[A-CG51] [JJ] 沿岸海洋生態系──１．水循環と陸海相互作用

[ACG51-09] 付着性二枚貝の貝殻に記録された炭素安定同位体比を用いた海底湧水環境の評価

*富永　 修¹、杉本 亮¹、北川 勝博¹、竹内 優¹、山田 誠²、小路 淳³、本田 尚美²、小林 志保⁴、谷口 真人² (1.公立大学法人　福井県立大学、2.総合地球環境学研究所、3.広島大学、4.京都大学)

キーワード：海底湧水、付着性二枚貝、イワガキ、炭素安定同位体、海底湧水速度、淡水割合

Submarine Groundwater Discharge (SGD) is often characterized by high concentration of nutrients and documented as an important pathway between land and sea contributing to the biological productivity in coastal waters. In the present study we investigated two subjects 1)whether the δ¹³C of ambient water reflect the proportion of fresh water flux in SGD, 2)whether the δ¹³C recorded in the shell of the sessile bibalve reflect the that of the ambient water. The SGD flux and the proportion of fresh water flux in SGD were measured by the seepage meter at Kamaiso beach along the Mt. Chokai volcanic coast in June and September 2016.The rock-oyster ( Crossostrea nippona ) was also sampled at Kamaiso Beach and adjacent 3 areas ( Mega, Takinoura, Torisaki). There was a positive significant relationship between salinity and theδ13C of ambient water (p<0.01). Theδ¹³C of the rock-oyster shell was high where the SGD flow rate was high and the positive significant correlation was found between the δ¹³C of the rock-oyster shell and that of ambient water. In order to estimate the proportion of fresh water flux in SGD from the δ¹³C of the rock-oyster shell, we used the two end member mixing equation including DIC concentration of both sea water and underground water. The average proportion of fresh water flux in SGD estimated from the mixing model ranged from 4 % (Torisaki) to 35 % (Mega). These values are higher than those estimated from the δ¹³C of ambient water (1.3 % Torisaki and 18.1 % Mega). The difference of these results are seems to be the difference of local SGD environment around rock-oyster.