Sulfur stable isotopes indicate the source of sinking materials in a coastal bay: Otsuchi Bay, Sanriku, Japan
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- Carvalho de Carvalho, M., Hayashizaki, Ki. & Ogawa, H. J Oceanogr (2008) 64: 705. doi:10.1007/s10872-008-0059-4
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Through 2004 and 2005, δ34S of sinking material from Otsuchi Bay was measured at the center and rocky shore of the bay. At the center of the bay δ34S was high (18∼21‰) in the material collected from April to November. However, δ34S was low (9∼14‰) in the material collected from December to March. The increase in δ34S in April was attributed to an increase in phytoplankton biomass because marine phytoplanktonic δ34S is high. When δ34S of sinking material was low, input of riverine material or bottom sediment resuspension were considered as the probable causes, because their δ34S is low. Marine sulfur was always high (more than 70%) at both stations. The difference between the δ34S of sinking material collected from the different sampling stations indicates that marine macroalgae contribute to sinking material near the shore when phytoplankton is scarce. In conclusion, the relative influence of different material sources to sinking materials could be successfully estimated using δ34S.