Atmospheric noble gases enter the water body of lakes and oceans by gas exchange at the air/water interface according to the local pressure, temperature and salinity conditions. During the deposition of sediment particles at the bottom of water bodies a part of the water (and the noble-gas species dissolved in it) overlying the sediment/water boundary is “trapped” in the pore space of the growing sediment column. As noble gases are in general not affected by any biogeochemical processes, deviations from the expected atmospheric equilibrium concentrations can be used to identify the relevant physical processes that affect the abundance of solutes in the sediment column. The characterization of the solute transport in the sediment column is necessary to understand the temporal evolution of concentration signals generated by, for example, climate forcing or fluids emanating from geochemical reservoirs located below the sediments.
After a short introduction on the methods to determine noble-gas abundances in the pore water of unconsolidated sediments, two recent case studies will be discussed:
- The spatial variability of the He release from solid earth determined in the sediments of Lake Van (Turkey).
- The strong attenuation of diffusive transport processes observed in a sediment core from the Stockholm Archipelago (Sweden) where an approximately 100 year old mass movement included a large amount of atmospheric gases in the sediment column.
An outlook on the ongoing research projects related to the non- conventional environment of unconsolidated sediments will close the presentation.