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Ground ice chronometry with 36 Cl/ Cl

Ground ice chronometry with 36 Cl/ Cl. Alexander Blinov St. Petersburg State Polytechnic University, Saint Petersburg, Russia. Content and plan of the talk. We present the application of 36 Cl/Cl dating method to ground ice from the northeast Siberia and we discuss:

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Ground ice chronometry with 36 Cl/ Cl

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  1. Ground ice chronometry with 36Cl/Cl Alexander Blinov St. Petersburg State Polytechnic University, Saint Petersburg, Russia AMS Workshop, Bucharest, November 1, 2012

  2. Content and plan of the talk We present the application of 36Cl/Cl dating method to ground ice from the northeast Siberia and we discuss: • 36Cl as a potential chronometer • 36Clsources in ground ice • Ground ice collection for age determination • Measurements and results • Conclusions AMS Workshop, Bucharest, November 1, 2012

  3. Motivation of the research • Ground ice represents a unique natural archive containing ecological and climatic records • The most ancient permafrost from northeast Siberia could date back to 2 million years BP • In general the age of ice does not coincide with the age of surrounding sediments • Chronological methods beyond radiocarbon range reveal the age of sediments or organic remains and never the age of the ice AMS Workshop, Bucharest, November 1, 2012

  4. Constructing a radiochronology Three obligatory conditions of dating an object: The input function Q(t) is well defined The system stays closed during the dated time Additional internal sources I(t) are well defined Q(t) I(t) N(t) AMS Workshop, Bucharest, November 1, 2012

  5. Origin of 36Cl in the environment 36Cl → T1/2 = 301 thousand years Cosmic rays Cosmic ray induced nuclear cascade Atmospheric production Penetrating particles Primordial radioactivity 232Th, 238U, 235U In-situ production Man-made contamination? AMS Workshop, Bucharest, November 1, 2012

  6. 36Cl atmospheric transport Cosmogenic 36Cl produced in the atmosphere is involved in natural chlorine geochemical cycle mobile (HCl, CH3Cl) mobile (HCl, NaCl) 36Cl/Cl abundance is delivered to the ground level by atmospheric precipitation and then it is not changed by chemical reactions AMS Workshop, Bucharest, November 1, 2012

  7. 36Cl in modern precipitation across Europe From: Johnston, V. E., and F. McDermott (2008), The distribution of meteoric Cl-36 in precipitation across Europe in spring 2007, Earth Planet. Sci. Lett., 275, 154 – 164, doi:10.1016/j.epsl.2008.08.021 AMS Workshop, Bucharest, November 1, 2012

  8. 36Cl concentration in ground ice: a function of depth beneath the surface AMS Workshop, Bucharest, November 1, 2012

  9. Constructing the relative chronology Three obligatory conditions of the dating method: The 36Cl/Cl ratio is constant in surface precipitation After 36Cl/Cl is fixed in ice the system stays closed In situ production of 36Cl is negligible for moderate age The age of a datedsample relative to a reference sample can be calculatedbased on the law of radioactive decay whereτ36= 434 thousand years is the lifetime of36Cl. AMS Workshop, Bucharest, November 1, 2012

  10. Location of sampling sites in northeast Siberia A – Cape Svyatoy Nos B – Bol’shoy Lyakhovsky Island C – Oyogos Yar coast D – Khaptashinsky Yar E – Allaikha River F – Bol’shoy Khomus Yuryakh River AMS Workshop, Bucharest, November 1, 2012

  11. Overview schemes of the studied exposures Peat lenses and ice wedges of the Yukargirsky Suite covered by deposits of the Kuchchugui Suite (B, exposure L7-01) Ice wedge of the Yukagirsky Suite covered by deposits of the Kuchchugui Suite (B, subprofile L7-02) AMS Workshop, Bucharest, November 1, 2012

  12. AMS measurements of 36Cl/Cl AMS Workshop, Bucharest, November 1, 2012

  13. Field Data, Analytical Results and Calculated Ages AMS Workshop, Bucharest, November 1, 2012

  14. Field Data, Analytical Results, and Calculated Ages

  15. Local permafrost chronologies A – Cape Svyatoy Nos B – Bol’shoy Lyakhovsky Island C – Oyogos Yar coast D – Khaptashinsky Yar E – Allaikha River F – Bol’shoy Khomus Yuryakh River AMS Workshop, Bucharest, November 1, 2012

  16. Local permafrost chronologies A – Cape Svyatoy Nos B – Bol’shoy Lyakhovsky Island C – Oyogos Yar coast D – Khaptashinsky Yar E – Allaikha River F – Bol’shoy Khomus Yuryakh River AMS Workshop, Bucharest, November 1, 2012

  17. Problems • Holocene samples: reduced 36Cl/Cl ratio for most samples younger than 11 thousand years • Dating of small wedges could fail: possibility of boundary effects • No universaldating protocol AMS Workshop, Bucharest, November 1, 2012

  18. Conclusions 36Cl/Cl relative abundance in ground ice allowed revealing the previously unknown permafrost age. Existence of ground ice with age over 500 thousand years was demonstrated 36Cl/Cl ratios, which formed from 12–15 to 50 thousand years ago, may serve a base level for relative dating of ice sequences formed in the late and middle Pleistocene under similar climatic conditions Several local chronologies were constructed for syngenetic late and middle Pleistocene ground ice from northeast Siberia AMS Workshop, Bucharest, November 1, 2012

  19. Acknowledgments This work was carried out by several research teams and supported by different funds. The role of the team leaders is acknowledged. Prof. J. Beer Swiss Federal Institute of Aquatic Science and Technology, Duebendorf, Switzerland Prof. D. Gilichinsky Institute of Physicochemical and Biological Problems in Soil Science, Russian Academy of Sciences, Pushchino, Russia Dr. L. Schirrmeister Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany AMS Workshop, Bucharest, November 1, 2012

  20. Thank you for your attention!

  21. Bomb-peak in 36Cl ice-core records From: Heikkila U. et al., 36Cl bomb peak: comparison of modeled and measured data. Atmos. Chem. Phys., 9, 4145–4156, 2009 AMS Workshop, Bucharest, November 1, 2012

  22. 36Cl–Cl correlation in ground ice AMS Workshop, Bucharest, November 1, 2012

  23. 36Cl in rain water Dependence on precipitation rate Dependence on geographic position AMS Workshop, Bucharest, November 1, 2012

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