, Volume 64, Issue 5, pp 705-712
Date: 19 Sep 2008

Sulfur stable isotopes indicate the source of sinking materials in a coastal bay: Otsuchi Bay, Sanriku, Japan

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Through 2004 and 2005, δ 34S of sinking material from Otsuchi Bay was measured at the center and rocky shore of the bay. At the center of the bay δ 34S was high (18∼21‰) in the material collected from April to November. However, δ 34S was low (9∼14‰) in the material collected from December to March. The increase in δ 34S in April was attributed to an increase in phytoplankton biomass because marine phytoplanktonic δ 34S is high. When δ 34S of sinking material was low, input of riverine material or bottom sediment resuspension were considered as the probable causes, because their δ 34S is low. Marine sulfur was always high (more than 70%) at both stations. The difference between the δ 34S 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 δ 34S.