Dating of syngenetic ice wedges in permafrost with 36Cl

Stable isotope and gas properties of two climatically contrasting (Pleistocene and Holocene) ice wedges from Cape Mamontov Klyk, Laptev Sea, northern Siberia

“…The horizontal girdles of the c-axes with a localized maximum have several potential explanations: (a) gravity settling of individual snow grains in a narrow vertical crack; (b) deformation of ice in the ice wedge during cyclic contractions; or (c) a combination of these processes. The spherical bubbles indicate that this ice wedge was not formed exclusively by freezing of liquid water as in lake ice (Andersen et al, 1998;Lorrain et al, 2002) or in some ice wedges (St-Jean et al, 2011;French, 2007), supporting a snow-water mixture hypothesis rather than only water infilling for the ice wedge genesis. The total gas content is low in comparison with a dry firn densification process (between one-tenth and one-third of the value of a dry firnification process; Martinerie et al, 1992) implying liquid water contribution to the ice formation.…”

“…The lack of reaction of our ice wedge sediments to an HCl "attack" however does not support the existence of significant amounts of CaCO 3 . Biological respiration could be an active process since bacteria and microbial communities have been identified in permafrost ice and in ice wedges (Gilichinsky et al, 2007;Katayama et al, 2007;Steven et al, 2008). Specific studies on these organisms would enable confirmation of this hypothesis.…”

Sedimentary characteristics and origin of the Late Pleistocene Ice Complex on north-east Siberian Arctic coastal lowlands and islands – A review

“…Cryoplanation terraces are formed around these elevations at various levels. The lowest terrace at about 30 m asl is covered by Ice Complex deposits, which are underlain by Middle Pleistocene terrestrial deposits (Nikolskiy et al, 1999;Nikolskiy and Basilyan, 2004;Gilichinsky et al, 2007). The Ice Complex thickness is about 10 m. The width of ice wedges is 2e3 m and the spacing between ice wedges is 10e12 m. The cryostructure is predominantly ice-banded and lens-like reticulated between ice bands.…”

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

“…Continuous chronologies of permafrost do not extend beyond the limit of radiocarbon, and there are but few reports with indirect dates of mid‐Pleistocene permafrost [e.g., Froese et al , 2008]. The recently proposed geochronology method using the long‐lived cosmogenic radionuclide 36 Cl [ Gilichinsky et al , 2007] could potentially extend the dating range beyond several hundred thousand years; in so doing, this method would find a wide variety of applications in Quaternary paleoenvironmental and paleoecological reconstructions, e.g., estimating the time scale for the long‐term preservation of fossils, tracing the history of greenhouse gases, and determining the age of inclusions of viable microorganisms adapted to a permanently frozen environment.…”

“…The mean lifetime of 36 Cl is τ 36 = T 1/2 / ln 2 = 434,000 years. After the meteoric component following the surface water flow is incorporated into the permafrost, the ratio of 36 Cl to stable chlorine decreases with time by the process of exponential radioactive decay: It was assumed [ Gilichinsky et al , 2007] that after an ice wedge system closed, the time interval Δ t since formation of its horizons could be calculated according to from the corresponding 36 Cl/Cl ratios: For a surface base sample of zero age, gives the absolute age of the deeper sample. The precondition of the proposed method's validity is the constant surface 36 Cl/Cl over Δ t .…”