Extensive hydrogen supersaturations in the western South Atlantic Ocean suggest substantial underestimation of nitrogen fixation.

Moore, Robert M., Kienast, Markus, Fraser, Michael, Cullen, John J., Deutsch, Curtis, Dutkiewicz, Stephanie, Follows, Michael J. and Somes, Christopher J. (2014) Extensive hydrogen supersaturations in the western South Atlantic Ocean suggest substantial underestimation of nitrogen fixation. Open Access Journal of Geophysical Research: Oceans, 119 (7). pp. 4340-4350. DOI 10.1002/2014JC010017.

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Abstract

The nitrogen cycle is fundamental to Earth's biogeochemistry. Yet major uncertainties of quantification remain, particularly regarding the global oceanic nitrogen fixation rate. Hydrogen is produced during nitrogen fixation and will become supersaturated in surface waters if there is net release from diazotrophs. Ocean surveys of hydrogen supersaturation thus have the potential to illustrate the spatial and temporal distribution of nitrogen fixation, and to guide the far more onerous but quantitative methods for measuring it. Here we present the first transect of high resolution measurements of hydrogen supersaturations in surface waters along a meridional 10,000 km cruise track through the Atlantic. We compare measured saturations with published measurements of nitrogen fixation rates and also with model-derived values. If the primary source of excess hydrogen is nitrogen fixation and has a hydrogen release ratio similar to Trichodesmium, our hydrogen measurements would point to similar rates of fixation in the North and South Atlantic, roughly consistent with modelled fixation rates but not with measured rates, which are lower in the south. Possible explanations would include any substantial nitrogen fixation by newly discovered diazotrophs, particularly any having a hydrogen release ratio similar to or exceeding that of Trichodesmium; under-sampling of nitrogen fixation south of the equator related to excessive focus on Trichodesmium; and methodological shortcomings of nitrogen fixation techniques that cause a bias towards colonial diazotrophs relative to unicellular forms. Alternatively our data are affected by an unknown hydrogen source that is greater in the southern half of the cruise track than the northern.

Document Type: Article
Additional Information: WOS:000340415500019
Keywords: dissolved hydrogen; nitrogen fixation; Atlantic Ocean
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BM Biogeochemical Modeling
OceanRep > SFB 754 > B1
OceanRep > The Future Ocean - Cluster of Excellence
OceanRep > SFB 754
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1002/2014JC010017
ISSN: 2169-9275
Projects: SFB754, Future Ocean
Date Deposited: 08 Jul 2014 08:50
Last Modified: 04 Apr 2019 13:29
URI: http://oceanrep.geomar.de/id/eprint/25283

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