Last Glacial Maximum active layer thickness in Western Europe, and the issue of ‘tundra gleys’ in loess sequences

Abstract

Late Marine Isotope Stage (MIS) 3 and MIS 2 loess-palaeosol sequences in Western Europe comprise alternating loess layer and 3-to 30-cm-thick bleached soil horizons with Fe-Mn oxide precipitations, which are usually interpreted as waterlogged active layers and referred to as 'tundra gleys'. Active layer thickness data derived from a regional climate model simulation and the fossils (shells, earthworm granules) found in 'tundra gleys' argue against such an assumption. Most of these horizons better correspond to Fe-depleted, slightly humic topsoil horizons or subsurface eluvial horizons and should be referred to as (incipient) Ag or Eg horizons. They formed during climate ameliorations associated with vegetation (cryptogams, herbs) development, possibly limited by long-lasting snow cover. Strong mixing usually occurred in these horizons due to the activity of anecic earthworms and frost activity.

Characterization and mapping of MIS‐2 thermal contraction crack polygons in Western Transdanubia, Hungary

“…The LGM permafrost simulation by Stadelmaier et al 92 failed to reconstruct permafrost in the study area at a depth of −0.7 m. By contrast, Bertran et al, 93 using the same climate model but considering a representative ground level of −1.5 m, were able to reconstruct discontinuous permafrost in Hungary. Active layer thickness (ALT) was found to have ranged between 2 and 3 m in the region.…”

“…Temperatures >4 C suggest that the sampled area (the southern part of the Great Hungarian Plain) was not under permafrost during the LGM. However, the possibility that the coldest phases of the LGM were not captured by the analyses of aquifer NGTs should be kept in mind.The LGM permafrost simulation by Stadelmaier et al92 failed to reconstruct permafrost in the study area at a depth of À0.7 m. By contrast, Bertran et al,93 using the same climate model but considering a representative ground level of À1.5 m, were able to reconstruct discontinuous permafrost in Hungary. Active layer thickness (ALT) was found to have ranged between 2 and 3 m in the region.Together, this suggests strongly that (a) the area was close to the southern permafrost boundary and (b) the sand wedges developed within the active layer or in a context of deep seasonal frost (depending on local parameters).…”

Optically‐Stimulated‐Luminescence Ages and Paleo‐Environmental Implications of Relict Frost Wedges in North–Central Bohemia, Czech Republic

“…Nevertheless, the new ages provide important chronological controls on the presence of past permafrost in the Czech Republic, which have so far been completely lacking in previous attempts at empirical or model estimates of past permafrost extent across the European lowlands (cf. [3,8,11,16,19,[22][23][24][25][26][27][28][29][30]).…”

“…Frost-weathering features and cryogenic carbonates in caves indicated that permafrost in and around the Bohemian and Most basins was at least 30-65 m thick at elevations <450 m asl [55,115] and model simulations suggested that its maximum thickness was 70-130 m [76,78]. The LGM active-layer thickness in lowland soils probably attained ~1-2 m [23,77]. Around this time, there were also the lowest MAGTs and MAATs inferred from borehole logs and former active-layer thickness, respectively, of ~−6°C to ~−4°C [75,76,117] and ~−7°C to ~−3°C [77], as well as a pronounced decline in noble gas recharge temperatures to values close to zero [118], which signal coldclimate conditions and the existence of permafrost.…”

“…But their chronology remains poorly established, inhibiting our knowledge of past permafrost evolution and associated climate conditions that continue to be debated even for the best-explored Last Glacial Maximum (LGM) 26.5-19 ka [21] (cf. [3,8,11,16,19,[22][23][24][25][26][27][28][29][30]). Numerical ages (mostly optically-stimulated-luminescence [OSL], thermoluminescence, or radiocarbon [ 14 C]) are only available for a tiny fraction of the identified frost wedges, with the majority of wedges being chronologically constrained by their stratigraphic position (e.g., [31][32][33][34]) or not at all due to unknown sedimentary situation or high financial costs for numerical dating.…”