Showing papers in "Boreas in 2005"
TL;DR: Lehmkuhl et al. as mentioned in this paper reviewed the late Quaternary glaciation of Tibet and the bordering mountains and found that glaciers in high altitude regions tend to advance during times of increased precipitation, which is associated with insolation maxima during glacial times.
Abstract: Lehmkuhl, F. & Owen, L. A. 2005 (May): Late Quaternary glaciation of Tibet and the bordering mountains: a review. Boreas, Vol. 34, pp. 87–100. Oslo. ISSN 0300–9483.
Abundant glacial geologic evidence present throughout Tibet and the bordering mountains shows that glaciers have oscillated many times throughout the late Quaternary. Yet the timing and extent of glacial advances is still highly debated. Recent studies, however, suggest that glaciation was most extensive prior to the last glacial cycle. Furthermore, these studies show that in many regions of Tibet and the Himalaya glaciation was generally more extensive during the earlier part of the last glacial cycle and was limited in extent during the global Last Glacial Maximum (marine oxygen isotope stage 2). Holocene glacial advances were also limited in extent, with glaciers advancing just a few kilometers from their present ice margins. In the monsoon-influenced regions, glaciation appears to be strongly controlled by changes in insolation that govern the geographical extent of the monsoon and consequently precipitation distribution. Monsoonal precipitation distribution strongly influences glacier mass balances, allowing glaciers in high altitude regions to advance during times of increased precipitation, which are associated with insolation maxima during glacial times. Furthermore, there are strong topographic controls on glaciation, particular in regions where there are rainshadow effects. It is likely that glaciers, influenced by the different climatic systems, behaved differently at different times. However, more detailed geomorphic and geochronological studies are needed to fully explore regional variations. Changes in glacial ice volume in Tibet and the bordering mountains were relatively small after the global LGM as compared to the Northern Hemisphere ice sheets. It is therefore unlikely that meltwater draining from Tibet and the bordering mountains during the Lateglacial and early Holocene would have been sufficient to affect oceanic circulation. However, changes in surface albedo may have influenced the dynamics of monsoonal systems and this may have important implications for global climate change. Drainage development, including lake level changes on the Tibetan plateau and adjacent regions has been strongly controlled by climatic oscillations on centennial, decadal and especially millennial timescales. Since the Little Ice Age, and particularly during this century, glaciers have been progressively retreating. This pattern is likely to continue throughout the 21st century, exacerbated by human-induced global warming.
149 citations
TL;DR: In this article, a suite of glacial sediments in the Kongsfjordrenna cross-shelf trough can be traced southwards to the shelf west of Prins Karls Forland, indicating that glacial ice also covered the coastal lowlands of northwest Svalbard.
Abstract: New marine geological evidence provides a better understanding of ice-sheet dynamics along the western margin of the last Svalbard/Barents Sea Ice Sheet. A suite of glacial sediments in the Kongsfjordrenna cross-shelf trough can be traced southwards to the shelf west of Prins Karls Forland. A prominent moraine system on the shelf shows minimum Late Weichselian ice extent, indicating that glacial ice also covered the coastal lowlands of northwest Svalbard. Our results suggest that the cross-shelf trough was filled by a fast-flowing ice stream, with sharp boundaries to dynamically less active ice on the adjacent shelves and strandflats. The latter glacial mode favoured the preservation of older geological records adjacent to the main pathway of the Kongsfjorden glacial system. We suggest that the same model may apply to the Late Weichselian glacier drainage along other fjords of northwest Svalbard, as well as the western margin of the Barents Ice Sheet. Such differences in glacier regime may explain the apparent contradictions between the marine and land geological record, and may also serve as a model for glaciation dynamics in other fjord regions.
129 citations
TL;DR: Stalagmite SV1 from Grotta Savi, located at the SE margin of the European Alps (Italy), is the first Alpine speleothem that continuously spans the past c. 17kyr as mentioned in this paper.
Abstract: Stalagmite SV1 from Grotta Savi, located at the SE margin of the European Alps (Italy), is the first Alpine speleothem that continuously spans the past c. 17kyr. Extension rate and δ18Oc record for the Lateglacial probably reflect a combination of temperature and rainfall, with rainfall exerting the dominant effect. Low speleothem calcite δ18 Oc values were recorded from c. 14.5 and 12.35 kyr, during GI-1 (Bolling— Allerod) interstadial, which in our interpretation, was warm and wet. The GS-1 (Younger Dryas) was characterized by a shift to heavier δ18 Oc, coinciding with δ13Cc enrichment and extremely low extension rate (<8 μm/year). These characteristics indicate that GS-1 climate was cool and dry in the SE Alps. Calibration using historical data revealed that there is a positive δ18Oc/dT relationship. A 1°C rise in mean annual temperature should correspond to c. 2.85% increase of SV-1 δc18Oc. We reconstructed a slow and steady temperature rise of c. 0.5°C since 10 kyr BP, in broad agreement with reconstructions from pollen data for SE Europe. Stalagmite SV1 indicates that climate variability in the SE Alps has been influenced by the Mediterranean Sea for the past c. 17 kyr.
129 citations
TL;DR: Pilcher et al. as discussed by the authors established a tephrochronology for a peat bog in the Lofoten Islands that provides a dating framework for future lake and bog studies of climate variation in this climatically sensitive area.
Abstract: JON PILCHER, RAYMOND S. BRADLEY, PIERRE FRANCUS AND LESLEIGH ANDERSONPilcher, J., Bradley, R. S., Francus, P. & Anderson, L. 2005 (May): A Holocene tephra record from the LofotenIslands, Arctic Norway. Boreas, Vol. 34, pp. 136–156. Oslo. ISSN 0300-9483.A tephrochronology has been established for a peat bog in the Lofoten Islands that provides a dating frameworkfor future lake and bog studies of climate variation in this climatically sensitive area. Twenty-three tephra layerswere identified, all apparently of Icelandic origin. These included the historically dated tephras of AD 1875(Askja), AD 1362 (O¨raefajo¨kull), AD 1158 (Hekla), AD 1104 (Hekla) and the Landnam tephra identified atAD 875 in the GRIP ice core. Other layers, previously radiocarbon dated in Ireland and elsewhere, include theHekla eruptions of c. 2310 BC and c. 5990 BC. The basal clays below the peat contain tephra of both theAskja eruption of c. 9500 BC (10000 radiocarbon years BP) and the well-known Vedde Ash of c. 12 000 BP(10 030+80 BC in GRIP ice core).Jon Pilcher (e-mail: j.pilcher@qub.ac.uk), School of Archaeology and Palaeoecology, Queen’s University,Belfast, UK; Raymond S. Bradley and Lesleigh Anderson, Department of Geosciences, University of Massa-chusetts, Amherst, MA, USA; Pierre Francus, Institut National de la Recherche Scientifique, Universite´ duQue´bec, Saint-Foy, Que´bec, Canada; received 28th June 2004, accepted 7th December 2004.
124 citations
TL;DR: In this paper, three NW Iberia Cantabrian Mountain pollen records are presented, which reflect the main Holocene climatic shifts in the North Atlantic region as recorded in the isotopic data from Greenland ice, Irish speleothems and reconstructed sea surface temperatures.
Abstract: Three NW Iberia Cantabrian Mountain pollen records are presented. They reflect the main Holocene climatic shifts in the North Atlantic region as recorded in the isotopic data from Greenland ice, Irish speleothems and reconstructed sea surface temperatures. Two brief forest regression episodes reconstructed from pollen may be synchronous with GH-11.2 and GH-8.2 events. At mid-altitude, two woodland expansion phases (7000–6000 14C yr BP and 4000–2500 14C yr BP) are separated by a phase of heaths and peat deposits. Major woodland declines occurred during the Galician-Roman Period (which includes the Bronze Age, the Iron Age and the Roman occupation) and from the end of the Medieval Period. The pollen data, backed up by archaeological and historical sources, suggest climatic impact of the Iron Age Cold Period, but are indecisive concerning the Little Ice Age. However, the pollen records do not support any significant ‘Neoglacial’ period (4000–3000 14C yr BP) influence on NW Iberia.
119 citations
TL;DR: The taxonomic composition of chironomid, cladoceran and diatom assemblages in small lakes in the Alpine region shows a strong relationship with summer temperature as discussed by the authors.
Abstract: The taxonomic composition of chironomid, cladoceran and diatom assemblages in small lakes in the Alpine region shows a strong relationship with summer temperature. Since fossils of all three organism groups preserve well and remain identifiable in lake sediments, summer temperature transfer-functions can be developed based on the modern distribution of these organisms and applied to fossil records to reconstruct past summer temperature variability. We provide a summary of the chironomid-, cladoceran- and diatom-based transfer functions available from the Swiss Alps and discuss the potential problem of co-variation between summer temperature and lake nutrient conditions for transfer-function development. Whereas the diatom-based summer temperature transfer function remains to be evaluated in down-core reconstructions, the cladoceran- and chironomid-based transfer functions have been used successfully to produce summer temperature records on Lateglacial and Holocene time scales that are in good agreement with other temperature reconstructions in the Alps. Major problems that can be encountered when using fossil assemblages of aquatic organisms for temperature reconstruction in the Alpine region are biases in the inferred temperatures associated with human impact on lakes and parameters other than temperature affecting the fossil assemblages. A multi-proxy approach to palaeoenvironmental reconstruction is recommended to keep a close control on past catchment and within-lake processes during the time interval of interest.
104 citations
TL;DR: In this paper, the authors present 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.
Abstract: 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.
104 citations
TL;DR: In this article, the marginal subglacial bedrock bedforms of Jakobshavns Isbrae, West Greenland, were investigated to examine the processes governing bedform evolution in ice stream and ice sheet areas.
Abstract: This study investigates the marginal subglacial bedrock bedforms of Jakobshavns Isbrae, West Greenland, in order to examine the processes governing bedform evolution in ice stream and ice sheet areas, and to reconstruct the interplay between ice stream and ice sheet dynamics. Differences in bedform morphology (roche moutonnee or whaleback) are used to explore contrasts in basal conditions between fast and slow ice flow. Bedform density is higher in ice stream areas and whalebacks are common. We interpret that this is related to higher ice velocities and thicker ice which suppress bed separation. However, modification of whalebacks by plucking occurs during deglaciation due to ice thinning, flow deceleration, crevassing and fluctuations in basal water pressure. The bedform evidence points to widespread basal sliding during past advances of Jakobshavns Isbrae. This was encouraged by increased basal temperatures and melting at depth, as well as the steep marginal gradients of Jakobshavns Isfjord which allowed rapid downslope evacuation of meltwater leading to strong ice/bedrock coupling and scouring. In contrast to soft-bedded ice stream bedforms, the occurrence of fixed basal perturbations and higher bed roughness in rigid bed settings prevents the basal ice subsole from maintaining a stable form which, coupled with secondary plucking, counteracts the development of bedforms with high elongation ratios. Cross-cutting striae and double-plucked, rectilinear bedforms suggest that Jakobshavns Isbrae became partially unconfined during growth phases, causing localised diffluent flow and changes in ice sheet dynamics around Disko Bugt. It is likely that Disko Bugt harboured a convergent ice flow system during repeated glacial cycles, resulting in the formation of a large coalesced ice stream which reached the continental shelf edge.
103 citations
TL;DR: The Miage morainic amphitheatre (MMA) is composed of three subconcentric sets of c. 25 moraines and has been studied for two centuries as discussed by the authors.
Abstract: Holocene glacier variations pre-dating the Little Ice Age are poorly known in the western Alps. Studied for two centuries, the Miage morainic amphitheatre (MMA) is composed of three subconcentric sets of c. 25 moraines. Because of its location and of a dominant mode of morainic accretion, the MMA is a well-preserved marker of the glacier dynamics during the Neoglacial. Radiocarbon dates were obtained by digging and coring in intermorainic depressions of the MMA and through a deep core drilling in a dammed-lake infill (Combal); complementary data for the inner MMA were obtained by lichenometry and dendrochronology. Radiocarbon chronology shows that (i) the MMA not only pre-dates the Little Ice Age (LIA), but was built at least since 5029–4648 cal. yr BP (beginning of the Neoglacial); (ii) outer sets of moraines pre-date 2748–2362 cal. yr BP; (iii) the MMA dammed the Lake Combal from 4.8 to 1.5 cal. kyr BP, while lakes/ponds formed inside the moraines (e.g. from 2147–1928 to 1506–1295 cal. yr BP). The ‘Neoglacial model’ proposed here considers that the MMA formed during the whole Neoglacial by a succession of glacier advances at 4.8–4.6 cal. ky BP (early
93 citations
TL;DR: Bohner et al. as discussed by the authors developed a regional modeling concept for late Quaternary climate reconstructions and future climate impact assessments based on estimates of different climate parameters covering the entire Central and High Asia in a grid-cell spacing of 1 km2, climatic determinants of the recent spatial distribution of climate-sensitive environments (glacial and periglacial environments, forest) were explored.
Abstract: Bohner, J. & Lehmkuhl, F. 2005 (May): Environmental change modelling for Central and High Asia: Pleistocene, present and future scenarios. Boreas, Vol. 34, pp. 220–231. Oslo. ISSN 0300–9483.
A regional modelling concept was developed for late Quaternary climate reconstructions and future climate impact assessments. Based on estimates of different climate parameters covering the entire Central and High Asia in a grid-cell spacing of 1 km2, climatic determinants of the recent spatial distribution of climate-sensitive environments (glacial and periglacial environments, forest) were explored. Simple climatic threshold functions were established, defining critical climate values for modelling the spatial extension of environments considered. Using palaeogeomorphological indicators as a basis, late Quaternary climatic conditions were modelled in a Last Glacial Maximum (LGM) scenario consistent with palaeogeomorphological and palaeoclimatological data. The results enabled a validation of LGM palaeoclimate simulations performed by the ECHAM GCM. To assess the magnitude of possible future climatic impacts on the spatial distribution of glaciers, permafrost and potential forest stands, two GCM-based IPCC-SRES climate change scenarios (IPCC special report on emission scenarios) for the time period 2070–2099 were considered. Assuming future climates to be perturbed for long enough to affect the environments, a distinct loss of glaciated areas and permafrost must be expected.
92 citations
TL;DR: In this article, three distal tephra layers or cryptotephras have been detected within a sedimentary sequence from the Netherlands that spans the last glacial-interglacial transition.
Abstract: SIWAN M. DAVIES, WIM Z. HOEK, SJOERD J. P. BOHNCKE, J. JOHN LOWE, SEAN PYNE O’DONNELLAND CHRIS S. M. TURNEYDavies, S. M., Hoek, W. Z., Bohncke, S. J. P., Lowe, J. J., Pyne O’Donnell, S. & Turney, C. S. M. 2005 (May):Detection of Lateglacial distal tephra layers in the Netherlands. Boreas, Vol. 34, pp. 123–135. Oslo. ISSN 0300-9483.Three distal tephra layers or cryptotephras have been detected within a sedimentary sequence from the Nether-lands that spans the last glacial–interglacial transition. Geochemical analyses identify one as the Vedde Ash,which represents the southernmost discovery of this mid-Younger Dryas tephra so far. This tephra was found asa distinct horizon in three different cores sampled within the basin. The remaining two tephras have not beengeochemically ‘fingerprinted’, partly due to low concentrations and uneven distributions of shards within thesequences sampled. Nevertheless, there is the potential for tracing these tephra layers throughout the Nether-lands and into other parts of continental Europe. Accordingly, the possibilities for precise correlation of Dutchpalaeoenvironmental records with other continental, marine and ice-core records from the North Atlantic regionare highlighted.Siwan M. Davies (e-mail: siwan.davies@swansea.ac.uk), Department of Geography, University of WalesSwansea, Singleton Park, Swansea, Wales, SA2 8PP, UK; Wim Z. Hoek, Department of Physical Geography,Universiteit Utrecht, Heidelberglaan 2, 3508 TC Utrecht, Netherlands; Sjoerd J. P. Bohncke, Department ofQuaternary Geology and Geomorphology, Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan1085, 1081 HV Amsterdam, Netherlands; J. John Lowe and Sean Pyne O’Donnell, Centre for QuaternaryResearch, Department of Geography, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK;Chris S. M. Turney, GeoQuEST Research Group, School of Earth and Environmental Sciences, University ofWollongong, Wollongong, NSW 2522, Australia; received 28th June 2004, accepted 8th December 2004.
TL;DR: Rinterknecht et al. as discussed by the authors measured the 10Be concentrations in boulders collected from the Pomeranian Moraine in Poland, providing the first direct dating of the southern margin of the Scandinavian Ice Sheet (SIS) in the Polish Lowland.
Abstract: Rinterknecht, V R, Marks, L, Piotrowski, J A, Raisbeck, G M, Yiou, F, Brook, E J & Clark, P U 2005 (May): Cosmogenic 10Be ages on the Pomeranian Moraine, Poland Boreas, Vol 34, pp 186–191 Oslo ISSN 0300–9483
We measured the 10Be concentrations in boulders collected from the Pomeranian Moraine in Poland, providing the first direct dating of the southern margin of the Scandinavian Ice Sheet (SIS) in the Polish Lowland The mean age of 8 10Be ages of the Pomeranian Moraine in northwestern Poland is 14308 10Be ka, while in northeastern Poland the mean age of 19 10Be ages of the moraine is 15005 10Be ka Given the excellent agreement between the two age groups, we calculate a mean age of 14804 10Be ka for final deposition of the Pomeranian Moraine of northern Poland The age of the Pomeranian Moraine suggests that the southern margin of the SIS was near its maximum extent in Poland at a younger time than previously inferred, and that retreat from the moraine at 14804 10Be ka probably occurred in response to the onset of the Bolling interstade
TL;DR: The status of the Quaternary, long regarded as a geological period effectively coincident with the main climatic deterioration of the current Ice Age, has recently been questioned as a formal stratigraphic unit as mentioned in this paper.
Abstract: The status of the Quaternary, long regarded as a geological period effectively coincident with the main climatic deterioration of the current Ice Age, has recently been questioned as a formal stratigraphic unit We argue here that it should be retained as a formal period of geological time Furthermore, we consider that its beginning should be placed at the Gauss-Matuyama magnetic chron boundary at about 26 Ma, rather than at its current position at about 18 Ma The Quaternary would be formally subdivided into the Pleistocene and Holocene epochs The global chronostratigraphical correlation table proposed is enclosed at the back of this issue
TL;DR: The authors investigated the past distribution of Abies alba via analysis of wood charcoal buried in natural soils (identification, weighing, dating) and of pollen and macro-remains from peat to understand its present-day expansion.
Abstract: The expansion of silver fir (Abies alba) during the 20th century in the European inner Alps calls into question the causes of the observed dynamics. We investigate the past distribution of Abies alba via analysis of wood charcoal buried in natural soils (identification, weighing, dating) and of pollen and macro-remains from peat to help us understand its present-day expansion. Material was sampled in the driest areas of the inner French Alps — some samples from calcareous sites, and most from southern exposures that should exclude Abies alba, which is a drought and carbonate intolerant species. The regional tree limit of the silver fir has not changed significantly since the middle Holocene. Abies alba grew on southern exposures, even on calcareous soils, but its importance was higher on northern slopes. From 4000 to 2000 cal. yr BP, depending on sites, the species has experienced local extinction associated with fire history. Human impact, more than climate, appears to be the main factor for local extinction, indicating that the marked present-day expansion of silver fir may result from land-use abandonment.
TL;DR: In this paper, the authors used sub-bottom seismic profiling and multidisciplinary analysis of well-dated sediment cores to study the Holocene evolution of Rhone River clastic sediment supply in Lake Le Bourget.
Abstract: The Holocene evolution of Rhone River clastic sediment supply in Lake Le Bourget is documented by sub-bottom seismic profiling and multidisciplinary analysis of well-dated sediment cores. Six high-amplitude reflectors within the lacustrine drape can be correlated to periods of enhanced inter- and underflow deposition in sediment cores. Based on the synthesis of major environmental changes in the NW Alps and on the age-depth model covering the past 7500 years in Lake Le Bourget, periods of enhanced Rhone River flood events in the lake can be related to abrupt climate changes and/or to increasing land use since c. 2700 cal. yr BP. For example, significant land use under rather stable climate conditions during the Roman Empire may be responsible for large flood deposits in the northern part of Lake Le Bourget between AD 966 and 1093. However, during the Little Ice Age (LIA), well-documented major environmental changes in the catchment area essentially resulted from climate change and formed basin-wide major flood deposits in Lake Le Bourget. Up to five ‘LIA-like’ Holocene cold periods developing enhanced Rhone River flooding activity in Lake Le Bourget are documented at c. 7200, 5200, 2800, 1600 and 200 cal. yr BP. These abrupt climate changes were associated in the NW Alps with Mont Blanc glacier advances, enhanced glaciofluvial regimes and high lake levels. Correlations with European lake level fluctuations and winter precipitation regimes inferred from glacier fluctuations in western Norway suggest that these five Holocene cooling events at 45°N were associated with enhanced westerlies, possibly resulting from a persistent negative mode of the North Atlantic Oscillation.
TL;DR: In this paper, two malacological sequences sampled in loess sections P1 and P3 of Nussloch (Rhine Valley, Germany) provide the most complete and precise molluscan record of western Europe for the Weichselian Lower and Middle Pleniglacial from about 70 to 34 cal. kyr BP.
Abstract: Two malacological sequences sampled in loess sections P1 and P3 of Nussloch (Rhine Valley, Germany) provide the most complete and precise molluscan record of western Europe for the Weichselian Lower and Middle Pleniglacial from about 70 to 34 cal. kyr BP. Qualitative and statistical analyses were performed on 134 mollusc samples. In the most complete Lower Pleniglacial record (P1), malacofauna changes reflect three short phases of vegetation development and climatic improvement related to soils and probably interstadials. A steppe to herb/shrub tundra shift characterizes the Lower-Middle Pleniglacial transition and is followed in both malacological records by the same general environmental trend (decline in vegetation and humidity increase) ending with a new increase in temperature and vegetation cover at the top of P3. In the Middle Pleniglacial, the impact of each shorter climatic change on the malacofauna is less recognizable due to a higher sediment compaction and also to being differently recorded in both sequences as the local topography affects soil water resources, soil and vegetation development and malacofauna adaptation. A comparison shows that the western European biostratigraphical framework can thus be improved by coupling molluscan records from loess sections to pollen sequences.
TL;DR: In this article, a weighted averaging-partial least squares (WA-PLS) stomatocyst/date-of-spring-mixing regression and calibration model (R2boot= 0.85) was developed to predict dates of ice break-up and spring mixing.
Abstract: Chrysophyte algae produce siliceous resting stages (stomatocysts) that are indicators of past environmental conditions. The objective of this study was to assess their strength for climate reconstructions. Stomatocysts were collected using sediment traps exposed in 45 mountain lakes (1502–2309m a.s.l., Austrian Alps). Bi-hourly water-temperature measurements were used to determine dates of freezing and break-up, spring and autumn mixing. Canonical correspondence analyses revealed that the stomatocyst assemblages were related to the dates of ice break-up and spring mixing. The two dates are controlled by winter/spring air temperature. We developed a weighted averaging-partial least squares (WA-PLS) stomatocyst/date-of-spring-mixing regression and calibration model (R2boot= 0.85), and reconstructed ‘dates of spring mixing’ for Jezero v Ledvici (1824 m a.s.l., Slovenian Alps) from AD 1842 to 1996. Sample-specific standard errors of prediction corresponded to 0.6°C - 1.0°C. Despite dating uncertainties and poor fits of fossil assemblages with the training set, reconstructed ‘dates of spring mixing’ were significantly correlated with the mean March—April air temperature, which is known to drive break-up dates. Furthermore, the record was in agreement with glacier advances during the Little Ice Age.
TL;DR: For example, this article showed that the inner part of Adventfjorden, central Spitsbergen, was ice-free shortly before 10 025±160yr BP and a glacier advanced across the regressive, frozen beach terraces and into shallow water, 58 m above the present sea level, where a small wave-influenced ice-contact delta was formed, 9775±125 yr BP.
Abstract: Raised marine beach gravel at 62 m a.s.l. in Bolterdalen indicates that the inner part of Adventfjorden, central Spitsbergen, was ice-free shortly before 10 025±160yr BP. A glacier advanced across the regressive, frozen beach terraces and into shallow water, 58 m above the present sea level, where a small wave-influenced ice-contact delta was formed, 9775±125 yr BP. Maximum ice-front position was reached 9625±95 yr BP, 7 km outside the present ice margin. The advance was climatically forced and of several decades' duration, as seen from abundant molluscs growing in the prograding foreset beds. Today, the beaches appear as a continuous regressive sequence with no geomorphic evidence of the former ice margin. Sedimentological studies show, however, that a thin (≤1 m) deformation till was emplaced, the substrate was subglacially sheared to a depth of 1 m, and elongated clasts in the beach gravel were reoriented in an ice-flow parallel direction. The glacial deposits and structures, formed within 200 m from the ice front, highlight some important aspects of subglacial to ice-marginal processes in permafrost terrain. As the dead ice melted, the released debris was redistributed into thin sediment sheets down to 40 m a.s.l., which means that the postglacial meltwater-controlled reworking lasted c. 500 years. Similar isolated depocentra may be a key for future identifications of former ice margins at high latitudes.
TL;DR: In this paper, the authors present a revised interpretation of the build-up and decay of Loch Lomond Stadial ice in the study area, one that suggests a maximum ice surface altitude of c. 900 m a.s.l., east and southeastward iceflow and active recession of a dynamic margin.
Abstract: Current understanding of the Younger Dryas (Loch Lomond Stadial) ice cap in Scotland is dominated by reconstructions derived solely from field evidence. We use an area in the western Scottish Highlands to evaluate three examples of this approach by comparing the proposed glacier reconstructions with new empirical data and the predictions of a high-resolution numerical model. Particular emphasis is placed on accurately determining the maximum surface altitude attained by the ice cap, dominant palaeo-iceflow directions and the style of ice-cap recession. By combining new geomorphological and sedimentological data with model predictions, we present a revised interpretation of the build-up and decay of Loch Lomond Stadial ice in the study area—one that suggests a maximum ice-surface altitude of c. 900 m a.s.l., east and southeastward iceflow and active recession of a dynamic margin. Good agreement between the new field-based interpretation and the predictions of the numerical model validates the latter and by implication extends confidence in its veracity beyond the study area.
TL;DR: In this paper, the authors presented a comprehensive evolution model of the Petit-Lac and its surrounding region, which used high-resolution seismics, sediment core analysis (macroscopic description, grain-size analysis, mineralogy) and palynology to infer the changes in the lake's environment from deglaciation to the present.
Abstract: During the past decade, the presentation of seismic and sedimentological data has allowed reconstruction of the environment and climate history of the Petit-Lac (western Lake Geneva). Methods such as high-resolution seismics, sediment core analysis (macroscopic description, grain-size analysis, mineralogy) and palynology have been used to infer the changes in the lake's environment from deglaciation to the present. However, no final synthesis has been attempted to link this information in the development of a comprehensive evolution model of the Petit-Lac and its surrounding region. The Petit-Lac deglaciation occurred in three phases during the Rhone glacier retreat: the Geneva stage and the Coppet and Nyon re-advances. In the Versoix area, rivers developed just after the retreat of the Rhone glacier from the Nyon stage. The Nyon fan delta started at the end of the Bolling, and its lobe fluctuated in size and orientation in six phases from the Lateglacial to the present. The action of bottom currents (i.e. erosion, non-deposition surfaces) arising at the beginning of the Holocene indicates that the frequency and direction of strong wind regimes varied greatly. Lacustrine mass failures occurred at different time intervals: two between deglaciation and the end of the Oldest Dryas, two between the Bolling and the Younger Dryas, and four during the Holocene. From the Oldest Dryas to the Contemporary Epoch, the vegetation changed from a steppe to a climate-influenced forest, and finally to a mostly humancontrolled forest.
TL;DR: Velichko et al. as mentioned in this paper analyzed pollen data from Central and Eastern Europe and provided insight into the climate and vegetation dynamics throughout the Eemian interglacial (including preceding and succeeding transitional phases).
Abstract: Velichko, A. A., Novenko, E. Y., Pisareva, V. V., Zelikson, E. M., Boettger, T. & Junge, F. W. 2005 (May): Vegetation and climate changes during the Eemian interglacial in Central and Eastern Europe: comparative analysis of pollen data. Boreas, Vol. 34, pp. 207–219. Oslo. ISSN 0300–9483.
The article discusses pollen data from Central and Eastern Europe and provides insight into the climate and vegetation dynamics throughout the Eemian interglacial (including preceding and succeeding transitional phases). Three sections with high resolution pollen records are presented. Comparison of the data indicates that the range of climatic and environmental changes increased from west to east, whereas the main phases of vegetation development appear to have been similar throughout the latitudinal belt. At the interglacial optimum, the vegetation in both Central and Eastern Europe was essentially homogeneous. An abrupt change marks the Saalian/Eemian boundary (transition from OIS 6 to OIS 5e), where environmental fluctuations were similar to those detected at the transition from the Weichselian to the Holocene (Allerod and Dryas 3). Transition from the Eemian to the Weichselian was gradual in the western part of the transect, with forest persisting. In the east, fluctuations of climate and vegetation were more dramatic; forest deteriorated and was replaced by cold open landscapes.
TL;DR: Using Scots pine (Pinus sylvestris L.) tree-ring data, a time series was yielded that contained information on winter precipitation (Pw) using tree rings, only a small part of the interannual Pw variability could be explained.
Abstract: Using Scots pine (Pinus sylvestris L.) tree-ring data, winter (September–April) precipitation variability in west central Scandinavia was reconstructed for the past five centuries. The main growth-limiting factor for pine growing in the studied area is summer temperature, but there is an additional influence of precipitation. Using principal components analysis on three tree-ring-width chronologies, a time series was yielded that contained information on winter precipitation (Pw). Using tree rings, only a small part (20%) of the interannual Pw variability could be explained. However, better agreement between the modelled and measured Pw data on semidecadal time scales (45% variance explained) suggests that tree-ring data from the west-central part of Scandinavia contain useful information on those time scales. The driest winters, disregarding the absolute beginning of the record, were found at the beginning of the 18th century; the last half of the 20th century seems to be the wettest, at least for the past 400 years. Since our precipitation reconstruction agrees fairly well with previously published precipitation proxies, it is suggested that tree rings may add useful information to future multi-proxy reconstructions.
TL;DR: In this paper, surface exposure ages from 22 tors and bedrock samples from Wrangel Island, northeast Siberia, indicate that the East Siberian and Chukchi shelves were ice-free during the Last Glacial Maximum (LGM) and that the lack of moisture due to the continental climate on the emergent Bering Land Bridge is the most likely reason for limited ice in this part of the Arctic.
Abstract: 10Be and 26Al surface exposure ages from 22 tors and bedrock samples from Wrangel Island, northeast Siberia, indicate that the East Siberian and Chukchi shelves were ice-free during the Last Glacial Maximum (LGM). The paucity of glacial landforms and deposits, the absence of erratics and the presence of radiocarbon dates on plant and mammal fossils that span the LGM suggest that Wrangel Island also remained free of extensive glacial ice during the LGM. The lack of moisture due to the continental climate on the emergent Bering Land Bridge is the most likely reason for limited ice in this part of the Arctic. Alternative interpretations regarding the age and origin of ‘glaciogenic’ bedforms on the Chukchi shelf should be considered.
TL;DR: In this paper, a large network of high-elevation temperature-sensitive tree sites from the European Alps was processed to preserve the relative frequency and magnitude of extreme events, and temporal changes in year-to-year tree-ring width variability were found.
Abstract: The understanding of extremes and their temporal distribution is useful in characterizing the behaviour of the climate system, and necessary for understanding their social and economic costs and risks. This task is analogous to the study of pointer years in dendrochronological investigations. Commonly used dendroclimatological methods, however, tend to result in an equalization of variance throughout the record by normalizing variability within moving windows. Here, we analyse a larger network of high-elevation temperature-sensitive tree sites from the European Alps processed to preserve the relative frequency and magnitude of extreme events. In so doing, temporal changes in year-to-year tree-ring width variability were found. These decadal length periods of increased or decreased likelihood of extremes coincide with variability measures from a long-instrumental summer temperature record representative of high-elevation conditions in the Alps. Intervention analysis, using an F-test to identify shifts in variance, on both the tree-ring and instrumental series, resulted in the identification of common transitional years. Based on a well-replicated network of sites reflecting common climatic variation, our study demonstrates that the annual growth rings of trees can be utilized to quantify past frequency and amplitude changes in extreme variability. Furthermore, the approach outlined is suited to address questions about the role of external forcing, ocean—atmosphere interactions, or synoptic scale changes in determining patterns of observed extremes prior to the instrumental period.
TL;DR: In this paper, a basin-wide re-evaluation of Irish Sea glacigenic deposits is presented, which aims to test whether diamicts represent in situ glacimarine sediments or sediments that have been reworked or deformed by the Last Glacial Maximum Irish Sea Glacier.
Abstract: This study is part of a basin-wide re-evaluation of Irish Sea glacigenic deposits which aims to test whether diamicts, collectively known as Irish Sea Tills, represent in situ glacimarine sediments or sediments that have been reworked or deformed by the Last Glacial Maximum Irish Sea Glacier. New results are presented for two key localities at Abermawr and Traeth y Mwnt in Wales. Unlike previous studies in the Irish Sea region that have focused on macro-scale sedimentology and structural analyses, this study combines macro-scale and micro-scale sedimentary analyses. This approach reveals that the dominant diamict facies at Abermawr are subglacially deformed primary (glaci)marine deposits, emplaced by the Irish Sea Glacier. An inland glacial source is unlikely. The Traeth y Mwnt diamicts are likely to be subaqueous in origin, possibly formed in an ice-dammed lake in the Mwnt embayment. There are no indications of subglacial deformation or shearing at Mwnt; deformation structures are related to gravity-driven or density-driven mechanisms.
TL;DR: In this paper, the authors reconstructed the deglaciation history of the Malangen-Malselv fjord and valley area proximally to the Tromso-Lyngen (Younger Dryas) moraine at Bakkejord, Malangens, northern Norway, based on morphostratigraphic, lithostrigraphic and geophysical evidence, and 25 radiocarbon dates from marine shells and foraminifera.
Abstract: The deglaciation history of the Malangen-Malselv fjord and valley area proximally to the Tromso-Lyngen (Younger Dryas) moraine at Bakkejord, Malangen, northern Norway, is reconstructed based on morphostratigraphic, lithostratigraphic and geophysical evidence, and 25 radiocarbon dates from marine shells and foraminifera. The results show that following the Skarpnes event c. 12 200 14Cyr BP, and prior to the Younger Dryas readvance, the area was deglaciated at least as far as Sandmo situated 22 km proximally to the Tromso-Lyngen moraine. Two moraine ridges crossing the fjord at Sandmo and buried beneath thick glaciomarine sediments are correlated with this period. The area was subsequently deglaciated between 10 300 and 9200 14Cyr BP, following the Tromso-Lyngen (Younger Dryas) readvance. Five ice-front accumulations post-dating the Tromso-Lyngen moraine and situated 19, 27, 42, 55 and 77 km behind it are identified and dated based on radiocarbon dates and correlation of marine limits: Malsnes (c. 10 050 14Cyr BP), Kjerresnes (c. 10 000 14Cyr BP), Solli (c. 9750 14Cyr BP), Bardufoss-Brentmoen-Storskogmoen (c. 9600–9700 14Cyr BP) and Alapmoen (c. 9200 Cyr BP). The largest of these, at Bardufoss-Storskogmoen, possibly accumulated as a response to an ice advance. Fourteen dates of apparent late Allerod/Younger Dryas age (11 100–10 000 14Cyr BP), obtained from fossils in glaciomarine sediments in the Malselv valley up to 77 km proximally to the Tromso-Lyngen moraine, are interpreted as postdating rather than predating this moraine. Several of these are considered to be too old because of uncertain reservoir age, carbon-dating plateaus and/or contamination. This highlights uncertainties associated with radiocarbon-dating and the profound effect such uncertainties may have on interpreting geological events.
TL;DR: A multi-proxy palaeoecological study of Alanen Laanijarvi, a boreal-forest lake in Swedish Lapland, is presented in this article.
Abstract: A multi-proxy palaeoecological study of Alanen Laanijarvi, a boreal-forest lake in Swedish Lapland
TL;DR: Evans, D. J. A. as discussed by the authors and Benn, I. I. (eds.) 2004: A Practical Guide to the Study of Glacial Sediments, ed. Edward Arnold, London, 266 pp.
Abstract: Evans, D. J. A. & Benn, D. I. (eds.) 2004: A Practical Guide to the Study of Glacial Sediments. Edward Arnold, London, 266 pp. ISBN 0–340–75959–3 (pb). GBP 19.99.
TL;DR: Kovanen et al. as mentioned in this paper used radiocarbon dates from detrital logs in drift that were buried during an advance of the Deming Glacier during possibly the Younger Dryas interval.
Abstract: Kovanen, D. J. & Slaymaker, O. 2005 (May): Fluctuations of the Deming Glacier and theoretical equilibrium line altitudes during the Late Pleistocene and Early Holocene on Mount Baker, Washington, USA. Boreas, Vol. 34, pp. 157–175. Oslo. ISSN 0300–9483.
The Deming Glacier is presently nourished by an ice-cap type accumulation area on Mount Baker (3285 m a.s.l.). The specific meso-scale (>10km) form and isolation of the Mount Baker stratovolcano seem to influence temperature and precipitation gradients (contemporary climate data). These data are used as a reference when calculating paleo-equilibrium-line altitudes (ELAs). Six radiocarbon dates are reported, between 10 680 70 and 10 500 70 14C yr BP (12 903–12 183 cal. yr BP) from detrital logs in drift that were buried during an advance of the Deming Glacier (altitude 3230–1158 m) during possibly the Younger Dryas interval. The calculated range of theoretical ELA depressions (ΔELA) relative to modern is 400–355 m using two different methods. Assuming no change in precipitation, ablation-season temperature would have been 2.5–2.2C cooler, which is consistent with other paleoclimatic reconstructions in this region. Alternatively, assuming that the modern reference climate is appropriate, and based on regressions of modern-day glacial conditions, the predicted mean winter precipitation necessary to support the former Deming Glacier was in the order of 200–150% (mean 175%) or 119–86% (mean 103%). This amount of precipitation could result from reinvigorated moisture transport into the North Cascades and increased seasonality at the end of the last glaciation.
TL;DR: In this paper, a network of tree-ring chronologies which have been processed in a consistent way would allow the robust reconstruction of spatial summer temperature variability for high elevations in Central Europe.
Abstract: Most palaeoclimate studies in Central Europe, utilizing annually resolved proxies such as tree-ring and documentary sources to reconstruct past temperatures, have focused mainly upon single sites or regional studies. The combined information of published summer temperature reconstructions from the Alpine region show a generally coherent picture of cool conditions for the periods c. 1450–1475, 1575–1610, 1660–1710, 1800–1850 and 1875–1925. These reconstructed cool periods can be partly explained by external forcing (e.g. low solar activity and volcanic events). However, these reconstructions, in their present form, cannot be used to comparatively assess spatial summer temperature variability through the region due to methodological differences in their development and the fact that many of them were not originally developed to emphasize spatial patterns. We propose that a network of tree-ring chronologies which have been processed in a consistent way would allow the robust reconstruction of spatial summer temperature variability for high elevations in Central Europe. Unfortunately, most living tree-ring chronologies only go back into the 18th century — so restricting the length of reconstruction. As a possible solution, we introduce a historical database of ring-width series, measured from string instruments, that could be used to extend high elevation spruce chronologies in Central Europe back for at least 500 years.