Detection of submarine fresh groundwater discharge and its relation to onshore groundwater flow system: An example from offshore Kurobe alluvial fan

Distribution of the points of submarine fresh groundwater discharge was investigated at the offshore Kurobe alluvial fan. In this study, electric conductivity and temperature of seawater with less than one meter above seafloor were measured by towing electric conductivity and temperature sensors, and we found several discharge points where anomalies of electric conductivity were observed. Comparison of major chemical constituents of both submarine fresh groundwater and onshore groundwater indicated that the submarine fresh groundwater can be correlated with shallow groundwater of onshore Kurobe alluvial fan. Higher concentration of NO3_| in submarine fresh groundwater compared with that in river water suggested the possible importance of submarine groundwater discharge as its potential of being a contaminant pathway to coastal sea.