Sleuthing the Fate of Water in Ancient Aquifers and Ice Cores

Precision analytical techniques developed for fundamental experiments in nuclear physics now enable routine measurements of ultra-low concentrations of Krypton radioisotopes in samples of water, ice, and gas.

Image courtesy of Argonne National Laboratory

The Science

A specialized magneto-optical atom trap called Atom Trap Trace Analysis (ATTA) allows scientists to detect single atoms of Krypton (Argon) at and below the part-per-trillion (part-per-quadrillion) level. Detecting the rare krypton-81 isotope (⁸¹Kr) with this unprecedented analytic sensitivity helps reveal the fate of water in ancient aquifers. Knowing how long water has been underground helps researchers understand how fast aquifers are recharged by surface water and how fast they move, leading to more accurate geological models.

The Impact

Rare isotope ^81,85Kr-, 39Ar-dating opens up new opportunities in the Earth sciences including practical water resource management, ocean circulations, and the study of our planet’s ancient climate.

Summary

A state-of-the-art Atom Trap Trace Analysis (ATTA) instrument has been developed by a team of physicists working at Argonne National Laboratory working in collaboration with Earth scientists and other supporting agencies in the U.S. and worldwide. The ages of groundwater, ranging from 200,000 to 1,000,000 years old, in the Nubian Aquifer underneath the Eastern Sahara Desert, the Great Artesian Basin of Australia, and the Guarani Aquifer of South America have been measured. These results reveal hydrologic behavior of huge aquifers, with important implications for climate history and water resource management. Application of rare isotope ^81,85Kr-, ³⁹Ar-dating using ATTA in other areas of Earth sciences now appears feasible. The radioisotope 85Kr is routinely measured as a residence-time tracer for young (<60 years) shallow groundwaters that are most susceptible to contamination. When combined with other tracers, ⁸⁵Kr measurements will improve the quality and reliability of groundwater flow and vulnerability assessments. A systematic survey of ³⁹Ar throughout the oceans could fill major gaps in our knowledge of deep ocean circulation and mixing, and allow better predictions of oceanic sequestration of atmospheric CO2. Polar ice cores have been used to reconstruct Earth’s past climate and atmospheric composition as far back as 800,000 years in time. ⁸¹Kr could potentially be used for dating of old ice with ages ranging from 100,000 – 1,500,000 years. In volcanic and geothermal systems, the analysis of crustal fluid samples for noble radionuclides ³⁹Ar, ⁸¹Kr, and ⁸⁵Kr could provide information on the origin, evolution, and migration of crustal fluids.

Contact

Dr. Zheng-Tian Lu
Argonne National Laboratory
[email protected]

Funding

Office of Science Nuclear Physics (NP) program

Publications

Sturchio, N. C. “One million year old groundwater in the Sahara revealed by krypton-81 and chlorine-36.” Geophys. Res. Lett. 31 L05503 (2004). [DOI: 10.1029/2003GL019234]