Millennial-scale fluctuations of palaeo-ice margin at the southern fringe of the last Fennoscandian Ice Sheet

Abstract

Abstract. The paper presents the first terrestrial record of millennial-scale palaeo-ice margin oscillations at the southern fringe of the last Fennoscandian Ice Sheet (FIS) during the last glacial cycle. The study area is located in northern Poland close to the last FIS maximum limit. The chronology and dynamics of palaeo-ice margin oscillations at the southern fringe of the FIS are based on combined luminescence and 10Be surface exposure dating. Optically stimulated luminescence (OSL) was used to date sandy deposits (fluvioglacial sediments and aeolian deposits filling fossil periglacial wedges) intercalating basal till layers. The most likely age of the tills was constrained by Bayesian modelling of the sequence of OSL ages and lithostratigraphy. 10Be surface exposure dating was used on erratic boulders left during the final retreat of the last FIS and resting on the surface of glacial landforms. Our results, which are mainly based on OSL chronology and Bayesian modelling, indicate millennial-scale oscillations of the last FIS in northern Poland between ∼19 and ∼17 ka. The last FIS retreated and re-advanced over a relatively short period of time (2–3 ka), leaving lithostratigraphic records (basal tills) of three ice re-advances over a millennial-scale cycle: 19.2±1.1, 17.8±0.5 and 16.9±0.5 ka. Despite 10Be surface exposure ages obtained for 14 erratic boulders being poorly clustered, the main mode of age distribution occurs at ∼18 ka and indicates a possible signal of the ice sheet retreat after one of the re-advances. We explore the dynamics of these oscillations and compare the proposed cycles of the southern FIS advances and retreats with existing patterns of the last deglaciation and millennial-scale fluctuations of the last FIS inferred from marine records.

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

“…The pairwise OSL ages tended to be randomly distributed within the individual frost wedges (Table 3; Figure 2), which is consistent with other studies (e.g., [22,41,46,48]). This may be due either to spatially uneven cracking and infilling, possible secondary mixing with materials brought in later, or uncertainties in the OSL ages.…”

“…However, wedge activity peaked at 16.1 ± 1.3 ka under cold-climate conditions of Heinrich Stadial 1/Greenland Stadial 2.1a (Figure 3). The development of the frost wedges at Uhersko was consistent with the timing of indirectly dated frost wedges in the southern Bohemia, Czech Republic, which probably originated after 18.7 ± 1.9 ka [64], as well as with an extensive formation of frost wedges and other kinds of patterned ground in other central and western European lowlands, such as Belgium [35], France [22], Hungary [40,41], Poland [44,[46][47][48], and the United Kingdom [110], which may have been even stronger than during LGM (Figure 4). This mismatch may, however, be due to a relatively small number of samples and/or sampling sites in the Czech Republic.…”

“…These cryogenic cave carbonates may therefore relate to short episodes of permafrost degradation caused by rapid and pronounced climate warming during pre-LGM interstadials (Figure 3) between 38.1 ± 0.6 ka and 26.0 ± 1.5 ka [115,116]. Because the frost wedges in lowlands as well as the periglacial features in uplands of the Czech Republic were active Denmark [32,37], France [22,39,105,106], Germany [32], Hungary [40,41], the Netherlands [32,43], Poland [32, [44][45][46][47][48][49], Sweden [107], and the United Kingdom [32,51]. Means and standard deviations for the OSL ages (rectangles) are based on the central age model [95], while those for the 14 C ages (triangles) are based on the IntCal20 calibration curve [108] and the OxCal 4.4 software [109].…”

“…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. The most extensive direct numerical datings of relict frost wedges have been carried out mainly in the last two decades in connection with advances in modern geochronological methods, especially in Belgium [35,36], Denmark ( [37,38]), France [22,39], Hungary [40][41][42], the Netherlands [36,43], Germany [36], Poland ( [36,[44][45][46][47][48][49][50]), and the United Kingdom [51]. Generally, these studies have shown that frost wedges developed throughout the last glacial period [22].…”