Constraining ice core chronologies with 39Ar and 81Kr

Paleoclimate reconstructions from ice core records can be hampered due to the lack of a reliable chronology, especially when the stratigraphy is disturbed and conventional dating methods cannot be readily applied. The noble-gas radioisotopes ⁸¹Kr and ³⁹Ar can in these cases provide robust constraints as they yield absolute, radiometric ages. ⁸¹Kr (half-life 229 ka) covers the time span of 50-1300 ka, which is particularly relevant for polar ice cores, whereas ³⁹Ar (half-life 269 a) with a dating range of 50-1800 a is suitable for high mountain glaciers. For a long time the use of ⁸¹Kr and ³⁹Ar for dating of ice samples was hampered by the lack of a detection technique that can meet its extremely small abundance at a reasonable sample size.

Here, we present ⁸¹Kr and ³⁹Ar dating of Antarctic and Tibetan ice cores with the detection method Atom Trap Trace Analysis (ATTA), using 5-10 kg of ice for ⁸¹Kr and 2-5 kg for ³⁹Ar. Recent advances in further decreasing the sample size and increasing the dating precision will be discussed. Current studies include ⁸¹Kr dating in shallow ice cores from the Larsen Blue ice area, East Antarctica, in order to retrieve climate signals from the last glacial termination. Moreover, an ³⁹Ar profile from a central Tibetan ice core has been obtained in combination with layer counting based on isotopic and visual stratigraphic signals. The presented studies demonstrate how ⁸¹Kr and ³⁹Ar can constrain the age range of ice cores and complement other methods in developing an ice core chronology.

 

[1] Z.-T. Lu, Tracer applications of noble gas radionuclides in the geosciences, Earth-Science Reviews 138, 196-214, (2014)
[2] C. Buizert, Radiometric ⁸¹Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica, Proceedings of the National Academy of Sciences, 111, 6876, (2014)

[3] L. Tian, ⁸¹Kr Dating at the Guliya Ice Cap, Tibetan Plateau, Geophysical Research Letters, (2019)

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