Dating of syngenetic ice wedges in permafrost with 36Cl

A new method of permafrost dating with the cosmogenic radionuclide Cl-36 is presented. In the first application, syngenetic ice wedges are dated using the ratio of Cl-36 and Cl concentrations in ice as the signal. Cl-36 is produced in the atmosphere by nuclear reactions of cosmic rays on argon. Stable chlorine enters the atmosphere from the oceans. Their ratio does not depend on chloride concentration in precipitations and on sublimation of snow. In situ production of Cl-36 in permafrost ice via cosmic ray-induced reactions and neutron capture are calculated and the dating age limit is estimated as 3 million years. Cl-36/Cl ratios in permafrost samples from cape Svyatoy Nos (Laptev Sea coast), North-Eastern Siberia, are measured by accelerator mass spectrometry. Analysis of the first results and the calculated dates support the feasibility of the Cl-36 permafrost dating method. (C)2007 Elsevier Ltd. All rights reserved.