Assessment of Excess Nitrate Development in the Subtropical North Atlantic
Geochemical estimates of N2 fixation in the North Atlantic often serve as a foundation for estimating global marine diazotrophy. Yet despite being well-studied, estimations of nitrogen fixation rates in this basin vary widely. Here we investigate the variability in published estimates of excess nitr...
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ELSEVIER SCIENCE BV
2007
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Online Access: | https://publications.jrc.ec.europa.eu/repository/handle/JRC38205 https://doi.org/10.1016/j.marchem.2007.06.005 |
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ftjrc:oai:publications.jrc.ec.europa.eu:JRC38205 2024-09-15T18:21:22+00:00 Assessment of Excess Nitrate Development in the Subtropical North Atlantic HANSEL Dennis DENTENER Franciscus OLSON D. B. ZAMORA L. M. 2007 Print https://publications.jrc.ec.europa.eu/repository/handle/JRC38205 https://doi.org/10.1016/j.marchem.2007.06.005 eng eng ELSEVIER SCIENCE BV JRC38205 2007 ftjrc https://doi.org/10.1016/j.marchem.2007.06.005 2024-07-22T04:42:14Z Geochemical estimates of N2 fixation in the North Atlantic often serve as a foundation for estimating global marine diazotrophy. Yet despite being well-studied, estimations of nitrogen fixation rates in this basin vary widely. Here we investigate the variability in published estimates of excess nitrogen accumulation rates in the main thermocline of the subtropical North Atlantic, testing the assumptions and choices made in the analyses. Employing one of these previously described methods, modified here with improved estimates of excess N spatial gradients and ventilation rates of the main thermocline, we determine a total excess N accumulation rate of 7.8±1.7×10^11mol N yr-1;1. Contributions to excess N development include atmospheric deposition of high N:P nutrients (adding excess N at a rate of 3.0±0.9×1011 mol N yr-1;1 for ∼38% of the total), high N:P dissolved organic matter advected into and mineralized in the main thermocline (adding excess N at 2.2±1.1×1011 mol N yr-1;1 for ∼28% of the total), and, calculated by mass balance of the excess N field, N2 fixation (adding excess N at 2.6±2.2×1011 mol N yr−1 for ∼33% of the total). Assuming an N:P of 40 and this rate of excess N accumulation due to the process, N2 fixation in the North Atlantic subtropical gyre is estimated at ∼4×1011mol N yr−1. This relatively low rate of N2 fixation suggests that i) the rate of N2 fixation in the North Atlantic is greatly overestimated in some previous analyses, ii) the main thermocline is not the primary repository of N fixed by diazotrophs, and/or iii) the N:P ratio of exported diazotrophic organic matter is much lower than generally assumed. It is this last possibility, and our uncertainty in the N:P ratios of exported material supporting excess N development, that greatly lessens our confidence in geochemical measures of N2 fixation. JRC.H.2 - Climate change Other/Unknown Material North Atlantic Joint Research Centre, European Commission: JRC Publications Repository Marine Chemistry 106 3-4 562 579 |
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Open Polar |
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Joint Research Centre, European Commission: JRC Publications Repository |
op_collection_id |
ftjrc |
language |
English |
description |
Geochemical estimates of N2 fixation in the North Atlantic often serve as a foundation for estimating global marine diazotrophy. Yet despite being well-studied, estimations of nitrogen fixation rates in this basin vary widely. Here we investigate the variability in published estimates of excess nitrogen accumulation rates in the main thermocline of the subtropical North Atlantic, testing the assumptions and choices made in the analyses. Employing one of these previously described methods, modified here with improved estimates of excess N spatial gradients and ventilation rates of the main thermocline, we determine a total excess N accumulation rate of 7.8±1.7×10^11mol N yr-1;1. Contributions to excess N development include atmospheric deposition of high N:P nutrients (adding excess N at a rate of 3.0±0.9×1011 mol N yr-1;1 for ∼38% of the total), high N:P dissolved organic matter advected into and mineralized in the main thermocline (adding excess N at 2.2±1.1×1011 mol N yr-1;1 for ∼28% of the total), and, calculated by mass balance of the excess N field, N2 fixation (adding excess N at 2.6±2.2×1011 mol N yr−1 for ∼33% of the total). Assuming an N:P of 40 and this rate of excess N accumulation due to the process, N2 fixation in the North Atlantic subtropical gyre is estimated at ∼4×1011mol N yr−1. This relatively low rate of N2 fixation suggests that i) the rate of N2 fixation in the North Atlantic is greatly overestimated in some previous analyses, ii) the main thermocline is not the primary repository of N fixed by diazotrophs, and/or iii) the N:P ratio of exported diazotrophic organic matter is much lower than generally assumed. It is this last possibility, and our uncertainty in the N:P ratios of exported material supporting excess N development, that greatly lessens our confidence in geochemical measures of N2 fixation. JRC.H.2 - Climate change |
author |
HANSEL Dennis DENTENER Franciscus OLSON D. B. ZAMORA L. M. |
spellingShingle |
HANSEL Dennis DENTENER Franciscus OLSON D. B. ZAMORA L. M. Assessment of Excess Nitrate Development in the Subtropical North Atlantic |
author_facet |
HANSEL Dennis DENTENER Franciscus OLSON D. B. ZAMORA L. M. |
author_sort |
HANSEL Dennis |
title |
Assessment of Excess Nitrate Development in the Subtropical North Atlantic |
title_short |
Assessment of Excess Nitrate Development in the Subtropical North Atlantic |
title_full |
Assessment of Excess Nitrate Development in the Subtropical North Atlantic |
title_fullStr |
Assessment of Excess Nitrate Development in the Subtropical North Atlantic |
title_full_unstemmed |
Assessment of Excess Nitrate Development in the Subtropical North Atlantic |
title_sort |
assessment of excess nitrate development in the subtropical north atlantic |
publisher |
ELSEVIER SCIENCE BV |
publishDate |
2007 |
url |
https://publications.jrc.ec.europa.eu/repository/handle/JRC38205 https://doi.org/10.1016/j.marchem.2007.06.005 |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_relation |
JRC38205 |
op_doi |
https://doi.org/10.1016/j.marchem.2007.06.005 |
container_title |
Marine Chemistry |
container_volume |
106 |
container_issue |
3-4 |
container_start_page |
562 |
op_container_end_page |
579 |
_version_ |
1810459899696513024 |