Weichselian Research Articles

Early Holocene thinning and final demise of the Scandinavian Ice Sheet across the main drainage divide of southern Norway

The thinning and final decay of the Scandinavian Ice Sheet in the Gudbrandsdalen area in central southern Norway is described, based on (1) cosmogenic 10Be surface exposure dating of 25 glacially transported boulders, (2) radiocarbon dating of plant remains in the basal strata in four lakes and (3) mapping of large ice-dammed lakes that formed at different elevations and at different times during the last deglacation. We complement the new chronology with previously published 10Be-ages from the same region. The dated samples are spread from mountain summits 1800 m a.s.l. to the valley floor at 250 m a.s.l. Our results suggest that the ice sheet surface remained well above 1800 m a.s.l. in northern Gudbrandsdalen throughout the Younger Dryas. During the Early Holocene the ice sheet thinned rapidly, at rates estimated to 1.7–5.8 m yr−1. The final phase of deglaciation involved formation of large ice-dammed lakes, most notably the Store Dølasjø which was formed after 10.4 ka BP and finally drained around 10.0 ka BP. The ice-marginal landforms that characterize the mountain region of northern Gudbrandsdalen, i.e., moraine ridges, lateral meltwater channels, as well as deposits and shorelines from ice-dammed lakes, thus collectively originate from a period of rapid ice sheet downwasting over ca. 1600 years.

Development of a Gilbert-type delta in the kame environment: An example from NE Poland

Pleistocene kame deltas are known mainly from glaciomarginal environments, whereas there are fewer examples of deltas where kames formed within decaying ice sheets. In this article, we describe deposits of a Gilbert-type delta formed inside a glacial system. The delta succession was identified in the upper part of the hill, a glacial landform developed within the southern sector of the Scandinavian ice sheet in NE Poland during the Warthian glaciation. The landform is interpreted as a kame, the sediments of which were accumulated in an elongated ice crevasse oriented perpendicularly to the front of the ice sheet. The kame was formed in several stages. In the main stage of development, the crevasse was filled with a lake into which the delta prograded. The lake subsequently underwent a few phases of shallowing, and even an episode of complete drainage.The main delta unit was identified in the outcrop. It is composed of a delta slope and prodelta sediments. A partly preserved older deltaic unit of the initial phase of delta sedimentation also was found. The steep (22–42°) slope of the delta is dominated by gravel and sand. The gravels were deposited from high-energy grain flows and grain falls. Sands were deposited mainly from traction currents during periods when the delta-supplying system was less active. Aggradation of the prodelta was mainly due to sand deposition from traction underflows. Deposition from turbidity currents occurred sporadically there. We explain this unusual situation by the fact that the gravelly sediments feeding the delta slope were relatively well-sorted and contained only small admixtures of fine sand and silt. The sediment sorting process took place in a system of englacial or supraglacial conduits, where the gravels were depleted of fine-grained particles. The development of the Gilbert-type delta was possible because the glacial lake, at least 6–8 m deep, periodically maintained a relatively constant water level, which allowed the delta to prograde. This process required the existence of a steady outflow of water from the lake, which was then an open hydrological system. In the final stage of kame formation, when the lake was completely drained, gravel accumulated from shallow sheet flows.

Ice-dammed lakes and deglaciation history of the Scandinavian Ice Sheet in central Jämtland, Sweden

Extensive glacial lakes dammed in the Scandinavian Mountains during the retreat of the last Scandinavian Ice Sheet were first hypothesised over a century ago. Here, using high-resolution LiDAR, we report >4500 relict shorelines, deltas and palaeo-channels related to ice-dammed lakes over a ∼30 000 km2 area of central Jämtland, west-central Sweden. Shorelines occur as flights on the valley sides, a consequence of sequential lowering of palaeo-lake levels during ice margin retreat and lower threshold outlets becoming ice-free. Based on the extent and elevation of shorelines, we identify requisite lake-damming ice-margin positions and lake drainage outlets, and we reconstruct the coupled evolution of ice-dammed lakes and the retreating ice margin. Beginning as a series of smaller ice-dammed lakes along the Swedish-Norwegian border, draining westward across the present-day water divide and into the Atlantic Ocean, the lakes successively coalesced during eastward ice margin retreat to form water bodies covering 1000s of km2 with 10s of km-long calving margins. Ultimately, the lake system coalesced into a single lake: the Central Jämtland Ice Lake, which exceeded 3500 km2 in area and 360 km3 in volume. Eventually, the damming ice-margin split in two, resulting in a large (∼200 km2) catastrophic glacial lake outburst flood (GLOF) that reversed the drainage of the entire lake system from the west to an eastern outlet draining to the Baltic basin. We present new radiocarbon ages for one lake drainage event prior to the eastward outburst flood and, together with previously published deglacial ages and local varve records, we suggest that the region was possibly deglaciated within just 350 years, sometime between 10.5 and 9.2 cal ka BP. We tentatively correlate the penultimate drainage of the Central Jämtland Ice Lake to the zero-varve of the Swedish Time Scale, a drainage varve at Döviken, eastern Jämtland, raising the tantalising prospect of using the evolution of the ice-dammed lake system to tie the varve-based Swedish Time Scale to the radiocarbon timescale with a new programme of radiocarbon dating in central Jämtland.

The morphostratigraphic imprint of the Baltic Ice Lake drainage event in southern Finland

Digital elevation models, based on laser scanning imageries (LiDAR-DEM) and aided by ground penetrating radar (GPR) data, were used to study glaciofluvial Gilbert-type ice-contact deltas in the Younger Dryas Salpausselkä end-moraine zone in southern Finland. The geomorphological data analysed were used to reconstruct the water-level drop of the late glacial Baltic Ice Lake to the early Holocene Yoldia Sea and tie these changes to a wider stratigraphic context. The results indicate that the sudden drainage event at around 11 650 cal. yrs BP left its imprint not only on the varved sediments but also on ice-contact glaciofluvial deltas in the Second Salpausselkä zone throughout southern Finland. This morphostratigraphic boundary can be placed at locations where the ice-contact deltas occur at two different levels; the higher-level deltas formed during the Baltic Ice Lake B III water-level stage and the lower-level deltas during the Yoldia Sea Y I water-level stage. This morphostratigraphically defined boundary in southern Finland marks the Pleistocene/Holocene chronostratigraphic boundary in southern Finland and shows the corresponding positions of the Scandinavian Ice Sheet’s Finnish Lake District Ice Lobe and the Baltic Sea Ice Lobe.

Water blister geomorphology and subglacial drainage sediments: an example from the bed of the Fennoscandian Ice Sheet in SW Finland

Abstract This study presents the first light detection and ranging (LiDAR)-based morphometric description of a water blister from a past ice-sheet bed caused by rapid supraglacial drainage. The blister formed during the rapid early Holocene deglaciation of the Fennoscandian Ice Sheet (FIS). It is located in southwest Finland within a subglacial meltwater route interpreted to represent the transition from a distributed to a channelized drainage system. A LiDAR digital elevation model was supplemented with sedimentological and ground-penetrating radar data on blister outflow channels and sedimentology of downflow polymorphous mounds and ridges (PMRs). Unlike the water blisters recorded from the rapid drainage of supraglacial lakes on the Greenland Ice Sheet, the smaller blister size here was either due to crevasse or moulin drainage, or was a supraglacial lake drainage that tapped into a pre-existing, relatively efficient drainage system and related semi-sorted sediments, promoting rapid drainage and reworking of PMRs along the meltwater route. The preservation potential or exposure probability of blister marks is presumably low but they can provide important information about evolution of subglacial drainage systems that is of value to modern interpretations of glacial hydrology.

Upper-flow regime bedforms in a subglacial triangular-shaped landform (murtoo), Late Pleistocene, SW Finland: Implications for flow dynamics and sediment transport in (semi-)distributed subglacial meltwater drainage systems

We know less about subglacial meltwater flow properties in distributed inefficient and semi-efficient systems in comparison to those of ice marginal eskers and proglacial environments. While previous studies have indicated the overall common presence of upper-flow-regime (UFR) bedforms in glacigenic settings, facies expressions of subglacial meltwater flows remain poorly documented. Three ca. 3 m deep and up to 70 m long trenches excavated across a triangle-shaped subglacial landform called a murtoo in a Lateglacial to Holocene meltwater route in SW Finland provide a detailed window into sedimentary structures presumably formed ca. 40–50 km away from the coeval subaqueous margin of the Fennoscandian Ice Sheet (FIS). The aim of this paper is to document small-scale bedforms, which formed subglacially by meltwater flow and to characterize the proximal and central parts of the studied murtoo during its early evolutionary phase. We defined seven main facies types that characterize the depositional processes of the unit. Overall, the studied deposits reflect increasing meltwater delivery through time and are characterized by abrupt lateral changes in sedimentary structures and grain size. While the initial deposits are dominated by massive and horizontally laminated silt with sand lenses interpreted as lower-flow-regime deposits, the latter sediments are characterized by sinusoidal stratification, sigmoidal cross-stratification and scours with backsets or chaotic fill interpreted as deposits of antidunes, humpback dunes, chutes-and-pools and cyclic steps of the upper-flow regime. The upper-flow-regime bedforms developed on a 1 m high and 15 m long bed slope and are associated with the formation of a short-lived enlarged water-filled cavity or pond, where supercritical density flows allowed for the deposition of upper-flow regime bedforms. The final coarse-grained murtoo head-bar development, characterized by planar-cross stratified gravel and pebbly sand, indicates avalanche processes that were controlled by grain size.Our results confirm that the core of the murtoo is depositional and meltwater processes played a key role in its deposition. Despite the subglacial setting with a subaqueous ice-sheet margin, the meltwater flow was not permanently characterized by pipe-flow conditions. Overall, the findings contribute to the understanding of semi-distributed subglacial meltwater systems during the retreat of a continental ice sheet (FIS) in a rapidly warming climate.

Did the Eurasian ice sheets melt completely in early Marine Isotope Stage 3? New evidence from Norway and a synthesis for Eurasia

We describe glaci-lacustrine sediments buried under thick tills in Folldalen, south-east Norway, a site located close to the former centre of the Scandinavian Ice Sheet. Thus, the location implies that the ice sheet had melted when the sediments were deposited. The exposed ground was occupied by arctic vegetation. The best age estimate from 20 quartz luminescence dates is 55.6 ± 4.6 ka. Due to possible incomplete bleaching, an age in the younger part of the time range is most probable. We conclude that the Scandinavian Ice Sheet melted almost completely away early in Marine Isotope Stage (MIS) 3. Our review shows that the other Eurasian ice sheets also disappeared in that period. In north-western Germany, there were forests, containing warmth-demanding trees early in MIS 3, indicating a summer climate only slightly cooler than at present, thus supporting the evidence that the adjacent ice sheets had melted. The melting of the Eurasian ice sheets contributed to 50–100% of the sea-level rise from MIS 4 to MIS 3, implying that the much larger North American ice sheets did not melt much. In contrast, the Eurasian ice sheets contributed only about 30% to the sea-level drop from MIS 3 to MIS 2, meaning that the North American ice sheets during that period expanded strongly.

Genesis of subglacial triangular‐shaped landforms (murtoos) formed by the Fennoscandian Ice Sheet

AbstractThe purpose of this paper is to describe the internal structure and composition of recently discovered subglacial landforms called “murtoos” in order to interpret their formative processes and depositional environment. So far, murtoos have only been reported from Finland and Sweden, but they probably exist in all areas covered by past ice sheets. Murtoos mainly occur in fields along subglacial meltwater routes or corridors in close relation to eskers and ribbed moraine tracts. Murtoos were excavated perpendicular to the long axes of the triangular murtoo heads in six locations. Murtoos were found to be composed of silt/clay‐poor, sandy and gravelly diamictons interbedded with sorted sediments, and are suggested to be produced by pulsed, highly sediment‐concentrated flows during weak glaciotectonic deformation, indicating effective pressure close to zero. Murtoos can be divided into three main depositional units: 1) the core, 2) the murtoo body and 3) the murtoo mantle. The initial deposition of murtoos took place in a network of low canals and conduits or cavities with fluctuating stream flow likely over 50 km from the ice margin. Murtoos reveal an increasing influence of subglacial meltwater flow in rapidly widening broad and low conduits with increasing sediment transport over short distances. The results of this work suggest that murtoos were formed time‐transgressively over yearly meltwater cycles in a semi‐distributed drainage system not recognised before, in which was high‐pressure porewater conditions with rapid mobilisation of subglacial saturated sediments, a critical factor in the development of semi‐efficient drainage. Murtoos are suggested as missing element between distributed and channelised drainage systems not included in current glaciohydrological models or even in the theoretical basis of glacial hydrology.

Active tectonics of the Circum-Pannonian region in the light of updated GNSS network data

The Pannonian basin is an extensional back-arc basin that has undergone neotectonic inversion and is currently shortening. The understanding and quantification of present-day deformation processes during this inversion are still incomplete. To this end, we investigate the active deformation of the Circum-Pannonian region via the interpolation of GNSS-derived velocity field and the derivation of the strain rate fields. For the interpolation of the velocity field, we use ordinary kriging, a strochastic interpolation method. Our results show that estimating a strain rate field that is virtually free of short-wavelength noise requires the scaling of the velocity uncertainties, i.e. assuming a minimum standard deviation of 1 mm/yr in our case. The deformation of the Circum-Pannonian region is defined by the 2–3 mm/yr, NNE-directed motion of the Dinarides, and by the 0.5–1.5 mm/yr, WSW to SSW directed motion of the eastern areas (European foreland, East Carpathians, South Carpathians, Transylvanian basin). These opposite-sense motions define a large-scale, on average NE-SW shortening and transpression-type deformation in the Dinarides as well as in the Pannonian basin, while the East and South Carpathians undergo regional N–S extension. Neotectonic structures generally show good agreement with the strain rate field, for example in the Dinarides, Eastern Alps, or in the western Pannonian basin. However, the presence of fault-parallel shortening or biaxial shortening along sinistral neotectonic structures in the central and eastern Pannonian basin show some discrepancy between current geodetic and observed neotectonic deformation. The vertical velocity field shows dominantly 100 and 1000 km wavelength signals, the former is probably related to the response of the Pannonian lithosphere-asthenosphere system to neotectonic basin inversion, while latter can possibly be explained by far-field subsidence patterns induced by the mantle response to melting of the Fennoscandian ice sheet during the current interglacial period.

The Scandinavian ice sheet against the Atlantic ocean: How the scandinavian ice sheet affected European small mammal assemblage during the Greenland stadial GS-2.1

The Scandinavian ice sheet against the Atlantic ocean: How the scandinavian ice sheet affected European small mammal assemblage during the Greenland stadial GS-2.1

Offshore murtoos indicate warm-based Fennoscandian ice-sheet conditions during the Bølling warming in the northern Gulf of Riga, Baltic Sea

Glacial landforms provide invaluable information on the dynamics and extent of past ice sheets. In planform view, murtoos are triangular-shaped subglacial landforms that have recently been described from areas previously covered by the Fennoscandian Ice Sheet and whose formation has been linked to meltwater activity. We document the first occurrence of offshore murtoos and associated eskers in a high-resolution multibeam and sub-bottom profile dataset from the northern Gulf of Riga, Baltic Sea. In this study area, the murtoos appear to be longer (range 43–748 m), narrower (range 12–394 m) and less high (range 0.5–7.8 m), on average, compared to those previously reported on land, although this may be partly due to post-glacial sediments that smooth the present-day seafloor topography and may have buried smaller murtoos. The direction of murtoo longitudinal axes suggests a local NNE–SSW paleo-ice stream direction. In sub-bottom boomer profiles, the murtoos are characterized by moderate amplitude, sub-parallel discontinuous internal reflectors, indicating a varying sandy diamicton and sand composition, which is compatible with the previously interpreted mode of deposition by pulsed subglacial meltwater flow. Eskers that are found in close association with the murtoos are shorter (mean length 538 m) and more curved than their counterparts on nearby land areas, and they lack a general alignment. In boomer profiles, the eskers are characterized by low-amplitude, sub-parallel continuous reflectors, suggesting a better-sorted sandy composition. The curved and poorly aligned external form of the eskers suggests deposition under restricted subglacial drainage conditions. We conclude that murtoos and related landforms in the northern Gulf of Riga were formed during the Bølling warming at ca. 14.5–14.1 cal kyr BP, when large amounts of meltwater were delivered to the ice-sheet bed.

Pleistocene glaciations in southern Poland – a revision

A revised stratigraphy the Lower and Middle Pleistocene in southern Poland is presented, based on geological evidence from key sites, better constraints on the number and age of Scandinavian ice sheet advances, and the stratigraphic setting of the interglacial sequences. Identification of the palaeomagnetic Brunhes/Matuyama boundary and an admixture of glacially derived material of northern provenance in fluvial deposits demonstrate that the oldest Scandinavian ice sheet advance (Nidanian Glaciation) in Poland and the first warming of the oldest interglacial (Podlasian) occurred in the late Early Pleistocene. The first ice sheet advance in the Oowiecim Basin is recorded by a till of the Nidanian Glaciation. A single till and its geological setting relative to deposits of the Podlasian and Ferdynandovian interglacials show that, contrary to previous opinions, the ice sheet advance of the early Middle Pleistocene Sanian 1 Glaciation was a single, the most extensive glacial event in the Sandomierz Basin and in western Ukraine. The Sanian 2 and the Odranian ice sheets were considerably less extensive in eastern Poland. The revised Pleistocene stratigraphy and palaeogeography of southern Poland is a significant step forward towards reliable correlation of the Polish climatostratigraphic units with the European stratigraphy

Weichselian Glaciation of the Faroe Islands

This paper presents a new complete field mapping of glacial landscapes, landforms and sediments in the Faroe Islands, supplemented by observations from bathymetric maps of the Faroe Shelf. In addition, previous investigations of Quaternary and espe-cially the Weichselian glaciation of the archipelago are reviewed. New cosmogenic nuclide exposure ages indicate that the last extensive glaciation of the Faroe Islands occurred during the Late Weichselian, most likely during the Last Glacial Maximum (LGM; c. 26.5–19.0 cal. ka BP), although a Younger Dryas (c. 12.9–11.7 cal. ka BP) age cannot be entirely excluded. Geomorphological mapping provides a background for reconstructing the extent and type of the glaciation of the Faroe Islands. The reconstructed Weichselian glaciation appears to have had the character of an exten-sive valley glaciation, with several marine glacier termini. The present glaciation of southern Spitsbergen, Svalbard, represents a modern analogue of the reconstructed Weichselian glaciation in the Faroe Islands. The lack of raised coastal features in the Faroe Islands, also at protected sites, suggests that postglacial isostatic uplift was smaller than post-LGM eustatic sea level rise. Numerical glacier reconstructions carried out for different extents of the last extensive Faroese glaciation suggest that such limited postglacial isostatic crustal uplift requires that the Faroe Shelf was not extensively glaciated during the Late Weichselian, but it doubtless was so during at least one of the previous Quaternary glaciations.

Climate changes during the Late Glacial in southern Europe: new insights based on pollen and brGDGTs of Lake Matese in Italy

Abstract. The Late Glacial (14 700–11 700 cal BP) is a key climate period marked by rapid but contrasted changes in the Northern Hemisphere. Indeed, regional climate differences have been evidenced during the Late Glacial in Europe and the northern Mediterranean. However, past climate patterns are still debated since temperature and precipitation changes are poorly investigated towards the lower European latitudes. Lake Matese in southern Italy is a key site in the central Mediterranean to investigate climate patterns during the Late Glacial. This study aims to reconstruct climate changes and their impacts at Matese using a multi-proxy approach including magnetic susceptibility, geochemistry (XRF core scanning), pollen data and molecular biomarkers like branched glycerol dialkyl glycerol tetraethers (brGDGTs). Paleotemperatures and paleo-precipitation patterns are quantitatively inferred from pollen assemblages (multi-method approach: modern analogue technique, weighted averaging partial least-squares regression, random forest and boosted regression trees) and brGDGT calibrations. The results are compared to a latitudinal selection of regional climate reconstructions in Italy to better understand climate processes in Europe and in the circum-Mediterranean region. A warm Bølling–Allerød and a marked cold Younger Dryas are revealed in all climate reconstructions inferred from various proxies (chironomids, ostracods, speleothems, pollen, brGDGTs), showing no latitudinal differences in terms of temperatures across Italy. During the Bølling–Allerød, no significant changes in terms of precipitation are recorded; however, a contrasted pattern is visible during the Younger Dryas. Slightly wetter conditions are recorded south of 42∘ N, whereas dry conditions are recorded north of 42∘ N. During the Younger Dryas, cold conditions can be attributed to the southward position of North Atlantic sea ice and of the polar frontal jet stream, whereas the increase in precipitation in southern Italy seems to be linked to relocation of Atlantic storm tracks into the Mediterranean, induced by the Fennoscandian ice sheet and the North European Plain. By contrast, warm conditions during the Bølling–Allerød can be linked to the northward position of North Atlantic sea ice and of the polar frontal jet stream.

Palaeogeographic reconstruction of the Late Weichselian ice sheet in north‐central Poland based on relief analysis

ABSTRACTNorth‐central Poland was originally shaped by the Płock lobe of the ice sheet formed during the Weichselian Glaciation. The majority of the studied area comprises the Dobrzyń Lakeland, where numerous terminal moraine hills preserve a record of recession of the ice sheet from the maximum extent of the last glaciation (LGM). Analysis of a digital elevation model enabled the determination of a network of morpholineaments, referring to the formation of linear glacial forms. Recession of the ice sheet from the LGM extent in north‐central Poland was uneven and proceeded in stages. Ice‐sheet recession stages were interspersed with local or regional ice‐sheet advance stages. During these individual periods of ice‐sheet behaviour, ice‐sheet movement changed direction from WNW–ESE to NNW–SSE. Transgression of the ice sheet into the central part of the study area as well as the Kujawy–Dobrzyń subphase may be related to cooling of the climate during 18.5–17.7 ka before ad 2000.

The impact of spatially varying ice sheet basal conditions on sliding at glacial time scales

AbstractSpatially variable basal conditions are thought to govern how ice sheets behave at glacial time scales (>1000 years) and responsible for changes in dynamics between the core and peripheral regions of the Laurentide and Fennoscandian ice sheets. Basal motion is accomplished via the deformation of unconsolidated sediments, or via sliding of the ice over an undeformable bed. We present an ice sheet sliding module for the Parallel Ice Sheet Model (PISM) that takes into account changes in sediment cover and incorporates surface meltwater. This model routes meltwater, produced at the surface and base of the ice sheet, toward the margin of the ice sheet. Basal sliding is accomplished through the deformation of water saturated sediments, or sliding at the ice-bed interface. In areas with continuous, water saturated sediments, sliding is almost always accomplished through sediment deformation. In areas with incomplete cover, sliding has a stronger dependence on the supply of water. We find that the addition of surface meltwater to the base is a more important factor for ice sheet evolution than the style of sliding. In a glacial cycle simulation, our model causes a more rapid buildup of the Laurentide Ice Sheet.

Palaeoclimatic and regional implications of Older Dryas and Younger Dryas local glacier activity in the low‐Arctic valley Finnkongdalen, Andøya, northern Norway

Continuous glacier margin and equilibrium‐line altitude fluctuations of a former glacier on central Andøya, northern Norway, are reconstructed during the Lateglacial based on moraines and AMS 14C‐dated sediments from the distal glacier‐fed lake Ner‐Finnkongdalsvatnet. The results indicate that a valley glacier occupied the entire valley during the Last Glacial Maximum (before 21 970±620 cal. a BP). The glacier remained large throughout the early Lateglacial until a significant glacier retreat took place about 14 300±330 cal. a BP. Major advances occurred during the Older Dryas (OD) and during the Younger Dryas (YD), while minor advances are suggested to have taken place during the Intra Allerød Cold Period and the Late Allerød Cooling. Additionally, three smaller glacier retreats/re‐advances within the YD are suggested to have taken place, the latter being the largest. The glacier re‐formations/advances during the Lateglacial are consistent with increases in temperature, and they are thus suggested to be the result of increased winter precipitation. Comparing the results with relevant glacier and sea‐surface temperature records, a south–north migration of storm tracks may have occurred between 12 100–11 810±220 cal. a BP. The high temporal resolution of local glacier activity in Finnkongdalen improves our understanding of the climate forcing of the regional glacier fluctuations of the northwestern sector of the Scandinavian Ice Sheet during the Skarpnes‐ (OD) and Tromsø‐Lyngen (YD) re‐advances.

Atmospheric River Contributions to Ice Sheet Hydroclimate at the Last Glacial Maximum

AbstractAtmospheric rivers (ARs) are an important driver of surface mass balance over today's Greenland and Antarctic ice sheets. Using paleoclimate simulations with the Community Earth System Model, we find ARs also had a key influence on the extensive ice sheets of the Last Glacial Maximum (LGM). ARs provide up to 53% of total precipitation along the margins of the eastern Laurentide ice sheet and up to 22%–27% of precipitation along the margins of the Patagonian, western Cordilleran, and western Fennoscandian ice sheets. Despite overall cold conditions at the LGM, surface temperatures during AR events are often above freezing, resulting in more rain than snow along ice sheet margins and conditions that promote surface melt. The results suggest ARs may have had an important role in ice sheet growth and melt during previous glacial periods and may have accelerated ice sheet retreat following the LGM.

Age assessment of the Jasmund Glacitectonic Complex (SW Baltic Sea) by quartz luminescence dating of syn-kinematic deposits

The development of the Fennoscandian Ice Sheet (FIS) in its SW Baltic Sea sector during MIS 2 led to the formation of the Jasmund Glacitectonic Complex (JGC). The evolutional stages of the latter reflect small-dimensioned ice sheet oscillations. A glacitectonically formed piggyback basin is in focus to give direct information on the evolution of the JGC. We present a set of five OSL ages from syn-kinematic glacilacustrine and alluvial fan sediments deposited between ice margin-parallel thrust-bounded ridges from the southern margin of the JGC. The ice front proximal depositional environment and short transport distances of the sediments implicate a possible insufficient bleaching of the luminescence signal. Nonetheless, we were able to gain reliable ages of ~22 ka for the growth of the southern JGC. The samples pre-date the Oder ice stream reaching its maximum extent, the Pomeranian ice marginal belt at ~18–20 ka. A comparison of our data with the existing age data related to the evolution of the JGC will contribute to a better understanding of the FIS dynamics in the research area and the timing of the Pomeranian phase in NE Germany.

Middle to Late Quaternary changes in ice rafting and deep current transport on the Alpha Ridge, central Arctic Ocean and their responses to climatic cyclicities

To address the Arctic Ocean response to the Quaternary climate change, three sediment cores from the Alpha Ridge, central Arctic Ocean, were analyzed for proxies of sediment transport and depositional mechanisms. The identified end-member grain-size components - clayey EM1, fine-silty EM2, and silty-sandy EM3 - are interpreted as proxies of sea ice transport, near-bottom current, and iceberg inputs, respectively. The sea-ice and iceberg transport proxies, EM1 and EM3, have opposing patterns peaking in the interglacials/interstadials and glacials/stadials, respectively. The near-bottom current proxy EM2 shows an overall gradual decrease with secondary variations indicating current slow-down during intervals of enhanced iceberg discharge. EM3 peaks during Marine Isotope Stages (MIS) 12, 10, 8, and MIS 7 stadials co-occur with high Ca content indicative of iceberg inputs from the Laurentide ice sheet via the Beaufort Gyre. Other EM3 peaks, notably during MIS 6 and MIS 4/3 likely originated from the Siberian margin based on elevated Zr content, thus indicating expanded Eurasian ice sheet and the Transpolar Drift extension towards the central Arctic Ocean. High coherences in the spectral analysis between the sea ice and iceberg proxies versus the global ice volume and orbital parameters on the 100-kyr and 23-kyr time bands illustrate the strong responses of sea ice and glaciations to eccentricity and precessional cycles. A persistent precessional impact of low latitude processes on high Arctic environment indicates a potential link to the low latitudes via atmospheric moisture and heat transport.