@misc{berthelot_carbon_2015,
	address = {UNESCO, Paris, France},
	type = {Poster},
	title = {Carbon production and export are fuelled by dinitrogen fixation and dissolved organic nitrogen in the {South}-western {Pacific} {Ocean}: results from the {VAHINE} mesocosms experiment},
	abstract = {The oligotrophic ocean represents 80 \% of the global surface ocean. Its role on CO2 sequestration has long been considered to be low, but this view is currently challenged by new studies highlighting alternative pathways for carbon export to the deep ocean. In these systems, carbon production is limited due to nitrogen (N) scarcity but dinitrogen (N2) fixation and dissolved organic nitrogen (DON) would represent significant nitrogen (N) sources for the ecosystem. Here we deployed in New Caledonia large in situ mesocosms in order to investigate (1) the contribution of  N2 fixation and DON use to primary production (PP) and particle export and (2) the fate of the freshly produced particulate organic N (PON) i.e. whether it is preferentially accumulated and recycled in the water column or exported out of the system. The mesocosms were fertilized with phosphate (P) in order to prevent P-limitation and promote N2 fixation. The diazotrophic community was dominated by diatoms-diazotrophs associations (DDAs) during the first part of the experiment for 10 days (P1) followed by the unicellular N2-fixing cyanobacteria UCYN-C the 9 last days (P2) of the experiment. N2 fixation rates averaged 9.8±4.0 nM d-1 and 27.7±8.6 nM d-1 during P1 and P2, respectively. NO3- concentrations ({\textless}40 nM) in the mesocosms were a negligible source of N indicating that N2 fixation was the main driver of new production all along the experiment. The contribution of N2 fixation to PP was not significantly different during P1 (9.0±3.3 \%) and P2 (12.6±6.1 \%). However, the e-ratio that quantifies the efficiency of a system to export particulate organic carbon (POCexport) compared to PP (e-ratio = POCexport/PP) was significantly higher (p{\textless}0.05) during P2 (39.7±24.9 \%) than during P1 (23.9±20.2 \%) indicating that the production sustained by UCYN-C was more efficient at promoting C export than the production sustained by DDAs. During P1, PON was stable and the total amount of N provided by N2 fixation (0.10±0.02 µM) was not significantly different from the total amount of PON exported (0.10±0.04 µM), suggesting a rapid and probably direct export of the recently fixed N2 by the DDAs. During P2, both PON concentrations and PON export increased in the mesocosms by a factor 1.5-2. Unlike in P1, this PON production was not totally explained by the new N provided by N2 fixation. The use of DON, which concentrations decreased significantly from 5.3±0.5 µM to 4.4±0.5 µM, appeared to be the missing N source. The DON consumption of about 0.9 µM during P2 is even higher than the total amount of new N brought by N2 fixation (about 0.25 µM) during the same period. These results suggest that while DDAs mainly rely on N2 fixation for their N requirements, both N2 fixation and DON can be significant N-sources for carbon production and export following UCYN-C blooms in New Caledonia and by extension in the N-limited Ocean where similar events are likely to occur. This study confirms that in the South West Pacific, N2 fixation is a biogeochemically relevant process able to provide sufficient new N to drive new carbon production and export. These results are particularly important in the context of increasing temperatures that will probably increase the diazotrophic activity in the future ocean.},
	author = {Berthelot, H and Moutin, T and L'Helguen, S and Leblanc, K. and Hélias, S and Grosso, O and Leblond, N and Charrière, B and Bonnet, S},
	year = {2015},
	keywords = {ACTI, E3}
}

{"_id":"nJekqR3G2J2n8T4nL","bibbaseid":"berthelot-moutin-lhelguen-leblanc-hlias-grosso-leblond-charrire-etal-carbonproductionandexportarefuelledbydinitrogenfixationanddissolvedorganicnitrogeninthesouthwesternpacificoceanresultsfromthevahinemesocosmsexperiment-2015","downloads":0,"creationDate":"2016-02-08T11:47:57.905Z","title":"Carbon production and export are fuelled by dinitrogen fixation and dissolved organic nitrogen in the South-western Pacific Ocean: results from the VAHINE mesocosms experiment","author_short":["Berthelot, H","Moutin, T","L'Helguen, S","Leblanc, K.","Hélias, S","Grosso, O","Leblond, N","Charrière, B","Bonnet, S"],"year":2015,"bibtype":"misc","biburl":"http://bibbase.org/zotero/LEMARLAB","bibdata":{"bibtype":"misc","type":"Poster","address":"UNESCO, Paris, France","title":"Carbon production and export are fuelled by dinitrogen fixation and dissolved organic nitrogen in the South-western Pacific Ocean: results from the VAHINE mesocosms experiment","abstract":"The oligotrophic ocean represents 80 % of the global surface ocean. Its role on CO2 sequestration has long been considered to be low, but this view is currently challenged by new studies highlighting alternative pathways for carbon export to the deep ocean. In these systems, carbon production is limited due to nitrogen (N) scarcity but dinitrogen (N2) fixation and dissolved organic nitrogen (DON) would represent significant nitrogen (N) sources for the ecosystem. Here we deployed in New Caledonia large in situ mesocosms in order to investigate (1) the contribution of N2 fixation and DON use to primary production (PP) and particle export and (2) the fate of the freshly produced particulate organic N (PON) i.e. whether it is preferentially accumulated and recycled in the water column or exported out of the system. The mesocosms were fertilized with phosphate (P) in order to prevent P-limitation and promote N2 fixation. The diazotrophic community was dominated by diatoms-diazotrophs associations (DDAs) during the first part of the experiment for 10 days (P1) followed by the unicellular N2-fixing cyanobacteria UCYN-C the 9 last days (P2) of the experiment. N2 fixation rates averaged 9.8±4.0 nM d-1 and 27.7±8.6 nM d-1 during P1 and P2, respectively. NO3- concentrations (\\textless40 nM) in the mesocosms were a negligible source of N indicating that N2 fixation was the main driver of new production all along the experiment. The contribution of N2 fixation to PP was not significantly different during P1 (9.0±3.3 %) and P2 (12.6±6.1 %). However, the e-ratio that quantifies the efficiency of a system to export particulate organic carbon (POCexport) compared to PP (e-ratio = POCexport/PP) was significantly higher (p\\textless0.05) during P2 (39.7±24.9 %) than during P1 (23.9±20.2 %) indicating that the production sustained by UCYN-C was more efficient at promoting C export than the production sustained by DDAs. During P1, PON was stable and the total amount of N provided by N2 fixation (0.10±0.02 µM) was not significantly different from the total amount of PON exported (0.10±0.04 µM), suggesting a rapid and probably direct export of the recently fixed N2 by the DDAs. During P2, both PON concentrations and PON export increased in the mesocosms by a factor 1.5-2. Unlike in P1, this PON production was not totally explained by the new N provided by N2 fixation. The use of DON, which concentrations decreased significantly from 5.3±0.5 µM to 4.4±0.5 µM, appeared to be the missing N source. The DON consumption of about 0.9 µM during P2 is even higher than the total amount of new N brought by N2 fixation (about 0.25 µM) during the same period. These results suggest that while DDAs mainly rely on N2 fixation for their N requirements, both N2 fixation and DON can be significant N-sources for carbon production and export following UCYN-C blooms in New Caledonia and by extension in the N-limited Ocean where similar events are likely to occur. This study confirms that in the South West Pacific, N2 fixation is a biogeochemically relevant process able to provide sufficient new N to drive new carbon production and export. These results are particularly important in the context of increasing temperatures that will probably increase the diazotrophic activity in the future ocean.","author":[{"propositions":[],"lastnames":["Berthelot"],"firstnames":["H"],"suffixes":[]},{"propositions":[],"lastnames":["Moutin"],"firstnames":["T"],"suffixes":[]},{"propositions":[],"lastnames":["L'Helguen"],"firstnames":["S"],"suffixes":[]},{"propositions":[],"lastnames":["Leblanc"],"firstnames":["K."],"suffixes":[]},{"propositions":[],"lastnames":["Hélias"],"firstnames":["S"],"suffixes":[]},{"propositions":[],"lastnames":["Grosso"],"firstnames":["O"],"suffixes":[]},{"propositions":[],"lastnames":["Leblond"],"firstnames":["N"],"suffixes":[]},{"propositions":[],"lastnames":["Charrière"],"firstnames":["B"],"suffixes":[]},{"propositions":[],"lastnames":["Bonnet"],"firstnames":["S"],"suffixes":[]}],"year":"2015","keywords":"ACTI, E3","bibtex":"@misc{berthelot_carbon_2015,\n\taddress = {UNESCO, Paris, France},\n\ttype = {Poster},\n\ttitle = {Carbon production and export are fuelled by dinitrogen fixation and dissolved organic nitrogen in the {South}-western {Pacific} {Ocean}: results from the {VAHINE} mesocosms experiment},\n\tabstract = {The oligotrophic ocean represents 80 \\% of the global surface ocean. Its role on CO2 sequestration has long been considered to be low, but this view is currently challenged by new studies highlighting alternative pathways for carbon export to the deep ocean. In these systems, carbon production is limited due to nitrogen (N) scarcity but dinitrogen (N2) fixation and dissolved organic nitrogen (DON) would represent significant nitrogen (N) sources for the ecosystem. Here we deployed in New Caledonia large in situ mesocosms in order to investigate (1) the contribution of N2 fixation and DON use to primary production (PP) and particle export and (2) the fate of the freshly produced particulate organic N (PON) i.e. whether it is preferentially accumulated and recycled in the water column or exported out of the system. The mesocosms were fertilized with phosphate (P) in order to prevent P-limitation and promote N2 fixation. The diazotrophic community was dominated by diatoms-diazotrophs associations (DDAs) during the first part of the experiment for 10 days (P1) followed by the unicellular N2-fixing cyanobacteria UCYN-C the 9 last days (P2) of the experiment. N2 fixation rates averaged 9.8±4.0 nM d-1 and 27.7±8.6 nM d-1 during P1 and P2, respectively. NO3- concentrations ({\\textless}40 nM) in the mesocosms were a negligible source of N indicating that N2 fixation was the main driver of new production all along the experiment. The contribution of N2 fixation to PP was not significantly different during P1 (9.0±3.3 \\%) and P2 (12.6±6.1 \\%). However, the e-ratio that quantifies the efficiency of a system to export particulate organic carbon (POCexport) compared to PP (e-ratio = POCexport/PP) was significantly higher (p{\\textless}0.05) during P2 (39.7±24.9 \\%) than during P1 (23.9±20.2 \\%) indicating that the production sustained by UCYN-C was more efficient at promoting C export than the production sustained by DDAs. During P1, PON was stable and the total amount of N provided by N2 fixation (0.10±0.02 µM) was not significantly different from the total amount of PON exported (0.10±0.04 µM), suggesting a rapid and probably direct export of the recently fixed N2 by the DDAs. During P2, both PON concentrations and PON export increased in the mesocosms by a factor 1.5-2. Unlike in P1, this PON production was not totally explained by the new N provided by N2 fixation. The use of DON, which concentrations decreased significantly from 5.3±0.5 µM to 4.4±0.5 µM, appeared to be the missing N source. The DON consumption of about 0.9 µM during P2 is even higher than the total amount of new N brought by N2 fixation (about 0.25 µM) during the same period. These results suggest that while DDAs mainly rely on N2 fixation for their N requirements, both N2 fixation and DON can be significant N-sources for carbon production and export following UCYN-C blooms in New Caledonia and by extension in the N-limited Ocean where similar events are likely to occur. This study confirms that in the South West Pacific, N2 fixation is a biogeochemically relevant process able to provide sufficient new N to drive new carbon production and export. These results are particularly important in the context of increasing temperatures that will probably increase the diazotrophic activity in the future ocean.},\n\tauthor = {Berthelot, H and Moutin, T and L'Helguen, S and Leblanc, K. and Hélias, S and Grosso, O and Leblond, N and Charrière, B and Bonnet, S},\n\tyear = {2015},\n\tkeywords = {ACTI, E3}\n}\n\n","author_short":["Berthelot, H","Moutin, T","L'Helguen, S","Leblanc, K.","Hélias, S","Grosso, O","Leblond, N","Charrière, B","Bonnet, S"],"key":"berthelot_carbon_2015","id":"berthelot_carbon_2015","bibbaseid":"berthelot-moutin-lhelguen-leblanc-hlias-grosso-leblond-charrire-etal-carbonproductionandexportarefuelledbydinitrogenfixationanddissolvedorganicnitrogeninthesouthwesternpacificoceanresultsfromthevahinemesocosmsexperiment-2015","role":"author","urls":{},"keyword":["ACTI","E3"],"downloads":0,"html":""},"search_terms":["carbon","production","export","fuelled","dinitrogen","fixation","dissolved","organic","nitrogen","south","western","pacific","ocean","results","vahine","mesocosms","experiment","berthelot","moutin","l'helguen","leblanc","hélias","grosso","leblond","charrière","bonnet"],"keywords":["acti","e3"],"authorIDs":[],"dataSources":["SawGM9CiMpS8S2icT"]}