bluuebunny/crossref_metadata_2025 huggingface dataset:
A Holocene seabird record from Raffles Sø sediments, East Greenland, in response to climatic and oceanic changes
Authors: WAGNER BERND , MELLES MARTIN
Published: July 2010

A 3.5‐m‐long sediment sequence from a lake on Raffles Ø, off Liverpool Land, East Greenland, was investigated for chronology, lithology, palynology and biogeochemistry. Radiocarbon‐dating of plant remains and the lithology of the sediment succession indicate continuous sedimentation since deglaciation of the area prior to 10000 cal. yr BP. The postglacial palynological record shows little variation and evidence of a wind‐transported pollen supply, both resulting from the geographical characteristics of Raffles Ø. Significant variations in the biogeochemical data reflect changes in aquatic bioproduction. These changes depend to some extent on climatic changes; however, they are mainly due to variations in seabird breeding colonies in the catchment which influence nutrient and cadmium supply to the lake. Large seabird breeding colonies were present between 7500 and 1900, from 1000 to 500, and sincec.100 cal. yr BP. Their absence prior to 7500 cal. yr BP may be the result of unsuitable feeding conditions close to Raffles Ø caused by a too dense or too open sea‐ice cover. In contrast, between 1900 and 1000 and from 500 to 100 cal. yr BP, the seabird settlement was probably restricted by an insufficiently long breeding season due to cold climate conditions in East Greenland.
The late Miocene to Pleistocene ice‐rafting history of southeast Greenland
Authors: JOHN KRISTEN E. K. ST. , KRISSEK LAWRENCE A.
Published: July 2010

Analysis of a Miocene‐Pleistocene ice‐rafted debris (IRD) record from the western Irminger Basin provides evidence for the initiation and long‐term behavior of the SE portion of the Greenland Ice Sheet. In the late Miocene (˜7.3 Ma), IRD supply to Ocean Drilling Program site 918 increased significantly indicating that glaciers large enough to reach sea level were present in SE Greenland long before the onset of widespread Northern Hemisphere glaciation. IRD accumulated at this site throughout the Pliocene and Pleistocene, supporting the hypothesis that SE Greenland was a key nucleation area for the formation of the Greenland Ice Sheet. Since glacial onset, the western Irminger Basin IRD record is characterized by a succession of episodes with high IRD mass accumulation rates (MARs). The site 918 IRD record indicates that greatest iceberg production in SE Greenland occurred during major climatic transitions (e.g. widespread Northern Hemisphere glacial expansion at 2.7 Ma and the mid‐Pleistocene climate shift at 0.9 Ma), and that SE Greenland sometimes also led the northern North Atlantic region in glacial response to climatic forcing (e.g. glacial intensification at ˜4.8 and, along with NE Greenland, at ˜3.5 Ma).
Comparing X‐ray densitometry and BSE‐image analysis of thin section in varved sediments
Authors: OJALA ANTTI E. K. , FRANCUS PIERRE
Published: July 2010

A 10‐cm long section from varved sequence of Lake Nautajärvi, Finland, has been analysed using both X‐ray densitometry and image analysis of Backscattered Scanning Electron microscope Images (BSEI) of thin sections. Lake Nautajärvi's clastic‐organi c varves appear in X‐ray images as a succession of dark and pale stripes, pale ones being the spring detrital minerogenic layers and dark ones organic matter laid down during the time of summer, autumn and winter ice cover. Owing to the sharp contrast of the minerogenic spring layer, a semiautomatic tree‐ring width and density measurement DendroScan system was applied to obtain seasonal/annual data of relative X‐ray density. Mean density of BSEI was also acquired. Then BSEI were processed to produce black and white images, where white pixels represent the clay‐rich sedimentary matrix and black pixels the particles in the matrix: silt‐ or sand‐sized, terrigenous grains, authigenic particles and diatoms. Measurements of the size of the detrital particles forming the varves were obtained. For each varve, mean grey‐level values in BSEI correlated well with the mean grey‐level values of X‐ray images, but grain size obtained on BSEI did not correlate with any parameters computed from X‐ray radiography.
Glacier margin fluctuations, Skaftafellsjökull, Iceland: implications for sandur evolution
Authors: MARREN PHILIP M.
Published: July 2010

This paper relates recent proglacial fluvial channel change at Skaftafellsjökull, southeast Iceland, to glacier margin fluctuations. Observations of the western portion of the proglacial braided sandur were made annually between 1996 and 2000. Between 1996 and 1998, during a period of glacier advance, the proximal proglacial outwash surface at the western end of the glacier margin was characterized by a complex braided channel pattern active over the entire sandur surface. Retreat of the glacier margin since 1998 led to rapid incision, so that by 1999 abandonment of the proximal terrace surface and reorganization of the proglacial fluvial system into a single, entrenched channel had occurred. Further retreat and incision occurred during 1999–2000. These observations demonstrate that glacier retreat at Skaftafellsjökull is accompanied by short‐lived rapid incision events and terrace formation, separated by long intervals of relatively minor change rather than progressive incision over long time periods. The margin of Skaftafellsjökull is thought to be particularly sensitive to retreat, as the glacier occupies an overdeepening behind the snout and results in lowering of the river's point of exit from the glacier, necessitating adjustment of the river's long profile.
Morphologic and stratigraphic evidence for Allerød and Younger Dryas age glacier fluctuations of the Cordilleran Ice Sheet, British Columbia, Canada and Northwest Washington, U.S.A.
Authors: KOVANEN DORI J.
Published: July 2010

The late Wisconsin deglaciation of the Fraser Lowland is reconstructed by integrating surficial mapping, stratigraphic, palynological, oceanographic (from previous studies), radiocarbon, and shaded digital topographic data Moraines associated with glacier fluctuations along the southwestern margin of the Cordilleran Ice Sheet are recognized for the first time and their chronology is established from 70 radiocarbon dates secured by morphologic and stratigraphic evidence. Following emergence of the lowland at c. 11.6 14C kyr BP, three periods of glacier readvance occurred 11.6–11.4 and 10.9–10.2 14C kyr BP during the Sumas interval. The spatial and temporal relationships of Sumas Drift indicate four recognizable phases, which unifies and extends the surficial geology across the U.S.‐Canadian border.
Relative sea‐level trends during the early–middle Holocene along the eastern coast of mainland Scotland, UK
Authors: SMITH DAVID E. , FIRTH CALLUM R. , CULLINGFORD ROBIN A.
Published: July 2010

Previously published radiocarbon‐dated horizons relating to early and middle Holocene relative sea‐level change along the eastern coast of mainland Scotland are examined and trends determined. The data are modified to ensure comparability and are compared against the pattern of glacio‐isostatic uplift in the area. Results show that the rate of relative sea‐level rise during the Main Postglacial Transgression in the middle Holocene becomes greater towards the edge of the uplifted area, whilst the age of the Main Postglacial Shoreline becomes younger in the same direction. Linear and quadratic regression analyses disclose trends which indicate that at the 0 m HWMOST isobase of the Main Postglacial Shoreline the rate of relative sea level rise between c. 8400 and c. 7000 14C years BP (c. 9500 to c. 7900 cal. BP) was 5–11 mm/radiocarbon year or 6–11 mm/calibrated year, whilst at the same isobase the Main Postglacial Shoreline was reached between 5500 and 6100 14C years BP (between 6300 and 7000 cal. BP). The relative sea‐level changes identified are compatible with a rising sea surface level offshore, which may have involved three episodes, possibly related to regional and wider deglaciation.
Are long subglacial bedforms indicative of fast ice flow?
Authors: STOKES CHRIS R. , CLARK CHRIS D.
Published: July 2010

It has been suggested that extremely long subglacial bedforms (e.g. attenuated drumlins and mega‐scale glacial lineations) record former areas of fast‐flowing ice and that bedform elongation ratio is a useful proxy for ice velocity. Despite the availability of much data pertaining to the measurement and analysis of subglacial bed‐forms, these assumptions have rarely been explicitly addressed in detail. In this paper, we demonstrate that long subglacial bedforms (length:width ratios 10:1) are indicative of fast ice flow. Using satellite imagery, we mapped over 8000 lineaments associated with a highly convergent flow pattern near Dubawnt Lake, District of Keewatin, Canada. This flow pattern is unusual in that it displays a large zone of convergence feeding into a main ‘trunk’ and then diverging towards the inferred ice margin. The ‘bottleneck’ pattern is taken to record an increase and subsequent decrease in ice velocity and we analysed transverse and longitudinal variations in bedform morphometry. The main trunk of the flow pattern (down‐ice of the convergent zone) is characterized by mega‐scale glacial lineations of great length (up to 13 km) and high elongation ratios (up to 43:1). The down‐ice variations in elongation ratio reflect exactly what we would expect from a terrestrial ice stream whose velocity increases in the onset zone passes through a maximum in the main trunk and slows down as the ice diverges at the terminus. It is suggested that any unifying theory of drumlin formation must be able to account for the association between long subglacial bedforms and fast ice flow, although it is not assumed that fast ice flow always produces attenuated bedforms. A further implication of this work is that many more ice streams may be identified on the basis of attenuated subglacial bedforms, radically altering our views on the flow dynamics of former ice sheets.
Testing the case for a Middle Pleistocene Scandinavian glaciation in Eastern England: evidence for a Scottish ice source for tills within the Corton Formation of East Anglia, UK
Authors: LEE JONATHAN R. , ROSE JAMES , RIDING JAMES B. , MOORLOCK BRIAN S. P. , HAMBLIN RICHARD J. O.
Published: July 2010

The provenance of the Happisburgh Till and Corton Till of the Corton Formation is investigated using erratic clast lithologie s and allochthonou s palynomorph s to test whether the long held assumptio n that they were deposited by ice that originated in Scandinavia is valid. The results show a wide range of lithologie s including Carboniferous Limestone and Coal Measures, and Permian Magnesian Limestone that are not found in Scandinavia, and an absence of distinctive Scandinavian material such as rhomb porphyry and larvikite. Lithologies found indicate deposition by an ice sheet which flowed southwards into north‐east East Anglia from central and southern Scotland eroding and transporting materials derived from outcrops in these areas and from eastern England and the western margins of the southern North Sea Basin. It is concluded that the long held assumption that the Happisburgh Till and Corton Till of the Corton Formation were deposited by a Scandinavian ice sheet is erroneous and that they were instead deposited by Scottish ice.
Glacial deposits and ice‐sheet dynamics in the north‐central Baltic Sea during the last deglaciation
Authors: NOORMETS RIKO , FLODÉN TOM
Published: July 2010

Nine seismic stratigraphic units were distinguished, and their distribution mapped, in an 80 × 130 km submeridionally oriented area in the north‐central Baltic Sea, east of Gotska Sandön and Farö. Analysis of these units revealed a great influence of the bedrock topography on the structure and distribution of the glacial deposits. Major glacially eroded valleys in the Baltic Clint, connecting the Faro Deep and the North Central Baltic Basin (Harff & Winterhalter 1996) across a narrow sill, form an extensive submeridional bedrock depression. The concentration of ice flow into this depression is reflected in the drumlinized surface of the till near the Baltic Clint. Large eskers in the elongated bedrock depressions and on the Ordovician Plateau mark the locations of former subglacial meltwater conduits. Termination of the eskers with extensive glacio fluvial outwash fans at the northern limit of the Farö Deep, the presence of subaquatic melt‐out till in the bottom of it, and wedge‐shaped ice‐marginal grounding‐line deposit on the Silurian Plateau suggest floating ice margin conditions in the low‐lying areas and a local ice shelf confined to the Frö Deep during the deglaciation.
Rice domestication and climatic change: phytolith evidence from East China
Authors: LU HOUYUAN , LIU ZHENXIA , WU NAIQIN , BERNÉ SERGE , SAITO YOSHIKI , LIU BAOZHU , WANG LUO
Published: July 2010

Fossil rice phytoliths have been identified from a lateglacial to Holocene sequence of epicontinental sediments in the East China Sea that were probably transported by the Yangtze River from its middle and/or lower reaches. The rice phytoliths occurred first in the sequence at about 13 900 cal. yr BP and disappeared during the period of 13 000–10000 cal. yr BP, implying the earliest domesticated cereal crops of the world ever reported. Based on the records of phytoliths, pollen, diatoms and foraminifera from the sequence, the climate between 13 000 and 10 000 cal. yr BP was notably colder (Younger Dryas). The coincidence of disappearance of domesticated rice phytoliths with cold climate conditions may suggest a great climatic influence on human activities during that time. Warmer and wetter conditions during the period 13900 to 13000 cal. yr BP and after 10000 cal. yr BP have probably favoured rice domestication in the area.
Timing of Late Quaternary glaciation along the southwestern slopes of the Qilian Shan, Tibet
Authors: OWEN LEWIS A. , SPENCER JOEL Q. , HAIZHOU MA , BARNARD PATRICK L. , DERBYSHIRE EDWARD , FINKEL ROBERT C. , CAFFEE MARC W. , NIAN ZENG YONG
Published: July 2010

Moraines along the southwestern slopes of the Qilian Shan were dated using cosmogenic radionuclide (CRN) surface exposure techniques to help define the timing of glaciation in northernmost Tibet. The CRN data show glaciers extending 5–10 km beyond their present positions during the global Last Glacial Maximum (LGM) and probably maintained at their maximum extent until the Lateglacial. These data help support the view that glaciers throughout Tibet and the Himalaya were maintained at or near their maximum LGM extent until the Lateglacial. An optically stimulated luminescence date of 11.8 ± 1.0 ka on silt that caps a latero‐frontal moraine shows that glaciers had retreated significantly by the end of the Pleistocene and that loess was beginning to form in this region in response to the changing climate during and after the Younger Dryas Stade.
Stable isotope records of plant cover change and monsoon variation in the past 2200 years: evidence from laminated stalagmites in Beijing, China
Authors: HOU JU ZHI , TAN MING , CHENG HAI , LIU TUNG SHENG
Published: July 2010

Two stalagmites collected from the Shihua cave in the southwestern suburb of Beijing were dated by annual layer counting. The results are consistent with thermal ionization mass spectrometry 230Th dating. Stable carbon isotope variation of stalagmites is dominated by plant cover change, which largely reflects climate change and monsoon variation. Oxygen isotopes are mainly affected by precipitation, which is related to summer and winter monsoon intensity. The combination of carbon and oxygen isotopes can therefore be a proxy of plant cover change and monsoon variation. Our stable isotope results show that lower carbon isotope values of the stalagmites between 200 BC and AD 1000 probably imply dense plant cover and an episode dominated by humid summer monsoon. From ˜1000 to AD 1450, the dominant monsoon alternated between the winter monsoon and the summer monsoon. Since ˜AD 1450, a significant jump in carbon isotope ratios and increasing oxygen isotope ratios has been demonstrated, indicating less plant cover and the probable dominance of dry winter monsoon. The results are consistent with historical documents of the region.
Large‐scale glaciotectonic deformation in the Great Lakes basin, USA‐Canada
Authors: LARSON GRAHAME J. , EHLERS JÜRGEN , GIBBARD PHILIP L.
Published: July 2010

Investigation of the sedimentology, stratigraphy and deformation structures of an exposed sedimentary sequence associated with an isolated large ridge along the eastern shore of Lake Michigan reveals that it is part of a broad grounding‐line fan complex that was subjected to extensive glaciotectonic deformation. It is concluded that the sequence formed following melting back of the margin of the Lake Michigan lobe and was subsequently overridden and deformed during advance of the ice margin probably to the Port Huron moraine. The lack of reported major glaciotectonic structures in the Lake Michigan basin compared to that in the North Sea and Baltic Sea basins is most likely due to paucity of soft and incompetent bedrock and/or lack of continuous permafrost conditions during deglaciation.
Lodgement till deposition and deformation investigated by macroscopic observation, thin‐section analysis and electron microscope study at site Dçbe, central Poland
Authors: RUSZCZYŃSKA‐SZENAJCH HANNA , TRZCIŃSKI JERZY , JAROSIŃSKA URSZULA
Published: July 2010

Macroscopic observation, thin‐section analysis and electron microscope study were used in a detailed examination of till exposed in a valley escarpment. The till displays two kinds of bedding: (1) beds of different colour (lithology) that are not separated from one another by distinct boundaries, and (2) beds that are separated by distinct subhorizontal planes of discontinuity, commonly consisting of several beds of the first type. Beds showing no clear separation are interpreted as having been deposited through continuous lodgement, while the distinct discontinuities most probably record sliding planes of the glacier sole during breaks in till deposition. These features, along with the qualitative and quantitative microscopic evidence, indicate that the lower and middle parts of the till were deposited by hard lodgement. The process of deposition was interrupted several times by episodes of non‐deposition, some of them accompanied by glacial erosion. The upper part of the till was deposited by continuous lodgement that was transitional between hard and soft lodgement processes. Such a succession indicates the prevalence of a cooler subglacial thermal regime which changed upwards into a milder one. The till examined displays mainly brittle deformation – namely Riedel shears that are primarily concentrated between the subhorizontal discontinuities characteristic of the lower and middle parts of the section. A dense set of Riedel shears also cuts thicker portions of the upper part of the till and, in some places, such shears combine along additional subhorizontal (discrete) shear planes. The direction of the fractures, as well as the strong fabric orientation of stone a‐axes within the till, indicate an ice flow in the studied area from NW to SE.
Late Pleistocene and Holocene vegetation and climate on the northern Taymyr Peninsula, Arctic Russia
Authors: ANDREEV ANDREI A. , TARASOV PAVEL E. , SIEGERT CHRISTINE , EBEL TOBIAS , KLIMANOV VLADIMIR A. , MELLES MARTIN , BOBROV ANATOLY A. , DEREVIAGIN ALEXANDR YU. , LUBINSKI DAVID J. , HUBBERTEN HANS‐WOLFGANG
Published: July 2010

Pollen data from a Levinson‐Lessing Lake sediment core (74°28'N, 98°38'E) and Cape Sabler, Taymyr Lake permafrost sequences (74°33'N, 100°32'E) reveal substantial environmental changes on the northern Taymyr Peninsula during the last c. 32000 14C years. The continuous records confirm that a scarce steppe‐like vegetation with Poaceae, Artemisia and Cyperaceae dominated c. 32 000–10300 14C yr BP, while tundra‐like vegetation with Oxyria, Ranunculaceae and Caryophyllaceae grew in wetter areas. The coldest interval occurred c. 18000 yr BP. Lateglacial pollen data show several warming events followed by a climate deterioration c. 10500 14C yr BP, which may correspond with the Younger Dryas. The Late Pleistocene/Holocene transition, c. 10300–10000 14C yr BP, is characterized by a change from the herb‐dominated vegetation to shrubby tundra with Betula sect. Nanae and Salix. Alnus fruticosa arrived locally c. 9000–8500 14Cyr BP and disappeared c. 4000–3500 14Cyr BP. Communities of Betula sect. Nanae, broadly distributed at c. 10000–3500 14Cyr BP, almost disappeared when vegetation became similar to the modern herb tundra after 3500–3000 14Cyr BP. Quantitative climate reconstructions show Last Glacial Maximum summer temperature about 4°C below the present and Preboreal (c. 10 000 14C yr BP) temperature 2–4°C above the present. Maximum summer temperature occurred between 10 000 and 5500 14C yr BP; later summers were similar to present or slightly warmer.
Last Interglacial peopling of Siberia: the Middle Palaeolithic site Ust‘‐Izhul’, the upper Yenisei area
Authors: CHLACHULA JIRI , DROZDOV NIKOLAI I. , OVODOV NIKOLAI D.
Published: July 2010

Multidisciplinary Quaternary investigations in the Minusinsk Basin in the upper Yenisei River region and other southern Siberian continental depressions have produced evidence of prehistoric peopling pre‐dating the last glacial stage (>100 ka BP). Abundant ‘pebble tools’ and bone artefacts exposed from eroded alluvia of the Yenisei River terraces indicate repeated occupation of this territory since the Middle Pleistocene. A new stage of expansion of the early human occupation habitat occurred around the last interglacial (OIS 5e) by a Middle Palaeolithic (Neanderthaloid?) population characterized by a core and flake stone industry and open‐air occupation sites. The key camp/kill‐processing site at Ust‘‐Izhul’, dated to c. 125 ka BP and documenting complex behavioural activities, is so far the most complete in situ pre‐Late Palaeolithic site found in Siberia. This unique record provides new insights into the timing and the palaeoenvironmental conditions of the Pleistocene colonization of north‐central Asia.
Holocene climate in the subarctic fjord Malangen, northern Norway: a multi‐proxy study
Authors: HALD MORTEN , HUSUM KATRINE , VORREN TORE O. , GRØSFJELD KARI , JENSEN HENNING B. , SHARAPOVA ALLA
Published: July 2010

A Holocene sedimentary record from the deep‐silled Malangen fjord in northern Norway reveals regional changes in sedimentary environment and climate. Down‐core analysis of two sediment cores includes multi‐core sensor logging, grain size, x‐radiography, foraminifera, oxygen isotopes, dinoflagellates, pollen, trace elements and radiocarbon datings. The cores are located just proximal to the submarine Younger Dryas moraine complex, and reveal the deglaciation after Younger Dryas and the postglacial evolution. Five sedimentary units have been identified. The oldest units, V and IV, bracket the Younger Dryas glacial readvance in the fjord between 12700 cal. years BP and 11 800 cal. years BP. This is followed by deposition of glaciomarine sediments (units IV and III) starting around 12100 cal. years BP. Glaciomarine sedimentation ceased in the fjord c. 10300 cal. years BP and was replaced by open marine sedimentation (units II and I). A rapid stepwise warming occurred during the Preboreal. Onset of surface water warming lagged bottom water warming by several hundred years. The δ18 O record indicates a significant, gradual bottom water cooling (c. 4°C) between 8000 and 2000 cal. years BP, a trend also supported by the other proxy data. Other records in the region, as well as GCM simulations, also support this long‐term climatic evolution. Superimposed on this cooling were brief warmings around 6000 cal. years BP and 2000 cal. years BP. The long‐term change may be driven by orbitally forced reduction in insolation, whereas the short‐term changes may be linked to for example solar forcing, meltwater and NAO changes all causing regional changes in the North Atlantic heat transport.
A 3000‐year palaeoenvironmental record from annually laminated sediment of Lake Korttajarvi, central Finland
Authors: TILJANDER MIA , SAARNISTO MATTI , OJALA ANTTI E. K. , SAARINEN TIMO
Published: July 2010

High‐resolution physical analyses (varve thickness and relative X‐ray density) were conducted on a 3000‐year varved sediment sequence in Lake Korttajarvi, central Finland. Climate and the local environment strongly influence the properties of the lake sediments, and, through a combination of physical proxies, severe and favourable climate periods and anthropogenic effects on sedimentation with an annual to decadal resolution could be detected. We observed previously identified historical climate periods in the Lake Korttajarvi varve record. The Medieval Climate Anomaly (often termed the Medieval Warm Period) of AD 980–1250, which is characterized by highly organic sediment and a minor minerogenic flux during mild winters, started and terminated abruptly, but also included a short (30‐year) colder period lasting between AD 1115 and AD 1145. The Little Ice Age, however, was not clear in our record, although there were two minor cooling periods in AD 1580–1630 and AD 1650–1710. Natural variability in the sediment record was disrupted by increased human impact in the catchment area at AD 1720. There is a distinct positive anomaly in mineral matter accumulation between 907 and 875 BC, which indicates more severe climate conditions. This period exists contemporary with a cold event, recorded worldwide, c. 2800 years ago.
Pleistocene sandur deposits represent braidplains, not alluvial fans
Authors: ZIELINSKI TOMASZ , VAN LOON ANTONIUS J.
Published: July 2010

Weichselian sandar in NE Poland show characteristics that are inconsistent with the commonly accepted alluvial‐fan‐like model for outwash deposition and sandur formation. Analysis of the lithofacies and their vertical and lateral transitions indicates that the Polish sandar developed as braidplains, not as alluvial fans. Analysis of the geomorphic conditions under which modern sandar form, indicates that these conditions (which are characterized by deposition in a narrow belt between ice‐covered mountain ranges and the sea) cannot be considered representative of those that prevailed in the geological past when sandar developed as braidplains in confined valleys, to end up in a lowland area where the deposits could spread out further in lateral directions. The latter conditions have been found consistently for all Polish Weichselian sandar that were investigated in much sedimentological detail. This raises the question whether sandar are alluvial fans or not. Because the development of the sandar in NE Poland seems to be much more representative for outwash deposition than the present‐day sandar in Iceland and elsewhere, the current alluvial‐fan‐like sandur model — based on the fairly exceptional present‐day situation with deposition in a narrow belt — should therefore be replaced by the braidplain‐like sandur model — based on deposition in a valley and in a wider lowland area in front — that has been established for the Polish examples.
Upper Pleistocene stratigraphy at the Medininkai site, eastern Lithuania: a continuous record of the Eemian‐Weichselian sequence
Authors: SATKUNAS JONAS , GRIGIENE ALMA , VELICHKEVICH FELIX , ROBERTSSON ANN‐MARIE , SANDGREN PER
Published: July 2010

Eemian—Weichselian sequences, located outside the maximum limit of the Late Weichselian ice sheet, provide excellent opportunities for the discovery of continuous sedimentary records encompassing the whole Last Interglacial/Glacial cycle. Such a sequence is recorded in a borehole (117P) through the succession in a small kettlehole lake located at Medininkai, eastern Lithuania. The succession consists of peat, gyttja and silt deposited on top of a Saalian till. Pollen and plant macrofossil analysis, lithological analysis, U/Th dating and mineral magnetic measurements on the sediments have allowed 19 lithostratigraphic units and 16 local pollen assemblage zones (LPAZ) to be identified. The palaeocarpological record reveals a clear transition from the Saalian Glacial to the Weichselian stadial and interstadial phases. The mineral magnetic parameters suggest a good correlation between the concentration of magnetic minerals and stadial and interstadial periods. The Merkine (Eemian) Interglacial and two Early Weichselian Interstadials, Jonionys 1 (Brörup) and Jonionys 2 (Odderade), separated by cryomers, are identified. Intervals interpreted as analogous to the Middle Weichselian Denekamp and Hengelo interstadials are also recognized on the basis of pollen assemblages. The results show alternating periglacial and interstadial palaeoenvironments in Lithuania during the Early and Middle Weichselian and are of importance for Late Pleistocene palaeoenvironmental reconstruction of the Baltic area as a whole.
Laurentide and Cordilleran fast ice flow: some sedimentological evidence from Wisconsinan subglacial till and its substrate
Authors: LIAN OLAV B. , HICOCK STEPHEN R. , DREIMANIS ALEKSIS
Published: July 2010

With the aid of three case studies we summarize sedimentological and structural evidence in Wisconsinan subglacial till and its substrate that can be used to infer the presence of former fast‐moving ice. We compare sedimentological characteristics of till with its stone fabric, stone surface erosional features and orientations of fractures, faults and folds in till and substrate, in order to interpret the processes that formed the till. In the cases we studied, stones in tills that experienced ductile deformation (inferred to be associated with fast‐moving ice) show variable alignment of latest surface striae. Moreover, striae are inconsistent with the orientations of lee ends and chattermarks on the same stones, and with the dip directions of shallow shear planes and (or) steeper tension fractures in the till matrix. These observations indicate that stones were rotating in a flowing till matrix prior to their final emplacement. Ductile shear of fine‐textured, water‐saturated till and Jeffrey‐like rotation of stones are invoked where most of the following occur together: (i) delicate striae follow the curvature of stone surfaces; (ii) a‐axis fabrics are multimodal to girdle‐like; (iii) stone a axis eigenvectors, striae orientation and stone lee end alignments fall between the modes of stone fabrics; (iv) stone pavements are uneven with vertically oriented and inverted bullet‐shaped stones; (v) soft sediment clasts and (or) fragile fossils are preserved.
Ice‐flow patterns and dispersal of erratics at the southwestern margin of the last Scandinavian Ice Sheet: signature of palaeo‐ice streams
Authors: KJæR KURT H. , HOUMARK‐NIELSEN MICHAEL , RICHARDT NIELS
Published: July 2010

An extensive set of proxy‐data was acquired from eastern and central Denmark in order to study the dynamic behaviour of the southwestern margin of the last Scandinavian Ice Sheet. We examine the last three glacier advances of the Late Weichselian: the Main advance from central Sweden, representing the maximum ice extent at this time (c. 21–20 ka BP), and the two succeeding Baltic advances (c. 18–15 ka BP). Directional properties from tills and glaciotectonic overprints are used to reveal large‐scale flowline patterns. Together with the geomorphological outline of ice margins, flowlines were successively more fan‐shaped, indicating that the dependence of the subglacial topography increases as ice advances become younger. It is suggested that while the ice thickness decreases, more lobate configurations of ice margins are created as a result. Clast‐compositional data derived from the fine‐gravel fraction in tills are used to reconstruct dispersal patterns of erratic material. The dispersal patterns during the three advances show a gradually diminishing influence of local Pre‐Quaternary bedrocks and older glacial deposits, and progressively longer transport distances of far‐travelled erratics. We speculate that the principal factor governing this development is a successively decreasing interaction between the ice and its bed, which influences the concentration of erratics, debris comminution processes and the basal ice velocity. We envisage the Main advance from central Sweden as a slow‐flowing inter‐stream ice body with high bed interaction compared to the succeeding Baltic advances, which we regard to have been rapid flowing ice streams with limited bed interaction.
Middle to Late Weichselian Norwegian Channel Ice Stream deposits and morphology on Jæren, southwestern Norway and the eastern North Sea area
Authors: STALSBERG KNUT , LARSEN EILIV , OTTESEN DAG , SEJRUP HANS PETTER
Published: July 2010

Glacial lineations on a bank area and a coastal lowland, both bordering the Norwegian Channel, are studied with regard to morphology and distribution by means of side‐scan sonar data, detailed digital maps and fieldwork. Their genesis and age are further elucidated through stratigraphic and sedimentologic information from excavations in one typical coast‐parallel drumlin. Four excavated sections revealed four lithologic units: Prodeltaic glaciomarine sand, glaciofluvial gravel, glaciomarine diamicton and deformation till. After Middle Weichselian delta progradation, glaciomarine diamicton was deposited and later subglacially reworked by a northwards flowing glacier. The two upper diamictons form the main volume of the ridge, which is interpreted as a drumlin, and imply a reinterpretation of the Jæren part of the so‐called Lista moraine. Preconsolidation of glaciomarine diamicton suggests a maximum ice thickness of 500 m during drumlin formation, indicating an ice surface slope of 1 m/km. The occurrence of sediments that provided low basal shear stresses, and the orientation of drumlins and megaflutes indicating ice confluence both point to high glacier flow velocities and suggest that an ice stream, rather than a slower moving part of the ice sheet, occupied the Norwegian Channel during the Late Weichselian maximum. Deformation till overlying, more or less, undeformed glaciomarine diamicton suggests that high glacier velocities during periods of low driving stresses were possible due to a subglacial deformable layer.
Reconstructing the basal thermal regime of an ice stream in a landscape of selective linear erosion: Glen Avon, Cairngorm Mountains, Scotland
Authors: HALL ADRIAN M. , GLASSER NEIL F.
Published: July 2010

The Cairngorm Mountain area of Scotland is a classic example of a landscape of selective linear glacial erosion, with sharp contrasts in the intensity of glacial erosion between the deeply incised troughs and valleys and the undulating high plateau. This article examines the Quaternary development of Glen Avon, a 200 m deep glacial trough set within the high plateau of the mountains. Evidence concerning the aggregate basal thermal regimes of the topographically controlled ice streams that formerly developed in this area is reconstructed from the geomorphological record, including bedforms indicative of wet‐based, sliding ice and of dry‐based ice frozen to its bed. This mapping indicates that basal sliding was not confined exclusively to the troughs but extended towards valley heads and on to parts of the plateau adjacent to troughs. The extent of basal sliding appears to have been greatest beneath pre‐Late Devensian ice sheets. Basal ice temperatures are modelled under steady‐state conditions for the last ice sheet at c. 18 ka BP. Basal thermal regimes are predicted using a reconstruction of the preglacial relief and for the current topography of the area. Convergent flow of ice through the preglacial valley system appears to have been sufficient to induce basal melting and therefore to initiate valley deepening. This effect is enhanced when the model is run across the present topography. Comparison of results of the geomorphological mapping and the modelling reveals significant differences between the actual and predicted extent of basal sliding outside the main ice stream. The overall conclusion is that many ice streams in mountainous terrain are inherited from the locations of preglacial valleys, which serve to accelerate ice flow and promote frictional heating beneath ice sheets.
Late Weichselian deglacial history of Disko Bugt, West Greenland, and the dynamics of the Jakobshavns Isbrae ice stream
Authors: LONG ANTONY J. , ROBERTS DAVID H.
Published: July 2010

New relative sea‐level (RSL) data from Disko Bugt, a large marine embayment in West Greenland, are used to examine the deglacial history of the Jakobshavns Isbrae ice stream. RSL data show rapid deglaciation after 10.3 ka cal. yr BP. Once deglaciation began, a bedrock high in the west of the bay exerted no discernible influence on the deglacial chronology. Following initial rapid retreat, ice stream recession slowed as it approached the eastern shores of the bay. Seabed elevations increase here and the ice stream terminus lingered for several thousand years before retreating into the narrow bedrock‐confined Jakobshavns Isfjord. The seabed topography of Disko Bugt includes several deep channels which probably record the former course of the ice stream. Using a simple water depth/calving velocity relationship it is estimated that the maximum calving velocity on deglaciation wasc.4.8 km a‐1. This is less than the present rate (6–7 km a‐1), although ice discharge was two to four times that observed today. Initiation of rapid ice stream retreat was probably caused by ice stream thinning and increased surface melting. A critical point in time was the retreat of the ice stream from shallow continental shelf waters (c.400 m) into the deep bedrock trough (>800 m) which marks the entrance to Disko Bugt.
Configuration and timing of Ungava Bay ice streams, Labrador–Ungava, Canada
Authors: JANSSON KRISTER N. , STROEVEN ARJEN P. , KLEMAN JOHAN
Published: July 2010

The prominent Ungava Bay landform swarm (UBLS), covering an area of ˜260000 km2 south of Ungava Bay, Canada, is defined by drumlins, crag‐and‐tails, horned crag‐and‐tails and flutes indicating convergent ice flow towards Ungava Bay. The UBLS has been difficult to interpret in terms of ice‐sheet configuration, dynamics and age. Aerial photograph and satellite image interpretations of the Labrador‐Ungava region reveal a previously unrecognized level of complexity within the UBLS consisting of several well‐defined segments, most interpreted as representing discrete stream‐flow events. Each of the segments is characterized by one or more of the criteria (convergent flow patterns at their heads, attenuated till lineations and abrupt lateral margins) previously suggested as diagnostic for formation by fast‐flowing ice (ice streams). The UBLS reflects the most direct and probably fastest contact (in terms of sediment transport) between the Laurentide Ice Sheet interior and the ocean. It is therefore a prime candidate for abrupt changes in glacial‐age northwest Atlantic seafloor sedimentation.
The Dubawnt Lake palaeo‐ice stream: evidence for dynamic ice sheet behaviour on the Canadian Shield and insights regarding the controls on ice‐stream location and vigour
Authors: STOKES CHRIS R. , CLARK CHRIS D.
Published: July 2010

We report evidence for a major ice stream that operated over the northwestern Canadian Shield in the Keewatin Sector of the Laurentide Ice Sheet during the last deglaciation 9000–8200 (uncalibrated) yr BP. It is reconstructed at 450 km in length, 140 km in width, and had an estimated catchment area of 190000 km2. Mapping from satellite imagery reveals a suite of bedforms (‘flow‐set’) characterized by a highly convergent onset zone, abrupt lateral margins, and where flow was presumed to have been fastest, a remarkably coherent pattern of mega‐scale glacial lineations with lengths approaching 13 km and elongation ratios in excess of 40:1. Spatial variations in bedform elongation within the flow‐set match the expected velocity field of a terrestrial ice stream. The flow pattern does not appear to be steered by topography and its location on the hard bedrock of the Canadian Shield is surprising. A soft sedimentary basin may have influenced ice‐stream activity by lubricating the bed over the downstream crystalline bedrock, but it is unlikely that it operated over a pervasively deforming till layer. The location of the ice stream challenges the view that they only arise in deep bedrock troughs or over thick deposits of ‘soft’ fine‐grained sediments. We speculate that fast ice flow may have been triggered when a steep ice sheet surface gradient with high driving stresses contacted a proglacial lake. An increase in velocity through calving could have propagated fast ice flow upstream (in the vicinity of the Keewatin Ice Divide) through a series of thermomechanical feedback mechanisms. It exerted a considerable impact on the Laurentide Ice Sheet, forcing the demise of one of the last major ice centres.
Late Holocene climatic history of northern Germany and Denmark: peat macrofossil investigations at Dosenmoor, Schleswig‐Holstein, and Svanemose, Jutland
Authors: BARBER KEITH E. , CHAMBERS FRANK M. , MADDY DARREL
Published: July 2010

Plant macrofossil remains have been analysed from two raised peat bogs in northern Germany and Denmark. The quantified vegetation reconstructions of each profile were subjected to multivariate analyses to extract records of changing bog surface wetness (BSW), which are interpreted in these rain‐fed bogs as being proxy climate signals. Age/depth models were constructed using radiocarbon dates and a number of drier and wetter phases were defined. The records both register cooler/wetter conditions around 2700, 1800 and 1400 cal. yr BP, and at the beginning of the Little Ice Age around AD 1250–1350. These rising bog water tables must have been reflected in poorer conditions for agriculture, and in particular near Dosenmoor where the profile records a catastrophic change to such conditions culminating at 2750–2600 cal. yr BP.
Landscape development in response to climatic change during Oxygen Isotope Stage 5 in the southern Siberian loess region
Authors: CHLACHULA JIRI , KEMP ROB A. , JESSEN CATHERINE A. , PALMER ADRIAN P. , TOMS PHILLIP S.
Published: July 2010

Two high‐resolution loess‐palaeosol sections from the Ob Loess Plateau (Iskitim) and the Minusinsk Basin (Kurtak 33) provide new detailed information on the last interglacial climate variations and landscape development in the parkland‐steppe zone of southern Siberia. The complete last interglacialsensu lato(130–74 ka BP) records of the two sites, documented by magnetic susceptibility, grain‐size, CaCO3and organic carbon content as proxy climatic data, and supplemented by thin‐section studies, indicate several short warm and very cold intervals correlated with OIS 5e‐5a. A strongly continental warm climate culminated around the peak of the last interglacialsensu stricto(OIS 5e) and cooler conditions occurred during the following interstadial stages (OIS 5c and 5a), corresponding to shifts in palaeolandscape development with gradual replacement of parkland‐steppe and mixed southern taiga by boreal forest. During stadial stages (OIS 5d and 5b), the palaeolandscape was transformed into a cold arid periglacial tundra‐steppe. Evidence for a major cooling in Siberia during OIS 5d, corroborating the palaeolimnological record from Lake Baikal, is provided by deep frost‐wedge casts distorting the OIS 5e chernozemic palaeosol, suggesting formation of permafrost shortly after the last interglacial climatic optimum. The pedosedimentary record, reflecting the effects of syndepositional pedogenic processes, attests to a dynamic climate pulsation during the last interglacial stage.
Towards a chronology of the Late Pleistocene in the northern Alpine Foreland
Authors: PREUSSER FRANK
Published: July 2010

Dating results from terrestrial records in the northern foreland of the Alps have been compiled in order to establish an independent chronostratigraphy for the climate history of this region. U/Th dates of peat deposited during the final phase of the Last Interglacial indicate that it lasted until at least c. 115 000 yr ago. The Early Würmian started with a period of severe cold climate causing a substitution of forest by tundra‐like vegetation. It is assumed that during this period glaciers advanced to the margin of the foreland of at least the Western Alps. Sediments attributed to this glaciation are dated to about 103 000 yr. Three subsequent interstadials, all characterized by coniferous forest, were interrupted by cold stadials with steppe to tundra‐like vegetation. The first interstadial is dated to about 95 000 yr. There is evidence for an interstadial with open coniferous woodland and three phases of steppe vegetation during the Middle Würmian, between c. 50000 and 30 000 yr ago. The last glaciation of the Alpine Foreland reached its maximum extension between 24 000 and 21 500 yr and glaciers rapidly collapsed before ˜17 500 yr ago. A series of minor re‐advances during the Lateglacial is reported from within the Alps, but the glaciers barely reached the main Alpine valleys during this time. The last of these advances formed the Egesen moraine and occurred at about 11 800 yr ago during the Younger Dryas.
Late Quaternary development of the southern sector of the Greenland Ice Sheet, with particular reference to the Qassimiut lobe
Authors: WEIDICK ANKER , KELLY MICHAEL , BENNIKE OLE
Published: July 2010

The evolution of the southern Greenland Ice Sheet is interpreted from a synthesis of geological data and palaeoclimatic information provided by the ice‐sheet cores. At the Last Glacial Maximum the ice margin would have been at the shelf break and the ice sheet was fringed by shelf ice. Virtually all of the present ice‐free land was glaciated. The initial ice retreat was controlled by eustatic sea level rise and was mainly by calving. When temperatures increased, melt ablation led to further ice‐margin retreat and areas at the outer coast and mountain tops were deglaciated. Retreat was interrupted by a readvance during the Neria stade that may correlate with the Younger Dryas cooling. The abrupt temperature rise at the Younger Dryas—Holocene transition led to a fast retreat of the ice margin, and after ˜9 ka BP the ice sheet was smaller than at present. Expansion of the ice cover began in the Late Holocene, with a maximum generally during the Little Ice Age. The greatest changes in ice cover occurred in lowland areas, i.e. in the region of the Qassimiut lobe. The date of the historical maximum advance shows considerable spatial variability and varies between AD 1600 and the present. Local anomalous readvances are seen at possibly 7–8 ka and at c. 2 ka BP. A marked relative sea level rise is seen in the Late Holocene; this is believed to reflect a direct glacio‐isostatic response to increasing ice load.
A test of the englacial thrusting hypothesis of ‘hummocky’ moraine formation: case studies from the northwest Highlands, Scotland
Authors: LUKAS SVEN
Published: July 2010

The melt‐out of material contained within englacial thrust planes has been proposed to result in the formation of stacked moraine sequences with characteristic proximal rectilinear slopes. This model has been applied to explain the formation of Scottish Younger Dryas ice‐marginal (‘hummocky’) moraines on the basis of these morphological characteristics. However, no sedimentological data exist to support this proposal. This article reviews hitherto proposed models of ‘hummocky’ moraine formation and presents detailed geomorphological and sedimentological results from the NW Scottish Highlands with the aims of reconstructing the dynamics of Younger Dryas glaciers and of testing the applicability of the englacial thrusting model. Exposures demonstrate that moraines represent terrestrial ice‐contact fans throughout, with a variety of postdepositional deformation structures being identified in most cases, indicating that glacier retreat was incremental and oscillatory; proximal rectilinear slopes are interpreted as ice‐contact faces formed after ice support was withdrawn during retreat. This evidence strongly suggests a temperate glacier regime and short glacier response times similar to those in present‐day SW Norway or Iceland. It contradicts the thrusting model and the proposal that Svalbard might form a suitable analogue for Younger Dryas moraines in Scotland.