Heterotrophic denitrification vs. autotrophic anammox – quantifying collateral effects on the oceanic carbon cycle
The conversion of fixed nitrogen to N<sub>2</sub> in suboxic waters is estimated to contribute roughly a third to total oceanic losses of fixed nitrogen and is hence understood to be of major importance to global oceanic production and, therefore, to the role of the ocean...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2010-08-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/7/2327/2010/bg-7-2327-2010.pdf |
| _version_ | 1818806107116666880 |
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| author | W. Koeve P. Kähler |
| author_facet | W. Koeve P. Kähler |
| author_sort | W. Koeve |
| collection | DOAJ |
| description | The conversion of fixed nitrogen to N<sub>2</sub> in suboxic waters is estimated to contribute roughly a third to total oceanic losses of fixed nitrogen and is hence understood to be of major importance to global oceanic production and, therefore, to the role of the ocean as a sink of atmospheric CO<sub>2</sub>. At present heterotrophic denitrification and autotrophic anammox are considered the dominant sinks of fixed nitrogen. Recently, it has been suggested that the trophic nature of pelagic N<sub>2</sub>-production may have additional, "collateral" effects on the carbon cycle, where heterotrophic denitrification provides a shallow source of CO<sub>2</sub> and autotrophic anammox a shallow sink. Here, we analyse the stoichiometries of nitrogen and associated carbon conversions in marine oxygen minimum zones (OMZ) focusing on heterotrophic denitrification, autotrophic anammox, and dissimilatory nitrate reduction to nitrite and ammonium in order to test this hypothesis quantitatively. For open ocean OMZs the combined effects of these processes turn out to be clearly heterotrophic, even with high shares of the autotrophic anammox reaction in total N<sub>2</sub>-production and including various combinations of dissimilatory processes which provide the substrates to anammox. In such systems, the degree of heterotrophy (ΔCO<sub>2</sub>:ΔN<sub>2</sub>), varying between 1.7 and 6.5, is a function of the efficiency of nitrogen conversion. On the contrary, in systems like the Black Sea, where suboxic N-conversions are supported by diffusive fluxes of NH<sub>4</sub><sup>+</sup> originating from neighbouring waters with sulphate reduction, much lower values of ΔCO<sub>2</sub>:ΔN<sub>2</sub> can be found. However, accounting for concomitant diffusive fluxes of CO<sub>2</sub>, the ratio approaches higher values similar to those computed for open ocean OMZs. Based on this analysis, we question the significance of collateral effects concerning the trophic nature of suboxic N-conversions on the marine carbon cycle. |
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| id | doaj.art-6c8cbaec847b4960ac47b7f5521a3ce2 |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-12-18T19:04:30Z |
| publishDate | 2010-08-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj.art-6c8cbaec847b4960ac47b7f5521a3ce22022-12-21T20:56:26ZengCopernicus PublicationsBiogeosciences1726-41701726-41892010-08-01782327233710.5194/bg-7-2327-2010Heterotrophic denitrification vs. autotrophic anammox – quantifying collateral effects on the oceanic carbon cycleW. KoeveP. KählerThe conversion of fixed nitrogen to N<sub>2</sub> in suboxic waters is estimated to contribute roughly a third to total oceanic losses of fixed nitrogen and is hence understood to be of major importance to global oceanic production and, therefore, to the role of the ocean as a sink of atmospheric CO<sub>2</sub>. At present heterotrophic denitrification and autotrophic anammox are considered the dominant sinks of fixed nitrogen. Recently, it has been suggested that the trophic nature of pelagic N<sub>2</sub>-production may have additional, "collateral" effects on the carbon cycle, where heterotrophic denitrification provides a shallow source of CO<sub>2</sub> and autotrophic anammox a shallow sink. Here, we analyse the stoichiometries of nitrogen and associated carbon conversions in marine oxygen minimum zones (OMZ) focusing on heterotrophic denitrification, autotrophic anammox, and dissimilatory nitrate reduction to nitrite and ammonium in order to test this hypothesis quantitatively. For open ocean OMZs the combined effects of these processes turn out to be clearly heterotrophic, even with high shares of the autotrophic anammox reaction in total N<sub>2</sub>-production and including various combinations of dissimilatory processes which provide the substrates to anammox. In such systems, the degree of heterotrophy (ΔCO<sub>2</sub>:ΔN<sub>2</sub>), varying between 1.7 and 6.5, is a function of the efficiency of nitrogen conversion. On the contrary, in systems like the Black Sea, where suboxic N-conversions are supported by diffusive fluxes of NH<sub>4</sub><sup>+</sup> originating from neighbouring waters with sulphate reduction, much lower values of ΔCO<sub>2</sub>:ΔN<sub>2</sub> can be found. However, accounting for concomitant diffusive fluxes of CO<sub>2</sub>, the ratio approaches higher values similar to those computed for open ocean OMZs. Based on this analysis, we question the significance of collateral effects concerning the trophic nature of suboxic N-conversions on the marine carbon cycle.http://www.biogeosciences.net/7/2327/2010/bg-7-2327-2010.pdf |
| spellingShingle | W. Koeve P. Kähler Heterotrophic denitrification vs. autotrophic anammox – quantifying collateral effects on the oceanic carbon cycle Biogeosciences |
| title | Heterotrophic denitrification vs. autotrophic anammox – quantifying collateral effects on the oceanic carbon cycle |
| title_full | Heterotrophic denitrification vs. autotrophic anammox – quantifying collateral effects on the oceanic carbon cycle |
| title_fullStr | Heterotrophic denitrification vs. autotrophic anammox – quantifying collateral effects on the oceanic carbon cycle |
| title_full_unstemmed | Heterotrophic denitrification vs. autotrophic anammox – quantifying collateral effects on the oceanic carbon cycle |
| title_short | Heterotrophic denitrification vs. autotrophic anammox – quantifying collateral effects on the oceanic carbon cycle |
| title_sort | heterotrophic denitrification vs autotrophic anammox quantifying collateral effects on the oceanic carbon cycle |
| url | http://www.biogeosciences.net/7/2327/2010/bg-7-2327-2010.pdf |
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