Past climate changes and permafrost depth at the Lake El'gygytgyn site: implications from data and thermal modeling

Abstract

Abstract. This study focuses on the temperature field observed in boreholes drilled as part of interdisciplinary scientific campaign targeting the El'gygytgyn Crater Lake in NE Russia. Temperature data are available from two sites: the lake borehole 5011-1 located near the center of the lake reaching 400 m depth, and the land borehole 5011-3 at the rim of the lake, with a depth of 140 m. Constraints on permafrost depth and past climate changes are derived from numerical simulation of the thermal regime associated with the lake-related talik structure. The thermal properties of the subsurface needed for these simulations are based on laboratory measurements of representative cores from the quaternary sediments and the underlying impact-affected rock, complemented by further information from geophysical logs and data from published literature.The temperature observations in the lake borehole 5011-1 are dominated by thermal perturbations related to the drilling process, and thus only give reliable values for the lowermost value in the borehole. Undisturbed temperature data recorded over more than two years are available in the 140 m deep land-based borehole 5011-3. The analysis of these observations allows determination of not only the recent mean annual ground surface temperature, but also the ground surface temperature history, though with large uncertainties. Although the depth of this borehole is by far too insufficient for a complete reconstruction of past temperatures back to the Last Glacial Maximum, it still affects the thermal regime, and thus permafrost depth. This effect is constrained by numerical modeling: assuming that the lake borehole observations are hardly influenced by the past changes in surface air temperature, an estimate of steady-state conditions is possible, leading to a meaningful value of 14 ± 5 K for the post-glacial warming. The strong curvature of the temperature data in shallower depths around 60 m can be explained by a comparatively large amplitude of the Little Ice Age (up to 4 K), with low temperatures prevailing far into the 20th century. Other mechanisms, like varying porosity, may also have an influence on the temperature profile, however, our modeling studies imply a major contribution from recent climate changes.

Multivariate statistic and time series analyses of grain-size data in quaternary sediments of Lake El'gygytgyn, NE Russia

“…Gurov et al, 2007;Stone et al, 2009). The lake is surrounded by continuous permafrost, whose onset can presumably be traced back to the late Pliocene (Glushkova and Smirnov, 2007), and which is assumed to have a thickness of about 330-360 m with an unfrozen talik underneath the lake today (Mottaghy et al, 2013). The recent geomorphologic shape of the lake (Fedorov and Kupolov, 2005); red line: profile A to B.…”

Preliminary estimation of Lake El'gygytgyn water balance and sediment income

“…Lake El'gygytgyn is located in the zone of continuous permafrost (Yershov, 1998;Schwamborn et al, 2012). The thickness of permafrost in the crater is estimated to be about 350 m (Mottaghy et al, 2013;Schwamborn et al, 2012). In summer 2003 the active layer varied between 0.4 m in silty material and 0.8 m in sand and gravel (Schwamborn et al, 2012).…”

Taliks, cryopegs, and permafrost dynamics related to channel migration, Colville River Delta, Alaska

“…Some direct observations on the geometry and properties of taliks and cryopegs are available in the literature, with most of them focused at shallow depths and/or obtained from limited data, implying that conclusions may have been partially based on assumptions rather than mainly on field measurements. Thorough field assessments that include drilling, soil sampling, laboratory testing, and measuring ground temperatures and groundwater levels at depths greater than tens of meters are typically challenging and expensive.…”