The kinetics of ammonium uptake and oxidation across the Southern Ocean
Abstract Central to the Southern Ocean's role in setting atmospheric CO 2 is the seasonal alternation between upward mixing of nutrients and their subsequent consumption by phytoplankton. Active nutrient cycling within the mixed layer, including the release of ammonium (NH 4 + ) and its removal...
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crwiley:10.1002/lno.12050 2024-09-15T18:37:01+00:00 The kinetics of ammonium uptake and oxidation across the Southern Ocean Mdutyana, Mhlangabezi Sun, Xin Burger, Jessica M. Flynn, Raquel F. Smith, Shantelle van Horsten, Natasha R. Roychoudhury, Alakendra N. Planquette, Hélène Bucciarelli, Eva Thomalla, Sandy J. Ward, Bess B. Fawcett, Sarah E. 2022 http://dx.doi.org/10.1002/lno.12050 https://onlinelibrary.wiley.com/doi/pdf/10.1002/lno.12050 https://onlinelibrary.wiley.com/doi/full-xml/10.1002/lno.12050 https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.1002/lno.12050 en eng Wiley http://onlinelibrary.wiley.com/termsAndConditions#vor Limnology and Oceanography volume 67, issue 4, page 973-991 ISSN 0024-3590 1939-5590 journal-article 2022 crwiley https://doi.org/10.1002/lno.12050 2024-08-27T04:30:37Z Abstract Central to the Southern Ocean's role in setting atmospheric CO 2 is the seasonal alternation between upward mixing of nutrients and their subsequent consumption by phytoplankton. Active nutrient cycling within the mixed layer, including the release of ammonium (NH 4 + ) and its removal by phytoplankton and nitrifiers, also affects Southern Ocean CO 2 drawdown, yet remains poorly understood. We conducted kinetics experiments across the Southern Ocean south of Africa to investigate the dependence of NH 4 + uptake (summer, winter) and oxidation (winter) on NH 4 + concentration. NH 4 + uptake followed a Michaelis–Menten function in both seasons, with the maximum rate ( V max ) decreasing poleward, apparently controlled mainly by light in winter and temperature in summer. The half‐saturation constant ( K m ) increased poleward with increasing ambient NH 4 + ([NH 4 + ] amb ) and was threefold higher in winter (150–405 nM) than in summer (41–115 nM), suggesting that summertime phytoplankton are adapted to low‐NH 4 + conditions while winter communities typically receive a higher NH 4 + supply. NH 4 + oxidation showed a high affinity for NH 4 + ( K m = 28–137 nM), suggesting a dominant role for ammonia‐oxidizing archaea, and followed a Michaelis–Menten curve only when [NH 4 + ] amb was ≤ 90 nM. V max was near‐constant across the region regardless of [NH 4 + ] amb , temperature, or light. From coincident mixed‐layer NH 4 + oxidation and iron measurements, we hypothesize that iron availability may (co‐)limit the V max of NH 4 + oxidation. If verified, this suggestion has implications for models that parameterize nitrification as a linear function of [NH 4 + ] amb . Additionally, iron depletion may limit the role of mixed‐layer nitrification, which is dominant in the winter Southern Ocean, in offsetting phytoplankton CO 2 drawdown annually. Article in Journal/Newspaper Southern Ocean Wiley Online Library Limnology and Oceanography 67 4 973 991 |
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Wiley Online Library |
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English |
description |
Abstract Central to the Southern Ocean's role in setting atmospheric CO 2 is the seasonal alternation between upward mixing of nutrients and their subsequent consumption by phytoplankton. Active nutrient cycling within the mixed layer, including the release of ammonium (NH 4 + ) and its removal by phytoplankton and nitrifiers, also affects Southern Ocean CO 2 drawdown, yet remains poorly understood. We conducted kinetics experiments across the Southern Ocean south of Africa to investigate the dependence of NH 4 + uptake (summer, winter) and oxidation (winter) on NH 4 + concentration. NH 4 + uptake followed a Michaelis–Menten function in both seasons, with the maximum rate ( V max ) decreasing poleward, apparently controlled mainly by light in winter and temperature in summer. The half‐saturation constant ( K m ) increased poleward with increasing ambient NH 4 + ([NH 4 + ] amb ) and was threefold higher in winter (150–405 nM) than in summer (41–115 nM), suggesting that summertime phytoplankton are adapted to low‐NH 4 + conditions while winter communities typically receive a higher NH 4 + supply. NH 4 + oxidation showed a high affinity for NH 4 + ( K m = 28–137 nM), suggesting a dominant role for ammonia‐oxidizing archaea, and followed a Michaelis–Menten curve only when [NH 4 + ] amb was ≤ 90 nM. V max was near‐constant across the region regardless of [NH 4 + ] amb , temperature, or light. From coincident mixed‐layer NH 4 + oxidation and iron measurements, we hypothesize that iron availability may (co‐)limit the V max of NH 4 + oxidation. If verified, this suggestion has implications for models that parameterize nitrification as a linear function of [NH 4 + ] amb . Additionally, iron depletion may limit the role of mixed‐layer nitrification, which is dominant in the winter Southern Ocean, in offsetting phytoplankton CO 2 drawdown annually. |
format |
Article in Journal/Newspaper |
author |
Mdutyana, Mhlangabezi Sun, Xin Burger, Jessica M. Flynn, Raquel F. Smith, Shantelle van Horsten, Natasha R. Roychoudhury, Alakendra N. Planquette, Hélène Bucciarelli, Eva Thomalla, Sandy J. Ward, Bess B. Fawcett, Sarah E. |
spellingShingle |
Mdutyana, Mhlangabezi Sun, Xin Burger, Jessica M. Flynn, Raquel F. Smith, Shantelle van Horsten, Natasha R. Roychoudhury, Alakendra N. Planquette, Hélène Bucciarelli, Eva Thomalla, Sandy J. Ward, Bess B. Fawcett, Sarah E. The kinetics of ammonium uptake and oxidation across the Southern Ocean |
author_facet |
Mdutyana, Mhlangabezi Sun, Xin Burger, Jessica M. Flynn, Raquel F. Smith, Shantelle van Horsten, Natasha R. Roychoudhury, Alakendra N. Planquette, Hélène Bucciarelli, Eva Thomalla, Sandy J. Ward, Bess B. Fawcett, Sarah E. |
author_sort |
Mdutyana, Mhlangabezi |
title |
The kinetics of ammonium uptake and oxidation across the Southern Ocean |
title_short |
The kinetics of ammonium uptake and oxidation across the Southern Ocean |
title_full |
The kinetics of ammonium uptake and oxidation across the Southern Ocean |
title_fullStr |
The kinetics of ammonium uptake and oxidation across the Southern Ocean |
title_full_unstemmed |
The kinetics of ammonium uptake and oxidation across the Southern Ocean |
title_sort |
kinetics of ammonium uptake and oxidation across the southern ocean |
publisher |
Wiley |
publishDate |
2022 |
url |
http://dx.doi.org/10.1002/lno.12050 https://onlinelibrary.wiley.com/doi/pdf/10.1002/lno.12050 https://onlinelibrary.wiley.com/doi/full-xml/10.1002/lno.12050 https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.1002/lno.12050 |
genre |
Southern Ocean |
genre_facet |
Southern Ocean |
op_source |
Limnology and Oceanography volume 67, issue 4, page 973-991 ISSN 0024-3590 1939-5590 |
op_rights |
http://onlinelibrary.wiley.com/termsAndConditions#vor |
op_doi |
https://doi.org/10.1002/lno.12050 |
container_title |
Limnology and Oceanography |
container_volume |
67 |
container_issue |
4 |
container_start_page |
973 |
op_container_end_page |
991 |
_version_ |
1810481150103126016 |