Benthic foraminiferal Mn / Ca ratios reflect microhabitat preferences

Other literature type English OPEN
Koho, Karoliina A. ; Nooijer, Lennart J. ; Fontanier, Christophe ; Toyofuku, Takashi ; Kazumasa, Oguri ; Kitazato, Hiroshi ; Reichart, Gert-Jan (2017)

The Mn&thinsp;/&thinsp;Ca of carbonate tests of living (rose Bengal stained) benthic foraminifera (<i>Elphidium batialis</i>, <i>Uvigerina spp.</i>, <i>Bolivina spissa</i>, <i>Nonionellina labradorica</i> and <i>Chilostomellina fimbriata</i>) 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&thinsp;/&thinsp;Ca and redox chemistry, therefore allowing disentangling of previously observed trends. The Mn&thinsp;/&thinsp;Ca ratios were analyzed using laser ablation ICP-MS, allowing single-chamber determination of Mn&thinsp;/&thinsp;Ca. Incorporation of Mn into the carbonate tests reflects environmental conditions and is not influenced by ontogeny. The inter-species variability in Mn&thinsp;/&thinsp;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&thinsp;/&thinsp;Ca concentrations were always lower in the shallow infaunal <i>E. batialis</i> compared to those in the intermediate infaunal <i>Uvigerina spp.</i> The highest Mn&thinsp;/&thinsp;Ca was always recorded by the deep infaunal species <i>N. labradorica</i> and <i>C. fimbriata</i>. These results suggest that although partitioning differs, Mn&thinsp;/&thinsp;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.
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