Dark oxygen in the deep geobiosphere of the geological repository (DODGE)

In Finland and Sweden, the spent nuclear fuel repositories are situated at a depth of 400 – 450 m below the ground surface in bedrock chambers where strictly anoxic conditions are predicted to decrease the rate of biotic and abiotic processes that could adversely affect the long-term stability of the repository sites. Recently, the presence and production of oxygen in the dark deep subsurface has been demonstrated which may necessitate a re-evaluation of the biogeochemical processes that affect the long-term safety of the deep geological repository environment. The objective of the SAFER2028 funded DODGE project is to evaluate the presence of free oxygen in continental deep groundwater environments, understand its origin and production pathways, and assess its effects on microbial processes in the deep biosphere. The project contains both field and laboratory studies and is planned for 2 years. During the first year, fluid sampling, laboratory incubations, and hydrogeochemical and microbiological analyses have been performed to examine the O2 and H2 content in the dissolved and gas phase, to determine isotopic composition and source of these gases, and to assess the microbial communities and their metabolic potential affecting the production and consumption of oxygen and hydrogen as well as related cycles of redox sensitive nutrients in the deep geobiosphere.