[A-CG55] 沿岸海洋⽣態系─１．⽔循環と陸海相互作⽤

[ACG55-P01] アサリ貝殻の炭素・酸素安定同位体比を用いた近過去の地下水環境復元

*富永 修¹、戸邉 星良¹、石田 健大¹ (1.公立大学法人　福井県立大学)

キーワード：海底湧水、炭素安定同位体、酸素安定同位体、貝殻

We tried to reconstitute the environmental condition of Submarine Groundwater Discharge (SGD) in the near past by using carbon and oxygen stable isotope ratio in the shell of Manila clam (Ruditapes philippinarum). We conducted the rearing experiments of Manila clam collected at Mie Prefecture under field conditions. The field experiment was carried out at 5 sites under different SGD condition in Obama Bay, Japan from September 5th to October 24th 2019. A small piece of the shell was cut from the shell edge along the major growth axis. A cross section (1mm thick) was then cut . Calcium carbonates samples were drilled to a depth of 500 μm in the middle of the prismatic layer using a high-precision micromill “GEOMILL326” fitted with a 300 μm diameter drill bit. The contribution rates (FGRc and FGRo) of SGD were calculated by using the two end member mixing equation. In Obama Bay, The FGRc estimated from the shell were well consistent with that estimated from the δ¹³C of ambient water. However, FGRo (which was calculated byδ¹⁸O) was not always consistent. Possible reason for the error as follows; the water temperature substituted in the equation which was used for estimating the δ¹⁸O in the ambient water in the near past was not suitable.