N and O isotope ratios of NO3- as a tracer for nitrogen cycling and water mass distribution
Nitrogen plays a central role in marine biogeochemistry. Its distribution, chemical speciation and ratio relative to other nutrients governs the presence and abundance of microbial communities, and of large scale ocean production. In this respect, my thesis examines how biochemical and physical proc...
Main Author: | |
---|---|
Other Authors: | , , , , , , , , |
Format: | Thesis |
Language: | English |
Published: |
2021
|
Subjects: | |
Online Access: | http://hdl.handle.net/10222/80178 |
id |
ftdalhouse:oai:DalSpace.library.dal.ca:10222/80178 |
---|---|
record_format |
openpolar |
spelling |
ftdalhouse:oai:DalSpace.library.dal.ca:10222/80178 2023-05-15T14:29:02+02:00 N and O isotope ratios of NO3- as a tracer for nitrogen cycling and water mass distribution Lehmann, Nadine Department of Oceanography Doctor of Philosophy Dr. Roberta C. Hamme Dr. Markus Kienast Dr. Carolyn Buchwald Dr. Katja Fennel Dr. Helmuth Thomas Not Applicable Yes 2021-01-07T18:28:12Z http://hdl.handle.net/10222/80178 en_US eng http://hdl.handle.net/10222/80178 Nitrogen cycling Stable isotopes biogeochemistry Thesis 2021 ftdalhouse 2022-03-06T00:10:49Z Nitrogen plays a central role in marine biogeochemistry. Its distribution, chemical speciation and ratio relative to other nutrients governs the presence and abundance of microbial communities, and of large scale ocean production. In this respect, my thesis examines how biochemical and physical processes regulate the distribution of different nitrogen (N) species and their transformation in various marine environments by evaluating the spatial distribution of nitrogen and oxygen isotopes of nitrate (NO3-), in combination with a varying set of complementary biogeochemical tracers. Chapter 2 examines the isotopic composition of NO3- and total dissolved inorganic carbon (DIC) to elucidate the hydrography of the Western Equatorial Pacific (WEP) and biogeochemical evolution of water masses that contribute to the Equatorial Undercurrent (EUC). Based on isotope data and water mass mixing estimates, I highlight the different biogeochemical histories of nutrients feeding the northern and southern WEP, and provide support for the theory of a predominantly Southern Ocean source of NO3- to the EUC. Chapter 3 focuses on Baffin Bay, which represents a major link between the high Arctic and the northwestern Atlantic, owing to its effect on the salt and nutrient budgets of the adjacent Labrador Sea and the wider Atlantic Ocean. I combine NO3- isotope ratios with nitrous oxide (N2O) isotope measurements to identify the origin of the pronounced N-deficit and N2O supersaturation prevalent in deep Baffin Bay. The set of isotopic tracers used in this study allows the identification of different, yet complementary, N transformation processes. NO3- isotopes reflect substantial in situ remineralization of organic matter originating from surface productivity fueled by Pacific-derived nutrients, whereas N2O isotopomer abundances point to sedimentary denitrification as a potential source of the N-deficiency observed in the deep basin. In chapter 4, I use NO3- isotope ratios measured in the Canada Basin and in the Baffin Bay together with hydrographic data and nutrient ratios as a baseline to evaluate the distribution of Pacific- and Atlantic-derived water masses throughout the Arctic Archipelago. With this work, I highlight the importance and applicability of dual isotope measurements as water mass tracers and provide insights into individual processes within the N cycle. Thesis Arctic Archipelago Arctic Baffin Bay Baffin Bay Baffin canada basin Labrador Sea Southern Ocean Dalhousie University: DalSpace Institutional Repository Arctic Baffin Bay Canada Pacific Southern Ocean |
institution |
Open Polar |
collection |
Dalhousie University: DalSpace Institutional Repository |
op_collection_id |
ftdalhouse |
language |
English |
topic |
Nitrogen cycling Stable isotopes biogeochemistry |
spellingShingle |
Nitrogen cycling Stable isotopes biogeochemistry Lehmann, Nadine N and O isotope ratios of NO3- as a tracer for nitrogen cycling and water mass distribution |
topic_facet |
Nitrogen cycling Stable isotopes biogeochemistry |
description |
Nitrogen plays a central role in marine biogeochemistry. Its distribution, chemical speciation and ratio relative to other nutrients governs the presence and abundance of microbial communities, and of large scale ocean production. In this respect, my thesis examines how biochemical and physical processes regulate the distribution of different nitrogen (N) species and their transformation in various marine environments by evaluating the spatial distribution of nitrogen and oxygen isotopes of nitrate (NO3-), in combination with a varying set of complementary biogeochemical tracers. Chapter 2 examines the isotopic composition of NO3- and total dissolved inorganic carbon (DIC) to elucidate the hydrography of the Western Equatorial Pacific (WEP) and biogeochemical evolution of water masses that contribute to the Equatorial Undercurrent (EUC). Based on isotope data and water mass mixing estimates, I highlight the different biogeochemical histories of nutrients feeding the northern and southern WEP, and provide support for the theory of a predominantly Southern Ocean source of NO3- to the EUC. Chapter 3 focuses on Baffin Bay, which represents a major link between the high Arctic and the northwestern Atlantic, owing to its effect on the salt and nutrient budgets of the adjacent Labrador Sea and the wider Atlantic Ocean. I combine NO3- isotope ratios with nitrous oxide (N2O) isotope measurements to identify the origin of the pronounced N-deficit and N2O supersaturation prevalent in deep Baffin Bay. The set of isotopic tracers used in this study allows the identification of different, yet complementary, N transformation processes. NO3- isotopes reflect substantial in situ remineralization of organic matter originating from surface productivity fueled by Pacific-derived nutrients, whereas N2O isotopomer abundances point to sedimentary denitrification as a potential source of the N-deficiency observed in the deep basin. In chapter 4, I use NO3- isotope ratios measured in the Canada Basin and in the Baffin Bay together with hydrographic data and nutrient ratios as a baseline to evaluate the distribution of Pacific- and Atlantic-derived water masses throughout the Arctic Archipelago. With this work, I highlight the importance and applicability of dual isotope measurements as water mass tracers and provide insights into individual processes within the N cycle. |
author2 |
Department of Oceanography Doctor of Philosophy Dr. Roberta C. Hamme Dr. Markus Kienast Dr. Carolyn Buchwald Dr. Katja Fennel Dr. Helmuth Thomas Not Applicable Yes |
format |
Thesis |
author |
Lehmann, Nadine |
author_facet |
Lehmann, Nadine |
author_sort |
Lehmann, Nadine |
title |
N and O isotope ratios of NO3- as a tracer for nitrogen cycling and water mass distribution |
title_short |
N and O isotope ratios of NO3- as a tracer for nitrogen cycling and water mass distribution |
title_full |
N and O isotope ratios of NO3- as a tracer for nitrogen cycling and water mass distribution |
title_fullStr |
N and O isotope ratios of NO3- as a tracer for nitrogen cycling and water mass distribution |
title_full_unstemmed |
N and O isotope ratios of NO3- as a tracer for nitrogen cycling and water mass distribution |
title_sort |
n and o isotope ratios of no3- as a tracer for nitrogen cycling and water mass distribution |
publishDate |
2021 |
url |
http://hdl.handle.net/10222/80178 |
geographic |
Arctic Baffin Bay Canada Pacific Southern Ocean |
geographic_facet |
Arctic Baffin Bay Canada Pacific Southern Ocean |
genre |
Arctic Archipelago Arctic Baffin Bay Baffin Bay Baffin canada basin Labrador Sea Southern Ocean |
genre_facet |
Arctic Archipelago Arctic Baffin Bay Baffin Bay Baffin canada basin Labrador Sea Southern Ocean |
op_relation |
http://hdl.handle.net/10222/80178 |
_version_ |
1766303140805607424 |