on the 1470 year pacing of dansgaard oeschger warm events 1 the oxygen isotope record from the greenland ice sheet project 2 gisp2 ice core was reanalyzed in the frequency and time domains the prominent 1470 year spectral peak which has been associated with the occurrence of dansgaard oeschger interstadial events is solely caused by dansgaard oeschger events 5 6 and 7 this result emphasizes the nonstationary character of the oxygen isotope time series nevertheless a fundamental pacing period of 1470 years seems to control the timing of the onset of the dansgaard oeschger events a trapezoidal time series model is introduced which provides a template for the pacing of the dansgaard oeschger events statistical analysis indicates only a 3 probability that the number of matches between observed and template derived onsets of dansgaard oeschger events between 13 and 46 kyr b p resulted by chance during this interval the spacing of the dansgaard oeschger onsets varied by 20 around the fundamental 1470 year period and multiples thereof the pacing seems unaffected by variations in the strength of north atlantic deep water formation suggesting that the thermohaline circulation was not the primary controlling factor of the pacing period

aspects of climate variability in the north atlantic sector discussion and relation to the greenland ice sheet project 2 high resolution isotopic signal this paper reviews aspects of climate variability in the north atlantic sector that may influence the seasonal to decadal scale isotopic signal in the greenland ice sheet project 2 gisp2 ice core interpretation of the isotopic signal and its spatial applicability at the seasonal level requires investigation into synoptic scale climatology we discuss possible climatic influences of 1 likely source regions of precipitation reaching the gisp2 site 2 the characteristics of cyclone activity over the north atlantic sector and 3 changes in major atmospheric features such as the mean sea level icelandic low and azores high pressure systems the north atlantic oscillation and the baffin trough next we evaluate correlations between the gisp2 deuterium isotopic signal and coastal temperatures with atmospheric pressure patterns thereby deriving climatic interpretations of the high resolution isotopic record the gisp2 site is influenced by both the icelandic low to the southeast and davis strait baffin bay storms to the southwest and west the north atlantic oscillation influences the gisp2 isotopic signal through the seesaw in winter temperatures between west greenland and northern europe agreement in excursion directions of gisp2 isotopes and east greenland and iceland temperature records is associated with different positions of the baffin trough in winter and also with anomalous 500 mbar net geostrophic flow linkages between isotopic excursion direction and atmospheric variability need to be explored further by comparison with additional seasonal data sets from other greenland ice cores

is the north atlantic oscillation reflected in scandinavian glacier mass balance records the north atlantic oscillation nao is one of the modes of climate variability in the north atlantic region the atmospheric circulation during the winter season in this region commonly displays a strong meridional north south pressure contrast with low air pressure cyclone centred close to iceland and high air pressure anticyclone near the azores this pressure gradient drives the mean surface winds and the mid latitude winter storms from west to east across the north atlantic bringing mild moist air to northwest europe the nao index is based on the difference of normalised sea level pressures slp between ponta delgada azores and stykkisholmur iceland the slp anomalies at these stations are normalised by division of each monthly pressure by the long term 1865 1984 standard deviation interannual atmospheric climate variability in northwest europe especially over great britain and western scandinavia has during the last decades been attributed mainly to the nao causing variations in the winter weather over the northeast north atlantic and the adjacent land areas a comparison between the nao index and the winter december march precipitation between ad 1864 and 1995 in western norway shows that these are strongly linked correlation coefficient 0 77 variations in the nao index are also reflected in the mass balance records of glaciers in western scandinavia the nao index is best correlated with mass balance data from maritime glaciers in southern norway e g alfotbreen r 2 0 51 the record of holocene last ca 11 500 cal yr glacier variations of maritime glaciers in western scandinavia is thus a proxy of pre instrumental nao variations copyright 2000 john wiley sons ltd

climate and oceanographic variability in the sw barents sea during the holocene the holocene section of the marine sediment core psh 5159n located in the sw barents sea has been studied at high resolution with a multiproxy approach a well stratified water column occurred at the site 11 9 8 ka bp the stratification was probably a result of a winter sea ice cover and or fresh warm surface waters during summer stratification and resultant reduction in air sea interaction allowed for warmer bottom water temperatures the general situation 11 9 8 ka bp could have been associated with an anomalous high pressure system over the nordic seas and the arctic ocean during the 11 10 5 ka bp interval the polar front was located close to the barents sea margin the polar front moved towards the site from 10 5 ka bp and from 9 8 to 7 5 ka bp it was probably located close to the site at 7 5 ka bp the polar front retreated eastwards as the present day oceanographic pattern established the mid holocene was in general characterized by rather stable conditions in contrast highly variable cond

slope water current over the laurentian fan on interannual to millennial time scales the strength and position of surface and deep currents in the slope water south of newfoundland are thought to vary as a coupled system in relation to the dipole in atmospheric sea level pressure known as the north atlantic oscillation nao paleoceanographic data from the laurentian fan used as a proxy for sea surface temperature reveal that surface slope waters north of the gulf stream experienced warming during the little ice age of the 16th to 19th centuries and support the notion of an nao driven coupled system the nao may be a useful model for millennial scale ocean variability during interglacial climate states

evidence of 550 year and 1000 year cyclicities in north atlantic circulation patterns during the holocene sedimentological colour data obtained from north atlantic deep sea sediment core neap15k pro vide a continuous climate record for the last 11500 yr with a mean sampling interval of 15 yr variations in sediment lightness a proxy for changes in north atlantic deep water nadw circulation are characterized by high frequency fluctuations with periodicities equivalent to 550 and 1000 yr as well as a 1600 yr cyclicity comparable to that reported in other studies of holocene climate cross spectral analysis suggests that the 550 yr and 1000 yr cyclical variations in nadw circulation were coherent with fluctuations in atmospheric con ditions over greenland where both these periodicities have been identified previously in the holocene gisp2 d18o record stuiver et al 1995 a similar statistical comparison provides evidence that high frequency 550 yr variability in nadw circulation patterns may have been linked to short term variations in atmospheric 14c values during the holocene in general nadw pro

a major widespread climatic change around 5300 cal yr bp at the time of the alpine iceman palaeoenvironmental and archaeological data from arbon bleiche lake constance switzerland give evidence of a rapid rise in lake level dated by tree ring and radiocarbon to 5320 cal yr bp this rise event was the latest in a series of three successive episodes of higher lake level between 5550 and 5300 cal yr bp coinciding with glacier advance and tree limit decline in the alps this west central european climate change may have favoured the quick burial and the preservation of the alpine iceman recently found in the tyrolean alps it has possible equivalents in many records from various regions in both hemispheres dating to 5600 5000 cal yr bp and corresponds to global cooling and contrasting patterns of hydrological changes this major mid holocene climate event marks the hypsithermal neoglaciation transition possibly resulting from a combination of different factors including orbital forcing changes in ocean circulation and variations in solar activity copyright 2004 john wiley sons ltd

major features and forcing of high latitude northern hemisphere atmospheric circulation using a 110 000 year long glaciochemical series the greenland ice sheet project 2 glaciochemical series sodium potassium ammonium calcium magnesium sulfate nitrate and chloride provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid low latitudes of the northern hemisphere interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants volcanic and biomass burning events storminess over marine surfaces continental aridity and biogenic source strength plus information related to the controls on both high and low frequency climate events of the last 110 000 years climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long term behavior of atmospheric circulation patterns through changes in ice volume sea level events such as the heinrich events massive discharges of icebergs first identified in the marine record that are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics and rapid climate change events massive reorganizations of atmospheric circulation that are demonstrated to operate on 1450 year cycles changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events explanation for the exact timing and global synchroneity of these events is however more complicated preliminary evidence points to possible solar variability climate associations for these events and perhaps others that are embedded in our ice core derived atmospheric circulation records

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

palaeoflood and floodplain records from spain evidence for long term climate variability and environmental changes abstract palaeoflood chronologies from seven spanish river basins and floodplain aggradation chronologies from thirteen rivers are analysed these fluvial records were divided in to two sub sets namely atlantic 10 ka record and mediterranean 3 ka record river basins which represent distinct modern hydroclimatic conditions in atlantic basins floods result from intense widespread rainfalls associated with atlantic frontal systems transported by westerly airflow mediterranean river flooding is related to heavy rainfall induced by mesoscale convective systems mcss during autumn months evidence from radiocarbon dates in slackwater flood deposits shows six periods of flood clusters at 10 750 10 240 9550 9130 4820 4440 2865 2350 960 790 and 520 290 cal bp despite the different flood producing weather conditions in atlantic and mediterranean rivers the radiocarbon sample clusters overlap and indicate changes in large scale atmospheric circulation and climatic conditions in the iberian peninsula comparison with proxy records of mean temperature for the northern hemisphere demonstrates a relationship between the period of slackwater flood deposition and cold climatic phases e g the 2650 yr bp climatic event or ad 1590 1650 period of the little ice age radiocarbon dates from aggraded floodplain sediments were clustered at 2710 2320 2000 1830 and 910 500 cal bp the first cluster period is in phase with the timing of slackwater deposition whereas the third 910 500 cal bp occurs in between two periods of increased flood frequency as indicated by the palaeoflood and documentary flood records it is argued that the 910 500 cal bp floodplain aggradation period reflects the first post roman evidence of environmental change related to generalised land use changes at the catchment scale which produced high sediment load transported to overbank areas during high flows

size sorting in marine muds processes pitfalls and prospects for paleoflow speed proxies the basis for and use of fine grain size parameters for inference of paleoflow speeds is reviewed here the basis resides in data on deposited sediment taken in conjunction with flow speed measurements in the field experimental data on suspended sediment transport and deposition and theoretical treatments of the generation of size distributions of deposits from suspension controlled by particle settling velocity and flow speed in the deep sea sorting events occur under resuspension deposition events in benthic storms at flow speeds below 10 15 cm s 1 size in the noncohesive sortable silt 10 63 m range is controlled by selective deposition whereas above that range removal of finer material by winnowing also plays a role the best particle size instruments to measure a flow speed related grain size employ the settling velocity method while laser diffraction sizers can yield misleading results because of particle shape effects potential problems including source effects downslope supply on continental margins spatial variability of flow over bedforms and influence of ice rafted detritus are examined a number of studies using the sortable silt flow speed proxy are reviewed and inverse modeling of grain size distributions is examined outstanding problems are that corroboration is sparse because almost no studies have yet used the full range of proxies for flow rate and water mass identification and that the sortable silt mean size is not yet properly calibrated in terms of flow speed

scandinavian glacial and climatic fluctuations during the holocene abstract historical documents and lichenometric studies give a detailed picture of the little ice age in scandinavia there was a large advance in norway which has been dated at a few places to 1750 small readvances during the retreat occurred around a d 1780 1810 1840 1850 1850 1870 1890 1910 and 1930 in sweden most of these advances have been recognized and in addition extensive advances are dated by lichenometry to around a d 1600 1650 and 1700 1720 soils buried beneath moraines often yield radiocarbon dates that are much too old methods dependent on these must therefore be used with care evidence for pre little ice age advances are often considered equivocal the most reliable information is probably provided by studies of lacustrine sediments combining information from all sources the most significant pre little ice age glacier advances most likely occurred in 7 5 5 1 4 5 3 2 2 8 2 2 1 9 and 1 5 1 1 radiocarbon ka bp advances that were less extensive or for which there is less evidence occurred around 6300 5600 2500 940 600 560 and 380 bp

holocene glacial and climatic variations on spitsbergen svalbard holocene glacial and climatic variations have been inferred from investigations of sediment cores from the proglacial lake linnevatnet western spitsbergen a low content of glacially derived coal absence of regular laminations and a slow sedimentation rate in the lower part of the lacustrine sediments indicate that the former glaciers that existed within the catchment area during the last ice age melted quickly away as a result of the younger dryas holocene warming and during the next 6000 years there were no glaciers in the valley increasing coal content incipient laminations and rising sedimentation rates indicate that the glacier linnebreen started to form 4000 5000 years ago probably as a response to the late holocene cooling the holocene maximum extent of the glacier occurred during the little ice age starting with a pronounced ice advance in the thirteenth or fourteenth century a well dated core from billefjorden which is assumed to reflect glacial fluctuations in the inner part of the i

ash layers from iceland in the greenland grip ice core correlated with oceanic and land sediments four previously known ash layers ash zones i and ii saksunarvatn and the settlement layer all originating in iceland have been identified in the central greenland ice core grip this correlation of the ash between the different environments is achieved by comparison of the chemical composition of glass shards from the ash this establishes and confirms detailed correlations between the different types of depositional records and the absolute dating of the younger part of the ice core by counting annual layers dates the eruptions accurately a precise connection with dates obtained by14c beyond the range of dendrochronology is established which provides an excellent confirmation of230th 234u dates from corals four additional icelandic ash layers have also been identified in the core but not yet correlated with known ash deposits

early holocene large scale meltwater discharge from greenland documented by foraminifera and sediment parameters records of foraminiferal assemblages combined with lithological properties grain size magnetic parameters and xrf data of marine sediment cores from west greenland coastal waters and the adjacent labrador sea document widespread early holocene meltwater discharge this discharge is concluded to originate from large scale melting of the greenland ice sheet gis having started prior to 8600 cal yr bp and ended at about 7700 7500 cal yr bp when the gis margin had withdrawn from the fjords and become mainly land based the benthic foraminiferal record from one of the coastal sites mainly reflects west greenland current wgc subsurface water properties and to a minor degree surface productivity the most significant feature in this record is an abrupt shift to a higher productivity regime around 7700 cal yr bp we suggest that the cessation of a widespread gis meltwater discharge at that time favoured an increased influence of sub surface water of atlantic origin and initiation of modern subpolar gyre circulation enabling labrador sea deep convection further offshore a record of planktonic foraminiferal assemblages shows an oceanographic change at ca 9500 cal yr bp whilst a gradual but marked change in the planktonic foraminiferal assemblage between 8800 and 7000 cal yr bp may be related to a narrowing of the wgc low salinity surface water belt the oceanic regime off west greenland prior to 7800 cal yr bp was thus characterised by the presence of a permanent and widespread meltwater surface layer presumably preventing deep convection in this region apart from indications of a slight decrease in meltwater discharge by the benthic foraminiferal fauna data neither of the records show any clear signal of a regionally important 8 2 ka event

holocene climate variability of the norwegian atlantic current during high and low solar insolation forcing 1 a high resolution sediment core from the voring plateau has been studied to document the centennial to millennial variability of the surface water conditions during the holocene climate optimum hco and the late holocene period lhp in order to evaluate the effects of solar insolation on surface ocean climatology quantitative august summer sea surface temperatures sssts with a time resolution of 2 40 years are reconstructed by using three different diatom transfer function methods spectral and scale space methods are applied to the records to explore the variability present in the time series at different time scales the ssst development in core md95 2011 shows a delayed response to northern hemisphere maximum summer insolation at 11 000 years b p the record shows the maximum ssst of the hco to be from 7 3 to 8 9 kyr b p which implies that the site was located in the regional warm water pool removed from the oceanic fronts and arctic waters superimposed on the general cooling trend are higher frequency variabilities at time scales of 80 120 210 320 320 640 and 640 1280 years the climate variations at the time scale of 320 640 years are documented both for periods of high and low solar orbital insolation we found evidence that the submillennial scale mode of variability 640 900 years in ssst evident during the lhp is directly associated with varying solar forcing at the shorter scale of 260 450 years the ssst during the lhp displays a lagged response to solar forcing with a phase locked behavior indicating the existence of a feedback mechanism in the climate system triggered by variations in the solar constant as well as the role of the thermal inertia of the ocean the abruptness of the cooling events in the lhp especially pronounced during the onsets of the holocene cold period i approximately 2300 years b p and the little ice age approximately 550 years b p can be explained by a shutdown of deep convection in the nordic seas in response to negative solar insolation anomalies these cooling events are on the order of 1 5 c

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

permian continental paleoenvironments in southeastern asia new insights from the luang prabang basin laos in laos southeastern asia late paleozoic sediments were identified by early french explorations across indochina during the late 19th century pavie missions but little work was undertaken to characterize the sedimentological and stratigraphical context until now from detailed sedimentological and paleontological studies we propose an interpretation of the depositional environment and of the stratigraphic context of series located on the right bank of the mekong river in the luang prabang basin where three main formations were described the silicoclastic red claystone formation attributed to alluvial plain environment contains large fragments of unidentified dicynodonts the limestones and sandstones formation preserves a new macrofloral assemblage displaying affinities with middle to late permian cathaysian floras of south china this assemblage occurs as an intercalation within marine calcareous sandstones that have yielded a marine fauna including the ammonoid pseudotirolites sp which indicates a late permian changhsingian age the well developed purple claystones formation yielded an abundant and well preserved late permian fauna composed of a carnivorous amphibian and numerous dicynodon cranial and postcranial elements this formation shows a vertical evolution from braided river to alluvial plain with sheet flood sand bed and bed load rivers with a constant supply of volcanic clasts results from the analysis of the paleontological associations in the luang prabang basin suggest that a continental communication between laurussia and the indochina block existed during the permian allowing for migration of the terrestrial dicynodon fauna

the greenland 8200 cal yr bp event detected in loss on ignition profiles in norwegian lacustrine sediment sequences high resolution loss on ignition analyses of lacustrine sediment cores from both proglacial and non glacial lakes in southern norway have revealed a specific pattern characterised by a significant two peaked reduction of the loss on ignition values in the basal half of the cores in non glacier fed lakes the loss on ignition variations are interpreted to reflect mainly lake productivity and hence variability in surface summer air temperature sediments deposited in proglacial lakes however reflect mainly the glacier activity in the lake catchment bulk ams radiocarbon dates from the core sequences and the loss on ignition curve pattern suggest that this event correlates with the 8200 cal yr bp event recorded in the grip and gisp2 greenland ice cores termed the finse event in southern norway copyright 2001 john wiley sons ltd

plant wax δd values record changing eastern mediterranean atmospheric circulation patterns during the 8 2 kyr b p climatic event abstract throughout the holocene the climate of the mediterranean region has been strongly influenced by variability in the atmospheric circulation of the high and low latitudes a prominent example for such holocene climate perturbations is the 8 2 kyr b p climatic event reorganization of northern hemisphere atmospheric circulation patterns resulted in variations of temperature and precipitation distribution across the mediterranean the effects of changing high and low latitude atmospheric circulation on mediterranean climate in relation to the 8 2 kyr b p climatic event are however not well understood here we present a high resolution record of stable hydrogen isotope composition of plant wax n alkanes dwax across the 8 2 kyr b p climatic event from the tenaghi philippon peat deposit ne greece in order to characterize patterns of precipitation and changes in atmospheric circulation in the eastern mediterranean region our record reveals pronounced changes in dwax that correlate closely with previously published palynological data a long term decline in dwax values characterizes the lower part of the section the 8 2 kyr b p climatic event itself is connected to two distinct positive dwax excursions a minor shift in dwax around 8 2 kyr b p and a major shift in dwax between ca 8 1 and 8 0 kyr b p the upper part of the section shows a progressive trend towards higher dwax values we link shifts in dwax to changes in mediterranean air mass trajectories supplying precipitation to ne greece caused by variations in the relative contributions of northerly derived d depleted moisture and southerly derived d enriched moisture possible control mechanisms for alternating air mass trajectories include changes in the influence of the siberian high and differences in the influence of the african and asian monsoon circulation on anticyclonic conditions in the mediterranean region as well as regional inflow of moist air masses from the aegean sea

northward oceanic heat transport in the main branch of the norwegian atlantic current over the late holocene the norwegian atlantic current represents the northernmost reaches of the sub surface limb of the atlantic meridional overturning circulation its shelf edge branch the norwegian atlantic slope c

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

interdecadal variations of the thermohaline circulation in a coupled ocean atmosphere model abstract a fully coupled ocean atmosphere model is shown to have irregular oscillations of the thermohaline circulation in the north atlantic ocean with a time scale of approximately 50 years the irregular oscillation appears to be driven by density anomalies in the sinking region of the thermohaline circulation approximately 52 n to 72 n combined with much smaller density anomalies of opposite sign in the broad rising region the spatial pattern of see surface temperature anomalies associated with this irregular oscillation bears an encouraging resemblance to a pattern of observed interdecadal variability in the north atlantic the anomalies of sea surface temperature induce model surface air temperature anomalies over the northern north atlantic arctic and northwestern europe

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

atmospheric response to mid holocene warming in the northeastern atlantic implications for future storminess in the ireland uk region abstract there is increasing evidence that accelerated warming at high latitudes is associated with increased climate variability at mid latitudes including the frequency and intensity of storms however due to short instrumental records our understanding of how ocean atmosphere dynamics operate during warmer than present climates remains limited here we present a palaeoceanographic investigation of the transition between the middle holocene intervals of the northgrippian 8 2 4 2 ka and the late holocene interval of the meghalayan 4 2 0 ka to test the hypothesis of an eastward shift of the icelandic low under warmer than present climate scenarios reconstructions of bottom water temperatures bwt and stable oxygen isotopes mg ca 18o using the benthic foraminifera hyalinea balthica reveal warmer than present bwt of up to 2 6 0 7 c on the irish continental shelf until circa 4 2 ka the results suggest that atlantic waters of subtropical origins were more prevalent in the eastern subpolar gyre spg and on the irish continental shelf we link this oceanographic signature to an eastward shift of the icelandic low we then place our local temperature record into an extra regional context using a combination of modern observations and existing palaeo datasets which enables us to assess the impact of changing atmospheric modes on ocean atmosphere climate linkages within the north atlantic region the enhanced influence of warm subtropical atlantic waters recirculating along the boundaries of the spg under this scenario would potentially have enhanced melt rates of marine terminating glaciers on the east greenland shelf during the northgrippian

late holocene 1500 yr climatic periodicities and their implications fourier and nonlinear regression analysis of a 4000 yr paleoclimate proxy record in western canada shows strong periodicities of 1500 yr and several weaker century to millenial scale periodicities in conjunction with the 23 708 yr milankovitch periodicity these produce a model of climate fluctuation through the postglacial consistent with recognized paleoclimatic fluctuations of the past 15 000 yr in the northern mid latitudes these results suggest that postglacial climatic anomalies such as the little ice age and the younger dryas were at least in part periodic phenomena rather than the result of unique aperiodic events projecting these periodicities into the future suggests that even in the absence of anthropogenic climate forcing a natural warming trend will continue until ca a d 2400

patterns of temperature variability on multidecadal to centennial timescales the spatiotemporal structure of low frequency temperature variability as reflected in a paleonetwork covering the north american and european domains is studied using a combination of statistical techniques including principal component analysis and univariate and multivariate singular spectrum analysis on timescales longer than 50 years two statistically significant modes of temperature variability are identified one on multidecadal timescale and one on centennial timescale the first mode is oscillatory with in the narrow range 60 80 years the spatial pattern of this multidecadal mode implies coherent oscillations over europe and over northeastern north america with maximum amplitudes in europe over northwestern north america this mode is absent its geographic shape suggests a connection to the north atlantic oscillation a relation with solar forcing could not be detected the second mode which dominates low frequency variability at high latitudes describes temperature variations in a wide interval of timescales 100 years in the longest records a weak 120 year oscillation can be identified with confidence the temporal pattern of the centennial mode shows a multiple phase little ice age and a prolonged medieval warm period the interpretation of centennial mode is difficult given its rather variable large scale pattern and the uncertainty associated with centennial timescales in the data the present data set gives indications that in north america centennial variability is independent of season while the multidecadal mode might exhibit seasonally dependent features in europe both low frequency modes of temperature variability are season specific

a 9000 year oxygen and carbon isotope record of hydrological change in a small ethiopian crater lake the stable isotope composition of authigenic calcites in a core from lake tilo a small crater lake in the ethiopian rift valley provides a subcentury scale record of lake response to climatic change over the last 8850 14c yrs 9850 cal yrs an unusually high range of 18o and 13c values 15 is attributed in part to major changes in hydrothermal groundwater flux although hydrothermal groundwater influx to the lake was high during the early holocene its flow rate was relatively stable and thus climatically induced changes to the water budget can be inferred from variations in 18o and 13c ratios a major decline in hydrothermal groundwater input from 5500 14c yrs bp increased lakewater residence time and led to substantial increases in 18o and 13c before the mid holocene transition to more arid conditions during the last 2700 14c years diagenetic processes have resulted in extremely varied 18o and 13c values the holocene isotope record from lake tilo challenges the widely held assumpti

fennoscandian summers from ad 500 temperature changes on short and long timescales quantitative estimates of 1480 years of summer temperatures in northern fennoscandia have previously been derived from continuous treering records from northern sweden here we show the results of spectral analyses of these data only a few peaks in the spectra are consistently significant when the data are analyzed over a number of sub periods relatively timestable peaks are apparent at periods of 2 1 2 5 3 1 3 6 4 8 32 33 and for a range between 55 100 years these results offer no strong evidence for solar related forcing of summer temperatures in these regions our previously published reconstruction was limited in its ability to represent long timescale temperature change because of the method used to standardize the original tree ring data here we employ an alternative standardization technique which enables us to capture temperature change on longer timescales considerable variance is now reconstructed on timescales of several centuries in comparison with modern normals 1951 70 generally extended periods when cool conditions prevailed prior to the start of the instrumental record include 500 700 790 870 1110 1150 1190 1360 1570 1750 a d with the most significant cold troughs centred on about 660 800 1140 1580 1620 and 1640 predominantly warm conditions occurred in 720 790 870 1110 and 1360 1570 with peaks of warmth around 750 930 990 1060 1090 1160 1410 1430 1760 and 1820

latest pleistocene and holocene alpine glacier fluctuations in scandinavia abstract during the early holocene abrupt decadal to centennial scale climate variations caused significant glacier variations in norway increased freshwater inflow to the north atlantic and arctic oceans has been suggested as one of the most likely mechanisms to explain the abrupt and significant lateglacial and early holocene climatic events in nw europe the largest early holocene glacier readvances occurred 11 200 10 500 10 100 9700 9200 and 8400 8000 cal yr bp the studied norwegian glaciers apparently melted away at least once during the early mid holocene the period with the most contracted glaciers in scandinavia was between 6600 and 6000 cal yr bp subsequent to 6000 cal yr bp the glaciers started to advance and the most extensive glaciers existed at about 5600 4400 3300 2300 1600 cal yr bp and during the little ice age times with overall less glacier activity were apparently around 5000 4000 3000 2000 and 1200 cal yr bp it has been proposed that several glacier advances occurred in scandinavia including northern sweden at 8500 7900 7400 7200 6300 6100 5900 5800 5600 5300 5100 4800 4600 4200 3400 3200 3000 2800 2700 2000 1900 1600 1200 1000 and 700 200 cal yr bp glaciers in northern sweden probably reached their greatest little ice age extent between the 17th and the beginning of the 18th centuries evidence for early holocene glacier advances in northern scandinavia however has been questioned by more recent multi disciplinary studies the early to mid holocene glacier episodes in northern sweden may therefore be questioned most norwegian glaciers attained their maximum little ice age extent during the mid 18th century cumulative glacier length variations in southern norway based on marginal moraines dated by lichenometry and historic evidence show an overall retreat from the mid 18th century until the 1930s 40s subsequently most norwegian glaciers retreated significantly maritime outlet glaciers with short frontal time lags 15 20 years continued their retreat to the 1970s and 1980s however maritime glaciers started to advance as a response to higher winter accumulation during the first part of the 1990s after 2000 several of the observed glaciers have retreated remarkably fast annual frontal retreat 100 m mainly due to high summer temperatures the general glacier retreat during the early holocene and the neoglacial advances after 6000 cal yr bp are in line with orbital forcing due to the decrease of northern hemisphere summer solar insolation and the increase in winter insolation in addition regional weather modes such as the north atlantic oscillation nao and the arctic oscillation ao play a significant role with respect to decadal and multi decadal climate variability

variability of fram strait ice flux and north atlantic oscillation we estimate the winter sea ice export through the fram strait using ice motion from satellite passive microwave data sea ice motion october may is obtained by tracking the displacement of common features in sequential 85 and 37 ghz brightness temperature fields the average winter area flux over the 18 year record 1978 1996 is 670 000 km2 7 of the area of the arctic ocean the winter area flux ranges from a minimum of 450 000 km2 in 1984 to a maximum of 906 000 km2 in 1995 the daily monthly and interannual variabilities of the ice area flux are high there is an upward trend in the ice area flux over the 18 year record the average winter volume flux over the winters of october 1990 through may 1995 is 1745 km3 ranging from a low of 1375 km3 in the 1990 flux to a high of 2791 km3 in 1994 the sea level pressure gradient across the fram strait explains more than 80 of the variance in the ice flux over the 18 year record we use the coefficients from the regression of the time series of area flux versus pressure gradient across the fram strait and ice thickness data to estimate the summer area and volume flux the average 12 month area flux and volume flux are 919 000 km2 and 2366 km3 we find a significant correlation r 0 86 between the area flux and positive phases of the north atlantic oscillation nao index over the months of december march correlation between our 5 years of volume flux estimates and the nao index gives r 0 56 during the high nao years a more intense icelandic low increases the gradient in the sea level pressure by almost 1 mbar across the fram strait thus increasing the atmospheric forcing on ice transport correlation is reduced during the negative nao years because of decreased dominance of this large scale atmospheric pattern on the sea level pressure gradient across the fram strait

holocene sea subsurface and surface water masses in the fram strait comparisons of temperature and sea ice reconstructions highlights holocene sea subsurface temperatures after husum hald 2012 estimated from planktic foraminifer fauna in e fram strait biomarkers and ip25 derived indices including dip25 indicate surface water variability delayed onset of early holocene conditions in subsurface 10 6 ka compared to surface 11 7 ka water conditions warm atlantic layer likely occupied uppermost 200 m in eastern fram strait between 10 and 9 ka diverging late holocene trends in surface and subsurface conditions linked to presence of strong pycnocline stratification abstract two high resolution sediment cores from eastern fram strait have been investigated for sea subsurface and surface temperature variability during the holocene the past ca 12 000 years the transfer function developed by husum and hald 2012 has been applied to sediment cores in order to reconstruct fluctuations of sea subsurface temperatures throughout the period additional biomarker and foraminiferal proxy data are used to elucidate variability between surface and subsurface water mass conditions and to conclude on the holocene climate and oceanographic variability on the west spitsbergen continental margin results consistently reveal warm sea surface to subsurface temperatures of up to 6 c until ca 5 cal ka bp with maximum seawater temperatures around 10 cal ka bp likely related to maximum july insolation occurring at that time maximum atlantic water aw advection occurred at surface and subsurface between 10 6 and 8 5 cal ka bp based on both foraminiferal and dinocyst temperature reconstructions probably a less stratified ice free nutrient rich surface ocean with strong aw advection prevailed in the eastern fram strait between 10 and 9 cal ka bp weakened aw contribution is found after ca 5 cal ka bp when subsurface temperatures strongly decrease with minimum values between ca 4 and 3 cal ka bp cold late holocene conditions are furthermore supported by high planktic foraminifer shell fragmentation and high 18o values of the subpolar planktic foraminifer species turborotalita quinqueloba while ip25 associated indices as well as dinocyst data suggest a sustained cooling due to a decrease in early summer insolation and consequently sea ice increase since about 7 cal ka bp in surface waters planktic foraminiferal data including stable isotopes indicate a slight return of stronger subsurface aw influx since ca 3 cal ka bp the observed decoupling of surface and subsurface waters during the later holocene is most likely attributed to a strong pycnocline layer separating cold sea ice fed surface waters from enhanced subsurface aw advection this may be related to changes in north atlantic subpolar versus subtropical gyre activity

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

neogloboquadrina pachyderma dex and sin mg ca and δ18o records from the norwegian sea magnesium calcium mg ca records based on n pachyderma dex and n pachyderma sin from the last 1200 years have been retrieved from high resolution cores in the norwegian sea comparing temperatures inferred from mg ca and the oxygen isotopic composition of calcite 18oc with instrumental temperature records from ocean weather ship mike suggests that n pachyderma calcifies during the summer season with an offset to oxygen isotope equilibrium of 0 6 in this region summer temperatures below the thermocline are related to the winter season ventilation and breakdown of the seasonal thermocline hence the deeper dwelling n pachyderma sin provides a winter season signal down core n pachyderma dex mg ca temperatures display larger variance than observed in 18oc temperatures record derived from the same morphotype the smaller variance in the 18ocn pachyderma dex temperatures is probably linked to salinity changes in the upper 50 m of the water column the mg ca temperature and 18oc records are used to reconstruct changes in the oxygen isotopic composition of water 18ow during the last 1200 years the reconstructed 18ow records show variation within a realistic range allowing the influence of other water masses than those present at the site today and suggest that the mg ca signal in morphotypes of n pachyderma in the norwegian sea responds to changes in climatic parameters

reconstruction of mid to late holocene winter temperatures in the skagerrak region using benthic foraminiferal mg ca and δ18o reconstruction of skagerrak deep water renewal is used to assess regional changes in winter thermal conditions over the past 6800 years changes in winter climate conditions from the skagerrak region are in turn linked to shifts in holocene large scale atmospheric circulation patterns prevailing over northern europe we use melonis barleeanus mg ca from two sediment cores in the central skagerrak to reconstruct temperature of skagerrak intermediate water representing the warm season temperature variability and deep water for monitoring skagerrak deep water renewal reflecting the winter temperature variability in addition m barleeanus 18o is used from the deeper core to reconstruct salinity also monitoring the deep water renewal our results show that the skagerrak deep water experienced phases of particularly enhanced renewal during the mid holocene reflecting severe winter conditions followed by a general shift to reduced renewal as a consequence of milder winter conditions over the north sea a

palaeoceanographic reconstruction of surface ocean changes in the southern norwegian sea for the last 130 000 years based on diatoms and with comparison to foraminiferal records abstract fossil marine diatom assemblages in a sediment core from the central northern faroe slope in the norwegian sea were used to reconstruct palaeoceanographic changes in the surface water mixed layer from the last 130 000 years marine isotope stage mis 6 5 transition to mis 1 including the eemian and holocene interglacials and to compare the results with previously published results on planktic foraminifera representing the subsurface conditions of the thermocline diatom floras from mis 5 of the nordic seas have rarely been studied in detail before and never the entire period from pre eemian to present the composition of diatom species together with maxima in absolute abundance of diatoms indicate two periods of warmer sea surface temperatures correlating with the eemian and holocene interglacials respectively the eemian differs from the holocene in that the iceland faroe front never developed suggesting the cold east icelandic current originating from the east greenland current running north of iceland was reduced or more mixed with atlantic water than during the holocene and that the surface temperature and salinity gradients were weaker the northern faroe slope was in the early weichselian of mis 5d 5a mainly influenced by weaker inflow of atlantic water and stronger influence of the east icelandic current and by seasonal sea ice cover during the later part of the weichselian mis 4 mis 2 cold conditions prevailed with extensive sea ice cover except during the warmer interstadials the diatom floras were more sensitive to climate changes than the planktic foraminifera and indicate longer periods with warm surface conditions and increased influence of the warm atlantic surface water from the faroe current in mis 5 suggesting a shallower and much steeper thermocline during the transitional periods compared to today the diatoms are good indicators for atlantic water inflow and possible convection in the nordic seas not merely reflecting orbital variations in insolation as previously suggested

the cold event 8200 years ago documented in oxygen isotope records of precipitation in europe and greenland stable oxygen isotope ratios of ostracod valves in late glacial and holocene sediments of core as 92 5 from deep lake ammersee southern germany reflect variations of mean oxygen isotope ratios in past atmospheric precipitation the record reconfirms the strong similarity of climate evolution in europe and greenland during the last deglaciation for the first time in europe we find a 200 year long negative 18o excursion which is contemporaneous with the strongest negative 18o excursion in the greenland ice around 8 2 ky before present the 8 2 ky isotopic event on both sides of the north atlantic ocean is interpreted as a cold period most probably induced by a perturbation of the north atlantic thermohaline circulation we discuss two possible triggering mechanisms 1 weak forcing as proposed by alley et al and 2 forcing by a strong and sudden freshwater pulse from the collapse of the hudson ice dome

impact of shallow living radiolarian flux variations on north atlantic cycladophora davisiana percentages abstract the cause of high cycladophora davisiana percentages a deep living maximum abundance 200 m radiolarian species in high latitude 45 late pleistocene deep sea sediments has been much debated in this paper we show that in four subpolar north atlantic cores these late pleistocene high percentages 20 result more from a reduction of other radiolarian flux predominantly shallow living species c davisiana flux relative to holocene flux these findings are similar to those reported from the north pacific hays et al 2013 in both oceans the late pleistocene to holocene shallow living species flux increase is larger than the concomitant decrease of c davisiana flux similarly high c davisiana percentages 20 found today in okhotsk sea holocene sediments kruglikova 1975 robertson 1975 morley and hays 1983 result from low radiolarian concentrations in the overlying dicothermal layer 20 150 m where year round temperatures are near 0 c it is likely that the high c davisiana percentages in north atlantic late pleistocene sediments were caused by a similar overlying stratification that had important biological consequences for radiolarians and other plankton a more significant time transgressive increase in shallow and others radiolarian assemblage flux occurs initially in the southernmost core in mid holocene ultimately recorded at the northernmost site during the late holocene here flux of the deep assemblage and c davisiana also increases

palaeoceanographic changes off north iceland through the last 1200 years foraminifera stable isotopes diatoms and ice rafted debris abstract palaeoclimatic changes through the last 1200 calibrated years have been documented by high resolution multi proxy studies of three cores from about 400 m water depth on the north icelandic shelf benthic and planktonic foraminiferal assemblages and stable isotope values as well as ice rafted debris ird concentrations are compared with diatom based sea surface water temperatures and the reconstructed mean temperature for the northern hemisphere changes in surface and bottom water characteristics are mainly due to variations in the strength of the relatively warm high salinity irminger current and the cold east icelandic current the time period between 1200 and around 7 800 cal years bp including the medieval warm period was characterized by relatively high bottom and surface water temperatures due to the inflow of atlantic water masses after that a general temperature decrease in the area marks the transition to a period with increased influence of the east icelandic current and at the sea floor the norwegian sea deep water this corresponds to the transition to the little ice age after about 3 400 cal bp the inflow of cold east icelandic current was further enhanced in particular this had a strong influence on the surface waters while the sea floor was under some influence of atlantic water masses resulting in stratification of the water masses there is no clear indication of any warming in the area during the last decades

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

a regional 8200 cal yr bp cooling event in northwest europe induced by final stages of the laurentide ice sheet deglaciation the most notable change in 18o in greenland ice cores during the holocene occurs at 8200 cal yr bp here we present a new high resolution marine record from the northern north sea along with tree ring data from germany which contain evidence of a pronounced temperature drop 2 c contemporaneous with that of the greenland ice core records the synchronous timing of the cooling event in the greenland ice cores marine record and tree ring data from northwest europe reflects a regional influence on the north atlantic ocean atmospheric system suggesting a prominent role of the north atlantic thermohaline circulation the operation of the north atlantic ocean circulation is sensitive to variation in the freshwater budget implying that any change in freshwater flux is capable of altering the north atlantic circulation system we hypothesise minor but long term freshwater fluxes in the final stages of the deglaciation of the laurentide ice sheet as a forcing mechanism 1998 john wiley sons ltd

a new approach to calculating holocene winter precipitation by combining glacier equilibrium line altitudes and pine tree limits a case stud from hardangerjokulen central southern norway at hardangerjokulen central southern norway detailed knowledge of the number age and magnitude of holocene glacier fluctuations is used to reconstruct variations in equilibrium line altitude ela for the last 10 000 years present and past elas are based on an accumulation area ratio aar of 0 7 and are adjusted for land uplift a synchronous relationship between advanced glacier positions and the highest pine tree limits pinus sylvestris l is demonstrated for the early to mid holocene in southern scandinavia which indicates that warm summers were compensated for by high winter precipitation based on pine tree limit fluctuations as a measure of mean ablation season temperature holocene variations in winter precipitation at hardangerjokulen have been calculated by substitution in the close exponential relationship between mean ablation season temperature and winter precipitation at the ela of norwegian glaciers setting the winter precipitation during the period ad 1961 1990 at 100 mean values

influence of insolation and glaciation on atmospheric circulation in the north atlantic sector implications of general circulation model experiments for the late quaternary climatology of europe abstract atmospheric general circulation models have been used to simulate the sensitivity of regional climates to late quaternary changes in insolation ice sheets and atmospheric co 2 model results for full glacial conditions 18 ka show the atlantic westerly jet strengthened and shifted south a corresponding southward shift of the icelandic low and a strengthening and northward shift of the subtropical anticyclone sta a glacial anticyclone developed over the european ice sheet and cold dry conditions prevailed over much of europe the full glacial climate anomaly for the north atlantic sector is explained by a combination of low atmospheric co 2 reducing global surface temperatures and circulation changes caused by the ice sheets by the early holocene 9 ka the ice sheets were much reduced while the orbital anomaly was near its maximum producing mid continental summer warming and winter cooling and a reduced latitudinal temperature gradient in the northern hemisphere in both seasons the jet and the icelandic low were displaced to north of their present position producing strong onshore flow and mild wet winters in northern europe while the sta was also shifted northwards producing offshore flow and dry summers in the same region during the late glacial transition the effects of insolation and glaciation were antagonistic for some features of the circulation and synergistic for others the model results suggest palaeoclimatic hypotheses that could be directly tested by comparison with palaeoclimatic data mapped at a synoptic scale

holocene glacier and climate fluctuations on franz josef land arctic russia 80 n fluctuations in glacier extent provide the first comprehensive record of holocene paleoclimate for franz josef land glacier fluctuations were constrained using 45 14c ages from 16 glacier margins many glaciers were behind present margins before 9 4 kyr possibly as early as 10 3 kyr and probably remained so until at least 4 4 kyr where kyr 14c yr b p 1000 subsequently glaciers expanded probably reaching present margins before 3 2 kyr but certainly by 2 kyr a prominent neoglacial advance occurred ca 1 kyr and was followed by little ice age advances including one in the middle 1600s a d glaciers were larger than present at the turn of the century followed by widespread retreat soon after the holocene glacier record closely mimics that of svalbard 500 to 1000 km to the west suggesting similar glacier mass balance changes over a broad region of the eurasian arctia independent paleoclimate evidence from svalbard indicates higher than present summer air temperatures during the early to middle holocene when glaciers were behind present margins followed by generally cooler summer conditions and intermittent glacier advances and retreats holocene glacier variations were probably more influenced by summer temperature than winter precipitation

sub sea surface temperatures in the polar north atlantic during the holocene planktic foraminiferal mg ca temperature reconstructions holocene sea surface temperatures in the eastern fram strait are reconstructed based on mg ca ratios measured on the planktic foraminifer neogloboquadrina pachyderma sin the reconstructed sub sea surface temperatures ssstmg ca fluctuate markedly during the earliest holocene at 11 7 and 10 5 kyr bp this is probably in response to the varying presence of sea ice and deglacial meltwater between 10 5 7 9 kyr bp the ssstmg ca values are relatively high 4 c and more stable reflecting high insolation and intensified poleward advection of atlantic water after 7 9 kyr bp the ssstmg ca values decline to an average of 3 c throughout the mid holocene these changes can be attributed to a combined effect of reduced poleward oceanic heat advection and a decline in insolation as well as a gradually increased influence of eastward migrating arctic water the ssstmg ca values increase and vary between 2 1 c and 5 8 c from 2 7 kyr bp to the present this warming is in contrast to declining late holocene in

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

rapid changes in the mechanism of ocean convection during the last glacial period high amplitude rapid climate fluctuations are common features of glacial times the prominent changes in air temperature recorded in the greenland ice cores1 2 are coherent with shifts in the magnitude of the northward heat flux carried by the north atlantic surface ocean3 4 changes in the ocean s thermohaline circulation are a key component in many explanations of this climate flickering5 here we use stable isotope and other sedimentological data to reveal specific oceanic reorganizations during these rapid climate change events deep water was generated more or less continuously in the nordic seas during the latter part of the last glacial period 60 to 10 thousand years ago but by two different mechanisms the deep water formation occurred by convection in the open ocean during warmer periods interstadials but during colder phases stadials a freshening of the surface ocean reduced or stopped open ocean convection and deep water formation was instead driven by brine release during sea ice freezing these shifting magnitudes and modes nested within the overall continuity of deep water formation were probably important for the structuring and rapidity of the prevailing climate changes

coherent high and low latitude climate variability during the holocene warm period a faunal record of sea surface temperature sst variations off west africa documents a series of abrupt millennial scale cooling events which punctuated the holocene warm period these events evidently resulted from increased southward advection of cooler temperate or subpolar waters to this subtropical location or from enhanced regional upwelling the most recent of these events was the little ice age which occurred between 1300 to 1850 a d when subtropical ssts were reduced by 3 to 4 c these events were synchronous with holocene changes in subpolar north atlantic ssts documenting a strong in phase link between millennial scale variations in high and low latitude climate during the holocene

centennial scale climate cooling with a sudden cold event around 8 200 years ago the extent of climate variability during the current interglacial period the holocene is still debated temperature records derived from central greenland ice cores show one significant temperature anomaly between 8 200 and 8 100 years ago which is often attributed to a meltwater outflow into the north atlantic ocean and a slowdown of north atlantic deep water formation this anomaly provides an opportunity to study such processes with relevance to present day freshening of the north atlantic anomalies in climate proxy records from locations around the globe are often correlated with this sharp event in greenland but the anomalies in many of these records span 400 to 600 years start from about 8 600 years ago and form part of a repeating pattern within the holocene more sudden climate changes around 8 200 years ago appear superimposed on this longer term cooling the compounded nature of the signals implies that far field climate anomalies around 8 200 years ago cannot be used in a straightforward manner to assess the impact of a slowdown of north atlantic deep water formation and the geographical extent of the rapid cooling event 8 200 years ago remains to be determined

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

late holocene effective precipitation variations in the maritime regions of south west scandinavia at present the climate in south west scandinavia is predominantly controlled by westerlies carrying moist atlantic air which forms a main source of precipitation in all seasons past variations in the ratio between precipitation and evaporation effective precipitation from terrestrial sites however may indicate changes in the degree of maritime influence palaeoclimatic archives in this region are thus ideally situated to study past changes in atmospheric circulation patterns in this study multi proxy comparisons of records from three peat bogs and two lakes are used to reconstruct regional scale variations of effective precipitation in south west sweden during the late holocene the total aeolian sediment influx into two peat bogs is used as a proxy for storm activity the frequency of storm phases increases strongly after ca 2500 cal yrs bp dry conditions occur on a regional scale around 4800 4400 2000 1700 1300 1000 700 500 and 300 100 cal yrs bp in addition a comparison to winter precipitation reconstructed from four norwegian glaciers shows similar variations during the past ca 2000 years this indicates that the climate in both regions was controlled by large scale atmospheric circulation dynamics of the north atlantic region the strong variability of effective precipitation and storm activity after ca 2500 cal yrs bp indicates a highly variable climate

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

mid and late holocene climatic changes a test of periodicity and solar forcing in proxy climate data from blanket peat bogs a wide range of palaeoenvironmental evidence from the holocene has suggested periodicities in the earth s climate of 10s to 1000s of years identifying these millennial century and decadal periodicities and their impacts is critical in developing a fuller understanding of natural climate variability any solar induced climatic change needs to be distinguished from other causes of natural climate variability and from short term catastrophic events induced either by external or internal processes such events might themselves generate a periodicity or in combination with other forcing factors they may contribute towards a periodicity and so spuriously imply a universal and continuing periodicity in the climate record or they may resonate with a solar induced periodicity here evidence from peat records for periodicity in climate change over the mid to late holocene is reviewed and this is followed by a test of the replicability of claimed periodicities using blanket peat data covering the past 2000 yr from four sites in the british isles results suggest that the mires studied do go through phases of being responsive to periodic forcing factors with ca 200 ca 80 and 60 50 yr wavelengths reflected in some data sets however the patterns shown are not consistent this could be the result of local conditions at individual mires human impact sensitivity and vegetation succession or of changes in the strength or nature of global forcing factors assessing a solar mire link remains difficult because the century scale variations of the sun show different intervals between solar minima the durations of which are themselves unequal and because the proxy climate data sets from peat profiles may themselves not be dated with sufficient precision and or accuracy

variability in terrigenous sedimentation processes off northwest africa and its relation to climate changes inferences from grain size distributions of a holocene marine sediment record variations in deposition of terrigenous fine sediments and their grain size distributions from a high resolution marine sediment record offshore northwest africa 30 51 0 n 10 16 1 w document climate changes on the african continent during the holocene end member grain size distributions of the terrigenous silt fraction which are related to fluvial and aeolian dust transport indicate millennial scale variability in the dominant transport processes at the investigation site off northwest africa as well as recurring periods of dry conditions in northwest africa during the holocene the terrigenous record from the subtropical north atlantic reflects generally humid conditions before the younger dryas during the early to mid holocene as well as after 1 3 kyr bp by contrast continental runoff was reduced and arid conditions were prevalent at the beginning of the younger dryas and during the mid and late holocene a comparison with high and low latitude holocene climate records reveals a strong link between northwest african climate and northern hemisphere atmospheric circulation throughout the holocene due to its proximal position close to an ephemeral river system draining the atlas mountains as well as the adjacent saharan desert this detailed marine sediment record which has a temporal resolution between 15 and 120 years is ideally suited to enhance our understanding of ocean continent atmosphere interactions in african climates and the hydrological cycle of northern africa after the last deglaciation

a 4500 year reconstruction of sea surface temperature variability at decadal time scales off north iceland marine paleo records acquired at high temporal resolution provide critical data for testing numerical climate models and help to understand processes underlying ocean variability this study presents a unique 4500 year reconstruction of sea surface temperature sst obtained from alkenones in the north atlantic polar front area off north iceland at an average temporal resolution of 4 5 years spectral analysis of this signal shows dominant multidecadal oscillations which occurred with a stronger amplitude between 2500 and 4200 years bp hand in hand with fluctuations of bottom currents indicated by paleomagnetic proxies contemporaneous large excursions of the inter tropical convergence zone itcz are also recorded by the distant cariaco titanium time series suggesting a link with low latitude atlantic climate we speculate that the oscillations reflect changes of the meridional overturning circulation moc induced by increased enso activity

physical and biological characteristics of the pelagic system across fram strait to kongsfjorden abstract the fram strait is very important with regard to heat and mass exchange in the arctic ocean and the large quantities of heat carried north by the west spitsbergen current wsc influence the climate in the arctic region as a whole a large volume of water and ice is transported through fram strait with net water transport of 1 7 3 2 sv southward in the east greenland current and a volume ice flux in the range of 0 06 0 11 sv the mean annual ice flux is about 866 000 km2 yr 1 the kongsfjorden krossfjorden fjord system on the coast of spitsbergen or at the eastern extreme of fram strait is mainly affected by the northbound transport of water in the wsc mixing processes on the shelf result in transformed atlantic water in the fjords and the advection of atlantic water also carries boreal fauna into the fjords the phytoplankton production is about 80 g c m 2 yr 1 in fram strait and has been estimated both below and above this for kongsfjorden the zooplankton fauna is diverse but dominated in terms of biomass by calanoid copepods particularly calanus glacialis and c finmarchicus other important copepods include c hyperboreus metridia longa and the smaller more numerous pseudocalanus p minutus and p acuspes microcalanus m pusillus and m pygmaeus and oithona similis the most important species of other taxa appear to be the amphipods themisto libellula and t abyssorum the euphausiids thysanoessa inermis and t longicaudata and the chaetognaths sagitta elegans and eukrohnia hamata a comparison between the open ocean of fram strait and the restricted fjord system of kongsfjorden krossfjorden can be made within limitations the same species tend to dominate but the fram strait zooplankton fauna differs by the presence of meso and bathypelagic copepods the seasonal and inter annual variation in zooplankton is described for kongsfjorden based on the record during july 1996 2002 the ice macrofauna is much less diverse consisting of a handful of amphipod species and the polar cod the ice associated biomass transport of ice amphipods was calculated based on the ice area transport at about 3 55 106 ton wet weight per year or about 4 2 105 t c yr 1 this represents a large energy input to the greenland sea but also a drain on the core population residing in the multi year pack ice myi in the arctic ocean a continuous habitat loss of myi due to climate warming will likely reduce dramatically the sympagic food source the pelagic and sympagic food web structures were revealed by stable isotopes the carbon sources of particulate organic matter pom being ice pom and pelagic pom revealed different isotopic signals in the organisms of the food web and also provided information about the sympagic pelagic and pelagic benthic couplings the marine food web and energy pathways were further determined by fatty acid trophic markers which to a large extent supported the stable isotope picture of the marine food web although some discrepancies were noted particularly with regard to predator prey relationships of ctenophores and pteropods

a high resolution study of holocene paleoclimatic and paleoceanographic changes in the nordic seas 1 high resolution records from images core md95 2011 in the eastern norwegian sea provide evidence for relatively large and small scale high latitude climate variability throughout the holocene during the early and mid holocene a situation possibly driven by consistent stronger westerlies increased the eastward influence of arctic intermediate and near surface waters for the late holocene a relaxation of the atmospheric forcing resulted in increased influence of atlantic water the main changes in holocene climate show no obvious connection to changing solar irradiance and spectral analysis reveals no consistent signature for any periodic behavior of holocene climate at millennial or centennial timescales there are however indications of consistent multidecadal variability

9 400 yr b p the mortality of mollusk shell mya truncata at high arctic is associated with a sudden cooling event an 118 cm long well preserved sediment profile was collected from a paleo notch formed by ocean wave action before rising to the terrace on ny alesund svalbard norway a large number of mollusk shell fragments predominantly mya truncata were found in the sediment profile ams 14c dating and stable oxygen and carbon isotope analyses were performed on the shell fragments samples the reservoir corrected radiocarbon ages averaged 9 400 yr b p which accurately dates the raised terrace and the upper marine limit after kongsfjorden was completely deglaciated the calibrated aragonite isotopic temperature equation was established for ny alesund by comparing the 18o profiles of modern mollusks as follows t c 16 26 3 68 18oaragonite pdb 18owater vsmow the reconstructed paleotemperature range was 0 52 to 4 78 c warmer than today by about 1 c which was further confirmed by reconstructed sea surface temperature sst in west svalbard moreover the mortality of mollusks was very likely caused by an abrupt cooling event at about 9 400 yr b p which was triggered by reduced insolation weakened thermohaline circulation and abruptly decreased sst more evidences for this distinct but short cooling event centered at about 9 400 yr b p were found in northern siberia north atlantic alps and eastern europe

tectonic geomorphology of the qilian shan in the northeastern tibetan plateau insights into the plateau formation processes abstract we examined the regional scale topography of the qilian shan on the northeastern margin of the tibetan plateau longitudinal profiles and geomorphometric indices such as slope local relief and channel steepness reveal that the qilian shan was developed as a local plateau with high relief steep marginal ranges and interior low relief topography landscape mapping across this local plateau revealed spatially varied origins of the low relief landscape in the qilian shan north of the haiyuan fault universal massive intermontane aggradation was identified however the low relief plateau to the south of the haiyuan fault was dominated by relict erosional surfaces even though accompany basin filling still contributes the geomorphologic contrasts led us to integrate both the basin filling processes and antecedent low relief erosional surfaces into a new insight into the development of the qilian shan plateau in the northeastern tibet our present study highlights that explanation for the low relief plateau formation needs to consider the complex geological evolution of the qilian shan and the tibetan plateau itself

paleoceanographic development in the sw barents sea during the late weichselian early holocene transition abstract the late weichselian early holocene variability of the north atlantic current has been studied with focus on the zonal component of this meridional transport during the transition from glacial to interglacial conditions the investigated sediment core is from 409 m water depth in the sw barents sea eight accelerator mass spectrometry ams 14c dates show that the core covers the last 20 000 cal yr b p with a centennial scale resolution during late weichselian early holocene planktic foraminiferal assemblages were analyzed using the 100 m size fraction and foraminiferal planktic and benthic 13c and 18o isotopes were measured furthermore a range of physical and chemical analyses has been carried out on the bulk sediment samples four time periods have been identified which represent the varying oceanographic conditions in ingoydjupet a glacial trough located off the north coast of norway in the sw barents sea 1 the late glacial before ca 15 000 cal yr b p influenced by the nearby ice sheets with high amounts of sea ice or iceberg transported detritus 2 the late oldest dryas stadial and the bolling allerod interstadial ca 15 000 12 700 cal yr b p with cold surface water conditions influenced by the collapse of the nearby ice sheets high amounts of sea ice or iceberg transported detritus and melt water and weak subsurface inflow of atlantic water 3 the younger dryas cold stadial 12 700 11 650 cal yr b p with low primary productivity and extensive sea ice cover and 4 the preboreal and early holocene 11 650 6800 cal yr b p cal yr b p with strong influx of atlantic water into the area near absence of ice rafted debris and generally ameliorated conditions in both surface and bottom water masses as seen from a high flux of foraminifera and increased marine primary production

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