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This paper investigates the time-transgressive evolution of the Fennoscandian Ice Sheet (FIS) during the Late Weichselian glaciation. Recent models of the Last Glacial Maximum (LGM) strongly challenge a synchronous development of the FIS in the SW Baltic Sea area. Especially in northern Germany, a time-transgressive LGM is controversial. We present a new set of optically stimulated luminescence (OSL) ages, from sediments deposited at locations previously ascribed to the LGM main stationary line, from which numerical age data have not been published so far. The aim of this study was to contribute to the research on the maximum Weichselian ice extent in northern Germany, and to close the gap between Denmark in the north and the area in Germany and Poland in the SE, for which numerical age data of the LGM extent of the FIS are available. Samples were taken from sandur deposits proximal to the former ice margin. In total nine OSL samples were taken and analysed on quasi-single-grain level, taking into account possible effects of insufficient bleaching of sample material. With an average age of ~23±1 ka, the samples indicate LGM sandur formation during Marine Isotope Stage (MIS) 2. Our dating provides new insights into Late Weichselian (MIS 2, 27–11.7 ka) ice-sheet dynamics and strongly challenge a synchronous development of the FIS in the SW Baltic Sea area. The integration of our results into regional models argues for a small-scale asynchronous extent of the last FIS in northern Germany.

Subglacial overdeepenings are of interest for a number of applied and academic reasons, for example as groundwater reservoirs or as sedimentary archives of environmental change. Thus, efforts have been made to compile and morphometrically analyse such features on a large scale. While this includes several prominent studies focusing on the western part of the European Alps and their foreland, their eastern part lacks information. We present an inventory of >100 individual overdeepened basins in southern Germany and Austria compiled from heterogeneous sources. These basins are typically incised ~200 m (max. ~1000 m) below ground surface and ~20 km (max. ~100 km) long, and thus of similar dimensions as overdeepenings in the western (Swiss) Alps and foreland. We observe a positive correlation of overdeepening area and depth with catchment size and both peak and average elevations, although large and deep basins also occur in small catchments. Generally, large overdeepenings are restricted to inner-Alpine fault zones or the primarily weak foreland Molasse. Especially in inner-Alpine settings, longitudinal profiles are highly irregular. In the eastern Alpine foreland, individual basins are frequently arranged in a radial pattern, a morphology that is not typical of the western foreland, and is a result of less constrained ice flow. On the valley scale, the depth of overdeepened basins correlates with modelled ice-flow parameters, thickness and basal velocity at peak glacial conditions. Together with their occurrence in low-elevation reaches, this suggests a rapid formation over a few millennia at most. On a smaller, local scale, basin depth is highly irregular. Finally, the existence of several generations of (similarly) large foreland overdeepenings, sometimes superimposed, indicates that these basins do not grow progressively over consecutive glacial cycles but that a negative feedback, likely related to the freezing of supercooled basal water, limits their dimensions.

Tunnel valleys are impressive subglacial erosional landforms and may attain depths of almost 600 m. Climatic and glaciological factors exert the primary control on tunnel-valley formation. Furthermore, regional geological features, e.g. faults and salt structures, have been suggested as controlling factors for tunnel-valley formation. To improve the understanding of the impact of these geological factors on tunnel-valley incision, we compare the distribution and orientations of buried Pleistocene tunnel valleys in the North German Basin with regional geological features, such as basin geometry and infill, faults and salt structures. Our analysis shows that deep tunnel valleys are restricted to areas with thick erodible Cenozoic deposits. The correlation between the trends of tunnel valleys, faults and salt structures varies between the analysed regions. The orientations of tunnel valleys commonly follow the trends of faults and salt structures in regions where the structural trend is NNW–SSE to east–west and ice-flow directions were approximately parallel to this trend. However, correlations are rarely observed if the regional structural trend is NW–SE to WNW–ESE and ice advances occurred thus normal or oblique to the regional fault trend. Potential future tunnel-valley incision is regarded as a major challenge for the long-term safety of radioactive waste repositories because incision may reach depths under consideration for repositories. The presence and orientations of faults and salt structures, however, do not provide consistent indicators for future tunnel-valley incision.

In the context of climate change, a long-term perspective is essential to understand future trajectories of mountain vegetation. We analysed the sediment record of Golzerensee (1411 m a.s.l.), a mountain lake in the transitional zone between the montane and subalpine vegetation belt in Uri, Central Switzerland. We reconstructed past vegetation responses to anthropogenic impact, fire activity and climatic changes dating back to c. 14 550 cal. a BP using pollen, stomata, macrofossil and microcharcoal analyses. The tree line, composed of Betula and Pinus sylvestris, reached Golzerensee during the Allerød c. 13 200 years ago, but tundra vegetation re-expanded during the Younger Dryas cooling (12 800–11 700 cal. a BP). With the rapid temperature increase at the onset of the Holocene, a closed forest established within a few decades around the study site. Concurrently, temperate taxa (Ulmus, Tilia, Acer, Corylus avellana) increased in the lowlands, likely reaching the elevation of the lake. Abies alba established locally during the Holocene Thermal Maximum (HTM) at 9600 cal. a BP and dominated closed, montane forests, delaying the westward expansion of Picea abies that established only from c. 7700 cal. a BP onwards. The concomitant occurrence of cultural indicator taxa, as well as an increase in charcoal influx and fungal dung spore concentrations suggest that human impact has facilitated the expansion of Picea abies by negatively affecting important competitors such as Abies alba through fire and browsing disturbance. With rising temperatures due to current climate change, Abies alba and other temperate species may regain their former relevance, leading to diverse mixed forests that were abundant during the HTM c. 10 000–5000 cal. a BP. However, future forest composition and landscape diversity will also be influenced by browsing disturbance and land use management.

Investigations of the geomorphological fingerprints of palaeo-ice streams are essential for enhancing our understanding of ice-stream behaviour. Cross-cutting flowsets of palaeo-ice streams, during and following the Last Glacial Maximum, have been suggested in northeast Iceland based on the mapping of streamlined subglacial bedforms (SSBs). To increase our understanding of the dynamics of the Icelandic Ice Sheet (IIS) during deglaciation, we investigate transverse ridges, together with glacifluvial and ice-marginal landforms, within the largest flowset. The main emphasis is on the transverse ridges, which are primarily interpreted as ribbed moraines – the first to be described in Iceland. Morphological data are combined with sedimentological analyses of the ribbed moraines. Our results show that the ribbed moraines are composed of pre-existing material, often exhibiting a base of stratified glacifluvial sediments draped with subglacial till. Deformation and thrust structures within both units suggest compressional flow during the formation of the ridges. Our results suggest the ribbed moraines develop due to velocity gradients under the lateral shear margin of an ice stream based on their distribution and often oblique orientation in relation to SSBs. The ribbed moraines superimpose and thus post-date the SSBs, signifying the waning stage of ice streaming. We suggest that the ridges formed during ice-stream shutdown following the Younger Dryas and/or Preboreal re-advances. Eskers and ice-marginal landforms imply channelized water drainage during the final deglaciation interrupted by short-lived re-advances. This study has implications for the style of deglaciation associated with ice streaming in the northeastern part of the IIS. We characterize the role of ribbed moraines within the ice sheet and identify directions for future work.

De Geer moraines (DGMs) may act as valuable ice margin indicators; however, to date, their variable mode of formation has presented challenges for this utility. Morphometric investigations provide useful insights into formation processes, which can be developed using sedimentological and geophysical methods. Here we present sedimentological and ground penetrating radar (GPR) data of DGMs located in southwest Finland. Individual lithofacies were identified and interpreted using sediment architectural elements. These were correlated with neighbouring GPR radargrams and extrapolated across the wider study area. Generally, internal architecture presents a multi-phase structure with lower units representing subglacial traction till and ice margin infill deposits, truncated by a larger prominent push unit, which is then successively deformed via the overriding of active ice. Significantly, there are notable differences between proximal and distal structures, with proximal sides characterized by silts, clays, and diamicton with laminae, stratification and thrust planes, and distal sides characterized by poorly consolidated diamicton and proglacial water current reworkings. Internal architecture of both prominent and intermediate ridges is very similar, reflecting similar formation processes, however, slight differences also reflect inter-seasonal variations. Based on our findings, we present an integrated conceptual model for the genesis of DGMs whereby inter-seasonal ridge forming processes occur within a sub-aqueous ice-marginal environment. Our model highlights that DGMs can be subcategorized as: (i) sediment deposition at an unstable margin during summer calving, and/or (ii) sediment pushing at a stabilized margin during a winter re-advance. We do not find evidence of crevasse filling as a mechanism for DGM formation. We propose a landform assemblage classification whereby ‘De Geer terrain’ is used to describe series of parallel ridges arranged in a typical washboard-like configuration. This classification identifies all DGMs derived within a sub-aqueous ice-marginal environment, whilst also capturing the equifinal characteristics between individual landforms.

Wind activity is a powerful force that shapes the landscapes of deserts, coastal areas, and regions adjacent to ice sheets, and it has significant implications for human settlement. In southern Greenland, it has been proposed that the increased wind and soil erosion observed around Norse settlements (~985–1450 CE) were caused by overgrazing by animals, which ultimately contributed to the decline of the Norse culture. Alternatively, some studies have linked the observed intensification of aeolian activity to changes in large-scale atmospheric circulation patterns in the North Atlantic. However, the timing and impact of this increased aeolian activity in southern Greenland remain uncertain due to a lack of well-dated records. In this study, we use a lake record and optically stimulated luminescence (OSL) dating of adjacent dunes to reconstruct the Holocene history of aeolian activity at Igaliku Kujalleq (Søndre Igaliku) in southern Greenland. Our findings indicate two periods of intensified aeolian activity over the past 10 000 years: from ~500 to 1200 CE and ~1450 CE. Importantly, the peak aeolian activity observed in the Igaliku Kujalleq records was unrelated to Norse activities and their decline. Instead, we suggest that changes in the North Atlantic atmospheric circulation pattern combined with Neoglacial glacier advances led to increased katabatic wind activity and triggered increased aeolian activity from large outwash plains.

Arctic ecotones contain dynamic freshwater ecosystems where aquatic biota vary across these transitions and as such can be especially susceptible to environmental change. Here, we examine the palaeoecology of two ponds in the ecotonal Hudson Bay Lowlands, subarctic Canada, to understand how aquatic biota have responded in an increasingly climate-stressed Anthropocene, and to better anticipate future changes. Using a multi-proxy palaeolimnological approach, we reconstruct past environmental conditions through the examination of subfossil chironomids (Diptera: Chironomidae) and compare these records to organic carbon and nitrogen elemental and isotope composition, and previously published cellulose-inferred lake water oxygen isotope records. Despite their close proximity, we found different chironomid assemblages in each pond that reflected differences in hydrological trajectories since 1940; an isolated pond exposed to evaporative stress showed an increasingly littoral chironomid assemblage, while a nearby basin that began receiving waters from a channel fen lost semi-terrestrial taxa associated with flooded grassy margins that became more permanently submerged. Even though large catchment-mediated changes resulted in a shift in some chironomids of both ponds, chironomid-based palaeo-temperature reconstructions demonstrated similar warming trends. Shifts in the ecology of subarctic lakes and ponds are expected to increase as the effects of climate change become more severe.

Subglacial processes exert a major control on ice streaming. Constraining subglacial conditions thus allows for more accurate predictions of ice mass loss. Due to the difficulty in observing large-scale conditions of the modern subglacial environment, we turn to geological records of ice streaming in deglaciated environments. Morphometric values of streamlined subglacial bedforms provide valuable information about the relative speed, direction, and maturity of past ice streams and the relationship between ice streaming and subglacial erosion and deposition. However, manually identifying streamlined subglacial bedforms across deglaciated landscapes, sometimes in clusters of several thousand, is an arduous task with difficult-to-control sources of variability and human-biased errors. This paper presents a new tool that utilizes a machine learning approach to automatically identify glacially derived streamlined features. Slope variations across a landscape, identified by topographic position index, undergo analysis from a series of supervised machine learning models trained from over 600 000 data points identified across the deglaciated Northern Hemisphere. A filtered data set produced through the combination of scientifically driven preprocessing and statistical downsampling improved the robustness of our approach. After cross-validation, we found that Random Forest detected the most true positives, up to 94.5% on a withheld test set, and an ensemble average of machine learning models provided the highest stability when applied within the range of applicable data sets, performing at up to 79% identification of true positives on an out of distribution area of interest. We build these models into an open-source Python package, bedfinder, and apply it to new data in the Green Bay Lobe region, USA, finding the general ice-flow direction and average streamlined subglacial bedform elongation with minimal effort. This type of open, reproducible machine learning analysis is at the leading edge of glacial geomorphology research and will continue to improve with integration of newly acquired and previously collected data.

Jan Mayen is a small volcanic island situated in the Norwegian–Greenland Sea. The entire island was covered by a contiguous ice cap during the Last Glacial Maximum. The deglaciation of the ice cap was interrupted by a glacier advance in the southern part of the island in the Early Holocene. Today, there are no glaciers in this area, and until now it has been unknown whether any glaciers survived there into the Middle–Late Holocene. We show here that glaciers existed at several sites in the mountain areas of southern Jan Mayen. The investigations were triggered by the discovery of a relict glacier completely covered by tephra and impacted by a lava flow. Samples of ice from the glacier have ¹⁸O values that are isotopically indistinguishable from modern precipitation values and fall along the local meteoric water line trend. The lava flow in the glacier catchment and sculpted forms along the base of dry meltwater channels in bedrock show that glacier melting was abrupt and marked by sudden meltwater outbursts (jökulhlaups). Three more sites in southern Jan Mayen have meltwater channels with sculpted beds, gorges and/or sediments associated with lava flows and can be attributed to jökulhlaups caused by rapidly melting glaciers. Radiocarbon dates associated with glacial outwash sediments, cosmogenic dates of meltwater channel incisions, and cosmogenic and K-Ar dates of lava flows associated with former periods of rapid glacier melting show that the four glaciers collapsed at different times in the Holocene. None of the glaciers reformed after their collapses despite subsequent cooling event(s). Likely, the glaciers were on the brink of existence before their sudden demise.