a flexible approach to assessing synchroneity of past events using bayesian reconstructions of sedimentation history the dating of depths in two or more cores is frequently followed by a study of the synchroneity or otherwise of events reflected in the cores the difficulties most frequently encountered are a determining precisely the depths associated with the events and b determining the ages associated with the depths there has been much progress in recent years in developing tools for the study of uncertainties in establishing chronologies this has not yet been matched by similar progress in modelling event depth relationships this paper proposes a simple and flexible approach showing how uncertain events can be married to uncertain chronologies difficulties in studying event depth age relationships typically involve a confounding of two different problems first what exactly do we mean by an event a point in history a single depth in the core corresponding to a single time or a depth time range sometimes event is in fact a shorthand for a space time process do the data reflect more than one type of event process this can reflect vagueness in definition second what are the sources and implications of the uncertainties here we illustrate the issues involved by examination of several features seen in north european holocene pollen records the alnus rise is regarded as a diachronous early holocene event in contrast the ulmus decline is widely seen as a near synchronous event in the mid holocene the third feature we examine is the interval between the ulmus decline and the first occurrence of cerealia type pollen the evidence for these events lies in cores of lake sediment from which are determined a the proportions of pollen at many depths and b radiocarbon age estimates from usually fewer depths for this illustration we focus on six sites we draw attention to a new and flexible method implemented in the free r software package bchron haslett j parnell a 2008 a simple monotone process with application to radiocarbon dated depth chronologies journal of the royal statistical society series c 57 4 399 418 for the establishment of the uncertainties surrounding the dating of samples in such cores we illustrate its flexibility by assessing the synchroneity of past events

correlation based interpretations of paleoclimate data where statistics meet past climates abstract correlation analysis is omnipresent in paleoclimatology and often serves to support the proposed climatic interpretation of a given proxy record however this analysis presents several statistical challenges each of which is sufficient to nullify the interpretation the loss of degrees of freedom due to serial correlation the test multiplicity problem in connection with a climate field and the presence of age uncertainties while these issues have long been known to statisticians they are not widely appreciated by the wider paleoclimate community yet they can have a first order impact on scientific conclusions here we use three examples from the recent paleoclimate literature to highlight how spurious correlations affect the published interpretations of paleoclimate proxies and suggest that future studies should address these issues to strengthen their conclusions in some cases correlations that were previously claimed to be significant are found insignificant thereby challenging published interpretations in other cases minor adjustments can be made to safeguard against these concerns because such problems arise so commonly with paleoclimate data we provide open source code to address them ultimately we conclude that statistics alone cannot ground truth a proxy and recommend establishing a mechanistic understanding of a proxy signal as a sounder basis for interpretation

ams radiocarbon dating and varve chronology of lake soppensee 6000 to 12000 14c years bp for the extension of the radiocarbon calibration curve beyond 10000 14c y bp laminated sediment from lake soppensee central switzerland was dated the radiocarbon time scale was obtained using accelerator mass spectrometry ams dating of terrestrial macrofossils selected from the soppensee sediment because of an unlaminated sediment section during the younger dryas 10000 11000 14c y bp the absolute time scale based on counting annual layers varves had to be corrected for missing varves the soppensee radiocarbon verve chronology covers the time period from 6000 to 12000 14c y bp on the radiocarbon time scale and 7000 to 13000 calendar y bp on the absolute time scale the good agreement with the tree ring curve in the interval from 7000 to 11450 cal y bp cal y indicates calendar year proves the annual character of the laminations the ash layer of the vasset killian tephra massif central france is dated at 8230 140 14c y bp and 9407 44 cal y bp the boundaries of the younger dryas biozone are placed at 10986 69 cal y bp younger dryas preboreal and 1212 86 cal y bp allerod younger dryas on the absolute time scale the absolute age of the laacher see tephra layer dated with the radiocarbon method at 10 800 to 11200 14c y bp is estimated at 12350 135 cal y bp the oldest radiocarbon age of 14190 120 14c y bp was obtained on macrofossils of pioneer vegetation which were found in the lowermost part of the sediment profile for the late glacial the offset between the radiocarbon 10000 12000 14c y bp and the absolute time scale 11400 13000 cal y bp in the soppensee chronology is not greater than 1000 years which differs from the trend of the u th radiocarbon curve derived from corals

multiproxy assessment of holocene relative sea level changes in the western mediterranean sea level variability and improvements in the definition of the isostatic signal abstract a review of 917 relative sea level rsl data points has resulted in the first quality controlled database constraining the holocene sea level histories of the western mediterranean sea spain france italy slovenia croatia malta and tunisia we reviewed and standardized the geological rsl data points using a new multi proxy methodology based on 1 modern taxa assemblages in mediterranean lagoons and marshes 2 beachrock characteristics cement fabric and chemistry sedimentary structures and 3 the modern distribution of mediterranean fixed biological indicators these rsl data points were coupled with the large number of archaeological rsl indicators available for the western mediterranean we assessed the spatial variability of rsl histories for 22 regions and compared these with the ice 5g vm2 gia model in the western mediterranean rsl rose continuously for the whole holocene with a sudden slowdown at 7 5 ka bp and a further deceleration during the last 4 0 ka bp after which time observed rsl changes are mainly related to variability in isostatic adjustment the sole exception is southern tunisia where data show evidence of a mid holocene high stand compatible with the isostatic impacts of the melting history of the remote antarctic ice sheet our results indicate that late holocene sea level rise was significantly slower than the current one first estimates of gia contribution indicate that at least in the northwestern sector it accounts at least for the 25 30 of the ongoing sea level rise recorded by mediterranean tidal gauges such contribution is less constrained at lower latitudes due to the lower quality of the late holocene index points future applications of spatio temporal statistical techniques are required to better quantify the gradient of the isostatic contribution and to provide improved context for the assessment of 20th century acceleration of mediterranean sea level rise

salt exchange in the indian atlantic ocean gateway since the last glacial maximum a compensating effect between agulhas current changes and salinity variations the import of relatively salty water masses from the indian ocean to the atlantic is considered to be important for the operational mode of the atlantic meridional overturning circulation amoc however the occurrence and the origin of changes in this import behavior on millennial and glacial interglacial timescales remains equivocal here we reconstruct multiproxy paleosalinity changes in the agulhas current since the last glacial maximum and compare the salinity pattern with records from the indian atlantic ocean gateway i aog and model simulations using a fully coupled atmosphere ocean general circulation model the reconstructed paleosalinity pattern in the agulhas current displays coherent variability with changes recorded in the wider i aog region over the last glacial termination we infer that salinities simultaneously increased in both areas consistent with a quasi interhemispheric salt seesaw response analogous to the thermal bipolar seesaw in response to a reduced cross hemispheric heat and salt exchange during times of weakened amoc interestingly these hydrographic shifts can also be recognized in the wider southern hemisphere which indicates that salinity anomalies are not purely restricted to the agulhas current system itself more saline upstream agulhas waters were propagated to the i aog during heinrich stadial 1 hs1 however the salt flux into the south atlantic might have been reduced due to a decreased volume transport through the i aog during the amoc slowdown associated with hs1 hence our combined data model interpretation suggests that intervals with higher salinity in the agulhas current source region are not necessarily an indicator for an increased salt import via the i aog into the south atlantic

were last glacial climate events simultaneous between greenland and france a quantitative comparison using non tuned chronologies several large abrupt climate fluctuations during the last glacial have been recorded in greenland ice cores and archives from other regions often these dansgaard oeschger events are assumed to have been synchronous over wide areas and then used as tie points to link chronologies between the proxy archives however it has not yet been tested independently whether or not these events were indeed synchronous over large areas here we compare dansgaard oeschger type events in a well dated record from southeastern france with those in greenland ice cores instead of assuming simultaneous climate events between both archives we keep their age models independent even these well dated archives possess large chronological uncertainties that prevent us from inferring synchronous climate events at decadal to multi centennial time scales if possible comparisons between proxy archives should be based on independent non tuned time scales copyright 2009 john wiley sons ltd

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

paleolimnological record of the pampean plains argentina as a natural archive of south american hydroclimatic variability since the lgm to the current warm period abstract laguna mar chiquita lmc 30 54 s 62 51 w is a highly variable and shallow saline lake located in the pampean plains of argentina the paleolimnological record of lmc contains information on the environmental variability that occurred in a large area of southern south america since the last glacial maximum lgm until the present as inferred from the diatom assemblages sedimentary features and geochemical proxies prolonged intervals of high and lowstands have caused variations in water salinity trophic state and sedimentary processes this is the first paleolimnological reconstruction covering the hydroclimatic variability that occurred over the last 25 000 cal yr bp in the argentinean pampean region results are in accordance with well known global climatic phases the late pleistocene record is characterized by a scenario dominated by lowstands hypersaline and oligotrophic lake conditions radiocarbon ages 25 000 19 000 cal yr bp indicate that the onset of the record is coeval with the lgm later a progressive lake water level increase was registered at 17 000 cal yr bp which can be assigned to the heinrich stadial 1 a shift toward comparatively drier conditions identified in the record between 14 700 and 13 000 cal yr bp can be chronologically related to the antarctic cold reversal the transition from the late pleistocene to the holocene 13 500 10 500 cal yr bp is recorded by highstand phases while the early holocene record is characterized by high to intermediate water levels the hydrological reconstruction corresponding to the mid holocene is characterized by alternating phases of high lowstands the onset of the late holocene record is marked by the development of dry conditions and thus lowstand phases while around 1300 cal yr bp a distinct water lake level increase is recognized this humid phase ascribed to the medieval climatic anomaly is followed by the record of lowstands between 500 and 1000 cal yr bp being coeval with the little ice age the uppermost part of the record of lmc encompasses the current warm period showing a marked shift towards high lake water level conditions the hydrological variability registered in the paleolimnological record highlights the importance of laguna mar chiquita as an outstanding paleoclimate sensor of hydroclimatic variations for a large area of south eastern south america

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

chronological evidence fails to support claim of an isochronous widespread layer of cosmic impact indicators dated to 12 800 years ago according to the younger dryas impact hypothesis ydih 12 800 calendar years before present north america experienced an extraterrestrial impact that triggered the younger dryas and devastated human populations and biotic communities on this continent and elsewhere this supposed event is reportedly marked by multiple impact indicators but critics have challenged this evidence and considerable controversy now surrounds the ydih proponents of the ydih state that a key test of the hypothesis is whether those indicators are isochronous and securely dated to the younger dryas onset they are not we have examined the age basis of the supposed younger dryas boundary layer at the 29 sites and regions in north and south america europe and the middle east in which proponents report its occurrence several of the sites lack any age control others have radiometric ages that are chronologically irrelevant nearly a dozen have ages inferred by statistically and chronologically flawed age depth interpolations and in several the ages directly on the supposed impact layer are older or younger than 12 800 calendar years ago only 3 of the 29 sites fall within the temporal window of the yd onset as defined by ydih proponents the ydih fails the critical chronological test of an isochronous event at the yd onset which coupled with the many published concerns about the extraterrestrial origin of the purported impact markers renders the ydih unsupported there is no reason or compelling evidence to accept the claim that a cosmic impact occurred 12 800 y ago and caused the younger dryas

active tectonics around the yakutat indentor new geomorphological constraints on the eastern denali totschunda and duke river faults abstract the yakutat collision in se alaska sw yukon is an outstanding example of indentor tectonics the impinging yakutat block strongly controls the pattern of deformation inland however the relationship between this collision system and inherited tectonic structures such as the denali totschunda and duke river faults remains debated a detailed geomorphological analysis based on high resolution imagery digital elevation models field observations and cosmogenic nuclide dating allow us to estimate new slip rates along these active structures our results show a vertical motion of 0 9 0 3 mm yr along the whole eastern denali fault while the dextral component of the fault tapers to less than 1 mm yr 80 km south of the denali totschunda junction in contrast the totschunda fault accommodates 14 6 2 7 mm yr of right lateral strike slip along its central section 100 km south of the junction further south preliminary observations suggest a slip rate comprised between 3 5 and 6 5 mm yr along the westernmost part of the duke river thrust fault our results highlight the complex partitioning of deformation inland of the yakutat collision where the role and slip rate of the main faults vary significantly over distances of 100 km or less we propose a schematic model of present day tectonics that suggests ongoing partitioning and reorganization of deformation between major inherited structures relay zones and regions of distributed deformation in response to the radial stress and strain pattern around the yakutat collision eastern syntaxis

timing and magnitude of recent accelerated sea level rise north carolina united states we provide records of relative sea level since a d 1500 from two salt marshes in north carolina to complement existing tide gauge records and to determine when recent rates of accelerated sea level rise commenced reconstructions were developed using foraminifera based transfer functions and composite chronologies which were validated against regional twentieth century tide gauge records the measured rate of relative sea level rise in north carolina during the twentieth century was 3 0 3 3 mm a consisting of a background rate of 1 mm a plus an abrupt increase of 2 2 mm a which began between a d 1879 and 1915 this acceleration is broadly synchronous with other studies from the atlantic coast the magnitude of the acceleration at both sites is larger than at sites farther north along the u s and canadian atlantic coast and may be indicative of a latitudinal trend

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

bayesian glaciological modelling to quantify uncertainties in ice core chronologies abstract valuable information about the environment and climate of the past is preserved in ice cores which are drilled through ice sheets in polar and alpine regions a pivotal part of interpreting the information held within the cores is to build ice core chronologies i e to relate time to depth existing dating methods can be categorised as follows 1 layer counting using the seasonality in signals 2 glaciological modelling describing processes such as snow accumulation and plastic deformation of ice 3 comparison with other dated records or 4 any combination of these conventionally implementation of these approaches does not use statistical methods in order to quantify dating uncertainties in this paper we develop the approach of category 2 further first the sources of uncertainty involved in glaciological models are formalised feeding these into a statistical framework that we call bayesian glaciological modelling bgm allows us to demonstrate the effect that uncertainty in the glaciological model has on the chronology bgm may also include additional information to constrain the resulting chronology for example from layer counting or other dated records such as traces from volcanic eruptions our case study involves applying bgm to date an antarctic ice core a dyer plateau core working through this example allows us to emphasise the importance of properly assessing uncertain elements in order to arrive at accurate chronologies including valid dating uncertainties valid dating uncertainties in turn facilitate the interpretation of environmental and climatic conditions at the location of the ice core as well as the comparison and development of ice core chronologies from different locations

calibration of radiocarbon results pertaining to related archaeological events with the advent of the high precision radiocarbon calibration curve there is an increasing demand from archaeologists for results previously reported on the radiocarbon scale to be expressed on the calendar scale furthermore there is a general realization within the archaeological community that much more information can be derived from radiocarbon dating if the samples are taken from coherent well chosen contexts and if any available substantive archaeological information is included in the data analysis this paper describes how the bayesian approach to statistical data analysis can be used for the calibration of groups of radiocarbon results in situations where archaeological information is available a priori about the relationships between the contexts being dated recent innovations in the implementation of the bayesian paradigm are used and the methodology is illustrated by the analysis of data arising from two archaeological excavations

branching mechanism of the tsushima current in the korea strait abstract hydrographic studies show the seasonal variation of the east korean warm current ekwc which is a branch of the tsushima current along the korean coast to understand the dynamics of the branching mechanism of the tc in the korea strait a hydraulic model with two active layers was investigated in a rectangular strait with varying depth when the lower cold water flows southward in a shallow meridional channel from the deep northern basin it separates from the eastern boundary because of the sloping bottom to conserve potential vorticity after separation the lower layer hugs the western boundary as the channel becomes shallow in a region where the lower layer is absent due to separation the northward flow in the upper layer has a positive relative vorticity to conserve potential vorticity because the bottom topography becomes deeper from south to north the northward velocity has its maximum on the eastern boundary this mechanism may explain the formation of the branch along the japanese

reconstructing common era relative sea level change on the gulf coast of florida abstract to address a paucity of common era data in the gulf of mexico we reconstructed 1 1 m of relative sea level rsl rise over the past 2000 years at little manatee river gulf coast of florida usa we applied a regional scale foraminiferal transfer function to fossil assemblages preserved in a core of salt marsh peat and organic silt that was dated using radiocarbon and recognition of pollution 137cs and pollen chronohorizons our proxy reconstruction was combined with tide gauge data from four nearby sites spanning 1913 2014 ce application of an errors in variables integrated gaussian process eiv igp model to the combined proxy and instrumental dataset demonstrates that rsl fell from 350 to 100 bce before rising continuously to present this initial rsl fall was likely the result of local scale processes e g silting up of a tidal flat or shallow sub tidal shoal as salt marsh development at the site began since 0 ce we consider the reconstruction to be representative of regional scale rsl trends we removed a linear rate of 0 3 mm yr from the rsl record using the eiv igp model to estimate climate driven sea level trends and to facilitate comparison among sites this analysis demonstrates that since 0 ce sea level did not deviate significantly from zero until accelerating continuously from 1500 ce to present sea level was rising at 1 33 mm yr in 1900 ce and accelerated until 2014 ce when a rate of 2 02 mm yr was attained which is the fastest century scale trend in the 2000 year record comparison to existing reconstructions from the gulf coast of louisiana and the atlantic coast of northern florida reveal similar sea level histories at all three sites we explored the influence of compaction and fluvial processes on our reconstruction and concluded that compaction was likely insignificant fluvial processes were also likely insignificant but further proxy evidence is needed to fully test this hypothesis our results indicate that no significant common era sea level changes took place on the gulf and southeastern atlantic u s coasts until the onset of modern sea level rise in the late 19th century

millennial scale climate oscillations recorded in the lower danube loess over the last glacial period abstract in this study we provide a correlative age model for last glacial loess at the rasova valea cu pietre site in the lower danube region based on the correlation of palaeoenvironmental proxies to independently dated palaeoclimate archives luminescence dating and independent age control provided by the geochemically confirmed presence of the campanian ignimbrite ci tephra the ci tephra originating in the phlegrean fields of southern italy has been dated elsewhere by 40ar 39ar to 39 40 ka bp and is frequently found in the lower danube loess as such the ci tephra represents a valuable temporal and stratigraphic maker across loess deposits in the region our age model facilitates high resolution correlation of palaeoenvironmental features observed at rasova to palaeoclimate archives in greenland and the black sea mediterranean area we observe semi cyclic behaviour of the frequency dependent magnetic susceptibility throughout the profile which we ascribe to millennial scale climate variability also observed elsewhere in the black sea region this is the first study to clearly identify millennial scale climate variability over the holocene and last glacial in the lower danube loess proxy variability in the holocene indicates continuous aeolian sedimentation through this epoch

a numerical approach to 14c wiggle match dating of organic deposits best fits and confidence intervals c 14 wiggle match dating wmd of peat deposits uses the non linear relationship between c 14 age and calendar age to match the shape of a sequence of closely spaced peat c 14 dates with the c 14 calibration curve a numerical approach to wmd enables the quantitative assessment of various possible wiggle match solutions and of calendar year confidence intervals for sequences of c 14 dates we assess the assumptions advantages and limitations of the method several case studies show that wmd results in more precise chronologies than when individual c 14 dates are calibrated wmd is most successful during periods with major excursions in the c 14 calibration curve e g in one case wmd could narrow down confidence intervals from 230 to 36 yr c 2003 elsevier science ltd all rights reserved

lake sediment records of holocene hydroclimate and impacts of the mount mazama eruption north central washington usa abstract multi proxy sediment records from castor lake and scanlon lake north central washington provide a late quaternary perspective on lake catchment hydrologic and ecosystem responses to climate change and the mazama volcanic ashfall event analyses of authigenic carbonate mineral oxygen and carbon isotope values organic carbon and nitrogen content and sedimentological facies were conducted on sediment from castor lake in order to reconstruct lake catchment hydrologic balance the source and abundance of organic matter and variations in lake level sedimentary facies characterization was conducted on the scanlon lake sediment in order to provide supporting evidence for the lake level shifts inferred from the castor lake data marked changes in castor lake proxy values occur from 12 860 to 11 440 calendar years before present yr bp suggesting lake catchment responses to the younger dryas cold reversal including higher lake levels substantial variability in productivity and increased catchment erosion high 18o values at 9630 yr bp indicate that lake levels were lower than at present and that the early holocene was dry sedimentological analyses and 18o data demonstrate that subsequent to the mazama climactic eruption 7600 yr bp a transition to the lowest lake levels of the holocene occurred over several centuries with maximum 18o values at 7290 90 uncertainty range 7020 7500 yr bp and low lake levels persisting until 6190 5960 6410 yr bp lithological changes in the scanlon lake record support these inferences the lowest 18o values of the holocene occur in sediment from 5000 yr bp indicating high lake levels at this time after which a secular trend toward higher 18o values and lower lake levels occurred the prolonged lowstand in the centuries following the mazama eruption suggests that catchment hydrologic characteristics were strongly impacted by the ashfall through effects on soil water retention capacity that similar responses may have occurred in comparable settings within the mazama ashfall zone and that such volcanic events have the potential confound the climate signal in lake sediment records were a similar event to happen in the future catchment hydrology stream river discharge and lake catchment ecosystem dynamics could be affected for centuries

deposition models for chronological records abstract long term sedimentary sequences provide a wealth of useful information for research into the palaeo environment especially in relation to past climate change shorter records provide similar information in many archaeological contexts however if such records are to be used to provide precise timing of events and more critically the relative timing between different records methods are needed to provide accurate and precise age depth models for these sequences given the imprecision of individual calibrated radiocarbon determinations it is necessary to use the information we have about the deposition process to refine our chronologies and also to provide interpolation between dated levels in any sequence even with layer counted chronologies the uncertainties are sometimes hard to quantify this paper outlines a range of bayesian models for deposition which have been implemented in the computer programme oxcal these models can be used to combine information from the sediments themselves with radiocarbon or other direct dating information such models have the potential to integrate information between different records and provide a coherent chronology on which to base environmental or archaeological research