多変量解析法を用いた北海道函館平野における深部地下水の供給源の推定

抄録

Chemical compositions and sulfur isotopic ratios of sulfate of deep groundwater in Hakodate Plane, Japan, were analyzed in order to characterize a deep groundwater system in this area. Most samples are classified into two groups: non-carbonate alkali and carbonate alkali waters. Based on the principle components analysis, one of multivariate analysis, the groundwaters in this study can be described by mixing with at least three end-member components of waters, i.e., seawater, deep groundwater containing volcanic material, and dilute shallow groundwater. The seawater component contributed more than the other components. Sulfur isotopic ratios (δ³⁴S) are in the range from +7.2 to +24.7%o. The δ³⁴S values higher than that of seawater (+20.3‰) would be attributed to the effect of bacterial sulfate reduction. The δ³⁴S values lower than that of seawater in two samples may result from the contribution of sulfur derived from volcanic material. These sample locations aligned along the northwest-southeast line in the Hakodate plane. Since the crater of Zenikamezawa, a submarine volcano erupted about 33,000-45,000 years ago, is located on the extension of the line, the volcanic material from this volcano may affect the deep groundwater chemistry and sulfur isotopic composition.