δ15NNO3 and δ18ONO3 from partial utilisation by algae. This enrichment in δ15NNO3 is not present in the subtropical North Atlantic or the return flow of the North Atlantic Deep Water (NADW), which decreases from ~5.9‰ in the newly formed intermediate waters to ~4.8‰ in the NADW at 40°S. The modification of isotopic signatures through the ... Doctoral or Postdoctoral Thesis NADW North Atlantic Deep Water North Atlantic South Atlantic Ocean Edinburgh Research Archive (ERA - University of Edinburgh) |
institution |
Open Polar |
collection |
Edinburgh Research Archive (ERA - University of Edinburgh) |
op_collection_id |
ftunivedinburgh |
language |
English |
topic |
nitrogen isotope carbon South Atlantic |
spellingShingle |
nitrogen isotope carbon South Atlantic Tuerena, Robyn Elizabeth Nitrogen and carbon cycling in the South Atlantic Ocean: A stable isotope study along a 40°S transect (UK GEOTRACES) |
topic_facet |
nitrogen isotope carbon South Atlantic |
description |
Fixed N (nitrate, nitrite, and ammonium) is a limiting nutrient for photosynthesis in the surface ocean. The rates and relative importance of N cycling processes, however, are temporally and spatially complex, which hamper their direct measurement and quantification. The South Atlantic subtropical front separates the Atlantic Ocean and the subantarctic, an area which can elucidate information about water masses both entering and leaving the basin. Through the GEOTRACES programme, an oceanographic section across 40°S in the South Atlantic is used to investigate biogeochemical cycling of nitrogen and carbon in this region. Hydrographic data, in combination with the isotopic composition of nitrate (NO3-), particulate organic carbon and particulate nitrogen (δ15NNO3, δ18ONO3, δ13CPOC, δ15NPN), is used to provide integrative measurements for temporally and spatially variable processes of the marine N-cycle and C-cycle. A thorough examination of the stable isotope cycling of particulate and dissolved N across the subtropical front is used to quantify the supply of fixed N to the mixed layer. The relative importance of nitrate from the subsurface, N2 fixation, terrestrial input and atmospheric deposition in supplying production is determined. Typically, 30-50% of the export flux in the subtropical water masses is sourced from N2 fixers and up to 75% within the Brazil Current. This finding suggests that diazotrophs may be abundant in the South West Atlantic providing a source of new N to this region. To assess the basin scale N-cycling processes, the deep water masses were analysed to reveal the origin and history of NO3-. Intermediate waters formed in the subantarctic are enriched in δ15NNO3 and δ18ONO3 from partial utilisation by algae. This enrichment in δ15NNO3 is not present in the subtropical North Atlantic or the return flow of the North Atlantic Deep Water (NADW), which decreases from ~5.9‰ in the newly formed intermediate waters to ~4.8‰ in the NADW at 40°S. The modification of isotopic signatures through the ... |
author2 |
Ganeshram, Raja Geibert, Walter Natural Environment Research Council (NERC) |
format |
Doctoral or Postdoctoral Thesis |
author |
Tuerena, Robyn Elizabeth |
author_facet |
Tuerena, Robyn Elizabeth |
author_sort |
Tuerena, Robyn Elizabeth |
title |
Nitrogen and carbon cycling in the South Atlantic Ocean: A stable isotope study along a 40°S transect (UK GEOTRACES) |
title_short |
Nitrogen and carbon cycling in the South Atlantic Ocean: A stable isotope study along a 40°S transect (UK GEOTRACES) |
title_full |
Nitrogen and carbon cycling in the South Atlantic Ocean: A stable isotope study along a 40°S transect (UK GEOTRACES) |
title_fullStr |
Nitrogen and carbon cycling in the South Atlantic Ocean: A stable isotope study along a 40°S transect (UK GEOTRACES) |
title_full_unstemmed |
Nitrogen and carbon cycling in the South Atlantic Ocean: A stable isotope study along a 40°S transect (UK GEOTRACES) |
title_sort |
nitrogen and carbon cycling in the south atlantic ocean: a stable isotope study along a 40°s transect (uk geotraces) |
publisher |
The University of Edinburgh |
publishDate |
2015 |
url |
http://hdl.handle.net/1842/10443 |
genre |
NADW North Atlantic Deep Water North Atlantic South Atlantic Ocean |
genre_facet |
NADW North Atlantic Deep Water North Atlantic South Atlantic Ocean |
op_relation |
http://hdl.handle.net/1842/10443 |
_version_ |
1772816614543065088 |