lateglacial vegetation development in denmark new evidence based on macrofossils and pollen from slotseng a small scale site in southern jutland abstract this paper presents the first unambiguous terrestrial palaeoecological record for the late glacial bolling warming in denmark pollen and macrofossil stratigraphies from pre bolling to 10 800 cal yr bp are presented from a small kettle hole in southwest denmark during which the lake basin developed from an immature stage after the deglaciation to complete infilling in the early holocene results show that the recently deglaciated landscape bore a discontinuous vegetation of pioneer plants after the bolling warming an open dryas octopetala betula nana community developed with helianthemum oelandicum subarctic species were dominant and local successions were probably delayed by relatively unstable and infertile soils there is no indication of a climate cooling during the period corresponding to the older dryas but the occurrence of several drought tolerant and steppe species indicates that the period was relatively dry in the allerod period the dryas b nana vegetation was initially replaced by an open salix and grass dominated vegetation and some 400 years later the first tree birches were documented presumably occupying moist and sheltered soils while drier land remained open in the younger dryas period trees disappeared and the vegetation became open again and dominated by subarctic species following climate warming at the younger dryas holocene transition a shrub community of empetrum and juniperus developed after approximately 200 years it was replaced by birch forest overall the late glacial vegetation cover had a more open and patchy character than inferred from previous pollen studies as assessment of the vegetation succession based on macrofossil evidence is essential the inferred general vegetation development corresponds well with results of other studies in the region canonical ordinations rda indicate that vegetation changes at the landscape scale during the lateglacial period were driven by changes in climate soils and competition for light

calcium carbonate dissolution rates in deep sea bivalve shells on the east pacific rise at 21 n results of an 8 year in situ experiment abstract analysis of shell fragments of two common deep sea hydrothermal vent bivalves the vesicomyid clam calyptogena magnifica and the mytilid bathymodiolus thermophilus deployed more than 100 m from any active hydrothermal vent location at 20 50 n 109 06 w on the east pacific rise indicates significant variation of calcium carbonate dissolution in in situ exposures of more than 8 years shell fragments embedded in epoxy blocks mounted on a buoyed and anchored polypropylene line and deployed by dsv alvin depth 2615 m were continuously exposed to ambient seawater 2 c conditions immediately above the seafloor the mean dissolution rate for the aragonitic shell of c magnifica amounted to 27 7 m yr dissolution rates varied significantly among different shell layers of the clam with the middle fine to irregular complex crossed lamellar shell layer exhibiting the lowest rates mean 22 2 m yr and the irregular prismatic shell layer the highest rates mean 36 9 m yr in the mytilid b thermophilus the dissolution rate of the aragonitic shell layer averaged 41 6 m yr while that of the calcitic shell layer was immeasurable the rates of calcium carbonate dissolution reported here for a ridge crest site remote from any active hydrothermal vent are much lower than those previously documented for active vent sites at 21 n the guaymas basin southern trough and galapagos rift rose garden assuming a constant rate of dissolution we estimate that empty adult shell valves of c magnifica at the experimental site would dissolve completely in a period of 300 years which has important implications for determining the longevity of hydrothermal vent activity along the rise axis

an asymmetric upwind flow yellow sea warm current 2 arrested topographic waves in response to the northwesterly wind 1 a warm and salty water mass exists along the yellow sea trough yst in winter this oceanic water mass is distinct from the ambient shelf water and is distributed on the western side of the yst it has long been reasoned that a yellow sea warm current yswc must exist a recent observational study indeed supports the existence of the yswc and shows that its position moved progressively westward as the warm water intrudes further shoreward toward the northwest in this paper we explain mechanisms for sustaining the yswc and for its westward displacement the northwesterly monsoonal wind prevails in the winter and is directed against the yswc the cross trough scale is small compared with the spatial scale of monsoonal variation so one can assume to the first order that the wind stress is uniform across the trough the curl of depth averaged wind stress has opposite signs on the two sides of the trough consequently two oppositely rotating gyres develop initially and they converge along the trough giving rise to a barotropic upwind flow but this upwind flow lasts only for a few days as the two gyres evolve and propagate as topographic waves for a northerly wind both gyres move westward since the positive negative potential vorticity flux on the western eastern side of the trough pushes the water toward shore trough if the bottom friction is negligible the steady response becomes a large anticyclonic gyre over the trough and the upwind current is squeezed toward the shore line in this case no yswc is sustained along or near the trough this runaway warm current can be arrested by a moderate bottom friction we therefore propose that the yswc is actually arrested topographic waves in response to local wind stress forcing

lateglacial insect assemblages from the palaeolithic site slotseng new evidence concerning climate and environment in sw denmark the site slotseng represents paleolithic settlements of the havelte phase of the hamburgian culture c 15 to 14 cal yr bp the lateglacial sediment stratigraphy of an adjacent kettle hole was stu

taphonomic field experiments and the role of the shelf and slope experimental taphonomy initiative abstract fossilization of organism remains is the result of biological physical and chemical processes at work in the environment of deposition the pathways taken by the remains of organisms through death decay burial and diagenesis known as taphonomic pathways affect the fossil record of life in important ways from complete removal and recycling of remains to preservation of hard parts and sometimes to exceptional preservation of soft tissues our understanding of taphonomic processes informs our interpretations of the fossil record and helps in the reconstruction of ancient environments research into taphonomic pathways in modern environments provides important insight into the fossilization process in 1993 a group of paleontologists formed the shelf and slope experimental taphonomy initiative sseti and began a long term comparative study of taphofacies and differential decay of taxonomic groups by placing experimental arrays containing bivalves gastropods decapod crustaceans sea urchins and wood species at multiple marine shelf and slope sites in the bahamas and gulf of mexico the goal of sseti is to observe taphonomic processes over a period of decades to better understand taphonomic pathways for these various groups of taxa in a wide variety of depositional environments beyond the shallow near shore region this special volume brings together eight studies that are the result of the sseti program the focus of this contribution is to first review the body of published work concerned with the fossilization process through the experimental manipulation of the remains of organisms in modern marine environments we also present the methods of the sseti project and its contributions to our understanding of taphonomic processes in relation to carbonate and wood recycling and preservation

reinvestigation of the classic late glacial bolling so sequence denmark chronology macrofossils cladocera and chydorid ephippia the late glacial bolling period was first identified by johs iversen on the basis of pollen results from lake bolling so in denmark because there were no radiocarbon dates from the sequence the bolling chronozone 12 000 13 000 14c yr bp was later established on the basis of dates from other sites a new project is reinvestigating the sediments from the bolling so sequence with ams radiocarbon dating and multiproxy analyses here we present results of ams radiocarbon dating macrofossil analyses cladoceran analyses cladocera concentrations and chydorid ephippia and pediastrum analyses concentrations the ams dates on land plant remains show that the lower part of the sequence is around 12 500 14c yr bp and thus clearly pre dates the allerod chronozone however construction of a chronology for the sequence was problematic partly because of reworking of macroscopic plant remains the climate ameliorated after glacial conditions to such an extent that growth of plants could begin at ca 12 500 14c yr bp but the results of multiproxy analyses show little evidence for a further warming period during the pre allerod part of the sequence lake productivity was low and tree birch rare or maybe absent this may reflect widespread occurrence of dead ice unstable soils heavy in wash of minerogenic matter to the lake resulting in turbid water and rapid sedimentation the early pioneer vegetation was characterised by salix polaris and dryas octopetala and by herbs the allerod chronozone and especially its initial part appears to have been relatively warm but reduced cladoceran concentrations and increased proportion of chydorid ephippia suggest that climate cooled in the middle allerod and that the late allerod was colder than the early part the early younger dryas was probably colder than the late younger dryas clear warming is apparent at the beginning of the holocene where the first macrofossil evidence of trees betula pubescens populus tremula is found copyright 2004 john wiley sons ltd

carbonate preservation in shallow marine environments unexpected role of tropical siliciclastics abstract coordinated taphonomic geochronologic and geochemical studies of bivalve death assemblages and their sedimentary environments of san blas caribbean panama permit us to identify the major factors controlling skeletal degradation in mixed carbonate siliciclastic tropical shelf sediments ten sites were studied along environmental gradients including water nutrients grain size and sediment chemistry carbonate organic carbon and reactive iron contents taphonomic data were derived from naturally occurring bivalve death assemblages and experimentally deployed specimens of mytilus edulis and mercenaria mercenaria to determine environmental controls on types and intensities of postmortem damage to skeletal hardparts and to quantify short term rates of damage accrual death assemblage shells were dated using 14c and amino acid racemization techniques to examine shell persistence scales of time averaging and long term rates of damage accrual including correlations between shell damage and she

upwelling off yangtze river estuary in summer 1 the mechanisms of upwelling off the yangtze river estuary yre and in the adjacent waters in boreal summer are studied using numerical modeling first the persistent feature of this phenomenon is confirmed using cruise observations satellite sea surface temperature sst and sst climatologic data then the masnum marine science and numerical modeling wave tide circulation coupled numerical model is employed to simulate the upwelling patterns on the basis of the simulation a set of numerical experiments are designed to explore the main mechanisms inducing the upwelling the results suggest that tidal mixing plays a predominant role in inducing the upwelling in offshore waters strong tidal mixing results in considerable horizontal density gradient across tidal fronts upwelling is induced as a branch of the secondary circulation which is stimulated by the cross frontal density gradient topography also exerts profound influences on upwelling by steering bottom currents to ascend upward and regulating tidal fronts in both location and intensity besides the tides and topography other dynamical factors also alter the strength of upwelling locally the yangtze river discharge yrd and taiwan warm current twc account partly for the upwelling off the yre and near zhoushan islands respectively the influence of wind on upwelling is small in the coastal waters near zhoushan islands the wind forcing exerts negative influences on upwelling by weakening the encroachment of twc onto the continental shelf which may exceed the positive effects of ekman pumping

southwest scandinavia 40 15 kyr bp palaeogeography and environmental change twelve palaeogeographical reconstructions illustrate environmental changes at the southwest rim of the scandinavian ice sheet 40 15 kyr bp synchronised land sea and glacier configurations are based on the lithostratigraphy of tills and intertill sediments dating is provided by optically stimulated luminescence and calibrated accelerator mass spectrometry radiocarbon an interstadial sequence ca 40 30 kyr bp with boreo arctic proglacial fjords and subarctic flora and occasional glaciation in the baltic was succeeded by a last glacial maximum sequence ca 3020 kyr bp with the closure of fjords and subsequent ice streams in glacial lake basins in kattegat and the baltic steadily flowing ice from sweden bordered the norwegian channel ice stream a deglaciation sequence ca 20 15 kyr bp indicates the transgression of arctic waters retreat of the swedish ice and advance of baltic ice streams succeeded by a return to interstadial conditions when ameliorated ice free conditions prevailed in maritime regions glaciers advanced through the baltic and when interstadial regimes dominated the baltic glaciers expanded off the norwegian coast the largest glacier extent was reached in the north sea around 29 kyr bp about 22 kyr bp in denmark and ca 18 kyr bp in the baltic our model provides new data for future numerical and qualitative landform based models copyright c 2003 john wiley sons ltd less

a rapid climatic change at the end of the younger dryas in south sweden palaeoclimatic and palaeoenvironmental reconstructions based on fossil insect assemblages a rapid climatic change at the end of the younger dryas in s sweden palaeoclimatic and palaeo environmental reconstructions based on fossil insect assemblages

holocene recolonization and extinction of the pond turtle emys orbicularis l 1758 in europe we reconstruct the holocene range fluctuations of the european pond turtle emys orbicularis for northern and central europe based on 529 subfossil records and radiocarbon dating of critical finds we provide evidence that e orbicularis experienced a rapid range expansion with holocene warming phylogeographic data argue for a colonization of northern and central europe from a glacial refuge located in the south eastern balkans already in the late preboreal 9100 8600 cal bc the species occurred in northern central europe and was widespread in denmark and southern sweden skane during the boreal 8600 7100 cal bc the maximum range extension occurred during the holocene climatic optimum atlantic 7100 3750 cal bc with records in southern england middle sweden and northern estonia after the early subboreal 3750 1750 cal bc northern populations collapsed coinciding with a climatic cooling and oceanization northern populations were most likely established via long distance dispersal rafting using rivers debouching in the north and baltic seas after northern europe was reached a minimum dispersal of 50 km per 100 years may be hypothesized for the boreal c 2007 elsevier ltd all rights reserved

why did ancient chemosynthetic seep and vent assemblages occur in shallower water than they do today cold seep communities have relatively low diversity are dominated by one or two taxa present in high density and high biomass in comparison with the surrounding fauna and are restricted to aphotic habitats their associated heterotrophic fauna are usually distinctive from the fauna of their surroundings in contrast a more commonplace chemoautotrophically based community occurs in shallow photic habitats the associated heterotrophic fauna includes many of the species typical of the surrounding communities and typically dominates abundance whereas the species with chemoautotrophic symbionts dominate biomass all modern seep assemblages are deeper than 550 m many fossil seep assemblages occurred in water as shallow as the mid shelf 200 m in contrast communities where species with chemoautotrophic symbionts are biomass dominants but not numerical dominants are common in shallow waters at present but rarely reported in the geological record we suggest that the absence of cold seep communities on the continental shelf presently is due to a combination of predation and competitive exclusion by primary consumers limiting the presence of species dependent on chemoautotrophic symbionts we suggest that cold seep assemblages are more common at shelf depths in the fossil record for two reasons a the biases of preservation have accentuated their distribution by transforming communities where species with chemoautotrophic symbionts dominate by biomass but not numerically into cold seep appearing assemblages b the importance of predation pressure and oligotrophy has varied with decreased predation pressure accompanying increased oligotrophy favoring cold seep communities we suggest that the paucity of shallow water assemblages with species harboring chemoautotrophic symbionts as biomass dominants in the fossil record is based on the reliance of paleoecological analysis on numerical abundance data when energy flow analyses are required to identify these assemblages the distinctiveness of the fossil seep assemblage is intensified by taphonomic processes that bias the assemblage against small individuals and epifaunal species so that diversity declines the small heterotrophic component of the assemblage is significantly reduced and the epifaunal component is minimized the final assemblage is usually dominated by the better preserved large infaunal clams which perchance are also the species with chemoautotrophic symbionts in contrast preservation does not enhance the distinctiveness of these chemoautotroph harboring species in shallow water

stomatal proxy record of co2 concentrations from the last termination suggests an important role for co2 at climate change transitions a new stomatal proxy based record of co2 concentrations co2 based on betula nana dwarf birch leaves from the hasseldala port sedimentary sequence in south eastern sweden is presented the record is of high chronological resolution and spans most of greenland interstadial 1 gi 1a to 1c allerod pollen zone greenland stadial 1 gs 1 younger dryas pollen zone and the very beginning of the holocene preboreal pollen zone the record clearly demonstrates that i co2 were significantly higher than usually reported for the last termination and ii the overall pattern of co2 evolution through the studied time period is fairly dynamic with significant abrupt fluctuations in co2 when the climate moved from interstadial to stadial state and vice versa a new loss on ignition chemical record used here as a proxy for temperature lends independent support to the hasseldala port co2 record the large amplitude fluctuations around the climate change transitions may indicate unstable climates and that tippingpoint situations were involved in last termination climate evolution the scenario presented here is in contrast to co2 records reconstructed from air bubbles trapped in ice which indicate lower concentrations and a gradual linear increase of co2 through time the prevalent explanation for the main climate forcer during the last termination being ocean circulation patterns needs to re examined and a larger role for atmospheric co2 considered

westward shift of the yellow sea warm salty tongue 1 the accumulated in situ hydrographic survey as well as the satellite observed sea surface temperature sst show consistent westward shifting of the yellow sea warm salty tongue yswst in winter a 2 d thermal model is used to show the westward shifting of the yswst due to cooling and advection the mitgcm is applied to simulate the circulation in the yellow and east china seas under the northern monsoon wind in winter the sea surface height ssh is adjusted to have a ridge in the channel and a trough in the 50 70 m iso bath in the yellow sea the barotropic transport of ssh and baroclinic transport of horizontal density gradient play the major role for the shifting of the yswst while the ekman wind drift plays a minor role

can shallow and deep water chemoautotrophic and heterotrophic communities be discriminated in the fossil record abstract the recognition of marine chemoautotrophic paleocommunities has added a new dimension to the interpretation of the fossil record we compared the death assemblages formed by chemoautotrophic and heterotrophic molluscan faunas of the continental slope with their counterparts in shallow water and with a fossil chemoautotrophic analogue from the tepee buttes of the pierre shale cretaceous to determine whether differences between them could be ascribed to differences in community structure or taphonomy evaluation of guild and tier structure and size frequency distribution using abundance and energy flow paleoproduction and paleoingestion suggests that differences between inshore and offshore recent heterotrophic assemblages reflect autecologic differences in the living communities forming them rather than differences in preservation in contrast the degree of similarity between chemoautotrophic assemblages is a function of their taphonomic and autecologic history the differences observed amongst recent chemoautotrophic assemblages issue from changes in the abundance and preservability of the small heterotrophic fauna relatively poorly preserved offshore and the presence of a large heterotrophic fauna essentially restricted to shallow water taphonomic removal of the small heterotrophs and juveniles of larger species and the autecologic absence of large heterotrophs could produce an assemblage equivalent to that of the cretaceous tepee buttes from any one of the recent inshore or continental slope chemoautotrophic assemblages our analysis indicates that shelf communities represent the shallowest communities likely to be identified as fossil cold seep faunas farther inshore community attributes normally used to distinguish chemoautotrophic and heterotrophic faunas are no longer discriminative nearshore communities may have included a dominant chemoautotrophic guild but recognition would rely solely on the identification of known chemoautotrophic taxa community trophic structure has classically been evaluated on the basis of numerical abundance and species composition comparing these chemoautotrophic and heterotrophic assemblages demonstrates the importance of evaluating community structure on criteria that more clearly document the way energy flowed through the community namely paleoproduction and paleoingestion many of the unique structural attributes of these assemblages only became obvious using these measures

preferential dissolution of carbonate shells driven by petroleum seep activity in the gulf of mexico abstract authigenic carbonates are common at deep sea petroleum seeps as a result of excess bicarbonate production during microbial degradation of hydrocarbons coupled to sulfate reduction consequently these seep environments are supersaturated with respect to carbonates this finding conflicts with taphonomic data that dissolution is the most pervasive mode of shell alteration at seeps we provide here the first study linking the preservational process with the chemical characterization of the taphonomically active zone at petroleum seep sites this characterization is made possible using fine scale porewater carbonate chemistry data and skeletal material deployed for 8 years at petroleum seep sites in the northwestern gulf of mexico microelectrode measurements of ph and pco2 identify a very restricted zone of caco3 undersaturation immediately below the sediment water interface in otherwise supersaturated environments i e sandwiched between supersaturated bottom seawater and sediment porewater this zonation characterizes the taphonomically active zone and is a result of a highly compressed redox front between acid generating aerobic oxidation of reduced chemical species including hydrocarbons h2s and planktonic and terrestrial organic carbon and base generating sulfate reduction coupled to ch4 oxidation porewater geochemistry is spatially variable at seep sites and produces variable shell dissolution signatures shells deployed at seep sites have moderate to severe dissolution that is consistent with a much higher flux of total dissolved inorganic carbon dic from the porewater to the bottom water therefore a mosaic of preservational conditions is directly related to the spatially and chemically varying taphonomically active zones found at seep sites these findings support the variability of carbonate preservation reported for globally distributed phanerozoic fossil seeps and the view that data from field taphonomy can significantly upgrade and validate carbonate destruction rates used in geochemical and climatic models carbon mass balance analyses also lead to an important conclusion that carbonate dissolution forms a very important mechanism for benthic carbon recycling possibly accounting for 50 of the benthic dic flux to the bottom water in northern gulf of mexico petroleum seep sediments

bathymetric zonation of modern microborers in dead coral substrates from new caledonia implications for paleodepth reconstructions in holocene corals abstract microboring endoliths were studied in dead modern corals collected at various depths and in growth position on la surprise atoll in new caledonia eight taxa of microborers were regularly observed three cyanobacteria hyella caespitosa mastigocoleus testarum and plectonema terebrans two chlorophytes ostreobium quekettii and phaeophila dendroides and three fungal forms dodgella priscus and two unidentified fungi the relative abundance of each taxon was determined in the modern corals throughout the studied sampling interval from 0 down to 40 m water depth this allowed us to propose for the first time a bathymetric model based on microendolith assemblages colonizing in situ hard substrates of corals in this model the occurrence of the cyanobacteria hyella and mastigocoleus indicates a bathymetric range from 0 down to a water depth of 3 and 6 m respectively the chlorophyta o quekettii associated with the cyanobacterium p terebrans and fungi is dominant from 10 to 40 m depth which is the lower limit of our sampling the distribution ranges of individual taxa observed in the dead coral substrates from new caledonia are much narrower than those reported in the literature for other substrates the bathymetric model based on distribution of microborers in modern corals was then applied to interpret the trace assemblages of microborers observed in holocene corals collected by drilling on two reef sites of new caledonia la surprise islet in the vicinity of the sampling sites of the modern corals and the barrier reef of bayes on the ne coast of grande terre the paleodepth interpretations performed at various levels along the cores allow identification of several shallowing upward sequences during the last 7000 years of reef growth in new caledonia differences in the thickness of these sequences between la surprise and bayes sites were interpreted as differences in the space available for accommodation between the two sites in turn related to the differential subsidence that affected new caledonia during holocene times the use of the microendolith trace assemblages in paleodepth reconstructions of holocene reefs from new caledonia allowed detection of relative sea level variations finer than those deduced from changes in coralgal assemblages

data model comparison of the younger dryas event discussion rutter et al 2000 present an interesting overview of global evidence for the younger dryas event yd 11 500 13 000 calendar years ago as inferred from various kinds of proxy data such an overview is important for a better understanding of mechanisms behind rapid climate change moreover rutter et al make an effort to compare these data with a coupled atmosphere ocean model experiment on the yd performed by fanning and weaver 1997 in this experiment the production of north atlantic deep water nadw collapses after the release of a large amount of fresh water in the north atlantic based on the data model comparison rutter et al conclude that the model results reveal a global pattern and regional magnitude which generally agree with temperature changes interpreted from paleoclimatic reconstructions abstract p 811 this implies that the yd temperature change is

atmospheric variability over the 14 7 kyr bp stadial interstadial transition in the north atlantic region as simulated by an agcm the echam4 t42 atmospheric general circulation model was applied to study the change in atmospheric variability in the north atlantic region over the similar to14 7 kyr cal bp climatic transition from greenland stadial 2a gs 2a end of pleniglacial to greenland interstadial le gi le start late glacial the following three climates are simulated 1 present day 2 gs 2a and 3 gi le we focus on climatic parameters near the earth s surface temperature precipitation and sea level pressure results on two different temporal scales are analysed seasonal and daily the seasonal fields show that the main change over the 14 7 kyr bp transition occurred in winter we calculated daily standard deviations of temperature and pressure about the seasonal means and the high pass filtered less than six days variability of pressure the largest change in atmospheric variability occurred in northwest europe here the daily temperature variability decreased by 50 whereas storm activity also decreased substantially these changes are related to a northward shift of the atlantic sea ice margin at 14 7 kyr bp leading to a northward relocation of the atlantic storm track in the gs 2a experiment a strong storm track was located over northwest europe where frequent depressions produced alternations of northerly air flow below 30 degreesc and southerly air flow close to 0 degreesc this strong daily atmospheric variability decreased in gi le because the storm track had a sw ne orientation over the atlantic towards iceland the decrease in atmospheric variability at 14 7 kyr bp probably contributed to landscape stabilization for instance through decreasing eolian transport

bathymetric effect on the winter sea surface temperature and climate of the yellow and east china seas 1 whether and how the atmosphere reacts to changes in extratropical sea surface temperature sst is under intense debate and this lack of understanding has been a major obstacle in the study of non el nino climate variability using new satellite measurements we detect clear ocean to atmospheric feedback in the yellow and east china yec seas that is triggered by the submerged ocean bottom topography under intense surface cooling in winter water properties are well mixed up to 100 m deep ocean depth thus has a strong influence on sst of the continental shelf leading to a remarkable collocation of warm tongues and deep channels high winds and increased cloudiness are found over these warm tongues one such band of ocean atmospheric co variation meanders through the basin following a deep channel for an amazing distance of 1000 km in addition to these climatic effects the kuroshio front where the warm current meets the much colder shelf water strengthens the growth of storms

taphonomy of holocene cryptic biotas from st croix virgin islands information loss and preservational biases surveys of submarine caves and overhanging ledges from st croix virgin islands provide new insights into the preservational processes active therein and into the taphonomy of ancient counterparts comparisons of preservable skeletonized versus nonpreservable unskeletonized components of these modern cryptic communities indicate that there is significant information loss in areals coverage taxonomic richness and diversity of fossilized examples quantitative estimates of such losses have been made in addition skeletal differences between early and late stage successional groups suggest biased representation of the former in the geologic record nonpreservable later colonizers may further erase the record of skeletonized forms through destructive life processes such forms of taphonomic information loss are probable in ancient counterparts and must be considered in accurate reconstruction of cryptic paleocommunities

a late weichselian stable isotope stratigraphy compared with biostratigraphical data a case study from southern sweden late weichselian lake sediments from a site in southern sweden were analysed for stable carbon and oxygen isotopes as well as plant macrofossils and insect remains by comparison of independent d

taphonomic losses become taphonomic gains an experimental approach using the rocky shore gastropod tegula funebralis abstract the gaps in the fossil record are not liabilities for paleontologists but rather assets for evolutionary and paleoecological studies the fossil record of rocky shore invertebrates is deemed poor resulting from the bias of a high energy physical environment the poor fossil record of the pleistocene rocky shore gastropod tegula funebralis appears to be no exception to this rule however field studies including experimentally deployed shells in two habitats reveal five important taphonomic processes that affect the resultant fossil resource for these gastropods 1 the predilection for tegula shells by the intertidal hermit crab pagurus samuelis affects the longevity of the shells 2 hermit crab occupied shells of tegula have a distinct array of bionts distinguishable from the living snail and empty experimentally tethered shells 3 biont types on tethered shells differ between two habitats mudflat and rocky intertidal and are thus useful for paleoenvironmental determinations 4 physical processes greatly affected intact shell longevity of experimental shells at the rocky intertidal site whereas at the mudflat site mistaken predation by durophagous crabs was the most important agent of shell destruction and 5 despite these taphonomic losses the pleistocene fossil record of tegula retains a good record of the biological factors that affect its preservation that of pagurid crustaceans and their gastropod shell associated bionts taphonomic losses when viewed from a hierarchy of shell users then are gains in biological information that indicate the level of complexity within the shell using community and this record is not completely lost in high energy regimes

floral evidence for high summer temperatures in southern scandinavia during 15 11 cal ka bp abstract the global climate transition from the lateglacial to the early holocene is dominated by a rapid warming trend driven by an increase in orbital summer insolation over high northern latitudes and related feedbacks the warming trend was interrupted by several abrupt shifts between colder stadial and warmer interstadial climate states following instabilities of the atlantic meridional overturning circulation amoc in response to rapidly melting ice sheets the sequence of abrupt shifts between extreme climate states had profound impacts on ecosystems which make it challenging to reliably quantify state variables like july temperatures within a non analogue climate envelope for europe there is increasing albeit inconclusive evidence for higher stadial summer temperatures than initially thought here we present a comprehensive floral compilation of plant macrofossils from lake sediment cores of 15 sites from s scandinavia covering the period 15 to 11 ka bp we find evidence for a continued presence of plant species indicating high july temperatures throughout the last deglaciation the presence of hemiboreal plants in close vicinity to the southern margin of the fennoscandian ice sheet implies a strong thermal summer forcing for the rapid ice sheet melt consistent with some recent studies we do not find evidence for a general stadial summer cooling which indicates that other reasons than summer temperatures caused drastic setbacks in proxy signals possibly driven by extreme winter cooling and or shorter warm seasons

the devensian weichselian lateglacial palaeoenvironmental record from gransmoor east yorkshire england a contribution to the north atlantic seaboard programme of igcp 253 termination of the pleistocene abstract palynological and coleopteran data are described from a section through late devensian weichselian deposits at gransmoor east yorkshire england the pollen evidence shows that following an initial open habitat episode first juniperus scrub and later betula woodland became established in the area during the lateglacial interstadial this woodland was replaced during the loch lomond younger dryas stadial by a predominatly herbaceous flora with arctic alpine steppe and halophytic elements the coleopteran evidence indicates a similar local environment and that the thermal maximum of the interstadial when mean july temperatures may well have exceeded 18 c occurred prior to the deposition of the earliest polleniferous sediments by the time of the juniperus expansion summer temperatures had fallen by 2 4 c to levels comparable with those of the present day a further temperature decline followed the expansion of betula during the later interstadial and another fall occurred at the lateglacial interstadial loch lomond stadial boundary during the loch lomond stadial mean july temperatures of 9 11 c are implied with winter temperatures as low as 15 to 20 c collectively the evidence reemphasises the point that for the first 1000 years or so of the lateglacial interstadial there was a disequilibrium between the palynological and coleopteran records in terms of climatic signal during the later interstadial however a closer relationship is apparent between both proxy data sources of particular significance in this respect is the fluctuation in reconstructed summer and winter temperatures and a rise and subsequent fall in betula pollen frequencies this may be the correlative of one of the pre younger dryas climatic oscillations recorded in other proxy data sources including palynological records from britain and eastern canada oxygen isotope traces from swiss lake sediments isotopic and electrical conductivity profiles from the greenland ice sheet and diatom and foraminiferal records in cores from the norwegian sea and the north atlantic ocean

impacts of light penetration on the bathymetry of reef microboring communities implications for the development of microendolithic trace assemblages abstract sediment samples recovered from three proximate reef environments in north jamaica characterised by different light penetration regimes reveal marked variations in the bathymetric range of sediment microboring communities in contrast to clear water environments assemblages developed in turbid water conditions undergo both bathymetric restriction and compression in their range in clear water sites the upper photic lower photic zone transition occurs between depths of 20 30 m this is marked by a shift from a predominance of cyanobacterial e g eurygonum nodosum scolecia filosa fasciculus frutex and fasciculus dactylus and chlorophyte e g rhopalia catenata fasciculus grandis reticulina elegans and scolecia botulifera traces to assemblages dominated by the traces e nodosum and s filosa cyanobacteria f grandis chlorophyte palaeoconchocelis starmarchii rhodophyte and orthogonum fusiferum and saccomorpha sphaerula fungi at sites characterised by intermediate levels of turbidity this same assemblage transition occurs at around 15 20 m depth and at the most turbid site at depths of only 5 10 m integration of assemblage data and light readings indicates that this transition occurs where percentages of surface light illumination are reduced to around 10 15 compression of the lower photic zone is so extreme at the most turbid site that microboring assemblages at only 30 m depth show evidence of a transition to an assemblage associated with dysphotic

reconstruction of a lateglacial younger dryas mountain ice field in sutherland northwestern scotland and its palaeoclimatic implications quaternary geomorphological and geological mapping of a large area 1800 km2 in the northwestern scottish highlands has led to the reconstruction of a coherent mountain ice field approximately 45 km long and 30 km wide at its maximum extent this west sutherland ice field covered an area of 350 km2 and had a mean equilibrium line altitude of 334 m assuming that the outlet glaciers all reached their maxima simultaneously numerical dating strongly suggests a younger dryas 12 9 11 7 ka age of the mapped limits of this mountain ice field this study also shows that the area of northwestern scotland covered by younger dryas glaciers was five times larger than previously thought palaeo temperature estimates obtained from chironomid and beetle assemblages elsewhere have been used to reconstruct palaeo precipitation during the younger dryas for west sutherland using a previously published global empirical dataset annual precipitation of 2344 248 mm a 1 at sea level is inferred from our new palaeo glacier reconstruction suggesting slightly wetter conditions compared to the present day these figures are in good agreement with those reconstructed for other parts of the scottish highlands and islands and this may indicate a marked w e palaeo precipitation gradient during the younger dryas this paper goes on to discuss the wider validity of palaeo climatic reconstructions from inferred palaeo glacier geometries and presents a number of possible scottish lateglacial climate scenarios which warrant further testing copyright 2010 john wiley sons ltd

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

a late middle pleistocene temperate periglacial temperate sequence oxygen isotope stages 7 5e near marsworth buckinghamshire uk abstract river channel and colluvial deposits near marsworth buckinghamshire record a temperate periglacial temperate sequence during the late middle pleistocene the deposits of a lower channel contain tufa clasts bearing leaf impressions that include acer sp and sorbus aucuparia and containing temperate arboreal pollen attributed to ash dominated woodland the tufa probably formed at the mouth of a limestone spring before being redeposited in a small river whose deposits contain plant remains mollusca coleoptera ostracoda and vertebrate bones of temperate affinities the sediments sedimentary structures and limited biological remains above the lower channel deposits indicate that fluvial deposition preceded climatic cooling into periglacial conditions fluvial deposition recurred during a later temperate episode as shown by the mammalian bone assemblage in stratigraphically higher channel deposits the upper channel deposits are confidently attributed to oxygen isotope sub stage 5e ipswichian on the basis of their vertebrate remains however the age of the lower channel deposits is less clear the mammalian and coleopteran remains in the lower channel strongly suggest correlation with oxygen isotope stage 7 on the basis of their similarities to other sites whose stratigraphy is better known and the clear difference of the lower channel assemblage from well established faunas of ipswichian or any other age by contrast u th dating of the tufa clasts suggests an age post 160 ka bp while aile ile ratios on mollusca point to an ipswichian age and younger four ways of interpreting this age discrepancy are considered the preferred one correlating the lower channel deposits with oxygen isotope stage 7

wave induced mixing in the upper ocean distribution and application to a global ocean circulation model 1 from the reynolds stress expression the wave induced vertical viscosity or diffusivity bv is defined which can be used as a parameter to estimate the strength of wave induced mixing in addition a parameter d5 is introduced to represent a wave induced mixing penetration depth the global distribution of bv averaged over the upper 20 m is calculated and its latitudinal transects in boreal summer and winter is discussed the results show that in summer the wave induced mixing is strong in the southern oceans south of 30 s and in winter it is strong in the north pacific and the north atlantic north of 30 n as well as in the southern oceans south of 40 s adding bv to the vertical diffusivity in a global ocean circulation model yields a temperature structure in the upper 100 m that is closer to the observed climatology than a model without the wave induced mixing

weichselian upper pleniglacial environmental variability in north western europe reconstructed from terrestrial mollusc faunas and its relationship with the presence absence of human settlements abstract during the weichselian glaciation millennial timescale climatic changes are a major cause of environmental variability which influence the composition of large mammal fauna and the geographical distribution of human prehistoric populations nevertheless precise environmental contexts of archaeological artefacts may remain unknown due to an unclear stratigraphy and or to the bad preservation of paleoenvironmental proxies as pollen is badly preserved in glacial loess deposits a compilation of age constrained high resolution molluscan records is used to initiate the establishment of a canvas of millennial timescale spatial and temporal environmental changes in the european loess belt during the weichselian upper pleniglacial ca 37 20 ka to look for relationships with spatial distribution of human settlements in this study new terrestrial mollusc assemblages have been added to the database previously established for north western europe they strengthen the position of the limit between the two molluscan based biogeographical domains initially highlighted for north western europe a flat and poorly vegetated western domain extending around the channel and in belgium and a hilly domain with more diversified vegetation to the east the analysis of molluscan data shows the persistence of these two domains throughout alternations of loess deposition phases interstadial stadial transitions and stadial phases with phases of development and degradation of tundra gley horizon stadial interstadial transitions and interstadial phases the interpretation of malacofauna from both domains combined with associated pedological and sedimentological features climate modelling and comparisons with present tundra environments reveals a significant effect of both seasonality and snow cover along a longitudinal gradient between both domains but also between phases of loess deposition and phases of tundra gley development during interstadial phases the intense functioning of the active layer and the degradation of permafrost in north western europe led to more homogeneous environments which were less favourable for the diversity of both vegetation and terrestrial mollusc fauna presently uncertainties of numerical ages still preclude precise correlations of loess units and tundra gley horizons between different sites and with nonlocal prehistoric occupations however a first raw comparison of the molluscan data with spatial distributions of aurignacian gravettian and solutrean upper magdalenian lithic cultures reveals that the northern limit of the first two ones fits well with the south eastern border of the poorly vegetated western domain also characterised by well developed ice wedge networks during phases of permafrost installation later an important southward shift of human populations in western europe resulted from the extreme aridity of the last glacial maximum

influence of seasonality on glacier mass balance and implications for palaeoclimate reconstructions climates inferred from former glacier geometries in some areas exhibit discrepancies with regional palaeoclimates predicted by general circulation models gcms and modelling of palaeoecological data possibly as a consequence of their differing treatments of climatic seasonality since glacier based climate reconstructions potentially offer an important tool in the calibration of gcms which themselves need validation if used to predict future climate scenarios we attempt to resolve mismatches between these techniques by 1 investigating the influence of seasonality on glacier mass balance and 2 refining the methodology used for the derivation of glacier based palaeoclimates focussing on the younger dryas stadial glaciation of scotland northeast atlantic we show that sea ice amplified seasonality led to a significantly drier climate than has been suggested by glacier based interpretations this was characterised by a relatively short ablation season and the survival of a more substantial winter snowpack we suggest that if palaeoglaciological studies were to account for changes in seasonal temperature and precipitation variability their results would agree more closely with the cold arid northeast atlantic palaeoenvironment predicted by atmospheric modelling and northwest european pollen studies and would therefore provide more accurate constraints for gcm calibration

early holocene coastal environments and climate in southeast sweden a reconstruction based on macrofossils from submarine deposits early holocene coastal environments and climate in southeast sweden a reconstruction based on macrofossils from submarine deposits

chironomid inferred summer temperatures for the last glacial interglacial transition from a lake sediment sequence in muir park reservoir west central scotland lake sediments spanning the last glacial interglacial transition lgit ca 14 7 to 8 ka bp from muir park reservoir mpr in west central scotland were analysed for chironomids the site lies just outside the southern limit of a former glacier that advanced into the loch lomond basin during the loch lomond younger dryas stadial chironomid inferred mean july temperatures were derived using a modern norwegian calibration dataset three tephra layers constrain the sequence chronologically inferred temperatures decline from a high value early in the interstadial punctuated by two cold oscillations probably equivalent to gi 1d and gi 1b in the greenland ice core record and a warm oscillation equivalent to gi 1a immediately before the severe cooling at the start of the loch lomond stadial gs 1 when summer temperatures fell by about 5 c below the interstadial average summer temperatures fell by about 3 c below the interstadial average during gi 1d which is less severe than inferred from other chironomid records from eastern scotland and may reflect the influence of an oceanic continental gradient cooling during gi 1b was particularly strong at mpr when minimum temperatures were about the same as those reached during gi 1d unlike other sites investigated where gi 1d is usually between 1 and 2 c cooler than gi 1b

palaeoecology of a late allerod peat bed at godoy western norway a peat bed found under solifluction deposits on godoya island western norway accumulated during a few decades around 11 000 yr bp at the end of the allerod period of the late weichselian palaeoecological investigations showed a local vegetation succession on wet sand culminating in a mire community dominated by carex nigra periodic flooding brought in sand and silt which decreased as drainage was impeded sufficiently for standing water to develop the surrounding terrestrial vegetation was dominated by salix scrub with some open heath and alpine habitats nearby apart from two aquatic species the 29 insect taxa recorded are characteristic of alpine heaths plant litter under salix scrub and stream sides their remains together with the terrestrial plant macrofossils were washed into the mire from nearby because the fossils are locally derived the environmental reconstructions are of the actual conditions at godoy at ca 11 000 yr bp palaeotemperature estimates from beetles and plants are in agreement the coleopteran estimates mutual climatic range method suggest mean july temperatures of 10 13 c slightly cooler than today 13 5 and january temperatures between 1 and 10 c similar to or much colder than today summer temperature estimates from individual plant taxa indicate that temperatures during the allerod period were similar to today s but estimates from the reconstructed vegetation and timber line positions give estimates up to 3 5 cooler temperatures fell 2 5 7 5 c at the younger dryas this abrupt and severe cooling initiated the solifluction processes on godoya that buried the peat the godoy peat bed and its contained fossils provide a rare glimpse of allerod biota and environments at the local site scale

chironomidae insecta diptera succession in żabieniec bog and its palaeo lake central poland through the late weichselian and holocene abstract subfossil chironomidae assemblages were studied in a sediment sequence from abieniec bog in central poland the climate history and habitat changes in the palaeo lake were reconstructed from these assemblages currently no chironomid based climate calibration set is available from poland and so past mean july air temperatures were inferred from chironomid climate calibration data sets from norway russia and switzerland during the late weichselian the three calibration functions from these data sets provided similar temperature inferences but there was some divergence in the reconstructions for the younger dryas and holocene in the late pleniglacial inferred summer air temperature was relatively low 8 12 c and the lake was oligotrophic at about 16 5 ka bp temperature rapidly rose to 15 c and assemblage diversity substantially increased during the interstadial temperature stayed at this level in the younger dryas july air temperature was only 1 2 c lower than in the interstadial as inferred from the norwegian calibration data set whereas the russian and swiss calibration functions did not indicate any temperature decrease from the beginning of the holocene taxa typical of meso eutrophic conditions dominated there was an increased abundance of phytophilous species and the assemblage composition was also influenced by changes in water level palaeotemperature reconstructions differed in their values from 8 0 to 8 7 ka bp inferences based on the swiss and russian data sets indicated a cold oscillation while reconstructions based on the norwegian data set did not show any temperature decrease after 2 5 ka bp assemblage diversity and head capsule concentrations decreased in the last millennium semi terrestrial taxa dominated except from late medieval to early modern times when shallow water species reappeared

the environment of upper palaeolithic magdalenian and azilian hunters at hauterive champreveyres neuchâtel switzerland interpreted from coleopteran remains an excavation primarily intended to investigate the bronze age deposits at hautrive champreveyres neuch tel switzerland encountered beneath the bronze age levels a sequence of late glacial sediments that were deposited between about 13000 yr bp and 11800 yr bp within these deposits upper palaeolithic hearths bones and flint implements were found in a context that left no doubt that they accumulated on the actual living floors two separate cultures were involved an earlier magdalenian one overlain by a rather later azilian assemblage coleoptera from the associated organic silts and sands provide detailed ecological and climatic information about the time when these people lived in the area radiocarbon dates indicate that the magdalenians lived in the area at about 13000 yr bp the coleoptera show that the mean july temperature at this time was about 9 c and mean temperature of the coldest month was about 25 c the landscape was bare of trees with an open patchy vegetation shortly after the area was abandoned by the magdalenian hunters the climate became suddenly warmer and mean july temperatures rose abruptly to at least 16 c and winter temperatures rose to levels not much different from those of the present day there is evidence that at this time intense slope instability and mud flows may have rendered the locality unsuitable for human occupation about seven centuries after the episode of sudden climatic warming namely at about 12300 yr bp palaeolithic azilian hunters occupied the area at a time when the climate was thoroughly temperate and the landscape was clothed in birch and willow woodland this was gradually replaced by pine forest at the top of the sequence and late glacial deposition ceased by about 11800 yr bp copyright 2000 john wiley sons ltd

temperature gradients in northern europe during the last glacial holocene transition 14 914c kyr bp interpreted from coleopteran assemblages late glacial and early holocene climatic conditions have been reconstructed for northern europe using the mutual climatic range mcr palaeoclimate method based on fossil coleopteran assemblages altogether beetle faunas from 77 sites have been analysed ranging from ireland in the west to poland and finland in the east and mcr estimates calculated the results are plotted on 16 maps each representative of a selected time slice covering the period from 14 5 14c kyr bp to 9 0 14c kyr bp eight of the maps show the mcr estimates of tmax mean temperature of the warmest month derived from each site for which data are available while the remainder show estimated tmax isotherms interpolated from these values it can be demonstrated that at times the thermal climate was fairly uniform throughout the study area whereas at others temperature gradients were much steeper than they are in the region today there also appears to be a distinct contrast between cold periods when contours trended nw se and warmer periods when contours trend w e or even ne sw the pattern of climatic changes that emerges is shown to be very different from the traditional view that has been used up to now as a template for classifying late glacial climatic events on a wide even global scale the suddenness and intensity of changes in the thermal climate may have been partially responsible for an apparent lack of equilibrium between the flora and fauna of the time and the physical environment in which they lived 1998 john wiley sons ltd

experiments on the settling overturning and entrainment of bivalve shells and related models an experimental and theoretical examination has been made of the settling entrainment and overturning of 176 valves representing 16 common northwest european marine bivalve species together with a comparative study of 15 plastic models in the form of segments from cylindrical tubes settling behaviour in both stagnant and moving water depends on particle mass symmetry and concavo convexity separated empty bivalve shells spin and spiral while settling and if sufficiently elongated also pitch at the observed reynolds numbers the shells and models fall concave up the terminal fall velocity increasing as the square root of the unit immersed mass or weight the drag coefficient is independent of reynolds number but increases with surface roughness and particularly particle elongation turbulence slightly lowers the critical elongation for pitching a separation vortex lies captive on the upper side of each descending particle consequently an empty bivalve shell traversing a suspension of sand traps grains on its upper side at a rate proportional to their volume concentration and terminal fall velocity this process increasing the effective shell mass is limited only by the capacity of the shell and grain spillage due to the possible onset of pitching the ratio non dimensional of a quantity proportional to the applied fluid force and the particle unit immersed weight consistently describes the entrainment of concave up and convex up particles and also the immediate overturning of a valve on settling concave up to the bed these thresholds vary in relative magnitude with bed particle friction and particle concavo convexity in general convex up particles are the most stable the concave up entrainment and overturning thresholds are of a substantially lower but similar magnitude the high frequency of concave up bivalve attitudes in turbidites is understandable largely in terms of the ability of a settling valve to increase in effective mass by grain entrapment convex up attitudes in the lower parts of turbidites may record currents stronger than the overturning threshold

direct comparison of uk temperatures and greenland snow accumulation rates 15000 12000 yr ago a palaeotemperature record based on fossil coleopteran evidence and dated by accelerator mass spectroscopy ams 14c determinations on plant macrofossils has been obtained for the last glacial interglacial transition from the site of gransmoor in eastern england calibration of the radiocarbon measurements enabled a direct comparison to be made between this palaeotemperature curve and the snow accumulation record from the gisp 2 greenland ice core the similarity between the two data sets suggests a degree of correspondence in the pattern and timing of climatic change in greenland and the british isles at the end of the last cold stage

grain susceptibility to the effects of microboring implications for the preservation of skeletal carbonates the boring activity of microendolithic organisms such as cyanobacteria chlorophytes rhodophytes and fungi represents a major destructive process affecting sediment preservation within reef environments this study demonstrates the presence of two distinct assemblages of microborers within sediments collected from the fringing reefs of north jamaica correlating to the upper 18 m depth photic zones the upper photic zone assemblage is dominated by cyanobacteria and chlorophytes whilst rhodophytes and fungi become more abundant with increasing water depth most significant from a grain preservation perspective is the variable nature of grain infestation observed between different reef sites and different carbonate grain types the highest degree of grain infestation occurs within shallow low energy back reef environments and the most susceptible grains at all sites are corals molluscs and foraminifera coralline algae halimeda and echinoid fragments are rarely heavily infested high rates of infestation at back reef sites result in rapid diminution of the most susceptible grains especially coral which are either underrepresented or contribute only to the finer sediment fractions in the subsurface fore reef grain assemblages undergo relatively little alteration microboring therefore has potential to bias the fossil record by removing the most susceptible skeletal grains the impact of microboring upon back reef grain assemblages must be considered when attempting to model depositional processes within both modern and ancient reef environments

geochronology of betula extensions in pollen diagrams of alpine late glacial lake deposits a case study of the late glacial deposits of the gasserplatz soil archives vorarlberg austria pollen diagrams of alpine late glacial calcareous lake deposits show several extensions of betula the geochronology of these extensions cannot be based on radiocarbon dating due to reservoir effects of such lakes on the radiocarbon ages a robust geochronology can be based on the oxygen isotope stratigraphy additionally recognition of 12 920 calbp lst in the sediment cores provides a secure time marker the combined results of pollen macro remains and stable isotope analyses of the gasserplatz cores point to a correlation of the betula extensions with the oscillations in the oxygen isotope curve and are related to global climatic oscillations this is sustained by the correlation of the gasserplatz isotope oscillations with the oscillations as registered in the greenland ice cores comparison of the results of the gasserplatz cores with the results of similar alpine lake deposits makes clear that the fluctuations in the betula curve are not a local but a regional phenomenon

an event stratigraphy for the last termination in the north atlantic region based on the greenland ice core record a proposal by the intimate group it is suggested that the grip greenland ice core should constitute the stratotype for the last termination based on the oxygen isotope signal in that core a new event stratigraphy spanning the time interval from ca 22 0 to 11 5 k grip yr bp ca 19 0 10 0 k 14 c yr bp is proposed for the north atlantic region this covers the period from the last glacial maximum through termination 1 of the deep ocean record to the pleistocene holocene boundary and encompasses the last glacial late glacial of the traditional northwest european stratigraphy the isotopic record for this period is divided into two stadial episodes greenland stadials 1 gs 1 and 2 gs 2 and two interstadial events greenland interstadials 1 gi 1 and 2 gi 2 in addition gi 1 and gs 2 are further subdivided into shorter episodes the event stratigraphy is equally applicable to ice core marine and terrestrial records and is considered to be a more appropriate classificatory scheme than the terrestrially based radiocarbon dated chronostratigraphy that has been used hitherto 1998 john wiley sons ltd

three dimensional structure of the summertime circulation in the yellow sea from a wave tide circulation coupled model 1 the three dimensional structure of the summertime circulation of the yellow sea hereafter ys is studied by using a prognostic wave tide circulation coupled model based on the princeton ocean model pom and a surface wave model the simulated tidal harmonic constants and temperature structure agree with the observations well the patterns of the simulated salinity generally agree also with the observations the simulated results show that the horizontal circulation has a three layer structure in the surface layer 0 4 m the prevailing current direction is northeastward in the upper layer 4 40 m it is dominated by a basin scale anticlockwise cyclonic gyre in the bottom layer below 40 m the water diverges from the center area and there exists a weak southward current along the ys trough the stream function of the ys shows that the net circulation of the ys is an anticlockwise cyclonic one and the net transport is about 0 1 sv diagnostic analysis of the momentum balance and sensitivity show that the cyclonic circulation in the upper layers is mainly a quasi geostrophic flow along tidal induced temperature front and it is also strengthened by the tide residual currents the tidal residual current and the compensation for northward surface layer wind transport contribute to the formation of southward flow in the bottom layer the vertical circulations vary along different sections a circulation cell is found in the frontal area near the korean coast and an upwelling is found along the slope

a multiproxy study of younger dryas and early holocene climatic conditions from the grabia river paleo oxbow lake central poland abstract a multi proxy reconstruction of water depth temperature and precipitation inferred from cladocera chironomidae and pollen assemblages has been obtained from wierczyna paleo oxbow central poland during the younger dryas yd and early holocene results suggest that the yd was relatively cold and comprised two main phases the first ca 12 500 12 000 cal yrs bp is characterized by a continental climatic regime and a decrease in winter temperatures and precipitation but an increase in spring summer precipitation the second phase ca 12 000 11 500 cal yrs bp was more mild with a variable continental climate an increase in summer and winter temperature a lengthening of the growing season and increased annual precipitation the reconstructed water level generally follows changes in spring and summer precipitation and length of growing season the frequency and timing of hydroclimatic oscillations at wierczyna show strong similarities to records from other sites in europe this confirms that oxbows and valley mire ecosystems respond to rapid climate change during the yd and early holocene this study therefore brings new insights into the effects of climate changes on river environments especially during the yd we also discuss the limitations of water depth temperature and precipitation reconstructions inferred from the studied biotic assemblages

taphonomic tiering experimental field taphonomy of molluscs and foraminifera above and below the sediment water interface abstract a review and synthesis of field based taphonomic experiments using molluscs and foraminiferans in marine systems reveal differing patterns of hardpart accumulation and destruction for these two major groups of fossil organisms for benthic molluscs most destruction appears to occur at the sediment water interface in siliciclastic settings mollusc preservation is suggested to be high once the shell is buried below the taphonomically active zone although this observation has not been experimentally addressed foraminiferal preservation however depends on microhabitat biogeochemical conditions within the sediments and test composition the taphonomically active zone for foraminiferans appears to be the upper 10 cm in most depositional settings from shallow to deep sea the preservation of tests or shells however has not been examined below the sediment water interface using field based experiments pore water geochemistry and associated microbial processes may be the most important factors in which to examine subsurface taphonomy the term taphonomic tiering is applied to variations in taphonomic activity within the sediments that differentially affect hard parts in essence the subsurface region where hardparts are presumed to be preserved is one of the new frontiers in experimental field taphonomy

taphonomy on the continental shelf and slope two year trends gulf of mexico and bahamas abstract the shelf and slope experimental taphonomy initiative was established to measure taphonomic rates in a range of continental shelf and slope environments of deposition eods over a multiyear period we deployed experiments on the forereef slope off lee stocking island bahamas and on the continental shelf and slope of the gulf of mexico for 2 yr in 18 distinctive eods at depths from 15 to 530 m overall most shells deployed at most sites had relatively minor changes in shell condition most eods generated relatively similar taphonomic signatures a few sites did produce taphonomic signatures clearly distinguishable from the central group and these sites were characterized by one or more of the following high rates of oxidation of reduced compounds presence in the photic zone and significant burial and exhumation events thus unique taphonomic signatures are created by unique combinations of environmental conditions that include variables associated with regional gradients such as depth and light and variables associated with edaphic processes such as the seepage of brine or petroleum or the resuspension and redeposition of sediment most sites however showed similar taphonomic signatures despite the variety of eod characteristics present suggesting that insufficient time had elapsed over 2 yr to generate a more diverse array of taphonomic signatures discoloration and dissolution were by far the dominant processes over the 2 yr deployment period periostracum breakdown loss of shell weight and chipping and breakage was less noticeable eods were chosen based on the expectation that the process of burial and the influence of depth and sediment type should play the greatest roles in determining between eod differences in taphonomic signature eod specific edaphic factors often overrode the influence of geographic scale environmental gradients taphonomic alteration was greater on hardgrounds and in brine exposed sites than on terrigenous muds dissolution was less effective at sites where burial was greatest discoloration occurred most rapidly at shallower sites and on hardgrounds water depth was less influential in determining taphonomic signature than burial state or sediment type the limited influence of water depth is likely due to the presence of shallow sites that for one reason or another were protected from certain taphonomic processes and deeper sites that were characterized by unusually strong taphonomic signals

a well mixed warm water column in the central bohai sea in summer effects of tidal and surface wave mixing 1 a well mixed water column is observed over a 20 m ridge in the central bohai sea surrounded by stratified water of much colder temperatures we use a three dimensional model to investigate its formation mechanisms the results show that both tidal and surface wave mixing are important for homogenizing the water column the former reaching 10 m above the bottom and the latter penetrating 10 m beneath the sea surface the ridge enhances the intensity and vertical extent of tidal mixing allowing it to connect with the downward penetration of wave mixing removing either the bathymetric ridge or wave mixing fails to reproduce this well mixed water column the inclusion of the surface wave mixing warms the bottom water by 5 6 c in both the warm water column and surrounding cold water wave mixing displays a maximum in the central bohai sea basin which is confirmed by satellite altimeter data and a wave model simulation

effects of the yellow sea warm current on the winter temperature distribution in a numerical model 1 the temperature distribution and circulation patterns in the yellow sea ys are examined by using a wave tide circulation coupled numerical model this model sufficiently reproduces the variation of the warm tongue structure of the yellow sea warm current yswc from the double branches flowing along the ys trough and the western 60 m isobath in january to the single stream along the western temperature front in march this is observed in both the long term monthly climatology and the satellite based sea surface temperature images in recent years examining the local heat balance in the numerical model during the entire cooling period it is found that the yswc has a very important influence on the ys warm tongue structure compared with the surface cooling the influence of the advection is small in the coastal shallow area but large in the deep warm tongue area up to 50 of the magnitude of heat flux although bathymetry is the essential factor which causes the temperature front the yswc is the key factor which positions shapes and maintains the warm tongue structure this helps to affirm the existence of the yswc at least as a monthly mean flow however more high resolution current observations in deeper layers west of cheju island and the western fork of the ys trough are needed to confirm the existence of the yswc and its characteristic timescale in the real ys

a numerical study of transport dynamics and seasonal variability of the yellow river sediment in the bohai and yellow seas abstract a sediment numerical model was embedded into a wave tide circulation coupled model to simulate the transport processes of the yellow river derived sediment considering the wave induced vertical mixing bv and the wave current coupled bottom shear stress bss numerical results show that the main stream of the yellow river derived sediment moves first eastward off the northern shandong peninsula and then southward into the south yellow sea all year round in spring the sediment moves northeastward in the bohai sea in summer there is a northeastward branch of sediment in the bohai sea off the west coast of the liaodong peninsula while the main part goes eastward to the yellow sea the yellow river derived sediment transport from the bohai sea to the north yellow sea across the bohai strait is mainly limited to the top 10 m and with a maximum centered at 37 9 n in summer the transport from the north yellow sea to the south yellow sea across the transect of 37 n is mainly in the 0 30 m layer with a maximum around 123 7 e in autumn the simulated yellow river discharged sediment deposits along the shandong peninsula and between 20 and 30 m isobaths in the yellow sea which is consistent with observation if surface waves are not considered in the model the sediment deposits westward to the nearshore area in the south yellow sea the sediment would deposit further southward in the numerical experiment results without wind influence in the numerical experiment of no tide there is hardly any sediment deposited on the yellow sea floor while in the bohai sea most of the sediment is transported southward and northwestward around the river mouth instead of eastward as in the control run indicating the tides play a key role in forming the deposition pattern

paleoceanographic reconstructions of surface ocean conditions in the greenland iceland and norwegian seas through the last 14 ka based on diatoms prior reconstructions of the last glacial maximum and the holocene did not include detailed paleoclimate data from the greenland iceland and norwegian gin seas which cover sensitive areas for oceanographic boundaries sea ice distribution and deep water formation in order to fill this gap we studied nine well dated sediment cores from this area and reconstructed the paleoceanographic conditions of the surface gin seas at 2000 year intervals since 13 400 bp based on the diatom record results show that a n s extending sea ice free corridor had opened along norway already at 13 400 bp indicating a northward flow of a branch of the north atlantic drift possibly caused by a change in the jet stream flow due to the decreased height of the north american ice sheet a major change of climatic conditions occurred over the gin seas as the insolation anomaly reached its maximum around 9000 bp when the sea ice cover and the oceanic fronts retreated to a northwesterly position along greenland and the ocean temperatures rose the first half of the holocene is recorded as the warmest period during the last 13 400 bp in the gin seas the duration of this climatic optimum decreased both toward the north and toward the margins of the area the second half of the holocene is characterized by a cooling trend in step with the decreasing insolation these results support the proposal of imbrie et al 1992 that the gin seas region acts as an initial responder to insolation changes

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