Characterisation and isotopic evolution of saline waters of the Outokumpu Deep Drill Hole, Finland - Implications for water origin and deep terrestrial biosphere

► δ2H, δ18O, and 87Sr/86Sr of saline groundwater in bedrock down to 2.5 km depth. ► Separate water and typesisolated ecosystems at different depths. ► Water evolution modelled with silicate hydrolysis. ► Water origin: meteoric water recharged under warmer climate. ► Inferred residence times of groundwater tens of millions of years.