The final meltdown of dead-ice at the Holocene Thermal Maximum (8500–7400 cal. yr BP) in western Latvia, eastern Baltic

Abstract

It is commonly assumed that the majority of buried ice-blocks in Europe melted at the end of Late Glacial period and during the first part of the early-Holocene. We show, however, that scattered dead-ice-blocks may have been preserved in the ground until 8500 cal. yr BP. We analysed thermokarst features in Lake Ķikuru, western Latvia, by means of a multi-proxy approach (pollen, non-pollen palynomorphs, plant macrofossils, diatoms, loss-on-ignition, magnetic susceptibility, C:N ratio, carbon accumulation rate and radiocarbon dating). Abiotic and biotic processes following the ice-block meltdown suggests abrupt development of a thermokarst from 8500 to 7400 cal. yr BP. Important changes in local vegetation occurred with the deepening of a kettle-hole during the transition from a fen to a lake that nearly coincided with the appearance of the first fish at 7800 cal. yr BP, thus forming a clear indication of a lacustrine environment. Our study shows that a thin peat layer formed at first and, due to the meltdown of the ice-block, it gradually lowered to the bottom of the kettle-hole, and gyttja begun to accumulate afterwards. Given that thermokarst arise when the mean summer air temperature gradually increases to a value above the present-day temperature, we must assume that the local conditions must have been exceptional to secure ice-block from the meltdown for so long. Therefore, the legacy of the last ice age was still evident even ca. 5500 years after the Weichselian ice retreat from the eastern Baltic.

A submerged pine forest from the early Holocene in the Mecklenburg Lake District, northern Germany

“…) and to the Atlantic for northeastern Europe (Stivrins et al . ). Alternatively, local subsidence may have been triggered by karst processes in Palaeozoic (salt) or Mesozoic (carbonate, gypsum) sediments in the Pre‐Pleistocene underground.…”

Palaeosols and their cover sediments of a glacial landscape in northern central Europe: Spatial distribution, pedostratigraphy and evidence on landscape evolution

“…mostly record of basal peat under lacustrine gyttja) is considered to be mainly responsible for the formation of lake and mire basins in the Weichselian glacial belt of northern central Europe and beyond (e.g. Słowinski et al, 2015;Stivrins et al, 2017;Kaiser et al, 2018). The small round mire at FUER10-4 (40 m in diameter) can be hydrogenetically classified as a kettlehole mire (Kaiser et al, 2014a), generally being a typical feature of the Serrahn area, where c. 50 of them were recorded (Rowinsky and Kobel, 2011).…”

Geophysical, topographic and stratigraphic analyses of perialpine kettles and implications for postglacial mire formation

“…Peat formation in kettlehole mires (Joosten and Clarke 2002) was hypothesized in terms of two different mechanisms by Gaudig et al (2006): Through (i) the centripetal growth of a floating mat and the deposition of peat underneath (top-down, 'floating mat terrestrialisation') and (ii) the upward growth of peat (bottom-up, 'self-sealing mechanism'). As shown by a recent study of Stivrins et al (2017), peat formation in kettle holes can also begin very early during the initial meltdown of a totally buried ice block. In the course of subsequent melt-out, a lake has formed, the peat layer gradually lowered to the bottom of the kettle hole, and gyttja begun to accumulate on top.…”