Isotopic Characteristics of Thermal Waters in the Mosfellssveit and ReykjavÌk Low-Temperature Areas, Iceland

Abstract

The paper focuses on the isotopic composition of thermal waters in five low-temperature areas within the Reykjavik region, Iceland. The waters have been utilized for decades and very little change in oxygen and hydrogen isotope ratios have been observed with time. The thermal waters are depleted in the stable isotopes of oxygen and hydrogen compared to the local precipitation but to a different degree. This is explained by the origin of the waters, which may either be represented by precipitation in the mountainous areas northeast of the Reykjavik region where isotopic composition of local precipitation is similar to the isotopic composition of the thermal waters or by the presence of a pre-Holocene component in some of the thermal fields. For the first time carbon isotopes are systematically studied within the areas. A clear and systematic difference is observed both in the 13C and 14C values for different fields. Accordingly, the carbon isotopes help in defining the systems and the origin of thermal waters. However, further studies are needed to conclude whether or not a pre-Holocene component is present in some of the geothermal waters.