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1.
  • Björkman, Leif, et al. (författare)
  • Lateglacial and early Holocene vegetation development in the Gutaiului Mountains, northwestern Romania
  • 2002
  • Ingår i: Quaternary Science Reviews. - 0277-3791 .- 1873-457X. ; 21:8-9, s. 1039-1059
  • Tidskriftsartikel (refereegranskat)abstract
    • Pollen analyses and AMS C-14 measurements were performed on lacustrine sediments and peat sequences from two former crater lakes (Preluca Tiganului, Steregoiu) situated in the Gutaiului Mountains in northwestern Romania, in order to reconstruct the vegetation development during the Lateglacial and Early Holocene. Before c. 14,700 cal. years BP (GS-2) open vegetation with shrubs (Salix, Juniperus), grasses and herbs (e.g. Artemisia and Chenopodiaceae) prevailed in the area. Around c. 14,700 cal. years BP and coinciding with the beginning of GI-le, Pinus expanded, and patchy vegetation with scattered Pinus stands developed. The last 100 years of GI-le (14,150-14,050 cal. years BP) were characterised by an increase in Pinus and Betula and an expansion of open forest communities. This development was shortly interrupted between 14,050 and 13,800 cal. years BP (likely corresponding to the cold phase GI-ld), when the tree cover became reduced and open vegetation with scattered Pinus individuals became frequent. The period with a significant expansion of Betula and Picea and the formation of an open forest (including Pinus and Omits), which took place between 13,800 and c. 12,950 cal. years BP, is tentatively correlated with GI-lc-a. A renewed reduction in tree cover (decrease of Picea and Betula, disappearance of Ulms) started at similar to 12,950 cal. years BP and at 12,600 cal. years BP forest stands were rapidly replaced by open vegetation communities with low shrubs (Salix, Juniperus), grasses and herbs (e.g. Artemisia and Chenopodiaceae). The period between 12,900 and 11,500 is correlated with the cold phase GS-1. At 11,500 cal. years BP, most likely as a response to the warmer climatic conditions at the beginning of the Holocene, an expansion of Betula and Alnus and, slightly later, also of Ulmus can be observed. Between 11,500 and 11,250 cal. years BP, open forests with Betula, Pinus and Ulmus were widespread in the area. At 11,250 cal. years BP dense forests dominated by Ulmus replaced the open forest type. Around 10,700cal. years BP Quercus, Tilia and Fraxinus expanded strongly, and Acer and Corylus became established. Mixed deciduous forest with Picea dominated the upland vegetation between 10,700 and 10, 150 cal. years BP. At 10,150 cal. years BP Corylus increased significantly and between 10,150 and 8500 cal. years BP, dense mixed deciduous forests with Picea and Corylus were abundant in the area. Climatic fluctuations seem to have been the driving force behind vegetation changes during the Lateglacial period, while the forest development during the Early Holocene was mainly driven by migrational and successional processes.
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2.
  • Björck, Jonas, et al. (författare)
  • An event stratigraphy for the Last Glacial-Holocene transition in eastern middle Sweden : results from investigations of varved clay and terrestrial sequences
  • 2002
  • Ingår i: Quaternary Science Reviews. - 0277-3791 .- 1873-457X. ; 21:12/13, s. 1489-1501
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents an event stratigraphy for the Last Glacial-Holocene transition in eastern middle Sweden. The event stratigraphy for eastern middle Sweden comprises ten events and covers the time-span from ca 12,900 to 10,200 cal yr BP. The local event stratigraphy has been linked to the GRIP isotopic event stratigraphy by different correlations. The onset of the Younger Dryas is dated to 12,650 cal yr BP. This cold event lasted for ca 1125 cal yr in the area. The Vedde Ash (ca 12,000 cal yr BP) has been recorded in two terrestrial sequences, which makes it possible to exactly link the event stratigraphy to the GRIP ice-core and to marine cores in the North Atlantic region. The final drainage of the Baltic Ice Lake has been dated to ca 11,560 cal yr BP, which predates the Younger Dryas/Preboreal climatic boundary with ca 35 yr. An early Holocene cold event has been detected both in terrestrial and varved clay sequences at ca 11,305-11,185 cal yr BP. This cold event coincides almost exactly with a brackish water phase in the Baltic Sea. A previously unrecorded early Holocene tephra horizon has been found in lacustrine sediments at ca 10,200 cal yr BP.
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3.
  • Wohlfarth, B, et al. (författare)
  • Environment and Climate in Southwestern Switzerland during the Last Termination, 15-10 ka BP
  • 1994
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 13:4, s. 361-394
  • Tidskriftsartikel (refereegranskat)abstract
    • Various records from sites ranging in altitude between 372 and 2290 m along a NW-SE transect through SW Switzerland were compiled and correlated within well defined chrono- and biostratigraphic units. Deglaciation of lowland areas is estimated at ca. 15,000-14,000 BP (minimum age), while the lower part of the Rhone valley and the Jura Mountains may have become ice free later. A significant climatic warming is clearly indicated by several palaeoecological records at ca. 12,600 BP. The compiled data give no clear evidence of a cooler phase between 12,200-12,000 BP. Oxygen isotope data point to a slight and progressive decrease in the deltaO-18 values between ca. 12,500-11,000 BP, which is followed by a marked drop at 11,000 BP. A very distinct change in lithology, rock glacier development and in mollusc and vegetation records characterises many low and high altitude sites ca. 300 years later, at 10,700 BP. Between 11,000 and 10,000 BP oxygen isotope records seem to respond more rapidly to the climatic shifts than the biostratigraphical records. Possible explanations for these time-lags are discussed. Our compilation shows that further multidisciplinary research in key sites would provide more precise palaeoclimatological information, both qualitatively and quantitatively. Higher time resolution and quantitative estimates of climatic parameters are needed to evaluate in detail the mechanisms and consequences of these rapid climatic changes in SW Switzerland.
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4.
  • Abbott, Peter M., et al. (författare)
  • A detailed framework of Marine Isotope Stages 4 and 5 volcanic events recorded in two Greenland ice-cores
  • 2012
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 36, s. 59-77
  • Tidskriftsartikel (refereegranskat)abstract
    • Sulphate records from Greenland ice-cores indicate that Marine Isotope Stages 4 and 5 were charactensed by a higher incidence of large volcanic eruptions than other periods during the last glacial period, however, few investigations have focused on tephra deposits associated with these volcanic eruptions and the nature and origin of the events. Here we present a detailed tephrochronological framework of the products of 15 volcanic events spanning this interval: the majority of which have been preserved as cryptotephra horizons within the Greenland records. The major element compositions of individual glass shards within these horizons indicate that 13 of the eruptions originated from Iceland and 6 of these events can be correlated to the specific volcanic systems of Katla, Grimsvotn, Grimsvotn-Kverkfjoll and either Reykjanes or Veidivotn-Bardarbunga. For the remaining Icelandic horizons a source from either the rift zone or a flank zone can be suggested based on rock suite affinities. Two horizons have been correlated to a source from the Jan Mayen volcanic system which represents the first discovery of material from this system within any Greenland ice-cores. The robust geochemical characterisations, independent ages for these horizons (derived from the GICCO5 ice-core chronology) and stratigraphic positions relative to the Dansgaard-Oeschger climate events recorded in the Greenland ice-cores represent a critical framework that provides new information on the frequency and nature of volcanic events occurring in the North Atlantic region during MIS 4 and 5. This framework can now be utilised in the assessment of the differential timing and rate of response to the millennial-scale climatic events that characterised this period, through the use of the tephra horizons as time-synchronous tie-lines to other palaeoclimatic sequences.
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5.
  • Ahmed, Engy, et al. (författare)
  • Archaeal community changes in Lateglacial lake sediments: Evidence from ancient DNA
  • 2018
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 181, s. 19-29
  • Tidskriftsartikel (refereegranskat)abstract
    • The Lateglacial/early Holocene sediments from the ancient lake at Hässeldala Port, southern Sweden provide an important archive for the environmental and climatic shifts at the end of the last ice age and the transition into the present Interglacial. The existing multi-proxy data set highlights the complex interplay of physical and ecological changes in response to climatic shifts and lake status changes. Yet, it remains unclear how microorganisms, such as Archaea, which do not leave microscopic features in the sedimentary record, were affected by these climatic shifts. Here we present the metagenomic data set of Hässeldala Port with a special focus on the abundance and biodiversity of Archaea. This allows reconstructing for the first time the temporal succession of major Archaea groups between 13.9 and 10.8 ka BP by using ancient environmental DNA metagenomics and fossil archaeal cell membrane lipids. We then evaluate to which extent these findings reflect physical changes of the lake system, due to changes in lake-water summer temperature and seasonal lake-ice cover. We show that variations in archaeal composition and diversity were related to a variety of factors (e.g., changes in lake water temperature, duration of lake ice cover, rapid sediment infilling), which influenced bottom water conditions and the sediment-water interface. Methanogenic Archaea dominated during the Allerød and Younger Dryas pollen zones, when the ancient lake was likely stratified and anoxic for large parts of the year. The increase in archaeal diversity at the Younger Dryas/Holocene transition is explained by sediment infilling and formation of a mire/peatbog.
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6.
  • Alexanderson, Helena, et al. (författare)
  • An Arctic perspective on dating Mid-Late Pleistocene environmental history
  • 2014
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 92, s. 9-31
  • Forskningsöversikt (refereegranskat)abstract
    • To better understand Pleistocene climatic changes in the Arctic, integrated palaeoenvironmental andpalaeoclimatic signals from a variety of marine and terrestrial geological records as well as geochronologicage control are required, not least for correlation to extra-Arctic records. In this paper we discuss,from an Arctic perspective, methods and correlation tools that are commonly used to date ArcticPleistocene marine and terrestrial events. We review the state of the art of Arctic geochronology, withfocus on factors that affect the possibility and quality of dating, and support this overview by examples ofapplication of modern dating methods to Arctic terrestrial and marine sequences.Event stratigraphy and numerical ages are important tools used in the Arctic to correlate fragmentedterrestrial records and to establish regional stratigraphic schemes. Age control is commonly provided byradiocarbon, luminescence or cosmogenic exposure ages. Arctic Ocean deep-sea sediment successionscan be correlated over large distances based on geochemical and physical property proxies for sedimentcomposition, patterns in palaeomagnetic records and, increasingly, biostratigraphic data. Many of theseproxies reveal cyclical patterns that provide a basis for astronomical tuning.Recent advances in dating technology, calibration and age modelling allow for measuring smallerquantities of material and to more precisely date previously undatable material (i.e. foraminifera for 14C,and single-grain luminescence). However, for much of the Pleistocene there are still limits to the resolutionof most dating methods. Consequently improving the accuracy and precision (analytical andgeological uncertainty) of dating methods through technological advances and better understanding ofprocesses are important tasks for the future. Another challenge is to better integrate marine andterrestrial records, which could be aided by targeting continental shelf and lake records, exploringproxies that occur in both settings, and by creating joint research networks that promote collaborationbetween marine and terrestrial geologists and modellers.
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7.
  • Alsos, Inger Greve, et al. (författare)
  • Ancient sedimentary DNA shows rapid post-glacial colonisation of Iceland followed by relatively stable vegetation until the Norse settlement (Landnam) AD 870
  • 2021
  • Ingår i: Quaternary Science Reviews. - : Elsevier. - 0277-3791 .- 1873-457X. ; 259
  • Tidskriftsartikel (refereegranskat)abstract
    • Understanding patterns of colonisation is important for explaining both the distribution of single species and anticipating how ecosystems may respond to global warming. Insular flora may be especially vulnerable because oceans represent severe dispersal barriers. Here we analyse two lake sediment cores from Iceland for ancient sedimentary DNA to infer patterns of colonisation and Holocene vegetation development. Our cores from lakes Torfdalsvatn and Nykurvatn span the last c. 12,000 cal yr BP and c. 8600 cal yr BP, respectively. With near-centennial resolution, we identified a total of 191 plant taxa, with 152 taxa identified in the sedimentary record of Torfdalsvatn and 172 plant taxa in the sedimentary record of Nykurvatn. The terrestrial vegetation at Torfdalsvatn was initially dominated by bryophytes, arctic herbs such as Saxifraga spp. and grasses. Around 10,100 cal yr BP, a massive immigration of new taxa was observed, and shrubs and dwarf shrubs became common whereas aquatic macrophytes became dominant. At Nykurvatn, the dominant taxa were all present in the earliest samples; shrubs and dwarf shrubs were more abundant at this site than at Torfdalsvatn. There was an overall steep increase both in the local accumulated richness and regional species pool until 8000 cal yr BP, by which time 3/4 of all taxa identified had arrived. The period 4500-1000 cal yr BP witnessed the appearance of a a small number of bryophytes, graminoids and forbs that were not recorded in earlier samples. The last millennium, after human settlement of the island (Landnam), is characterised by a sudden disappearance of Juniperus communis, but also reappearance of some high arctic forbs and dwarf shrubs. Notable immigration during the Holocene coincides with periods of increased incidence of sea ice, and we hypothesise that this may have acted as a dispersal vector. Thus, although ongoing climate change might provide a suitable habitat in Iceland for a large range of species only found in the neighbouring regions today, the reduction of sea ice may in fact limit the natural colonisation of new plant species.
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8.
  • Ampel, Linda, et al. (författare)
  • Modest summer temperature variability during DO cycles in western Europe
  • 2010
  • Ingår i: Quaternary Science Reviews. - : Elsevier. - 0277-3791 .- 1873-457X. ; 29:11-12, s. 1322-1327
  • Tidskriftsartikel (refereegranskat)abstract
    • Abrupt climatic shifts between cold stadials and warm interstadials, termed Dansgaard-Oeschger (DO) cycles, occurred frequently during the Last Glacial. Their imprint is registered in paleorecords worldwide, but little is known about the actual temperature change both annually and seasonally in different regions. A recent hypothesis based on modelling studies, suggests that DO cycles were characterised by distinct changes in seasonality in the Northern Hemisphere. The largest temperature change between stadial and interstadial phases would have occurred during the winter and spring seasons, whereas the summer seasons would have experienced a rather muted temperature shift. Here we present a temporally high-resolved reconstruction of summer temperatures for eastern France during a sequence of DO cycles between 36 and 18 thousand years before present. The reconstruction is based on fossil diatom assemblages from the paleolake Les Echets and indicates summer temperature changes of ca 0.5–2 °C between stadials and interstadials. This study is the first to reconstruct temperatures with a sufficient time resolution to investigate DO climate variability in continental Europe. It is therefore also the first proxy record that can test and support the hypothesis that temperature changes during DO cycles were modest during the summer season.
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9.
  • Anchukaitis, Kevin, et al. (författare)
  • Last millennium Northern Hemisphere summer temperatures from tree rings: Part II, spatially resolved reconstructions
  • 2017
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 163, s. 1-22
  • Tidskriftsartikel (refereegranskat)abstract
    • Climate field reconstructions from networks of tree-ring proxy data can be used to characterize regionalscale climate changes, reveal spatial anomaly patterns associated with atmospheric circulation changes, radiative forcing, and large-scale modes of ocean-atmosphere variability, and provide spatiotemporal targets for climate model comparison and evaluation. Here we use a multiproxy network of tree-ring chronologies to reconstruct spatially resolved warm season (MayeAugust) mean temperatures across the extratropical Northern Hemisphere (40-90N) using Point-by-Point Regression (PPR). The resulting annual maps of temperature anomalies (750e1988 CE) reveal a consistent imprint of volcanism, with 96% of reconstructed grid points experiencing colder conditions following eruptions. Solar influences are detected at the bicentennial (de Vries) frequency, although at other time scales the influence of insolation variability is weak. Approximately 90% of reconstructed grid points show warmer temperatures during the Medieval Climate Anomaly when compared to the Little Ice Age, although the magnitude varies spatially across the hemisphere. Estimates of field reconstruction skill through time and over space can guide future temporal extension and spatial expansion of the proxy network.
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10.
  • Andersen, J. L., et al. (författare)
  • Ice surface changes during recent glacial cycles along the Jutulstraumen and Penck Trough ice streams in western Dronning Maud Land, East Antarctica
  • 2020
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 249
  • Tidskriftsartikel (refereegranskat)abstract
    • Reconstructing past ice-sheet surface changes is key to testing and improving ice-sheet models. Data constraining the past behaviour of the East Antarctic Ice Sheet are sparse, limiting our understanding of its response to past, present and future climate change. Here, we report the first cosmogenic multinuclide (Be-10, Al-26, Cl-36) data from bedrock and erratics on nunataks along the Jutulstraumen and Penck Trough ice streams in western Dronning Maud Land, East Antarctica. Spanning elevations between 741 and 2394 m above sea level, the samples have apparent exposure ages between 2 ka and 5 Ma. The highest-elevation bedrock sample indicates (near-) continuous minimum exposure since the Pliocene, with a low apparent erosion rate of 0.15 +/- 0.03 m Ma(-1), which is similar to results from eastern Dronning Maud Land. In contrast to studies in eastern Dronning Maud Land, however, our data show clear indications of a thicker-than-present ice sheet within the last glacial cycle, with a thinning of similar to 35-120 m during the Holocene (similar to 2-11 ka). Difficulties in separating suitable amounts of quartz from the often quartz-poor rock-types in the area, and cosmogenic nuclides inherited from exposure prior to the last deglaciation, prevented robust thinning estimates from elevational profiles. Nevertheless, the results clearly demonstrate ice-surface fluctuations of several hundred meters between the current grounding line and the edge of the polar plateau for the last glacial cycle, a constraint that should be considered in future ice-sheet model simulations.
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11.
  • Anderson, John B., et al. (författare)
  • Ross Sea paleo-ice sheet drainage and deglacial history during and since the LGM
  • 2014
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 100, s. 31-54
  • Tidskriftsartikel (refereegranskat)abstract
    • Onshore and offshore studies show that an expanded, grounded ice sheet occupied the Ross Sea Embayment during the Last Glacial Maximum (LGM). Results from studies of till provenance and the orientation of geomorphic features on the continental shelf show that more than half of the grounded ice sheet consisted of East Antarctic ice flowing through Transantarctic Mountain (TAM) outlet glaciers; the remainder came from West Antarctica. Terrestrial data indicate little or no thickening in the upper catchment regions in both West and East Antarctica during the LGM. In contrast, evidence from the mouths of the southern and central TAM outlet glaciers indicate surface elevations between 1000 m and 1100 m (above present-day sea level). Farther north along the western margin of the Ross Ice Sheet, surface elevations reached 720 m on Ross Island, and 400 m at Terra Nova Bay. Evidence from Marie Byrd Land at the eastern margin of the ice sheet indicates that the elevation near the present-day grounding line was more than 800 m asl, while at Siple Dome in the central Ross Embayment, the surface elevation was about 950 m asl. Farther north, evidence that the ice sheet was grounded on the middle and the outer continental shelf during the LGM implies that surface elevations had to be at least 100 m above the LGM sea level. The apparent low surface profile and implied low basal shear stress in the central and eastern embayment suggests that although the ice streams may have slowed during the LGM, they remained active. Ice-sheet retreat from the western Ross Embayment during the Holocene is constrained by marine and terrestrial data. Ages from marine sediments suggest that the grounding line had retreated from its LGM outer shelf location only a few tens of kilometer to a location south of Coulman Island by similar to 13 ka BP. The ice sheet margin was located in the vicinity of the Drygalski Ice Tongue by similar to 11 ka BP, just north of Ross Island by similar to 7.8 ka BP, and near Hatherton Glacier by similar to 6.8 ka BP. Farther south, Be-10 exposure ages from glacial erratics on nunataks near the mouths of Reedy, Scott and Beardmore Glaciers indicate thinning during the mid to late Holocene, but the grounding line did not reach its present position until 2 to 3 ka BP. Marine dates, which are almost exclusively Acid Insoluble Organic (AIO) dates, are consistently older than those derived from terrestrial data. However, even these ages indicate that the ice sheet experienced significant retreat after similar to 13 ka BP. Geomorphic features indicate that during the final stages of ice sheet retreat ice flowing through the TAM remained grounded on the shallow western margin of Ross Sea. The timing of retreat from the central Ross Sea remains unresolved; the simplest reconstruction is to assume that the grounding line here started to retreat from the continental shelf more or less in step with the retreat from the western and eastern sectors. An alternative hypothesis, which relies on the validity of radiocarbon ages from marine sediments, is that grounded ice had retreated from the outer continental shelf prior to the LGM. More reliable ages from marine sediments in the central Ross Embayment are needed to test and validate this hypothesis.
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12.
  • Baker, Andrea, et al. (författare)
  • Climatic variability in Mfabeni peatlands (South Africa) since the late Pleistocene
  • 2017
  • Ingår i: Quaternary Science Reviews. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0277-3791 .- 1873-457X. ; 160, s. 57-66
  • Tidskriftsartikel (refereegranskat)abstract
    • It has been postulated that a bipolar seesaw interhemispheric mechanism dominated the relationship between the Northern and Southern hemisphere climates since the late Pleistocene. A key test for this proposition would be to undertake palaeoenvironmental studies on terrestrial archives in climatically sensitive regions. Southern Africas contemporary C-3 and C-4 terrestrial plant distributions display a definitive geographical pattern dictated by different growing season rainfall and temperature zones; however, the region is generally archive poor due to its overall semi-arid climate and high relief topography. The Mfabeni peatland, with a basal age of c. 47 k yrs calibrated before present (kcal yr BP), is one of the oldest continuous coastal peat deposits in Southern Africa. Molecular leaf wax isotopes (delta C-13(wax)) were generated for a 810 cm long core, and combined with previously published bulk geochemical (delta C-13(bulk), %TOC), palynological, and stratigraphic data, to reconstruct the late Pleistocene and Holocene palaeoenvironments. We interpreted environmental shifts associated with the Heinrich 4, Last Glacial Maximum, deglacial and Holocene periods, which are consistent with adjacent Indian Ocean sea surface temperature records. However, the other shorter climate perturbations during the Heinrich 5, 3, 2, 1, Antarctic cold reversal and Younger Dryas, were muted, most likely due to local hydrological overprinting on the Mfabeni record. A general anti-phase sequence was observed between the Mfabeni record and better established Northern Hemisphere events, underpinning the bipolar seesaw interhemispheric mechanism proposed for global climate forcing since the Late Pleistocene. (C) 2017 Elsevier Ltd. All rights reserved.
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13.
  • Baykal, Yunus, et al. (författare)
  • Detrital zircon U–Pb age analysis of last glacial loess sources and proglacial sediment dynamics in the Northern European Plain
  • 2021
  • Ingår i: Quaternary Science Reviews. - : Elsevier. - 0277-3791 .- 1873-457X. ; 274
  • Tidskriftsartikel (refereegranskat)abstract
    • Loess deposits along the northern fringe of the European loess belt potentially record past changes in dust emission from areas proximal to former ice sheets. Recent chronologies from loess deposits across this region generally agree on greatly enhanced dust deposition rates when the Fennoscandian Ice Sheet reached its maximum extent during the late last glacial. However, uncertainties over the material's source and origin limit understanding of the causes of this enhanced dust activity. In particular, loess in southwestern Poland has been attributed to multiple origins, mainly involving glaciofluvial outwash plains along the Fennoscandian Ice Sheet margin and/or local sources in the mountainous areas of the Sudetes and Western Carpathians. Here we apply detrital zircon U–Pb age analyses for a large number of grains recovered from four loess samples taken from different stratigraphic units exposed at Biały Kościół in southwestern Poland, previously luminescence dated to MIS 4–2, to assess loess provenance as well as its temporal evolution during last glacial Fennoscandian Ice Sheet fluctuations. Furthermore, we analysed the detrital zircon U–Pb age spectra of five samples from potential source sediments to constrain the history of sediment recycling and mixing within the Northern European Plain prior to deflation and loess deposition. The broad range of zircon age components detected in the four loess samples suggests both Fennoscandian and closer Peri-Gondwanan proto-sources while a narrow, dominant Carboniferous age peak is consistent with sourcing from the local Strzelin Hills in the Sudetic foreland. However, the presence of both Fennoscandian and Peri-Gondwanan derived grains in samples from potential source sediments reveals that this mixture of sediment sources is widespread across the Northern European Plain, as a result of long-term glacial and fluvial reworking of cover sediments in the proglacial area throughout the Quaternary. Local rivers draining the Sudetic foreland transported this Fennoscandian-Peri-Gondwanan sediment mixture along with particles denuded from the Strzelin Hills, resulting in a nearby, temporally stable dust source for the Biały Kościół loess during MIS 4–2, while dust emission rates were substantially increased during the last glacial maximum. Given that our model for loess formation at Biały Kościół essentially involves sediment distribution via rivers prior to short distance aeolian transport, we infer that the proportion of northern ice sheet derived particles in European loess deposits is mainly controlled by the drainage pattern of major rivers in relation to Pleistocene ice margins where glaciofluvial sediment is abundant. Based on the presence of Fennoscandian derived zircon grains in European loess deposits, we constrain a southern limit of the influence of northern ice sheet dust sources along the central European highlands that currently divide drainage between the Northern European Plain and the Danube Basins.
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14.
  • Baykal, Yunus, et al. (författare)
  • Eurasian Ice Sheet derived meltwater pulses and their role in driving atmospheric dust activity: Late Quaternary loess sources in SE England
  • 2022
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 296, s. 107804-107804
  • Tidskriftsartikel (refereegranskat)abstract
    • The role of Quaternary ice sheet fluctuations in driving meltwater pulses and ocean circulation perturbations is widely acknowledged. What is less clear is the role of these processes in driving changes in past atmospheric dust activity, and possible wider links between dust and climate. Terrestrial windblown dust (loess) deposits along the northern fringe of the European loess belt potentially record past atmospheric dust emission from regions close to the former Eurasian Ice Sheet (EIS) and provide a means to evaluate the role of ice sheet fluctuations in the past dust cycle. Numerical loess chronologies across this region generally agree on greatly enhanced dust deposition rates during MIS 2, when the EIS reached its maximum extent. Yet, uncertainties over the sources of this material prevent understanding of the precise causes of this greatly enhanced atmospheric dustiness, and any potential link to ice sheet fluctuations and climate. In southeast England, loess accumulation dominantly occurred in two phases centered on 25–23.5 ka and 20–19 ka, matching the timing of coalescence of the Fennoscandian and British-Irish ice sheets and specifically advances and retreats of nearby ice lobes in the western North Sea. As such, these deposits provide an ideal test of the role of ice sheet fluctuations in atmospheric dust dynamics. Here we undertake such a test through a detailed provenance study of loess in southeast England and potential dust source sediments across the North Sea region. We group extensive new and published data sets of detrital zircon U–Pb ages from basement rocks and Cenozoic sediments in the North Sea area, which not only provide new insight into both loess source, but also the nature of sediment transport over NW Europe into the North Sea basin more widely. Multi-proxy evidence allows us to unambiguously identify ice sheet derived sediments in the exposed North Sea basin as the dominant source of loess in southeast England, while fluvial sediments delivered by rivers draining Continental Europe possibly contributed additional source material to the first loess accumulation phase. We propose that sudden retreats of the North Sea Lobe released substantial amounts of sediment rich meltwater into the southern North Sea and Channel basins, driving accelerated dust emission, loess deposition and provenance variability in NW Europe during MIS 2. Moreover, we propose that this model of dust activity driven by proglacial sediment availability may be applicable for EIS marginal regions more widely, even where resultant loess cover is rarely preserved due to extensive erosion and reworking along the ice marginal spillway. This implies the role of ice sheets in controlling wider dust emission may be underestimated. In addition to driving changes in ocean circulation through meltwater pulses, ice sheet dynamics in the Quaternary may have also driven substantial and abrupt changes in atmospheric dust activity. This mechanism may in part explain the coupling between dust and climate events widely seen in Quaternary dust sediment records and suggests a possible major role of high latitude dust emission in MIS 2 dustiness across Europe and beyond.
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15.
  • Belle, Simon (författare)
  • Contrasting responses to long-term climate change of carbon flows to benthic consumers in two different sized lakes in the Baltic area
  • 2018
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 187, s. 168-176
  • Tidskriftsartikel (refereegranskat)abstract
    • The study of lake sediments and archived biological remains is a promising approach to better understand the impacts of climate change on aquatic ecosystems. Small lakes have been shown to be strongly sensitive to past climate change, but similar information is lacking for large lakes. By identifying responses to climate change of carbon flows through benthic food web in two different sized lakes, we aimed to understand how lake morphometry can mediate the effects of climate change. We reconstructed the dynamics of phytoplankton community composition and carbon resources sustaining chironomid biomass during the Holocene from the combined analysis of sedimentary pigment quantification and carbon stable isotopic composition of subfossil chironomid head capsules (delta C-13(Hc)) in a large lake in the Baltic area (Estonia). Our results showed that chironomid biomass in the large lake was mainly sustained by phytoplankton, with no significant relationship between delta C-13(Hc) values and temperature fluctuations. We suggest that lake morphometry (including distance of the sampling zone to the shoreline, and lake volume for primary producers) mediates the effects of climate change, making large lakes less sensitive to climate change. Complementary studies are needed to better understand differences in organic matter dynamics in different sized lakes and to characterize the response of the aquatic carbon cycle to past climate change. 2018 Elsevier Ltd. All rights reserved.
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16.
  • Belle, Simon (författare)
  • Environmental drivers and abrupt changes of phytoplankton community in temperate lake Lielais Svetinu, Eastern Latvia, over the last Post-Glacial period from 14.5 kyr
  • 2021
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 263
  • Tidskriftsartikel (refereegranskat)abstract
    • Understanding the long-term dynamics of ecological communities on the centuries-to-millennia scale is important for explaining the emergence of present-day biodiversity patterns and for predicting possible future scenarios. Fossil pigments and ancient DNA present in various sedimentary deposits can be analysed to study long-term changes in ecological communities. We analysed recent compilations of data, including fossil pigments, microfossils, and molecular inventories from the sedimentary archives, to understand the impact of gradual versus abrupt climate changes on the ecosystem status of a regional model lake over the last similar to 14.5 kyr. Such long and complete paleo-archives are scarce in North-Eastern Europe. The study site lies in a sensitive area, both climatically and in respect to vegetation. Namely the maritime-continentality line runs west to east in the central Baltic area to NE Europe and its south-north transect lies within the gradual decay of the nemoral forest into a boreal environment. Therefore, the selected location is an ideal sampling point to decipher long term environmental changes in the temperate climate zone. The main objective of the present study was to find out external factors influencing phototroph dynamics at temperate Lake Lielais Svetinu over the post-glacial period (similar to 14.5 kyr). We were able to model climate change together with vegetation change and the appearance of anthropogenic forcing, either as a gradual change or as abrupt events that influenced the phototrophs, which are keystone groups within the lacustrine ecosystem. Most interestingly, the gradual increase of species richness of phototrophs was linked to similar increase in fungal parasites of the same group - phototrophs. Abrupt climate change in the Late Glacial period caused abrupt events in the ecosystem but equally abrupt events were caused by gradual changes during the stable period of the Holocene Thermal Maximum (HTM). In addition, we highlight the increased frequency and degree of perturbation in pristine lakes due to low impact human activity over a larger region. Both observations demonstrate an impaired relationship between gradual external drivers and ecosystem response and apply to future scenarios of climate warming and increased human impact in north-eastern Europe. (C) 2021 The Authors. Published by Elsevier Ltd.
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17.
  • Belle, Simon (författare)
  • Food availability and temperature optima shaped functional composition of chironomid assemblages during the Late Glacial-Holocene transition in Northern Europe
  • 2021
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 266
  • Tidskriftsartikel (refereegranskat)abstract
    • Non-biting midges (Chironomidae) are the most diverse and abundant invertebrate group in boreal lakes and are strongly responsive to climate change, thus they are a valuable palaeoecological proxy for studying aquatic biodiversity response in the face of climate change. Here, we aim to decipher the influence of climate-induced changes on temporal patterns in chironomid assemblages. We apply a novel approach combining traditional taxon-based analysis and species-trait framework to subfossil chironomid assemblages in a sediment core covering the Late Glacial-Holocene transition in Northern Europe. We produce pollen-based July and January temperature reconstructions to characterize past climate fluctuations that show a distinct Early Holocene warming for continuous 1700 years with considerably greater warming in winter (ca. 10 degrees C) than summer (ca. 4 degrees C) temperature. Overall, chironomid taxonomic changes were mainly induced by the temperature tolerances and optima of species, as temporal dynamics showed agreement with temperature reconstructions. Our results suggest that vegetation dynamics could also play a role in structuring chironomid assemblages by selecting taxa with the highest ability to exploit available food resources, thus potentially confounding chironomid-based summer climate reconstructions. We demonstrate that the study of the hidden chironomid functional composition could help to identify secondary drivers and thus strengthen the reliability of climate reconstruction based on subfossil chironomids. (C) 2021 Elsevier Ltd. All rights reserved.
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18.
  • Bentley, Michael J., et al. (författare)
  • A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum
  • 2014
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 100, s. 1-9
  • Tidskriftsartikel (refereegranskat)abstract
    • A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20 ka, 15 ka, 10 ka and 5 ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse la. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorities for future work. The synthesis is intended to be a resource for the modelling and glacial geological community.
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19.
  • Bird, Anna, et al. (författare)
  • A constant Chinese Loess Plateau dust source since the late Miocene
  • 2020
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 227
  • Tidskriftsartikel (refereegranskat)abstract
    • The Pliocene-Pleistocene boundary marks a major change in global climate and East Asian monsoon dynamic. However, the role of the global atmospheric dust-cycle over this time is unclear; in particular the degree to which changes in the dust cycle influenced climate change, were driven by climate change, and how these processes interacted. Chinese loess records past dust-cycle history and the influences of aridification and monsoon circulation over the last 40 Ma. Previous work on the Chinese Loess Plateau argue over whether changes in dust source occur at the Pliocene-Pleistocene boundary, or at 1.2 Ma, despite these intervals marking major shifts in monsoon dynamics. We present Sr, Nd and Hf isotope data from multiple sites and show that dust source largely remains unchanged across these boundaries. Shifts in geochemistry are due to changes in grain-size and weathering. While the transport pathway (river, deserts, direct aeolian) is unclear, these tracer isotopes show that dust was dominantly sourced from the Northern Tibetan Plateau, with some input from the local bedrock. This shows that a major established and constant dust source on the Tibetan Plateau has been active and unchanged since late Miocene, despite dramatically changing climate conditions. Changes in loess accumulation are a function of climate change in Tibetan Plateau source regions rather than effects from increased aridification over the Pliocene-Pleistocene boundary.
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20.
  • Blockley, Simon, et al. (författare)
  • Building and testing age models for radiocarbon dates in Lateglacial and Early Holocene sediments
  • 2007
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 26:15-16, s. 1915-1926
  • Tidskriftsartikel (refereegranskat)abstract
    • The growing importance of understanding past abrupt climate variability at a regional and global scale has led to the realisation that independent chronologies of past environmental change need to be compared between various archives. This has in turn led to attempts at significant improvements in the required precision at which records can be dated. Radiocarbon dating is still the most prominent method for dating organic material from terrestrial and marine archives, and as such many of the recent developments in improving precision have been aimed at this technique. These include: (1) selection of the most suitable datable fractions within a record, (2) the development of better calibration curves, and (3) more precise age modelling techniques. While much attention has been focussed on the first two items, testing the possibilities of the relatively new age modelling approaches has not received much attention. Here, we test the potential for methods designed to significantly improve precision in radiocarbon-based age models, wiggle match dating and various forms of Bayesian analyses. We demonstrate that while all of the methods can perform very well, in some scenarios, caution must be taken when applying them. It appears that an integrated approach is required in real life dating situations where more than one model is applied, with strict error calculation, and with the integration of radiocarbon data with sedimentological analyses of site formation processes.
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21.
  • Blomdin, Robin, et al. (författare)
  • Evaluating the timing of former glacier expansions in the Tian Shan : A key step towards robust spatial correlations
  • 2016
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 153, s. 78-96
  • Tidskriftsartikel (refereegranskat)abstract
    • The timing of past glaciation across the Tian Shan provides a proxy for past climate change in this critical area. Correlating glacial stages across the region is difficult but cosmogenic exposure ages have considerable potential. A drawback is the large observed scatter in Be-10 surface exposure data. To quantify the robustness of the dating, we compile, recalculate, and perform statistical analyses on sets of 10Be surface exposure ages from 25 moraines, consisting of 114 new and previously published ages. We assess boulder age scatter by dividing boulder groups into quality classes and rejecting boulder groups of poor quality. This allows us to distinguish and correlate robustly dated glacier limits, resulting in a more conservative chronology than advanced in previous publications. Our analysis shows that only one regional glacial stage can be reliably correlated across the Tian Shan, with glacier expansions occurring between 15 and 281 a during marine oxygen isotope stage (MIS) 2. However, there are examples of older more extensive indicators of glacial stages between MIS 3 and MIS 6. Paleoglacier extent during MIS 2 was mainly restricted to valley glaciation. Local deviations occur: in the central Kyrgyz Tian Shan paleoglaciers were more extensive and we propose that the topographic context explains this pattern. Correlation between glacial stages prior to late MIS 2 is less reliable, because of the low number of samples and/or the poor resolution of the dating. With the current resolution and spatial coverage of robustly-dated glacier limits we advise that paleoclimatic implications for the Tian Shan glacial chronology beyond MIS 2 are speculative and that continued work toward robust glacial chronologies is needed to resolve questions regarding drivers of past glaciation in the Tian Shan and Central Asia.
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22.
  • Boethius, Adam, et al. (författare)
  • Mesolithic Scandinavian foraging patterns and hunting grounds targeted through laser ablation derived 87Sr/86Sr ratios at the Early-Mid Holocene site of Huseby Klev on the west coast of Sweden
  • 2022
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 293
  • Tidskriftsartikel (refereegranskat)abstract
    • Mobility is one of the most fundamental aspects of a foraging society. Since prehistoric mobility is often difficult to identify in the archaeological record, our understanding is largely based on comparison with ethnographic communities. In recent years the application of 87Sr/86Sr isotope analysis has, however, greatly broadened our knowledge of mobility in the past. Despite this, few studies have been undertaken on faunal remains to explore their mobility patterns and infer human exploitation patterns with more precision. In this contribution we sampled 28 mammal teeth from three different occupation phases at the Early to Mid-Holocene coastal site of Huseby Klev, Sweden. We first established the local baseline for seven geographical areas in the region surrounding Huseby Klev. Then, by applying laser ablation-multi collector-inductively coupled plasma-mass spectrometry to the selected teeth, we identified the likely origins of a range of terrestrial and marine fauna, and the possible human mobility patterns required in their exploitation. Overall, our results demonstrate that the prehistoric communities inhabiting Huseby Klev undertook both short- and long-distance forays for the exploitation of particular species. By relating inferences on hunting grounds, derived from strontium isotope data, to zooarchaeological evidence from the site and ethnographic human mobility patterns, we establish and discuss the prerequisites for landscape utilization. Lastly, we demonstrate that glacial meltwater may have temporally affected the local oceanic Sr ratios – suggesting significantly increased soil and bedrock weathering may influence the Sr values in aquatic ecosystems and, consequently, should be considered in such regions and at times of melting glaciers. By applying the method to additional sites and assemblages in the future, our understanding of prehistoric mobility will be greatly enhanced.
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23.
  • Buylaert, J. -P, et al. (författare)
  • Luminescence dating of the PASADO core 5022-1D from Laguna Potrok Aike (Argentina) using IRSL signals from feldspar
  • 2013
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 71, s. 70-80
  • Tidskriftsartikel (refereegranskat)abstract
    • We have measured and tested a luminescence chronology for the PASADO core 5022-1D from the maar lake of Laguna Potrok Aike. Because of unsuitable quartz OSL characteristics, sand-sized K-feldspar extracts were chosen as a dosimeter and the dose was measured using a post-IR IRSL (pIRIR(290)) measurement protocol. Using this approach we were able to access a stable signal and thus avoid the ubiquitous problem of feldspar signal instability. Extensive laboratory tests show that the chosen pIRIR(290) protocol is applicable to these samples. We also developed a new criterion based on known relative bleaching rates of the conventional IRSL signal (IR50) and the pIRIR(290) signal and the relationship between resulting equivalent doses; this is used to identify and reject poorly bleached samples. Eighteen samples out of 47 were rejected based on this criterion, without reference to absolute doses or stratigraphy; the resulting age-depth profile is self-consistent, increases smoothly with depth and is in agreement with independent age control based on volcanic ash layers (Reclus, Mt Burney and Hudson tephras) at the top and middle of the core. Our new luminescence chronology suggests that the 5022-1D core reaches back to similar to 65 ka at similar to 96 m below lake floor.
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24.
  • Capraro, L., et al. (författare)
  • Chronology of the Lower-Middle Pleistocene succession of the south-western part of the Crotone Basin (Calabria, Southern Italy)
  • 2011
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 30:9-10, s. 1185-1200
  • Tidskriftsartikel (refereegranskat)abstract
    • Biostratigraphy based on calcareous nannofossils, integrated by magnetostratigraphic, geochronological and isotopic data, allowed establishing a precise chronological framework for the Pleistocene succession within the south-western sector of the Crotone Basin (Calabria, Southern Italy), where the Pliocene-Pleistocene global stratotype section and point is defined, thus demonstrating that sedimentation was quasi-continuous during most of the Lower and Middle Pleistocene. At a large scale, the Pleistocene succession in this sector of the Crotone Basin is characterized by an evident shallowing-upwards trend, showing facies changes from bathyal to shelfal to littoral/continental. However, comparison between adjacent sectors within the investigated area demonstrates that stratigraphic architectures change vastly on very short distances. Our chronological constraints indicate that such changes in sedimentation styles probably occurred in response to differential subsidence rates, which originated tectonically-controlled synsedimentary structures where accommodation space and sediment yield were allotted unevenly. This articulated physiography led to striking differences in the overall thicknesses and organization of Pleistocene stratigraphies and, eventually, to a distinct diachroneity in the first appearance of shallow-marine deposits. In addition, superimposed are complex interplays between regional and local tectonics, eustasy and orbitally-forced climate changes. These interactions have been highlighted by the oxygen isotope stratigraphy established for a part of the studied succession, which is likely to document almost continuously the interval from Marine Isotope Stage (MIS) 26 to MIS 17. In its younger part (post-MIS 17), chronological ties are poor, as the succession is dominated by shallow-water to continental deposits showing a prominent organization into cyclothems. Nevertheless, based on the chronology of the underlying units, it is feasible that basin infill ended during MIS 15-MIS 14 times.
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25.
  • Chauhan, T., et al. (författare)
  • Glacial history and paleoceanography of the southern Yermak Plateausince 132 ka BP
  • 2014
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 92, s. 155-169
  • Tidskriftsartikel (refereegranskat)abstract
    • The southern Yermak Plateau (YP) is situated at the entrance to the Arctic Ocean in the narrow MarginalIce Zone (MIZ) between the Polar and Arctic Fronts, north-west of Svalbard. A gravity core JM10-02GChas been analysed in order to reconstruct paleoceanographic conditions and the movement of the seaice margin as well as the glacier ice conditions of the SvalbardeBarents Sea Ice Sheet (SBIS) during theLast InterglacialeGlacial cycle. The distribution of planktic and benthic foraminifera, planktic and benthicoxygen and carbon isotopes and variations in ice-rafted debris (IRD) has been investigated. The sedimentcore covers the time interval from the Marine Isotope Stage (MIS) 6/5e transition (Termination II, c.132 ka BP) to the early Holocene. During Termination II (TII), the SBIS retreated and the sea ice marginwas in distal position whereas during MIS 5 to MIS 4 the sea ice margin was close to the core site. Severalcore intervals interpreted as representing MIS 5e, MIS 5c, MIS 5a, MIS 3 and MIS 1 were barren ofcalcareous microfossils whereas the intervals representing MIS 4 and MIS 2 were characterised by highproductivity (HP) of planktic and benthic foraminifera. These “glacial” HP zones were associated with theopen water conditions resulting from the advection of Atlantic Water (AW) and retreat of the sea icemargin. The barren zones during MIS 5, MIS 3 and MIS 1 resulted from the proximity of the sea icemargin whereas during MIS 2 the likely cause was an advance of the SBIS.
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26.
  • Chawchai, Sakonvan, et al. (författare)
  • Hydroclimate variability of central Indo-Pacific region during the Holocene
  • 2021
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 253
  • Tidskriftsartikel (refereegranskat)abstract
    • Here we present a decadal-resolved hydroclimate record covering the past 11 thousand years based on δ18O data of three stalagmites from Klang Cave (TK) on the Thai-Malay Peninsula, southern Thailand. The δ18O values indicate wetter conditions/more rainfall during the early Holocene from 11 to 7 thousand years before present (kyr BP). A large increase of 2‰ in δ18O is observed from 7.0 to 6.0 kyr BP, indicating a millennial drying period followed by drought conditions between 6.0 and 5.2 kyr BP. After a long hiatus (5.2–2.7 kyr BP), δ18O data show a millennium-long trend toward dry conditions. An abrupt positive change of 0.8–1.0‰ in δ18O is noticed between 8.29 and 8.17 kyr BP, reflecting the 8.2-ka event; however, the amplitude of the δ18O shift is much smaller comparing to that of the event of 6.0–5.2 kyr BP. On orbital time-scales, the TK record agrees with insolation-dominated speleothem records in the Asian-Australian monsoon realm. Noticeable inconsistencies among records in the Southeast Asia region (between 8°N and 4°N–8°S) have been documented on multi-centennial scales. Lower δ18O values are likely associated with the mean position of the Intertropical Convergence Zone (ITCZ). A new reconstruction of Holocene ITCZ shifts index within the central Indo-Pacific region, based on stalagmite δ18O records from Klang Cave (8°N) and Liang Luar Cave (8°S), shows that the ITCZ played an important role in hydroclimate variability in the Asian-Australian monsoon regions. The southward shift of the ITCZ in the central Indo-Pacific region, controlled by the interhemispheric extratropical insolation gradient, may strongly correlate with the El Niño-Southern Oscillation (ENSO) activities in the Holocene.
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27.
  • Chawchai, Sakonvan, et al. (författare)
  • Hydroclimatic shifts in northeast Thailand during the last two millennia - the record of Lake Pa Kho
  • 2015
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 111, s. 62-71
  • Forskningsöversikt (refereegranskat)abstract
    • The Southeast Asian mainland is located in the central path of the Asian summer monsoon, a region where paleoclimatic data are still sparse. Here we present a multi-proxy (TOC, C/N, delta C-13, biogenic silica, and XRF elemental data) study of a 1.5 m sediment/peat sequence from Lake Pa Kho, northeast Thailand, which is supported by 20 AMS C-14 ages. Hydroclimatic reconstructions for Pa Kho suggest a strengthened summer monsoon between BC 170-AD 370, AD 800-960, and after AD 1450; and a weakening of the summer monsoon between AD 370-800, and AD 1300-1450. Increased run-off and a higher nutrient supply after AD 1700 can be linked to agricultural intensification and land-use changes in the region. This study fills an important gap in data coverage with respect to summer monsoon variability over Southeast Asia during the past 2000 years and enables the mean position of the Intertropical Convergence Zone (ITCZ) to be inferred based on comparisons with other regional studies. Intervals of strengthened/weaker summer monsoon rainfall suggest that the mean position of the ITCZ was located as far north as 35 degrees N between BC 170-AD 370 and AD 800-960, whereas it likely did not reach above 17 degrees N during the drought intervals of AD 370-800 and AD 1300-1450. The spatial pattern of rainfall variation seems to have changed after AD 1450, when the inferred moisture history for Pa Kho indicates a more southerly location of the mean position of the summer ITCZ.
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28.
  • Chawchai, Sakonvan, et al. (författare)
  • Lake Kumphawapi - an archive of Holocene palaeoenvironmental and palaeoclimatic changes in northeast Thailand
  • 2013
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 68, s. 59-75
  • Tidskriftsartikel (refereegranskat)abstract
    • The long-term climatic and environmental history of Southeast Asia, and of Thailand in particular, is still fragmentary. Here we present a new C-14-dated, multi-proxy sediment record (TOC, C/N, CNS isotopes, Si, Zr, K, Ti, Rb, Ca elemental data, biogenic silica) for Lake Kumphawapi, the second largest natural lake in northeast Thailand. The data set provides a reconstruction of changes in lake status, groundwater fluctuations, and catchment run-off during the Holocene. A comparison of multiple sediment sequences and their proxies suggests that the summer monsoon was stronger between c. 9800 and 7000 cal yr BP. Lake status and water level changes around 7000 cal yr BP signify a shift to lower effective moisture. By c. 6500 cal yr BP parts of the lake had been transformed into a peatland, while areas of shallow water still occupied the deeper part of the basin until c. 5400-5200 cal yr BP. The driest interval in Kumphawapi's history occurred between c. 5200 and 3200 cal yr BP, when peat extended over large parts of the basin. After 3200 cal yr BP, the deepest part of the lake again turned into a wetland, which existed until c. 1600 cal yr BP. The observed lake-level rise after 1600 cal yr BP could have been caused by higher moisture availability, although increased human influence in the catchment cannot be ruled out. The present study highlights the use of multiple sediment sequences and proxies to study large lakes, such as Lake Kumphawapi in order to correctly assess the time transgressive response to past changes in hydroclimate conditions. Our new data set from northeast Thailand adds important palaeoclimatic information for a region in Southeast Asia and allows discussing Holocene monsoon variability and ITCZ movement in greater detail.
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29.
  • Chen, Jie, et al. (författare)
  • Northwestward shift of the northern boundary of the East Asian summer monsoon during the mid-Holocene caused by orbital forcing and vegetation feedbacks
  • 2021
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 268
  • Tidskriftsartikel (refereegranskat)abstract
    • The East Asian summer monsoon (EASM) northern boundary is a critical indicator of EASM variations. Movement of the boundary is modulated by both the EASM and the mid-latitude westerlies. Here, we use the Earth system model EC-Earth to quantify the contribution of orbital forcing and vegetation feedbacks in modulating the movement of EASM northern boundary. The results show that the simulated EASM northern boundary during the mid-Holocene shifts by a maximum of ∼213 km northwestward due to orbital forcing. When the model was coupled with a dynamic vegetation module LPJ-GUESS, the northern boundary shifts further northwestward by a maximum of ∼90 km, indicating the importance of vegetation feedbacks. During the mid-Holocene, temperature increased in the mid-latitude during the boreal summer due to insolation, leading to increased meridional air temperature differences (MTDs) over the region north of 45°N and to decreased MTDs to the south. The changes in the temperature gradient weakened the East Asian Westly Jet (EAWJ) and displaced it northward, resulting in an earlier transition of the Meiyu stage and a more prolonged Midsummer stage. The northward movement of EAWJ, combined with the enhanced southerly moisture flow from South China, caused more precipitation in North China and eventually to a northwestward shift of the northern boundary of the EASM. The coupled dynamic vegetation module LPJ-GUESS simulated more grassland and less forest over Northeast Asia during the mid-Holocene. The increased surface albedo tended to lower the temperature in the region, and further enhanced the MTDs in mid-latitude East Asia, leading to the further northward movement of the EAWJ and a northwestward shift of the EASM northern boundary. Although the simulated vegetation distribution in several regions may be not accurate, it reflects the substantial contribution of climate-vegetation interaction on modulating the EASM.
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30.
  • Clark, Chris D., et al. (författare)
  • Pattern and timing of retreat of the last British Irish ice sheet
  • 2012
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 44, s. 112-146
  • Tidskriftsartikel (refereegranskat)abstract
    • During the last glacial the ice sheet that subsumed most of Britain, Ireland and the North Sea attained its maximum extent by 27 ka BP and with an ice volume sufficient to raise global sea level by ca 2.5 m when it melted. We reconstruct the demise of this British-Irish Ice Sheet (BIIS) and present palaeo-glaciological maps of retreat stages between 27 and 15 ka BR The whole land area was investigated using remote sensing data and we present maps of moraines, meltwater channels, eskers, and drumlins and a methodology of how to interpret and bring them together. For the continental shelf, numerous large moraines were discovered recording an extensive pattern of retreat stretching from SW Ireland to the Shetland Isles. From an integration of this new mapping of glacial geomorphology (>26,000 landforms) with previously published evidence, compiled in the BRITICE database, we derive a pattern of retreat for the whole BIIS. We review and compile relevant dates (881 examples) that constrain the timing of retreat. All data are held within a Geographic Information System (GIS), and are deciphered to produce a best-estimate of the combined pattern and timing of retreat. Pattern information reveals an ice sheet mainly comprised of a shelf-parallel configuration from SW Ireland to NE Scotland but it spread far enough to the south to incorporate outlying ice domes over Wales, the Lake District and Kerry. Final disintegration was into a number of separate ice caps, rather than reduction as a single mass, and paradoxically, retreat was not always back to high ground. By 23 ka BP ice withdrew along its northern boundaries at the same time as the southern margins were expanding, including transient ice streaming down the Irish Sea and advances of lobes in the Cheshire Basin, Vale of York and east coast of England. Ice divides migrated south. By 19 ka the ice sheet was in crisis with widespread marine-based ice losses, particularly in the northern North Sea and the Irish Sea. Considerable dynamic-thinning occurred during this phase. Final collapse of all marine sectors occurred by 17 ka BP and with most margins beginning to back-step onshore. Disintegration of the North Sea 'ice bridge' between Britain and Norway remains loosely constrained in time but the possibility of catastrophic collapse of this sector is highlighted. The North Channel and Irish Sea ice streams had finally cleaved the ice sheet into separate Irish and Scottish ice sheets by 16 ka BP. Rates of ice loss were found to vary widely over space and time (e.g., 65-260 km(3) per year). The role of ice streams and calving losses of marine-based sectors are examined. Retreat rates of up to ca 150 ma(-1) were found for some ice stream margins. That large parts (2/3) of the BIIS were marine-based, drained by ice streams, and possibly with fringing ice shelves in places, makes it a useful analogue for the West Antarctic Ice Sheet (WAIS). This is especially so because the BIIS deglaciated in response to rising temperatures and a rising sea level (driven by melting of other ice masses) which are the current forcings that might cause collapse of the WAIS. Our reconstruction, when viewed from the opposite perspective, documents when fresh land became exposed for exploitation by plants, animals and Man, and records for how long such land has been available for soil and geochemical development and ecological succession.
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31.
  • Cohen, T. J., et al. (författare)
  • A pluvial episode identified in arid Australia during the Medieval Climatic Anomaly
  • 2012
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 56, s. 167-171
  • Tidskriftsartikel (refereegranskat)abstract
    • Optically stimulated luminescence (OSL) ages from a relict shoreline on Lake Callabonna record a major pluvial episode in southern central Australia between 1050  70 and 1100  60 Common Era (CE), within the Medieval Climatic Anomaly (MCA). During this pluvial interval Lake Callabonna filled to 10e12 times the volume of the largest historical filling (1974) and reached maximum depths of 4e5 m, compared to the 0.5e1.0 m achieved today. Until now there has been no direct evidence for the MCA in the arid interior of Australia. A multi-proxy, analogue-based atmospheric circulation reconstruction indicates that the pluvial episode was associated with an anomalous meridional atmospheric circulation pattern over the Southern extratropics, with high sea-level pressure ridges in the central Indian Ocean and Tasman Sea, and a trough extending from the Southern Ocean into central Australia. A major decline in the mobility of the Australian aboriginal hunter-gatherer coincides with this MCA period, in southern central Australia.
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32.
  • Colleoni, Florence, et al. (författare)
  • An East Siberian ice shelf during the Late Pleistocene glaciations : Numerical reconstructions
  • 2016
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 147:SI, s. 148-163
  • Tidskriftsartikel (refereegranskat)abstract
    • A recent data campaign in the East Siberian Sea has revealed evidence of grounded and floating ice dynamics in regions of up to 1000 m water depth, and which are attributed to glaciations older than the Last Glacial Maximum (21 kyrs BP). The main hypothesis based on this evidence is that a small ice cap developed over Beringia and expanded over the East Siberian continental margin during some of the Late Pleistocene glaciations. Other similar evidence of ice dynamics that have been previously collected on the shallow continental shelves of the Arctic Ocean have been attributed to the penultimate glaciation, i.e. Marine Isotopes Stage 6 (approximate to 140 kyrs BP). We use an ice sheet model, forced by two previously simulated MIS 6 glacial maximum climates, to carry out a series of sensitivity experiments testing the impact of dynamics and mass-balance related parameters on the geometry of the East Siberian ice cap and ice shelf. Results show that the ice cap developing over Beringia connects to the Eurasian ice sheet in all simulations and that its volume ranges between 6 and 14 m SLE, depending on the climate forcing. This ice cap generates an ice shelf of dimensions comparable with or larger than the present-day Ross ice shelf in West Antarctica. Although the ice shelf extent strongly depends on the ice flux through the grounding line, it is particularly sensitive to the choice of the calving and basal melting parameters. Finally, inhibiting a merging of the Beringia ice cap with the Eurasian ice sheet affects the expansion of the ice shelf only in the simulations where the ice cap fluxes are not large enough to compensate for the fluxes coming from the Eurasian ice sheet.
  •  
33.
  • Colleoni, Florence, et al. (författare)
  • The role of an Arctic ice shelf in the climate of the last glacial maximum of MIS 6 (140 ka)
  • 2010
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 29:25-26, s. 3590-3597
  • Tidskriftsartikel (refereegranskat)abstract
    • During the last decade, Arctic icebreaker and nuclear submarine expeditions have revealed large-scale Pleistocene glacial erosion on the Lomonosov Ridge, Chukchi Borderland and along the Northern Alaskan margin indicating that the glacial Arctic Ocean hosted large Antarctic-style ice shelves. Dating of sediment cores indicates that the most extensive and deepest ice grounding occurred during Marine Isotope Stage (MIS) 6. The precise extents of Pleistocene ice shelves in the Arctic Ocean are unknown but seem comparable to present existing Antarctic ice shelves. How would an Antarctic-style ice shelf in the MIS 6 Arctic Ocean influence the Northern Hemisphere climate? Could it have impacted on the surface mass balance (SMB) of the MIS 6 Eurasian ice sheet and contributed to its large southward extent? We use an Atmospheric General Circulation Model (AGCM) to investigate the climatic impacts of both a limited MIS 6 ice shelf covering portions of the Canada Basin and a fully ice shelf covered Arctic Ocean. The AGCM results show that both ice shelves cause a temperature cooling of about 3 °C over the Arctic Ocean mainly due to the combined effect of ice elevation and isolation from the underlying ocean heat fluxes stopping the snow cover from melting during summer. The calculated SMB of the ice shelves are positive. The ice front horizontal velocity of the Canada Basin ice shelf is estimated to ≈ 1 km yr−1 which is comparable to the recent measurements of the Ross ice shelf, Antarctica. The existence of a large continuous ice shelf covering the entire Arctic Ocean would imply a mean annual velocity of icebergs of ≈12 km yr−1 through the Fram Strait. Our modeling results show that both ice shelf configurations could be viable under the MIS 6 climatic conditions. However, the cooling caused by these ice shelves only affects the Arctic margins of the continental ice sheets and is not strong enough to significantly influence the surface mass balance of the entire MIS 6 Eurasian ice sheet.
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34.
  • Croke, Jacky, et al. (författare)
  • A 100 ka record of fluvial activity in the Fitzroy River Basin, tropical northeastern Australia
  • 2011
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 30:13-14, s. 1681-1695
  • Tidskriftsartikel (refereegranskat)abstract
    • This study reports the nature and timing of Quaternary fluvial activity in the Fitzroy River basin, which drains a diverse 143,000 km(2) area in northeastern Queensland, before discharging into the Great Barrier Reef Marine Park. The catchment consists of an extensive array of channel and floodplain types that we show have undergone large-scale fluvial adjustment in-channel planform, geometry and sinuosity. Optically stimulated luminescence (OSL) dating of quartz sediments from fifteen (3-18 m) floodplain cores throughout the basin indicates several discrete phases of active bedload activity: at similar to 105-85 ka in Marine Isotope Stage (MIS) 5, at similar to 50-40 ka (MIS 3), and at similar to 30-10 ka (MIS 3/2). The overall timing of late Quaternary fluvial activity correlates well with previous accounts from across Australia with rivers being primarily active during interstadials. Fluvial activity, however, does not appear to have been synchronous throughout the basin's major sub-catchments. Fluvial activity throughout MIS 2 (i.e. across the Last Glacial Maximum) in the meandering channels of the Fitzroy correlates well with regional data in tropical northeastern Queensland, and casts new light on the river response to reduced rainfall and vegetation cover suggested by regional palaeoclimate indicators. Moreover, the absence of a strong Holocene signal is at odds with previous accounts from elsewhere throughout Australia. The latitudinal position of the Fitzroy across the Tropic of Capricorn places this catchment at a key location for elucidating the main hydrological drivers of Quaternary fluvial activity in northeastern Australia, and especially for determining tropical moisture sources feeding into the headwaters of Cooper Creek, a major river system of the continental interior.
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35.
  • Cronin, T. M., et al. (författare)
  • Quaternary Sea-ice history in the Arctic Ocean based on a new Ostracode sea-ice proxy
  • 2010
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 29:25-26, s. 3415-3429
  • Tidskriftsartikel (refereegranskat)abstract
    • Paleo-sea-ice history in the Arctic Ocean was reconstructed using the sea-ice dwelling ostracode Acetabulastoma arcticum from late Quaternary sediments from the Mendeleyev, Lomonosov, and Gakkel Ridges, the Morris Jesup Rise and the Yermak Plateau. Results suggest intermittently high levels of perennial sea ice in the central Arctic Ocean during Marine Isotope Stage (MIS) 3 (25–45 ka), minimal sea ice during the last deglacial (16–11 ka) and early Holocene thermal maximum (11–5 ka) and increasing sea ice during the mid-to-late Holocene (5–0 ka). Sediment core records from the Iceland and Rockall Plateaus show that perennial sea ice existed in these regions only during glacial intervals MIS 2, 4, and 6. These results show that sea ice exhibits complex temporal and spatial variability during different climatic regimes and that the development of modern perennial sea ice may be a relatively recent phenomenon.
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36.
  • Czymzik, Markus, et al. (författare)
  • A varved lake sediment record of the Be-10 solar activity proxy for the Lateglacial-Holocene transition
  • 2016
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 153, s. 31-39
  • Tidskriftsartikel (refereegranskat)abstract
    • Solar modulated variations in cosmogenic radionuclide production provide both information on past changes in the activity of the Sun and a global synchronization tool. However, to date the use of cosmogenic radionuclides for these applications is almost exclusively based on Be-10 records from ice cores and C-14 time-series from tree rings, all including archive-specific limitations. We present the first Be-10 record from annually laminated (varved) lake sediments for the Lateglacial-Holocene transition from Meerfelder Maar. We quantify environmental influences on the catchment and, consequently, Be-10 deposition using a new approach based on regression analyses between our Be-10 record and environmental proxy time-series from the same archive. Our analyses suggest that environmental influences contribute to up to 37% of the variability in our Be-10 record, but cannot be the main explanation for major Be-10 excursions. Corrected for these environmental influences, our Be-10 record is interpreted to dominantly reflect changes in solar modulated cosmogenic radionuclide production. The preservation of a solar production signal in Be-10 from varved lake sediments highlights the largely unexplored potential of these archives for solar activity reconstruction, as global synchronization tool and, thus, for more robust paleoclimate studies.
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37.
  • Dalton, April S., et al. (författare)
  • Deglaciation of the north American ice sheet complex in calendar years based on a comprehensive database of chronological data: NADI-1
  • 2023
  • Ingår i: QUATERNARY SCIENCE REVIEWS. - 0277-3791 .- 1873-457X. ; 321
  • Tidskriftsartikel (refereegranskat)abstract
    • The most recent deglaciation of the North American Ice Sheet Complex (NAISC: comprising the Innuitian, Cordilleran, and Laurentide ice sheets) offers a broad perspective from which to analyze the timing and rate of ice retreat, deglacial sea-level rise, and abrupt climate change events. Previous efforts to portray the retreat of the NAISC have been focused largely on minimum-limiting radiocarbon ages and ice margin location(s) tied to deglacial landforms that were not, for the most part, chronologically constrained. Here, we present the first version of North American Deglaciation Isochrones (NADI-1) spanning 25 to 1 ka in calendar years before present. Key new features of this work are (i) the incorporation of cosmogenic nuclide data, which offer a direct constraint on the timing of ice recession; (ii) presentation of all data and time-steps in calendar years; (iii) optimal, minimum, and maximum ice extents for each time-step that are designed to capture uncertainties in the ice margin position, and; (iv) extensive documentation and justification for the placement of each ice margin. Our data compilation includes 2229 measurements of Be-10, 459 measurements of Al-26 and 35 measurements of Cl-36 from a variety of settings, including boulders, bedrock surfaces, cobbles, pebbles, and sediments. We also updated a previous radiocarbon dataset (n = 4947), assembled luminescence ages (n = 397) and gathered uranium-series data (n = 2). After scrutiny of the geochronological dataset, we consider >90% of data to be reliable or likely reliable. Key findings include (i) a highly asynchronous maximum glacial extent in North America, occurring as early as 27 ka to as late as 17 ka, within and between ice sheets. In most marine realms, extension of the ice margin to the continental shelf break at 25 ka is somewhat speculative because it is based on undated and spatially scattered ice stream and geomorphic evidence; (ii) detachment of the Laurentide and Cordilleran ice sheets took place gradually via southerly and northerly 'unzipping' of the ice masses, starting at 17.5 ka and ending around 14 ka; (iii) the final deglaciation of Hudson Bay began at 8.5 ka, with the collapse completed by 8 ka. The maximum extent of ice during the last glaciation occurred at 22 ka and covered 15,470,000 km(2). All North American ice sheets merged at 22 ka for the first time in the Quaternary. The highly asynchronous Last Glacial Maximum in North America means that our isochrones (starting at 25 ka) capture ice advance across some areas, which is based on limited evidence and is therefore somewhat speculative. In the Supplementary Data, the complete NADI-1 chronology is available in PDF, GIF and shapefile format, together with additional visualizations and spreadsheets of geochronological data. The NADI-1 shapefiles are also available at https://doi.org/10.5281/zenodo.8161764.
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38.
  • Davies, Siwan M., et al. (författare)
  • Integrating the INTIMATE records using tephrochronology : rising to the challenge
  • 2012
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 36, s. 11-27
  • Tidskriftsartikel (refereegranskat)abstract
    • Little has challenged our understanding of climate change more so than the abruptness with which large-scale shifts in temperature occurred during the Late Quaternary. The causal mechanisms driving these rapid changes are poorly understood, largely due to the inherent difficulties of integrating palaeoclimate records which represents the key focus of the INTIMATEI project. Tephrochronology has become central to the synchronisation goals of INTIMATE, the overall aim of which is to test the degree of climatic synchroneity in relation to these rapid climatic events. Here we present a European framework of 12 volcanic events that hold considerable promise for achieving the INTIMATE goals and effecting precise correlation of widespread palaeoarchives. These tephras are widespread and fall stratigraphically in close association to rapid climatic changes. We believe that these represent the most valuable tephras for the European INTIMATE project, but also highlight those that require urgent investigation to refine their geochemical signatures, eruptive context and chronological and stratigraphical uncertainties. For instance, new data are presented for the Saksunarvatn Ash that question the sole reliance on major-element analysis for tephra characterisation and highlights some of the challenges that remain for tephra studies. Accordingly, we outline a number of key recommendations relating to geochemical characterisation, data comparison, assessing the depositional integrity of tephra horizons as well as methods for improving age estimates - all of which will optimise the application of tephrochronology to meet the INTIMATE goals.
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39.
  • de Boer, Erik J., et al. (författare)
  • Rapid succession of plant associations on the small ocean island of Mauritius at the onset of the Holocene
  • 2013
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 68, s. 114-125
  • Tidskriftsartikel (refereegranskat)abstract
    • The island of Mauritius offers the opportunity to study the poorly understood vegetation response to climate change on a small tropical oceanic island. A high-resolution pollen record from a 10 m long peat core from Kanaka Crater (560 m elevation, Mauritius, Indian Ocean) shows that vegetation shifted from a stable open wet forest Last Glacial state to a stable closed-stratified-tall-forest Holocene state. An ecological threshold was crossed at similar to 11.5 cal ka BP, propelling the forest ecosystem into an unstable period lasting similar to 4000 years. The shift between the two steady states involves a cascade of four abrupt (<150 years) forest transitions in which different tree species dominated the vegetation for a quasi-stable period of respectively similar to 1900, similar to 1100 and similar to 900 years. We interpret the first forest transition as climate-driven, reflecting the response of a small low topography oceanic island where significant spatial biome migration is impossible. The three subsequent forest transitions are not evidently linked to climate events, and are suggested to be driven by internal forest dynamics. The cascade of four consecutive events of species turnover occurred at a remarkably fast rate compared to changes during the preceding and following periods, and might therefore be considered as a composite tipping point in the ecosystem. We hypothesize that wet gallery forest, spatially and temporally stabilized by the drainage system, served as a long lasting reservoir of biodiversity and facilitated a rapid exchange of species with the montane forests to allow for a rapid cascade of plant associations.
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40.
  • Dehasque, Marianne, et al. (författare)
  • Combining Bayesian age models and genetics to investigate population dynamics and extinction of the last mammoths in northern Siberia
  • 2021
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 259
  • Tidskriftsartikel (refereegranskat)abstract
    • To understand the causes and implications of an extinction event, detailed information is necessary. However, this can be challenging when working with poorly resolved paleontological data sets. One approach to increase the data resolution is by combining different methods. In this study, we used both radiocarbon and genetic data to reconstruct the population history and extinction dynamics of the woolly mammoth in northern Siberia. We generated 88 new radiocarbon dates and combined these with previously published dates from 626 specimens to construct Bayesian age models. These models show that mammoths disappeared on the eastern Siberian mainland before the onset of the Younger Dryas (12.9–11.7 ky cal BP). Mammoths did however persist in the northernmost parts of central and western Siberia until the early Holocene. Further genetic results of 131 high quality mitogenomes, including 22 new mitogenomes generated in this study, support the hypothesis that mammoths from, or closely related to, a central and/or west- Siberian population recolonized Wrangel Island over the now submerged northern Siberian plains. As mammoths became trapped on the island due to rising sea levels, they lived another ca. 6000 years on Wrangel Island before eventually going extinct ca. 4000 years ago.
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41.
  • Delmonte, B, et al. (författare)
  • Causes of dust size variability in central East Antarctica (Dome B):Atmospheric transport from expanded South American sources during Marine Isotope Stage 2
  • 2017
  • Ingår i: Quaternary Science Reviews. - : Elsevier. - 0277-3791 .- 1873-457X. ; 168, s. 55-68
  • Tidskriftsartikel (refereegranskat)abstract
    • We here investigate the spatial and temporal variability of eolian dust particle sorting recorded in the Dome B (77 05 S, 94 55 E) ice core, central East Antarctica, during Marine Isotope Stage (MIS) 2. We address the question whether such changes reflect variable transport pathways from a unique source area or rather a variable apportionment from diverse Southern Hemisphere sources transported at different elevation in the troposphere. The Sr-Nd radiogenic isotope composition of glacial dust samples as well as single-particle Raman mineralogy support the hypothesis of a single dust provenance both for coarse and fine mode dust events at Dome B. The southern South American provenance of glacial dust in Antarctica deduced from these results indicate a dust composition coherent with a mixture of volcanic material and minerals derived from metamorphic and plutonic rocks. Additionally, Dome B glacial samples contain aragonite particles along with diatom valves of marine benthic/epiphytic species and freshwater species living today in the northern Antarctic Peninsula and southern South America. These data suggest contribution from the exposed Patagonian continental shelf and glacial outwash plains of southern Patagonia at the time when sea level reached its minimum. Our results confirm that dust sorting is controlled by the relative intensity of the two main patterns of tropospheric dust transport onto the inner Plateau, i.e. fast low-level advection and long-range high-altitude transport including air subsidence over Antarctica.
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42.
  • Delmonte, B., et al. (författare)
  • Geographic provenance of aeolian dust in East Antarctica during Pleistocene glaciations : preliminary results from Talos Dome and comparison with East Antarctic and new Andean ice core data
  • 2010
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 29:02-jan, s. 256-264
  • Tidskriftsartikel (refereegranskat)abstract
    • The strontium and neodymium isotopic signature of aeolian mineral particles archived in polar ice cores provides constraints on the geographic provenance of dust and paleo-atmospheric circulation patterns. Data from different ice cores drilled in the centre of the East Antarctic plateau such as EPICA-Dome C (EDC, 75 degrees 06'S: 123 degrees 21'E) and Vostok (78 degrees 28'S, 106 degrees 48'E) suggested a uniform geographic provenance for dust during Pleistocene glacial ages, likely from southern South America (SSA). In this work the existing dust isotopic data from EDC have been integrated with new data from Marine Isotopic Stage (MIS) 14 (about 536 ka before 1950AD) and in parallel some first results are shown for the new TALDICE ice core which was drilled on the edge of the East Antarctic Plateau (Talos Dome, 72 degrees 48'S, 159 degrees 06'E) on the opposite side with respect to SSA. Interestingly, the isotopic composition of TALDICE glacial dust is remarkably similar to that obtained from glacial dust from sites located in the East Antarctic interior. Overall, the glacial dust isotopic field obtained from six East Antarctic ice cores matches well South American data obtained from target areas. In this respect, it was recently suggested that dust exported long-range from South America originates from Patagonia and from the Puna-Altiplano plateau. To test this hypothesis, we analysed the isotopic composition of dust from an ice core drilled on the Illimani glacier (Bolivia, 16 degrees 37'S, 67 degrees 46'W; 6350 m a.s.l.) in order to obtain information on the isotopic composition of regional mineral aerosol uplifted from the Altiplano area and likely transported over a long distance. Altogether, ice core and source data strongly suggest that the westerly circulation pattern allowed efficient transfer of dust from South America to the East Antarctic plateau under cold Quaternary climates. Isotopic data support the hypothesis of a possible mixing of dust from Patagonia and from the Puna-Altiplano plateau. Interestingly, high glacial dust inputs to Antarctica are characterized by less radiogenic Nd values, an issue suggesting that enhanced dust production in Patagonia was associated with the activation of a secondary source. Still, Patagonia was the most important supplier for dust to central East Antarctica during Quaternary glaciations.
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43.
  • Dominguez-Rodrigo, M., et al. (författare)
  • Earliest Acheulian paleolandscape reveals a 1.7 million-year-old megasite at Olduvai Gorge (Tanzania)
  • 2023
  • Ingår i: Quaternary Science Reviews. - 0277-3791 .- 1873-457X. ; 316
  • Tidskriftsartikel (refereegranskat)abstract
    • FLK West (Bed II, Olduvai Gorge) contains the oldest association of Acheulian stone tools and exploitation of fauna (including megafauna) by hominins in the Pleistocene. Recently, the FLK West paleolandscape has been intensively studied, unveiling a spatial association between archaeological materials and hydrothermal resources. A new type of landscape use by hominins has also been documented around the area where the penecontemporaneous FLK West and HWK site complex were formed, resulting in an array of habitats spanning thousands of square meters covered with large amounts of lithic artefacts. Here, we show how the intensive use of certain environments by hominins resulted in these megasites, in which hominins engaged in a variety of activities, complementary to those performed at discrete archaeological clusters like FLK West. Despite using these habitats redundantly as quarries, hominins performed extensive core reduction of several types of raw materials indicating a dexterity and careful planning undocumented in earlier periods. Here, we also show how palaeoecological reconstructions must be based on fine-scale geological analyses, given the palimpsestic nature of both geological and anthropogenic processes. The research reported here also uncovered an additional unknown source of metamorphic rocks for hominins at Olduvai, which questions a large part of previous modeling based on hominin provisioning exclusively at Naibor Soit. We also show that the manufacture of handaxes was slightly older than documented at FLK West and that they occur in isolation on the landscape in addition to being clustered at sites. This implies that at the beginning of the Acheulian, hominins were not only using and discarding handaxes at specific loci, but they also transported these tools for various activities across the landscape as part of their strategized adaptation to those environments. The occurrence of these intensively-used megasites hints at some territorial behaviors by early Acheulian hominins.
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44.
  • Dowdeswell, J. A., et al. (författare)
  • High-resolution geophysical observations of the Yermak Plateau and northern Svalbard margin : Implications for ice-sheet grounding and deep-keeled icebergs
  • 2010
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 29:25-26, s. 3518-3531
  • Tidskriftsartikel (refereegranskat)abstract
    • High-resolution geophysical evidence on the seafloor morphology and acoustic stratigraphy of the Yermak Plateau and northern Svalbard margin between 79°20′ and 81°30′N and 5° and 22°E is presented. Geophysical datasets are derived from swath bathymetry and sub-bottom acoustic profiling and are combined with existing cores to derive chronological control. Seafloor landforms, in the form of ice-produced lineations, iceberg ploughmarks of various dimensions (including features over 80 m deep and down to about 1000 m), and a moat indicating strong currents are found. The shallow stratigraphy of the Yermak Plateau shows three acoustic units: the first with well-developed stratification produced by hemipelagic sedimentation, often draped over a strong and undulating internal reflector; a second with an undulating upper surface and little acoustic penetration, indicative of the action of ice; a third unit of an acoustically transparent facies, resulting from debris flows. Core chronology suggests a MIS 6 age for the undulating seafloor above about 580 m. There are several possible explanations, including: (a) the flow of a major grounded ice sheet across the plateau crest from Svalbard (least likely given the consolidation state of the underlying sediments); (b) the more transient encroachment of relatively thin ice from Svalbard; or (c) the drift across the plateau of an ice-shelf remnant or megaberg from the Arctic Basin. The latter is our favoured explanation given the evidence currently at our disposal.
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45.
  • Drobyshev, Igor (författare)
  • Temperature and fire controls on vegetation dynamics in Northern Ural (Russia) boreal forests during the Holocene based on brGDGT and pollen data
  • 2023
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 305
  • Tidskriftsartikel (refereegranskat)abstract
    • Boreal vegetation is influenced by multiple factors such as climate and fire, but interactions between long-and short-term effects of climate upon fire activity are complex and remain poorly studied, especially in Eurasia. To understand the relationships between climate, fire and vegetation in Eurasia, we reconstruct the climate changes during the Holocene for the western section of the Northern Urals re-gion, in the southern part of the Republic of Komi. We relate these temperature reconstructions to pollen and charcoal records from the same region (Yaksha site, Republic of Komi, Russia). We use here a combined approach based on pollen and molecular biomarkers (branched Glycerol Dialkyl Glycerol Tetraethers or brGDGTs) to provide independent estimates of past temperatures. Our objectives were: (1) to understand the relationships between climate, fire, vegetation and human activity during the Holo-cene at the local scale of Yaksha and (2) to provide a robust regional-scale climatic reconstruction of the southern part of the Republic of Komi. Our study shows that climate had a major influence on the regional vegetation between 10,000 and 4000 cal Yr BP. Subsequently, fire activity had a joint and growing impact on vegetation dynamics between 4000 and 600 cal Yr BP. Finally, from 600 until the present (2016 CE), human presence and activities had a greater impact on the fire regime and vegetation than earlier in time, and combined with climate to influence the dynamics of the boreal forest. At the regional scale of the Republic of Komi and the local scale of Yaksha, the Holocene Thermal Maximum was detected between 6800 and 4000 cal Yr BP, using pollen-based temperature estimates but at 4000 cal Yr BP using brGDGT calibrations applied from the literature. These results are consistent with evidence from neighboring regions in the Eurasian boreal biome which were studied for different proxies (pollen, chironomids), and also with reference to climate models (General Circulation Models).(c) 2023 Elsevier Ltd. All rights reserved.
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46.
  • Dulfer, Helen E., et al. (författare)
  • Reconstructing the advance and retreat dynamics of the central sector of the last Cordilleran Ice Sheet
  • 2022
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 284
  • Tidskriftsartikel (refereegranskat)abstract
    • The advance of the Cordilleran Ice Sheet (CIS) towards its Last Glacial Maximum (LGM) configuration and its subsequent retreat remain poorly understood. We use the glacial landform record to determine ice dynamics for the central sector of the CIS in northern British Columbia, Canada, beneath the LGM ice divide. We classify seventy ice-flow indicator flowsets based on morphology, elevation, orientation and cross-cutting relationships into one of three stages, whereby stage 1 is oldest and stage 3 youngest. Combined with ice-contact geomorphology, our reconstruction highlights complex changes in ice flow over time as a result of ice divide migrations through the LGM and deglacial phases. The orientation and distribution of landforms indicates active post-LGM ice retreat westward through the Cassiar and Omineca mountains. We map the regional distribution of independent mountain glaciers, ice caps, and ice fields that regrew during a cooling event in the Late Glacial and show that some of these readvance glaciers were subsequently overrun by advancing outlet glaciers of the CIS. We use the cross-cutting relationship between readvance glaciers and CIS outlet glaciers and available chronological data to reconstruct the eastern CIS margin during the Late Glacial for the first time.
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47.
  • Dutton, Andrea, et al. (författare)
  • Tropical tales of polar ice : evidence of Last Interglacial polar ice sheet retreat recorded by fossil reefs of the granitic Seychelles islands
  • 2015
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 107, s. 182-196
  • Tidskriftsartikel (refereegranskat)abstract
    • In the search for a record of eustatic sea level change on glacial-interglacial timescales, the Seychelles ranks as one of the best places on the planet to study. Owing to its location with respect to the former margins of Northern Hemisphere ice sheets that wax and wane on orbital cycles, the local-or relative-sea level history is predicted to lie within a few meters of the globally averaged eustatic signal during the Last Interglacial period. We have surveyed and dated Last Interglacial fossil corals to ascertain peak sea level and hence infer maximum retreat of polar ice sheets during this time interval. We observe a pattern of gradually rising sea level in the Seychelles between similar to 129 and 125 thousand years ago (ka), with peak eustatic sea level attained after 125 ka at 7.6 +/- 1.7 m higher than present. After accounting for thermal expansion and loss of mountain glaciers, this sea-level budget would require similar to 5-8 m of polar ice sheet contribution, relative to today's volume, of which only similar to 2 m came from the Greenland ice sheet. This result clearly identifies the Antarctic ice sheet as a significant source of melt water, most likely derived from one of the unstable, marine-based sectors in the West and/or East Antarctic ice sheet. Furthermore, the establishment of a +5.9 +/- 1.7 m eustatic sea level position by 128.6 +/- 0.8 ka would require that partial AIS collapse was coincident with the onset of the sea level highstand.
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48.
  • Dögg Eddudottir, Sigrun, et al. (författare)
  • Landscape change in the Icelandic highland : A long-term record of the impacts of land use, climate and volcanism
  • 2020
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 240
  • Tidskriftsartikel (refereegranskat)abstract
    • Agriculture has been practiced in Iceland since settlement (landnam; AD 877). This has caused changes in vegetation communities, soil erosion, desertification and loss of carbon stocks. Little data exist regarding vegetation and ecosystems in the Icelandic highland before landnam and therefore the impact of land use over time is poorly understood. The objectives of the study are to examine the timing, nature and causes of land degradation in the highland of Northwest Iceland. Specifically, to determine the resilience of the pre-landnam highland environment to disturbances (i.e. climate cooling and volcanism) and whether land use pressure was of sufficient magnitude to facilitate ecosystem change. A sediment core was taken from the highland lake Galtabol. A chronology for the core was constructed using known tephra layers and radiocarbon dated plant macrofossils. Pollen analysis (vegetation), coprophilous fungal spores (proxy for grazing), and sediment properties (proxies for erosion) were used to provide a high-resolution, integrated vegetation and paleoenvironmental reconstruction. The pre-landnam environment showed resilience to climate cooling and repeated tephra fall. Soon after landnam the vegetation community changed and instability increased, indicated by changes in sediment properties. The pollen and spore record suggest introduction of grazing herbivores into the area after landnam. Following landnam, indicators of soil erosion appear in the sediment properties. Intensification of soil erosion occurred during the 17th century. The Galtabol record clearly demonstrates what can happen in landscapes without adequate management of natural resources and underestimation of landscape sensitivity. Introduction of land use resulted in changes in vegetation communities, loss of resilience and onset of increased soil erosion. Paleoenvironmental reconstructions may inform future decisions on management of the highland by providing baselines for natural variability in the pre-landmim environment.
  •  
49.
  • Edvardsson, Johannes, et al. (författare)
  • Periodicities in mid- to late-Holocene peatland hydrology identified from Swedish and Lithuanian tree-ring data
  • 2016
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 137, s. 200-208
  • Tidskriftsartikel (refereegranskat)abstract
    • Twenty-five tree-ring width (TRW) chronologies, developed from moisture sensitive peatland trees in Sweden and Lithuania, and representing eight periods during the mid-Holocene to present, were analysed regarding common periodicities (cycles). Periods of 13e15, 20e22, and 30e35 years were found in most chronologies, while 8e10, 18e19, and 60e65 year periodicities were observed as well, but less commonly. Similar periodicities, especially about 15 and 30 years in duration, were detected in both living and subfossil trees, indicating that the trees have responded to similar forcing mechanisms on those timescales through time. Some of the detected periods may be related to solar variability and lunar nodal tides, but most of the detected periodicities are more likely linked to hydrological changes in the peatlands associated to atmospheric patterns such as the North Atlantic Oscillation (NAO), or variations in sea surface temperatures (i.e. the Atlantic Multidecadal Oscillation, AMO). However, no significant relationships between tree growth, NAO and AMO could be formally established, possibly due to hydrological lag and feedback effects which are typical for peatlands but render in-depth assessments rather difficult.
  •  
50.
  • Edwards, Thomas W. D., et al. (författare)
  • Seasonal variability in Northern Hemisphere atmospheric circulation during the Medieval Climate Anomaly and the Little Ice Age
  • 2017
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 165, s. 102-110
  • Tidskriftsartikel (refereegranskat)abstract
    • Here we report new reconstructions of winter temperature and summer moisture during the past millennium in southeastern Sweden, based on stable-isotope data from a composite tree-ring sequence, that further enhances our knowledge and understanding of seasonal climate variability in the Northern Hemisphere over the past millennium. Key features of these new climate proxy records include evidence for distinctive fluctuations in winter temperature in SE Sweden, superimposed upon the general pattern of cooling between the so-called Medieval Climate Anomaly (MCA) of the early millennium and the Little Ice Age (LIA) of the late millennium, as well as evidence for sustained summer wetness during the MCA, followed by drier and less variable conditions during the LIA. We also explore these new records within a circumpolar spatial context by employing self-organizing map analysis of meteorological reanalysis data to identify potential modern analogues of mid-tropospheric synoptic circulation types in the Northern Hemisphere extratropics that can reconcile varying seasonal climate states during the MCA and LIA in SE Sweden with less variable conditions in southwestern Canada, as portrayed by paleoclimate records developed in the same manner in an earlier study.
  •  
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