Ratio of ³⁶Cl/Cl in ground ice of east Siberia and its application for chronometry

Abstract

Abundance of the cosmogenic nuclide chlorine‐36 (36Cl) was measured together with the chloride (Cl−) concentration in different horizons of Quaternary permafrost samples collected from various types of ground ice in the northeastern part of Siberia. The 36Cl/Cl in 32 samples ranged in value from 2.4 × 10−14 to 1.4 × 10−12. Nonetheless, after a few extreme values were excluded, these 36Cl/Cl ratios provided a local permafrost chronometry. The general concordance of the modeled ages with geological expectations and other chronological methods supports the potential power of the proposed dating method. However, the large observed change in ratios from higher to lower values during the transition from Last Glacial Maximum to Holocene climatic conditions remains unexplained. An attempt to make use of the corresponding beryllium‐10 (10Be) absolute concentrations in the same samples failed because input of 10Be attached to particulate matter into permafrost is unknown. Further 36Cl/Cl serial measurements of modern precipitation and fossil ground ice are needed to refine this dating method into a practical tool with a clear protocol.

Ice Complex permafrost of MIS5 age in the Dmitry Laptev Strait coastal region (East Siberian Arctic)

“…Krbetschek et al, 2000;Andreev et al, 2004;Schirrmeister et al, 2010Schirrmeister et al, , 2011c, thermo-luminescence (TL; e.g. Arkhangelov et al, 1996), 230 Th/U radioisotope disequilibria of frozen peat Wetterich et al, 2008), or ground ice 36 Cl/Cl radionuclide ratios (Gilichinsky et al, 2007;Tikhomirov and Blinov, 2009;Blinov et al, 2009), there are still large uncertainties when comparing different geochronological results. Some uncertainties are probably related to unknown influences of permafrost processes on chemical and physical parameters important to the age determination techniques.…”

“…The ice-wedgebased median base age in Oy7-03-101 IW is younger than expected, but the rather broad minimumemaximum age range indicated falls at least in the 230 Th/U age range. Blinov et al (2009) propose influences on the age determination by fractionation of the chlorine isotope ratio in the water phase during transport from the surface to ice wedges due to evaporation, condensation and/or chemical binding. Post-depositional lateral ion exchange between ice and the surrounding frozen sediment along concentration gradients, as well as partial ground-ice melt, might also alter the 36 Cl/Cl ages.…”

“…Using cosmogenic nuclides preserved in ice-wedges of the Buchchagy IC as a dating tool was first applied by Blinov et al (2009) . The ice-wedgebased median base age in Oy7-03-101 IW is younger than expected, but the rather broad minimumemaximum age range indicated falls at least in the 230 Th/U age range.…”

Ground-ice stable isotopes and cryostratigraphy reflect late Quaternary palaeoclimate in the Northeast Siberian Arctic (Oyogos Yar coast, Dmitry Laptev Strait)

“…the south coast of Bol'shoy Lyakhovsky Island, represents one of the best-studied Quaternary permafrost sites in northeast Siberia. To reconstruct the environmental dynamics of west Beringia since the mid-Pleistocene, extensive studies of the exposed frozen sediments and ground ice have been carried out (Arkhangelov et al, 1996;Kunitsky, 1996;Meyer et al, 2002b;Schirrmeister et al, 2002aSchirrmeister et al, , 2011bAndreev et al, 590 T. Opel et al: Ground-ice stable isotopes and cryostratigraphy reflect late Quaternary palaeoclimate Tumskoy, 2012;Wetterich et al, , 2014. In addition, the permafrost exposures of the Oyogos Yar mainland coast at the south shore of the Dmitry Laptev Strait have been studied, but less extensively (Ivanov, 1972;Gravis, 1978;Konishchev and Kolesnikov, 1981;Kaplina and Lozhkin, 1984;Tomirdiaro, 1984;Nagaoka et al, 1995;Kienast et al, 2011;Opel et al, 2011;Schirrmeister et al, 2011b;Rudaya et al, 2015, and references therein).…”

“…Moreover, the ages of late Pleistocene ice wedges are often close to or beyond the age limit of radiocarbon dating. However, new dating tools are in development and comprise Uranium isotopes (Ewing et al, 2015) as well as 36 Cl / Cl − dating for Middle to Late Pleistocene ground ice (Blinov et al, 2009). In many cases, syngenetic ice wedges are only indirectly dated by age determination of the surrounding host sediments.…”