formal definition and dating of the gssp global stratotype section and point for the base of the holocene using the greenland ngrip ice core and selected auxiliary records the greenland ice core from northgrip ngrip contains a proxy climate record across the pleistocene holocene boundary of unprecedented clarity and resolution analysis of an array of physical and chemical parameters within the ice enables the base of the holocene as reflected in the first signs of climatic warming at the end of the younger dryas greenland stadial 1 cold phase to be located with a high degree of precision this climatic event is most clearly reflected in an abrupt shift in deuterium excess values accompanied by more gradual changes in d 18 o dust concentration a range of chemical species and annual layer thickness a timescale based on multi parameter annual layer counting provides an age of 11 700 calendar yr b2 k before ad 2000 for the base of the holocene with a maximum counting error of 99 yr a proposal that an archived core from this unique sequence should constitute the global stratotype section and point gssp for the base of the holocene series epoch quaternary system period has been ratified by the international union of geological sciences five auxiliary stratotypes for the pleistocene holocene boundary have also been recognised copyright 2008 john wiley sons ltd

accelerator mass spectrometer ages for the younger dryas event in atlantic canada abstract in atlantic canada bulk sediment dates for the onset of a late glacial cooling widely regarded as the younger dryas event are highly variable ranging from 14 300 270 to 10 800 100 yr b p we present the first accelerator mass spectrometer ams 14c dates from atlantic canada at or close to the boundaries of this event from six sites in new brunswick and nova scotia the mean of five dates places the onset of this cooling at ca 10 770 yr b p the inclusion of a sixth perhaps anomalously old date changes the mean to 10 880 yr b p the termination averages three dates ca 10 000 yr b p these dates place the timing of the younger dryas event in atlantic canada closer in line with the traditional chronozone boundaries of 11 000 and 10 000 yr b p in northwest europe

episodic reductions in bottom water currents since the last ice age although north atlantic deep water formation was greatly reduced during the last glacial maximum bottom water currents were as vigorous as at present however they were weakened during periods of north atlantic surface freshening a strong correlation can be seen between bottom water current strength and greenland air temperature records thus confirming a close connection between ocean circulation and abrupt climate change past changes in the freshwater balance of the surface north atlantic ocean are thought to have influenced the rate of deep water formation and consequently climate1 2 although water mass proxies are generally consistent with an impact of freshwater input on meridional overturning circulation3 there has been little dynamic evidence to support this linkage here we present a 25 000 year record of variations in sediment grain size from south of iceland which indicates vigorous bottom water currents during both the last glacial maximum and the holocene period together with reconstructions of north atlantic water mass distribution vigorous bottom currents suggest a shorter residence time of northern source waters during the last glacial maximum relative to the holocene period the most significant reductions in flow strength occur during periods that have been associated with freshening of the surface north atlantic the short term deglacial oscillations in bottom current strength are closely coupled to changes in greenland air temperature with a minimum during the younger dryas cold reversal and a maximum at the time of rapid warming at the onset of the holocene our results support a strong connection between ocean circulation and rapid climate change

a midge based late glacial temperature reconstruction from southwestern nova scotia we present a quantitative reconstruction of the thermal regime spanning the late glacial period of nova scotia 14 700 to 11 600 bp as inferred by analyzing fossil midges from a small lake lac a magie in southwestern nova scotia the gs 1 event equivalent to the younger dryas dating from 12 700 to 11 600 bp in maritime canada was marked by a 5 c decline in inferred mean july surface water temperatures and a 15 drop in organic content previous pollen and plant macrofossil analyses of this site demonstrate a response of vegetation to gs 1 cooling these data coupled with a midge inferred temperature reconstruction from a nearby site suggest that late glacial climate change was less pronounced in southern nova scotia than in other sites in maritime canada and adjacent eastern north america

the last glacial interglacial transition lgit in the western mid latitudes of the north atlantic abrupt sea surface temperature change and sea level implications abstract high resolution reconstructions of sea surface temperature uk 37 sst coccolithophore associations and continental input total organic carbon higher plant n alkanes n alkan 1 ols in core d13882 from the shallow tagus mud patch are compared to sst records from deep sea core md03 2699 and other western iberian margin cores results reveal millennial scale climate variability over the last deglaciation in particular during the lgit in the iberian margin heinrich event 1 h1 and the younger dryas yd represent two extreme episodes of cold sea surface condition separated by a marine warm phase that coincides with the bolling allerod interval b a on the neighboring continent following the yd event an abrupt sea surface warming marks the beginning of the holocene in this region ssts recorded in core d13882 changed however faster than those at deep sea site md03 2699 and at the other available palaeoclimate sequences from the region while the sst values from most deep sea cores reflect the latitudinal gradient detected in the iberian peninsula atmospheric temperature proxies during h1 and the b a the tagus mud patch core d13882 experienced colder ssts during both events this is most certainly related to a supplementary input of cold freshwater from the continent to the tagus mud patch a hypothesis supported by the high contents of terrigenous biomarkers and total organic carbon as well as by the dominance of tetra unsaturated alkenone c37 4 observed at this site the comparison of all western iberia sst records suggests that the sst increase that characterizes the b a event in this region started 1000 yr before meltwater pulse 1a mwp 1a and reached its maximum values during or slightly after this episode of substantial sea level rise in contrast during the yd holocene transition the sharp sst rise in the tagus mud patch is synchronous with meltwater pulse 1b the decrease of continental input to the mud patch confirms a sea level rise in the region thus the synchronism between the maximum warming in the mid latitudes off the western iberian margin the adjacent landmasses and greenland indicates that mwp 1b and the associated sea level rise probably initiated in the northern hemisphere rather than in the south

gisp2 oxygen isotope ratios the gisp2 oxygen isotope record with its high resolution detail yields crucial information on past climate change the glacial 18o oscillations of the gisp2 core with their very fast onsets are templates of a prototype oscillation of variable duration with an amplitude of 3 9 the halfway mark of the cold warm transition is reached in 2 years the top is reached in 50 years the 18o time gradient of the leading front is about 7 8 per 100 yr after reaching the top 18o slowly declines by 0 14 per 100 yr the duration of 18o decline varies from a couple of centuries for fast oscillations to about 4000 yr for slower ones the subsequent 18o downturn during the warm cold transition has a 18o time gradient of 3 2 per 100 yr and lasts about 80 yr

post younger dryas climate interval linked to circumpolar vortex variability isotopic evidence from fayetteville green lake new york the late glacial holocene transition in the north atlantic european sectors has long been known to be a period of rapid climate change there is however a continued need for acquiring and developing paleoclimate archives spanning this interval from continental settings here we report on a lacustrine fayetteville green lake isotope record sampled at a 10 year resolution from the ne usa over the late glacial holocene interval 14 600 8000 cal year bp based on prior isotopic and hydrologic research from green lake the 18o calcite values predominantly reflect winter moisture source and thus winter atmospheric patterns furthermore we use historic ad 1948 1980 winter circulation data and 18o calcite values from varved sediments to examine the relationship between the circumpolar vortex latitude and isotopes which results in a strong r 0 79 r2 0 63 negative relationship using the linear regression from the isotope vortex relationship we model the winter vortex latitude for the late glacial holocene transition over the ne usa in addition we identify an interval from 11 600 to 10 300 cal year bp the post younger dryas climate interval wherein the mean winter vortex over the ne usa was expanded by 6 latitude 36 1 n i e 630 km from its mean historic position between ad 1948 1998 41 8 n renewal of more vigorous thermohaline circulation following the younger dryas cold event may have forced the post younger dryas climate interval increased poleward heat transport due to an active oceanic conveyor would have strengthened the thermal contrast between the ne usa and the north atlantic thereby enhancing atmospheric pressure gradients and firmly establishing the semi permanent winter trough over the ne usa consequently storms tracked more frequently up the east coast of the united states from the gulf of mexico and atlantic regions delivering precipitation with relatively high 18o values to the ne usa alternatively the relative dominance of seasonal precipitation may have changed resulting in less total winter precipitation low 18o causing lake waters to become relatively enriched in high 18o summer precipitation both hypotheses are good candidates for testing by global circulation modeling gcm the termination of the post yd interval at 10 300 cal year bp and the beginning of the holocene was likely forced by a gradual decrease in thermohaline circulation and poleward heat transport as freshwater input from melting of high latitude ice sheets increased

effect of commercial trawling on the deep sedimentation in a mediterranean submarine canyon abstract in order to study sediment accumulation rates in the palamos submarine canyon northwestern mediterranean during the last century three sediment cores were extracted from the canyon axis at depths of 450 1200 and 1750 m respectively where instrumented moorings were previously located estimated sedimentation rates based on 210 pb and 137 cs profiles suggest that the contemporary trends of sediment transfer and accumulation in the canyon may be different from secular trends during the seventies a two fold increase of the sediment accumulation rate took place at the 1750 m depth site this change has been associated to trawling activities and is attributed to the rapid technical development that the local trawling fleet underwent during the seventies the surroundings and rims of submarine canyons are frequently targeted by commercial trawling fisheries an activity that may enhance the input of resuspended particles into canyons and eventually trigger sediment gravity flows our results suggest that the effects of trawling over the dynamics of the seafloor may extend further and deeper from the fishing grounds eventually extending to bathyal depths hence the anthropogenic influence on the sedimentary budget of some deep submarine environments may be more important than previously thought

a temperature reversal within the rapid younger dryas holocene warming in the north atlantic abstract the onset of the holocene has been generally considered rapid and uninterrupted in the circum atlantic region loss on ignition loi an index of organic carbon profiles from 18 lateglacial aged lakes in nova scotia canada together with chironomid inferred temperature reconstructions at 5 sites demonstrate that the rapid warming from the younger dryas gs 1 to the holocene was interrupted by a cooling of 1 6 6 4 c in summer surface lake water temperature the resulting inflection or reversal on the rising temperature curve has also been identified at 35 sites outside nova scotia from terrestrial and marine settings indicating that this cool step is a robust feature throughout the north atlantic and is likely the result of major oceanic and atmospheric reorganization of the holocene climate system

chironomid inferred air temperatures from lateglacial and holocene sites in north west europe progress and problems abstract non biting midges insecta diptera chironomidae are now widely recognised as powerful biological proxies for inferring past climatic change in this paper the response of chironomid assemblages to lateglacial and holocene climatic change from sites in scotland and norway is discussed analyses have shown that midge assemblages have responded to major and minor climatic fluctuations during the last 15 000 yr such as the aegelsee oscillation gerzensee oscillation and younger dryas in the lateglacial and the thermal optimum little ice age and cooling events at 8 2 and 2 0 cal ka bp in the holocene in an attempt to quantify these and other climatic fluctuations a chironomid mean july air temperature inference model based on a modern calibration set of 109 lakes in norway and svalbard has been developed the 3 component weighted averaging partial least squares inference model performs well with a root mean squared error of prediction of 0 90 c and a maximum bias of 0 59 c both based on leave one out cross validation which is lower than chironomid temperature inference models developed in canada switzerland and finland however while temperature inference models perform well in the lateglacial the more subtle climatic changes of the holocene are more difficult to reconstruct because the likely temperature changes are close to the limits of the prediction errors of the existing models to address this problem future work is required to refine and develop the calibration set by further improving taxonomic resolution by adding more lakes to the calibration set and by investigating the influence of other environmental variables on chironomid distributions and abundances

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

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

a review of multi proxy data for the younger dryas in atlantic canada abstract multi proxy data obtained from lake sediments and buried organic sequences is reviewed and discussed as evidence for the younger dryas cooling event in atlantic canada sedimentological studies indicate that lake basins were subject to increased erosion due to climate cooling while glacial and periglacial sediments overlying peats have been attributed to the effects of small younger dryas ice caps building up in highland areas of nova scotia pollen evidence from over 30 sites shows two broad patterns of lateglacial vegetation change in the region the younger dryas cooling caused the replacement of closed boreal forest by shrub tundra in southern new brunswick and central mainland nova scotia and the replacement of shrub tundra by herb tundra in central new brunswick northern nova scotia and newfoundland chironomid data indicate that the younger dryas was marked by a drop in summer lake surface water temperatures of ca 6 c while diatom data suggest that marked limnological changes also occurred based on ams 14c dates from terrestrial plant macrofossils of 8 sites the younger dryas event in atlantic canada lasted from ca 10 830 to 10 000 bp these dates match most of those from northwest and central europe suggesting that this climatic event affected the entire north atlantic region essentially simultaneously

rapid oceanic and atmospheric changes during the younger dryas cold period the younger dryas event which began approximately 12 900 years ago was a period of rapid cooling in the northern hemisphere driven by large scale reorganizations of patterns of atmospheric and oceanic circulation 1 3 environmental changes during this period have been documented by both proxy based reconstructions 3 and model simulations 4 but there is currently no consensus on the exact mechanisms of onset stabilization or termination of the younger dryas 5 8 here we present high resolution records from two sediment cores obtained from lake krakenes in western norway and the nordic seas multiple proxies from lake krakenes are indicative of rapid alternations between glacial growth and melting during the later younger dryas meanwhile reconstructed sea surface temperature and salinity from the nordic seas show an alternation between sea ice cover and the influx of warm salty north atlantic waters we suggest that the influx of warm water enabled the westerly wind systems to drift northward closer to their present day positions the winds thus brought relatively warm maritime air to northern europe resulting in rising temperatures and the melting of glaciers subsequent input of this fresh meltwater into the ocean spurred the formation of sea ice which forced the westerly winds back to the south cooling northern europe we conclude that rapid alternations between these two states immediately preceded the termination of the younger dryas and the permanent transition to an interglacial state the impact of freshwater pulses released from northern hemisphere ice sheets on the north atlantic meridional overturning circulation has been suggested as a likely mechanism for the younger dryas cooling 7 11 in addition a responsive sea ice cover has been proposed as a mechanism that could rapidly alter the heat exchange between the ocean and atmosphere during the last glacial period 12 13 the roles of the ocean and the atmosphere in triggering the climate shifts around the younger dryas are much discussed 9 these hypotheses are difficult to resolve partly because the temporal resolution of most palaeoclimate archives is too coarse to enable the anatomy of the younger dryas stadial to be adequately described 14 to address these questions we here present a lake sediment record at sub annual resolution together with new data on the sea surface conditions of the norwegian atlantic current nwac throughouttheyoungerdryasstadial fig 1

a late glacial holocene palaeoecological record from pye lake on the eastern shore of nova scotia canadageological survey of canada contribution 20080395 pollen and chironomid analyses and radiocarbon dating at pye lake on the eastern shore of nova scotia are used to outline the vegetation and climatic history of the area the coast was deglaciated prior to 12 200 14c bp 14 300 cal bp and herbaceous tundra vegetation invaded the area midge inferred maximum summer surface water temperatures in the lake ranged between 9 and 11 c subsequent gradual warming to 18 c by 10 800 14c bp 12 725 cal bp favoured the migration of a variety of herbaceous and shrub taxa into the region rapid cooling to 10 c saw vegetation revert to herbaceous tundra communities this interval related to the younger dryas cold interval of the north atlantic and europe lasted until 10 000 14c bp 11 630 cal bp the climate then warmed again to conditions similar to those that prevailed immediately before onset of younger dryas cooling further warming saw successive tree species migrate into the area until by the mid holocene the forests contained most of the taxa preva

middle miocene ice sheet expansion in the arctic views from the barents sea 1 revised core data from ocean drilling program odp leg 151 hole 909c and preglacial paleorelief and bathymetric reconstructions in the barents sea and the arctic gateway region indicate that large scale glaciations were already developed in the northern barents sea during the middle miocene climate transition mmct 15 14 million years ago our findings show that subsequent to an ice free period during the miocene climate optimum mco 17 15 ma glacially eroded materials from the uplifted northern barents sea were transported by iceberg flotillas toward the fram strait the simultaneous opening of the north atlantic arctic gateway provided pathways for iceberg transport from the north the expansive ice growth is probably induced by both large scale changes in ocean circulation due to enhanced flow of atlantic water into the arctic ocean during opening of the gateway and concurrent global cooling during the mmct

rapid response of forested vegetation to multiple climatic oscillations during the last deglaciation in the northeastern united states abstract isotopic and pollen results from a marl lake white lake in the mid atlantic region of usa indicate the coupling of climate and vegetation changes oxygen isotopes of calcite from this site show multiple oscillations at millennial and centennial scales including the younger dryas with 3 negative shifts in 18o at 12 4 11 4 ka 1 ka 1000 cal yr bp and three cold events of magnitude 1 2 shifts during the bolling allerod warm period boa at 14 3 12 4 ka pollen data from the same core show nearly synchronous close correspondence with isotope inferred climate shifts indicating rapid forest response to deglacial climate oscillations in southern new england a plateau like boa is similar to other records around the north atlantic ocean

termination of the last glaciation in the iberian peninsula inferred from the pollen sequence of quintanar de la sierra abstract a 4 5 m thick late glacial pollen sequence supported by 17 ams14c dates has been investigated at the quintanar de la sierra marshland iberian cordillera north central spain pollen zones were defined that correspond to successive phases in vegetation history during the end of the late wurm late glacial interstade and younger dryas periods a transfer function approach has been adopted to derive quantitative climate estimates from the pollen assemblage data a first expansion ofjuniperusandhippophae about 13 50014c yr b p indicates the beginning of the late glacial interstade which is characterized by ajuniperus betula pinussuccession that suggests higher temperatures and moisture than during full glacial time the younger dryas interval is recorded by a 120 cm thick sediment unit that is dominated by herbaceous pollen transfer function estimates suggest that the climate during this period was cold with low precipitation during most of the year although not in summer the holocene arboreal recolonization in the area started about 10 00014c yr b p with a renewedjuniperus betula pinussuccession related to a strong increase in annual temperature and precipitation the start of this process was synchronous with mean sea surface temperature changes as recorded from the nearby su 81 18 marine core the strong affinity with other european late glacial pollen sequences demonstrates that the pattern of climatic changes during the last glacial interglacial transition was similar in both northwestern and southwestern europe

the low latitude monsoon climate during dansgaard oeschger cycles and heinrich events during the last 100 000 years dansgaard oeschger cycles d o cycles and heinrich events have been the dominant signal of past climate variability over greenland and the north atlantic the succession of stadials cold and interstadials warm associated with these cycles has been documented in records from the entire northern hemisphere south america new zealand antarctica the south atlantic and the southern ocean evidently climate forcing in the d o band affects both hemispheres the origin and cause of these teleconnected patterns is still unknown even if a large proportion of the cooling in europe and northern asia during heinrich events is a meteorological response to cold surface water in the north atlantic resulting from the surge of the laurentian and scandinavian ice sheets but this does not imply that the d o cycles are a priori caused by the collapse of these large icesheets a severe challenge to a primary origin from the northern ice sheet and north atlantic comes from the observation that warming in antarctica and the circumpolar current leads the north atlantic changes by some 1500 years charles et al 1996 blunier et al 1998 in the second part of the paper we investigate new deep sea records from the low latitude monsoon system mainly corroborating the result of schulz et al 1998 that the indian monsoon showed d o variability the abundance of eolian dust indicating continental humidity aridity in core 70kl from the arabian sea shows humid intervals which seem to correlate with temperature maxima in the antarctic vostok ice core apparently the low frequency sub milankovitch variability of the monsoon is associated with the southern hemisphere the d o scale component in the monsoonal climate on the other hand shows a succession of short humid intervals the sequence is most closely comparable to the greenland temperature record and to the stadial interstadial succession in the pacific santa barbara basin odp 893 in order to understand the global forcing of climate change in the d o band it appears necessary to quantify the phase relationships not only between d o cycles in the polar ice cores bender et al 1994 blunier et al 1998 steig et al 1998 but also between the low latitude pacific indian ocean and the high latitude records

precise 14c ages of the vedde and saksunarvatn ashes and the younger dryas boundaries from western norway and their comparison with the greenland ice core gicc05 chronology the greenland ice cores with the gicc05 chronology represent a standard for late quaternary climate events and their ages whereas many other palaeoclimatic archives are dependent on 14 c dates it is therefore critical to know if the ice core and the calibrated 14 c chronologies are identical and if not to quantify the offset between them we present bayesian age depth modelling of 118 accelerator mass spectrometry 14 c dates from kraukenes lake calibrated using intcal09 that provide high precision ages of 12 066 42 and 10 210 35 cal a bp for the vedde and saksunarvatn ashes respectively the lower and upper younger dryas boundaries have ages of 12 710 52 and 11 546 59 cal a bp respectively the four dated levels coincide with correlative levels in gicc05 within the dating uncertainties but are all consistently younger at kraukenes the ages of the tephra chronostratigraphic markers suggest a mean offset of 70 years to older ages in the gicc05 compared with the intcal09 time scale responses to small climate changes 30 years before the younger dryas boundaries at kraukenes are suggested to correspond to the defined greenland stadial 1 boundaries this suggested difference in timing 30 years and time scale offset 70 years mean that the greenland stadial 1 boundaries appear 100 years older than the younger dryas boundaries copyright 2013 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

intensification and variability of ocean thermohaline circulation through the last deglaciation neodymium isotope ratios in the authigenic ferromanganese oxide component in a southeastern atlantic core reveal a history of the global overturning circulation intensity through the last deglaciation from a minimum during the last glacial maximum lgm north atlantic deep water nadw began to strengthen between 18 and 17 kyr cal bp approximately 2000 3000 years before the bolling warming it exhibits a gradually increasing baseline intensity that plateaus in the early holocene tracks increasing northern hemisphere insolation and parallels atmospheric co2 concentration millennial scale fluctuations are superimposed on this baseline nadw increase corresponding to events in northern hemisphere climate records the millennial excursions show sharp increases associated with the pre bolling retreat of continental glaciers and the bolling warming itself a decrease with allerod cooling and a recovery through the younger dryas and early holocene the data confirm a close link between deep ocean circulation and north atlantic climate changes there is no clear linkage with meltwater pulses indicating that rapid meltwater additions did not trigger observable mode changes in nadw production however rapid changes in north atlantic sea ice cover show a strong relationship with the millennial perturbations of nadw flux to the deep southern ocean the data indicate that the baseline intensity of nadw reaching the cape basin is paced by northern hemisphere insolation and that north atlantic sea ice coverage acts as a major amplifying link between the oceans and the atmosphere d 2004 elsevier b v all rights reserved

accumulation rates of major constituents of hemipelagic sediments in the deep alboran sea a centennial perspective of sedimentary dynamics the accumulation rates of sediment and major constituents in three different geographic areas of the alboran sea have been assessed by means of 210pb and 137cs concentration profiles mixing is present in the top layer of the sedimentary column with mixing coefficients estimated to range from 0 2 to 15 cm2 yr 1 overall apparent sedimentation rates for the last 100 years range from 0 014 to 0 182 g cm 2 yr 1 and show a tendency to decrease with distance to the coast and water column depth however specific characteristics of the sea floor for each physiographic environment govern the actual patterns of sediment accumulation particularly noticeable are the feeding role of submarine canyons the trapping effect of slope terraces and the isolation caused by ridges sediment accumulation induced by turbiditic flows is also observed north of the almeria oran area excess 210pb inventories and surface concentrations reveal a net effect of sediment focussing and point to the role of bottom nepheloid layers in supplying a significant fraction of sediments to the deep areas this is also evidenced by comparison of bottom sediment with the sediment trap data available from the malaga area we estimate that the particle advective input below 30 m above the bottom accounts for as much as 50 70 of the material that is ultimately deposited onto the sea floor the greater abundance of lithogenic material in the malaga zone 80 reflects its larger input in the western alboran sea conversely carbonate contents increase from less than 20 in this area to about 30 in the almeria oran zone reflecting the lesser importance of the dilution by lithogenic components biogenic silica was only detected in some surface samples and no significant preservation was observed below the eh boundary abundance and accumulation rates of organic matter are in accordance with the spatial patterns of primary production in the alboran sea higher in the western part due to the presence of the western alboran gyre however near bottom redistribution leads to the homogenisation of organic matter concentrations in bottom sediments of any given area finally from comparisons with sediment trap data the degradation of organic matter has been estimated to be approximately 30 40 of what reaches the bottom

oxygen 18 16 variability in greenland snow and ice with 10 3 to 105 year time resolution the 3 km long greenland ice sheet project 2 gisp2 ice core presents a 100 000 year detailed oxygen isotope profile covering almost a full glacial interglacial cycle measuranents of isotopic fluctuations in snow frost and atmospheric water vapor samples collected during summer field seasons up to 20 0 are compatible with the large and abrupt 80 160 changes observed in accumulated tim snow pit 15 80 profiles from the gisp2 summit area however show rapid smoothing of the 180 160 signal near the surface beyond about 2 m depth the smoothedi5180 signal is fairly well preserved and can be interpreted in terms of average local weather conditions and climate the longer climate fluctuations also have regional and often global significance in the older part of the record corresponding to marine isotope stages mis 5a to 5d the effect of orbital climate forcing via the 19 and 23 kyr precession cycles and the 41 kyr obliquity cycle is obvious from the end ofmis 5a at about 75 000 years b p till the end of the glacial at the younger dryas preboreal transition at 11 650 years b p the o180 160 record shows frequent rapid switches between intermediate interstadial and low stadial values fourier spectra of the oscillations that are superimposed on the orbitally induced changes contain a strong periodicity at 1 5 kyr a broad peak at 4 0 kyr and additional shorter periods detailed comparison of the gisp2 180 160 record with the vostok antarctica 15d record pacific ocean foraminiferal 180 160 grande pile france tree pollen and insolation indicates that a counterpart to many of the rapid 180 160 fluctuations of gisp2 can be found in the other records and that the gisp2 isotopic changes clearly are the local expression of climate changes of worldwide extent correlation of events on the independent gisp2 and specmap time scales for the interval 10 000 50 000 years b p shows excellent chronometric agreement except possibly for the event labeled 3 1 the glacial to interglacial transition evidently started simultaneously in the arctic and the antarctic but its development and its expression in greenland isotopes was later suppressed by the influence of meltwater especially from the barents sea ice sheet on deep water formation and ocean circulation meltwaters from different ice sheets bordering the north atlantic also influenced ocean circulation during the bolling allerod interstadial complex and the younger dryas and led to a distinct development of european climate and greenland 180 160 values the holocene interval with long term stable mean isotopic values contains several fluauations with periods from years to millennia dominant is a 6 3 year oscillation with amplitude up to 3 to 4 0 periodicities of 11 and 210 years also found in the solar modulated records of the cosmogenic isotopes 1obe and 14c suggest solar processes as the cause of these cycles depression of180 160 values cooling by volcanic eruptions is observed in stacked gisp215 80 records but the effect is small and not likely to trigger major climate changes

variability of the western mediterranean sea surface temperature during the last 25 000 years and its connection with the northern hemisphere climatic changes sea surface temperature sst profiles over the last 25 kyr derived from alkenone measurements are studied in four cores from a w e latitudinal transect encompassing the gulf of cadiz atlantic ocean the alboran sea and the southern tyrrhenian sea western mediterranean the results document the sensitivity of the mediterranean region to the short climatic changes of the north atlantic ocean particularly those involving the latitudinal position of the polar front the amplitude of the sst oscillations increases toward the tyrrhenian sea indicating an amplification effect of the atlantic signal by the climatic regime of the mediterranean region all studied cores show a shorter cooling phase 700 years for the younger dryas yd than that observed in the north atlantic region 1200 years this time diachroneity is related to an intra yd climatic change documented in the european continent minor oscillations in the southward displacement of the north atlantic polar front may also have driven this early warming in the studied area during the holocene a regional diachroneity propagating west to east is observed for the sst maxima 11 5 10 2 kyr b p in the gulf of cadiz 10 9 kyr b p in the alboran sea and 8 9 8 4 kyr b p in the thyrrenian sea a general cooling trend from these sst maxima to present day is observed during this stage which is marked by short cooling oscillations with a periodicity of 730 40 years and its harmonics

biogeochemical and micro facial fingerprints of ecosystem response to rapid late glacial climatic changes in varved sediments of meerfelder maar germany the response of a lacustrine ecosystem to climatic changes from 13 500 to 10 800 bp was studied in a varve dated sediment profile of lake meerfelder maar western germany bulk biogeochemical parameters stable carbon and nitrogen isotopes of sedimentary organic matter and micro facies analysis are used for a detailed investigation of the lake s development from the allerod interstadial al to the younger dryas stadial yd and into the early holocene preboreal varve micro facies reveal rapid changes in composition and seasonal structure of the depositional environment mainly in temporal accordance with changes of terrestrial biozones the respective responses of bulk proxy parameters bi decadal resolution indicate different sensitivities to diverse climatic changes a prominent transition took place within two decades at the al yd boundary 12 690 12 670 bp increased flux of nutrients released from redeposited littoral sediments and shorter yd summer seasons led to an acceleration and concentration of lacustrine primary production with reduced discrimination against 13c high lacustrine primary production was further favored by relatively warm yd summer temperatures at 12 240 varve years bp from 1 year to the next a regular deposition of detrital layers in spring set in which is related to local hydrologic threshold processes amplifying the response to increased snowmelt discharge this distinct change in the middle of the yd is clearly detected by varve micro facies but not equally recorded in organic bulk proxy data especially carbon isotope ratios remain constant and indicate a negligible effect of this process on the productivity of lacustrine algae the yd preboreal transition 11 645 11 585 bp is marked by a characteristic change in micro facies throughout this transition stable carbon isotope ratios strongly decline while the accumulation of opal and organic matter om remained constant this is seen as an increasing importance of spring and autumn for gross primary production at the onset of the holocene

210pb activities in and fluxes to sediments of the washington continental slope and shelf abstract surface sediments of the washington coast have 210 pb activites which average 104 48dpm g for submarine canyon and slope regimes and 18 12dpm g for the continental shelf regime 210 pb sedimentary fluxes are also higher in canyons averaging 18 13dpm cm 2 per yr compared to 5 2 3 1 dpm cm 2 per yr for slope and 4 8 1 8dpm cm 2 per year for shelf regions these 210 pb activities and fluxes are 2 7 times greater than those reported for other coastal regions inputs from the atmosphere and the columbia river are not sufficient to supply the 210 pb but advection of seawater containing dissolved 210 pb produced in situ from 226 ra provides an input several times larger than the sedimentary fluxes the sedimentary 210 pb flux is limited by scavenging reactions rather than by supply of dissolved 210 pb calculations of maximum biological uptake and fluxes of 210 pb and selective chemical leaching experiments all show that the primary scavenging processes are due to hydrous mn and fe oxides rather than biological phases the pattern of higher 210 pb depositional fluxes in canyons than in nearby open slope areas of comparable water depth is most reasonably explained by enhanced scavenging of dissolved 210 pb near the sea floor rather than by processes operating throughout the water column relatively rapid removal of dissolved 210 pb from the near bottom nepheloid layer to slope and canyon sediments is shown by its mean residence time of less than two years in this layer

the lateglacial and early holocene vegetation and environment in the dovre mountains central norway as signalled in two lateglacial nunatak lakes abstract by using heavy coring equipment in two high altitudinal lakes 1253 and 1316 m a s l at dovre central norway 1 1 5 m of unsorted coarsely minerogenic sediments were retrieved below the holocene organic sediments the minerogenic sequence contained well preserved pollen and chironomid remains revealing new and detailed palaeoenvironmental knowledge of the mountains in central norway during the last 5 6000 years of the lateglacial lg period however the lg chronology is based on biostratigraphical correlations and not on 14c dates due to low organic content in the minerogenic sediments the emerging lg nunataks probably indicating a thin and multi domed scandinavian ice sheet was rapidly inhabited by immigrating species which could explain the present centric distributions of certain arctic alpine plants the lg vegetation development included a pre interstadial dominated by mineral soil pioneers an interstadial dominated by shrubs and dwarf shrubs and the younger dryas cold period with recurring dominance of pioneers pollen and stomata of pinus and picea indicate their local lg presence at dovre lg climate oscillations are indicated by pollen stratigraphy and for the later part of lg also by chironomids these oscillations could correspond to heinrich event 1 gi 1d gi 1b and the younger dryas cold events the lg interstadial reached july mean temperatures of more than 7 8 c similar to the present chironomids colonized the lake already during the onset of the interstadial albeit at very low richness and abundances starting from yd there are sufficient chironomid head capsules to perform a temperature reconstruction the holocene warming of about 2 c initiated a vegetation closure from snow beds and dwarf shrub tundra to shrubs and forests birch forests established about 10 ka cal bp slightly earlier than pine forests alnus expanded ca 9 2 ka cal bp and a thinning of the local forests occurred from ca 7 ka cal bp two short lasting climate deteriorations found in the pollen record and the chironomid record may represent the preboreal oscillation and the 8 2 event the holocene thermal maximum is indicated around ca 7 8 7 3 ka cal bp showing a chironomid inferred july mean of at least 11 c this is ca 3 c warmer than today

the holocene younger dryas transition recorded at summit greenland analysis of ice from dye 3 greenland has demonstrated that the transition between the younger dryas and holocene climate periods occurred over a 40 year period a near annually resolved multiparameter record of the transition recorded in the gisp2 core from summit greenland shows that most of the transition occurred in a series of steps with durations of about 5 years some climate proxies associated with mid latitude sources appear to have changed about 15 years before climate proxies associated with more northern regions changes in atmospheric water vapor are likely to have played a large role in the climate transition

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

a stratigraphic framework for abrupt climatic changes during the last glacial period based on three synchronized greenland ice core records refining and extending the intimate event stratigraphy due to their outstanding resolution and well constrained chronologies greenland ice core records provide a master record of past climatic changes throughout the last interglacial glacial cycle in the north atlantic region as part of the intimate integration of ice core marine and terrestrial records project protocols have been proposed to ensure consistent and robust correlation between different records of past climate a key element of these protocols has been the formal definition and ordinal numbering of the sequence of greenland stadials gs and greenland interstadials gi within the most recent glacial period the gs and gi periods are the greenland expressions of the characteristic dansgaard oeschger events that represent cold and warm phases of the north atlantic region respectively we present here a more detailed and extended gs gi template for the whole of the last glacial period it is based on a synchronization of the ngrip grip and gisp2 ice core records that allows the parallel analysis of all three records on a common time scale the boundaries of the gs and gi periods are defined based on a combination of stable oxygen isotope ratios of the ice 18o reflecting mainly local temperature and calcium ion concentrations reflecting mainly atmospheric dust loading measured in the ice the data not only resolve the well known sequence of dansgaard oeschger events that were first defined and numbered in the ice core records more than two decades ago but also better resolve a number of short lived climatic oscillations some defined here for the first time using this revised scheme we propose a consistent approach for discriminating and naming all the significant abrupt climatic events of the last glacial period that are represented in the greenland ice records the final product constitutes an extended and better resolved greenland stratotype sequence against which other proxy records can be compared and correlated it also provides a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

from cold to cool in northernmost norway lateglacial and early holocene multi proxy environmental and climate reconstructions from jansvatnet hammerfest abstract a multi proxy palaeoecological study of the lateglacial and early holocene sediments of jansvatnet hammerfest northernmost norway 70 39 n showed that cold and arid conditions prevailed in both the lateglacial interstadial and the younger dryas terrestrial proxies are macrofossils and pollen aquatic proxies are plant and invertebrate macrofossils pollen diatoms and chironomids mean july temperatures were reconstructed using pollen and chironomid calibration functions and ecological knowledge of the fossil flora and fauna lake water ph was reconstructed using a diatom ph calibration function above sterile basal deglacial silts biotic activity was detected around 14600 years ago in the interstadial chronologically equivalent to the bolling allerod in the greenland ice core chronology catchment vegetation resembled polar desert and ultra cold stenothermic chironomids lived in the lake however diatom assemblages were diverse and dynamic in the younger dryas stadial conditions deteriorated in the early younger dryas chironomid inferred air temperatures ci tjul fell about 1 c pollen inferred temperatures pi tjul did not fall and the terrestrial vegetation hardly changed because of the extreme aridity the lake water was turbid from suspended clay which diminished aquatic life later in the younger dryas ca 12400 cal yr bp reconstructed mean july temperatures fell by a further 3 c and were close to the minimum to support life at around 3 4 c however decreased turbidity allowed moss growth on the lake bottom that provided habitats for invertebrates and diatoms in the last 200 years of the younger dryas temperatures increased by 2 3 c and terrestrial and aquatic organisms responded quickly at the start of the holocene a rapid increase of more than 3 c in pi tjul to 9 5 c initiated the replacement of sparse arctic tundra by low arctic dwarf shrub heath simultaneously a further 2 c increase in ci tjul to 10 11 c reflected a regime shift in the lake aquatic macrophytes rapidly replaced the moss carpet diatom assemblages stabilised and diatom plankton developed and cold stenotherm chironomids were replaced by cool temperate taxa productivity increased as ci tjul reached a steady maximum of around 12 c and pi tjul reached 10 5 c at about 10000 cal yr bp at this time tree birch arrived and woodland developed over the catchment birch could have immigrated from the south up the west coast or from the east along the barents sea coast acidophilous aquatic taxa increased as diatom inferred ph gradually decreased from 7 3 to 6 6 after ca 9380 cal yr bp the density and extent of birch woodland decreased and species of exposed rocky areas increased reflecting increased windiness precipitation and possibly a small decrease in july temperatures birch now formed the arctic tree line at jansvatnet the lateglacial climatic pattern at jansvatnet resembles patterns detected elsewhere in northern norway and svalbard and in marine records from the norwegian and barents seas but contrasts with patterns in southern norway

oxygen isotopes of lake marl at gerzensee and leysin switzerland covering the younger dryas and two minor oscillations and their correlation to the grip ice core the ratio of oxygen isotopes is a temperature proxy both in precipitation and in the calcite of lacustrine sediments the very similar oxygen isotope records from greenland ice cores and european lake sediments during the last glacial termination suggest that the drastic climatic changes occurred quasi simultaneously on an extra regional probably hemispheric scale in order to study temporal relations of the different parameters recorded in lake sediments for example biotic response times to rapid climatic changes a precise chronology is required in unlaminated lake sediments there is not yet available a method to provide a high resolution chronology especially for periods with radiocarbon plateaux alternatively an indirect time scale can be constructed by linking the lake stratigraphy with other well dated climate records new oxygen isotope records from gerzensee and leysin with an estimated sampling resolution of between 15 and 40 years match the greenlandic isotope record in many details under the assumption that the main variations in temperature and thus in oxygen isotopes occurred about simultaneously in greenland and switzerland we have assigned a time scale to the lake sediments of gerzensee and leysin by wiggle matching their stable isotope records with those of greenland ice cores which are among the best dated climatic archives we estimate a precision of 20 to 100 years during the last glacial termination

very fast environmental changes at the pleistocene holocene boundary recorded in laminated sediments of lake gościz poland abstract this paper presents a reconstruction of the climatic changes at the pleistocene holocene transition recorded in the annually laminated sediments of lake go ci a z poland this reconstruction is based on pollen stable isotope mineralogical and chemical analyses of sediments made with a time resolution of 1 4 yr it reveals a sequence of abrupt climatic changes which preceded and followed the major warming around 11 500 cal bp our data show that the warming period was preceded by a 30 yr long phase of increased winter and decreased summer precipitation 11 550 11 520 cal bp about 11 520 cal bp a very brief period of wetter conditions occurred simultaneously with the beginning of the major warming however most of the first phase of the major warming 11 520 11 500 cal bp was characterised by a generally dry climate presumably due to lowered winter precipitation our records suggest that in this phase the warming concerned winter seasons mostly in the second phase 11 500 11 460 cal bp the warming also concerned summer seasons also a distinct increase of humidity is noted in this period which caused moistening of soils and despite enhanced evaporation and evapotranspiration inhibited the process of lake level drop the following 70 years 11 460 11 390 cal bp were rather dry which caused a distinct lowering of the lake and probably also of groundwater level in this period maximum biological productivity per unit area in the lake is noted the whole sequence of phases of rather different climates was completed within a time interval 160 years spanning two human lifes only one should stress that the transitions between the consecutive phases were rather abrupt lasting no longer than 10 years

retreat velocity of the north atlantic polar front during the last deglaciation determined by 14 c accelerator mass spectrometry the glacial oscillations which dominate the quaternary global climate are closely related to changes in incoming solar radiation but the details of palaeoclimatic spectra suggest that other parameters usually referred to as feedback have significantly increased the climatic response to extraterrestrial forcing1 the last deglaciation appears to be one of the more characteristic examples of nonlinearity because its abruptness strongly contrasts with the smooth shape of the associated solar radiation maximum dated at 11 000 yr bp in addition the presence of the younger dryas cold event concomitant with the solar radiation maximum could be interpreted as a transitory phenomenon caused by the rapid meltwater influx linked to the first phase of the ice sheet s disintegration2 3 here using accelerator mass spectrometry we date precisely the movements of the polar front during the whole period of glacial retreat 15 000 8 000 yr bp our results show that the polar front has moved between 35 n and 55 n in 1 000 yr for the earliest retreat 12 500 12 000 bp and moved almost instantaneously that is 400 yr during the two abrupt climatic changes associated with the younger dry as cold event

a revised 10 4 c magnitude of the abrupt change in greenland temperature at the younger dryas termination using published gisp2 gas isotope data and air thermal diffusion constants abstract we revisit the portion of nature 391 1998 141 devoted to the abrupt temperature increase reconstruction at the younger dryas preboreal transition the original estimate of 5 to 10 c abrupt warming is revised to 10 4 c the gas isotope data from the original work were employed combined with recently measured precise air thermal diffusion constants geochim cosmochim acta 67 2003a 345 j phys chem 23a 2003b 4636 the new constants allow a robust interpretation of the gas isotope signal in terms of temperature change this was not possible at the time of the original work when no air constants were available three quasi independent approaches employed in this work all give the same result of a 10 c warming in several decades or less the new result provides a firm target for climate models that attempt to predict future climates

sediment accumulation rates in the southern barcelona continental margin nw mediterranean sea derived from 210pb and 137cs chronology sediment cores were collected from the southern barcelona continental margin including the foix canyon in order to study sediment accumulation in this area for this purpose 210pb 137cs and to a lesser extent 239 240pu and heavy metals were determined in sediment sections using state of the art techniques 210pb concentration profiles and 137cs 239 240pu and heavy metals profile features were used to establish the sediment chronologies further information was also obtained from granulometric analyses the magnitudes studied and correlated in this work included surface activities mixing rates accumulation rates and inventories sediments on the continental shelf showed a varied degree of mixing except possibly cn 23 sedimentation rates were relatively small and the sedimentary material probably had a common origin cores from the slope showed less mixing and in cores cn 36 and eb 2 located in the foix canyon axis the 137cs signal vs depth was clear and well preserved accumulation rates and total 210pb inventories were maximum in core cn 36 at mid slope of the canyon which was considered to be an active depocenter core cn 38 collected on the open slope showed a much smaller accumulation rate therefore it was concluded that shelf material is being transported alongshore by the prevailing currents and becomes focused in the canyon which is acting as a natural trap within the canyon this material is preferentially deposited at a mid slope depocenter little extra material reaches the lower canyon area in this area core eb 2 appeared to show signs of the presence of resuspended material possibly derived from the canyon walls finally observed changes in sedimentation rates during the 1930s could not be explained on the basis of current knowledge and this is suggested to be an important subject for further research