Long-term Investigation of Sr- Isotope and Rare Earth Element Fractionation Processes Within Three Major Aquifers in the aspo Hard Rock Laboratory (Sweden)

Abstract

The 450m deep aspo Hard Rock Laboratory (aspo HRL) provides a unique opportunity to access different aquifer systems within the Precambrian granodioritic basement of the Baltic Shield. In this study, emphasis will be placed on systematic variations of the isotopic and chemical composition including fractionation patterns of rare earth elements (REE) of three different aquifers. The aim is to identify end-member groundwater compositions and increase the knowledge and understanding of the groundwater evolution, and water rock interaction, parameters which are important for the subsurface microbial activity in the aspo HRL. Groundwaters at the shallow and intermediate aquifers were influenced most from Baltic Sea water and meteoric water. The analyses of Sr-data and REE show especially long-term groundwater-rock interaction and delta O-18 values indicate the presence of glacial meltwater in the deep aquifer. During the 5years of investigation, significant chemical changes caused by internal mixing processes or present microbial activity were not observed.