Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 14, issue 7
Biogeosciences, 14, 1825-1838, 2017
https://doi.org/10.5194/bg-14-1825-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 14, 1825-1838, 2017
https://doi.org/10.5194/bg-14-1825-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 05 Apr 2017

Research article | 05 Apr 2017

Particle export fluxes to the oxygen minimum zone of the eastern tropical North Atlantic

Anja Engel1, Hannes Wagner1, Frédéric A. C. Le Moigne1, and Samuel T. Wilson2 Anja Engel et al.
  • 1GEOMAR Helmholtz Centre for Ocean Research Kiel, 24105 Kiel, Germany
  • 2Daniel K. Inouye Center for Microbial Oceanography: Research and Education, Department of Oceanography, University of Hawaii, Honolulu, HI 96822, USA

Abstract. In the ocean, sinking of particulate organic matter (POM) drives carbon export from the euphotic zone and supplies nutrition to mesopelagic communities, the feeding and degradation activities of which in turn lead to export flux attenuation. Oxygen (O2) minimum zones (OMZs) with suboxic water layers (<5µmol O2kg−1) show a lower carbon flux attenuation compared to well-oxygenated waters (>100µmol O2kg−1), supposedly due to reduced heterotrophic activity. This study focuses on sinking particle fluxes through hypoxic mesopelagic waters (<60µmol O2kg−1); these represent  ∼ 100 times more ocean volume globally compared to suboxic waters, but they have less been studied. Particle export fluxes and attenuation coefficients were determined in the eastern tropical North Atlantic (ETNA) using two surface-tethered drifting sediment trap arrays with seven trapping depths located between 100 and 600m. Data on particulate matter fluxes were fitted to the normalized power function Fz = F100 (z∕100)b, with F100 being the flux at a depth (z) of 100m and b being the attenuation coefficient. Higher b values suggest stronger flux attenuation and are influenced by factors such as faster degradation at higher temperatures. In this study, b values of organic carbon fluxes varied between 0.74 and 0.80 and were in the intermediate range of previous reports, but lower than expected from seawater temperatures within the upper 500m. During this study, highest b values were determined for fluxes of particulate hydrolyzable amino acids (PHAA), followed by particulate organic phosphorus (POP), nitrogen (PN), carbon (POC), chlorophyll a (Chl a) and transparent exopolymer particles (TEP), pointing to a sequential degradation of organic matter components during sinking. Our study suggests that in addition to O2 concentration, organic matter composition co-determines transfer efficiency through the mesopelagic. The magnitude of future carbon export fluxes may therefore also depend on how organic matter quality in the surface ocean changes under influence of warming, acidification and enhanced stratification.

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To better understand the role of oxygen for the biological carbon pump, we studied particle fluxes through hypoxic waters in the eastern tropical North Atlantic. Attenuation of organic carbon fluxes over depth was lower than expected from seawater temperatures, indicating co-effects of oxygen concentration. Differences were observed for individual organic components, suggesting that future carbon export fluxes may depend on changes in surface ocean organic matter quality under global change.
To better understand the role of oxygen for the biological carbon pump, we studied particle...
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