reconstruction of late glacial summer temperatures from chironomid assemblages in lac lautrey jura france a chironomid july air temperature inference model based on chironomid assemblages in the surface sediments of 81 swiss lakes was used to reconstruct late glacial july air temperatures at lac lautrey jura eastern france the transfer function was based on weighted averaging partial least squares wa pls regression and featured a leave one out cross validated coefficient of determination r2 of 0 80 a root mean square error of prediction rmsep of 1 53 c and was applied to a chironomid record consisting of 154 samples covering the late glacial period back to the oldest dryas the model reconstructed july air temperatures of 11 12 c during the oldest dryas increasing temperatures between 14 and 16 5 c during the bolling temperatures around 16 5 17 0 c for most of the allerod temperatures of 14 15 c during the younger dryas and temperatures of ca 16 5 c during the preboreal the lac lautrey record features a two step july air temperature increase after the oldest dryas with an abrupt temperature increase of ca 3 3 5 c at the oldest dryas bolling transition followed by a more gradual warming between ca 14 200 and 13 700 bp the transfer function reconstructs a less rapid cooling at the allerod younger dryas transition than other published records possibly an artefact caused by the poor analogue situation during the earliest younger dryas and an abrupt warming at the younger dryas holocene transition during the allerod two centennial scale 1 5 2 0 c coolings are apparent in the record although chronologically not well constrained the first of these cold events may be synchronous with the beginning of the gerzensee oscillation the second is inferred just before deposition of the laachersee tephra at lac lautrey and is therefore coeval with the end of the gerzensee oscillation in contrast to the greenland oxygen isotope records the lac lautrey palaeotemperature reconstruction lacks a clearly defined greenland interstadial gi event 1d and the decreasing temperature trend during the bolling allerod interstadial copyright 2005 john wiley sons ltd

a mid european decadal isotope climate record from 15 500 to 5000 years b p oxygen isotope ratios of precipitation delta18op inferred from deep lake ostracods from the ammersee southern germany provide a climate record with decadal resolution the record in detail shows many of the rapid climate shifts seen in central greenland ice cores between 15 000 and 5000 years before the present b p negative excursions in the estimated delta18op from both of these records likely reflect short weakenings of the thermohaline circulation caused by episodic discharges of continental freshwater into the north atlantic deviating millennial scale trends however indicate that climate gradients between europe and greenland changed systematically reflecting a gradual rearrangement of north atlantic circulation during deglaciation

rapid climate change during the weichselian lateglacial in ireland chironomid inferred summer temperatures from fiddaun co galway a lacustrine sediment core from fiddaun western ireland was studied to reconstruct summer temperature changes during the weichselian lateglacial this site is located close to the atlantic ocean and so is potentially sensitive to climatic changes associated with changes in ocean circulation the record comprising the end of the weichselian pleniglacial to the early holocene was analysed for fossil chironomids lithology and oxygen and carbon isotopes in the sedimentary carbonates these proxies clearly show rapid warming at the onset of the lateglacial interstadial relatively high summer temperatures during the interstadial pronounced cooling during the younger dryas and subsequent warming at the transition to the holocene chironomid inferred mean july air temperatures for the interstadial are 12 5 14 5 c 7 5 c for the younger dryas and 15 0 c for the early holocene furthermore this research provides evidence for at least two cold events during the interstadial these more moderate temperature oscillations can be correlated to greenland interstadial events 1b and 1d on the basis of the age depth model for the fiddaun sequence based on multiple proxies the first cold oscillation gi 1d was the more severe of the two in ireland

late glacial fossil midge stratigraphies insecta diptera chironomidae from the swiss alps abstract chironomid midges insecta diptera chironomidae are sensitive indicators of environmental change but relatively few studies have been made of the response of european midge faunas to the high amplitude climatic oscillations of the late glacial in this study late glacial assemblages of chironomid midges from four swiss lakes or former lakes gerzensee 603 m leysin 1230 m regenmoos 1260 m and heremence 2300 m were compared and contrasted the study focused on the response of chironomid assemblages to the beginning and end of the younger dryas cold interval c 12 690 11 485 cal yr bp and to minor cold climatic fluctuations gerzensee oscillation c 13200 12800 cal yr bp and preboreal oscillation c 113 65 11 100 cal yr bp the durations of these climatic fluctuations were defined climato stratigraphically based on oxygen isotope boundaries and the chronology was derived by correlation with grip oxygen isotope records major differences in the composition of the four lakes chironomid assemblages reflected differences in altitude and local environmental conditions nevertheless each lake fauna showed a marked response to the major and minor climatic oscillations demonstrating that large scale temperature change had an overriding influence on the distribution of chironomid midges

distal volcanic ash layers in the lateglacial interstadial gi 1 problems of stratigraphic discrimination abstract a new icelandic ash layer has been detected in mid interstadial sediments in a number of scottish lateglacial sequences and has been named the penifiler tephra it is rhyolitic in composition and possesses a chemistry which is similar to the borrobol tephra of early lateglacial interstadial age which also occurs in a number of these same sequences where the borrobol tephra has been identified in these sequences it consistently exhibits a diffuse distribution accompanied in some cases by stratigraphic bimodality a number of sedimentological and taphonomic factors are considered in order to account for this distribution one possibility is that these distributions are produced by taphonomic factors another possibility is that the borrobol tephra may not be the product of a single icelandic eruption but of two events closely spaced in time in at least two of the sequences investigated in this study basaltic shards were found in association with the penifiler and borrobol tephras suggesting either a basaltic phase associated with these eruptions or coincident eruptions from a separate basaltic volcanic centre the discovery of the new penifiler tephra makes a contribution to the regional tephrostratigraphic framework and provides an additional isochron for assessing the synchroneity of palaeoenvironmental changes during the interstadial the true stratigraphic nature and age of the borrobol tephra however remains unresolved and therefore its use as an isochron is more problematic the possible occurrence of basaltic populations may strengthen correlations with basaltic tephras recently detected in the ngrip ice core

10be constrains the sediment sources and sediment yields to the great barrier reef from the tropical barron river catchment queensland australia abstract estimates of long term background sediment generation rates place current and future sediment fluxes to the great barrier reef in context without reliable estimates of sediment generation rates and without identification of the sources of sediment delivered to the reef prior to european settlement c 1850 determining the necessity and effectiveness of contemporary landscape management efforts is difficult here using the 2100 km 2 barron river catchment in queensland australia as a test case we use in situ produced 10 be to derive sediment generation rate estimates and use in situ and meteoric 10 be to identify the source of that sediment which enters the coral sea near cairns previous model based calculations suggested that background sediment yields were up to an order of magnitude lower than contemporary sediment yields in contrast in situ 10 be data indicate that background 43 t km 2 y 1 and contemporary sediment yields 45 t km 2 y 1 for the barron river are similar these data suggest that the reef became established in a sediment flux similar to what it receives today since western agricultural practices increased erosion rates large amounts of sediment mobilized from hillslopes during the last century are probably stored in queensland catchments and will eventually be transported to the coast most likely in flows triggered by rare but powerful tropical cyclones that were more common before european settlement and may increase in strength as climate change warms the south pacific ocean in situ and meteoric 10 be concentrations of coral sea beach sand near cairns are similar to those in rivers on the atherton tablelands suggesting that most sediment is derived from the extensive low gradient uplands rather than the steep more rapidly eroding but beach proximal escarpment

were abrupt lateglacial and early holocene climatic changes in northwest europe linked to freshwater outbursts to the north atlantic and arctic oceans during the lateglacial and early holocene abrupt millennial scale climatic variations are recorded in a wide range of high resolution proxy records from marine and terrestrial archives in nw europe our review of the evidence for these rapid climate events do not show an apparent link to possible forcing factors such as long term orbitally induced variations in solar radiation short term variations in solar activity as inferred from 14 c atmospheric carbon dioxide concentration or volcanic sulphate as recorded in the gisp2 ice core record there is however a remarkable degree of similarity with the number duration and timing of episodes of increased e ux of fresh water to the north atlantic and arctic oceans from the laurentide ice sheet and from the baltic ice lake in sw sweden these freshwater outburst events occurred when continental runoff from the laurentide ice sheet was rerouted from the mississippi river to the hudson river st lawrence river hudson strait and along the mackenzie river to the atlantic and arctic oceans and when the baltic ice lake in sw sweden drained to skagerrak periods of increased freshwater e ow to the north atlantic and arctic oceans may thus provide a mechanism to explain the abrupt and signie cant lateglacial and early holocene climate events in nw europe the idea that freshwater outbursts might drive abrupt climate events is not new but previous work may have underestimated the extent of support from proxy data and overestimated the ine uence of the laurentide ice sheet

environmental and climatic changes in the jura mountains eastern france during the lateglacial holocene transition a multi proxy record from lake lautrey this paper presents a multi proxy reconstruction of the climatic and environmental changes during the last glacial interglacial transition as recorded by a sediment sequence from lake lautrey jura eastern france this reconstruction is based on analysis of pollen chironomid organic matter oxygen isotope mineralogical magnetic susceptibility and inferred lake level data at a high temporal resolution the chronology is derived using ams radiocarbon dates the position of the laacher see tephra lst and of correlation between the lautrey and grip oxygen isotope records this data set reveals a detailed sequence of environmental changes in the jura mountains from greenland stadial 2a to the early holocene biotic and abiotic indicators allow the recognition of major abrupt changes associated with the gs 2a gi 1e gi 1a gs 1 and gs 1 preboreal transitions and other minor fluctuations related to the cold events gi 1d gi 1b and the preboreal oscillation pbo they also suggest additional cooling spells at ca 14 550 and 14 350 cal yr bp intra bolling cold periods at ca 13 500 and ca 12 700 cal yr bp just before the gs 1 onset and at ca 11 350 cal yr bp just before the pbo as well as an intriguing brief warming episode within gs 1 at ca 12 080 cal yr bp summer temperature increased by ca 5 c at the start of gi 1e and by 1 5 3 c at the holocene onset while it decreased by ca 3 4 c at the beginning of gs 1 major changes in local hydrology and in seasonality appear to be also associated with the gs 2a gi 1e gi 1a gs 1 and gs 1 preboreal transitions pollen and abiotic indicators suggest a greater sensitivity of the vegetation cover to climatic oscillations during the first part of the lateglacial interstadial than during the second part after ca 13 700 cal yr bp when a closed forest had been restored in this area by contrast the restoration of forest cover took less than 300 yr after the end of gs 1 at the beginning of gi 1e and gs 1 no lag occurs within the sampling resolution of 20 50 yr in the responses of aquatic chironomids and terrestrial pollen ecosystems while at the onset of the holocene the response of the vegetation appears slightly delayed in comparison with that of the chironomid community finally the recognition of two successive tephra layers which were deposited just before the lst at ca 12 950 cal yr bp and which originated from le puy de la nugere massif central france provides an additional tephrochronological tool for correlation between lateglacial european sequences

lateglacial environmental and climatic changes at the maloja pass central swiss alps as recorded by chironomids and pollen abstract chironomids and pollen were studied in a radiocarbon dated sediment sequence obtained from a former lake near the maloja pass in the central swiss alps 1865 m a s l to reconstruct the lateglacial environment pollen assemblages imply a vegetation development around the maloja pass from shrub tundra at the beginning of the allerod to coniferous forest during the early holocene with a lowering of the timberline during the younger dryas chironomid assemblages are characterized by several abrupt shifts in dominant taxa through the lateglacial the occurrence of taxa able to survive hypoxia in the second part of the allerod and during the preboreal and their disappearance at the onset of the younger dryas cold phase suggest summer thermal stratification and unfavourable hypolimnetic oxygen conditions in the palaeo lake during the warmer periods of the lateglacial interstadial and early holocene mean july air temperatures were reconstructed using a chironomid temperature transfer function from the alpine region the pattern of reconstructed temperature changes agrees well with the greenland 18 o record and other lateglacial temperature inferences from central europe the inferred july temperatures of ca 10 0 c during most of the allerod were slightly lower than modern values 10 8 c and increased up to ca 11 7 c i e above present day values at the end of the allerod the first part of the younger dryas was colder ca 8 8 c than the second part ca 9 8 c during most of the preboreal the temperatures persisted within the limits of 13 5 14 5 c i e ca 3 c above present day values the amplitudes of temperature changes at the allerod younger dryas preboreal transitions were ca 3 5 4 0 c the temperature reconstruction also shows three short lived cooling events of ca 1 5 2 0 c which may be attributed to the centennial scale greenland interstadial events gi 1d and gi 1b and the preboreal oscillation

chironomid inferred late glacial air temperatures at whitrig bog southeast scotland this paper presents the first chironomid inferred mean july air temperature reconstruction for the late glacial in britain the reconstruction suggests that the thermal maximum occurred early in the interstadial with temperatures reaching about 12 degreesc there was then a gradual downward trend to about 11 degreesc punctuated by four distinct cold oscillations of varying intensity at the beginning of the younger dryas mean july temperatures fell to about 7 5 degreesc but gradually increased to about 9 degreesc before a rapid rise at the onset of the holocene the chironomid inferred temperature curve agrees closely both in general trends and in detail with the grip ice core oxygen isotope curve the reconstructed temperatures are 2 4 degreesc lower than coleopteran inferred temperatures but are closer to those inferred from plant macrofossils and glacial equilibrium line altitudes during the younger dryas copyright c 2000 john wiley sons ltd

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

late glacial climatic oscillations as recorded in swiss lake sediments regional pollen assemblage zones for the late glacial period of the swiss plateau are introduced and defined they include four major zones artemisia juniperus hippophae betula pinus paz with several subzones pollen and oxygen isotope analyses on lacustrine sediments from several lakes in the area reveal four distinct phases of climatic oscillation in the time period of 13 000 9500 yr bp the first oscillation termed the aegelsee fluctuation occurs shortly before 12 000 yr bp and varve counts suggest its duration was ca 100 yr it is characterised by a short decrease in the oxygen isotopes as well as a short increase in nap associated with a depression in birch pollen values the second oscillation which occurs in the 18o record shortly before the deposition of the laacher see tephra ca 11 000 yr bp is termed the gerzensee fluctuation it occurs during a pine dominated phase and its vegetational effects cannot be determined palynologically the most prominent regressive phase is the younger dryas biozone ca 10 700 10 000 yr bp characterised by an increase in heliophilous nap and low 18o values the younger dryas biozone can often be subdivided palynologically into two parts a first part rich in grasses and juniper and a second part with higher filipendula and birch values during the preboreal biozone another distinct oscillation is evidenced only in the oxygen isotope ratios comparison of the swiss oxygen isotope profiles with the greenland dye 3 record suggests that not only the three major shifts in the 18o curves but also the minor ones are closely comparable suggesting some common climatic control

extent and timing of the last glacial maximum lgm in britain and ireland a review the last glacial maximum lgm of marine isotope stage mis 2 is defined here as the period either of maximum global ice volume or in which major ice sheets reached their maximum extent both definitions lack clarity as there is no reason to suppose that maximum volumes or limits were reached simultaneously at either all ice sheets or around the margins of individual ice sheets here we review the traditional terrestrial limits of the biis british irish ice sheet examine developments in understanding the offshore record and attempt a redefinition of the extent and timing of the mis 2 maximum as a working chronological model the build up of the biis is assigned to after 35 32 ka the maximum to the period 27 21 ka and a more limited readvance after 19 ka as marginal oscillations driven by ice sheet dynamics appear to have characterised much of the advance and especially the retreat of the biis caution should be exercised in assigning climatic significance to the many identified ice limits or still stands while much of the terrestrial limit in britain remains relatively unaltered significant revision is required offshore around britain and ireland to portray an extensive ice advance to the shelf edge and a period when the biis was conjoined with the adjacent fenno scandinavian ice sheet although there appears to be a broad synchrony between the biis and other major ice sheets local controls have produced some variation in the timing of advance to and retreat from maximum limits for particular ice streams or lobes but much of the offshore limit remains very poorly age constrained consequently a key objective in future research should be to improve and refine the chronological control for all portions of the maximum margin of the biis and its subsequent retreat stages copyright 2010 john wiley sons ltd

nongeometrically converted shear waves in marine streamer data under certain circumstances marine streamer data contain nongeometrical shear body wave arrivals that can be used for imaging these shear waves are generated via an evanescent compressional wave in the water and convert to propagating shear waves at the water bottom they are called nongeometrical because the evanescent part in the water does not satisfy snell s law for real angles but only for complex angles the propagating shear waves then undergo reflection and refraction in the subsurface and arrive at the receivers via an evanescent compressional wave the required circumstances are that sources and receivers are near the water bottom irrespective of the total water depth and that the shear wave velocity of the water bottom is smaller than the p wave velocity in the water most often the normal situation this claim has been tested during a seismic experiment in the river danube south of budapest hungary to show that the shear related arrivals are body rather than surface waves a borehole was drilled and used for multicomponent recordings the streamer data indeed show evidence of shear waves propagating as body waves and the borehole data confirm that these arrivals are refracted shear waves to illustrate the effect finite difference modeling has been performed and it confirmed the presence of such shear waves the streamer data were subsequently processed to obtain a shear wave refraction section this was obtained by removing the scholte wave arrival separating the wavefield into different refracted arrivals stacking and depth converting each refracted arrival before adding the different depth sections together the obtained section can be compared directly with the standard p wave reflection section the comparison shows that this approach can deliver refracted shear wave sections from streamer data in an efficient manner because neither the source nor receivers need to be situated on the water bottom

studying converted waves in shallow marine environment for many years waves converted from compressional to shear mode have been successfully applied in hydrocarbon exploration to image and characterize the subsurface since shear waves propagate with a velocity that is dependent on the shear modulus and are thus directly related to the shear strength of the sediment they are very useful for geotechnical purposes generally p wave reflection amplitudes contain s wave information but riedel et al 2001 showed that these reflections are not very sensitive to this an alternative approach is to obtain s wave information directly from converted waves however it is not clear whether these waves can be applied for geotechnical aims the main focus will be on understanding the dependence of mode conversion on the seismic properties in this study we investigate the possibility of acquiring converted waves in marine unconsolidated sediments from our numerical experiments we found that the conversion is maximal at two angles where the smallest angle appears to be more favorable in the environment of interest furthermore we show how and where converted waves can be observed on a seismogram and the optimum field configuration to acquire them

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

evidence for heinrich event 1 in the british isles in the north irish sea basin isb sedimentary successions constrained by ams 14c dates obtained from marine microfaunas record three major palaeoenvironmental shifts during the last deglacial cycle i marine muds cooley point interstadial dated to between 16 7 and 14 7 14c kyr bp record a major deglaciation of the isb following the late glacial maximum lgm ii terminal outwash and ice contact landforms killard point stadial were deposited during an extensive ice readvance which occurred after 14 7 14c kyr bp and reached a maximum extent at ca 14 14c kyr bp at this time the lowlands surrounding the north isb were drumlinised coeval flowlines reconstructed from these bedforms end at prominent moraines killard point bride st bees and indicate contemporaneity of drumlinisation from separate ice dispersal centres substrate erosion by fast ice flow and subglacial sediment transfer to ice sheet margins in north central ireland bed reorganisation associated with this fast ice flow phase involved overprinting and drumlinisation of earlier transverse ridges rogen type moraines by headward erosion along ice streams that exited through tidewater ice margins this is the first direct terrestrial evidence that the british ice sheet bis participated in heinrich event 1 h1 iii regional mud drapes directly overlying drumlins record high relative sea level rsl with stagnation zone retreat after 13 7 14c kyr bp rough island interstadial elsewhere in lowland areas of northern britain ice marginal sediments and morainic belts record millennial scale oscillations of the bis which post date the lgm advance on to the continental shelf and pre date the loch lomond stadial younger dryas advance in the highlands of western scotland ca 11 10 14c kyr bp in western northwestern and northern ireland killard point stadial h1 ice limits are reconstructed from ice flow lines that are coeval with those in the north isb and end at prominent moraines on the scottish continental shelf possible h1 age ice limits are reconstructed from dated marine muds and associated ice marginal moraines it is argued that the last major offshore ice expansion from the scottish mountains post dated ca 15 14c kyr bp and is therefore part of the h1 event in eastern england the stratigraphic significance of the dimlington silts is re evaluated because evidence shows that there was only one major ice oscillation post dating ca 18 14c kyr bp in these lowlands in a wider context the sequence of deglacial events in the isb widespread deglaciation of southern part of the bis major readvance during h1 ice sheet collapse is similar to records of ice sheet variability from the southern margins of the laurentide ice sheet lis well dated ice marginal records however show that during the killard point readvance the bis was at its maximum position when retreat of the lis was well underway this phasing relationship supports the idea that the bis readvance was a response to north atlantic cooling induced by collapse of the lis 1998 john wiley sons ltd

multidisciplinary investigations including stable isotope studies of thick late glacial sediments from tory hill co limerick western ireland abstract multidisciplinary investigations of a 10 m long marl rich late glacial core from tory hill co limerick have enabled environmental change including estimates of summer temperature st to be reconstructed for the late glacial period the sequence opens with fine partially laminated silt clay that has varve like microstructure a cold steppic environment from the final phase of the pleniglacial is represented here it is estimated to span almost 2000 years ca 16 9 15 cal ka b p ca 14 6 12 7 ka b p substantial development of woody vegetation is limited to the early part of the late glacial interstadial cf bolling this consists mainly of juniper and birch including tree birch betula pubescens as well as herb dominated communities these developments in vegetation and also the evidence from a variety of other proxies including stable isotope records 18o and 13c show that the thermal maximum was achieved early in the interstadial but st probably did not exceeded 14 c within this relatively warm period the various biological chemical and physical proxies suggest at least one substantial but short lived climatic oscillation the later part of the bolling allerod interstadial after ca 14 cal ka b p ca 12 ka b p began with a considerable and more or less sustained fall in temperature the low temperature regime was maintained until immediately before the younger dryas when a modest but distinct amelioration is recorded by all proxies this feature referred to as a pre younger dryas warming pydw and which is seen in land ocean and greenland ice core records from the northeast atlantic region has not been previously highlighted in the literature the younger dryas stadial when st may have fallen to ca 6 c has a distinctive pollen assemblage characterised mainly by gramineae thalictrum and artemisia but for reasons not readily explainable the early part of the stadial is not well defined in the stable isotope record as in most records from the northeast atlantic region the transition to the holocene is sharp and clearly recorded the importance of juniperus in the irish late glacial record as an indicator of temperature change is discussed and also the possible role played by ephedra and secale species at tory hill the apparent absence of temperature gradients within ireland is commented on and the evidence for much lower st in ireland compared with great britain is discussed

converted waves in a shallow marine environment experimental and modeling studies seismic waves converted from compressional to shear mode in the shallow subsurface can be useful not only for obtaining shear wave velocity information but also for improved processing of deeper reflection data these waves generated at deep seas have been used successfully in hydrocarbon exploration however acquisition of good quality converted wave data in shallow marine environments remains challenging we have looked into this problem through field experiments and synthetic modeling a high resolution seismic survey was conducted in a shallow water canal using different types of seismic sources data were recorded with a four component water bottom cable observed events in the field data were validated through modeling studies compressional waves converted to shear waves at the water bot tom and at shallow reflectors were identified the shear waves showed distinct linear polarization in the horizontal plane and low velocities in the marine sediments modeling results indicated the presence of a nongeometric shear wave arrival excited only when the dominant wavelength exceeded the height of the source with respect to the water sediment interface as observed in air gun data this type of shear wave has a traveltime that corresponds to the raypath originating not at the source but at the interface directly below the source thus these shear waves excited by the source water bottom coupled system kinematically behave as if they were generated by an s wave source placed at the water bottom in a shallow water environment the condition appears to be favorable for exciting such shear waves with nongeometric arrivals these waves can provide useful information of shear wave velocity in the sediments

avo investigations of shallow marine sediments amplitude variation with offset avo analysis is based on the zoeppritz equations which enable the computation of reflection and transmission coefficients as a function of offset or angle of incidence high frequency up to 700 hz avo studies presented here have been used to determine the physical properties of sediments in a shallow marine environment 20 m water depth the properties that can be constrained are p and s wave velocities bulk density and acoustic attenuation the use of higher frequencies requires special analysis including careful geometry and source and receiver directivity corrections in the past marine sediments have been modelled as elastic materials however viscoelastic models which include absorption are more realistic at angles of incidence greater than 40 degrees avo functions derived from viscoelastic models differ from those with purely elastic properties in the absence of a critical angle of incidence the influence of s wave velocity on the reflection coefficient is small especially for low s wave velocities encountered at the sea floor thus it is difficult to extract the s wave parameter from avo trends on the other hand p wave velocity and density show a considerably stronger effect attenuation described by the quality factor q influences the reflection coefficient but could not be determined uniquely from the avo functions in order to measure the reflection coefficient in a seismogram the amplitudes of the direct wave and the sea floor reflection in a common midpoint cmp gather are determined and corrected for spherical divergence as well as source and streamer directivity at cmp locations showing the different avo characteristics of a mud and a boulder clay the sediment physical properties are determined by using a sequential quadratic programming sqp inversion technique the inverted sediment physical properties for the mud are p wave velocity alpha 1450 25 m s s wave velocity beta 90 35 m s density rho 1220 45 kg m 3 quality factor for p wave qp 15 200 quality factor for s wave qs 10 30 the inverted sediment physical properties for the boulder clay are alpha 1620 45 m s beta 360 200 m s rho 1380 85 kg m 3 qp 790 660 qs 25 10

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

lateglacial vegetation and environment in ireland first results from four western sites a contribution to the north atlantic seaboard programme of igcp 253 termination of the pleistocene abstract first results of investigations that include pollen and chemical analyses of lateglacial lake sediments from four sites in western ireland are presented and the evidence for environmental change from these and previously published studies is reviewed fresh evidence is presented for a period with a cold arid continental type climate immediately after deglaciation this period is informally defined as the pre interstadial it is represented by a pinus artemisia gramineae pollen assemblage with a high proportion of long distance transported pollen recorded in highly minerogenic sediments immediately overlying outwash gravels and sands the interval between this and the younger dryas stadial informally defined as the lateglacial interstadial is characterised in the early part by maximum tall shrub development consisting mainly of juniperus tall shrub vegetation is subsequently replaced by gramineae and cyperaceae dominated open vegetation at many sites it is argued that the lateglacial interstadial is characterised by a number of climatic oscillations the most severe and sustained being responsible for this general shift in favour of herbaceous taxa at mid interstadial ca 12 ka bp prior to the onset of the younger dryas deterioration a modest expansion of juniperus at several sites and betula at some sites suggests a period of ameliorating climate the severity of climatic conditions during the younger dryas stadial is well expressed in the pollen lithological and chemical data there is some evidence to suggest that vegetation development in terrestrial environments at the transition to the holocene lagged behind developments in aquatic habitats and the thermal environment generally

synchronisation of palaeoenvironmental events in the north atlantic region during the last termination a revised protocol recommended by the intimate group abstract the north atlantic intimate group of the inqua palaeoclimate commission has previously recommended an event stratigraphy approach for the synchronisation of records of the last termination using the greenland grip isotopic record as the regional stratotype and intcal98 for the calibration of radiocarbon dates lowe j j hoek w intimate group 2001 inter regional correlation of palaeoclimatic records for the last glacial interglacial transition a protocol for improved precision recommended by the intimate project group quaternary science reviews 20 1175 1187 here we present a revised protocol for time stratigraphic correlation in the north atlantic region over a more extended time period 30 8 ka this employs the new ngrip isotopic record and associated greenland ice core chronology 2005 gicc05 as the regional stratotype intcal04 for the calibration of radiocarbon dates bayesian based statistical procedures for the construction of age models and tephrochronology to validate correlations between regional site records

pattern and timing of retreat of the last british irish ice sheet during the last glacial the ice sheet that subsumed most of britain ireland and the north sea attained its maximum extent by 27 ka bp and with an ice volume sufficient to raise global sea level by ca 2 5 m when it melted we reconstruct the demise of this british irish ice sheet biis and present palaeo glaciological maps of retreat stages between 27 and 15 ka bp the whole land area was investigated using remote sensing data and we present maps of moraines meltwater channels eskers and drumlins and a methodology of how to interpret and bring them together for the continental shelf numerous large moraines were discovered recording an extensive pattern of retreat stretching from sw ireland to the shetland isles from an integration of this new mapping of glacial geomorphology 26 000 landforms with previously published evidence compiled in the britice database we derive a pattern of retreat for the whole biis we review and compile relevant dates 881 examples that constrain the timing of retreat all data are held within a geographic information system gis and are deciphered to produce a best estimate of the combined pattern and timing of retreat pattern information reveals an ice sheet mainly comprised of a shelf parallel configuration from sw ireland to ne scotland but it spread far enough to the south to incorporate outlying ice domes over wales the lake district and kerry final disintegration was into a number of separate ice caps rather than reduction as a single mass and paradoxically retreat was not always back to high ground by 23 ka bp ice withdrew along its northern boundaries at the same time as the southern margins were expanding including transient ice streaming down the irish sea and advances of lobes in the cheshire basin vale of york and east coast of england ice divides migrated south by 19 ka the ice sheet was in crisis with widespread marine based ice losses particularly in the northern north sea and the irish sea considerable dynamic thinning occurred during this phase final collapse of all marine sectors occurred by 17 ka bp and with most margins beginning to back step onshore disintegration of the north sea ice bridge between britain and norway remains loosely constrained in time but the possibility of catastrophic collapse of this sector is highlighted the north channel and irish sea ice streams had finally cleaved the ice sheet into separate irish and scottish ice sheets by 16 ka bp rates of ice loss were found to vary widely over space and time e g 65 260 km3 per year the role of ice streams and calving losses of marine based sectors are examined retreat rates of up to ca 150 ma 1 were found for some ice stream margins that large parts 2 3 of the biis were marine based drained by ice streams and possibly with fringing ice shelves in places makes it a useful analogue for the west antarctic ice sheet wais this is especially so because the biis deglaciated in response to rising temperatures and a rising sea level driven by melting of other ice masses which are the current forcings that might cause collapse of the wais our reconstruction when viewed from the opposite perspective documents when fresh land became exposed for exploitation by plants animals and man and records for how long such land has been available for soil and geochemical development and ecological succession

regional consistency in lateglacial chironomid inferred temperatures from five sites in north west england abstract high resolution lateglacial ice core records from greenland show both millennial and centennial scale change and have been used as a benchmark for lateglacial climatic stratigraphy throughout the north atlantic region and beyond in this study we assess the local reflection in north west europe of climatic events recognised in ice cores and identify differences in the climate signature between greenland uk and sites in continental europe this study uses chironomid inferred temperature analysis and loss on ignition data from five carbonate lakes in north west england to determine the pattern of lateglacial climatic change and demonstrates the reproducibility of chironomid inferred temperature reconstructions both within a catchment and from sites within a small area at both millennial and centennial scales our results show statistical similarities between sites giving a clear regional signal chironomid assemblages pick out the rapid shifts at the major event boundaries at all sites and indicate temperatures of between 12 and 13 c for the region at the beginning of greenland interstadial 1 a rapid fall of around 4 c into the younger dryas and a rise of around 5 c in the early holocene at a finer scale four centennial cooling events are identified within the interstadial together with an oscillation in the early holocene which we tentatively identify as the pre boreal event the records were analysed statistically using redundancy analysis and sequence slotting techniques differences in the impact of individual climatic events demonstrate that subtle changes in the chironomid inferred temperatures reflect the local geographical setting and morphology of the lakes with more marked impact registered in higher altitude and more wind exposed sites whilst the overall pattern of lateglacial climate can be recognised from greenland to central europe important regional differences that can be attributed to marine influence and perhaps changes in atmospheric circulation are beginning to emerge

freshwater forcing of abrupt climate change during the last glaciation large millennial scale fluctuations of the southern margin of the north american laurentide ice sheet occurred during the last deglaciation when the margin was located between about 43 and 49 n fluctuations of the ice margin triggered episodic increases in the flux of freshwater to the north atlantic by rerouting continental runoff from the mississippi river drainage to the hudson or st lawrence rivers we found that periods of increased freshwater flow to the north atlantic occurred at the same time as reductions in the formation of north atlantic deep water thus providing a mechanism for observed climate variability that may be generally characteristic of times of intermediate global ice volume

biotic responses to rapid climatic changes abstract qualitative and quantitative changes in fossil flora and fauna have been used in many studies to infer climatic change here we ask a different question how do flora and fauna respond to climatic changes such as rapid warming or cooling as an independent proxy for paleotemperature we take the ratio of oxygen isotopes in biogenically precipitated lake marl and in ostracod shells this introductory paper describes the project design and the five sites on an altitudinal transect from 600 m to about 2300 m asl in the western swiss alps as cases of climatic cooling and warming we use the beginning and end of the younger dryas as major changes and the gerzensee and preboreal oscillations as minor changes at the two sites of gerzensee and leysin these changes are recorded in stable isotope ratios and there the time scales can be derived by correlations to the grip ice core schwander et al 2000 von grafenstein et al 2000 biotic responses to climate changes are treated in individual papers using pollen wick 2000 plant macrofossils tobolski and ammann 2000 and remains of chironomids brooks 2000 beetles and other insects lemdahl 2000 and chydorid cladocera hofmann 2000 they are followed by a synthesis focusing on quantification of biotic responses ammann et al 2000 in addition a reconstruction of summer temperatures for the allerod and the younger dryas at gerzensee is provided by lotter et al 2000

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