ORIGIN OF C-14 IN ICELANDIC GROUNDWATER

We report the first attempt to data Icelandic groundwater by the radio carbon dating technique. We propose that boron concentrations of the w ater samples can be taken as a measure of the amount of dead CO2 in th e groundwater leached from rock. By assuming that the ratio of boron t o CO2 is the same in the rock and groundwater it is possible to correc t the C-14 concentration for the contribution of rock-derived carbon i n the groundwater and thus calculate the initial (undiluted) C-14 conc entration. When this correction is applied, the values for the cold an d warm waters lie in the range 60 to 110 pMC, which is in accordance w ith the estimated residence time for the groundwater. We have also cal culated the fractions of atmospheric and organic carbon in the water, based on the delta(13)C measurements, and the results agree well with the general hydrology and vegetational cover of the areas. Results fro m geothermal systems indicate that it is possible to use C-14 to estim ate relative age differences of the water in a particular geothermal a rea.