the role of oceanic forcing in mid holocene northern hemisphere climatic change previous model investigations suggested that changes in orbital forcing and feedbacks associated with northward expansion of the boreal forest were both required to explain the full magnitude of enhanced high latitude northern hemisphere summer warming at 6 ka thus implying that biospheric feedbacks decreased planetary albedo associated with forest expansion may be large in the future foley et al 1994 tempo testing earth system models with paleo observations 1996 before the magnitude of past biospheric and other feedbacks can be estimated with confidence however the role of realistic high latitude oceanic forcing i e sea surface temperature sst increases and sea ice reductions should also be considered here we review existing paleoceanographic observations that suggest portions of the north atlantic were up to 4 c warmer than today at 6 ka we then combine our estimates of mid holocene north atlantic sst and sea ice conditions with new climate model simulations to suggest that a significant portion of high latitude summer warming at 6 ka in the northern hemisphere can be accounted for by altered orbital forcing ssts and sea ice relative to today our results underscore the importance of incorporating realistic boundary conditions when using paleoenvironmental data to evaluate the climate system s sensitivity to altered forcing and suggest that high latitude oceanic feedbacks were major contributors to enhanced high latitude summer warming in the northern hemisphere at 6 ka

living coccolithophore communities in the norwegian greenland sea and their record in sediments abstract investigation of epipelagic coccolithophore communities along a transect from the voring plateau off norway to scoresbysund east greenland and comparison with coccolith assemblages in underlying surface sediments reveal that sedimentation of coccoliths is dependent on the following factors 1 composition of the coccolithophore communities and their bloom phases 2 grazing and selective destruction by zooplanktonic organisms 3 type of vertical flux in fecal pellets and 4 varying carbonate dissolution in different water masses dissolution increases towards the boundaries of carbonate sedimentation as a result the original composition of the living communities becomes increasingly obscured in the impoverished taphocoenoses however differential resistance to dissolution of the two primary calcareous nannoplankton species emiliana huxleyi and coccolithus pelagicus is such that occurrence and ratio of the two species in surface sediments reflect the various water masses in the norwegian greenland sea

the magnetic fraction a tracer of deep water circulation in the north atlantic abstract we report on a mineral magnetic study of a series of holocene marine sedimentary sequences distributed from northern to southern bjorn and gardar drifts 56 n to 61 n and in the charlie gibbs fracture zone about 53 n all the cores are located at water depths bathed by the iceland scotland overflow water isow a precursor of the north atlantic ocean deep water formed in the nordic seas and flowing into northeast north atlantic after passing over the volcanic sills between iceland and scotland the magnetic fraction is composed of low ti content magnetites with a grain size distribution in the pseudo single domain range these grains originate from a unique source in the north through the erosion by the bottom waters of the icelandic basaltic province the magnetic grain size remains fairly constant in each core but on average progressively fines towards the south and downstream likewise the magnetic concentration and mean magnetic flux decrease towards the south the spatial evolution of the magnetic concentration and of the magnetic grain size suggests a transport of these magnetites by bottom currents associated with the overflow water downstream from the source with progressive deposition of this magnetic fraction along the path of the isow this study provides evidence that characterization of the magnetic parameters of sediments deposited in such an oceanographic context of a unique source upstream and a well defined water mass may be used to detect and trace deep oceanic circulation changes

late quaternary sediment flux on sedimentary drifts in the northeast atlantic abstract comparison between the last glacial and holocene periods of the terrigenous and carbonate sediment flux distributions in the whole northeastern atlantic basin points out the role of deep circulation relative to other processes during the holocene the global terrigenous flux is similar to that during the glacial period 4 compared with 4 7 g cm 2 ky 1 despite a general decrease of terrigenous supplies the flux distribution however is different high values are located in areas of bottom current sedimentation contourite drifts instead of along continental margins where downslope processes are dominant and areas with major ice rafting the global carbonate flux is higher during the holocene 3 compared with 1 5 g cm 2 ky 1 but the carbonate flux distribution matches that of the terrigenous flux both flux patterns are strongly controlled by reworking and redeposition of sediments by bottom currents flux variation in three cores collected on the feni gardar and faro drifts compared to areas of little or no bottom current activity highlights the deep water circulation fluctuations since the last glacial maximum in areas dominated by downslope processes bay of biscay or by ice rafted sediment deposition mid atlantic ridge around 45 n the sediment fluxes are maximum during the deglacial warming and minimum during the holocene period areas dominated by bottom current sedimentation are all characterized by highest sedimentation during the holocene but the flux variations reveal that the norwegian sea water overflow nswo and the mediterranean outflow mo fluctuated differently according to the regional climatic context and the latitudinal transgression of climatic warming on the feni and gardar drifts higher holocene fluxes coincide with the re initiation of nswo at about 10 000 yrs bp the highest flux on the gardar drift results from a stronger outflow across the iceland faeroe ridge than across the faeroe scotland ridge this flow is responsible for high sediment fluxes all along the eastern side of the mid atlantic ridge as far south as 45 n on the faro drift the reactivation of the mediterranean outflow mo took place earlier as three episodes of greater bottom current activity occurred since about 15 000 yrs bp fluxes are maximum during the deglacial warming and remain high during the holocene

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

holocene interdependences of changes in sea surface temperature productivity and fluvial inputs in the iberian continental shelf tagus mud patch 1 sea surface temperature sst marine productivity and fluvial input have been reconstructed for the last 11 5 calendar cal ka b p using a high resolution study of c37 alkenones coccolithophores iron content and higher plant n alkanes and n alkan 1 ols in sedimentary sequences from the inner shelf off the tagus river estuary in the portuguese margin the sst record is marked by a continuous decrease from 19 c at 10 5 and 7 ka to 15 c at present this trend is interrupted by a fall from 18 c during the roman and medieval warm periods to 16 c in the little ice age river input was very low in the early holocene but increased in the last 3 cal ka b p in association with an intensification of agriculture and deforestation and possibly the onset of the north atlantic oscillation atlantic multidecadal oscillation modes of variability river influence must have reinforced the marine cooling trend relative to the lower amplitude in similar latitude sites of the eastern atlantic the total concentration of alkenones reflects river induced productivity being low in the early holocene but increasing as river input became more important rapid cooling of 1 2 c occurring in 250 years is observed at 11 1 10 6 8 2 6 9 and 5 4 cal ka b p the estimated age of these events matches the ages of equivalent episodes common in the ne atlantic mediterranean region this synchronicity reveals a common widespread climate feature which considering the twentieth century analog between colder ssts and negative north atlantic oscillation nao is likely to reflect periods of strong negative nao

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

deglacial sea level record from tahiti corals and the timing of global meltwater discharge the timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets1 and their effects on the earth s surface2 3 moreover the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans which probably disturbed the ocean s thermohaline circulation and hence global climate4 7 sea level increases bear witness to the melting of continental ice sheets but only two such records from barbados8 9 and new guinea10 11 corals have been accurately dated but these corals overlie active subduction zones where tectonic movements are large and often discontinuous especially in new guinea so the apparent sea level records may be contaminated by a complex tectonic component here we date fossil corals from tahiti which is far from plate boundaries and thus is likely to be tectonically relatively stable and remote from the locations of large former ice sheets the resulting record indicates a large sea level jump shortly before 13 800 calendar years bp which corresponds to meltwater pulse 1a in the barbados coral records8 9 the timing of this event is more accurately constrained in the tahiti record revealing that the meltwater pulse coincides with a short and intense climate cooling event12 15 that followed the initiation of the bolling allerod warm period12 16 but preceded the younger dryas cold event by about 1 000 years

millennial scale climatic cycles in the early pliocene pollen record of ptolemais northern greece early pliocene lacustrine sediments from the ptolemais basin northern greece exhibit a climatically induced cyclicity which can be correlated with the orbital cycle of precession superimposed on precession controlled cycles palynological time series data reveal a higher order climatic cyclicity with periodicities of 10 2 5 and 1 5 ka these millennial scale vegetation changes are likely to reflect changes of the soil moisture gradient on mountain slopes caused by fluctuations in orographic winter precipitation such fluctuations corroborate the concept of a nao like north atlantic climatic teleconnection during early pliocene times the periodicities are similar to those of climate oscillations inferred from quaternary records the occurrence of millennial scale cyclicity in a time interval when the northern hemisphere was essentially ice free implies an ultimate forcing mechanism that operated independently of changes in the thermohaline circulation in the atlantic ocean the cycles are likely to be related to long period variations in solar activity

calculation of coccolith volume and its use in calibration of carbonate flux estimates abstract estimates of coccolith volume help in determining total coccolith carbonate fluxes and the relative contributions of various coccolith species it is argued here that the best approach to deriving such coccolith volumes is to calculate shape factors k s for each species separately based on reconstruction of cross profiles and to determine mean sizes from measurement of size variation in the sample of interest then volume k s l 3 values of k s are given for the most important extant coccolith species based on reconstruction of cross sections followed by calculation of a volume of rotation using an iterative routine implemented in an image analysis package substantial errors ca 50 are inevitable in such calculations but the resultant data are nonetheless of value coccolith assemblages from north atlantic 47 n 20 w jgofs 1989 sediment trap samples are analysed as a test case calculated coccolith pic fluxes constitute 30 80 of the chemically determined total pic fluxes

chronology for climate change developing age models for the biogeochemical ocean flux study cores we construct age models for a suite of cores from the northeast atlantic ocean by means of accelerator mass spectrometer dating of a key core bofs 5k and correlation with the rest of the suite the effects of bioturbation and foraminiferal species abundance gradients upon the age record are modeled using a simple equation the degree of bioturbation is estimated by comparing modeled profiles with dispersal of the vedde ash layer in core 5k and we find a mixing depth of roughly 8 cm for sand sized material using this value we estimate that age offsets between unbioturbated sediment and some foraminifera species after mixing may be up to 2500 years with lesser effect on fine carbonate 10 mu m ages the bioturbation model illustrates problems associated with the dating of instantaneous events such as ash layers and the heinrich peaks of ice rafted detritus correlations between core 5k and the other cores from the bofs suite are made on the basis of similarities in the downcore profiles of oxygen and carbon isotopes magnetic susceptibility water and carbonate content and via marker horizons in x radiographs and ash beds

reconstructed centennial variability of late holocene storminess from cors fochno wales uk future anthropogenic climate forcing is forecast to increase storm intensity and frequency over northern europe due to a northward shift of the storm tracks and a positive north atlantic oscillation however understanding the significance of such a change is difficult because the natural variability of storminess beyond the range of instrumental data is poorly known here we present a decadal resolution record of storminess covering the late holocene based on a 4 m long core taken from the peat bog of cors fochno in mid wales uk storminess is indicated by variations in the minerogenic content as well as bromine deposited from sea spray twelve episodes of enhanced storm activity are identified during the last 4 5 cal ka bp although the age model gives some uncertainty in the timings it appears that storminess increased at the onset and close of north atlantic cold events associated with oceanic changes with reduced storm activity at their peak cors fochno is strongly influenced by westerly moving storms so it is suggested that the patterns were due to variations in the intensity of westerly airflow and atmospheric circulation during times when the latitudinal temperature gradient was steepened

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

physical properties of reykjanes ridge sediments and their linkage to high resolution greenland ice sheet project 2 ice core data five gravity cores taken from the reykjanes ridge have been used to establish a link between sediment physical properties and atmospheric records documented by 18o variations in greenland ice cores over the last 45 000 calendar years marine gamma ray attenuation porosity evaluator density and magnetic susceptibility variations could be linked with the ice core dansgaard oeschger and bond cycles this is supported by ice rafted detritus ird grain size the quartz feldspar ratio and carbonate isotopic and foraminiferal records the covariation of the sediment physical properties and 18o in greenland ice indicates a coupling of atmospheric temperature and paleocirculation variations gradual reduced bottom currents iceland scotland overflow water and enhanced iceberg discharges have been reconstructed for cold atmospheric periods relative to interstadial times in the study area the magnetic susceptibility signal is not related to the ice rafted detritus input but most probably reflects the variations of the iceland scotland overflow water intensity transporting titanomagnetite into the reykjanes ridge region

early holocene temperature variability inferred from chironomid assemblages at hawes water northwest england this paper presents the first high resolution chironomid inferred mean july air temperature c it reconstruction for the early holocene from england the reconstruction is based on a core recovered from a terrestrialised carbonate bench at hawes water a small hard water lake in northwest england the record shows that temperatures rose rapidly after the younger dryas with temperatures reaching 14 0 c at the beginning of the holocene over millennial timescales the temperature record points to a slight rise in temperatures towards the top of the sequence at around 8000 years before the year 2000 b2k the trend is punctuated by a series of cool oscillations at 11 200 11 400 10 700 10 400 9300 and 8300 b2k and by a short period 11 300 to 10 250 b2k when temperatures were considerably warmer up to 14 9 c the five cool oscillations coincide with temperature reversals found elsewhere in the north atlantic region and in the greenland ice core records these cool events correlate well with both me

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

global ocean response to orbital forcing in the holocene 1 global upper ocean evolution in the holocene is studied in two coupled ocean atmosphere models under orbital forcing conditions at 3 6 8 and 11 ka the annual mean sea surface temperature sst changes in the early to mid holocene are found to be forced mainly by the annual mean insolation forcing with an overall symmetric response of colder equator 1 c in the arctic this sst change is consistent with a synthesis of mid holocene paleo sst records in contrast the temperature response in the thermocline is dominated by an antisymmetric pattern with a cooling warming in the northern southern hemisphere midlatitudes the thermocline response is determined predominantly by surface water subduction and ultimately the insolation forcing in local late winter

a decadal scale holocene sea surface temperature record from the subpolar north atlantic constructed using diatoms and statistics and its relation to other climate parameters 1 a sediment core from reykjanes ridge has been studied at 10 to 50 year time resolution to document variability of holocene surface water conditions in the western north atlantic and to evaluate effects of holocene ice rafting episodes diatom assemblages are converted to quantitative sea surface temperatures sst using three different transfer functions spectral and scale space methods are also applied on the records to explore variability at different timescales diatom assemblage and sst records clearly show that decaying remnants of the laurentide ice sheet strongly influenced early holocene climate in the western north atlantic this overrode the predominance of milankovitch forcing which played a key role in the development of holocene climate in the eastern north atlantic and nordic seas superimposed on general holocene climate change is high frequency sst variability on the order of 1 3 c the record also documents climatic oscillations with 600 to 1000 1500 and 2500 year periodicities with a time dependent dominance of different periodicities through the holocene a clear change in variability occurred about 5 ka bp the sst record also provides evidence for holocene cooling events hce that in some cases correlate to documented southward intrusions of ice into the north atlantic

surface sediment diatom distribution and holocene paleotemperature variations in the greenland iceland and norwegian sea one hundred and four surface sediment samples and two piston cores from the greenland iceland and the norwegian gin sea hopkins 1988 were analyzed diatoms were common to abundant in most surface sediment samples and throughout the holocene q mode factor analysis allowed the definition of six significantly different floral assemblages which explained 91 7 of the total variance mapping of the six factors showed their close affinity to hydrographic regimes these are the norwegian atlantic current assemblage thalassionema nitzschioides paralia sulcata proboscia alata arctic water assemblage thalassiosira gravidaspores sea ice assemblage nitzschia grunowii nitzschia cylindra thalassiosira hyalina arctic norwegian waters mixing assemblage rhizosolenia hebetata f semispina rhizosolenia borealis atlantic assemblage thalassiosira oestrupii and norwegian arctic waters mixing assemblage thalassiosira gravida vegetative cells transfer functions gint2 relating factor distributions to winter february and summer august surface water temperatures were generated the transfer functions have a standard error of estimate of 1 5 c august and 1 0 c february downcore studies of core 52 43 from the norwegian basin and core 57 5 from the iceland plateau revealed diatom abundance and sea surface paleotemperature trends in the area during the holocene the first appearance of diatoms in cores 52 43 and 57 5 occurs within the vedde ash layer 10 600 years b p and the saksunarvatn ash layer 9100 years b p respectively diatom abundances increase steadily throughout the pre boreal atlantic time to 25 and 35 million valves per gram dry sediment in the norwegian basin and iceland plateau cores respectively application of the temperature transfer functions gint2 to the two holocene records revealed higher than present sea surface temperatures during the boreal atlantic chronozones for the iceland plateau and during the middle younger dryas sub boreal chronozones for the norwegian basin core temperatures decreased steadily since then with a slight increase to the present values both the iceland and the norwegian seas experienced a strong influx of temperate atlantic surface waters in the beginning of the holocene sea surface temperatures dropped steadily in the latter part of the holocene as the influx of the atlantic surface waters diminished

rock magnetic properties of the gardar drift sedimentary sequence site iodp u1314 north atlantic implications for bottom current change through the mid pleistocene abstract the sediment obtained at integrated ocean drilling program iodp site u1314 on the gardar drift in the eastern flank of the reykjanes ridge was analyzed using rock magnetic techniques to study the depositional environment through the mid pleistocene climate transition the study area is under the influence of iceland scotland overflow water isow consequently the sedimentary record represents directly isow behavior over time a change in the depositional environment was documented as magnetic property changes that are the result of changes in concentration and grain size of magnetic minerals both of which decrease upward from around 0 9 ma because these shifts are accompanied by a change in magnetic fabrics which is interpreted as a change in bottom current directions from e w to nne ssw it is considered that the sedimentation pattern inferred from magnetic records at the site was modified by a change in the bottom current through the middle pleistocene

a high resolution holocene sediment record from hunafloaall n iceland margin centuryto millennial scale varability since the vedde tephra md99 2269 is a 25 m long core from hunafloaall a deep trough which runs northward towards the shelf break from the narrow neck of land which joins the northwest peninsula of iceland with the main land the core was recovered from the thickest part of an elongate shelf sediment body underlain by glacial diainictons with ages 26 ka bp 3 5 khz profiles indicate the presence of a reflector ri which can be traced over long distances twelve ams radiocarbon dates and the presence of the saksunarvatn tephra which is the origin for the ri reflector at 21 m core depth define a linear depth age relation with an accumulation rate of 200 cm ky the date on the core top is modern x radiographs indicate that the sediments are principally massive bioturbated muds the data were measured at resolutions of between 5 and 40 yr sample our primary data represent aspects of a multisensor track measurements b colour c grain size d sediment properties and e sediment magnetic properties principal component analysis pca was used to simplify the analysis of these five data sets and resulted in nine significant axes compared to over 70 original variables the explained variance on the first axes varied between 47 and 96 these time series were reduced to a common 50 yr sample interval which were then also subject to pca using the resulting pc scores we present three primary axes of environmental variability in hunafloaall that have century scale quasi periodicities and demonstrate that these are highly correlated with specific raw variables we focus on variables linked to changes in grain size and productivity and show regional coherence cores b997 321 and 330 in the coercivity grain size measure armj 20 armj 0 which have a close similarity to the detrended 14 c series this provides a potential link to the vigour of the thermohaline circulation to the north of the iceland shelf in the iceland and greenland seas our data indicate increas

holocene variability of the north atlantic irminger current on the south and northwest shelf of iceland abstract the irminger current ic transports heat and nutrients to the icelandic shelf and its fluctuations are strongly linked to variations in the strength of the north atlantic surface flow from the south by using benthic foraminiferal assemblages and their stable isotopic composition in two marine sediment cores located in the pathway of the ic on the west iceland shelf we were able to derive bottom water temperature estimates at a 100 year resolution and define the temperature difference between the core sites throughout the holocene these are the first transfer function bottom water temperatures presented from the icelandic shelf based on benthic foraminiferal assemblages our findings demonstrate a delayed holocene thermal maximum in the marine current system around iceland compared to the northern hemisphere summer insolation receipts the maximum heat transport in the ic occurred between 8 and 4 ka years later than some previous records report a reconstruction of the ambient seawater 18o based on paired samples of c2 transfer function temperature estimates and oxygen isotopic composition indicates repeated freshwater input to the n atlantic inflow in the early holocene impacting the current system before 8 ka two fundamental regime shifts are evident in the paleoceanography and foraminiferal properties during the holocene occurring around 8 ka towards more stable conditions and again around 4 ka towards more unstable conditions increasing fluctuation with similarities to the great salinity anomaly in the 1970s occur after 4 ka

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

the marine record of deglaciation from the continental margin off nova scotia continental margin sediments off nova scotia accumulate at high rates up to 360 cm kyr 1 and contain a history of millennial scale environmental changes which are dominated by the proximity of the laurentide ice sheet during the latest quaternary using stable isotope ratios of oxygen accelerator mass spectrometer radiocarbon dating micropaleontology and sedimentology we document these changes in six piston cores ranging in water depth from 450 to 4300 m we find that maximum 18o in n pachyderma occurred about 15 ka and preceded the maximum abundance of this species in these cores by 1000 years between 13 and 14 ka we find a second peak in abundance of n pachyderma minimum 18o and two pulses of ice rafting the sediment lithology supports terrestrial studies which indicate that there was a general withdrawal of ice beyond the upper paleozoic and mesozoic red beds by 14 ka in southeastern canada so the ice rafting events between 13 and 14 ka probably reflect ice stream activity in the st lawrence valley the younger dry as event is recognized as a peak in abundance of n pachyderma and ice rafting dated as 11 3 ka but meltwater discharge to the gulf of st lawrence was either too small or occurred over too long a time to leave a distinct 18o minimum off nova scotia at 7 1 ka in the middle of holocene warming we find a third peak in abundance of n pachyderma and another 18o minimum but no ice rafting we interpret these data as evidence of a late occurring meltwater event which if correct could have originated in the great lakes in the labrador ungava region or in both the final millennial scale phenomenon off nova scotia is the onset of neoglaciation marked by increased ice rafting and increased n pachyderma beginning about 5 kyr ago

coccolith evidence for instabilities in surface circulation south of iceland during holocene times abstract the coccolith based micropaleontological investigation of an exceptionally thick deep sea holocene sediment core was conducted in order to document the pattern and timing of surface circulation changes south of iceland over the gardar contour drift during the last 12 000 years fluctuations in bulk carbonate content at the core location are primarily driven by the coccolith fraction the observed overall correlation between bottom flow speed as given by the sortable silt mean size index and the bulk coccolith concentration abundance g dry sediment suggests that the accumulation of this fine carbonate fraction is as a first order controlled by processes of sediment redistribution by bottom current the down core variations in coccolith assemblage structure species indicate that changes in properties of surface waters south of iceland occurred as two distinct steps at ca 11 2 and 6 ka the onset of north atlantic drift water influence over the gardar drift after 11 2 ka was associated with excess export flux of coccolith carbonate in the vicinity of an active frontal system the period from 10 to 6 ka saw the progressive warming of the study area which culminated between 6 and 7 ka cooling of the surface waters after 6 ka as indicated changes in the relative abundances of the dominant coccolith species took place in two phases the present hydrological regime being only established after a last cooling step between 3 5 and 2 8 ka these long term reorganisations of the surface hydrology are interpreted as the response of the north atlantic to the combined force of the solar insolation and the waning laurentide ice sheet millennial scale perturbations of the surface hydrology are documented by changes in accumulation of the species emiliania huxleyi these successive decreases in the export fluxes of e huxleyi exhibit a distinct millennial pacing in phase with previously recorded holocene advection of cool ice bearing waters from the greenland iceland seas to the british islands from a clear analogy with the most recent extreme variation in global ocean climate we argue that mechanisms responsible for these observed millennial scale perturbations might be found in long term modulations of the atmospheric processes associated with the north atlantic oscillation nao

geochronological constraints on the trans hudsonian tectono metamorphic evolution of the pre athabasca basement within the wollaston mudjatik transition zone saskatchewan the hudsonian pressure temperature deformation time p t d t evolution of the pre athabasca crystalline basement 1700 ma of the wollaston mudjatik transition zone wmtz highlights two major tectono metamorphic events m1 d1 and m2 d2 the ages of these two event have been obtained by in situ la icpms u th pb dating of monazite from grt crd bearing pelitic gneiss and u pb analyses performed on zircons from pegmatites using both exposed basement and drill cores from the wolly mcclean exploration drilling project the m1 d1 event interpreted as the burial of the thinned hearne margin via southward thrusting to pressures varying from 10 to 6 kbar occurred between ca 1840 and 1813 ma the m2 d2 event producing the northeast structural trend of the wmtz was formed in a sinistral transpressional tectonic regime during the late stage of the hudsonian oblique collision between ca 1813 and 1770 ma thermobarometric estimates on the m2 d2 assemblages show that the entire studied area was reequilibrated at about 5 kbar and 750 825 c trans hudsonian pegmatites are viewed as the main proto ore of the uranium rich athabasca unconformity type deposits formation transfer and differenciation of these trans hudsonian pegmatites are replaced in this p t d t evolution during the 1840 1813 ma m1 d1 partial melting event the first batches of melt produced in the deep crust are the most likely enriched in uranium then these melts were transferred upwards to the upper crustal levels owing to the development of crustal scale steeply dipping d2 shear zones and finally were differentiated to form uranium enriched pegmatites between 1813 and 1770 ma some monazite and zircon grains within retrogressed migmatites recorded a later event at ca 1720 ma interpreted as the terminal cooling event down to 300 400 c responsible for partial retrogression of metamorphic assemblages this age provides new insights into the timing of the onset of the athabasca sedimentation that should therefore be at least 1710 ma old or younger

surface water dynamics in the reykjanes ridge area during the holocene as revealed by coccolith assemblages abstract the calcareous nannofossil assemblages from sediment core ds97 2p from the reykjanes ridge have been investigated to document oceanographic changes in surface water during the holocene the recorded variations in coccolithophore species assemblages and accumulation rates indicate that the region was subjected to rapid changes of surface water masses throughout the entire holocene coccolithophore assemblages generally are of low species diversity and consist mainly of emiliania huxleyi and coccolithus pelagicus ssp pelagicus two major events occurred at 8 5 7 ka and at 4 5 3 5 ka showing higher coccolith accumulation rates suggesting that the influence of relatively warm atlantic waters via the irminger current was strong in the investigated area the coccolithophore assemblages have been compared with diatom foraminifer and sedimentological records within the same core these data supported by a comparison with previously published proxy records add credit to the hypothesis that holocene changes did not occur uniformly across the north atlantic the results have highlighted the holocene pattern in the north atlantic as a period influenced by strong regionalism with discrepancies in the hydrographical trends and in the distribution of the planktonic proxies

coccolithophore fluxes in the norwegian greenland sea seasonality and assemblage alterations abstract coccolithophore fluxes were investigated by sediment trap studies at two well separated oceanographic sites in the norwegian and greenland seas from 1990 to 1992 each trap mooring comprised traps at 500 and 1000 m water depth and 300 m above the seafloor both sites were characterized by a strong seasonality in coccolithophore fluxes in the norwegian sea fluxes were about 10 to 20 times higher than in the greenland sea maximum fluxes 13 106 ind m 2d 1 for the norwegian sea and 2 4 106 ind m 2d 1 for the greenland sea were reached during high sedimentation phases in late summer and autumn the settling assemblages represented already highly altered remnants of the former living communities dominant species were emiliania huxleyi in the norwegian sea and coccolithus pelagicus in the greenland sea despite severe alterations the coccolithophore assemblages of each site were characterized by a distinct signature reflecting the local oceanography the settling assemblages underwent only minor alterations during sinking from 500 to 1000 m water depth by contrast resuspension and lateral advection within an extensive bottom nepheloid layer strongly influenced the assemblages of the deep sediment traps 300 m above the seafloor wiping out the distinct seasonality in coccolithophore fluxes and diminishing the differences in assemblage compositions between the two sites

centennial to millennial scale holocene climate deep water linkage in the north atlantic the stability of the earth s climate is strongly linked to the steadiness of the atmospheric and oceanic transport of heat from low to high latitudes high resolution holocene sedimentary records from the subpolar north atlantic demonstrate a persistent link between centennial to millennial scale fluctuations in the flow speed of iceland scotland overflow water inferred from granulometric proxy data and both the surface north atlantic current component of the meridional overturning circulation moc and published fennoscandian atmospheric temperature variability however these data also highlight the difficulties associated with the interpretation of geochemical and sedimentological deep water circulation proxies as they do not provide a wholly consistent picture the similarity between surface and deep ocean 13c records suggests a preformed component in the deep ocean 13c signal on the other hand the sedimentological results display a strong linkage to changing conditions in the overlying surface ocean waters suggesting this proxy better reflects the activity of the moc at least during the holocene of this region the most widespread oceanic perturbation coincides with an interval of possibly global climatic deterioration around 2700 years ago these results firmly establish deep water production in the nordic seas as a key component in the assortment of variables affecting climate during the holocene

evolution of the irminger and east icelandic current systems through the holocene revealed by diatom based sea surface temperature reconstructions abstract sediment core md99 2269 from the northern shelf of iceland has been studied to assess the stability of the east icelandic irminger current system during the holocene the 25 4 m long holocene section was studied with a 40 years average resolution the chronology is based on the combination of 24 14c ams dates and two tephra layers diatoms are utilized to quantify the development and variability of the august sea surface temperature sst for the last 11 5 cal kyr bp three different transfer function methods have been used to reconstruct august sst at the site weighted average partial least squares wa pls maximum likelihood ml and imbrie and kipp i k the combined use of the three methods allows the august sst reconstruction with a higher confidence level than with using only one statistical technique these three reconstructions generate very similar august sst trends through the holocene the onset of the holocene climate optimum is characterized at the site by a rapid august sst increase at 10 4 cal kyr bp of almost 4 c the holocene climate optimum is recorded between 10 4 and 4 7 cal kyr bp the august ssts were around 2 c warmer during the major part of the holocene compared with the august ssts for the later half of the holocene combining the diatom record with the benthic foraminifera records from the same core enables us to reconstruct the evolution of both surface and bottom water masses during the holocene this reconstruction shows dominance of the arctic waters throughout the water column at the onset of the holocene and subsequent increase of the influence of the atlantic water especially during the holocene climate optimum this strong dominance of atlantic water tends to decrease between 4 7 and 2 2 cal kyr bp especially in the upper part of the water column since 2 2 cal kyr bp the trend is reversed suggesting an increased influence of atlantic water at least in the upper water column

millennial surface water dynamics in the ria de vigo during the last 3000 years as revealed by coccoliths and molecular biomarkers a combined study of coccolith assemblages and biomarkers in a gravity core collected from the ria de vigo nw spain allowed us to reconstruct the paleoenvironmental conditions for the last 3000 years the quantitative distribution of coccolithophore species points to three different intervals within the core dated by ams radiocarbon measurements the first interval ca 975 bc 252 ad characterized by high abundances of calcidiscus leptoporus and gephyrocapsa muellerae i s thought to represent moderate water temperatures suggesting a transition from a warmer to a cooler period the second interval ca 252 1368 ad characterized by the dominance of coccolithus pelagicus helicosphaera carteri and syracosphaera spp and a high concentration of hexacosanol linked to terrestrial input is interpreted as having been a humid period with fluvial input the third interval ca 1368 ad 1950 is characterized by a high abundance of gephyrocapsa oceanica high alkenone values and low values of hexacosanol and is thought to represent a period dominated by oceanic conditions within the ria taking into account the ocean atmospheric system affecting the region studied here we propose an alternation in the mean state of north atlantic oscillation nao at millennial time scales awell developed upwelling system and an active ria ocean connection during the warmer interval i suggest a nao phase influenced by a hypsithermal period the occurrence of the humid and relatively warm interval ii is consistent with a negative phase in the nao as well as a relative restriction in ocean ria exchange interval iii which was drier and more productive again suggests the dominance of a positive phase in the nao with a more intense oceanic connection and more energized upwelling d 2004 elsevier b v all rights reserved

late holocene diatom derived seasonal variability in hydrological conditions off disko bay west greenland abstract a decadally resolved diatom record from a sediment core collected from disko bay central west greenland reveals variations in hydrological conditions for the late holocene the diatom flora record two clear trends in surface water temperatures a pronounced cooling of surface waters during the medieval climate anomaly mca and a progressive warming in surface waters during the little ice age lia previously identified in north atlantic studies our data support the existence of a previously identified anti phase relationship between surface water temperatures off west greenland and climate events recorded in the north east atlantic the diatom assemblages show relatively cool surface water conditions during warmer climatic intervals e g 3 6 2 7 cal ka bp the mca while relatively warm surface water conditions during colder climatic periods e g the dark ages da and the lia the exception to this is the roman warm period rwp which in west greenland shows warmer surface waters and climatic conditions our data also show the existence of anti phase relationship between surface and sub surface water temperatures in disko bay during the interval 3 6 2 7 cal ka bp cooler surface with warmer subsurface waters and towards the end of the lia warmer surface and cooler sub surface waters these anti phases patterns are possibly linked to 1 the local spring summer hydrological conditions e g warmer climatic intervals such as meltwater flux from sea ice continental ice and water stratification and 2 large scale ocean climate interactions e g cooler climatic intervals within the north atlantic oscillation nao type climate see saw between west greenland and north west europe associated with variability in the atlantic meridional overturning circulation amoc

north atlantic fennoscandian holocene climate trends and mechanisms abstract to investigate the mechanisms behind holocene regional climate trends from north of 58 n in the north atlantic fennoscandian region principal component analysis pca was performed and a temperature anomaly stack produced from 81 proxy derived summer temperature time series from 74 sites the pc results show distinctly different trends for near surface versus surface temperatures demonstrating the importance of handling these separately the first pc of weighted sea surface summer temperature time series and continental time series explains 45 8 of the variance where the uncertainty is the standard deviation of the distribution of variance explained across the 1000 age uncertain ensemble members pc1 has a relatively uniform expression over the whole region closely following the summer insolation at 65 n the second pc explains 22 4 of the variance and shows a non uniform expression with loadings in opposite directions in the northern and southeastern parts of the region comparing the pc time series with model runs and with the timing of the demise of the laurentide ice sheet lis suggest that this pattern reflects both topographic and albedo effects of the lis as well as release of meltwater into the north atlantic and arctic oceans comparing the stack of gridded records with published global stacks reveals an unusual holocene temperature development in the north atlantic fennoscandian region most likely resulting from the location relative to the decaying lis

holocene changes in marine productivity and terrestrial organic carbon inputs into an icelandic fjord application of molecular and bulk organic proxies this study examines the dynamics of organic carbon contributions from different sources to the sediments of a 39 m core from isafjar ardjup fjord northwest iceland throughout the holocene furth

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

holocene thermal maximum in the western arctic 0 180 w the spatio temporal pattern of peak holocene warmth holocene thermal maximum htm is traced over 140 sites across the western hemisphere of the arctic 0 180 w north of 60 n paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer than present conditions at 120 of these sites at the 16 terrestrial sites where quantitative estimates have been obtained local htm temperatures primarily summer estimates were on average 1 6 0 8 c higher than present approximate average of the 20th century but the warming was time transgressive across the western arctic as the precession driven summer insolation anomaly peaked 12 10 ka thousands of calendar years ago warming was concentrated in northwest north america while cool conditions lingered in the northeast alaska and northwest canada experienced the htm between ca 11 and 9 ka about 4000 yr prior to the htm in northeast canada the delayed warming in quebec and labrador was linked to the residual laurentide ice sheet which chilled the region through its impact on surface energy balance and ocean circulation the lingering ice also attests to the inherent asymmetry of atmospheric and oceanic circulation that predisposes the region to glaciation and modulates the pattern of climatic change the spatial asymmetry of warming during the htm resembles the pattern of warming observed in the arctic over the last several decades although the two warmings are described at different temporal scales and the htm was additionally affected by the residual laurentide ice the similarities suggest there might be a preferred mode of variability in the atmospheric circulation that generates a recurrent pattern of warming under positive radiative forcing unlike the htm however future warming will not be counterbalanced by the cooling effect of a residual north american ice sheet

radiocarbon vs calendar ages of major lateglacial hydrological events in north america abstract the age of late quaternary events has largely been established by radiocarbon dating which does not directly measure calendar sidereal years because the production of 14 c in the atmosphere has varied through time recent research allows the radiocarbon time scale to be converted to sidereal years back as far as the last deglacial period the calibration curve of stuiver and reimer 1993 radiocarbon 35 215 230 is presented and used to determine the true calendar age of several major lateglacial hydrological events in north america and to illustrate how the actual length of these events may substantially deviate from those calculated in radiocarbon years

late deglaciation of the central labrador coast and its implications for the age of glacial lakes naskaupi and mclean and for prehistory the age of the marine limit and associated deglaciation has been estimated from relative sea level curves for the hopedale and nain areas of the central labrador coast as approximately 7600 200 and 8500 200 yr ago respectively these ages indicate that the ice margin remained on the coast for up to 3000 yr longer than previously estimated because the central coast is due east of glacial lakes naskaupi and mclean the earliest the lakes could have formed was 8500 200 yr ago with their largest phases being fully established only after 7600 200 yr ago this suggests that the age of the lakes and associated deglaciation of the central labrador ungava region is younger by at least 1500 yr than previously estimated a late glacial marine based ice mass in ungava bay that dammed the lakes collapsed ca 7000 yr ago within this time frame therefore the glacial lakes only existed for 500 yr the persistence of the laurentide ice sheet margin on the central labrador coast until 7600 yr ago probably restricted the northward movement of early prehistoric people into northern labrador

reworked nannofossils in the north atlantic ocean and subpolar basins implications for heinrich events and ocean circulation the age and geographic distribution of reworked nannofossils in surface sediments from the north atlantic ocean suggest that their major source is northwest europe the concentration of reworked nannofossils in down core sediments indicates discharge of icebergs from the british and fennoscandian ice sheets throughout the last glacial interval during heinrich intervals 1 and 2 an increased number of icebergs from these sources reached the northeastern labrador sea these results suggest that the origin of heinrich intervals 1 and 2 involved both north american and european ice sheets

eemian and early weichselian 140 60 ka paleoceanography and paleoclimate in the nordic seas with comparisons to holocene conditions paleoceanographic and paleoclimatic time series were extracted from norwegian iceland and greenland sea the nordic seas sediment sequences covering the time intervals 60 140 ka and 0 15 ka on the basis of stable isotope stratigraphy planktonic foraminiferal faunas and sedimentological methods the proxy temperature records from the norwegian iceland sea display a number of high frequency and high amplitude variations within the last interglacial the eemian indicating marked changes in heat flux at high northern latitudes eemian holocene comparisons document that the climate of the norwegian iceland sea in the last interglacial was less stable than that of the present interglacial and that the distribution of surface water masses in the eemian differed from that of the holocene within the greenland sea uniform cold conditions prevailed throughout both interglacials cooling of the nordic seas as well as the initial growth of the surrounding ice sheets began within the eemian interval before the main increase in global ice volume heat flux to the nordic seas was significantly higher during the interglacials than at any time during the early weichselian 60 113 ka and no marked stadial interstadial changes in sea surface temperature and deep water ventilation are documented in the early weichselian records contrary to the pattern found in north atlantic sediment records however fluctuations in planktonic foraminiferal content planktonic 13c and ice rafting on suborbital timescales mostly comparable in number and age to the stadial interstadial fluctuations in the greenland ice cores are demonstrated in our records the ice rafted detritus records provide a more detailed account of ice sheet variability than previously known for the early weichselian period and demonstrate that glaciers advanced to sea level somewhere around the nordic seas several times during this interval

mid holocene emergence of a low frequency millennial oscillation in western mediterranean climate implications for past dynamics of the north atlantic atmospheric westerlies the nature and tempo of holocene climate variability is examined in the record of forest vegetation from western mediterranean marine core md95 2043 episodes of forest decline occurred at 10 1 9 2 8 3 7 4 5 4 4 5 and 3 7 2 9 cal ka bp and between 1 9 cal ka bp and the top of the record 1 3 cal ka bp wavelet analysis confirms a 900 yr periodicity prior to and during the early holocene and the dominance of a 1750 yr periodicity after 6 cal ka bp the 900 yr periodicity has counterparts in numerous north atlantic and northern hemisphere palaeoclimate records and in solar irradiance proxies 14c and 10be and may relate to a sun climate connection during the early holocene comparisons between the md95 2043 forest record and strategically located records from morocco iceland norway and israel suggest that the 1750 yr mid to late holocene oscillation reflects shifts between a prevailing strong and weak state of the zonal flow with impacts similar to the positive and negative modes of th

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

high resolution holocene record in the southeastern bay of biscay global versus regional climate signals abstract core ks10b north east atlantic 43 50 n 2 03 w water depth 550 m was recovered at a location of high sediment deposition and hence includes a high resolution palaeoclimatic record for the southeastern bay of biscay over the last 9000 cal yr bp the effect of global and regional climatic forcing factors e g orbital forcing north atlantic oscillation nao and their subsequent control on water temperature sea level hydrology and continental influence were investigated by studying planktic and benthic foraminiferal faunas 150 m sedimentology and stable isotopes results indicate probable episodic long term incursions of the warm and salty iberian poleward current ipc into the bay of biscay during the holocene by the intermittent presence of subtropical globigerinoides ruber in the otherwise temperate fauna these incursions seem to be triggered by negative nao like conditions our data show five main climatic periods which are in general agreement with the literature data on the climatic variability in the north atlantic and the iberian peninsula the early holocene 9000 7400 cal yr bp is characterized by low sea level significant downslope transport eutrophic benthic settings and high surface water productivity these environmental characteristics are probably due to the general wet and warm climate under a prevailing negative nao increasing precipitation and river runoff and favouring the incursion of the ipc into the bay of biscay the climatic optimum appears between 7400 and 6000 cal yr bp under a generally positive nao index in the following 6000 3500 cal yr bp surface water cooling is matching a steep decline of the northern hemisphere summer insolation meanwhile benthic settings are changing progressively towards present day trophic conditions the time interval from 3500 to 1800 cal yr bp encompasses the iberian roman humid period characterized by warm and humid conditions and increasing primary production under a prevailing negative nao index the last 1800 years were characterized by stable cool conditions reflecting a change towards a positive nao state

surface water changes in the norwegian sea during last deglacial and holocene times stable carbon and oxygen isotopes of the polar planktic foraminifera neogloboquadrina pachyderma sinistral from sediment cores of the norwegian sea reveal several anomalous 13c and 18o depletions in the surface water during the last glacial to interglacial transition and during the later holocene the depletions that are observed between the last glacial maximum lgm and the end of the main deglacial phase were caused by massive releases of freshwater from thawing icebergs which consequently resulted in a stratification of the uppermost surface water layer and a non equilibrium between the water below and the atmosphere at 8 5 ka 14c bp this strong iceberg melting activity ceased as defined by the cessation of the deposition of ice rafted detritus after this time the dominant polar and subpolar planktic foraminiferal species rapidly increased in numbers however this post deglacial evolution towards a modern type oceanographic environment was interupted by a hitherto undescribed isotopic event 7 8 ka which on a regional scale is only identified in eastern norwegian sea surface water this event may be associated with the final pulse of glacier meltwater release from fennoscandia which affected the onset of intensified coastal surface water circulation off norway during a time of regional sea level rise all these data indicate that surface water changes are an integral part of deglacial processes in general yet the youngest observed change noted around 3 ka gives evidence that such events with similar effects occur even during the later holocene when from a climatic point of view relativelystable conditions prevailed

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

plankton in the norwegian greenland sea from living communities to sediment assemblages an actualistic approach a synoptic study is carried out to reconstruct the development of the plankton community in the late quaternary in the norwegian greenland sea it comprises quantitative analyses of coccolithophores dinoflagellate cysts diatoms and radiolarians an actualistic approach is applied to evaluate the different fossil records of these plankton groups the preliminary results of the current investigation are reported here

late quaternary sea surface conditions in the laurentian fan evidence from coccolith and dinocyst assemblages abstract the analyses of coccoliths and dinocysts from the images core md95 2033 collected on the laurentian fan 44 39 87n 55 37 21w water depth 1412 m in the northwest north atlantic provide a new dataset to assess the magnitude of climatic changes during the holocene with a millennial time resolution coccolith and dinocyst data were combined to reconstruct changes in past sea surface conditions in addition the dinocyst assemblages were used to reconstruct the sea surface temperature sst and salinity sss based on the modern analog technique the distribution of the coccolith and dinocyst assemblages suggests a succession of climatic events during the late quaternary and early holocene linked to change in the influence of the labrador current and or the st lawrence river discharge the dinocyst assemblages recorded a thermal optimum during the mid holocene in the late holocene coccolith concentrations show two peaks at 2 3 and 1 1 ky which coincide with the presence of species with different ecological properties likely due to the localized influence of the slope water jet swj current the presence of this current has played a role in the development of the coccolith and dinocyst assemblages and sst fluctuations especially in the last 2 ky overall the interaction between the st lawrence river the swj the lc and the nac has all controlled the sss ssts and the development of the coccolith and dinocyst assemblages confirming a significant regionalism of the entire area