Radiokrypton Dating for Earth Sciences

A selected list of earth science projects applying radiokrypton dating is provided below.  An overview of the ATTA effort is provided under Laboratory for Radiokrypton Dating.

Guarani Aquifer, Brazil

Radiogenic 4He produced by the alpha-decay of uranium and thorium in the Earth's mantle and crust is degassed to the atmosphere and eventually escapes to outer space. The continental crustal flux has not been directly measured on the surface and its migration pathways to the atmosphere are poorly understood. Here, we show that crustal 4He reaches the atmosphere primarily by the surficial discharge of deep groundwater. This is based on a survey of 3He, 4He, and 81Kr in the deep, continental-scale Guarani aquifer in Brazil. Our results indicate that groundwater discharge regulates crustal degassing by integrating 4He produced over a half to one million year time scale, and suggest that the assumption of a steady-state between production and degassing fluxes, and the resulting atmospheric residence time of 4He, should be re-examined.

  • Aggarwal, P.K. et al., (2014) Nature Geoscience, in press, DOI:10.1038/ngeo2302

 

Taylor Glacier, Antarctica

We present the first successful 81Kr-Kr radiometric dating of ancient polar ice. Krypton was extracted from the air bubbles in four ~350 kg polar ice samples from Taylor Glacier in the McMurdo Dry Valleys, Antarctica, and dated using Atom Trap Trace Analysis. The 81Kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a root mean square offset of 6.5 +/- 2.5 ka. We show that ice from the Eemian interglacial period (130-115 ka BP) can be found in abundance near the surface of Taylor Glacier. Our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available, greatly enhancing their scientific value as archives of old ice and meteorites. As sample requirements continue to decrease, 81Kr dating of ice cores is a future possibility.

  • Buizert, C. et al., (2014) Proceedings of the National Academy of Sciences, 111, 6876, DOI:10.1073/pnas.132032911 (See accompanying Commentary : Aeschbach-Hertig, W. ibid)

 


Waste Isolation Pilot Plant (WIPP), New Mexico

We measured 81Kr in two Culebra monitoring wells near the WIPP site, and compared 81Kr model ages with reverse particle-tracking results of well-calibrated flow models.  The 81Kr model ages are ~130,000 and ~330,000 yr for high-transmissivity and low-transmissivity portions of the aquifer, respectively. Compared with flow model results that yield younger mean hydraulic ages, the 81Kr data imply substantial physical attenuation of conservative solutes in the Culebra Dolomite aquifer and provide limits on the effective diffusivity of contaminants into adjacent formations.


Yellowstone Geothermal Gas, Wyoming

A reconnaissance investigation of noble gas radionuclides (39Ar, 81Kr, and 85Kr) in gas emissions from several geothermal features at Yellowstone National Park was performed to explore tracer applications of these nuclides in an active hydrothermal system.


Nubian Aquifer, Egypt

Measurements of 81Kr/Kr in deep groundwater from the Nubian Aquifer (Egypt) were performed. 81Kr ages range from ∼2×105 to ∼1×106 yr, correlate with 36Cl/Cl ratios, and are consistent with lateral flow of groundwater from a recharge area near the Uweinat Uplift in SW Egypt. Low δ2H values of the 81Kr-dated groundwater reveal a recurrent Atlantic moisture source during Pleistocene pluvial periods. These results indicate that the 81Kr method for dating old groundwater is robust and such measurements can now be applied to a wide range of hydrologic problems.