Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 14, 941-958, 2017
https://doi.org/10.5194/bg-14-941-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
01 Mar 2017
Manganese and iron reduction dominate organic carbon oxidation in surface sediments of the deep Ulleung Basin, East Sea
Jung-Ho Hyun1, Sung-Han Kim1, Jin-Sook Mok1, Hyeyoun Cho1, Tongsup Lee2, Verona Vandieken3, and Bo Thamdrup4 1Department of Marine Science and Convergence Engineering, Hanyang University, 55 Hanyangdaehak-ro, Ansan, Gyeonggi-do 15588, South Korea
2Department of Oceanography, Pusan National University, 2 Busandaehak-ro, Busan, 46241, South Korea
3Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Carl-von-Ossietzky-Str. 9–11, 26129 Oldenburg, Germany
4Nordic Center for Earth Evolution, Department of Biology, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
Abstract. Rates and pathways of benthic organic carbon (Corg) oxidation were investigated in surface sediments of the Ulleung Basin (UB) characterized by high Corg contents ( >  2.5 %, dry wt.) and very high contents of Mn oxides ( >  200 µmol cm−3) and Fe oxides (up to 100 µmol cm−3). The combination of geochemical analyses and independently executed metabolic rate measurements revealed that Mn and Fe reduction were the dominant Corg oxidation pathways in the center of the UB, comprising 45 and 20 % of total Corg oxidation, respectively. By contrast, sulfate reduction was the dominant Corg oxidation pathway, accounting for 50 % of total Corg mineralization in sediments of the continental slope. The relative significance of each Corg oxidation pathway matched the depth distribution of the respective electron acceptors. The relative importance of Mn reduction for Corg oxidation displays saturation kinetics with respect to Mn oxide content with a low half-saturation value of 8.6 µmol cm−3, which further implies that Mn reduction can be a dominant Corg oxidation process even in sediments with lower MnO2 content as known from several other locations. This is the first report of a high contribution of manganese reduction to Corg oxidation in offshore sediments on the Asian margin. The high manganese oxide content in the surface sediment in the central UB was maintained by an extreme degree of recycling, with each Mn atom on average being reoxidized ∼ 3800 times before permanent burial. This is the highest degree of recycling so far reported for Mn-rich sediments, and it appears linked to the high benthic mineralization rates resulting from the high Corg content that indicate the UB as a biogeochemical hotspot for turnover of organic matter and nutrient regeneration.

Citation: Hyun, J.-H., Kim, S.-H., Mok, J.-S., Cho, H., Lee, T., Vandieken, V., and Thamdrup, B.: Manganese and iron reduction dominate organic carbon oxidation in surface sediments of the deep Ulleung Basin, East Sea, Biogeosciences, 14, 941-958, https://doi.org/10.5194/bg-14-941-2017, 2017.
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The surface sediments of the Ulleung Basin (UB) in the East Sea are characterized by high organic carbon contents (> 2.5 %, dry wt.) and very high concentrations of Mn oxides (> 200 μmol cm−3) and Fe oxides (up to 100 μmol cm−3). For the first time in deep offshore sediments on the Asian margin with water depth over 2000 m, we report that Mn reduction and Fe reduction were the dominant organic carbon (Corg) oxidation pathways, comprising 45 % and 20 % of total Corg oxidation, respectively.
The surface sediments of the Ulleung Basin (UB) in the East Sea are characterized by high...
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