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Biogeosciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/bg-2016-547
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
12 Jan 2017
Review status
This discussion paper is under review for the journal Biogeosciences (BG).
Benthic foraminiferal Mn / Ca ratios reflect microhabitat preferences
Karoliina A. Koho1,2, Lennart J. de Nooijer3, Christophe Fontanier4,5,6, Takashi Toyofuku7, Oguri Kazumasa7, Hiroshi Kitazato7,8, and Gert-Jan Reichart2,3 1Department of Environmental Sciences, P.O. Box 65 (Viikinkaari 1), 00014 University of Helsinki, Finland
2Department of Earth Sciences – Geochemistry, Faculty of Geosciences, Utrecht University, P.O. Box 80.021, 3508 TA Utrecht, The Netherlands
3Department of Ocean Systems, NIOZ-Royal Netherlands Institute for Sea Research and Utrecht University, Den Burg, The Netherlands
4Ifremer, Géosciences marines, Z.I. Pointe du Diable CS10070, F29280 Plouzané, France
5Univ. of Bordeaux, Environnements et Paléo-environnements Océaniques et Continentaux, UMR 5805, F33600 Talence, France
6Univ. of Angers, F49035 Angers, France
7Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka, 237-0061, Japan
8Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku 108-8477, Tokyo, Japan
Abstract. The Mn / Ca of carbonate tests of living (rose Bengal stained) benthic foraminifera (Elphidium batialis, Uvigerina spp., Bolivina spissa, Nonionellina labradorica and Chilostomellina fimbriata) were determined in relation to pore water manganese (Mn) concentrations for the first time along a bottom water oxygen gradient across the continental slope along the NE Japan margin (western Pacific). The local BWO gradient differs from previous field study sites focusing on foraminiferal Mn / Ca and redox chemistry, therefore allowing disentangling of previously observed trends. The Mn / Ca ratios were analyzed using laser ablation ICP-MS, allowing single-chamber determination of Mn / Ca. Incorporation of Mn into the carbonate tests reflects environmental conditions and is not influenced by ontogeny. The inter-species variability in Mn / Ca varied as a function of their in-sediment habitat preferences and associated pore water chemistry, but also shows large interspecific differences in Mn partitioning. At each station, the Mn / Ca concentrations were always lower in the shallow infaunal E. batialis compared to those in the intermediate infaunal Uvigerina spp. The highest Mn / Ca was always recorded by the deep infaunal species N. labradorica and C. fimbriata. These results suggest that although partitioning differs, Mn / Ca ratios in the intermediate infaunal taxa are promising tools for paleoceanographic reconstructions as their microhabitat exposes them to higher variability in pore water Mn, thereby making them relatively sensitive recorders of redox conditions and/or bottom water oxygenation.

Citation: Koho, K. A., de Nooijer, L. J., Fontanier, C., Toyofuku, T., Kazumasa, O., Kitazato, H., and Reichart, G.-J.: Benthic foraminiferal Mn / Ca ratios reflect microhabitat preferences, Biogeosciences Discuss., doi:10.5194/bg-2016-547, in review, 2017.
Karoliina A. Koho et al.
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Here we report Mn / Ca ratios in living benthic foraminifera from NE Japan margin. The results show that the Mn incorporation directly reflects the environment where the foraminifera calcify. Foraminifera that live deeper in sediment, under greater redox stress, generally incorporating more Mn into their carbonate skeletons. As such, foraminifera living close to the Mn-reduction zone in sediment appear promising tools for paleoceanographic reconstructions of sedimentary redox conditions.
Here we report Mn / Ca ratios in living benthic foraminifera from NE Japan margin. The results...
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