Showing papers in "Journal of Quaternary Science in 2012"

Formal subdivision of the Holocene Series/Epoch: a Discussion Paper by a Working Group of INTIMATE (Integration of ice‐core, marine and terrestrial records) and the Subcommission on Quaternary Stratigraphy (International Commission on Stratigraphy)

Abstract: This discussion paper, by a Working Group of INTIMATE (Integration of ice-core, marine and terrestrial records) and the Subcommision on Quaternary Stratigraphy (SQS) of the International Commission on Stratigraphy (ICS), considers the prospects for a formal subdivision of the Holocene Series/Epoch. Although previous attempts to subdivide the Holocene have proved inconclusive, recent developments in Quaternary stratigraphy, notably the definition of the Pleistocene-Holocene boundary and the emergence of formal subdivisions of the Pleistocene Series/ Epoch, mean that it may be timely to revisit this matter. The Quaternary literature reveals a widespread but variable informal usage of a tripartite division of the Holocene ('early', 'middle' or 'mid', and 'late'), and we argue that this de facto subdivision should now be formalized to ensure consistency in stratigraphic terminology. We propose an Early-Middle Holocene Boundary at 8200 a BP and a Middle-Late Holocene Boundary at 4200 a BP, each of which is linked to a Global Stratotype Section and Point (GSSP). Should the proposal find a broad measure of support from the Quaternary community, a submission will be made to the International Union of Geological Sciences (IUGS), via the SQS and the ICS, for formal ratification of this subdivision of the Holocene Series/Epoch. Copyright# 2012 John Wiley & Sons, Ltd.

Oxygen isotopes from Chinese caves: records not of monsoon rainfall but of circulation regime

Abstract: Oxygen isotope variations in Chinese stalagmites have been widely interpreted as a record of the amount of East Asian summer monsoonal rainfall. This interpretation infers decreasing monsoonal rainfall from the mid-Holocene and large, dipolar rainfall oscillations within glaciations. However, the speleothem δ18O variations conflict with independent palaeoclimate proxies (cave δ13C, loess/palaeosol magnetic properties, n-alkanes), which indicate no systematic decline in rainfall from the mid-Holocene, and no glacial rainfall maxima. Using mass balance calculations, we demonstrate that the cave δ18O variations cannot be accounted for by summer rainfall changes, nor rainfall seasonality nor winter cooling, but instead reflect changes in moisture source. A possible driver of the δ18O variations in Chinese stalagmites is precessional forcing of inter-hemispheric temperature gradients, and resultant shifts in the position and intensity of the subtropical pressure cells. Through such forcing, Indian monsoon-sourced δ18O may have dominated at times of high boreal summer insolation, local Pacific-sourced moisture at low insolation. Suppression of summer monsoonal rainfall during glacial stages may reflect diminished sea and land surface temperatures and the radiative impacts of increased regional dust fluxes.

Pleistocene Rhine–Thames landscapes: geological background for hominin occupation of the southern North Sea region

Abstract: This paper links research questions in Quaternary geology with those in Palaeolithic archaeology. A detailed geological reconstruction of The Netherlands' south-west offshore area provides a stratigraphical context for archaeological and palaeontological finds. Progressive environmental developments have left a strong imprint on the area's Palaeolithic record. We highlight aspects of landscape evolution and related taphonomical changes, visualized in maps for critical periods of the Pleistocene in the wider southern North Sea region. The Middle Pleistocene record is divided into two palaeogeographical stages: the pre-Anglian/Elsterian stage, during which a wide land bridge existed between England and Belgium even during marine highstands; and the Anglian/Elsterian to Saalian interglacial, with a narrower land bridge, lowered by proglacial erosion but not yet fully eroded. The Late Pleistocene landscape was very different, with the land bridge fully dissected by an axial Rhine-Thames valley, eroded deep enough to fully connect the English Channel and the North Sea during periods of highstand. This tripartite staging implies great differences in (i) possible migration routes of herds of herbivores as well as hominins preying upon them, (ii) the erosion base of axial and tributary rivers causing an increase in the availability of flint raw materials and (iii) conditions for loess accumulation in northern France and Belgium and the resulting preservation of Middle Palaeolithic sites. © 2011 John Wiley & Sons, Ltd.

Contrasting patterns of precipitation seasonality during the Holocene in the south- and north-central Mediterranean

Abstract: Pollen-based quantitative estimates of seasonal precipitation from Lake Pergusa and lake-level data from Lake Preola in Sicily (southern Italy) allow three successive periods to be distinguished within the Holocene: an early Holocene period before ca. 9800 cal a BP with rather dry climate conditions in winter and summer, a mid-Holocene period between ca. 9800 and 4500 cal a BP with maximum winter and summer wetness, and a late Holocene period after 4500 cal a BP with declining winter and summer wetness. This evolution observed in the south-central Mediterranean shows strong similarities to that recognized in the eastern Mediterranean. But, it contrasts with that reconstructed in north-central Italy, where the mid-Holocene appears to be characterized by a winter (summer) precipitation maximum (minimum), while the late Holocene coincided with a decrease (increase) in winter (summer) precipitation. Maximum precipitation at ca. 10 000–4500 cal a BP may have resulted from (i) increased local convection in response to a Holocene insolation maximum at 10 000 cal a BP and then (ii) the gradual weakening of the Hadley cell activity, which allowed the winter rainy westerlies to reach the Mediterranean area more frequently. After 4500 cal a BP, changes in precipitation seasonality may reflect non-linear responses to orbitally driven insolation decrease in addition to seasonal and inter-hemispheric changes of insolation. Copyright © 2011 John Wiley & Sons, Ltd.

Late glacial and holocene 10Be production rates for western Norway

Abstract: We present a new regional calibration of the 10Be production rate from two well-dated surfaces insouthern Norway: a rock avalanche with 14C-dated wood and a precisely dated Younger Dryas moraine. C ...

Late Holocene vertical land motion and relative sea-level changes: lessons from the British Isles

Abstract: Vertical land motion caused by continuing glacial isostatic adjustment is one of several important components of sea-level change and is not limited just to previously glaciated regions. A national-scale analysis for the British Isles shows an ellipse of present-day relative uplift (relative sea-level fall), ∼1.2 mm a−1, broadly centred on the deglaciated mountains of Scotland. The pattern of three foci of relative subsidence, ∼1 mm a−1, results from the additional interactions of the deglacial meltwater load on the Atlantic basin and the continental shelf, and the signal due to far-field ice sheets. At a local scale, sediment compaction can more than double the rate of relative land subsidence. Relative land-level change (the negative of relative sea-level change) is not the same as vertical land motion. There is a spatial pattern in the difference between relative land-level change and vertical land motion, with differences at present of approximately −0.1 to −0.3 mm a−1 around the British Isles and +2.5 to −1.5 mm a−1 globally. For the wider scientific and user community, whether or not the differences are considered significant will depend upon the location, time frame and spatial scale of the study that uses such information. Copyright © 2011 John Wiley & Sons, Ltd.

Did large ice caps persist on low ground in north‐west Scotland during the Lateglacial Interstade?

Abstract: Recent research based primarily on exposure ages of boulders on moraines has suggested that extensive ice masses persisted in fjords and across low ground in north-west Scotland throughout the Lateglacial Interstade (≈ Greenland Interstade 1, ca. 14.7–12.9 ka), and that glacier ice was much more extensive in this area during the Older Dryas chronozone (ca. 14.0 ka) than during the Younger Dryas Stade (ca. 12.9–11.7 ka). We have recalibrated the same exposure age data using locally derived 10Be production rates. This increases the original mean ages by 6.5–12%, implying moraine deposition between ca. 14.3 and ca. 15.1 ka, and we infer a most probable age of ca. 14.7 ka based on palaeoclimatic considerations. The internal consistency of the ages implies that the dated moraines represent a single readvance of the ice margin (the Wester Ross Readvance). Pollen–stratigraphic evidence from a Lateglacial site at Loch Droma on the present drainage divide demonstrates deglaciation before ca. 14.0 ka, and therefore implies extensive deglaciation of all low ground and fjords in this area during the first half of the interstade (ca. 14.7–14.0 ka). This inference appears consistent with Lateglacial radiocarbon dates for shells recovered from glacimarine sediments and a dated tephra layer. Our revised chronology conflicts with earlier proposals that substantial dynamic ice caps persisted in Scotland between 14 and 13 ka, that large active glaciers probably survived throughout the Lateglacial Interstade and that ice extent was greater during the Older Dryas period than during the Younger Dryas Stade. Copyright © 2011 John Wiley & Sons, Ltd.

Constraining Holocene 10Be production rates in Greenland

Abstract: The absence of a production rate calibration experiment on Greenland has limited the ability to link 10Be exposure dating chronologies of ice-margin change to independent records of rapid climate change. We use radiocarbon age control on Holocene glacial features near Jakobshavn Isbrae, western Greenland, to investigate 10Be production rates. The radiocarbon chronology is inconsistent with the 10Be age calculations based on the current globally averaged 10Be production rate calibration data set, but is consistent with the 10Be production rate calibration data set from north-eastern North America, which includes a calibration site nearby on north-eastern Baffin Island. Based on the best-dated feature available from the Jakobshavn Isbrae forefield, we derive a 10Be production rate value of 3.98 ± 0.24 atoms g a−1, using the ‘St’ scaling scheme, which overlaps with recently published reference 10Be production rates. We suggest that these 10Be production rate data, or the very similar data from north-eastern North America, are used on Greenland. Copyright © 2011 John Wiley & Sons, Ltd.

Multiproxy record for the last 4500 years from Lake Shkodra (Albania/Montenegro)

Abstract: A multi-proxy record is presented for approximately the last 4500 cal a BP from Lake Shkodra, Albania/ Montenegro. Lithological analyses, C/N ratio and d 13 C of the organic and inorganic carbon component suggest that organic matter and bulk carbonate are predominantly authigenic. The d 18 O record of bulk carbonate indicates the presence of two prominent wet periods: one at ca. 4300 cal a BP and one at ca. 2500-2000 cal a BP. The latter phase is also found in southern Spain and Central Italy, and represents a prominent event in the western and central Mediterranean. In the last 2000 years, four relatively wet intervals occurred between ca. 1800 and 1500 cal a BP (150-450 AD), 1350-1250 (600-700 AD), 1100-800 (850-1150 AD), and at ca. 90 cal a BP (1860 AD). Between ca. 4100 and 2500 cal a BP d 18 O values are relatively high, with three prominent peaks indicating drier conditions at ca. 4100-4000 cal a BP, ca. 3500 and at ca. 3300 cal a BP. Four additional drier events are identified at 1850 (ca. 100 AD), 1400 (ca. 550 AD), 1150 (800 AD) and ca.750 cal a BP (1200 AD). The pollen record does not show changes in accordance with these episodes owing to the poor sensitivity of vegetation in this area, which is dominated by an orographic rainfall effect and where changes in altitudinal vegetation belts do not affect the pollen rain in the lake catchment. However, since ca. 900 cal a BP a significant decrease in the percentage arboreal pollen and in pollen concentrations suggest major deforestation produced by human activities. Copyright # 2012 John Wiley & Sons, Ltd.

Evaluation of a numerical model of the British–Irish ice sheet using relative sea-level data: implications for the interpretation of trimline observations

Abstract: The glacial isostatic adjustment (GIA) of the British Isles is complex due to the interplay between local and non-local signals. A number of recent studies have modelled the GIA response of the British Isles using relative sea-level data. This study extends these previous analyses by using output from a numerical glaciological model as input to a GIA model. This is a necessary step towards more realistic GIA models, and although there have been similar studies for the major late Pleistocene ice sheets, this is the first study to do so for the British Isles. We test three reconstructions, classed as ‘minimal’, ‘median’ and ‘maximal’ in terms of their volume at maximum extent, and find it is possible to obtain good data–model fits. The minimal reconstruction is clearly preferred by the sea-level data. The ice reconstructions tested were not constrained by geomorphological information of past ice extent (lateral and vertical). As a consequence, the reconstructions extend further than much of this information suggests, particularly in terms of ice thickness. It is notable, however, that the reconstructions produce good fits to many sea-level data from central, mountainous regions (e.g. Scottish highlands), which lends support to the suggestion that trimlines, often used as an constraint on the palaeo ice surface location, are in fact features formed at the transition from warm- to cold-based ice and so mark a minimum constraint on the ice surface altitude. Based on data–model misfits, suggestions are made for improving the ice model reconstructions. However, in many locations, the cause of the misfit could be due to non-local, predominantly Fennoscandian ice and so interpretation is not straightforward. As a result, we suggest that future analyses of this type consider models and observations for both Fennoscandia and the British Isles. Copyright © 2012 John Wiley & Sons, Ltd.

The AD 1717 rock avalanche deposits in the upper Ferret Valley (Italy): a dating approach with cosmogenic 10Be

Abstract: On 12 September AD 1717, a rock volume larger than 10 million m3 collapsed onto the Triolet Glacier, mobilized a mass composed of ice and sediment and travelled more than 7 km downvalley in the upper Ferret Valley, Mont Blanc Massif (Italy). This rock avalanche destroyed two small settlements, causing seven casualties and loss of livestock. No detailed maps were made at the time. Later investigators attributed accumulations of granitic boulders and irregular ridges on the upper valley floor to either glacial deposition, or the AD 1717 rock avalanche, or a complex mixture of glacial deposition, earlier rock avalanche and AD 1717 rock avalanche origin. In this study, we present cosmogenic 10Be exposure ages from nine boulders in the extensive chaotic boulder deposit with irregular ridges, two from Holocene glacier-free areas, and one from a Little Ice Age moraine. Exposure ages between 330 ± 23 and 483 ± 123 a from eight of nine boulders from the chaotic deposit indicate that at least seven were deposited by the AD 1717 rock avalanche. The other three boulders yielded 10Be exposure ages of 10 900 ± 400, 9700 ± 400 and 244 ± 97 a, respectively. Our results are in good agreement with the existing chronology from dendrochronology and lichenometry, and radiocarbon analysis of wood samples, but not with older 14C ages from a peat bog in the upper part of the valley. Based on the new age control, the rock avalanche deposits cover the whole bottom of the upper Ferret valley. Copyright © 2012 John Wiley & Sons, Ltd.

Holocene palaeoflood events recorded by slackwater deposits along the lower Jinghe River valley, middle Yellow River basin, China

Abstract: Palaeoflood slackwater deposits (SWDs), are the natural record of overbank flooding and are often found within aeolian loess-soil profiles along the river valleys of the middle Yellow River basin. These pedo-stratigraphic sequences are studied using a multi-disciplinarily approach to reconstruct Holocene hydro-climatic variations. Our field investigations along the lower Jinghe River valley have identified palaeoflood SWDs at several sites along the riverbanks based on sedimentological criteria. Analytical results, including magnetic susceptibility, particle-size distribution and concentrations of chemical elements, indicate that these well-sorted palaeoflood SWD beds were deposited from the suspended sediment load in floodwaters. We identify two episodes of extraordinary palaeoflood events along the Jinghe River valley. These hydro-climatic events were dated to 4200–4000 and 3200–2800 a BP, by using the optically stimulated luminescence method in combination with archaeological dating of retrieved anthropogenic remains, and with pedo-stratigraphic correlations with the previously studied Holocene pedo-stratigraphy in the Jinghe River drainage basin. The flooding events are therefore considered to be a regional expression of known climatic events in the northern hemisphere and demonstrate Holocene climate was far from stable. This study provides important data in understanding the interactions between regional hydro-climatic systems and global change in semi-arid and sub-humid regions. Copyright © 2012 John Wiley & Sons, Ltd.

Strengthening of paleo-typhoon and autumn rainfall in Taiwan corresponding to the Southern Oscillation at late Holocene

Abstract: The purpose of this study is to improve prehistoric knowledge of paleo-typhoon and winter monsoon activity in the western North Pacific after 8 cal. ka BP. We examine two sediment cores derived from lakes located to the south and north of the Ilan Plain in northeastern Taiwan. Seasonal and typhoon rainfall data over the past several decades are collected for this study region. We also use mineral indicators, K/Rb ratios and grain size to estimate sediment sources, intensity of chemical weathering and rainfall intensity. The results show that the chemical weathering index (K/Rb ratio) of Meihua Lake indicates the continuing effects of autumn rainfall, while coarse grain sizes of Dahu Lake sediments suggest increased intensity in typhoon rainfall. Grain size results reveal that increasing El Nino–Southern Oscillation intensity in the tropical Pacific has intensified the activity of super typhoons in the western North Pacific. Finally, we find that frequent activity of super paleo-typhoons occurred in Taiwan during the La Nina-like state, and the strengthening winter monsoon activity and higher sea surface temperature enhanced plentiful autumn rainfall in El Nino-like state. After comparing our results with the paleo-typhoon data in Japan and south China, we suggest that the tracks of super typhoon are mainly affected by variations in the warm pool and subtropical Northwestern Pacific High in the western Pacific. Copyright © 2012 John Wiley & Sons, Ltd.

Elemental and isotopic carbon and nitrogen records of organic matter accumulation in a Holocene permafrost peat sequence in the East European Russian Arctic

Abstract: A peat deposit from the East European Russian Arctic, spanning nearly 10 000 years, was investigated to study soil organic matter degradation using analyses of bulk elemental and stable isotopic co ...

Lateglacial and early Holocene dynamics of adjacent valley glaciers in the Western Swiss Alps

Abstract: The Alps play a pivotal role for glacier and climate reconstructions within Europe. Detailed glacial chronologies provide important insights into mechanisms of glaciation and climate change. We present 26 10Be exposure dates of glacially transported boulders situated on moraines and ice-moulded bedrock samples at the Belalp cirque and the Great Aletsch valley, Switzerland. Weighted mean ages of ∼10.9, 11.1, 11.0 and 9.6 ka for the Belalp, on up to six individual moraine ridges, constrain these moraines to the Egesen, Kartell and Schams stadials during Lateglacial to early Holocene times. The weighted mean age of ∼12.5 ka for the right-lateral moraine of the Great Aletsch correlates with the Egesen stadial related to the Younger Dryas cooling. These data indicate that during the early Holocene between ∼11.7 and ∼9.2 ka, glaciers in the Swiss Alps seem to have been significantly affected by cold climatic conditions initiated during the Younger Dryas and the Preboreal Oscillation. These conditions resulted in glacier margin oscillations relating to climatic fluctuations during the second phase of the Younger Dryas – and continuing into Boreal times – as supported by correlation of the innermost moraine of the Belalp Cirque to the Schams (early) Holocene stage. Copyright © 2011 John Wiley & Sons, Ltd.

Late Pleistocene palaeolake in the interior of Oman: a potential key area for the dispersal of anatomically modern humans out-of-Africa?

Abstract: Relict fluvial and lacustrine deposits in the interior of Oman near Saiwan consist of waterlain breccias with pebble imbrications and current ripples, covered by algal laminites containing calcified reeds and charcoal pieces. Geomorphological evidence suggests that the palaeolake covered a maximum surface of 1400 km2 and had a maximum depth of about 25 m. Optically stimulated luminescence (OSL) and thermally transferred OSL dating indicate that this palaeolake existed sometime between 132 and 104 ka. The rich archaeological evidence in the area suggests substantial human occupation, possibly at the time when Palaeolake Saiwan existed. Interestingly, the lithic traditions of the archaeological material show no clear relation to coeval findings from neighbouring areas, putting a question mark on the origin of the culture found at Saiwan. This finding raises questions concerning the origin of the population inhabiting Saiwan, as the site lies along one possible route for the dispersal of anatomically modern humans out-of-Africa. Copyright © 2011 John Wiley & Sons, Ltd.

Holocene peatland development and hydrological variability inferred from bog‐pine dendrochronology and peat stratigraphy – a case study from southern Sweden

Abstract: Dendrochronological analysis was applied to subfossil remains of Scots pine (Pinus sylvestris L.) buried in a South Swedish peat deposit. In combination with peat stratigraphy, this approach was explored for its potential to provide information on the local hydrological and depositional history at the site, forming the basis for a regional palaeohydrological analysis. A 726-year ring-width chronology was developed and assigned an absolute age of 7233-6508cal a BP (5284-4559 BC) through cross-dating with German bog-pine chronologies, whereas two short additional records of older ages were radiocarbon dated. Registration of growth positions of individual trees allowed assessment of the spatial dynamics of the pine population in response to hydrological changes and peatland ontogeny. Annually resolved growth variability patterns in the pine population reveal several establishment and degeneration phases, probably reflecting fluctuations in bog-surface wetness. A major establishment phase at 7200-6900?cal a BP reflects the onset of a period of lowered groundwater level, also indicated by increased peat humification, and a development consistent with regional temperature and lake level reconstructions revealed from other proxies. This study demonstrates that subfossil bog-pine populations may provide annually to decadally resolved reconstructions of local groundwater variability, which are highly relevant in a long-term palaeoclimatic context. Copyright (c) 2012 John Wiley & Sons, Ltd.

A tephrochronology for the Lateglacial palynological record of the Endinger Bruch (Vorpommern, north‐east Germany)

Abstract: The tephrostratigraphy of lake sediments in the Endinger Bruch provides the first robust age model for the Lateglacial palynological records of Vorpommern (north-east Germany) Cryptotephra investigations revealed six tephra layers within sediments spanning from Open vegetation phase I (� Bolling, � 15 ka) to the Early Holocene Betula/Pinus forest phase (� Pre-boreal, � 105 ka) Four of these layers have been correlated with previously described tephra layers found in sites across Europe The Laacher See Tephra (Eifel Volcanic Field) is present in very high concentrations within sediments of the Lateglacial Betula (/Pinus) forest phase (� Allerod) The Vedde Ash (Iceland) lies midway through Open vegetation phase III (� Younger Dryas) The Hasseldalen and the Askja tephras (Iceland) lie in the Early Holocene Betula/Pinus forest phase (� Preboreal) These tephra layers have independently derived age estimates, which have been imported into the Endinger Bruch record Furthermore, the layers facilitate direct correlation of the regional vegetation record with other palaeoenvironmental archives, which contain one or more of the same tephra layers, from Greenland to Southern Europe In doing this, localized variations are confirmed in some aspects of the pollen stratigraphy; however, transitions between the main vegetation phases appear to occur synchronously (within centennial errors) with the equivalent environmental transitions observed in sites across the European continent Copyright # 2011 John Wiley & Sons, Ltd

How a Sphagnum fuscum-dominated bog changed into a calcareous fen: the unique Holocene history of a Slovak spring-fed mire

Abstract: Mires develop by autogenic succession from more groundwater-fed to more rainwater-fed. This study describes a similar development in the Early Holocene, followed by a reverse development in the Middle and Late Holocene. Pollen, macrofossil and testate amoeba analyses show that the site started as a minerotrophic open fen woodland. After 10 700 cal a BP autogenic succession led to the accumulation of at least 1?m of Sphagnum fuscum peat. Around 9000 cal a BP, as climate could no longer sustain a stable water regime, the bog desiccated and a fire broke out. The fire removed part of the peat layer and as a consequence relative water levels rose, leading to the establishment of a wet minerotrophic swamp carr. After 600 cal a BP, rapid peat accumulation with calcareous tufa formation resumed as a result of anthropogenic deforestation and hydrological changes in the catchment and resulting increased groundwater discharge.

Lateglacial and early Holocene summer temperatures in the southern Swiss Alps reconstructed using fossil chironomids

Abstract: We present a Lateglacial and early Holocene chironomid-based July air temperature reconstruction from Foppe (1470 m a.s.l.) in the Swiss Southern Alps. Our analysis suggests that chironomid assemblages have responded to major and minor climatic fluctuations during the past 17 000 years, such as the Oldest Dryas, the Younger Dryas and the Bolling/Allerod events in the Lateglacial and the Preboreal Oscillation at the beginning of the Holocene. Quantitative July air temperature estimates were produced by applying a combined Norwegian and Swiss temperature inference model consisting of 274 lakes to the fossil chironomid assemblages. The Foppe record infers average July air temperatures of ca. 9.9 8C during the Oldest Dryas, 12.2 8C during most of the Bolling/Allerod and 11.1 8C for the Younger Dryas. Mean July air temperatures during the Preboreal were 14 8C. Major temperature changes were observed at the Oldest Dryas/Bolling (þ2.7 8C), the Allerod/Younger Dryas (� 2 8C) and the Younger Dryas/Holocene transitions (þ3.9 8C). The temperature reconstruction also shows centennial-scale coolings of ca. 0.8-1.4 8C, which may be synchronous with the Aegelsee (Greenland Interstadial 1d) and the Preboreal Oscillations. A comparison of our results with other palaeoclimate records suggests noticeable temperature gradients across the Alps during the Lateglacial and early Holocene. Copyright # 2011 John Wiley & Sons, Ltd.

Wetland soil moisture complicates the use of Sporormiella to trace past herbivore populations

Abstract: Spores of the dung-fungi Sporormiella provide a proxy for assessing past changes in herbivore abundance, and for temporally linking these with shifts in vegetation communities (pollen) and fire frequency (charcoal). Although the proxy is now widely used, potential influences of local environmental conditions are poorly understood. Here we assess the reliability of Sporormiella as a proxy of herbivores by presenting five new spore records from the South Island of New Zealand; a land where the herbivore extinction/introduction chronology is well established, and where extinctions occurred independently of major climate change. We show that Sporormiella spores from relatively dry soils provide a good proxy for herbivore extinctions and introductions. However, spore abundances from saturated soil sites appear to fluctuate in close correlation with changes in local hydrology (represented by wetland herb pollen, testate amoebae and moisture sensitive mosses). Our results suggest Sporormiella records derived from wetlands require cautious interpretation, and that proxies for hydrological conditions should also be considered when interpreting such records. Copyright © 2011 John Wiley & Sons, Ltd.

Process length variation of the cyst of the dinoflagellate Protoceratium reticulatum in the North Pacific and Baltic-Skagerrak region: calibration as an annual density proxy and first evidence of pseudo-cryptic speciation

Abstract: Process length variation of cysts of the dinoflagellate Protoceratium reticulatum (Claparede et Lachmann) Butschli in surface sediments from the North Pacific was investigated. The average process ...

Central England temperature since AD 1850: the potential of stable carbon isotopes in British oak trees to reconstruct past summer temperatures

Abstract: In regions with seasonal temperate climatic regimes, tree growth is rarely controlled by any single environmental factor. As a consequence, the development of robust palaeoclimate reconstructions has proved challenging. Tree-ring stable carbon isotope ratios (δ13C), however, are controlled primarily by photosynthetic rate, not by net growth. Therefore, at sites where climatic controls on tree-ring growth are not strongly expressed, a robust (isotopic) palaeoclimate signal may still potentially be preserved. This hypothesis was tested using a 160-year record of δ13C measured from the pooled latewood cellulose of six Quercus petraea L. (sessile oak) trees from Allt Lan-las in West Wales, UK. Raw δ13C values were corrected for changes in the isotopic ratio of atmospheric carbon dioxide and for changes in the behaviour of trees due to the increasing availability of atmospheric CO2 since AD 1850. Strong correlations with local summer temperature and sunshine are reported, and also with the Central England Temperature record over the full length of the isotopic chronology (AD 1850–2010) (r = 0.69, P < 0.001). We conclude that tree-ring stable isotopes can be used to extract strong palaeoclimate signals even from oak trees growing in a temperate maritime climate. This demonstrates the potential for extracting robust palaeoclimatic information from the very long and well-replicated oak chronologies which have been developed in western and central Europe primarily for dating rather than palaeoclimatic research purposes. Copyright © 2012 John Wiley & Sons, Ltd.

Holocene changes in precipitation seasonality in the western Mediterranean Basin: a multi-species approach using δ13C of archaeobotanical remains

Abstract: Precipitation has been of utmost importance in shaping the evolution of landscapes and human settlements in the Mediterranean. However, information on seasonal precipitation patterns through the Holocene is scarce. This study attempts to quantify the evolution of seasonal precipitation in the East Iberian Peninsula (5000 BC to AD 600) based on the carbon isotope composition (δ13C) of archaeobotanical remains. Data on Holm oak, Aleppo pine and small-grain cereals were combined, and precipitation was inferred from models relating present-day records to the δ13C of modern samples. Subsequently, charred grains were used as a proxy for ancient moisture during April–May, whereas oak and pine charcoals provided complementary rainfall estimates for September–December and January–August, respectively. The results reveal aridity changes throughout the Holocene in the western Mediterranean. Past spring–summer precipitation was consistently higher than at present. In contrast, autumn and early winter precipitation showed stronger fluctuations, particularly during the first millennium BC, and often exhibited values below those of the present. The high contribution of autumn precipitation to the annual water budget, typical of the present Mediterranean climate, was definitively established at the beginning of the current era. This study shows how a combination of species holding complementary environmental signals can contribute to a wider knowledge of local precipitation dynamics.

Major and trace element characterization of tephra layers offshore Pantelleria Island: insights into the last 200 ka of volcanic activity and contribution to the Mediterranean tephrochronology

Abstract: A detailed tephrochronological study was carried out on the deep-sea core collected from Site 963A in the Sicily Channel during ODP Leg 160. The chronology of the succession is provided by an age–depth model based on isotope stratigraphy and quantitative eco-biostratigraphy. Major, trace and rare earth element content was obtained on single glass grains through electron probe micro-analysis and laser ablation–inductively coupled plasma mass spectrometry techniques from six well-preserved tephra layers, characterized by a discrete thickness found along the succession. These deposits were correlated with the volcanic activity of Pantelleria and dated at 42.5, 127.5, 128.1, 129.1, 188.7 and 197.7 ka. This detailed chemical characterization of the studied deposits aims to provide a valuable reference database for scientists working on both proximal and distal products erupted at Pantelleria island during the Late Pleistocene. This study, moreover, offers the opportunity to better identify Pantelleria-related marker tephras within the tephrochronological framework of the central and eastern Mediterranean area. Copyright © 2012 John Wiley & Sons, Ltd.

Application of stable carbon isotopes for reconstructing salt-marsh floral zones and relative sea level, New Jersey, USA

Abstract: We investigated use of δ13C in bulk organic sediment to define the botanical origin of samples preserved in coastal sediment as a means to reconstruct relative sea level in New Jersey, USA. Modern transects at three sites demonstrated that low and high salt-marsh floral zones dominated by C4 species (Spartina alterniflora and Spartina patens) were associated with sediment δ13C values between −18.9‰ and −15.8‰ and occurred from mean tide level (MTL) to mean higher high water (MHHW). Brackish transitional settings vegetated by Phragmites australis with Iva fructescens and Typha sp. (C3 species) and freshwater upland samples (C3 species) were characterized by bulk sediment δ13C values of −27.0‰ to −22.0‰ and existed above MHHW. Parallel transects at one site suggested that intra-site variability was not discernible. The utility of δ13C values for reconstructing relative sea level in New Jersey is limited by an inability to differentiate between brackish sediments related to sea level and freshwater upland samples. To facilitate this distinction in a 4.4 m core, we used a multi-proxy approach (δ13C values with presence or absence of agglutinated foraminifera) to recognize indicative meanings for four sample types. Sediment with δ13C values greater than −18.9‰ was derived from a vegetated salt-marsh and formed between MTL and MHHW. Sediment with δ13C values less than −22.0‰ and containing agglutinated foraminifera formed in a brackish transitional zone between MHHW and highest astronomical tide (HAT). This is the narrowest elevational range of the four sample types and most precise sea-level indicator. Sediment with δ13C values less than −22.0‰ and lacking foraminifera can only constrain the upper bound of former sea level. Samples with intermediate values (−22.0‰ to −18.9‰) formed between MTL and HAT. Using these indicative meanings and radiocarbon dates, we suggest that a transition from brackish to salt-marsh δ13C values recorded in the core took approximately 350 years (from 1800 to 1450 cal. a BP).

Paleoenvironmental reconstruction of a Late Quaternary lagoon system in southern Brazil (Jaguaruna region, Santa Catarina state) based on multi-proxy analysis

Abstract: This paper provides a paleoenvironmental reconstruction of a Late Quaternary lagoon system in the Jaguaruna region of Santa Catarina state, southern Brazil. Integrated results of bulk sedimentary organic matter characterization (d 13 C, d 15 N and C/N), microfossil (pollen and diatom) and grain-size analysis from three shallow cores (� 2.5 m depth) allowed us to propose an evolving paleogeographic scenario in this coastal region for the last ca. 5500 cal a BP. The lagoonal system in this area was more extensive during the mid-Holocene than today, with a gradual and continuous lagoon-sea disconnection until the present. We add to the debate regarding relative sea-level (RSL) variations for the Brazilian coast during the Holocene and discuss the importance of sedimentary dynamics for interpreting changes in coastal ecosystems. The multi-proxy analysis suggests that changes in coastal ecosystems could be directly related to local sedimentary processes, which are not necessarily linked to RSL fluctuations and/or to climatic variations. Copyright # 2011 John Wiley & Sons, Ltd.

Sea level at the last glacial maximum, constrained by oxygen isotopic curves of planktonic foraminifera in the Japan Sea

Abstract: The Japan Sea is connected with the Okhotsk Sea and Northwest Pacific through three straits, viz. Mamiya (Tartarskiy), Soya and Tsugaru, and with the East China Sea through Tsushima Strait, all having sill depths of 3% recorded in the MIS 3-4 sections of the studied cores. This observation indicates nearly similar surface water conditions in the Japan Sea during both the previous glacial maxima, and hence suggests negligible effect of strait tectonics on the sea level since the last 140 ka. Low d 18 OPF values with small amplitude are also observed at the cold stage MIS 6.4, but not observed at another cold stage MIS 4.2. This observation suggests that the low-salinity surface water in the Japan Sea started to develop at the sea level between MIS 4.2 and 6.4. Judging from the cross-section of the Tsushima Strait and the sea floor topography of the East China Sea, the sea level between MIS 4.2 and 6.4 must have been between 90 m and 100 m below the present. From a proportional relationship between the standard d 18 O curve (LR04) in deep-sea cores and globally averaged sea-level change, the eustatic sea level obtained for the LGM is 120 � 7 m below the present. Thus the Japan Sea, in a far-field location from the continental ice sheets, provides an important clue for estimation of the eustatic sea level at the LGM. Copyright # 2012 John Wiley & Sons, Ltd.

10Be and 26Al exposure-age dating of bedrock surfaces on the Aran ridge, Wales: evidence for a thick Welsh Ice Cap at the Last Glacial Maximum

Abstract: This paper presents results of the analysis of paired cosmogenic isotopes (10Be and 26Al) from eight quartz-rich samples collected from ice-moulded bedrock on the Aran ridge, the highest land in the British Isles south of Snowdon. On the Aran ridge, comprising the summits of Aran Fawddwy (905 m a.s.l.) and Aran Benllyn (885 m a.s.l.), 26Al and 10Be ages indicate complete ice coverage and glacial erosion at the global Last Glacial Maximum (LGM). Six samples from the summit ridge above 750–800 m a.s.l. yielded paired 10Be and 26Al ages ranging from 17.2 to 34.4 ka, respectively. Four of these samples are very close in age (10Be ages of 17.5 ± 0.6, 17.5 ± 0.7, 19.7 ± 0.8 and 20.0 ± 0.7 ka) and are interpreted as representing the exposure age of the summit ridge. Two other summit samples are much older (10Be ages of 27.5 ± 1.0 and 33.9 ± 1.2 ka) and these results may indicate nuclide inheritance. The 26Al/10Be ratios for all samples are indistinguishable within one-sigma uncertainty from the production rate ratio line, indicating that there is no evidence for a complex exposure history. These results indicate that the last Welsh Ice Cap was thick enough to completely cover the Aran ridge and achieve glacial erosion at the LGM. However, between c. 20 and 17 ka ridge summits were exposed as nunataks at a time when glacial erosion at lower elevations (below 750–800 m a.s.l.) was achieved by large outlet glaciers in the valleys surrounding the mountains. Copyright © 2011 John Wiley & Sons, Ltd.

Late Quaternary tephrostratigraphy, Ahklun Mountains, SW Alaska

Abstract: Radiocarbon-dated sediment cores from six lakes in the Ahklun Mountains, south-western Alaska, were used to interpolate the ages of late Quaternary tephra beds ranging in age from 25.4 to 0.4 ka. The lakes are located downwind of the Aleutian Arc and Alaska Peninsula volcanoes in the northern Bristol Bay area between 159° and 161°W at around 60°N. Sedimentation-rate age models for each lake were based on a published spline-fit procedure that uses Monte Carlo simulation to determine age model uncertainty. In all, 62 14C ages were used to construct the six age models, including 23 ages presented here for the first time. The age model from Lone Spruce Pond is based on 18 ages, and is currently the best-resolved Holocene age model available from the region, with an average 2σ age uncertainty of about ± 109 years over the past 14.5 ka. The sedimentary sequence from Lone Spruce Pond contains seven tephra beds, more than previously found in any other lake in the area. Of the 26 radiocarbon-dated tephra beds at the six lakes and from a soil pit, seven are correlated between two or more sites based on their ages. The major-element geochemistry of glass shards from most of these tephra beds supports the age-based correlations. The remaining tephra beds appear to be present at only one site based on their unique geochemistry or age. The 5.8 ka tephra is similar to the widespread Aniakchak tephra [3.7 ± 0.2 (1σ) ka], but can be distinguished conclusively based on its trace-element geochemistry. The 3.1 and 0.4 ka tephras have glass major- and trace-element geochemical compositions indistinguishable from prominent Aniakchak tephra, and might represent redeposited beds. Only two tephra beds are found in all lakes: the Aniakchak tephra (3.7 ± 0.2 ka) and Tephra B (6.1 ± 0.3 ka). The tephra beds can be used as chronostratigraphic markers for other sedimentary sequences in the region, including cores from Cascade and Sunday lakes, which were previously undated and were analyzed in this study to correlate with the new regional tephrostratigraphy. Copyright © 2012 John Wiley & Sons, Ltd.