testing the timing of radiocarbon dated events between proxy archives for interpreting past changes on a regional or global scale the timings of proxy inferred events are usually aligned with data from other locations however too often chronological uncertainties are ignored in proxy diagrams and multisite comparisons making it possible for researchers to fall into the trap of sucking separate events into one illusionary event or vice versa here we largely solve this suck in and smear syndrome for radiocarbon 14 c dated sequences in a bayesian framework millions of plausible age models are constructed to quantify the chronological uncertainties within and between proxy archives we test the technique on replicated high resolution 14 c dated peat cores deposited during the little ice age c ad 14001900 a period characterized by abrupt climate changes and severe 14 c calibration problems owing to internal variability in proxy data and uncertainties in age models these and possibly many more archives are not consistent in recording decadal climate change through explicit statistical tests of palaeoenvironmental hypotheses we can move forward to systematic interpretations of proxy data however chronological uncertainties of non annually resolved palaeoclimate records are too large for answering decadal timescale questions

multidisciplinary approach to reconstructing local pastoral activities an example from the pyrenean mountains pays basque in this study archaeology history and palaeoecology modern and fossil data sets of pollen and non pollen palynomorphs were used to reconstruct small scale pastoral activities in the pyrenees mountain during the last two millennia modern pollen assemblages from the major vegetation units both natural and anthropogenic are studied on one restricted watershed area a correlative model rda of 61 modern pollen spectra and 35 external variables distinguishes two groups of taxa providing information on the nature and spatial extent of human impact on the landscape the first pool indicates local pastoral activities and the second one implies regional input from outside the studied watershed and is not characteristic of a specific land use these pools are described as local pastoral pollen indicators lppi for this particular mountain region on crystalline bedrock and regional human activities pollen indicators rhapi the modern data set is used to aid interpretation of the local pollen sequence of sourzay that covers the last 2000 calendar years bp using rda reconstructions and best modern analogues as a means of comparing modern and fossil spectra the study also demonstrates agreement between the independent interpretations of two fossil proxies lppi and corophilous fungi

holocene fire related alluvial fan deposition and climate in ponderosa pine and mixed conifer forests sacramento mountains new mexico usa we employed 14c dating of alluvial fan deposits in ponderosa pine and mixed conifer forests of the sacramento mountains new mexico to document holocene fires and related geomorphic impacts rapid aggradation by charcoal rich debris flows occurred in the middle holocene 5800 4200 cal yr bp indicating episodic sedimentation following severe fires fire related deposition virtually ceased 4200 cal yr bp with most fan deposits indicating slower aggradation with cumulic soil development until 1800 cal yr bp from 1800 to 500 cal yr bp fire related sedimentation increased again although not to middle holocene levels a peak in fire related sedimentation c 650 cal yr bp corresponds to widespread severe drought in the southwestern usa limited fire related sedimentation is evident from 500 to 100 cal yr bp consistent with little ice age climate and tree ring records indicating frequent low severity fires although at least one severe fire burned in this interval increased fire related sediment

bayesian chronological analyses consistent with synchronous age of 12 835 12 735 cal b p for younger dryas boundary on four continents the younger dryas impact hypothesis posits that a cosmic impact across much of the northern hemisphere deposited the younger dryas boundary ydb layer containing peak abundances in a variable assemblage of proxies including magnetic and glassy impact related spherules high temperature minerals and melt glass nanodiamonds carbon spherules aciniform carbon platinum and osmium bayesian chronological modeling was applied to 354 dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled ydb age range for this event of 12 835 12 735 cal b p at 95 probability this range overlaps that of a peak in extraterrestrial platinum in the greenland ice sheet and of the earliest age of the younger dryas climate episode in six proxy records suggesting a causal connection between the ydb impact event and the younger dryas two statistical tests indicate that both modeled and unmodeled ages in the 30 records are consistent with synchronous deposition of the ydb layer within the limits of dating uncertainty 100 y the widespread distribution of the ydb layer suggests that it may serve as a datum layer

correction of deposit ages for inherited ages of charcoal implications for sediment dynamics inferred from random sampling of deposits on headwater valley floors abstract inherited age is defined herein as the difference between times of carbon fixation in a material and deposition of that material within sediments from which it is eventually sampled in order to estimate deposit age via radiocarbon dating inheritance generally leads to over estimation of the age by an unknown amount and therefore represents unquantified bias and uncertainty that could potentially lead to erroneous inferences inherited ages in charcoal are likely to be larger and therefore detectable relative to analytic error where forests are dominated by longer lived trees material is stored for longer periods upslope and downstream post fire delivery of that material is dominated by mass movements such as in the near coastal mountains of northwestern north america inherited age distribution functions were estimated from radiocarbon dating of 126 charcoal pieces from 14 stream bank exposures of debris flow deposits fluvial fines and fluvial gravels along a headwater stream in the southern oregon coast range usa in the region these 3 facies are representative of the nearly continuous coalescing fan fill complexes blanketing valley floors of headwater streams where the dominant transport mechanism shifts from debris flow to fluvial within each depositional unit and for each charcoal piece within that unit convolution of the calibrated age distribution with that of the youngest piece yielded an inherited age distribution for the unit fits to the normalized sums of inherited age distributions for units of like facies provided estimates of facies specific inherited age distribution functions finally convolution of these distribution functions with calibrated deposit age distributions yielded corrections to published valley floor deposit ages and residence time distributions from nearby similar sites residence time distributions were inferred from the normalized sums of distributions of 30 deposit ages at each of 4 sites 2 adjacent valley reaches 103 m long and within 102 m of 2 tributary confluences mean inherited ages from the observed distributions are 666 688 and 1506 yr for debris flow deposits fluvial fines and fluvial gravels respectively on average correction reduced estimates of individual deposit age means by a factor of 0 71 0 56 0 94 and increased standard deviations by a factor of 6 1 0 97 43 across sites mean residence times decreased by 24 0 and standard deviations by 12 5 on average corrected residence time distributions have thicker tails as indicated by gamma distribution fits with smaller shape factors and these changes are significant relative to the bootstrapped 95 confidence limits representing potential error in the sampling for inherited ages the ratio of the means of sediment age and residence time ranged from 1 03 to 1 80 across sites before correction and 1 21 to 2 18 after correction where a value of one implies that probability of evacuation from the reservoir comprising valley floor deposits is independent of time since deposition corrected values of this ratio therefore indicate that evacuation favors younger deposits at all sites whereas uncorrected results implied age independent evacuation from the more downstream valley reach

peat bank growth holocene palaeoecology and climate history of south georgia sub antarctica based on a botanical macrofossil record botanical macrofassil analysis of a more than 9000 years old radiocarbon dated peat sequence of a moss peat bank from south georgia shows a clear evolution in the vegetation seven ecological phases could be distinguished and they can be interpreted in terms of climate development during the holocene until 2200 years ago warnstorfia fontinatiopsis was the dominant moss species pointing to a wet environment lower numbers of this species in association with the presence of drier species are assumed to indicate drier periods such as occurring between ca 6000 5200 and 4400 3400 cal yr br the most prominent and definitive vegetation change took place around 2200 cal yr bp a polytilchum chollsodontium moss peat bank was formed which is still growing there today the forcing mechanism for this vegetation change is thought to be a temperature decrease rather than a precipitation decrease this conclusion is mainly based on the fact that today moss peat banks have their optimal occurrence range in the maritime antarctic a region were the mean annual temperature is ca 4 degrees c lower than on south georgia the remarkable change in the moss bank vegetation at 2200 cal yr bp raises the question whether this moment was only a short climatic deterioration or a definitive change to a cooler and wetter climate after a holocene climatic optimum period c 2008 elsevier ltd all rights reserved

environmental changes and the rise and fall of civilizations in the northern horn of africa an approach combining δd analyses of land plant derived fatty acids with multiple proxies in soil the domains of the ancient polities d mt and aksum in the horn of africa s highlands are a superior natural system for evaluating roles of environmental change on the rise and fall of civilizations to compare environmental changes of the times of the two polities we analyzed stable hydrogen isotopic ratios d of land plant derived fatty acids n c26 30 and other proxies from soil sequences spanning the holocene from the region three results suggest that trends in d values unambiguously reflect changes in rainfall first increases in d coincide with dry periods inferred from studies of eastern african lakes second changes in d values were parallel among sections during overlapping time intervals third consideration of vegetation history did not alter directions of trends in d values over time by unambiguously recording precipitation the d values also enhanced interpretations of proxies that are affected by both climate and land clearing both d mt ca 2750 2350 cal y bp and the aksumite ca 2100 1250 cal y bp rose during wetter intervals of the drier part of the holocene after ca 6000 cal y bp analyses of charred matter indicated that fire had been a common agent of land clearing in all sites the influence of climate on fire varied however prior to the emergence of d mt d values were correlated with c4 c3 plant ratios estimated from 13c values there are no c4 trees and precipitation may have been the main influence on canopy openness after ca 4300 cal y bp there was no significant relationship between d and c4 c3 plant ratios suggesting that factors such as fire influenced canopy openness regardless of climate furthermore the impact of land clearance differed between sites and between d mt and the aksumite s times in one site the interval from 3550 cal y bp to the decline of d mt had several anomalies that suggested dramatic increases in thermal severity of fire and human impact among these were a large contribution of charred matter to a high total organic carbon that low hydrogen and oxygen indices suggest was severely altered by other factors than humification these results support hypotheses about the rise of civilizations being favored by specific climatic conditions but suggest that patterns of land clearing differed during the declines of d mt and the aksumite

holocene environmental change at laguna saladilla coastal north hispaniola abstract we inferred environmental changes over the middle to late holocene in coastal north hispaniola using pollen microscopic charcoal mollusk shells and diatoms in an 8 5 m sediment core from laguna saladilla dominican republic 19 39 n 71 42 w 2 m above sea level changes in rhizophora red mangrove pollen percentages and in mollusk and diatom assemblages indicate major changes in salinity and water depth related to relative sea level rise and possible shifts in precipitation rhizophora percentages were highest at 7650 cal yr bp when mollusk shells indicate the lake was connected to the atlantic ocean laguna saladilla became progressively brackish ca 3500 cal yr bp and transitioned ca 2500 cal yr bp to its current freshwater condition high percentages of amaranthaceae pollen and increased charcoal concentrations over the last ca 2500 years signal dry climate and increased fires in coastal north hispaniola geomorphological changes over time at laguna saladilla partially mask evidence of climate change in the proxies examined and the record is equivocal before 2500 cal yr bp evidence for drier conditions since 2500 cal yr bp is consistent with late holocene shifts in the mean position of the intertropical convergence zone itcz that have been identified on the caribbean side of hispaniola we interpret the record as indicating that itcz migratory dynamics may also have affected precipitation on the atlantic edge of the greater antilles

chronological constraints on cordilleran ice sheet glaciomarine sedimentation from core md02 2496 off vancouver island western canada chronology based on 46 radiocarbon dates has been generated for md02 2496 western vancouver island canada subsequent correlation between glaciomarine sedimentary sequences within the core and the terrestrial stratigraphy of the cordilleran ice sheet for the last 50 ka provide new insight into cordilleran ice sheet processes glaciomarine sedimentation associated with the most recent advance fraser glaciation of the cordilleran ice sheet began at 30 5 cal kyr bp 25 14 c kyr bp extremely high sedimentation rates indicate the ice sheet became proximal to the site at 19 5 cal kyr bp 16 14 c kyr bp deposition of ice rafted detritus ird began at 17 cal kyr bp 14 14 c kyr bp and abruptly terminated at 16 2 cal kyr bp 13 5 14 c kyr bp indicating rapid regional ice sheet retreat a minor ird event followed at 14 7 cal kyr bp 12 5 14 c kyr bp glaciomarine sediment deposition abruptly ended at 10 2 cal kyr bp 8 8 14 c kyr bp with the resumption of biogenic sedimentation the olympia interstade is represented by an interval of hemipelagic sedimentation between 43 and 31 5 ka prior to 45 ka sediment deposition is controlled by glaciomarine processes with evidence for a significant ird event at 47 cal kyr bp 44171 06 14 c kyr bp

laboratory and field determinations of small strain shear modulus for a structured champlain clay values of small strain shear modulus gmax for a champlain sea clay deposit were obtained both under an embankment built 18 years ago and outside of the area influenced by this embankment the sma

a 15 000 year record of vegetation and climate change from a treeline lake in the rocky mountains wyoming usa future climate projections predict warming at high elevations that will impact treeline species but complex topographic relief in mountains complicates ecologic response and we have a limited number of long term studies examining vegetation change related to climate in this study pollen and conifer stomata were analyzed from a 2 3 m sediment core extending to 15 330 cal yr bp recovered from a treeline lake in the rocky mountains of wyoming both pollen and stomata record a sequence of vegetation and climate change similar in most respects to other regional studies with sagebrush steppe and lowered treeline during the late pleistocene rapid upward movement of treeline beginning about 11 500 cal yr bp treeline above modern between 9000 and 6000 cal yr bp and then moving downslope 5000 cal yr bp reaching modern limits by 3000 cal yr bp between 6000 and 5000 cal yr bp sediments become increasingly organic and sedimentation rates increase we interpret this as evidence for lower lake levels

evolution of a high latitude sediment drift inside a glacially carved trough based on high resolution seismic stratigraphy kveithola nw barents sea abstract kveithola is a glacially carved e w trending trough located in the nw barents sea an epicontinental shelf sea of the arctic ocean located off northern norway and russia a set of confined sediment drifts the kveithola drift is located in the inner part of the trough in general drift deposits are commonly characterized by high lateral continuity restricted occurrence of hiatuses and relatively high accumulation rates and thus represent excellent repositories of paleo environmental information we provide for the first time a detailed morphological and seismostratigraphic insight into this sediment drift which is further supported by some preliminary lithological and sedimentological analyses the complex morphology of the drift imaged by combining all available multibeam data includes a main and a minor drift body two drift lenses in the outer part of the trough more or less connected drift patches in the innermost part and small perched sediment patches in a structurally controlled channel to the north the seismic parasound data show that the main and minor drift bodies are mainly well stratified characterized by sub parallel reflections of moderate to high amplitude and good lateral continuity the reflectors show an abrupt pinch out on the northern edge where a distinct moat is present and a gradual tapering to the south internally we identify the base of the drift and four internal horizons which we correlate throughout the drift two units display high amplitude reflectors marked lensoidal character and restricted lateral extent suggesting the occurrence of more energetic sedimentary conditions facies typical for contourite deposition are found in the sediment cores with strongly bioturbated sediments and abundant silty sandy mottles that contain shell fragments these characteristics along with the morphological and seismic information suggest a strong control by a bottom current flowing along the moat on the northern edge of the drift though both atlantic and arctic waters are known to enter the trough from the west and the north respectively brine enriched shelf water bsw produced during winter and flowing westward in the moat is suggested to be responsible for the genesis of the kveithola drift the formation of bsw is inferred to have started around 13 cal ka bp the onset of drift deposition suggesting that conditions leading to atmospheric cooling of the surface waters and or the presence of coastal polynyas and wind or floating ice shelves have persisted on the western barents shelf since that time the units inferred to have been deposited under more energetic sedimentary conditions tentatively dated to the younger dryas and to 8 9 8 2 cal ka bp are suggestive of stronger bsw formation in general we infer that variations in the bottom current regime were mainly related to bsw formation due to atmospheric changes they could also have been a response to successive episodes of grounded and sea ice retreat that allowed for a first limited later open shelf current which progressively established on the western barents sea shelf

quantitative refinement of calibrated 14c distributions abstract a new method is presented for using known ordering or other relationships between 14c samples to reduce 14c dating uncertainty the order of sample formation is often known from for example stratigraphic superposition dendrochronology or crosscutting field relations constraints such as a minimum time between dates and limits from historical information are also readily included dendrochronologically calibrated calendric date histograms initially represent each date the method uses bayes theorem and the relational constraints to upweight date ranges in each date distribution consistent with the other date distributions and the constraints and downweight unlikely portions the reweighted date distributions retain all dating possibilities present in the initial calibrated date distributions but each date in the result now reflects the extra information such as ordering supplied through the constraints in addition one may add information incrementally and thus analyze systematically its effect on all the date distributions thus the method can be used to assess the consistency of the quantitative data at hand the bayesian approach also uses the empirical calibrated date distributions directly so information is not lost prematurely by summarized dates to a mean and variance or confidence intervals the approach is illustrated with data from two densely sampled paleoseismic sites on the san andreas fault in southern california an average reduction in 14 c date distribution variance of 59 is achieved using ordering information alone and 85 is achieved by also applying sedimentation rate constraints and historical information

late holocene paleoenvironmental change at mid elevation on the caribbean slope of the cordillera central dominican republic a multi site multi proxy analysis abstract high resolution proxy records from the circum caribbean region indicate significant variation in late holocene climate especially precipitation attributed primarily to shifts in the mean annual position of the intertropical convergence zone itcz the paleoenvironmental and cultural impacts of this late holocene climate variability have been analyzed intensively in the western caribbean and to a lesser extent in the southern caribbean however the occurrence and impacts of late holocene climate shifts in the eastern caribbean especially in island interiors has not been well documented here we present sediment records of late holocene paleoenvironmental change from two lakes located on the caribbean slope of the cordillera central in the dominican republic that span the last 3000 years sediment characteristics pollen charcoal biogenic carbonate assemblages and isotopic composition and bulk sedimentary carbon isotope values in laguna castilla and laguna de salvador indicate extreme shifts in hydrology vegetation and disturbance regimes in response to climate change and human activity in the lake watersheds close correspondence between the hydrological histories of the lakes and trace metal concentrations in sediments of the cariaco basin indicate that precipitation variability here responds to the same controls and may similarly reflect shifts in the mean annual position of the itcz human occupation of the watersheds appears to be closely linked to severe dry periods and may indicate larger scale cultural responses to precipitation variability on the island of hispaniola prehistoric human populations strongly affected vegetation and disturbance regimes in the lake watersheds impacts may have lasted several centuries and may have been more severe than impacts of modern populations

sedimentary evidence of landscape and climate history since the end of mis 3 in the krkonose mountains czech republic abstract a sedimentary core recovered from the cirque basin of labsk d l valley 1039 m a s l in the krkonose mountains reflects the environmental history for approximately the last 30 000 years analyses of magnetic susceptibility carbon content pollen assemblages and macrofossil data in a 15 m thick sediment sequence provide the first continuous record of lateglacial and holocene vegetation history in sudetes region of the czech republic the succession of sedimentary units in the lower part of the core suggests that the cirque was ice free before the onset of the last glaciation at the beginning of marine isotope stage 2 highly variable climate prevailed during this period with cold conditions culminating about 18 cal ka bp cold climates persisted until the lateglacial period evidenced by an identified warming and subsequent cooling event correlated with the younger dryas period sparse treeless vegetation dominated in the catchment area at that time the sequence of interrupted thinly laminated silts reflects the retreat and temporary readvance of a local glacier in the cirque during 12 5 10 8 cal ka bp subsequently the alpine treeline ecotone gradually shifted above the cirque floor palaeoclimatic conditions in the early holocene fluctuated strongly whereas since 5 1 cal ka bp conditions have been more stable pollen based climate reconstructions suggest significant cooling at around 9 8 9 3 7 7 7 5 and 4 0 3 3 cal ka bp spruce forests have dominated the site since 5 0 cal ka bp when the vegetation became similar to the modern one two phases of increased sedimentation were identified within the holocene culminating about 9 2 7 5 cal ka bp and 5 8 5 5 cal ka bp sediment yield was as high as 2 4 mm yr 1 during the period reflecting environmental changes during the atlantic sub boreal transition

10 be exposure dating of the timing of neoglacial glacier advances in the ecrins pelvoux massif southern french alps alpine glacier variations are known to be reliable proxies of holocene climate here we present a terrestrial cosmogenic nuclide tcn based glacier chronology relying on 24 new be 10 exposure ages which constrain maximum neoglacial positions of four small to mid sized glaciers rateau lautaret bonnepierre and etages in the ecrins pelvoux massif southern french alps glacier advances marked by mainly lateral moraine ridges that are located slightly outboard of the little ice age lia c 1250 1860 ad maximum positions were dated to 4 25 0 44 ka 3 66 0 09 ka 2 09 0 10 ka c 1 31 0 17 ka and to 0 92 0 02 ka the 4 2 ka advance albeit constrained by rather scattered dates is to our knowledge exposure dated here for the first time in the alps it is considered as one of the first major neoglacial advance in the western alps in agreement with other regional paleoclimatological proxies we further review alpine and northern hemisphere mid to high latitude evidence for climate change and glacier activity concomitant with the 4 2 ka event the 2 1 ka advance was not extensively dated in the alps and is thought to represent a prominent advance in early roman times other neoglacial advances dated here match the timing of previously described alpine neoglacial events our results also suggest that a neoglacial maximum occurred at etages glacier 0 9 ka ago i e during the medieval climate anomaly mca c 850 1250 ad at rateau glacier discordant results are thought to reflect exhumation and snow cover of the shortest moraine boulders overall this study highlights the need to combine several sites to develop robust neoglacial glacier chronologies in order to take into account the variability in moraine deposition pattern and landform obliteration and conservation

the use of summed radiocarbon probability distributions in archaeology a review of methods abstract using a database of australian archaeological radiocarbon dates n 2996 this paper explores three key methodological issues associated with the use of summed probability plots of radiocarbon data 1 the minimum sample size needed for a statistically reliable plot 2 the effect of radiocarbon calibration on the structure of these plots and 3 the application of a taphonomic correction to such time series data the results identify several protocols recommended as best practice when using summed probability plots 1 a minimum sample size of 500 radiocarbon dates should be used and the sample size and the mean of the standard deviations of the radiocarbon dates t in the sample should both be reported 2 a moving average trendline of 500 800 years should be used to offset the effects of the calibration process and 3 surovell et al correcting temporal frequency distributions for taphonomic bias journal of archaeological science 36 2009 1715 1724 is explored with modifications and temporal limits

late holocene paleoenvironmental history of bioluminescent laguna grande puerto rico abstract coastal lagoons are valuable natural resources and ecotourism hotspots that are at great risk due to human development and global climate change in order to protect these resources it is important that we fully understand the paleoenvironmental history of these unique ecosystems and their sensitivity to environmental change here we present a multi proxy pollen charcoal grain size dinoflagellate cyst stable isotope geochemistry and foraminifera 3600 cal yr b p record of paleoenvironmental change for laguna grande puerto rico which is a particularly unique coastal lagoon as it contains high abundances of the bioluminescent dinoflagellate pyrodinium bahamense sedimentary evidence indicates that the laguna grande basin began accumulating sediment 3600 cal yr b p coincident with regional sea level rise but the modern lagoon itself is geologically quite young and did not become fully enclosed until 575 cal yr b p due to longshore depositional processes and mangrove swamp development foraminifera assemblages suggest a potential breach of a protective barrier 1550 cal yr b p perhaps as a result of a tropical storm or tsunami and is coincident with an increase in fire activity only two high energy depositional units tempestites could be identified in the lagoon sediments over the last 575 cal yr b p indicating minimal impact by tropical storms or tsunamis on the lagoon since isolation from the open ocean fossil dinoflagellate cyst concentrations and influxes do not approach modern levels until 200 cal yr b p and are currently at the highest levels in the history of the lagoon indicating the lagoon may have become bioluminescent only recently perhaps as a result of anthropogenic nutrient additions sedimentation rates support this hypothesis indicating a recent tripling of sedimentation rates when compared to millennial scale sedimentation rates this study highlights the utility of paleolimnological data in the management and preservation of at risk coastal lagoon ecosystems

the effect of the yield and plastic potential deviatoric surfaces on the failure height of an embankment the paper investigates the effect of the deviatoric shape of the yield and plastic potential surfaces on the failure height of an embankment founded on a soft clay deposit different combinations of the shapes of the surfaces in the deviatoric plane are explored in a critical state model that predicts isotropic strength and which is used in order to model the clay foundation the shapes considered start from the widely used circular shape and move on to the mohr coulomb hexagon and advanced shapes such as the lade shape for all combinations the same undrained strength profile in triaxial compression is adopted for the clay foundation finite element analyses investigate the failure height of the embankment assuming plane strain conditions moreover two ways of modelling the fill material are adopted in the analyses and the effect of each of these on the failure height of the embankment is explored

a mid to late holocene history of floodplain and terrace reworking along the middle delaware river valley usa abstract this study tests and refines the traditional floodplain development model for the partly confined middle delaware river valley which has shown that the main channel was relatively stable and flanked by a 6000 8000 year old vertically accreting alluvial terrace the holocene alluvial processes and history presented here in 6 fluvial phases were reconstructed using morphostratigraphy 36 profile descriptions 332 grain size analyses and 82 14 c ages from soil trenches auger borings and archaeological excavations fluvial phases i iii largely validate previous reconstructions showing a late pleistocene i 10 7 ka braided stream transition into an early holocene wandering stream with prolonged floodplain stability ii 10 7 8 ka followed by early middle holocene erosion and then deposition iii 8 5 ka the early and middle holocene changes in alluvial stratigraphy and sedimentology broadly correlate with climatically derived holocene subdivisions suggesting climate change partly controls alluvial response along the middle delaware river valley this study documents for the first time a middle holocene episode of channel incision occurring sometime between 6 0 and 5 0 ka although the results reconfirm that the majority of alluvial landforms are composed of vertical accretion deposits we present here new evidence of oblique abandoned channel and lateral accretion deposits inset to similar landforms with different formation histories i e polycyclic terrace development depicting a river valley that has experienced floodplain and terrace reworking the majority of floodplain and terrace reworking occurs during the late middle and late holocene phases iv vi 5 5 0 ka following the middle holocene incision event these phases demonstrate floodplain reworking processes in the form of channel abandonment stripping flood channeling and convex bank erosion the subsequent space filled rapidly with evidence of multistory soil formation and eventually resulted in alluvial fill terraces with heights comparable to older surfaces the most recent fluvial phase vi 1 0 0 ka shows markedly faster sedimentation rates and coarser flood deposits associated with peak prehistoric population and the onset of euroamerican settlement the results presented here contribute newly documented evidence of erosion and depict a river valley that has undergone middle holocene incision and floodplain and terrace reworking since the late middle holocene stream modelers fluvial geomorphologists and geoarchaeologists working in the ne usa should consider floodplain reworking processes when examining alluvial history and predicting changes in stream dynamics

holocene sedimentation in the skagerrak interpreted from chirp sonar and core data high resolution chirp sonar profiling in the northeastern skagerrak shows acoustically stratified sediments draping a rough surfaced substratum a 32 metre long sediment core retrieved from the survey area encompasses the entire holocene and latest pleistocene the uppermost seismo acoustic units in the chirp profiles represent holocene marine sediments the lowermost unit is interpreted as ice proximal glacial marine sediments rapidly deposited during the last deglaciation the end of ice proximal sedimentation is marked by a strong reflector interpreted to have been formed during latest pleistocene time as a consequence of rapid ice retreat and drastically lowered sedimentation rate the subsequent distal glacial marine sediments were deposited with initially high sedimentation rates caused by an isostatic rebound associated sea level fall based on correlation between the core and the chirp sonar profiles using measured sediment physical properties and ams 14 c dating we propose a revised position for the pleistocene holocene boundary in the seismo acoustic stratigraphy of the investigated area copyright 2005 john wiley sons ltd

basin wide sedimentation changes and deglacial lake level rise in the hovsgol basin nw mongolia abstract a study of 15 gravity cores reveals consistent patterns of lithologic change throughout the lake hovsgol basin sediments of the last glacial are composed of calcareous clayey silt with an admixture of coarse material from sand to gravel during the last deglaciation a basin wide deposition of finely laminated carbonate mud took place and was ultimately succeeded by the deposition of diatomaceous clayey ooze during the entire holocene interval diatom productivity in lake hovsgol during the early holocene was higher than today but declined by ca 6 6 cal ka bp sedimentation rate estimates for post glacial section range from 1 5 to over 6 7 cm ka for different parts of lake hovsgol rates appear to have decreased in the late holocene the last glacial maximum lgm corresponded to a dramatic low stand of lake hovsgol on the order of 100 m below today s level as reflected by littoral facies retrieved in cores from intermediate depths age dating of plant fragments in these sediments suggests that lake level started rising no later than 15 4 cal ka bp by the beginning of the holocene lake hovsgol evolved from a low level closed basin lake to an overflowing freshwater lake the observed dramatic lithologic change and evidence for lake level change suggest that lake hovsgol may in fact serve as a sensitive water gauge in continental interior asia and that the hovsgol sedimentary record preserves reliable proxies for past changes in effective moisture balance in the lake baikal catchment area

late holocene vegetation dynamics on an atlantic mediterranean mountain in nw iberia abstract detailed studies on the late holocene vegetation dynamics of the mountains of nw iberia are rare furthermore the impact of human activities and changes in fire activity on the natural vegetation are not well known over these areas in order to improve the knowledge on these topics pollen and charcoal analyses were conducted on two new sedimentary sequences from the teleno mountains between ca 4500 and 3200 cal yr bp pinus type sylvestris and betula dominated the forests that covered the uplands of the teleno mountains at this point this pine birch forest was replaced with heathlands and grasslands which persisted during all the iron age and the roman period until ca 1500 cal yr bp this abrupt deforestation process could be caused by fire grazing and or mining activities linked to the exploitation of the metal resources of these mountains around 1250 cal yr bp a betula forest established in the uplands of the teleno mountains probably following a decrease in human activities the gradual rise in regional population density since ca 300 200 cal yr may be linked to the increase in fire activity that triggered the replacement of birch forest with heathlands lastly the extent of the pinus pinaster dominated forests in the lowlands is an illustrative example of how the economic activities of the local human population have controlled the vegetation cover in this area as it is very clear in the pollen record the recovery of natural p pinaster forests since ca ad 1900 associated to the start of resin exploitation

the intercept is a poor estimate of a calibrated radiocarbon age intercept based methods of generating a point estimate of a calibrated radiocarbon date are very popular but exhibit undesirable behaviour they are highly sensitive to the mean of the radiocarbon date and to adjustments of the calibration curve other methods give more stable results the weighted average of the probability distribution function is recommended as the best central point estimate but more consideration should be given to using the full probability distribution rather than a point estimate in developing age depth models

multi proxy evidence of rainfall variability recorded in subaqueous deltaic deposits off the adra river southeast iberian peninsula highlights multi proxy evidence of rainfall variability in subaqueous deltaic deposits low absolute abundances related with rainfall driven periods of increase supply raise of colonizers and opportunistic species during dry periods human activities led to a drastic reduction of sedimentation rates abstract the adra river deltaic system southeast iberian peninsula shows a steep topography and is subjected to strong climatic seasonality this system has been affected by alternating wet and dry periods and it has also undergone numerous anthropogenic activities such as deforestation mining activities river channel deviations and dam construction particularly during the last two centuries two sediment cores were retrieved off the adra river from the western ms v9 and eastern ms v4 lobes of the subaqueous deltaic deposit a multi proxy study was carried out including grain size benthic foraminiferal assemblages magnetic susceptibility and geochemical element analyses in order to understand the sedimentary expression of recent climatic cycles and anthropogenic interventions in the river basin periods of increased deposition of coarse grained sediments low absolute abundance of benthic foraminifera and high elemental ratios indicative of terrigenous contributions were interpreted as periods of increased sediment supply to the shelf four flooding events were recorded in core ms v9 and three events on core ms v4 of which two were observed in both cores they were related to periods with major floods that were documented on the southern iberian peninsula around 1770 1810 and 1860 1870 ad on the other hand sediment core intervals exhibiting increasing proportion of fine grained sediments and higher abundances of foraminiferal species assigned as successful colonizers textularia earlandi and opportunistic species that feed on bacteria or terrestrial organic matter bolivina ordinaria bulimina elongata eggerelloides scaber and ammonia beccarii or tepida indicate the establishment of new environments with new ecological constraints they were related to significant decreases of terrigenous sediment input during low rainfall or dry periods the increase of opportunistic species feeding on fresh phytodetritus nonionella iridea nonionella stella nonionella sp brizalina dilatata epistominella vitrea and bolivinellina pseudopuntata under more stable environmental conditions also point to a stronger marine influence on the prodeltaic environments during these periods the human interventions on the river basin after 1872 ad with the deviation of the main river channel to the east led to a drastic reduction of the sediment exported to the western delta lobe this study showed that the sedimentation on the adra subaqueous deltaic deposit was mainly controlled by rainfall variability from 1663 to 1872 ad and afterwards by anthropogenic interventions

the use of bomb spike calibration and high precision ams 14c analyses to date salt marsh sediments deposited during the past three centuries abstract a combination of bomb spike calibration and conventional calibration of ams 14c dating has been used to determine a detailed age depth model for a 1 m sediment section collected from a salt marsh in poole harbour southern england these data were compared with the chronology obtained from 210pb analysis and 137cs age markers we report post bomb values of over 1 46 f14c 146 modern 14c and both the rising and falling limbs of the atmospheric bomb spike are identified five pre bomb samples were analysed using multi target high precision 2 ams analysis and after the replicates were combined the one sigma uncertainty was as low as 9 14c yr on some ages these data and an additional three normal precision pre bomb 14c samples were calibrated using calib 5 0 and the chronology constrained using the prior knowledge of independent age markers obtained from the analysis of pollen and spheroidal carbonaceous particle scps no agreement was found between the 14c bomb spike dates and the crs 210pb chronology modelled for this sequence in addition poor agreement was found between the signal of the 1960s weapons test fallout indicated by the 14c bomb spike dates and the timing suggested by the 137cs data this disagreement is attributed to the influence of the local discharge of 137cs from the former ukaea site at winfrith we use our new chronology to confirm the existence of an acceleration in sedimentation rates in poole harbour during the last 100 yr previously reported for this site by long et al long a j scaife r g edwards r j 1999 pine pollen in intertidal sediments from poole harbour uk implications for late holocene sediment accretion rates and sea level rise quaternary international 55 3 16 and conclude that bomb spike 14c calibration dating may offer a more robust alternative to the use of 210pb chronologies for dating sediment deposition in salt marsh environments in addition we demonstrate how the use of high precision ams analysis has the potential for reducing some of the uncertainties involved in the high resolution dating of recent salt marsh sediments

marine calcium carbonate preservation vs climate change over the last two millennia in the fram strait implications for planktic foraminiferal paleostudies abstract we present a high resolution study of planktic foraminiferal distribution patterns in a deep sea core from the eastern fram strait position 78 55 n 06 46 e water depth 1497 m the sediment core is located below atlantic water masses flowing into the arctic ocean and spans the last 2400 years the investigation is based on planktic foraminiferal species distribution stable isotopes and sedimentological data the mean shell weight of neogloboquadrina pachyderma fragmentation organic and inorganic carbon content and the presence of benthic organic linings were also investigated as an indication of preservation changes the results indicate that the planktic foraminifera are affected by dissolution and point to five periods of especially poor preservation at 200 bce 300 650 ce 700 850 ce 1400 1500 ce and from 1800 ce to present in the last century small and fragile subpolar species turborotalita quinqueloba and globigerinita uvula are preserved the increased percentage of these subpolar species together with increases in the caco 3 toc and total foraminiferal flux would point to surface water warming however our data suggest that these fragile species may not have been preserved in sediments older than 1900 ce due to selective dissolution consequently the magnitude of the previously recorded recent surface water warming in the fram strait may be overestimated

pore pressure response to barometric pressure change in champlain clay prediction of the clay elastic properties abstract champlain sea clay deposits play a crucial role in limiting contaminant migration to underlying aquifers in the saint lawrence river valley champlain sea clays are well known as being prone to landslide and sample disturbance estimation of their elastic properties using their in situ loading efficiency would provide mechanical properties for the soil dynamic analyses and immediate settlement calculations encountered in geotechnical projects determination of loading efficiency can be envisioned as a very small strain test in this paper we describe a detailed monitoring program for 10 vibrating wire piezometers installed within sealed boreholes on 5 study sites near montreal in quebec canada the pore pressure response to barometric pressure variation was analyzed with three methods linear regression visual inspection and multiple regression which gave loading efficiencies between 0 7 and 0 95 these values were then used to estimate the elastic properties of the clay formation vertical compressibility and specific storage on the order of 1 10 6 kpa 1 and 1 10 5 m 1 were respectively obtained for most of the monitoring sites a comparison of compressibility values derived from the in situ loading efficiency method with those obtained with pressuremeter oedometer and pulse tests confirmed that clay compressibility is strain dependent the pore pressures measured on the study sites have been corrected by applying the multiple regression and visual inspection methods for most piezometers both methods provided nearly identical results however for deep piezometers the multiple regression method provided smoother pore pressure time series than the visual inspection method the vertical hydraulic gradient obtained with corrected pressure data was shown to change significantly on some test sites during the monitoring period

mid holocene coral community data as baselines for understanding contemporary reef ecological states land use changes and associated deteriorations in water quality are cited as major drivers of marine ecosystem change and can modify community abundance and diversity on coral reefs this study uses palaeoecological data derived from a mid holocene age coral reef in the wet tropics region of australia s great barrier reef to develop a record of coral community composition and diversity from a period that significantly pre dates european settlement in the region major changes in catchment sediment and nutrient yields since european settlement have been documented and thus the data presented provides a baseline against which to compare contemporary ecological datasets natural variations in coral assemblage composition as preserved in core records clearly occurred in this mid holocene reef and were associated with the reef shallowing to sea level as it accreted vertically comparisons between modern and mid holocene coral community data from equivalent water depths did not reveal marked shifts in coral community composition and diversity suggesting the long term persistence of a resilient coral assemblage over these time periods

holocene development of boreal forests and fire regimes on the kenai lowlands of alaska several studies have noted a relationship between vegetation type and fire frequency yet despite the importance of ecosystem processes such as fire the long term relationships between disturbance climate and vegetation type are incompletely understood we analysed pollen plant macrofossils and sedimentary charcoal from three lakes within the kenai lowlands to determine postglacial relationships between disturbance climate and vegetation for the boreal forest of southwest alaska an herb tundra was established in the lowlands following deglaciation by 13 000 cal bp salix alnus and probably betula kenaica expanded in the area after 10 700 cal bp followed by picea glauca by 8500 cal bp picea mariana became established by 4600 cal bp the early holocene was probably the driest time during the postglacial as determined by aquatic plant macrofossils and climate models lake levels reached near modern conditions by at least 8000 cal bp mean fire intervals mfi were longest during the shrubherb tundra phase 1389 65 yr decreased after expansion of b kenaica salix and populus 779 49 yr and picea glauca 819 41 yr and increased again with the arrival of p mariana 1309 66 yr unlike previous studies our data demonstrate the highest fire frequencies during the early to mid holocene and less frequent fire during the late holocene when p mariana forests dominated the lowlands early holocene forests of p glauca and b kenaica existed in summers that were longer and drier than today while the increasingly wetter and cooler climates of the late holocene probably hindered forest fire around paradox lake perhaps because of less frequent summer drought

new perspectives on holocene flooding in ireland using meta analysis of fluvial radiocarbon dates turner j n macklin m g jones a f lewis h 2010 new perspectives on holocene flooding in ireland using meta analysis of fluvial radiocarbon dates catena 82 3 183 190 sponsorship wag hefcw

forest vegetation change and disturbance interactions over the past 7500 years at sasquatch lake columbia mountains western canada abstract fire is the most important abiotic disturbance in the interior cedar hemlock ich and engelmann spruce subalpine fir essf forest zone of southeastern british columbia canada other disturbances are also important such as defoliator and boring insect outbreaks windthrow diseases and rapid mass movements few studies have examined the interaction between multiple types of disturbances in these forests over long timescales here we present high resolution analyses of biomass burning erosion and vegetation assemblage changes at sasquatch lake nel02 a valley lake in the columbia mountains the 531 5 cm sediment core was radiocarbon dated and provided a 7500 year stratigraphy that was used for pollen macroscopic charcoal 150 m and sedimentologic analyses pollen and charcoal data provided evidence of forest composition changes and fire activity magnetic susceptibility loss on ignition and particle size distribution analyses characterised changes in erosion into the basin the results show that coniferous forests with a high abundance of pinus pollen had established in the catchment by the beginning of the record and were subject to intermittent burning and high energy erosive events tsuga heterophylla expanded by 4400 cal bp and the modern interior cedar hemlock forests expanded throughout the lower elevations due to increased regional continentality since 4500 cal bp high energy erosional inputs to the lake were less frequent from 3500 to 750 cal bp and rapid mass movements may have increased in frequency during the little ice age dendrochronological evidence in these stands suggests a mixed severity fire regime during past 300 years which has not been fully examined for charcoal based fire event reconstruction here we use identified peaks as an indicator of increased biomass burning and charcoal movement in the catchment in relation to peaks in allochthonous clastic material to understand the potential relationships between biomass burning and erosion events at multiple temporal scales in the catchment this suggests that post fire conditions up to several decades were subject to increased erosion to the lake and erosion events were more common during the early holocene establishment of dense essf and ich forests decreased siliciclastic input to the lake throughout the mid holocene until a recent rockslide the high resolution sampling of this lake sediment record provides long term evidence of variability in the relationships between vegetation cover fire and erosion at a catchment scale

paleoenvironmental records of water level and climatic changes from the middle to late holocene at a lake erie coastal wetland ontario canada pollen and diatom assemblages and peat stratigraphies from a coastal wetland on the northern shore of lake erie were used to analyze water level and climatic changes since the middle holocene and their effects on wetland plant communities peat deposition began 4700 cal yr b p during the nipissing ii transgression which was driven by isostatic rebound at that time a diatom rich wild rice marsh existed at the site water level dropped at the end of the nipissing rise at least 2 m within 200 yr leading to the development of shallower water plant communities and an environment too dry for most diatoms to persist the sharp decline in water level was probably driven primarily by outlet incision but climate likely played some role the paleoecological records provide evidence for post nipissing century scale transgressions occurring around 2300 1160 700 and 450 cal yr b p the chronology for these transgressions correlates with other studies from the region and implies climatic forcing peat inception in shallow sloughs across part of the study area around 700 cal yr b p coincides with the little ice age these records considered alongside others from the region suggest that the little ice age may have resulted in a wetter climate across the eastern great lakes region

the beaver meadow complex revisited the role of beavers in post glacial floodplain development we evaluate the validity of the beaver meadow complex hypothesis used to explain the deposition of extensive fine sediment in broad low gradient valleys previous work establishes that beaver damming forms wet meadows with multi thread channels and enhanced sediment storage but the long term geomorphic effects of beaver are unclear we focus on two low gradient broad valleys beaver meadows and moraine park in rocky mountain national park colorado usa both valleys experienced a dramatic decrease in beaver population in the past century and provide an ideal setting for determining whether contemporary geomorphic conditions and sedimentation are within the historical range of variability of valley bottom processes we examine the geomorphic significance of beaver pond sediment by determining the rates and types of sedimentation since the middle holocene and the role of beaver in driving floodplain evolution through increased channel complexity and fine sediment deposition sediment analyses from cores and cutbanks indicate that 33 50 of the alluvial sediment in beaver meadows is ponded and 28 40 was deposited in channel in moraine park 32 41 is ponded sediment and 40 52 was deposited in channel radiocarbon ages spanning 4300 years indicate long term aggradation rates of 0 05 cm yr 1 the observed highly variable short term rates indicate temporal heterogeneity in aggradation which in turn reflects spatial heterogeneity in processes at any point in time channel complexity increases directly downstream of beaver dams the increased complexity forms a positive feedback for beaver induced sedimentation the multi thread channel increases potential channel length for further damming which increases the potential area occupied by beaver ponds and the volume of fine sediment trapped channel complexity decreased significantly as surveyed beaver population decreased beaver meadows and moraine park represent settings where beaver substantially influence post glacial floodplain aggradation these findings underscore the importance of understanding the historical range of variability of valley bottom processes and implications for environmental restoration copyright 2011 john wiley sons ltd

paleofire reconstruction for high elevation forests in the sierra nevada california with implications for wildfire synchrony and climate variability in the late holocene abstract here we present two high resolution records of macroscopic charcoal from high elevation lake sites in the sierra nevada california and evaluate the synchroneity of fire response for east and west side subalpine forests during the past 9200 yr charcoal influx was low between 11 200 and 8000 cal yr bp when vegetation consisted of sparse pinus dominated forest and montane chaparral shrubs high charcoal influx after 8000 cal yr bp marks the arrival of tsuga mertensiana and abies magnifica and a higher than present treeline that persisted into the mid holocene coeval decreases in fire episode frequency coincide with neoglacial advances and lower treeline in the sierra nevada after 3800 cal yr bp independent fire response occurs between 9200 and 5000 cal yr bp and significant synchrony at 100 to 1000 yr timescales emerges between 5000 cal yr bp and the present especially during the last 2500 yr indistinguishable fire return interval distributions and synchronous fires show that climatic control of fire became increasingly important during the late holocene fires after 1200 cal yr bp are often synchronous and corroborate with inferred droughts holocene fire activity in the high sierra nevada is driven by changes in climate linked to insolation and appears to be sensitive to the dynamics of the el nino southern oscillation

minimizing the edge effect in environmental reconstructions by trimming the calibration set chironomid inferred temperatures from spitsbergen a core from lake skardtjorna on western spitsbergen was analysed for subfossil chironomids with the aim of inferring past temperatures the core spans the last 1760 years and has a low concentration and low diversity of chironomids three taxa dominate the record oliveridia tricornis micropsectra radialistype and m insignilobus type the latter not previously recorded on svalbard compared with the full norwegian modern climate chironomid calibration data set skardtjorna is at the coldest end of the modern temperature gradient in an attempt to decrease potential bias caused by the numerical edge effect and to improve the taxon response functions the training set was trimmed by excluding lakes dissimilar to the study site two trimming approaches are tested in the first lakes at the warm end of the gradient are excluded in the second the calibration data set lakes are partitioned by twinspan on the basis of their modern chironomid assemblages and lakes most dissimilar to skardtjorna are exclude

tephrostratigraphy chronology and climatic events of the mediterranean basin during the holocene an overview the identification and characterisation of high frequency climatic changes during the holocene requires natural archives with precise and accurate chronological control which is usually difficult to achieve using only 14c chronologies the presence of time spaced tephra beds in quaternary mediterranean successions represents an additional independent tool for dating and correlating different sedimentary archives these tephra layers are potentially useful for resolving long standing issues in paleoclimatology and can help towards correlating terrestrial and marine paleoclimate archives known major tephras of regional extent derive from central and southern italy the hellenic arc and from anatolia a striking feature of major holocene tephra deposition events in the mediterranean is that they are clustered rather than randomly distributed in time several tephra layers occurred at the time of the s1 sapropel formation between c 8 4 and 9 0 ka bp mercato gabellotto fiumebianco e1 cappadocia and ot

all age depth models are wrong but how badly the uncertainty and error associated with fitted age depth models were investigated by fitting a range of models to sets of simulated radiocarbon dates based on varved sediments and comparing the modelled relationship with the varve timescale with large numbers of dates cubic smooth splines out perform other models with few dates no model reliably provides a good fit to reality and calculated confidence intervals are over optimistic c 2003 elsevier ltd all rights reserved

a review of statistical chronology models for high resolution proxy based holocene palaeoenvironmental reconstruction abstract in this paper we explain the background workings and results obtained from three recently developed statistical age depth models implemented in freely available general purpose software packages bpeat oxcal and bchron these models aim to reconstruct the sedimentation rate in a single core typically lake peat or ocean given a limited number of scientific date estimates usually radiocarbon and fixed depths most importantly they provide a suitably qualified estimate of the uncertainty in the age depth chronology and thus can be used in a variety of applications we perform a large data driven study of the three models and discuss their general utility in chronology construction for palaeoenvironmental research

stable carbon isotopes c3 c4 vegetation and 12 800years of climate change in central new mexico usa abstract a thick sequence of fine textured alluvium in central new mexico has provided an opportunity to reconstruct vegetation type and climate at the western edge of the great plains grassland the analysis of thirty eight ams radiocarbon ages 13 c values and modern weather data has produced a 12 800 cal yr record of changing c 3 c 4 vegetation temperature and precipitation the record begins with the younger dryas that was characterized by c 3 plants and was about 2 4 c cooler with over 100 mm rainfall than today after 11 000 cal yrs bp the climate became less cool and less wet reaching present day conditions by 9000 yrs the middle holocene was c 4 warm and dry although the 13 c record is incomplete for this interval from 3300 to 1400 cal yrs bp the climate was cool and wet with c 3 plants averaging 0 5 c cooler and 22 mm greater rainfall than today matching other records in the region for a wetter climate after 1400 cal yrs bp the local climate became warm and dry shifting to c 4 vegetation the severe second century drought first observed in tree rings in southern colorado is supported by the 13 c data and occurred during the interval a d 40 to a d 180 hiatuses in the local alluvial and 13 c record extend from 9000 to 6000 cal yrs bp and from 1000 cal yrs bp to present

oxygen isotope evidence of little ice age aridity on the caribbean slope of the cordillera central dominican republic climate change during the so called little ice age lia of the 15th to 19th centuries was once thought to be limited to the high northern latitudes but increasing evidence reflects significant climate change in the tropics one of the hypothesized features of lia climate in the low latitudes is a more southerly mean annual position of the intertropical convergence zone itcz which produced more arid conditions through much of the northern tropics high resolution stable oxygen isotope data and other sedimentary evidence from laguna de felipe located on the caribbean slope of the cordillera central of the dominican republic support the hypothesis that the mean annual position of the itcz was displaced significantly southward during much of the lia placed within the context of regional paleoclimate and paleoceanographic records and reconstructions of global lia climate this shift in mean annual itcz position appears to have been induced by lower solar insolation and internal dynamical responses of the global climate system our results from hispaniola further emphasize the global nature of lia climate change and the sensitivity of circum caribbean climate conditions to what are hypothesized to be relatively small variations in global energy budgets

late glacial and holocene paleoceanography in the skagerrak from high resolution grain size records abstract high resolution grain size analyses of the ams 14c dated 32 m long core md99 2286 from the northeastern skagerrak were performed in order to study late glacial and holocene paleoceanographic and sedimentary changes all ages in this study are given in calibrated thousand years before present ad 1950 abbreviated kyr unless otherwise noted the distinct ending of ird ice rafted debris in core md99 2286 which was retrieved from a location down current from the final calving ice margin in the region indicates that iceberg calving in the skagerrak ended between 10 6 and 10 2 kyr a clay rich sequence in core md99 2286 deposited between 11 3 and 10 3 kyr is attributed to outflow from the baltic basin across south central sweden the sequence is correlated to similar units from cores along the swedish west coast the onset of this clay rich deposition occurs progressively later in cores further south along the coast supporting a previous hypothesis that differential glacio isostatic uplift caused a southward migration of the baltic outflow from the otteid stenselva to the gota alv outlet a distinct coarsening towards younger sediments in core md99 2286 indicates a hydrographic shift at 8 5 kyr which is correlated to a shift previously reported in the skagerrak kattegat and the norwegian channel this shift reflects the establishment of the modern circulation system in the eastern north sea as a consequence of the opening of the english channel and the danish straits and increased atlantic water inflow and the subsequent development of the south jutland current a general trend of coarsening poorer sorting and increasing variability from 8 5 kyr until the present indicates increasing strength and influence of the variable south jutland current a series of changes from ca 6 3 to ca 3 8 kyr in core md99 2286 reflects strengthening of the jutland current towards the present day sedimentation system in the skagerrak kattegat these changes are correlated to previously reported hydrographic shifts at 5 5 14c years bp in the skagerrak and at 4 0 14c years bp in the kattegat it is suggested that these shifts were separate features of a transitional period related to strengthening of the current system the resulting changes are differently manifested in different parts of the skagerrak kattegat due to the complex circulation system the last 800 years are characterised by poorly sorted sediments with a relatively high and variable proportion of coarse material reflecting a circulation system significantly modified by regional climatic conditions especially the general wind directions and storm frequency over the southern north sea

late holocene human impact on the vegetation around mizorogaike pond in northern kyoto basin japan a comparison of pollen and charcoal records with archaeological and historical data abstract pollen and macroscopic charcoal analyses of ams radiocarbon dated sediment from mizorogaike pond located near japan s ancient capital established in ad 794 were used along with archaeological and historical data to reconstruct vegetation change in the northern kyoto basin since 7300 cal yr b p between ca 7300 and 3400 cal yr b p early to late jomon period the site was surrounded by warm temperate forest composed of quercus subgenus lepidobalanus and q subgenus cyclobalanopsis with celtis aphananthe trees with the occurrence of fire disturbance q subgenus lepidobalanus increased from ca 3400 to 1400 cal yr b p late jomon to kofun periods in the early seventh century asuka period pinus started to increase coinciding with a significant charcoal peak probably related to the operation of roof tile kilns near the site pinus continued to increase and q subgenus cyclobalanopsis decreased through the seventh to tenth centuries asuka to heian periods further increase of pinus occurred in the eleventh century possibly reflecting the establishment of the manor of kamigamo shrine from the eleventh to seventeenth centuries heian to medieval periods no significant vegetational change or fire disturbance took place in the eighteenth century the landscape became totally open with poor vegetation and sparse pinus woodland the medieval and early modern landscapes reconstructed from the palaeoecological record are rather similar to those described from studies of ancient artwork and historical documents this study demonstrates that late holocene vegetation change in the northern kyoto basin was closely tied to anthropogenic activities such as the pottery industry and fuel wood collection

buried iceberg keel scouring on the southern spitsbergenbanken nw barents sea abstract parasound 3 5 khz subbottom echosounder profiles acquired on the southern spitsbergenbanken nw barents sea show iceberg keel scouring features which are buried by sediment that accumulated during the post last glacial maximum lgm sea level rise four acoustic units units 1 to 4 in stratigraphic order were differentiated based on the characterization of their acoustic facies and reflection surfaces unit 1 shows a chaotic internal structure and is interpreted as a glacial till whereas the laminated units 2 to 4 accumulated by sediment settling from suspension clouds and bottom currents during the last deglaciation phase the top of unit 2 was frequently incised by iceberg keels resulting in up to 12 m deep ploughmarks which were later filled and buried by unit 3 and 4 sediments three main paleo evironmental changes controlled the evolution of the facies succession 1 the major shift from till formation unit 1 below grounded ice to the accumulation of laminated sediments unit 2 which are inferred to reflect ice lifting and meltwater release 2 iceberg keel scouring after sedimentation of unit 2 3 the probable abrupt termination of iceberg keel scouring related to the glacio eustatic sea level rise a linkage between these episodes of changes and short lasting phases of rapid post lgm sea level rise such as meltwater pulses is inferred although further studies are needed to better understand the temporal and genetic relationships between the sedimentary events recognized in the barents sea and climate changes

deglacial to holocene history of ice sheet retreat and bottom current strength on the western barents sea shelf abstract high resolution sediment echosounder data combined with radiocarbon dated sediment cores allowed us to reconstruct the late quaternary stratigraphic architecture of the kveithola trough and surrounding spitsbergenbanken the deposits display the successive deglacial retreat of the svalbard barents sea ice sheet basal subglacial till indicates that the grounded ice sheet covered both bank and trough during the late weichselian a glaciomarine blanket inside the trough coinciding with laminated plumites on the bank formed during the initial ice melting phase from at least 16 1 to 13 5 cal ka bp in close proximity to the ice margin after the establishment of open marine conditions at around 13 5 cal ka bp a sediment drift developed in the confined setting of the kveithola trough contemporary with crudely laminated mud an overlying lag deposit and modern bioclastic rich sand on spitsbergenbanken the kveithola drift shows a remarkable grain size coarsening from the moat towards the southern flank of the trough this trend contradicts the concept of a separated drift which would imply coarser grain sizes in proximity of the moat and indicates that the southern bank is the main sediment source for the coarse material building up the kveithola drift this depocenter represents therefore a yet undescribed combination of off bank wedge and confined drift although the deposits inside kveithola trough and on spitsbergenbanken display different depocenter geometries time equivalent grain size changes imply a region wide sediment dynamic connection we thus relate a phase of coarsest sediment supply 8 8 6 3 cal ka bp to an increase in bottom current strength which might be related to a stronger atlantic water inflow from the southeast across the bank leading to winnowing and off bank export of sandy sediments

mafic granulites from the eastern ghats india further evidence for extremely high temperature crustal metamorphism mafic granulites occurring as conformable lenses within khondalite leptynite and calc silicate rocks from the anantagiri araku areas of the eastern ghats belt contain orthopyroxene clinopyroxene garnet quartz ilmenite and plagioclase as major constituents orthopyroxene contains 100 lamellae of clinopyroxene and clinopyroxene contains 100 orthopyroxene lamellae and 001 spindles of pigeonite reaction textures indicate formation of garnet through coupling of two reactions viz orthopyroxene anorthite garnet clinopyroxene quartz and anorthite ilmenite hematite ss quartz garnet ilmenite o 2 thermobarometry indicates exsolution of pigeonite at 950 c of 100 clinopyroxene in orthopyroxene and vice versa at 750 820 c and formation of garnet at around 700 725 c 7 kb all in response to cooling of the rock this shows a nearly isobaric cooling path subsequent to peak metamorphic conditions subsequently the rock suffered nearly isothermal decompression to 5 kb

a multi proxy peat study of holocene vegetation history bog development and carbon accumulation on northern vancouver island pacific coast of canada we present a multi proxy paleoenvironmental study on a 10 400 cal yr peat sequence from an ombrotrophic bog in coastal british columbia canada pollen non pollen palynomorph plant macrofossil and physicochemical analyses bulk density c n 13c and 15n isotopes were used to document changes in vegetation bog development and carbon and nitrogen accumulation pollen assemblages indicate that regional vegetation in the warm relatively dry early holocene was mixed coniferous forest with scattered pseudotsuga menziesii herbaceous peat with a c n of 28 combined with nuphar microfossils and relatively high n suggests the presence of a herb dominated peatland with standing water and or bog pools carbon and nitrogen accumulation were at their highest during this early holocene period at mean rates of 30 6 and 1 2 g m2 cal yr respectively by 8000 cal yr bp and under a cooler wetter climate northern vancouver island supported tsuga heterophylla rainforest similar to today decreasing relat

mid holocene sea surface conditions and riverine influence on the inshore great barrier reef we present measurements of sr ca 18o and spectral luminescence ratios g b from a mid holocene porites sp microatoll recovered from the nearshore great barrier reef gbr these records were used as proxies to reconstruct sea surface temperature sst the 18o of surrounding seawater 18osw and riverine influence respectively and compared with records from a modern porites sp microatoll growing in the same environment strong riverine influence in the mid holocene record is indicated by 1 an increased annual 18osw range in the mid holocene record 2 negative peaks in 18o characteristic of flood events and 3 a higher g b luminescence ratio seasonal cycles in g b suggest that humic acid inputs were elevated for a longer portion of the year during the mid holocene the seasonal cycle of 18osw peaked earlier in the year in the mid holocene record relative to the modern while mean 18osw values from the mid holocene record were similar to modern values these records provide an insight into the oceanographic conditions the nearshore gbr experienced during mid holocene climatic shifts and are consistent with a strong australian indonesian summer monsoon aism system at 4700 cal yr bp

1500 years of lake sedimentation due to fire earthquakes floods and land clearance in the oregon coast range geomorphic sensitivity to floods during timber harvest period

late second early first millennium bc abrupt climate changes in coastal syria and their possible significance for the history of the eastern mediterranean the alluvial deposits near gibala tell tweini provide a unique record of environmental history and food availability estimates covering the late bronze age and the early iron age the refined pollen derived climatic proxy suggests that drier climatic conditions occurred in the mediterranean belt of syria from the late 13th early 12th centuries bc to the 9th century bc this period corresponds with the time frame of the late bronze age collapse and the subsequent dark age the abrupt climate change at the end of the late bronze age caused region wide crop failures leading towards socio economic crises and unsustainability forcing regional habitat tracking archaeological data show that the first conflagration of gibala occurred simultaneously with the destruction of the capital city ugarit currently dated between 1194 and 1175 bc gibala redeveloped shortly after this destruction with large scale urbanization visible in two main architectural phases during the early iron age i the later iron age i city was destroyed during a second conflagration which is radiocarbon dated at circa 2950 cal yr bp the data from gibala tell tweini provide evidence in support of the drought hypothesis as a triggering factor behind the late bronze age collapse in the eastern mediterranean

confidence intervals for age estimates and deposition times in late quaternary sediment sequences distribution sampling from sequences of radiocarbon ages is used to obtain confidence intervals for intermediate age estimates sediment deposition times and thence pollen deposition rates three

calibration of radiocarbon ages and the interpretation of paleoenvironmental records abstract calibration of the radiocarbon timescale of paleoecological records is essential if they are to be explained correctly in terms of their governing ecological or climatological controls the differences between calendar ages and radiocarbon ages that arise from variations in 14c production through time can distort the chronologies of individual records and the interpretations based on them misleading impressions of synchrony or diachrony of events among multiple records can result and estimates of the apparent duration of episodes and rates of sedimentation and local population changes can be biased displays of the temporal patterns of migration or extinction may also be affected spurious correlations may arise between records with radiocarbon controlled chronologies and time series of potential controls that are expressed on a calendar time scale support for particular explanations of features in a paleoecological record may vary depending on whether radiocarbon ages are calibrated or not this situation is illustrated using the eastern beringian populus subzone as an example when the radiocarbon ages that control the timing of the populus subzone are calibrated the contemporaneous decrease in ice volume and increase in summer insolation are implicated as the ultimate controls of the occurrence of the subzone

shear modulus and damping ratio of sensitive eastern canada clays the shear modulus and equivalent viscous damping ratio of three sensitive clays from the sediments of the champlain sea were investigated using a combined triaxial simple shear apparatus the tests

multiproxy paleoecological reconstruction of prehistoric land use history in the western region of the lower rio verde valley oaxaca mexico paleoecological archives from three paleomeander sites and one archeological feature located in the lower rio verde valley oaxaca mexico are used to develop a spatial understanding of the patter

tree ring crossdates for a first millennium ad advance of tebenkof glacier southern alaska tree ring crossdates from glacially killed logs show that tebenkof glacier advanced into a forefield forest in the ad 710s and 720s recession from this first millennium ad fma advance occurred before the 950s after which the ice margin readvanced in the 1280s to 1320s at the start of the little ice age lia a more extensive lia advance was underway from the 1640s to 1670s and the terminus stayed at or near its lia maximum until the 1890s these are the first absolute tree ring crossdates for a fma glacier advance in north america and support growing evidence from northwestern north america and europe for a significant cool interval in the centuries around ad 500