EGU2020-21651, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-21651
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Constraining ice core chronologies with 39Ar and 81Kr

Florian Ritterbusch1, Yan-Qing Chu1, Ilaria Crotti2, Xi-Ze Dong1, Ji-Qiang Gu1, Shui-Ming Hu1, Wei Jiang1, Amaelle Landais3, Volodya Lipenkov4, Zheng-Tian Lu1, Lili Shao5, Barbara Stenni2, Taldice Team6, Lide Tian5, A-Min Tong1, Wen-Hao Wang1, and Lei Zhao1
Florian Ritterbusch et al.
  • 1USTC Hefei, Hefei, China (florian@ustc.edu.cn)
  • 2Department of Environmental Sciences, Informatics and Statistics, Ca' Foscari University of Venice, Venice, Italy
  • 3IPSL/LSCE, CNRS/CEA/UVSQ/Université Paris Saclay, 91190 Gif sur Yvette, France
  • 4Arctic and Antarctic Research Institute, St Petersburg, Russia
  • 5Institute of International Rivers and Eco-security, Yunnan University
  • 6www.taldice.org

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 are not 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 from 50-1300 ka, which is particularly relevant for polar ice cores, whereas 39Ar (half-life 269 a) with a dating range of 50-1400 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 report on 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. Among others, we measured 81Kr in the lower section of Taldice ice core, which is difficult to date by conventional methods, and in the meteoric bottom of the Vostok ice core in comparison with an age scale derived from hydrate growth. Moreover, we have obtained an 39Ar profile for an ice core from central Tibet in combination with a timescale constructed by layer counting. The presented studies demonstrate how the obtained 81Kr and 39Ar ages can complement other methods in developing an ice core chronology, especially for the bottom part.

[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)

[4] http://atta.ustc.edu.cn

How to cite: Ritterbusch, F., Chu, Y.-Q., Crotti, I., Dong, X.-Z., Gu, J.-Q., Hu, S.-M., Jiang, W., Landais, A., Lipenkov, V., Lu, Z.-T., Shao, L., Stenni, B., Team, T., Tian, L., Tong, A.-M., Wang, W.-H., and Zhao, L.: Constraining ice core chronologies with 39Ar and 81Kr, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21651, https://doi.org/10.5194/egusphere-egu2020-21651, 2020

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Presentation version 1 – uploaded on 02 May 2020
  • CC1: Comment on EGU2020-21651, Giuliano Dreossi, 05 May 2020

    I've noticed something curious: in all the three dated cores (Vostok, Talos Dome, Tibetan Plateau), the penultimate 81Kr (Vostok and TALDICE) and the penultimate 39Kr (Tibetan Plateau) points are older than the last dated point, which appear to be deeper but younger; how is that possible? If it only happened once then it could be interpreted as disturbed layering of the ice, but three out of three times?

    • AC1: Reply to CC1, Florian Ritterbusch, 05 May 2020

      That's indeed curious for three completely independent ice cores. If it is just a statistical effect due to the large uncertainties of the Kr81 and Ar39 ages or if it really reflects disturbances in the stratigraphy, is something we are currently trying to find out for each case.
      For Vostok at that depth, one wouldn't expect such a strong folding (also from the hydrates) so here it is likely just the statistical uncertainty of the Kr81 ages. For Taldice (as you probably know better than me), the dO18 indicates that the bottom 60m are fairly homogenous which is supported by the Kr81 ages that barely increase towards the bottom. The middle point at 1576m was measured some time ago when our Kr81-analyzer had a lower precision which is why it has a larger error bar. For the tibetan ice core, the deepest Ar39 point is somewhat irritating. We are currently in the progress to check with Kr85, whether the sample has been contaminated with modern air (which would explain why it gets younger). We are also about to measure more samples from the bottom to clarify that point.
      In case it was a thought when asking that question: there is no background production from the bedrock or anything that could alter the Kr81 concentration.