Radiocarbon in Hydrologic Systems Containing Dissolved Magmatic Carbon Dioxide

In regions of active volcanism, the presence of magmatic carbon dioxide (CO 2 ) in regional hydrologic systems provides a radiocarbon-depleted tracer for delineating ground-water transport and mixing processes and provides a means of assessing regional magmatic carbon fluxes. Variations in the stable carbon isotopic composition (δ 13 C) and carbon-14 values of springs and surface waters from the southern Cascade Range show consistent patterns of carbon isotopic mixing between magmatic, biogenic, and atmospheric CO 2 reservoirs. Radiocarbon measurements of waters from the Lassen region in northern California were used to construct a ground-water carbon-14 contour map, revealing principal subsurface flow paths and a broad region of diffuse magmatic CO 2 flux.