Weichselian Research Articles

Geomorphic evidence of multiple surface ruptures of the Merasjärvi “postglacial fault”, northern Sweden

ABSTRACTPostglacial faults in Sweden are generally believed to have ruptured to the surface once either during or shortly after the late Weichselian deglaciation. Stratigraphic data from multiple scarps support or are consistent with this hypothesis and, until now, no data refute it. This study presents geomorphic evidence that a segment of the Merasjärvi fault in northern Sweden ruptured to the surface at least twice. The timing of the fault ruptures is poorly constrained because the scarp lies within a preserved glacial landscape. Crosscutting relationships indicate that the scarp is younger than the early Weichselian but suggest that parts of the scarp existed beneath the late Weichselian ice sheet.

Ice marginal dynamics of the last British-Irish Ice Sheet in the southern North Sea: Ice limits, timing and the influence of the Dogger Bank

The southern North Sea is a particularly important area for understanding the behaviour of the British-Irish Ice Sheet (BIIS) during the last glacial cycle. It preserves a record of the maximum extent of the eastern sector of the BIIS as well as evidence for multiple different ice flow phases and the dynamic re-organisation of the BIIS. However, to date, the known ice sheet history and geochronology of this region is predominantly derived from onshore geological evidence, and the offshore imprint and dynamic history of the last ice sheet remain largely unknown. Using new data collected by the BRITICE-CHRONO project this paper explores the origin and age of the Dogger Bank; re-assesses the extent and age of the glaciogenic deposits across the shallow areas of the North Sea between the Dogger Bank and the north Norfolk coast and; re-examines the dynamic behaviour of the BIIS in the southern North Sea between 31.6 and 21.5 ka.This paper shows the core of the Dogger Bank to be composed glaciolacustrine sediment deposited between 31.6 and 25.8 ka. Following its formation the western end of the Dogger lake was overridden with ice reaching ∼54°N where the ice margin is co-incident with the southerly extent of subglacial tills previously mapped as Bolders Bank Fm. This initial ice override and retreat northwards back across the Dogger lake was complete by 23.1 ka, but resulted in widespread compressive glaciotectonism of the lake sediments and the formation of thrust moraine complexes. Along the northern edge of the bank moraines are on-lapped by later phase glaciolacustrine and marine sediments but do not show evidence of subsequent ice override.The shallow seafloor to the west and southwest of the Dogger Bank records several later phases of ice advance and retreat as the North Sea Lobe flowed between the Dogger Bank and the Yorkshire/Lincolnshire coasts and reached North Norfolk. New optically stimulated luminescence (OSL) ages from Garrett Hill on outwash limit the arrival of the BIIS on the Norfolk coast to 22.8–21.5 ka. Multiple till sheets and chains of moraines on the seafloor north of Norfolk mark dynamic oscillation of the North Sea Lobe margin as it retreated northwards. This pattern of behaviour is broadly synchronous with the terrestrial record of deposition of subglacial, glaciofluvial and glaciolacustrine sediments along the Yorkshire coast which relate to post Dimlington Stadial ice marginal oscillations after 21.5 ka.With respect to forcing mechanisms it is likely that during the early phases of the last glacial maximum (∼30-23ka) the interaction between the southern margin of the BIIS and the Dogger Lake was critical in influencing flow instability and rapid ice advance and retreat. However, during the latter part of the last glacial maximum (22–21 ka) late-phase ice advance in the southern North Sea became restricted to the western side of the Dogger Bank which was a substantial topographic feature by this time. This topographic confinement, in addition to decoupling of the BIIS and the Fennoscandian Ice Sheet (FIS) further north, enabled ice to reach the north Norfolk coast, overprinting the seabed with late-phase tills of the Bolders Bank Fm.

Post-Younger Dryas fault instability and deformations on ice lineations in Finnish Lapland

The Younger Dryas phase, which occurred between 12.8 and 11.5 ka as a part of the cyclic pattern of global climatic changes, was concurrent with maximum fault instability (13–10 ka) in the Fennoscandian shield. Ice lineations, indicative of glacial streaming toward the Younger Dryas end moraines (YDEMs), may have faced earthquake impacts within the glacial isostatic adjustment (GIA). Morphometric analyses for airborne laser scanning (ALS) revealed that ice lineations were deformed subglacially and subaerially in Finnish Lapland. The subglacial water outburst flows diagonally eroded the drumlins, 50 km from the YDEMs in Utsjoki, northern Finnish Lapland. Similarly north, in the Sevetti area, 40 km from the YDEMs a large portion of the ice lineations were entirely distorted by the subglacial squeeze-up Pulju moraine and liquefaction bowl formations. In the interior part of the Fennoscandian Ice sheet (FIS) in Kemijärvi, representing onset of an ice-stream fan 200 km from the YDEMs, mass flows had reworked the ice lineations. Based on the electrical-sedimentry anisotropy, mass flow sediments deviated from the ice flow pattern. Postglacial liquefaction craters were created on the drumlins in Utsjoki and also in Kuusamo, eastern Finnish Lapland, 70 km from the YDEMs in Russian Karelia. We interpret these features as indications of paleoseismic events associated with GIA.

Morphology and pattern of Quaternary sedimentation in the North Sea Basin (52–62°N)

Abstract The Quaternary North Sea Basin, which extends from northwest mainland Europe in the south (52°N) to the Norwegian Sea in the north (62°N), contains a thick (up to 1 km) sedimentary succession that records the changing nature of sediment supply from surrounding land areas during the last c.2.6 Ma. We use an extensive 2D and 3D seismic database to correlate major Quaternary seismo-stratigraphic surfaces and units across the North Sea and reconstruct the broad-scale infill pattern of the entire Quaternary North Sea Basin. The total volume of Quaternary sediments in the North Sea (350 000 km2) is c.140 000 km3, while the area inside the 500 m contour of the base-Quaternary surface has a volume of 109 000 km3. Two largely independent depocentres developed in the North Sea Basin during the early Quaternary: the southern and central sub-basin was infilled by shelf fluvio-deltaic and prodeltaic sediments delivered from the east and south-east, whilst the northern sub-basin was infilled mainly by prograding glacigenic debris-flows deposited from an ice mass centred on the Norwegian mainland. Contour currents were an important mechanism of sediment deposition and reworking, with water circulation in the basin probably occurring in an anti-clockwise direction. Whilst most of the southern North Sea Basin was infilled by around 1.6–1.7 Ma, a depression persisted in the central North Sea until around 1 Ma. The analysis of landforms on 3D seismic data suggests that the Fennoscandian Ice Sheet (FIS) extended intermittently to the palaeo-shelf break in the northern North Sea during the earliest Quaternary and expanded into the central North Sea prior to the excavation of the Norwegian Channel.

OSL dating of Weichselian ice-free periods at Skorgenes, western Norway

During recent years, many sites with sediments pre-dating the Last Glacial Maximum have been identified in formerly glaciated areas. As more and better dates are presented from these sites, the dynamic behaviour of the Scandinavian Ice Sheet is becoming increasingly clear. In this study, we revisited the site Skorgenes in western Norway. Here, sediments from two ice-free periods are found below and interbedded with glacial diamicts. We present an updated chronology for the site, based on ten new Optically Stimulated Luminescence (OSL) dates, and discuss possible correlations. The samples had poor OSL properties but still provide a substantial improvement of the existing chronology. The oldest sediments identified at Skorgenes were deposited in a proglacial subaqueous setting at some point between 21 and 42 ka. This period was followed by a glacial advance and, during the subsequent ice retreat, a delta or subaqueous fan formed at Skorgenes. OSL ages from the foreset beds indicate deposition at some point between 17 and 30 ka, implying that the ice-front retreated east of Skorgenes at least once during the Late Weichselian. A substantial ice advance followed this retreat. The youngest sediments, forming a proglacial delta succession, were deposited during the final deglaciation of the site. (Less)

A postglacial relative sea-level database for the Russian Arctic coast

We present the first quality-controlled relative sea-level (RSL) database for the Russian Arctic coast from the Barents Sea in the west to Laptev Sea in the east (29–152oE and 63 to 81oN). The database consists of 385 sea-level index points and 249 limiting dates and spans 24 ka to present. Sea-level indicators are derived from multiple proxies, including isolation basins, raised beaches, glacial erratics, marine terraces, laidas (salt marshes), and deltaic salt marshes. Here, we calculate the indicative meanings for all indicators and evaluated possible elevation errors. We have estimated the ages and uncertainties of index points and limiting dates using the most recent calibration datasets.In the western Russian Arctic (Barents and White Seas), RSL was driven by glacial isostatic adjustment (GIA) due to deglaciation of the Eurasian ice sheet complex. For example, within the Baltic crystalline shield, RSL fell rapidly from 80 to 100 m at 11–12 ka to 15–25 m at ∼4–5 ka. In the Arctic Islands of Franz-Joseph Land and Novaya Zemlya, RSL gradually fell from 25 to 35 m at 9 ka to 5–10 m at 3 ka. The Timan coast and the Kara Sea shelf are characterized by constant RSL rise due to proglacial forebulge collapse; Yamal and the Gydan Peninsula and Novaya Zemlya are all marked by a high LGM position of RSL, followed by a lowstand and consequent rise to a late Holocene highstand of several meters. Data from the Laptev Sea coasts and shelf and the New Siberian Islands demonstrate post-LGM RSL rise with a Holocene highstand of up to 5–10 m, with scatter caused by differential tectonic movements along a diffuse lithospheric plate boundary. The collected database allowed to estimate and discuss the reasons of both spatial and temporal variability of RSL histories in different parts of the Russian Arctic.

Assessment of paleo-recharge under the Fennoscandian Ice Sheet and its impact on regional groundwater flow in the northern Baltic Artesian Basin using a numerical model

The study investigates the mechanism of glacial meltwater recharge under the Fennosciandian Ice Sheet during the last glacial maximum (LGM) and its impact on regional groundwater flow in the northern Baltic Artesian Basin (BAB) in Estonia and Latvia. The current hypothesis is that a flow reversal occurred in the BAB due to subglacial recharge during the LGM. This hypothesis is supported by an extensive dataset of geochemical and isotopic measurements in the groundwater of northern Estonia, exhibiting significant depletion in δ18O with respect to modern precipitation. To verify the consistency of this hypothesis and better understand groundwater flow dynamics during the LGM period, a numerical model is developed for this area. Two cross-sectional models have been created across the northern BAB, in which groundwater flow and the transport of δ18O have been simulated from the beginning of the LGM to present-day. Several simulations were performed with different subglacial boundary conditions, to investigate the uncertainty related to subglacial recharge of meltwater during the LGM and the subsequent flow reversal in the northern BAB. Several simulations provide a satisfying fit between computed and observed values of δ18O, which means that the hypothesis of subglacial recharge of meltwater is consistent with δ18O distribution. The numerical model suggests that preservation of meltwater in northern Estonia is controlled by confining layers and the proximity to the outcrop area of aquifers, located in the Gulf of Finland. The results also suggest that glacial meltwater has been preserved under the Baltic Sea in the Gulf of Riga.

Holocene sea-level database from the Atlantic coast of Europe

High-quality relative sea-level (RSL) data reveal spatial and temporal variations in crustal movements during the Holocene, which are used for many applications, ranging from calibrating models of earth rheology and ice sheet reconstructions to the development of coastal lowlands and human occupation. Here, we present a Holocene RSL database for the Atlantic coast of Europe (ACE) and estimate rates of RSL change from the ACE database using a spatio-temporal empirical hierarchical model. The database contains 214 index points, which locate the RSL position in space and time, and 126 limiting dates, which constrain RSL to above or below a certain elevation at a specific point in time. The temporal distribution extends from present to ∼11.5 ka, with only 42 index points older than 7 ka. The spatial distribution spans 1700 km from French Flanders (France) to Algarve (Portugal), with more than half of the index points concentrated along the French coast.The ACE database shows RSL was below present during the Holocene. Rates of RSL change were highest during the early Holocene, ranging between 6.8 ± 0.5 mm yr−1 in middle Portugal and 6.3 ± 0.8 mm yr−1 in southern France from 10 to 7 ka. Mid-to late-Holocene rates decreased over time with rates ranging between 0.9 ± 0.4 mm yr−1 in middle France and 0.1 ± 0.5 mm yr−1 in middle Portugal from 4 ka to present. Comparison of the RSL data to output from a glacial-isostatic adjustment model suggests that deglaciation of the British-Irish and Fennoscandian Ice Sheets dominates the large-scale variability captured by the ACE database, which reflects a decreasing influence of the collapsing British-Irish and Fennoscandian peripheral forebulge that migrated from the northeast to the northwest after ∼4 ka.

Evidence from seismites for glacio-isostatically induced crustal faulting in front of an advancing land-ice mass (Rügen Island, SW Baltic Sea)

It is hitherto commonly thought that earthquakes triggered by geologically rapid changes in the pressure caused by the fluctuating extent of thick land-ice masses occur exclusively during ice retreat. Our study of deformed sediment layers within an undeformed glaciolacustrine and glaciofluvial succession exposed in a coastal cliff on Rügen Island, south-western Baltic Sea, challenges this widespread idea. Based on their structural and deformational features, the layers under investigation are interpreted as seismites which formed as a result of seismically-induced liquefaction. The stratigraphic context aided by optically stimulated luminescence (OSL) dating indicate that the documented seismites must have formed shortly before the front of the Pleistocene Scandinavian Ice Sheet reached the study area during the Last Glacial Maximum, thus during a stage of ice advance. This implies that the flexural isostatic response of the Earth's crust as a consequence of the ice load during ice advance was accompanied by earthquakes probably due to local re-activation of pre-existing faults. The crustal response to an increasing ice load was consequently less gradual than previous studies about glaciation-related tectonics suggest.

Alaskan marine transgressions record out-of-phase Arctic Ocean glaciation during the last interglacial

Ongoing climate change focuses attention on the Arctic cryosphere’s responses to past and future climate states. Although it is now recognized the Arctic Ocean Basin was covered by ice sheets and their associated floating ice shelves several times during the Late Pleistocene, the timing and extent of these polar ice sheets remain uncertain. Here we relate a relict barrier-island system on the Beaufort Sea coast of northern Alaska to the isostatic effects of a previously unrecognized ice shelf grounded on the adjacent continental shelf. A new suite of optically stimulated luminescence dates show that this barrier system formed during one or more marine transgressions occurring late in Marine Isotope Stage 5 (MIS 5) between 113 ka and 71 ka. Because these transgressions occurred after the warmest part of the last interglacial (ca. 123 ka) and did not coincide with the global eustatic sea-level maximum during MIS 5e, this indicates Arctic ice sheets developed out-of-phase with lower-latitude sectors of the Laurentide and Fennoscandian ice sheets. We speculate that Arctic ice sheets began development during full interglacial conditions when abundant moisture penetrated to high latitudes, and low summer insolation favored glacier growth. These ice sheets reached their full extents at interglacial-glacial transitions, then wasted away at the heights of mid-latitude glaciations because of moisture limitations.

Prospects and limitations of heavy mineral analyses to discriminate preglacial/glacial transitions in Pleistocene sedimentary successions

Abstract The present study revolves around the identification of the stratigraphical boundary between Pleistocene formations that formed prior to the first advance of the Scandinavian ice sheet (Early Pleistocene, i.e., the so-called preglacial) and the overlying, glacially derived deposits (Middle Pleistocene). In particular, it focuses on variation in heavy mineral assemblages, which are an important tool for stratigraphers. The Neogene basement, described here, was most often the source of material that was redeposited by Early Pleistocene rivers. The geological structure and Early Pleistocene palaeogeographical scenarios for various Polish regions are discussed. Moreover, comparisons with other European preglacial formations are carried out. The mineral spectrum of Lower Pleistocene deposits is largely dependent of rocks of the Neogene and Mesozoic basement. If the incision of ancient catchments was into terrigenous rocks, the stratigraphical boundary between preglacial and glacial formations is easily determined with the help of a heavy mineral analysis. As a rule, this coincides with a noticeable change from resistant to non-resistant mineral associations. Such cases are noted for successions in central Poland and eastern England. On the other hand, outcrops of igneous or metamorphic rocks exist within preglacial river catchments in most parts of Europe. They were the local sources of non-resistant heavy minerals long before their glacial supply from the Baltic Shield. In these cases, mineralogical analysis fails in the search for the Early/Middle Pleistocene transition.

Atmosphere-driven ice sheet mass loss paced by topography: Insights from modelling the south-western Scandinavian Ice Sheet

Marine-terminating glaciers and ice streams are important controls of ice sheet mass balance. However, understanding of their long-term response to external forcing is limited by relatively short observational records of present-day glaciers and sparse geologic evidence for paleo-glaciers. Here we use a high-resolution ice sheet model with an accurate representation of grounding line dynamics to study the deglaciation of the marine-based south-western Norwegian sector of the Scandinavian Ice Sheet and its sensitivity to ocean and atmosphere forcing. We find that the regional response to a uniform climate change is highly dependent on the local bedrock topography, consistent with ice sheet reconstructions. Our simulations suggest that ocean warming is able to trigger initial retreat in several fjords, but is not sufficient to explain retreat everywhere. Widespread retreat requires additional ice thinning driven by surface melt. Once retreat is triggered, the underlying bedrock topography and fjord width control the rate and extent of retreat, while multi-millennial changes over the course of deglaciation are modulated by surface melt. We suggest that fjord geometry, ice-ocean interactions and grounding line dynamics are vital controls of decadal-to centennial scale ice sheet mass loss. However, we postulate that atmospheric changes are the most important drivers of widespread ice sheet demise, and will likely trump oceanic influence on future ice sheet mass loss and resulting sea level rise over centennial and longer time scales.

Improved Pleistocene sediment stratigraphy and paleoenvironmental implications for the western Arctic Ocean off the East Siberian and Chukchi margins

Sediment cores from the East Siberian and Chukchi margins and adjacent basins are used to refine the upper Pleistocene stratigraphy and better constrain the timing of major glacial advances in the western Arctic Ocean. Cores have been analysed using high-resolution non-destructive physical properties (density, magnetic susceptibility and colour) and X-ray fluorescence elemental measurements (manganese and calcium contents). All analysed cores reveal a spatially coherent stratigraphic pattern that enables robust correlations from the East Siberian margin to the Mendeleev and Northwind Ridges, thus highlighting the potential of such multiproxy approach for improving stratigraphic framework. The distribution of sedimentary units resulting from core correlation indicates decreasing sedimentation rates by more than one order of magnitude from the East Siberian margin east- and northwards, reflecting an increased distance from the main sediment sources, increasing sea-ice cover, and longer residence times in the Beaufort Gyre circulation. The stratigraphy presented, consistent with existing geophysical data, indicates the most recent major glacial advance from the East Siberian margin with ice grounding at water depth > 800 m during estimated Marine Isotope Stages 4/3, roughly contemporaneous with the Middle Weichselian glaciation in northern Eurasia. Earlier glacial events are potentially indicated by glaciogenic units in cores away from the margin, where they are not overprinted by a younger ice advance. Sediment thickness increase towards the Siberian margin also suggests the possibility of a limited MIS 2 glaciation, although no direct evidence for such an ice sheet has been found thus far.

Progressive ductile shearing during till accretion within the deforming bed of a palaeo-ice stream

This paper presents the results of a detailed microstructural study of a thick till formed beneath the Weichselian (Devensian) Odra palaeo-ice stream, west of Środa Wielkopolska, Poland. This SE-flowing ice stream was one of a number of corridors of faster flowing ice which drained the Scandinavian Ice Sheet in the Baltic region. Macroscopically, the massive, laterally extensive till which formed the bed of this ice stream lacks any obvious evidence of glaciotectonism (thrusting, folding). However, microscale analysis reveals that bed deformation was dominated by foliation development, recording progressive ductile shearing within a subhorizontal subglacial shear zone. Five successive generations of clast microfabric (S1 to S5) have been identified defining a set of up-ice and down-ice dipping Riedel shears, as well as a subhorizontal shear foliation coplanar to the ice-bed interface. Cross-cutting relationships between the shear fabrics record temporal changes in the style of deformation during this progressive shear event. Kinematic indicators (S-C and ECC-type fabrics) within the till indicate a consistent SE-directed shear sense, in agreement with the regional ice flow pattern. A model of bed deformation involving incremental progressive simple shear during till accretion is proposed. The relative age of this deformation was diachronous becoming progressively younger upwards, compatible with subglacial shearing having accompanied till accretion at the top of the deforming bed. Variation in the relative intensity of the microfabrics records changes in the magnitude of the cumulative strain imposed on the till and the degree of coupling between the ice and underlying bed during fast ice flow.

Orchid colonization: multiple parallel dispersal events and mosaic genetic structure in Dactylorhiza majalis ssp. lapponica on the Baltic island of Gotland.

The island of Gotland in the Baltic Sea has had no contact with surrounding continental areas since the withdrawal of the Weichselian ice sheet at approx. 17 ka BP. Plants present on Gotland must have arrived by long-distance dispersal, so populations are expected to exhibit reduced levels of genetic diversity compared with populations on surrounding mainlands. However, orchids have very small seeds, which appear well adapted to long-distance dispersal, and they should therefore be less affected than other plant species by colonization bottlenecks. The aim of this study was to analyse the genetic structure of orchids colonizing isolated islands, using the marsh orchid Dactylorhiza majalis ssp. lapponica as a case study. More than 500 samples from 27 populations were analysed for 15 plastid and eight nuclear marker loci. Population diversity and differentiation patterns were compared for nuclear and plastid marker systems and analysed in relation to geographical location. We found high genetic diversity but no clear geographical structure of genetic differentiation between populations on Gotland. However, the between-population differentiation in plastid and nuclear markers were correlated and the greatest diversity was found at sites at comparatively high elevations, which were the first to emerge above the water after the Ice Age. The regional population on Gotland has been established by a minimum of four dispersal events from continental regions. Subsequent gene flow between sites has not yet homogenized the differentiation pattern originating from initial colonization. We conclude that long-distance seed dispersal in orchids has a strong impact on structuring genetic diversity during periods of expansion and colonization, but contributes less to gene flow between populations once a stable population structure has been achieved.

A new approach for simulating the paleo-evolution of the Northern Hemisphere ice sheets

Abstract. Offline forcing methods for ice-sheet models often make use of an index approach in which temperature anomalies relative to the present are calculated by combining a simulated glacial–interglacial climatic anomaly field, interpolated through an index derived from the Greenland ice-core temperature reconstruction, with present-day climatologies. An important drawback of this approach is that it clearly misrepresents climate variability at millennial timescales. The reason for this is that the spatial glacial–interglacial anomaly field used is associated with orbital climatic variations, while it is scaled following the characteristic time evolution of the index, which includes orbital and millennial-scale climate variability. The spatial patterns of orbital and millennial variability are clearly not the same, as indicated by a wealth of models and data. As a result, this method can be expected to lead to a misrepresentation of climate variability and thus of the past evolution of Northern Hemisphere (NH) ice sheets. Here we illustrate the problems derived from this approach and propose a new offline climate forcing method that attempts to better represent the characteristic pattern of millennial-scale climate variability by including an additional spatial anomaly field associated with this timescale. To this end, three different synthetic transient forcing climatologies are developed for the past 120 kyr following a perturbative approach and are applied to an ice-sheet model. The impact of the climatologies on the paleo-evolution of the NH ice sheets is evaluated. The first method follows the usual index approach in which temperature anomalies relative to the present are calculated by combining a simulated glacial–interglacial climatic anomaly field, interpolated through an index derived from ice-core data, with present-day climatologies. In the second approach the representation of millennial-scale climate variability is improved by incorporating a simulated stadial–interstadial anomaly field. The third is a refinement of the second one in which the amplitudes of both orbital and millennial-scale variations are tuned to provide perfect agreement with a recently published absolute temperature reconstruction over Greenland. The comparison of the three climate forcing methods highlights the tendency of the usual index approach to overestimate the temperature variability over North America and Eurasia at millennial timescales. This leads to a relatively high NH ice-volume variability on these timescales. Through enhanced ablation, this results in too low an ice volume throughout the last glacial period (LGP), below or at the lower end of the uncertainty range of estimations. Improving the representation of millennial-scale variability alone yields an important increase in ice volume in all NH ice sheets but especially in the Fennoscandian Ice Sheet (FIS). Optimizing the amplitude of the temperature anomalies to match the Greenland reconstruction results in a further increase in the simulated ice-sheet volume throughout the LGP. Our new method provides a more realistic representation of orbital and millennial-scale climate variability and improves the transient forcing of ice sheets during the LGP. Interestingly, our new approach underestimates ice-volume variations on millennial timescales as indicated by sea-level records. This suggests that either the origin of the latter is not the NH or that processes not represented in our study, notably variations in oceanic conditions, need to be invoked to explain millennial-scale ice-volume fluctuations. We finally provide here both our derived climate evolution of the LGP using the three methods as well as the resulting ice-sheet configurations. These could be of interest for future studies dealing with the atmospheric or/and oceanic consequences of transient ice-sheet evolution throughout the LGP and as a source of climate input to other ice-sheet models.

Late Pleistocene palaeoenvironments and the last deglaciation on the Kola Peninsula, Russia

Key geological sections on the southern part of the Kola Peninsula were investigated to reveal the evolution of the Late Pleistocene palaeoenvironments and the history of the last deglaciation of the area. Methods used were conventional sedimentological techniques, including palaeocurrent analysis and geomorphological observations. Optically stimulated luminescence dating was used to determine the age of sand-rich sediment units exposed in sections. The results indicate that the Eemian (MIS 5e) marine environment in the onshore coastal areas gradually changed into a glaciolacustrine environment. The first ice advance into the western part of the study area took place already during the Early Weichselian (MIS 5b?). After deglaciation, glaciolacustrine conditions were re-established in the area. Only one younger until is observed in the area; it cannot be excluded that this stems from a Middle Weichselian (MIS 4) glaciation over the area, though it is more probable that it is from the last Scandinavian ice sheet advance over the area during the Last Glacial Maximum (LGM). The southern and central coastal areas of the Kola Peninsula deglaciated between 16,000 and 12,000 years ago. The most prominent end moraine ridges, the Keiva II and Keiva I end moraines were formed in an interlobate zone between ice mass in the interior of the Kola Peninsula and the White Sea ice lobe during the Younger Dryas.

Dating of paleolandslides in western Finnish Lapland

AbstractThe dating of landslide‐buried organic materials potentially indicates non‐stationary seismicity in northern Finland attributable to the release of lithospheric stresses during and after retreat of the Scandinavian Ice Sheet. The landslide age data reveals three episodes of increased slope instability and formation of landslides, from 9000 to 11 000 cal BP, from 5000 to 6000 cal BP, and from 1000 to 3000 cal BP. While a seismogenic origin cannot be unequivocally established, we interpret that at least the early Holocene episode reflects increased seismic activity in northern Finland in association with late‐glacial and postglacial faulting. The foci of slope instabilities changes through time, implying that different segments of the postglacial fault systems were active at different times during the Holocene. We also show that the correlation of landslide ages with the surface roughness and backwall slope is complicated. The morphology of landslide scarps is significantly affected by thickness of glacial sediments, liquefaction during landslide formation, and accumulation of peat upon landslide scars and deposits, and thus, the time‐dependent erosional smoothing of the surfaces should be considered as descriptive and non‐qualitative. Copyright © 2018 John Wiley & Sons, Ltd.

The Last Scottish Ice Sheet

ABSTRACTThe last Scottish Ice Sheet (SIS) expanded from a pre-existing ice cap after ∼35 ka. Highland ice dominated, with subsequent build-up of a Southern Uplands ice mass. The Outer Hebrides, Skye, Mull, the Cairngorms and Shetland supported persistent independent ice centres. Expansion was accompanied by ice-divide migration and switching flow directions. Ice nourished in Scotland reached the Atlantic Shelf break in some sectors but only mid-shelf in others, was confluent with the Fennoscandian Ice Sheet (FIS) in the North Sea Basin, extended into northern England, and fed the Irish Sea Ice Stream and a lobe that reached East Anglia. The timing of maximum extent was diachronous, from ∼30–27 ka on the Atlantic Shelf to ∼22–21 ka in Yorkshire. The SIS buried all mountains, but experienced periods of thickening alternating with drawdown driven by ice streams such as the Minch, the Hebrides and the Moray Firth Ice Streams. Submarine moraine banks indicate oscillating retreat and progressive decoupling of Highland ice from Orkney–Shetland ice. The pattern and timing of separation of the SIS and FIS in the North Sea Basin remain uncertain. Available evidence suggests that by ∼17 ka, much of the Sea of the Hebrides, the Outer Hebrides, Caithness and the coasts of E Scotland were deglaciated. By ∼16 ka, the Solway lowlands, Orkney and Shetland were deglaciated, the SIS and Irish Ice Sheet had separated, the ice margin lay along the western seaboard, nunataks had emerged in Wester Ross, the ice margin lay N of the Cairngorms and the sea had invaded the Tay and Forth estuaries. By ∼15 ka, most of the Southern Uplands, the Firth of Clyde, the Midland Valley and the upper Spey valley were deglaciated, and in NW Scotland ice was retreating from fjords and valleys. By the onset of rapid warming at ∼14.7 ka, much of the remnant SIS was confined within the limits of Younger Dryas glaciation. The SIS, therefore, lost most of its mass during the Dimlington Stade. It is uncertain whether fragments of the SIS persisted on high ground throughout the Lateglacial Interstade.

Late Pleistocene climate of Poland in the mid-European context

Proxy data from pollen and mollusc indicator species, periglacial phenomena, changes in geometry of mountain palaeoglaciers and based on selected lithological and geomorphological features enabled reconstruction of the Late Pleistocene climate characteristics in Poland and adjacent areas. Climate during the Eemian was generally stable but with a distinct west-east gradient in summer. Strong influence of the Atlantic air masses moving to the east resulted in the annual precipitation over 600 mm. Climate instability in the late Eemian as well as during stadials and interstadials of the Early Weichselian was expressed by progressive cooling and increasing temperature difference between winters and summers, reflecting stronger continentalism towards the west, accompanied by decreased precipitation. Periglacial frost crackings and polygonal patterns indicated occurrence of permafrost in Poland already at about 49 ka BP and its occurrence until the termination of the last glaciation. These periglacial structures have developed at mean annual temperatures from −9 to −4 °C, with winter extremes up to about −25 °C. Mean summer temperature reached likely around 10 °C as suggested by palaeobotanic record. Palaeoglaciological studies of mountain glaciers across Europe allowed inferring their activity and sensitivity to climatic fluctuations during the Late Weichselian. The Weichselian of central Europe was controlled mostly by the southerly and easterly circulation dominated by climate cyclones and anticyclones, respectively. An inflow of air masses from the west was significantly limited and concentrated mainly within the so-called periglacial corridor between the Scandinavian ice sheet and the Alps. Such circulation pattern determined serious reduction of precipitation during the Last Glacial Maximum that reached 60% in relation to modern conditions. The following Late Pleistocene cold phases (Oldest and Younger Dryas) were slightly warmer and wetter with increasing contribution of the westerlies that were strongly dependent on progressing shrinkage of the Northern Hemisphere ice sheets.