Proposal for the methods to characterize fossil seawater

- Distribution of anions, cations and stable isotopes, and estimation on the groundwater residence time by measuring ³⁶Cl at the Taiheiyou Coal Mine -

Abstract

Recently, the interface between freshwate r and seawater in sub-seabed has been discussed actively by using a numerical simulation for construction of huge underground buildings and/or for various wastes disposal in the coastal area. Generally, groundwater flow rate will possibly be small in seawater side behind the interface, and solute transport will be controlled by diffusion phenomena. However, salt-water found in the sub-seabed and a deep stratum has not yet been considerably characterized. Furthermore, there are no criteria and procedures to verify that saltwater behind the interface is not only stagnant but the fossil seawater. In this study, we propose the methodology to characterize it based on information on groundwater residence time using a ³⁶Cl dating method and on groundwater origin from stable isotopes.