Comparable Carbon Export Fluxes but Divergent Pathways across Contrasting N₂ Fixation Regimes

Comparable Carbon Export Fluxes but Divergent Pathways across Contrasting N₂ Fixation Regimes | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 23 December 2025 V1 Latest version Share on Comparable Carbon Export Fluxes but Divergent Pathways across Contrasting N₂ Fixation Regimes Authors : Matthieu Savarino 0009-0000-9777-2864 [email protected] , Frédéric A. C. Le Moigne 0000-0001-7316-5111 , Mercedes Jardin-Camps , Fatima-Ezzahra Ababou , Olivier Grosso , Emmanuel de Saint-Léger 0000-0003-1629-5803 , Arnaud Leridant , Emmanuel C. Laurenceau-Cornec 0000-0002-4041-4377 , Céline Bachelier , Damien Vignon , and Sophie Bonnet Authors Info & Affiliations https://doi.org/10.22541/au.176650665.54437898/v1 159 views 101 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract The biological carbon pump is considered poorly efficient in the oligotrophic ocean due to nitrate limitation for primary productivity. In these ecosystems, dinitrogen (N2) fixing organisms supply new nitrogen (N) to the surface ocean, stimulating particulate organic carbon (POC) export through the N₂-primed prokaryotic pump. As global warming intensifies ocean oligotrophication, understanding carbon export pathways in these regions is increasingly critical. Here, we investigated gravitational POC export fluxes and pathways at 4 oligotrophic stations: 2 naturally iron (Fe)-fertilized stations near the Tonga-Kermadec volcanic arc (TONGA), characterized by high N2 fixation (~1718 µmol N m-2 d-1) dominated by Trichodesmium and elevated net primary productivity (NPP ~ 1287 mg C m⁻² d⁻¹); and 2 stations off New Caledonia (HOPE), characterized by lower N2 fixation (~290 µmol N m-2 d-1) -mostly dominated by unicellular cyanobacteria diazotroph A1 (UCYN-A1)-, and NPP rates of ~313 mg C m-2 d-1. Despite contrasting regimes, POC export fluxes at the base of the euphotic zone (47-71 mg C m⁻² d⁻¹) and at 1000 m (17–25 mg C m⁻² d⁻¹) were similar, although export efficiency was higher at HOPE (24%) than at TONGA (4%). Export pathways differed markedly: TONGA fluxes were dominated by fecal aggregates (50–94%) and zooplankton carcasses (2–49%), whereas HOPE fluxes were mainly phytodetrital (44–73%) and mixed aggregates (19–23%). TONGA stations exhibited carbon sequestration efficiencies comparable to subpolar Fe-fertilized systems. These results reveal contrasting POC export pathways across oligotrophic regions and underscore how particle morphology and diazotroph communities shape carbon export dynamics. Supplementary Material File (1057618_0_merged_1764775394.pdf) Download 9.12 MB File (savarino-et-al-def_figfree.docx) Download 7.79 MB File (supporting information (si) - comparable carbon export fluxes but divergent pathways across contrasting nxxx fixation regimes.docx) Download 27.19 KB Information & Authors Information Version history V1 Version 1 23 December 2025 Copyright This work is licensed under a Creative Commons Attribution 4.0 International License Keywords biological carbon pump carbon export pathways diazotrophs export efficiency fe-fertilization Authors Affiliations Matthieu Savarino 0009-0000-9777-2864 [email protected] Aix-Marseille Universite View all articles by this author Frédéric A. C. Le Moigne 0000-0001-7316-5111 CNRS View all articles by this author Mercedes Jardin-Camps Institut de Recherche pour le Développement View all articles by this author Fatima-Ezzahra Ababou Aix Marseille University View all articles by this author Olivier Grosso MIO View all articles by this author Emmanuel de Saint-Léger 0000-0003-1629-5803 DT-INSU View all articles by this author Arnaud Leridant DT-INSU View all articles by this author Emmanuel C. Laurenceau-Cornec 0000-0002-4041-4377 CNRS, University of Western Brittany View all articles by this author Céline Bachelier IRD View all articles by this author Damien Vignon IRD View all articles by this author Sophie Bonnet Institut de Recherche pour le Développement View all articles by this author Funding Information H2020 European Research Council 101044637 Sophie Bonnet HORIZON EUROPE European Research Council 101044637 Sophie Bonnet Metrics & Citations Metrics Article Usage 159 views 101 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Matthieu Savarino, Frédéric A. C. Le Moigne, Mercedes Jardin-Camps, et al. Comparable Carbon Export Fluxes but Divergent Pathways across Contrasting N₂ Fixation Regimes. Authorea . 23 December 2025. DOI: https://doi.org/10.22541/au.176650665.54437898/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. 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