Nitrogen isotopes in a global ocean biogeochemical model : constraints on the coupling between denitrification and nitrogen fixation
We present a new nitrogen isotope model incorporated into the three-dimensional ocean component of a global Earth System Climate Model designed for millennial timescale simulations. The model includes prognostic tracers for the stable nitrogen isotopes, ¹⁴N and ¹⁵N, in the nitrate (NO₃ˉ), phytoplank...
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ftoregonstate:ir.library.oregonstate.edu:0z708z854 2024-09-15T18:37:23+00:00 Nitrogen isotopes in a global ocean biogeochemical model : constraints on the coupling between denitrification and nitrogen fixation Somes, Christopher J. Schmittner, Andreas Letelier, Ricardo Mix, Alan College of Oceanic and Atmospheric Sciences Oregon State University. Graduate School https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/0z708z854 English [eng] eng unknown Oregon State University https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/0z708z854 All rights reserved Nitrogen -- Fixation Nitrogen cycle -- Mathematical models Nitrogen -- Isotopes Seawater -- Nitrogen content -- Mathematical models Denitrification Marine chemical ecology -- Mathematical models Masters Thesis ftoregonstate 2024-07-22T18:06:06Z We present a new nitrogen isotope model incorporated into the three-dimensional ocean component of a global Earth System Climate Model designed for millennial timescale simulations. The model includes prognostic tracers for the stable nitrogen isotopes, ¹⁴N and ¹⁵N, in the nitrate (NO₃ˉ), phytoplankton, zooplankton, and detritus variables of the marine ecosystem model. The isotope effects of algal NO₃ˉ assimilation, water column denitrification, and zooplankton excretion are considered as well as the input of newly fixed nitrogen by diazotrophs. A global database of δ¹⁵NO₃ˉ observations is compiled from previous studies and compared to the model results on a regional basis where sufficient observations exist. The model is able to qualitatively and quantitatively reproduce the observed patterns such as high subsurface values in denitrification zones, the meridional and vertical gradients in the Southern Ocean, and the meridional gradient in the Central Equatorial Pacific. The observed subsurface minimum in the Atlantic is underestimated presumably owing to too little nitrogen fixation there. Sensitivity experiments show that algal NO₃ˉ assimilation, nitrogen fixation and water column denitrification have strong effects on the simulated distribution of nitrogen isotopes, whereas the effect from zooplankton excretion is weaker. Both water column and sedimentary denitrification also have important indirect effects on the nitrogen isotopes distribution by reducing the fixed nitrogen inventory, which creates an ecological niche for diazotrophs and stimulates additional nitrogen fixation. Water column denitrification has a strong but rather localized effect on the nitrogen isotope distribution in model versions without iron limitation of diazotrophy, in which a tight coupling of nitrogen fixation exists. However, including iron limitation of diazotrophy inhibits a tight coupling between water column denitrification and nitrogen fixation in the Eastern Pacific and shifts the main location of nitrogen fixation from the ... Master Thesis Southern Ocean ScholarsArchive@OSU (Oregon State University) |
institution |
Open Polar |
collection |
ScholarsArchive@OSU (Oregon State University) |
op_collection_id |
ftoregonstate |
language |
English unknown |
topic |
Nitrogen -- Fixation Nitrogen cycle -- Mathematical models Nitrogen -- Isotopes Seawater -- Nitrogen content -- Mathematical models Denitrification Marine chemical ecology -- Mathematical models |
spellingShingle |
Nitrogen -- Fixation Nitrogen cycle -- Mathematical models Nitrogen -- Isotopes Seawater -- Nitrogen content -- Mathematical models Denitrification Marine chemical ecology -- Mathematical models Somes, Christopher J. Nitrogen isotopes in a global ocean biogeochemical model : constraints on the coupling between denitrification and nitrogen fixation |
topic_facet |
Nitrogen -- Fixation Nitrogen cycle -- Mathematical models Nitrogen -- Isotopes Seawater -- Nitrogen content -- Mathematical models Denitrification Marine chemical ecology -- Mathematical models |
description |
We present a new nitrogen isotope model incorporated into the three-dimensional ocean component of a global Earth System Climate Model designed for millennial timescale simulations. The model includes prognostic tracers for the stable nitrogen isotopes, ¹⁴N and ¹⁵N, in the nitrate (NO₃ˉ), phytoplankton, zooplankton, and detritus variables of the marine ecosystem model. The isotope effects of algal NO₃ˉ assimilation, water column denitrification, and zooplankton excretion are considered as well as the input of newly fixed nitrogen by diazotrophs. A global database of δ¹⁵NO₃ˉ observations is compiled from previous studies and compared to the model results on a regional basis where sufficient observations exist. The model is able to qualitatively and quantitatively reproduce the observed patterns such as high subsurface values in denitrification zones, the meridional and vertical gradients in the Southern Ocean, and the meridional gradient in the Central Equatorial Pacific. The observed subsurface minimum in the Atlantic is underestimated presumably owing to too little nitrogen fixation there. Sensitivity experiments show that algal NO₃ˉ assimilation, nitrogen fixation and water column denitrification have strong effects on the simulated distribution of nitrogen isotopes, whereas the effect from zooplankton excretion is weaker. Both water column and sedimentary denitrification also have important indirect effects on the nitrogen isotopes distribution by reducing the fixed nitrogen inventory, which creates an ecological niche for diazotrophs and stimulates additional nitrogen fixation. Water column denitrification has a strong but rather localized effect on the nitrogen isotope distribution in model versions without iron limitation of diazotrophy, in which a tight coupling of nitrogen fixation exists. However, including iron limitation of diazotrophy inhibits a tight coupling between water column denitrification and nitrogen fixation in the Eastern Pacific and shifts the main location of nitrogen fixation from the ... |
author2 |
Schmittner, Andreas Letelier, Ricardo Mix, Alan College of Oceanic and Atmospheric Sciences Oregon State University. Graduate School |
format |
Master Thesis |
author |
Somes, Christopher J. |
author_facet |
Somes, Christopher J. |
author_sort |
Somes, Christopher J. |
title |
Nitrogen isotopes in a global ocean biogeochemical model : constraints on the coupling between denitrification and nitrogen fixation |
title_short |
Nitrogen isotopes in a global ocean biogeochemical model : constraints on the coupling between denitrification and nitrogen fixation |
title_full |
Nitrogen isotopes in a global ocean biogeochemical model : constraints on the coupling between denitrification and nitrogen fixation |
title_fullStr |
Nitrogen isotopes in a global ocean biogeochemical model : constraints on the coupling between denitrification and nitrogen fixation |
title_full_unstemmed |
Nitrogen isotopes in a global ocean biogeochemical model : constraints on the coupling between denitrification and nitrogen fixation |
title_sort |
nitrogen isotopes in a global ocean biogeochemical model : constraints on the coupling between denitrification and nitrogen fixation |
publisher |
Oregon State University |
url |
https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/0z708z854 |
genre |
Southern Ocean |
genre_facet |
Southern Ocean |
op_relation |
https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/0z708z854 |
op_rights |
All rights reserved |
_version_ |
1810481749348581376 |