Noble Gas Tracers in Groundwater Hydrology

Noble gas tracers have become indispensable tools in the study of groundwater systems due to their chemical inertness and well‐characterised physical properties. Dissolved concentrations of helium, neon, argon, krypton and xenon in aquifers record information on recharge temperature, palaeoclimate, subsurface residence time and mixing processes without being affected by biogeochemical reactions. Radiogenic and cosmogenic isotopes of these gases provide chronometers spanning decades to hundreds of millennia, while stable isotopic ratios of kr and xe can reconstruct water‐table depths and climatic shifts at the time of recharge. Advances in analytical techniques—from high‐precision mass spectrometry to atom‐trap trace analysis—now permit measurements on small sample volumes in field or laboratory settings. Collectively, these developments have broadened applications from dating and temperature reconstruction to quantifying surface water–groundwater exchange and evaluating the safety of deep geological repositories, thereby informing resource management and climate studies on a global scale.

Research from Nature Portfolio

Recent studies have demonstrated the power of noble gas tracers for reconstructing past hydrological changes and calibrating new dating methods. One investigation employed high‐precision measurements of dissolved kr and xe isotopic ratios in groundwater to reconstruct water‐table depth changes during the last deglaciation in Southern California. The results quantitatively captured a nearly 18 m decline in water‐table height linked to post‐glacial warming, illustrating a novel proxy for hydroclimatic transitions. In a separate study, the combination of iodine-129 dating with krypton-81 and helium-4 measurements in deep coastal aquifers revealed that in situ release of iodine from marine sediments can bias age interpretations. By calibrating iodine-129 against well‐constrained noble gas chronometers, researchers established a self-consistent framework for assessing groundwater residence times—an approach critical for siting and safety assessment of high-level radioactive waste repositories.

Noble Gas Tracers in Groundwater Hydrology publication trend

The graph below shows the total number of articles in noble gas tracers in groundwater hydrology across all publications each year (not limited to Nature Index journals).

Technical terms

Henry’s law: The principle that the concentration of a gas dissolved in water is proportional to its partial pressure in the contacting atmosphere, with solubility varying with temperature and pressure.

Cosmogenic isotope: A radioactive nuclide produced by interactions between cosmic rays and atoms in the atmosphere or subsurface (e.g., ³⁹Ar, ⁸¹Kr).

Noble gas temperature (NGT): A palaeothermometer derived from the equilibrium concentrations of multiple noble gases in groundwater, reflecting soil or surface air temperatures at recharge.

Excess air: Supersaturated noble gas concentrations in groundwater resulting from entrapped air bubbles at the moment of recharge, which can enhance tracer signals.

In situ production: Generation of isotopes within the aquifer matrix by radioactive decay or cosmic interactions rather than direct atmospheric equilibration.

References

1. Efficient injection of gas tracers into rivers: A tool to study Surface water–Groundwater interactions. Water Research (2024).
2. Evaluating the impact of muon-induced cosmogenic 39Ar and 37Ar underground production on groundwater dating with field observations and numerical modeling. The Science of The Total Environment (2023).
3. Reconstruction of the Pleistocene Paleoclimate From Deep Groundwater in Southern Germany From Noble Gas Temperatures Linked With Organic Radiocarbon Dating. Water Resources Research (2024).
4. Feasibility of 129I groundwater dating calibrated by both 81Kr and 4He for the assessment of deep geological repositories in Japan. Scientific Reports (2024).
5. Deglacial water-table decline in Southern California recorded by noble gas isotopes. Nature Communications (2019).