Showing papers in "Journal of Quaternary Science in 2004"
TL;DR: Duller et al. as discussed by the authors proposed a method for luminescence dating of quaternary sediments, which has been successfully applied in the field of geology.
Abstract: Duller, Geoffrey, (2004) 'Luminescence dating of Quaternary sediments: recent advances', Journal of Quaternary Science 19(2) pp.183-192 RAE2008
335 citations
TL;DR: A 9.5m core from an inland peatland in Kalimantan, Indonesia, reveals organic matter accumulation started around 26.000 cubic meters (cal) BP, providing the oldest reported initiation date for lowland ombrotrophic peat formation.
Abstract: A 9.5 m core from an inland peatland in Kalimantan, Indonesia, reveals organic matter accumulation started around 26 000 cal. yr BP, providing the oldest reported initiation date for lowland ombrotrophic peat formation in SE Asia. The core shows clear evidence for differential rates of peat formation and carbon storage. A short period of initial accumulation is followed by a slow rate during the LGM, with fastest accumulation during the Holocene. Between ∼13 000 and 8000 cal. yr BP, > 450 cm of peat were deposited, with highest rates of peat (> 2 mm yr−1) and carbon (> 90 g C m−2 yr−1) accumulation between 9530 and 8590 cal. yr BP. These data suggest that Kalimantan peatlands acted as a large sink of atmospheric CO2 at this time. Slower rates of peat (0.15–0.38 mm yr−1) and carbon (7.4–24.0 g C m−2 yr−1) accumulation between ∼8000 and 500 cal. yr BP coincide with rapid peat formation in coastal locations elsewhere in SE Asia. The average LORCA (long-term apparent carbon accumulation rate) for the 9.5 m core is 56 g C m−2 yr−1. These data suggest that studies of global carbon sources, sinks and their dynamics need to include information on the past and present sizeable peat deposits of the tropics. Copyright © 2004 John Wiley & Sons, Ltd.
312 citations
TL;DR: Palaeoenvironmental and archaeological data from Arbon Bleiche, Lake Constance (Switzerland) give evidence of a rapid rise in lake-level dated by tree-ring and radiocarbon to 5320.
Abstract: Palaeoenvironmental and archaeological data from Arbon Bleiche, Lake Constance (Switzerland) give evidence of a rapid rise in lake-level dated by tree-ring and radiocarbon to 5320 cal. yr BP. This rise event was the latest in a series of three successive episodes of higher lake-level between 5550 and 5300 cal. yr BP coinciding with glacier advance and tree-limit decline in the Alps. This west-central European climate change may have favoured the quick burial and the preservation of the Alpine Iceman recently found in the Tyrolean Alps. It has possible equivalents in many records from various regions in both hemispheres dating to 5600–5000 cal. yr BP and corresponds to global cooling and contrasting patterns of hydrological changes. This major mid-Holocene climate event marks the Hypsithermal/Neoglaciation transition possibly resulting from a combination of different factors including orbital forcing, changes in ocean circulation and variations in solar activity. Copyright © 2004 John Wiley & Sons, Ltd.
216 citations
TL;DR: The Holocene vegetation history of the Arabian Peninsula is poorly understood, with few palaeobotanical studies to date as discussed by the authors, and only one study has been carried out at Awafi, Ras al-Khaimah, UAE.
Abstract: The Holocene vegetation history of the Arabian Peninsula is poorly understood, with few palaeobotanical studies to date. At Awafi, Ras al-Khaimah, UAE, a 3.3 m lake sediment sequence records the vegetation development for the period 8500 cal. yr BP to � 3000 cal. yr BP. 13 C isotope, pollen and phytolith analyses indicate that C3 Pooid grassland with a strong woody element existed during the early Holocene (between 8500 and 6000 cal. yr BP) and became replaced by mixed C3 and C4 grasses with a strong C4 Panicoid tall grass element between 5900 and 5400 cal. yr BP. An intense, arid event occurred at 4100 cal. yr BP when the lake desiccated and was infilled by Aeolian sand. From 4100 cal. yr BP the vegetation was dominated by C4 Chloridoid types and Cyperaceae, suggesting an incomplete vegetation cover and Aeolian dune reactivation owing to increased regio- nal aridity. These data outline the ecosystem dynamics and carbon cycling in response to palaeomon- soon and north-westerly variability during the Holocene. Copyright 2004 John Wiley & Sons, Ltd.
151 citations
TL;DR: A pollen record from Lago Condorito (41 � 45'S, 73 � 07'W) shows prominent vegetation and climate changes at millennial time-scales, superimposed on multimillennial trends in tempera- ture and westerly activity in northwest Patagonia during the past 15 000 yr as mentioned in this paper.
Abstract: A pollen record from Lago Condorito (41 � 45'S, 73 � 07'W) shows prominent vegetation and climate changes at millennial time-scales, superimposed on multimillennial trends in tempera- ture and westerly activity in northwest Patagonia during the past 15 000 yr. The record shows that evergreen temperate rainforests have dominated the landscape over this interval, with floristic changes ranging from cold-resistant North Patagonian forests with podocarp conifers to Valdivian forests with thermophilous, summer-drought resistant species. The long-term trend shows that cool-temperate and humid conditions prevailed between 15 000 and 11 000 cal. yr BP, followed by an extreme warm and dry phase between 11 000 and 7600 cal. yr BP, and subsequent cooling events and increase in precipitation that peaked at ca. 5000 cal. yr BP, when Southern Hemisphere alpine glaciers achieved their first Neoglacial maximum. Modern conditions were established at ca. 1800 cal. yr BP, following a warm and dry phase between ca. 2900 and 1800 cal. yr BP. These results suggest that millennial-scale climate variability during deglacial and post-glacial times also affected the mid-latitude region of the South Pacific, supporting the idea that changes in the tropical Pacific might be a key factor in the initiation and/or propagation of millennial-scale climate variabil- ity at regional, hemispheric and global scales. Copyright 2004 John Wiley & Sons, Ltd.
149 citations
TL;DR: In this article, geomorphic features and palaeobiotic remains in now semi-arid northeastern Brazil indicate major palaeoenvironmental changes during past periods of increased rainfall, showing that the long hypothesised forested links between biodiversity-rich Amazon and Atlantic rain forests may indeed have existed during these moister phases.
Abstract: Several geomorphic features and palaeobiotic remains in now semi-arid northeastern Brazil indicate major palaeoenvironmental changes during past periods of increased rainfall. 230Th mass spectrometric ages of speleothems and travertines have allowed the determination of the timing and duration of wetter than present conditions. The data demonstrate that wet events have occurred throughout much of the Pleistocene, present dry conditions having been established at the end of the Younger Dryas. A markedly different fauna comprising megafaunal elements not adapted to the present low arboreal scrubland caatinga vegetation existed in the area. Palaeobotanical remains embedded in travertine indicate forested vegetation at these wetter intervals, suggesting that the caatinga was then replaced or mixed with a semi-deciduous forest. Due to the abundance of travertine sites containing fossil botanical remains in northeastern Brazil, it is believed that forest expansion occurred over large areas of the now semi-arid zone, showing that the long hypothesised forested links between biodiversity-rich Amazon and Atlantic rainforests may indeed have existed during these moister phases. Copyright © 2004 John Wiley & Sons, Ltd.
136 citations
TL;DR: In this paper, three fluvial sequences are examined as case studies, including the Severn-Avon system in the English Midlands, which has biostratgraphical evidence and an amino acid geochronology, together with marker inputs from three different glaciations.
Abstract: Fluvial sequences, particularly terrace staircases, represent archives of Quaternary palaeoclimatic fluctuation and can serve as stratigraphical frameworks for geochronology and for correlation with other depositional environments, in particular, the global marine oxygen isotope record. Fluvial lithostratigraphical frameworks also provide contexts for records, from fossils and artefacts, of faunal evolution and human occupation; conversely, both records can be means of relative dating of riverine sequences.
Three fluvial sequences are examined as case studies. First is the Severn-Avon system in the English Midlands, which has biostratgraphical evidence and an amino acid geochronology, together with marker inputs from three different glaciations. The Somme sequence of northern France, famous for its Palaeolithic artefact assemblages, again has biostratigraphy and an amino acid geochronology and has also been dated with reference to overlying loess/palaeosols sequences. The fluvial terraces of the River Arun, the final case study, lack dating evidence but are interspersed within the Sussex raised beach staircase. Although various lines of evidence suggest that the rivers discussed have formed terraces in response to climatic fluctuation, an intriguing difference is that interglacial sediments occur at the bases of terrace formations in the Severn-Avon, whereas in the Somme they occur at the tops of sequences, beneath loessic overburden.
130 citations
TL;DR: In this paper, a tephrostratigraphy-based analysis of tephra layers (cryptotephra) is proposed for the purpose of providing independent tests of the chronology and correlation of events during the Last Termination.
Abstract: The precise sequence of events during the Last Termination (18 000-9000 ka 14 Cy r BP), and the extent to which major environmental changes were synchronous, are difficult to estab- lish using the radiocarbon method alone because of serious distortions of the radiocarbon time-scale, as well as the influences of site-specific errors that can affect the materials dated. Attention has there- fore turned to other methods that can provide independent tests of the chronology and correlation of events during the Last Termination. With emphasis on European sequences, we summarise here the potential of tephrostratigraphy and tephrochronology to fulfil this role. Recent advances in the detection and analysis of 'hidden' tephra layers (cryptotephra) indicate that some tephras of Last Termination age are much more widespread in Europe than appreciated hitherto, and a number of new tephra deposits have also been identified. There is much potential for developing an integrated tephrochronological framework for Europe, which can help to underpin the overall chronology of events during the Last Termination. For that potential to be realised, however, there needs to be a more systematic and robust analysis of tephra layers than has been the practice in the past. We pro- pose a protocol for improving analytical and reporting procedures, as well as the establishment of a centralised data base of the results, which will provide an important geochronological tool to support a diverse range of stratigraphical studies, including opportunities to reassess volcanic hazards. Although aimed primarily at Europe, the protocol proposed here is of equal relevance to other regions and periods of interest. Copyright 2004 John Wiley & Sons, Ltd.
124 citations
TL;DR: This paper examined the validity of this 'dry forest refugia' hypothesis in the light of previously published fossil pollen data and vegetation model simulations, and suggested that a more parsimonious explanation for the current biogeographic pattern of these South American dry forests is population migration (perhaps by long-distance dispersal) since the LGM, rather than vicariance.
Abstract: Seasonally dry tropical forests exhibit a markedly discontinuous, disjunct distribution pattern across South America. Previous botanical inventories have revealed that these dry forest areas exhibit close floristic links with one another, which has led to the hypothesis that they constitute mod- ern-day refugia, resulting from vicariance (i.e. fragmentation) of a formerly more widespread, contin- uous distribution during more arid climatic conditions associated with the Last Glacial Maximum (LGM). This paper examines the validity of this 'dry forest refugia' hypothesis in the light of previously published fossil pollen data and vegetation model simulations. The model simulations suggest that major dry forest areas, such as the Bolivian Chiquitano Dry Forest, are not Pleistocene refugia, but instead developed during the Holocene by population expansions from parts of southern Amazonia presently covered by evergreen rainforest. The limited pollen data available indicate that glacial-age seasonally dry tropical forests, irrespective of their distribution, were floristically quite different from those of today, with key dry forest species, such as Anadenanthera, only appearing in the Holocene. I suggest that a more parsimonious explanation for the current biogeographic pattern of these South American dry forests is population migration (perhaps by long-distance dispersal) since the LGM, rather than vicariance. Copyright 2004 John Wiley & Sons, Ltd.
113 citations
TL;DR: Combined stable isotope (d18O and d13C) and trace element (Mg, Sr) geochemistry from an early Holocene British tufa reveal clear records of Holocene palaeoclimatic change.
Abstract: Combined stable isotope (d18O and d13C) and trace element (Mg, Sr) geochemistry from bulk tufa calcite and ostracod shell calcite from an early Holocene British tufa reveal clear records of Holocene palaeoclimatic change. Variation in d18O is caused principally by change in the isotopic composition of Holocene rainfall (recharge), itself caused mainly by change in air temperature. The d13C variability through much of the deposit reflects increasing influence of soil-zone CO2, owing to progressive woodland soil development. Bulk tufa Mg/Ca and Sr/Ca are controlled by their concentrations in the spring water. Importantly, Mg/Ca ratios are not related to d18O values and thus show no temperature dependence. First-order sympathetic relationships between d13C values and Mg/Ca and Sr/Ca are controlled by aquifer processes (residence times, CO2 degassing and calcite dissolution/reprecipitation) and probably record intensity of palaeorainfall (recharge) effects. Stable isotope records from ostracod shells show evidence of vital effects relative to bulk tufa data. The ostracod isotopic records are markedly ‘spiky’ because the ostracods record ‘snapshots’ of relatively short duration (years), whereas the bulk tufa samples record averages of longer time periods, probably decades. The d18O record appears to show early Holocene warming, a thermal maximum at ca. 8900?cal. yr?BP and the global 8200?yr BP cold event. Combined d13C, Mg/Ca and Sr/Ca data suggest that early Holocene warming was accompanied by decreasing rainfall intensity. The Mg/Ca data suggest that the 8200?yr BP cold event was also dry. Warmer and wetter conditions were re-established after the 8200?yr BP cold event until the top of the preserved tufa sequence at ca. 7100?cal. yr BP.
110 citations
TL;DR: In this paper, two ancient swamps in the western Loess Plateau, northwest China record the climate history between 8000 and 4000 cal. yr BP, distinctly humid and warm between 7400 and 6700 cal.
Abstract: Two ancient swamps in the western Loess Plateau, northwest China record the climate history between 8000 and 4000 cal. yr BP. Grain size, CaCO3, organic matter, mollusc fauna and pollen assemblages show that climate was wet between 8300 and 7400 cal. yr BP, distinctly humid and warm between 7400 and 6700 cal. yr BP, semi-humid from 6700 to 6300 cal. yr BP, and semi-arid between 6300 and 4000 cal. yr BP. The temporal and spatial distribution of archaeological sites shows that the prosperity of the neolithic cultures in the western part of the Chinese Loess Plateau did not appear until the climate changed to semi-arid, implying that the semi-arid climate was more favourable than wet and humid climate to neolithic peoples, whose subsistence was based on cereals adapted to and environments. Copyright (C) 2004 John Wiley Sons, Ltd.
TL;DR: In this paper, four short pollen and charcoal records from sites within and around Lake Pemerak on the margins of the Danau (Lake) Sentarum National Park in inland West Kalimantan, supported by modern surface samples from the Reserve, provide a partial picture of lowland equatorial vegetation and environments over at least the last 40 000 years.
Abstract: Four short pollen and charcoal records from sites within and around Lake Pemerak on the margins of the Danau (Lake) Sentarum National Park in inland West Kalimantan, supported by modern surface samples from the Reserve, provide a partial picture of lowland equatorial vegetation and environments over at least the last 40 000 years. They demonstrate general stability in the distribution of wetland and ombrotrophic (or raised) peatlands through the recorded period with dominance throughout of peatland and swamp forest. However, there was marked variation in sediment accumulation rates and in the floristic composition of the vegetation. The period prior to the last glacial maximum appears to have been the time of most active peatland growth and contrasts with the perception, from previous studies on largely coastal and subcoastal peatlands in Indonesia, that the Holocene was the time of major tropical peat accumulation. A general increase in charcoal, just prior to about 30 000 years ago, suggests that burning became more frequent, and is attributed to initial human impact rather than climate change. The subsequent latest Pleistocene period, embracing the Last Glacial Maximum, is marked by a peak in montane–submontane rainforest taxa, strongly indicating a substantial lowering of temperature. It appears that much of the Holocene is not recorded but recommencement of peat accumulation is evident within the last few thousand years. At the time of fieldwork access to the central part of the Lake Sentarum system was inhibited by strong El Nino drought conditions, but this area has the potential to provide a longer and more continuous history of environmental change for the region. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this paper, carbon-14 wiggle-match dating was used to produce an accurate chronology for part of an early Holocene peat sequence from the Borchert (The Netherlands).
Abstract: Accurate chronologies are essential for linking palaeoclimate archives. Carbon-14 wiggle-match dating was used to produce an accurate chronology for part of an early Holocene peat sequence from the Borchert (The Netherlands). Following the Younger Dryas-Preboreal transition, two climatic shifts could be inferred. Around 11 400 cal. yr BP the expansion of birch (Betula) forest was interrupted by a dry continental phase with dominantly open grassland vegetation, coeval with the PBO (Preboreal Oscillation), as observed in the GRIP ice core. At 11 250 cal. yr BP a sudden shift to a humid climate occurred. This second change appears to be contemporaneous with: (i) a sharp increase of atmospheric C-14; (ii) a temporary decline of atmospheric CO2; and (iii) an increase in the GRIP Be-10 flux. The close correspondence with excursions of cosmogenic nuclides points to a decline in solar activity, which may have forced the changes in climate and vegetation at around 11 250 cal. yr BP. Copyright (C) 2004 John Wiley Sons, Ltd.
TL;DR: More recent radiocarbon dates of penguin guano and remains, shells and seal skin afford ages for raised beaches adjacent to Terra Nova Bay, Antarctica as discussed by the authors, allowing construction of a new relative sea-level curve that bears on the timing of deglaciation.
Abstract: More than 100 radiocarbon dates of penguin guano and remains, shells and seal skin afford ages for raised beaches adjacent to Terra Nova Bay, Antarctica. These dates permit construction of a new relative sea-level curve that bears on the timing of deglaciation. Recession of the Ross Sea ice-sheet grounding line from Terra Nova Bay occurred no earlier than 7200 14C yr (8000 cal. yr) BP. Retreat along the Victoria Land coast may have been rapid, possibly contributing to eustatic sea-level rise centred at ca. 7600 cal. yr BP. The presence of a significant amount of ice remaining in the Ross Sea Embayment in Holocene time lessens the chance that Antarctica contributed significantly to meltwater pulse 1A several thousand years earlier. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this article, a two-part basal till at Knud Strand, Denmark reveals a uniform fabric pattern and strength, petrographical composition and clay mineralogy, and a time-transgressive model is suggested to explain the lack of vertical gradation in till properties in which debris released from the active ice sole is sheared in a thin zone moving upward as till accretion proceeds.
Abstract: A two-part basal till at Knud Strand, Denmark reveals a uniform fabric pattern and strength, petrographical composition and clay mineralogy. The nature of the contact with the underlying sediments, ductile deformation structures, partly intact soft sediment clasts, small meltwater channels and thin horizontal outwash stringers dispersed in the till indicate both bed deformation and basal decoupling by pressurised subglacial water. A time-transgressive model is suggested to explain the lack of vertical gradation in till properties in which debris released from the active ice sole is sheared in a thin zone moving upward as till accretion proceeds. It is suggested that, although strain indicators occur throughout the entire till thickness, the deformation at any point of time encompassed the uppermost part of the till only, allowing preservation of fragile clasts below. The substantial thickness of the till (up to 6 m) coupled with a much smaller (by more than one order of magnitude) inferred thickness of the deforming bed suggests that the bulk of till material was transported englacially prior to deposition. The lack of petrographical gradation in the till is attributed to effective mixing and homogenisation of material along the ice flow path. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: Using the surface exposure dating method, in particular the measurement of the cosmogenic nuclide 10 Be in rock surfaces, the authors obtained four ages for boulders on a prominent Egesen moraine of Great Aletsch Glacier, in the western Swiss Alps.
Abstract: Egesen moraines throughout the Alps mark a glacial advance that has been correlated with the Younger Dryas cold period. Using the surface exposure dating method, in particular the measurement of the cosmogenic nuclide 10 Be in rock surfaces, we attained four ages for boulders on a prominent Egesen moraine of Great Aletsch Glacier, in the western Swiss Alps. The 10 Be dates range from 10 460 � 1100 to 9040 � 1020 yr ago. Three 10 Be dates between 9630 � 810 and 9040 � 1020 yr ago are based upon samples from the surfaces of granite boulders. Two 10 Be dates, 10 460 � 1100 and 9910 � 970 yr ago, are based upon a sample from a quartz vein at the surface of a schist boulder. In consideration of the numerous factors that can influence apparently young 10 Be dates and the scatter within the data, we interpret the weighted mean of four boulder ages, 9640 � 430 yr (including the weighted mean of two 10 Be dates of the quartz vein), as a minimum age of deposition of the moraine. All 10 Be dates from the Great Aletsch Glacier Egesen moraine are consistent with radiocarbon dates of nearby bog-bottom organic sediments, which provide minimum ages of deglaciation from the moraine. The 10 Be dates from boulders on the Great Aletsch Glacier Egesen moraine also are similar to 10 Be dates from Egesen moraines of Vadret Lagrev Glacier on Julier Pass, in the eastern Swiss Alps. Both the morphology of the Great Aletsch Glacier Egesen moraine and the comparison with 10 Be dates from the inner Vadret Lagrev Egesen moraine support the hypothesis that the climatic cooling that occurred during the Younger Dryas cold episode influenced the glacial advance that deposited the Great Aletsch Glacier Egesen moraine. Because of the large size and slow response time of Great Aletsch Glacier, we suggest that the Great Aletsch Glacier Egesen moraine was formed during the last glacial advance of the multiphased Egesen cold period, the Kromer stage, during the Preboreal chron. Copyright 2004 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors suggest that organized convective radiation, the process that induces most wet season rainfall in Amazonia, should be treated as a phenomenon related to, but separate from, the passage of the inter-tropical convergence zone (ITCZ).
Abstract: Although accurate reconstructions of Amazonian palaeoclimates are central to under- standing the distribution and history of Neotropical biodiversity, current reconstructions based on proxy data are discordant and subject to intense debate. We review some current thinking in Amazonian climatology and incorporate some new ideas in an attempt to explain the apparently con- tradictory records of palaeoprecipitation from across the Amazon Basin. We suggest that palaeoecol- ogists need to recognise that organised convective radiation, the process that induces most wet season rainfall in Amazonia, should be treated as a phenomenon related to, but separate from, the passage of the inter-tropical convergence zone (ITCZ). Decoupling ITCZ migration from larger con- vective activity provides a mechanism to account for observed palaeoclimatic heterogeneity. Patterns of observed precipitation change are consistent with the long-term persistence of closed forest across much of Amazonia, indicating that the greatest changes in precipitation during the last glacial max- imum came during the wet season, which would have little negative impact on forest extent. Neo- tropical cooling at the last glacial maximum (LGM) is widely accepted, although the estimates of that cooling range between 1 � C and > 5 � C. In answering the basic question 'What is meant by cooling?' we observe that interhemispheric ice mass asymmetry may have caused cooling to be manifested differently according to location. A terrestrial cooling of ca. 5 � C, as well as radiative cooling and event-based cooling combined to induce vegetation change. Probably, both absolute temperature and mean monthly minima were reduced by polar air incursions in the northern Neotropics. How- ever, in the southern Neotropics, mean monthly minima were reduced by more frequent incursions of Patagonian air masses, but absolute minima may have been largely unchanged. Copyright 2004 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors used a Bayesian approach to the analysis of radiocarbon chronologies for two Late-glacial sites in the British Isles and one in the Adriatic Sea.
Abstract: Although there are many Late-glacial (ca. 15 000–11 000 cal. yr BP) proxy climate records from northwest Europe, some analysed at a very high temporal resolution (decadal to century scale), attempts to establish time-stratigraphical correlations between sequences are constrained by problems of radiocarbon dating. In an attempt to overcome some of these difficulties, we have used a Bayesian approach to the analysis of radiocarbon chronologies for two Late-glacial sites in the British Isles and one in the Adriatic Sea. The palaeoclimatic records from the three sites were then compared with that from the GRIP Greenland ice-core. Although there are some apparent differences in the timing of climatic events during the early part of the Late-glacial (pre-14 000 cal. yr BP), the results suggest that regional climatic changes appear to have been broadly comparable between Greenland, the British Isles and the Adriatic during the major part of the Late-glacial (i.e. between 14 000 and 11 000 cal. yr BP). The advantage of using the Bayesian approach is that it provides a means of testing the reliability of Late-glacial radiocarbon chronologies that is independent of regional chronostratigraphical (climatostratigraphical) frameworks. It also uses the full radiocarbon inventory available for each sequence and makes explicit any data selection applied. Potentially, therefore, it offers a more ‘objective’ basis for comparing regional radiocarbon chronologies than the conventional approaches that have been used hitherto. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: The Late Quaternary climate history of the Larsemann hills has been reconstructed using siliceous microfossils (diatoms, chrysophytes and silicoflagellates) in sediment cores extracted from three isolation lakes as discussed by the authors.
Abstract: The Late Quaternary climate history of the Larsemann Hills has been reconstructed using siliceous microfossils (diatoms, chrysophytes and silicoflagellates) in sediment cores extracted from three isolation lakes. Results show that the western peninsula, Stornes, and offshore islands were ice-covered between 30 000 yr BP and 13 500 cal. yr BP. From 13 500 cal. yr BP (shortly after the Antarctic Cold Reversal) the coastal lakes of the Larsemann Hills were deglaciated and biogenic sedi- mentation commenced. Between 13 500 and 11 500 cal. yr BP conditions were warmer and wetter than during the preceding glacial period, but still colder than today. From 11 500 to 9500 cal. yr BP there is evidence for wet and warm conditions, which probably is related to the early Holocene cli- mate optimum, recorded in Antarctic ice cores. Between 9500 and 7400 cal. yr BP dry and cold con- ditions are inferred from high lake-water salinities, and low water levels and an extended duration of nearshore sea-ice. A second climate optimum occurred between 7400 and 5230 cal. yr BP when stra- tified, open water conditions during spring and summer characterised the marine coast of Prydz Bay. From 5230 until 2750 cal. yr BP sea-ice duration in Prydz Bay increased, with conditions similar to the present day. A short return to stratified, open water conditions and a reduction in nearshore winter sea-ice extent is evident between 2750 and 2200 cal. yr BP. Simultaneously, reconstructions of lake water depth and salinity suggests relatively humid and warm conditions on land between 3000 and 2000 cal. yr BP, which corresponds to a Holocene Hypsithermal reported elsewhere in Antarctica. Finally, dry conditions are recorded around 2000, between 760 and 690, and between 280 and 140 cal. yr BP. These data are consistent with ice-core records from Antarctica and support the hypothesis that lacustrine and marine sediments on land can be used to evaluate the effect of long-term climate change on the terrestrial environment. Copyright 2004 John Wiley & Sons, Ltd.
TL;DR: Pollen was derived from fossil dung of herbivorous hyraxes, deposited in a rock shelter on the highest mountain in Namibia, Daˆures or Brandberg, situated on the Namib Desert margin this paper.
Abstract: Pollen was derived from fossil dung of herbivorous hyraxes, deposited in a rock shelteron the highest mountain in Namibia, Daˆures or Brandberg, situated on the Namib Desert margin.Radiocarbon dating ranging in age between modern times and 30000yrBP showed it representsthe first empirical pollen evidence of continental palaeovegetation during the Late Pleistocene alongthe western escarpment of southern Africa. The initial results indicate Last Glacial Maximum vegeta-tion differed totally from the current pattern as vegetation types were dominated by small Asteraceaeshrubs, in contrast to those of the Holocene and modern times which show more succulents, grassandwoody elements (arboreal pollen). The resultssuggest that Cape floral communities didnot reachinto thetropics along thewestern escarpment ofAfrica, despite such pollentypes occurring inmarinecores. Copyright 2004 John Wiley & Sons, Ltd. KEYWORDS: palynology; Namibia; Restionaceae; Late Pleistocene; Last Glacial Maximum.
TL;DR: In this paper, the applicability of three different techniques for equivalent dose (De) determination in the optical dating of quartz: the single aliquot regenerative-dose technique (SAR), the single-aliquot additive-dose (SAAD) and the multiple-alignot additive dose technique (MAAD) was made.
Abstract: A study was made of the applicability of three different techniques for equivalent dose (De) determination in the optical dating of quartz: the single-aliquot regenerative-dose technique (SAR), the single-aliquot additive-dose technique (SAAD) and the multiple-aliquot additive-dose technique (MAAD). For this purpose, quartz grains were extracted from a sequence of Upper Pleniglacial to Late-glacial coversands exposed at the locality of Ossendrecht in the southwestern Netherlands, a site for which both radiocarbon and earlier luminescence dates are available, providing independent age control.
Upon testing the different assumptions underlying each of the three OSL techniques investigated, the SAR protocol was found to be the technique of choice. The optical ages obtained with this protocol were in good agreement with the chronostratigraphical position of the sediments investigated and with the available chronostratigraphical information on the same and equivalent deposits. This confirms the suitability of the SAR technique for dating coversands. Furthermore, a small laboratory intercomparison of SAR-based De determinations yielded results that were in fair overall agreement. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors used the giant piston core MD95-2006 from the northeast Atlantic Ocean to study the geochemical characteristics of the North Atlantic Ash Zone (NAAZ) II and showed that the NAAZ II peak coincides with the rapid climate transition (cooling) at the end of interstadial 15, which can be assigned an age of 53'260±2660'yr'
Abstract: Rhyolitic tephra with the geochemical characteristics of North Atlantic Ash Zone (NAAZ) II are described from the giant piston core MD95-2006 from the northeast Atlantic Ocean. Shard size distribution indicates that the tephra represent a wind-sorted, primary air-fall deposit, but with a mode close to 200 μm they are too coarse to be air-fall deposits at the core site, which lies ca. 1000 km from the possible tephra source. Randomly sampled shards reveal a single geochemical population belonging to the Icelandic transitional alkali magma series, suggesting that they are unlikely to represent ice rafted debris derived from Icelandic icebergs. The tephra probably represent air-fall deposits, transported to the core site by sea ice within the northeast Atlantic gyre. The NAAZ II peak coincides with the rapid climate transition (cooling) at the end of interstadial 15, which can be assigned an age of 53 260±2660 yr BP from direct correlation with the Greenland ice-core (GISP2) record. A comparison of the MD95-2006 Neogloboquadrina pachyderma (sinistral) relative abundance and GISP2 δ18O records, relative to the NAAZ II isochron, suggests that this climatic event was synchronous across the North Atlantic. By direct correlation of interstadial maxima between the two records, the GISP2 time-scale is transferred to MD95-2006. Comparison of corrected and calibrated radiocarbon ages derived from monospecific foraminifers with the GISP2 ages at the same stratigraphical horizon suggest major age differences. These probably result from large variations in atmospheric 14C concentration and highlight the significant uncertainties associated with radiocarbon calibration during marine isotope stage 3. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors present total carbonate and δ18O records of benthic and planktic Foraminifera from nine sediment cores from the North Iceland Shelf.
Abstract: The region of north Iceland is highly sensitive climatically owing to its location with respect to atmospheric and oceanographic fronts. In this study we present total carbonate and δ18O records of benthic and planktic Foraminifera from nine sediment cores from the North Iceland Shelf. The results of this work indicate that the deglaciation of the Vestfirdir Peninsula was completed by 10 200 cal. yr BP. The 8200 cal. yr BP cold event is present only as a minor isotopic event, and seems not to have had much of a cooling effect on the bottom waters of the northwest Iceland shelf. The Holocene maximum warmth, attributed to a stronger North Icelandic Irminger Current, occurred between ca. 7800 and 6200 cal. yr BP. Over the past 4500 cal. yr BP a general cooling trend has occurred on the North Iceland Shelf, and superimposed on this overall cooling trend are a number of oscillations between periods when relatively warmer and cooler waters occupied the shelf. Relatively cooler waters were present at 4200–4000 cal. yr BP, 3200–2900 cal. yr BP, 2500–2350 cal. yr BP and 600–200 cal. yr BP, whereas relatively warmer waters were present on the shelf at 3750–3450 cal. yr BP, 2800–2600 cal. yr BP and 1700–1000 cal. yr BP. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this paper, a Holocene lake sediment record from Lake N14 situated on Angissoq island 15 km off the main coast of southern Greenland is presented, which is interpreted on the basis of flux and percentage content of biogenic silica, clastic material, organic material and sulphur as well as sedimentation rate, moss content and magnetic susceptibility.
Abstract: A Holocene lake sediment record is presented from Lake N14 situated on Angissoq island 15 km off the main coast of southern Greenland. The palaeoclimatic development has been interpreted on the basis of flux and percentage content of biogenic silica, clastic material, organic material and sulphur as well as sedimentation rate, moss content and magnetic susceptibility. A total of 43 radiocarbon dates has ensured a reliable chronology. It is argued that varying sediment composition mainly reflects changing precipitation. By analogy with the present meteorological conditions in southern Greenland, Holocene climate development is inferred. Between 11550 and 9300 cal. yr BP temperature and precipitation increase markedly, but this period is climatically unstable. From 9300 yr BP conditions become more stable and a Holocene climatic optimum, characterised by warm and humid conditions, is observed from 8000 to 5000 cal. yr BP. From 4700 cal. yr BP the first signs of a climatic deterioration are observed, and from 3700 cal. yr BP the climate has become more dry and cold. Superimposed on the climatic long-term trend is climate variability on a centennial time-scale that increases in amplitude after 3700 cal. yr BP. A climatic scenario related to the strength and position of the Greenland high-pressure cell and the Iceland low-pressure cell is proposed to explain the Holocene centennial climate variability. A comparison of the Lake N14 record with a terrestrial as well as a marine record from the eastern North Atlantic Ocean suggests that the centennial climate variability was uniform over large areas at certain times. (Less)
TL;DR: In this paper, the authors presented one of the most extensive Holocene tephra records found to date in Scandinavia, which was recorded in two ca. 2 m thick peat profiles at Klocka Bog in west-central Sweden.
Abstract: This paper presents one of the most extensive Holocene tephra records found to date in Scandinavia. Microtephra horizons originating from Icelandic eruptions were recorded in two ca. 2 m thick peat profiles at Klocka Bog in west-central Sweden. Five of the microtephra horizons were geochemically correlated to the Askja-1875, Hekla-3, Kebister, Hekla-4 and Lairg A tephras respectively. Radiocarbon-based dating of these tephras broadly agree with previously published ages from Iceland, Sweden, Germany and the British Isles. The identification of the Lairg A tephra demonstrates a more widespread distribution than previously thought, extending the usefulness of Icelandic Holocene tephrochronology further north into west-central Scandinavia. Long-lasting snow cover and seasonal wind distribution in the lower stratosphere are suggested as factors that may be responsible for fragmentary tephra deposition patterns in peat deposits of subarctic Scandinavia. (Less)
TL;DR: In this paper, the authors present a chronostratigraphic framework for environmental changes during the last 15,000 years in northwest Romania, to reconstruct the vegetation development, and to evaluate the underlying processes for forest dynamics.
Abstract: The objectives of this thesis are to establish a chronological framework for environmental changes during the last 15,000 years in northwest Romania, to reconstruct the vegetation development, and to evaluate the underlying processes for forest dynamics. Furthermore, an overview of earlier and ongoing pollenstratigraphic work in Romania is provided. Sediments from two former crater lakes, Preluca Tiganului and Steregoiu, situated in the Gutaiului Mountains, on the western extremity of the Eastern Carpathians at 730 m and 790 m a.s.l., respectively were obtained and analysed for high-resolution pollen, macrofossils, charcoal, mineral magnetic parameters and organic matter. The chronostratigraphic framework was provided by dense AMS 14C measurements. Cold and dry climatic conditions are indicated by the occurrence of open vegetation with shrubs and herbs, and cold lake water prior to 14,700 cal. yr BP. The climatic improvement at the beginning of the Lateglacial interstadial (around 14,700 cal. yr BP) is seen by the development of open forests. These were dominated by Pinus and Betula, but contained also new arriving tree taxa, such as Populus, Alnus and Prunus. The gradual establishment of forests may have led to a stabilization of the soils in the catchment. Between ca. 14,100 and 13,800 cal. yr BP the forest density became reduced to stands of Pinus, Betula, Alnus, Larix and Populus trees and grassland expanded, suggesting colder climatic conditions. Picea arrived as a new taxon at around 13,800 cal. yr BP, and between 13,800 and 12,900 cal. yr BP, the surroundings of the sites were predominantly covered by Picea forest. This forest included Betula, Pinus, Alnus, Larix and Populus and, from 13,200 cal. yr BP onwards also Ulmus. At ca. 12,900 cal. yr BP, the forest became significantly reduced and at 12,600 cal. yr BP, a recurrence of open vegetation with stands of Larix, Pinus, Betula, Salix and Alnus is documented, lasting until 11,500 cal. yr BP. This distinct change in vegetation may by taken as a strong decline in temperature and moisture availability.At the transition to the Holocene, at ca. 11,500 cal. yr BP, Pinus, Betula and Larix quickly expanded (from small local stands) and formed open forests, probably as a response to warmer and more humid climatic conditions. At 11,250 cal. yr BP Ulmus and Picea expanded and the landscape became completely forested. The rapid increase of Ulmus and Picea after 11,500 cal. yr BP may suggest the existence of small residual populations close to the study sites during the preceding cold interval. Ulmus was the first and most prominent deciduous taxa in the early Holocene in the Gutaiului Mountains. From ca. 10,750 cal. yr BP onwards Quercus, Tilia, Fraxinus and Acer expanded and Corylus arrived. A highly diverse, predominantly deciduous forest with Ulmus, Quercus, Tilia, Fraxinus, Acer, Corylus and Picea developed between 10,700 and 8200 cal. yr BP, which possibly signifies more continental climatic conditions. The development of a Picea-Corylus dominated forest between 8200 and 5700 cal. yr BP is likely connected to a more humid and cooler climate. The establishment of Carpinus and Fagus was dated to 5750 cal. yr BP and 5200 cal. yr BP, respectively. The dominance of Fagus during the late Holocene, from 4000 cal. yr BP onwards, may have been related to cooler and more humid climatic conditions. First signs of human activities are recorded around 2300 cal. yr BP, but only during the last 300 years did local human impact become significant. The vegetation development recorded in the Gutaiului Mountains during the Lateglacial is very similar to reconstructions based on lowland sites, whereas higher elevation sites seem not to have always experienced visible vegetation changes. The time of tree arrival and expansion during the past 11,500 cal. yr BP seems to have occurred almost synchronously across Romania. The composition of the forests during the Holocene in the Gutaiului Mountains is consistent with that reconstructed at mid-elevation sites, but differs from the forest composition at higher elevations. Important differences between the Gutaiului Mountains and other studied sites in Romania are a low representation of Carpinus and a late and weak human impact. The available data sets for Romania give evidence for the presence of coniferous and cold-tolerant deciduous trees before 14,700 cal. yr BP. Glacial refugia for Ulmus may have occurred in different parts of Romania, whereas the existence of Quercus, Tilia, Corylus and Fraxinus has not been corroborated.
TL;DR: The oxygen isotope records of both benthic and planktonic Foraminifera in five piston cores, collected from the region between the Oyashio and Kuroshio Currents near Japan, clearly show the marked latitudinal shifts of these two currents during the past 25 kyr as mentioned in this paper.
Abstract: The oxygen isotope records of both benthic and planktonic Foraminifera in five piston cores, collected from the region between the Oyashio and Kuroshio Currents near Japan, clearly show the marked latitudinal shifts of these two currents during the past 25 kyr. Under the present hydrographic condition, a clear relationship between the sea-surface temperature (SST) and oxygen isotope differences from benthic to planktonic Foraminifera is observed in this region. Using this relationship, we find decreased SSTs of 12–13°C (maximum 15°C) in the southernmost core site at the Last Glacial Maximum (LGM), indicating the Oyashio Current shifted southward. The SSTs at the southern two core sites abruptly increased more than 10°C at 10–11 ka, suggesting the Kuroshio Current shifted northward over these sites at 10–11 ka. In contrast, the northern two core sites have remained under the influence of the cold Oyashio Current for the past 25 kyr. With the reasonable estimate of bottom-water temperature decrease of 2.5°C at the LGM, the SSTs estimated by this new method give exactly the same SST values calculated from Mg/Ca ratio of planktonic Foraminifera, allowing palaeosea-surface salinities to be reconstructed. The result suggests that the ice volume effect was 1.0 ± 0.1‰ at the LGM. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this article, Schmidt hammer R-value data and clay-sized mineral contents of basal soil samples, demonstrate significant contrasts in the degree of weathering above and below the high-level weathering limit, suggesting that the ice mass which occupied the Gap of Dunloe at the LGM was warm based and flowed on a bedrock substrate.
Abstract: During the last main phase of glaciation (26–13 ka) an ice-cap developed in southwest Ireland and ice, from a dispersal centre in the vicinity of Kenmare, flowed north through the Gap of Dunloe in the Macgillycuddy's Reeks. On surrounding hillsides a weathering limit separates ice-moulded bedrock, on low ground, from frost-weathered terrain above. Assessment of bedrock dilation joint characteristics, Schmidt hammer R-value data and clay-sized mineral contents of basal soil samples, demonstrate significant contrasts in the degree of weathering above and below this limit. The weathering limit declines in altitude along former ice flow-lines and is confluent with morainic deposits on the eastern side of the Gap. This supports the assertion that the high-level weathering limit is a periglacial trimline that marks the former maximum upper limit of the body of ice which occupied the Gap of Dunloe during the Last Glacial Maximum (LGM). Reconstruction of the former ice-surface profile from periglacial trimline limits on the eastern side of the Gap yields a mean estimate for basal shear stress of 106.5 kPa. This value suggests that the ice mass which occupied the Gap of Dunloe at the LGM was warm based and flowed on a bedrock substrate. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this article, the results of a high-resolution Late-glacial chironomid stratigraphy from Hawes Water, a small carbonate lake in northern Lancashire, were presented.
Abstract: This paper presents the results of a high-resolution Late-glacial chironomid stratigraphy from Hawes Water, a small carbonate lake in northern Lancashire. The samples were from a core taken from the terrestrialised margin of the present lake, which represents an intermediate depth between the true littoral and the profundal. The chironomid assemblage showed a high degree of sensitivity to both broad-scale and short-term temperature changes. Comparison with an existing proxy temperature record (δ18O) for the site confirmed the presence of four temperature inversions within the Late-glacial Interstadial. A mean July air temperature inference model, derived from acid, soft-water lakes in Norway and Svalbard, was applied to the data. Despite the absence of carbonate lakes within the Norwegian training set, there was a close similarity between trends in estimated July air temperature and the δ18O trace, with a particularly strong correspondence in the periods of clay deposition. This suggests that this model is highly robust. The inferred maximum Interstadial temperature was 13.4°C, dropping initially to 7.5°C in the Loch Lomond Stadial. Temperatures reach a maximum of nearly 10°C in this period, cool for a short period before rising rapidly to 13.2°C at the start of the Holocene. These temperatures are similar to but slightly higher than those estimated for Whitrig Bog, southeast Scotland, and lower than those inferred from coleopteran-based models for sites in South Wales.
TL;DR: The first successful automated identification, with 100% accuracy, of a realistic number of taxa is shown, using a neural network classifier applied to surface texture data from light micro- scope images.
Abstract: The automation of palynology (the identification and counting of pollen grains and spores) will be a small step for image recognition, but a giant stride for palynology. Here we show the first successful automated identification, with 100% accuracy, of a realistic number of taxa. The technique used involves a neural network classifier applied to surface texture data from light micro- scope images. A further significance of the technique is that it could be adapted for the identification of a wide range of biological objects, both microscopic and macroscopic. Copyright 2004 John Wiley & Sons, Ltd.