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

exploring holocene continentality changes in fennoscandia using present and past tree distributions with global warming the distribution of warmth through the year is likely to change in the future and comparable changes may have occurred over the course of the holocene its effect on vegetation composition and species distribution can be compared to that of a continental versus an oceanic climate the distribution of five major tree species along a continentality gradient was studied in fennoscandia based on distribution maps and on their proportions of pollen in surface sediment samples both analyses indicate that the five arboreal species show similar patterns of response to a continentality index in the order ulmus glabra corylus avellana quercus robur tilia cordata and picea abies from the most oceanic to most continental continentality growing degree days above 5 degrees c and january temperature were reconstructed quantitatively from four pollen diagrams using transfer functions based on a combined fennoscandian pollen surface sample data set quantitative reconstructions indicate that the climate in fennoscandia has become increasingly more continental over the last 7000 years and this is largely an effect of winter cooling early holocene vegetation composition has poor analogues to the present vegetation in fennoscandia which hampers quantitative reconstructions qualitative reconstructions suggest that the early holocene in fennoscandia was the most oceanic period but probably with a high variability in temperature c 2008 elsevier ltd all rights reserved

rapid environmental changes in southern europe during the last glacial period oxygen isotope records from greenland ice cores1 2 indicate numerous rapid climate fluctuations during the last glacial period north atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice rafted debris3 4 5 in contrast very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents here we present high resolution geochemical physical and pollen data from lake sediments in italy and from a mediterranean sediment core linked by a common tephrochronology our lacustrine sequence extends to the past 102 000 years many of its features correlate well with the greenland ice core records demonstrating that the closely coupled ocean atmosphere system of the northern hemisphere during the last glacial4 extended its influence at least as far as the central mediterranean region numerous vegetation changes were rapid frequently occurring in less than 200 years showing that the terrestrial biosphere participated fully in last glacial climate variability earlier than 65 000 years ago our record shows more climate fluctuations than are apparent in the greenland ice cores together the multi proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials and provide a step towards determining the underlying mechanisms of the centennial millennial scale variability

a holocene lacustrine record in the central north atlantic proxies for volcanic activity short term nao mode variability and long term precipitation changes a holocene lacustrine record in the central north atlantic proxies for volcanic activity short term nao mode variability and long term precipitation changes

a highly unstable holocene climate in the subpolar north atlantic evidence from diatoms a composite record lo09 14 of three sediment cores from the subpolar north atlantic reykjanes ridge was investigated in order to assess surface ocean variability during the last 11 kyr the core site is today partly under the influence of the irminger current ic a branch of the north atlantic drift continuing northwestward around iceland however it is also proximal to the sub arctic front saf that may cause extra dynamic hydrographic conditions we used statistical methods applied to the fossil assemblages of diatoms to reconstruct quantitative sea surface temperatures ssts our investigations give evidence for different regional signatures of holocene surface oceanographic changes in the north atlantic core lo09 14 reveal relatively low and highly variable ssts during the early holocene indicating a weak ic and increased advection of subpolar water over the site a mid holocene thermal optimum with a strong ic occurs from 7 5 to 5 kyr and is followed by cooler and more stable late holocene surface conditions several intervals throughout the holocene are dominated by the diatom species rhizosolenia borealis which we suggest indicates proximity to a strongly defined convergence front most likely the saf several coolings reflecting southeastward advection of cold and ice bearing waters occur at 10 4 9 8 8 3 7 9 6 4 4 7 4 3 and 2 8 kyr the cooling events recorded in the lo09 14 ssts correlate well with both other surface records from the area and the nadw reductions observed at odp site 980 indicating a surface deepwater linkage through the holocene

temperature reconstructions for sw and n iceland waters over the last 10 cal ka based on δ18o records from planktic and benthic foraminifera abstract we have obtained 18 o carb data from planktic n pachyderma s and benthic foraminifera c lobatulu s m barleeanu s from eight cores between 40 and 500 m water depth along the sw core b997 347 and n iceland margins cores b997 321 324 327 328 329 330 and 332 that span the last 10 cal ka sampling resolution varies between centuries to millennial scales over this time range changes in 18 o carb in foraminifera are the product of changes in the global ice volume and the temperature and salinity of the water at the level in which the foraminifera live in order to evaluate the relative roles of these variables we investigate 1 the salinity s and 18 o water values for present day waters off iceland and 2 the present day relationships between 18 o carb or calcite values of foraminifera and water column temperature and salinity data we estimate the average error in the temperature estimate to be 0 3 c based on a monto carlo simulation of the various error terms we argue that around iceland the variations in 18 o carb of both benthic and planktic species over the last 10 cal ka are principally controlled by temperature variations while salinity changes prove less important spatial and temporal changes are examined for both bottom water and 50 m water temperature reconstructions based on six and four cores respectively reconstructed temperatures for sites around sw n iceland indicate that surface and seafloor water temperatures were warmest in the early holocene 10 6 cal ka beginning at 6 cal ka surface and seafloor temperatures began to cool in n iceland and to become less stratified in sw iceland over the last 5000 yrs sea surface temperature variations have been 1 c for 50 of the observations with a maximum range of 2 5 c a profound decrease in temperature of 1 5 c is recorded in our fjord site b997 328 during the little ice age an abrupt earlier cold event is well expressed in at least three n iceland cores around 5 cal ka

high resolution sea surface reconstructions off cape hatteras over the last 10 ka 1 this study presents high resolution foraminiferal based sea surface temperature sea surface salinity and upper water column stratification reconstructions off cape hatteras a region sensitive to atmospheric and thermohaline circulation changes associated with the gulf stream we focus on the last 10 000 years 10 ka to study the surface hydrology changes under our current climate conditions and discuss the centennial to millennial time scale variability we observed opposite evolutions between the conditions off cape hatteras and those south of iceland known today for the north atlantic oscillation pattern we interpret the temperature and salinity changes in both regions as co variation of activities of the subtropical and subpolar gyres around 8 3 ka and 5 2 3 5 ka positive salinity anomalies are reconstructed off cape hatteras we demonstrate for the 5 2 3 5 ka period that the salinity increase was caused by the cessation of the low salinity surface flow coming from the north a northward displacement of the gulf stream blocking the southbound low salinity flow concomitant to a reduced meridional overturning circulation is the most likely scenario finally wavelet transform analysis revealed a 1000 year period pacing the 18o signal over the early holocene this 1000 year frequency band is significantly coherent with the 1000 year frequency band of total solar irradiance tsi between 9 5 ka and 7 ka and both signals are in phase over the rest of the studied period

holocene and eemian sea surface temperature trends as revealed by alkenone and mg ca paleothermometry in this study we review a global set of alkenone and foraminiferal mg ca derived sea surface temperatures sst records from the holocene and compare them with a suite of published eemian sst records based on the same approach for the holocene the alkenone sst records belong to the actualized ghost database kim j h schneider r r 2004 ghost global database for alkenone derived holocene sea surface temperature records available from http www pangaea de projects ghost while the mg ca derived sst database represents a new compilation the actualized ghost database not only confirms the sst changes previously described but also documents the holocene temperature evolution in new oceanic regions such as the northwestern atlantic the eastern equatorial pacific and the southern ocean a comparison of holocene sst records stemming front the two commonly applied paleothermometry methods reveals contrasting sometimes divergent sst evolution particularly at low latitudes where sst records are abundant enough to infer systematic discrepancies at a regional scale opposite sst trends at particular locations could be explained by out of phase trends in seasonal insolation during the holocene this hypothesis assumes that a strong contrast in the ecological responses of coccolithophores and planktonic foraminifera to winter and summer oceanographic conditions is the ultimate reason for seasonal differences in the origin of the temperature signal provided by these organisms as a simple test for this hypothesis eemian sst records are considered because the holocene and eemian time periods experienced comparable changes in orbital configurations but had a higher magnitude in insolation variance during the eemian for several regions sst changes during both interglacials were of a similar sign but with higher magnitudes during the eemian as compared to the holocene this observation suggests that the ecological mechanism shaping sst trends during the holocene was comparable during the penultimate interglacial period although this ecology hypothesis fails to explain all of the available results we argue that any other mechanism would fail to satisfactorily explain the observed sst discrepancies among proxies c 2010 elsevier ltd all rights reserved

the north atlantic oscillation and its imprint on precipitation and ice accumulation in greenland interannual to decadal fluctuations in net precipitation and ice accumulation are examined over greenland it is shown that in western greenland these fluctuations are correlated with the north atlantic oscillation the analysis is based on two complementary data sources a highly resolved net precipitation and accumulation history over 15 years derived form the reanalysis data of the european centre for medium range weather forecasts and a composite ice accumulation record representative for the western part of central greenland it is suggested that western greenland snow accumulation is a good proxy for the nao index with the potential for the reconstruction of a long time series

investigating the sensitivity of the atmospheric general circulation model echam 3 to paleoclimatic boundary conditions we present atmospheric simulations of three different time slices of the late quaternary using the echam 3 general circulation model in t42 resolution in this work we describe the results of model runs for the time slices 6000 years bp last climate optimum 21 000 bp last glacial maximum and 115 000 years bp glacial inception although the solar insolation is known for all time slices a complete data set of the other boundary conditions which are necessary for running the atmospheric model exists only for the last glacial maximum in the form of the climap reconstruction for the other two time slices which are interglacial states like the modern climate sea surface temperatures land albedo and ice sheet topography are kept at modern values and only the solar insolation is changed appropriately the response of the model to solar insolation changes is quite reasonable the modelled anomalies are small and roughly opposite in sign for 6000 bp and 115 000 bp respectively in the case of last glacial maximum the glacial ice sheet topography and ice albedo produce a much larger climate anomaly in the model however to enable a real test of model performance under glacial boundary conditions the climap sea surface temperatures which are now known to be partly inaccurate should be replaced by an updated state of the art reconstruction

holocene cooling culminates in sea ice oscillations in fram strait a reconstruction of holocene sea ice conditions in the fram strait provides insight into the palaeoenvironmental and palaeoceanographic development of this climate sensitive area during the past 8500 years bp organic geochemical analyses of sediment cores from eastern and western fram strait enable the identification of variations in the ice coverage that can be linked to changes in the oceanic and atmospheric circulation system by means of the sea ice proxy ip25 phytoplankton derived biomarkers and ice rafted detritus ird increasing sea ice occurrences are traced along the western continental margin of spitsbergen throughout the holocene which supports previous palaeoenvironmental reconstructions that document a general cooling a further significant ice advance during the neoglacial is accompanied by distinct sea ice fluctuations which point to short term perturbations in either the atlantic water advection or arctic water outflow at this site at the continental shelf of east greenland the general holocene cooling however seems to be less pronounced and sea ice conditions remained rather stable here a major neoglacial increase in sea ice coverage did not occur before 1000 years bp phytoplankton ip25 indices pip25 index are used for more explicit sea ice estimates and display a mid holocene shift from a minor sea ice coverage to stable ice margin conditions in eastern fram strait while the inner east greenland shelf experienced less severe to marginal sea ice occurrences throughout the entire holocene highlights biomarker and ird data give insight into holocene sea ice conditions in fram strait we find increasing sea ice coverage off west spitsbergen throughout the holocene oceanic atmospheric variability caused neoglacial sea ice fluctuations ice conditions along east greenland shelf remain rather stable until 1000 years bp

arctic north atlantic oscillation signature in holocene sea surface temperature trends as obtained from alkenone data 1 the variability in alkenone derived sea surface temperatures ssts in the north atlantic realm shows that a continuous sst decrease in the northeast atlantic from the early to the late holocene was accompanied by a persistent warming over the western subtropical atlantic the eastern mediterranean sea and the northern red sea based on the analysis of the instrumental data and of atmospheric general circulation model experiments we show that this variation in ssts during the holocene can be attributed to a continuous weakening of a northern hemisphere atmospheric circulation pattern similar to that of the arctic north atlantic oscillation

high resolution tropical climate record for the last 6 000 years 1200 800 cal yrs b p the initial d 18 oi ncrease centered at 5 500 years ago is coincident with the development of arid conditions in the caribbean region and the end of the african humid period indicating a global drying of the northern tropics at this time synchronous with the aridification of the caribbean region are the onset of wetter conditions in the south american altiplano and the reoccupation of this region by humans this combination of contrasting climate conditions is attributed to a southward displacement of the intertropical convergence zone itcz that would have resulted in decreased precipitation and increased trade wind intensity in the caribbean region and increased rainfall over the altiplano index terms 4267 oceanography general paleoceanography 4231 oceanography general equatorial oceanography 4870 oceanography biological and chemical stable isotopes 4802 oceanography biological and chemical anoxic environments citation tedesco k and r thunell high resolution tropical climate record for the last 6 000 years geophys res lett 30 17 1891 doi 10 1029 2003gl017959 2003

holocene flooding history of the lower tagus valley portugal the present paper aims to reconstruct the lower tagus valley flooding history for the last ca 6500 a to explore the suitability of pollen based local vegetation development in supporting the reconstruction of flooding history and to explain fluvial activity changes in terms of allogenic climate human impact and autogenic system intrinsic processes the flooding history has been determined by cored sedimentary records located 18 km apart in distal low energy backswamps on both sides of the tagus channel in these low energy backswamps fine grained sediment layers deposited from suspended load of overbank flood water reflect periods with multiple overbank floods by means of a multi proxy approach sedimentology magnetic susceptibility grain size loss on ignition carbonate content and pollen sedimentary and environmental changes were identified at both sites synchronous lithological intervals accumulated suggesting a common origin for the changes in fluvial activity since ca 6500 cal a bp based on lithological changes three phases of high fluvial activity 6500 5500 4900 3500 and 1000 0 cal a bp and two phases of low fluvial activity 5500 4900 and 3500 1000 cal a bp were identified two periods with dominant allogenic controls on fluvial activity in the lower tagus valley were identified relative sea level 6500 5500 cal a bp and human impact 1000 0 cal a bp during the intermediate period changes in fluvial activity may have been caused by climate 5500 1000 cal bp but unambiguous correlations are difficult to make this is due to the way allogenic controls are translated through the fluvial system the geomorphological differences between upstream and downstream studies and autogenic processes the comparison of local vegetation development and flooding phases as reconstructed using sedimentology shows a limited added value of using local palynology as a proxy for fluvial activity 2010 john wiley sons ltd

arctic oscillation variability generated through inter ocean interactions 1 we investigate the structure of the northern hemisphere atmospheric circulation anomaly patterns associated with the dominant mode of interannual variability in the tropical pacific and the dominant mode of quasi decadal variability in the atlantic basin there is evidence that the superposition of the atmospheric patterns associated with these modes possesses an arctic oscillation like structure we suggest that part of the arctic oscillation variability is due to interactions between coupled ocean atmosphere modes originating in the tropical pacific and atlantic basins

paleoceanography of the barents sea during the holocene 1 we measured the oxygen isotopic composition of planktonic and benthic foraminifera in three cores collected at key positions to reconstruct the paleoceanography of the barents sea core asv 880 on the path of the northern branch of atlantic water inflowing from the arctic ocean core asv 1200 in the central basin near the polar front and core asv 1157 in the main area of brine formation modern seawater 18o measurements show that far from the coast 18o variations are linearly linked to the salinity changes associated with sea ice melting the foraminifer 18o records are dated by 14c measurements performed on mollusk shells and they provide a detailed reconstruction of the paleoceanographic evolution of the barents sea during the holocene four main steps were recognized the terminal phase of the deglaciation with melting of the main glaciers which were located on the surrounding continent and islands the short thermal optimum from 7 8 ka b p to 6 8 ka b p a cold mid holocene phase with a large reduction of the inflow of atlantic water and the inception of the modern hydrological pattern by 4 7 ka b p brine water formation was active during the whole holocene the paleoclimatic evolution of the barents sea was driven by both high latitude summer insolation and the intensity of the atlantic water inflow

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

nonuniform response of the major surface currents in the nordic seas to insolation forcing implications for the holocene climate variability 1 high resolution sediment cores from the voring plateau the north iceland shelf and the east greenland shelf have been studied to investigate the stability of major surface currents in the nordic seas during the holocene results from diatom assemblages and reconstructed sea surface temperatures ssts indicate a division of the holocene into three periods the holocene climate optimum 9500 6500 calendar cal years bp the holocene transition period 6500 3000 cal years bp and the cool late holocene period 3000 0 cal years bp the overall climate development is in step with the decreasing insolation on the northern hemisphere but regional differences occur regarding both timing and magnitude of sst changes sites under the direct influence of the norwegian atlantic current and the irminger current indicate sst cooling of 4 5 c from early holocene to present compared to 2 c recorded under the east greenland current superimposed on the general holocene cooling trend there is a high frequency sst variability which is in the order of 1 1 5 c for the voring plateau and the east greenland shelf and 2 5 3 c on the north iceland shelf

land sea climatic variability in the eastern north atlantic subtropical region over the last 14 200 years atmospheric and oceanic processes at different timescales high temporal resolution analysis of different climatic tracers pollen foraminiferal based winter sea surface temperature sst benthic foraminiferal 18o from marine core md95 2042 retrieved off sw iberia allows us to directly compare without any chronological ambiguity mediterranean vegetation and eastern north atlantic winter sst changes for the last 14 2 kyr we identify on land and in the ocean several climatic phases such as the end of the warm and humid bolling allerod the cold and dry younger dryas and the warm and humid holocene with the mediterranean forest mf optimum between 9 6 and 8 1 kyr this record shows that at multi centennial timescale 800 years declines in forest cover generally related to dry and cool periods in southern iberia are synchronous with cold sst in the eastern part of the north atlantic subtropical gyre at multi centennial timescale changes in thermohaline circulation via freshwater content fluctuations appear to be responsible for the coupling between dryness in iberia and sst cooling in eastern north atlantic subtropical gyre in contrast some holocene events include centennial scale oscillations 100 years marked by mf declines in southern iberia concomitant with sst warming in the eastern north atlantic subtropical gyre this climatic pattern is similar to that observed at decadal timescale under the influence of the positive mode of the north atlantic oscillation nao we suggest therefore that synchronous sw iberian dryness and sst warming at centennial timescale could be explained by atmospheric fluctuations related to nao changes

late glacial to mid holocene palaeoclimate development of southern greece inferred from the sediment sequence of lake stymphalia ne peloponnese abstract the sedimentary sequence of lake stymphalia ne peloponnese for the first time sheds light on the palaeoclimate development of southern greece from 15 to 5 ka bp new geochemical data based on high resolution x ray fluorescence scanning provide in situ and continuous analysis of predefined element suites on split core surfaces variations of elements over time were assessed constructing correlation matrices based on the calculation of pearson correlation coefficients the element suite includes al si k ca ti mn fe zn rb sr and zr a major result includes that changes in element behaviour are related to hydrological changes in the catchment precipitation lake level status and evaporation insolation solar activity and are ultimately driven by climate major trends shifts in elemental ratios correspond to the climate development in the eastern mediterranean region based on correlation of rb sr reflecting wet dry climates with foraminiferal proxies of marine core lc21 from the southern aegean sea and the stable oxygen isotope record of soreq cave israel the bolling allerod the younger dryas and the 8 2 ka cold event were identified

multicentennial scale hydrological changes in the black sea and northern red sea during the holocene and the arctic north atlantic oscillation 1 paleoenvironmental proxy data for ocean properties eolian sediment input and continental rainfall based on high resolution analyses of sediment cores from the southwestern black sea and the northernmost gulf of aqaba were used to infer hydroclimatic changes in northern anatolia and the northern red sea region during the last 7500 years pronounced and coherent multicentennial variations in these records reveal patterns that strongly resemble modern temperature and rainfall anomalies related to the arctic oscillation north atlantic oscillation ao nao these patterns suggest a prominent role of ao nao like atmospheric variability during the holocene beyond interannual to interdecadal timescales most likely originating from solar output changes

orbital forcing and role of the latitudinal insolation temperature gradient orbital forcing of the climate system is clearly shown in the earths record of glacial interglacial cycles but the mechanism underlying this forcing is poorly understood traditional milankovitch theory suggests that these cycles are driven by changes in high latitude summer insolation yet this forcing is dominated by precession and cannot account for the importance of obliquity in the ice age record here we investigate an alternative forcing based on the latitudinal insolation gradient lig which is dominated by both obliquity in summer and precession in winter the insolation gradient acts on the climate system through differential solar heating which creates the earths latitudinal temperature gradient ltg that drives the atmospheric and ocean circulation a new pollen based reconstruction of the ltg during the holocene is used to demonstrate that the ltg may be much more sensitive to changes in the lig than previously thought from this it is shown how lig forcing of the ltg may help explain the propagation of orbital signatures throughout the climate system including the monsoon arctic oscillation and ocean circulation these relationships are validated over the last eemian interglacial which occurred under a different orbital configuration to the holocene we conclude that lig forcing of the ltg explains many criticisms of classic milankovitch theory while being poorly represented in climate models

some physical drivers of changes in the winter storm tracks over the north atlantic and mediterranean during the holocene the winter climate of europe and the mediterranean is dominated by the weather systems of the mid latitude storm tracks the behaviour of the storm tracks is highly variable particularly in the eastern north atlantic and has a profound impact on the hydroclimate of the mediterranean region a deeper understanding of the storm tracks and the factors that drive them is therefore crucial for interpreting past changes in mediterranean climate and the civilizations it has supported over the last 12 000 years broadly the holocene period this paper presents a discussion of how changes in climate forcing e g orbital variations greenhouse gases ice sheet cover may have impacted on the basic ingredients controlling the mid latitude storm tracks over the north atlantic and the mediterranean on intermillennial time scales idealized simulations using the hadam3 atmospheric general circulation model gcm are used to explore the basic processes while a series of timeslice simulations from a similar atmospheric gcm coupled to a thermodynamic slab ocean hadsm3 are examined to identify the impact these drivers have on the storm track during the holocene the results suggest that the north atlantic storm track has moved northward and strengthened with time since the early to mid holocene in contrast the mediterranean storm track may have weakened over the same period it is however emphasized that much remains still to be understood about the evolution of the north atlantic and mediterranean storm tracks during the holocene period

reconstruction of sea level pressure fields over the eastern north atlantic and europe back to 1500 spatially and temporally high resolution estimates of past natural climate variability are important to assess recent significant climate trends the mid latitude atmospheric circulation is the dominant factor for regional changes in temperature rainfall and other climatic variables here we present reconstructions of gridded monthly sea level pressure slp fields back to 1659 and seasonal reconstructions from 1500 1658 for the eastern north atlantic european region 30 w to 40 e 30 n to 70 n these were developed using principal component regression analysis based on the combination of early instrumental station series pressure temperature and precipitation and documentary proxy data from eurasian sites the relationships were derived over the 1901 1960 calibration period and verified over 1961 1990 under the assumption of stationarity in the statistical relationships a transfer function derived over the 1901 1990 period was used to reconstruct the 500 year large scale slp fields systematic quality testing indicated reliable winter reconstructions throughout the entire period lower skill was obtained for the other seasons although meaningful monthly reconstructions were available from around 1700 onwards when station pressure series became available the quality and the reconstructed slp fields for two exceptionally cold years 1573 1740 are discussed and climatologically interpreted an eof analysis of the 1500 1999 winter slp revealed firstly a zonal flow pattern with pronounced decadal to centenial time scale variations secondly a monopole pattern over northwest europe and thirdly a pattern modulating the meridional flow component over europe these 500 year slp reconstructions should be useful for modelling studies particulary for analyses of low frequency atmospheric variability and for circulation dynamics

atmospheric river changes shaped mid latitude hydroclimate since the mid holocene abstract paleoclimate proxies indicate that changes in insolation since the mid holocene have driven widespread hydrologic changes across the midlatitudes it is unclear how atmospheric rivers ars which are fundamental to global moisture transport today may have contributed to these holocene hydroclimate changes here we use a set of climate model simulations with the community earth system model cesm and introduce an ar algorithm optimized to identify ars within different climate states to show that changes to the location and intensity of landfalling ars explain the majority of the precipitation difference between the mid holocene and the preindustrial period in several midlatitude regions during the mid holocene enhanced seasonality increased summer season ar vapor content and displaced ars poleward of their preindustrial period trajectories especially in the northern hemisphere consequently in high midlatitude coastal areas of western north america and east asia ars account for greater than 10 more of total precipitation during the mid holocene and nearly 100 of the simulated change in precipitation between the two climates the simulated ar changes are consistent with moisture sensitive proxy records and with present day relationships between ars and regional circulation enhancing confidence that ars served as the underlying synoptic mechanism responsible for mid holocene hydroclimate anomalies in several coastal mid latitude areas the results indicate that ars are sensitive to background climate state and suggest that changes in ars may have contributed to hydroclimate changes throughout earth s past

apparent long term cooling of the sea surface in the northeast atlantic and mediterranean during the holocene reconstructions of upper ocean temperature t during the holocene 10 0 ka b p were established using the alkenone method from seven high accumulation sediment cores raised from the northeast atlantic and the mediterranean sea 361n 751n all these paleo t records document an apparent long term cooling during the last 10 kyr in records with indication of a constant trend the apparent cooling ranges from 0 27 to 0 151c kyr 1 records with indication of time variable trend show peak to peak amplitudes in apparent temperatures of 1 2 2 91c a principal component analysis shows that there is one factor which accounts for a very large fraction 67 of the total variance in the biomarker paleo t records and which dominates these records over other potential secondary influences two possible contributions are 1 a widespread surface cooling which may be associated with the transition fromthe hypsithermal interval b9 5 7 ka b p to the neoglaciation b5 7 0 ka b p and 2 a change in the seasonal timing and or duration of the growth period of alkenone producers prymnesiophyte algae the first contribution is consistent with many climate proxy records from the northeast atlantic area and with climate model simulations including milankovitch forcing the second contribution is consistent with the divergence between biomarker and summer faunal paleo t fromearly to late holocene observed in two cores further work is necessary and in particular the apparent discordance between biomarker and faunal t records for the relative stable holocene period must be understood to better constrain the climatic and ecological contributions to the apparent cooling observed in the former records r 2002 elsevier science ltd all rights reserved

holocene sea ice history and climate variability along the main axis of the northwest passage canadian arctic 1 palynological geochemical and physical records were used to document holocene paleoceanographic changes in marine sediment core from dease strait in the western part of the main axis of the northwest passage core 2005 804 006 pc latitude 68 59 552 n longitude 106 34 413 w quantitative estimates of past sea surface conditions were inferred from the modern analog technique applied to dinoflagellate cyst assemblages the chronology of core 2005 804 006 pc is based on a combined use of the paleomagnetic secular variation records and the cals7k 2 time varying spherical harmonic model of the geomagnetic field the age depth model indicates that the core spans the last 7700 cal years b p with a sedimentation rate of 61 cm ka 1 the reconstructed sea surface parameters were compared with those from barrow strait and lancaster sound cores 2005 804 004 pc and 2004 804 009 pc respectively which allowed us to draw a millennial scale holocene sea ice history along the main axis of the northwest passage manwp overall our data are in good agreement with previous studies based on bowhead whale remains however dinoflagellate sea surface based reconstructions suggest several new features the presence of dinoflagellate cysts in the three cores for most of the holocene indicates that the manwp was partially ice free over the last 10 000 years this suggests that the recent warming observed in the manwp could be part of the natural climate variability at the millennial time scale whereas anthropogenic forcing could have accelerated the warming over the past decades we associate holocene climate variability in the manwp with a large scale atmospheric pattern such as the arctic oscillation which may have operated since the early holocene in addition to a large scale pattern more local conditions such as coastal current tidal effects or ice cap proximity may have played a role on the regional sea ice cover these findings highlight the need to further develop regional investigations in the arctic to provide realistic boundary conditions for climatic simulations

deep water renewal in the skagerrak during the last 1200 years triggered by the north atlantic oscillation evidence from benthic foraminiferal δ8o benthic foraminiferal tests of a sediment core from southwestern skagerrak northeastern north sea 420 m water depth were investigated for their ratio of stable oxygen isotopes during modern times sudden drops in temperature and salinity of skagerrak deep waters point to advection induced cascades of colder and denser central north sea waters entering the skagerrak these temperature drops which are recorded in benthic foraminiferal tests via the stable oxygen isotopic composition were used to reconstruct deep water renewal in the skagerrak in a second step we will show that at least during the last 1200 years skagerrak deep water renewal is triggered by the negative phase of the north atlantic oscillation nao the nao exerts a strong influence on the climate of northwestern europe it is currently under debate if the long term variability of the nao is capable of influencing northern hemisphere climate on long timescales the data presented here cannot reinforce these speculations our data sho

reorientation of vesta gravity and tectonic predictions 1 vesta s large southern hemisphere impact basin is likely to have caused reorientation however because the basin is not centred at the south pole vesta likely also has a remnant rotational figure reorientation of 6 is predicted to have occurred based on the dimensions of the basin existing measurements of vesta s shape are consistent with 20 or less reorientation and 20 or less despinning both the remnant rotational figure and the basin contribute to the degree 2 gravity coefficients which will be measured by the dawn mission and will provide a test of the reorientation hypothesis reorientation and despinning also give rise to stresses vesta s stress state is likely to be dominated by isotropic contraction due to cooling which does not affect the gravity coefficients however the orientation of the resulting thrust features will be controlled by the amount of reorientation and despinning providing another observational test

reorganization of the upper ocean circulation in the mid holocene in the northeastern atlantic a micropaleontological investigation was conducted on two sediment cores from the reykjanes ridge rr core lo09 14 59 12 30 n 31 05 94 w and the faroe shetland channel fsc core hm03 133 25 60 06 55 n 06 04 18 w to document hydrographical changes of the north atlantic current nac during the holocene dinocyst and coccolith assemblages were analyzed and quantitative reconstructions of sea surface temperatures ssts and sea surface salinities ssss were conducted based on dinocyst assemblages both proxies suggest a major reorganization of surface circulation patterns in the northeastern north atlantic between 7 and 5 4 ka bp at both sites ssss before 6 5 7 ka bp were lower than during the mid late holocene suggesting dispersal of meltwater through the nac long term trends of ssts however show higher than present summer ssts on the rr from 9 3 to 6 ka bp and lower than present ssts in the fsc until ca 5 4 ka bp the contrasted sst trends at the two sites suggest that decreasing summer

simulated precipitation changes in central asia since the last glacial maximum abstract the availability of freshwater has been and remains a crucial concern in westerlies dominated arid central asia understanding precipitation changes in this area and the underlying mechanisms therefore is of great importance this study explores precipitation changes in central asia 35 50 n and 50 70 e since the last glacial maximum lgm and their control factors using results from the simulation of transient climate evolution over the last 21 000 years transient simulations reveal that a wet climate occurred during the lgm the bolling allerod warm period and the middle holocene and a dry climate occurred during heinrich event 1 the younger dryas and the early holocene in this area model results are in good agreement with proxy records since the last deglaciation these changes were mainly controlled by earth s orbital parameters meltwater discharges into the oceans and continental ice sheets the contribution of ghg concentrations to precipitation changes was minor external forcing factors influenced the precipitation mainly through affecting the water vapor input from the north atlantic and mediterranean sea and vertical motions of the atmosphere over central asia the north atlantic oscillation was an important atmospheric bridge connecting the external forcings to precipitation changes in central asia there were complex relationships between precipitation changes in central asia and east asia since the lgm due to the differences of the dominating factors

arctic oscillation signature in a red sea coral we show that the winter time series of the ras umm sidd coral oxygen isotope record from the northern red sea approximately 28 n is linked to the arctic oscillation phenomenon the northern hemisphere s dominant mode of atmospheric variability until now the detection of this mode which is most prominent in winter in proxy climate records was difficult due to the lack of a clear seasonality in most paleoclimatic archives the results suggest that northern red sea corals can provide information about the low frequency variability of the northern hemisphere winter circulation during the pre instrumental period

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

a diatom based reconstruction of early holocene hydrographic and climatic change in a southwest greenland fjord abstract a diatom based reconstruction of surface water paleoclimatic and paleoceanographic changes in ameralik fjord southwest greenland is presented for the holocene interval 8800 to 3600 cal yrs b p a minor episode of cold surface water conditions is found at ca 8000 7800 cal yrs b p this may be due to the local conditions in the fjord and linked to the culmination of a strong melt water outflow rather than reflecting the widespread north atlantic 8 2 ka cooling event warming of surface water condition from 7800 to 7100 cal yrs b p probably corresponding to the early and warmest part of the holocene thermal maximum htm in this region is reflected in the diatom assemblages and supported by other proxies the west greenland current wgc influences the fjord strongly during this interval indicating enhanced advection of atlantic water masses derived from the irminger current ic a major sedimentary change with a hiatus between 6800 and 4400 cal yrs b p prevents a reconstruction of mid holocene paleoceanograpy the final and less prominent part of the htm is found after 4400 cal yrs b p previous studies from the same site have shown this final stage of the htm to end at 3200 cal yrs b p with the onset of the neoglaciation our study provides further evidence that the marine sedimentary record from west greenland fjords yields paleoenvironmental information reflecting a significant link between local and large scale north atlantic oceanographic and climatic changes

changes in the strength of the nordic seas overflows over the past 3000 years the nordic seas overflows constitute the densest component of the deep limb of the atlantic meridional overturning circulation amoc changes in the vigour of the overflows may have had important climatic effects in the past and may also have in the future yet evidence for multidecadal to millennial changes in the deep limb of the amoc and their potential relationship to north atlantic climate variability during the holocene remains weakly constrained here we present grain size data as a proxy for near bottom current speed from sub decadal to decadally resolved sediment cores located in the direct pathway of the two nordic overflows east and west of iceland the iceland scotland overflow water isow and the denmark strait overflow water dsow respectively the results show no clear relationship between reconstructed changes in the vigour of the nordic overflows and the well known periods of centennial scale climate variability recorded in the north atlantic region however well defined millennial scale trends are found in both of the overflow strength records over the last 3000 years which were possibly related to hydrographic reorganizations in the nordic seas driven by the decrease in northern hemisphere summer insolation over the neoglacial period a comparison between the near bottom flow speed reconstructions from isow and dsow suggests an anti phased relationship between the nordic seas overflows east and west of iceland over the last 3000 years this feature has been observed in climate models potentially as a result of shifts in the deep water formation sites as a response to changes in atmospheric patterns over the nordic seas

arctic sea ice cover from the early holocene the role of atmospheric circulation patterns abstract proxy evidence suggests that a mean atmospheric state reminiscent of the positive phase of the north atlantic arctic oscillation nao persisted throughout the early holocene and resulted in a dipole pattern in sea ice concentration between the north eastern and north western north atlantic a dynamic thermodynamic coupled sea ice ocean model is used to simulate the sea ice concentration and thickness in the arctic during the early holocene it is forced with winds ocean currents and surface air temperatures sat from recent years with a positive phase of the nao in conjunction with altered long and shortwave radiation and surface air ocean temperatures the simulation reproduces an east west dipole in sea ice cover of the arctic and is compatible with reconstructed sea ice conditions in the chukchi sea inferred from dinoflagellate cyst analysis of ocean sediment cores sensitivity studies were performed to investigate the individual effects of radiation ocean forcing sat and winds on sea ice cover results show that in the east siberian sea sat is the dominant forcing for changes in sea ice thickness whereas winds and sat are the dominant factors in sea ice concentration anomalies in the barents sea sea ice anomalies are influenced by air and sea surface temperatures and ocean currents

the climate of europe during the holocene a gridded pollen based reconstruction and its multi proxy evaluation we present a new gridded climate reconstruction for europe for the last 12 000 years based on pollen data the reconstruction is an update of davis et al 2003 using the same methodology but with a greatly expanded fossil and surface sample dataset and more rigorous quality control the modern pollen dataset has been increased by more than 80 and the fossil pollen dataset by more than 50 representing almost 60 000 individual pollen samples the climate parameters reconstructed include summer winter and annual temperatures and precipitation as well as a measure of moisture balance and growing degree days above 5 degrees c confidence limits were established for the reconstruction based on transfer function and interpolation uncertainties the reconstruction takes account of post glacial isostatic readjustment which resulted in a potential warming bias of up to 1 2 degrees c for parts of fennoscandia in the early holocene as well as changes in palaeogeography resulting from decaying ice sheets and rising post glacial sea levels this new dataset has been evaluated against previously published independent quantitative climate reconstructions from a variety of archives on a site by site basis across europe the results of this comparison are generally very good only chironomid based reconstructions showed substantial differences with our values our reconstruction is available for download as gridded maps throughout the holocene on a 1000 year time step the gridded format makes our reconstructions suitable for comparison with climate model output and for other applications such as vegetation and land use modelling our new climate reconstruction suggests that warming in europe during the mid holocene was greater in winter than in summer an apparent paradox that is not consistent with current climate model simulations and traditional interpretations of milankovitch theory c 2015 elsevier ltd all rights reserved

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

oxygen isotope records of holocene climate variability in the pacific northwest abstract oxygen isotope 18o measurements of authigenic carbonate from cleland lake southeastern british columbia paradise lake central british columbia and lime lake eastern washington provide a 9000 year holocene record of precipitation evaporation balance variations in the pacific northwest both cleland lake and paradise lake are small surficially closed basin systems with no active inflows or outflows lime lake is surficially open with a seasonally active overflow water isotope values from cleland and paradise plot along the local evaporation line indicating that precipitation evaporation balance is a strong influence on lake hydrology in contrast lime lake water isotope values plot on the local meteoric water line signifying minimal influence by evaporation to infer past hydrologic balance variations at a high temporal resolution we sampled the cleland paradise and lime lake sediment cores at 1 60 mm intervals 3 33 years per sample on average and measured the isotopic composition of fine grained

ocean atmosphere climate shift during the mid to late holocene transition article history climate records of the mid to late holocene transition between 3 4 thousand years before present ka often exhibit a rapid change in response to the gradual change in orbital insolation here we investigate north atlantic central water circulation as a possible mechanism regulating the latitudinal temperature gradient ltg which in turn amplifies climate sensitivity to small changes in solar irradiance through this mechanism sharp climate events and transitions are the result of a positive feedback process that propagates and amplifies climate events in the north atlantic region we explore these linkages using an intermediate water temperature record reconstructed from mg ca measurements of benthic foraminifera hyalinea balthica f rom as ediment core off nw africa 889 md epth between 0t o 5 5 ka our results show that eastern north atlantic central waters enacw cooled by 1 0 7 ca nd densities decreased by 0 4 0 2b etween 3 3 and 2 6 ka this shift in enacw hydrography illustrates at ransition towards enhanced mid latitude atmospheric circulation after 2 7 ka in particular during cold events of the late holocene the presented records demonstrate the important role of enacw circulation in propagating the climate signatures of the ltg by reducing the meridional heat transfer from high to low latitudes during the transition from the holocene thermal maximum to the late holocene in addition the dynamic response of enacw circulation to the gradual climate forcing of ltgs provides a prime example of an amplifying climate feedback mechanism published by elsevier b v

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

holocene and deglacial ocean temperature variability in the benguela upwelling region implications for low latitude atmospheric circulation 1 mg ca analyses of g bulloides and abundances of n pachyderma left coiling from ocean drilling program odp leg 175 hole 1084b in the benguela coastal upwelling system document lower sea surface temperatures during the last glacial maximum lgm younger dryas mid holocene and little ice age in the southeastern atlantic taking into consideration the possible effects of differential carbonate dissolution the mg ca data indicate younger dryas temperatures 2 3 c cooler than those of the early holocene and lgm temperatures 4 5 c cooler than those of the early holocene the cool interval during the deglacial period at hole 1084b matches the timing of younger dryas shifts in cariaco basin and greenland ice sheet records and that of a nearby alkenone record comparison of mid holocene cooling at hole odp1084b with other high resolution records of holocene and last deglacial sea surface temperatures from the tropical atlantic implies consistent basin wide changes in atmospheric circulation a brief period of 1 5 2 c cooling between 17 8 and 17 2 ka if related to heinrich event 1 is consistent with a previously hypothesized tropical origin of all heinrich climate change events

the meridional temperature gradient in the eastern north atlantic during mis 11 and its link to the ocean atmosphere system temporal and spatial patterns in eastern north atlantic sea surface temperatures sst were reconstructed for marine isotope stage mis 11c using a submeridional transect of five sediment cores the sst reconstructions are based on planktic foraminiferal abundances and alkenone indices and are supported by benthic and planktic stable isotope measurements as well as by ice rafted debris content in polar and middle latitudes additionally the larger scale dynamics of the precipitation regime over northern africa and the western mediterranean region was evaluated from iron concentrations in marine sediments off nw africa and planktic 13c in combination with analysis of planktic foraminiferal abundances down to the species level in the mediterranean sea compared to the modern situation it is revealed that during entire mis 11c sensu stricto ss i e between 420 and 398 ka according to our age models a cold sst anomaly in the nordic seas co existed with a warm sst anomaly in the middle latitudes and the subtropics resulting in steeper meridional sst gradients than during the holocene such a sst pattern correlates well with a prevalence of a negative mode of the modern north atlantic oscillation we suggest that our scenario might partly explain the longer duration of wet conditions in the northern africa during mis 11c compared to the holocene

dansgaard oeschger and heinrich event imprints in alboran sea paleotemperatures past sea surface temperature sst evolution in the alboran sea western mediterranean during the last 50 000 years has been inferred from the study of c37 alkenones in international marine global change studies md952043 core this record has a time resolution of 200 years allowing the study of millennial scale and even shorter climatic changes the observed sst curve displays characteristic sequences of extremely rapid warming and cooling events along the glacial period comparison of this alboran record with 18o from greenland ice greenland ice sheet project 2 core shows a strong parallelism between these sst oscillations and the dansgaard oeschger events five prominent cooling episodes standing out in the sst profile are accompanied by an anomalous high abundance of neogloboquadrina pachyderma sinistral which is confined to the duration of these cold intervals these features and the isotopic record reflect drastic changes in the surface hydrography of the alboran sea in association with heinrich events hl 5

integrated varve and pollen based temperature reconstruction from finland evidence for holocene seasonal temperature patterns at high latitudes a detailed understanding of decadal to millennial scale climate changes requires seasonal scale summer winter reconstructions of past precipitation and temperature fluctuations comparing seasonally resolved varve records with pollen based sum of growing degree days gdd reconstructions from lake nautajarvi we examined the intra annual nature of climate variability in central southern finland during the holocene the organic varve record and the gdd reconstruction show roughly comparable trends supporting the interpretation that both proxies predominantly reflect summer temperatures in the study area the records suggest low but rising early holocene 9500 to 8500 cal yr bp summer temperatures the holocene thermal maximum htm in the gdd record dates to about 7500 to 4500 cal yr bp but the organic varve record along with reconstructed changes in vegetation composition notably a peak of tilia pollen percentages indicate that during the htm there was a trend towards a more continental climate with maximum mid summer temperatures reached at 6500 to 4500 cal yr bp both records reflect the start of the post htm cooling at about 4500 cal yr bp simultaneously with an increase of the amount of catchment erosion and mineral matter influx into the lake suggesting gradually colder and or longer winters with high net accumulation of snow the organic varve record and the gdd record start to diverge at 2000 cal yr bp possibly owing to the human influence on catchment processes the reconstructed mid holocene summer temperature peak deviates from the regional climate model outputs which suggest highest summer temperatures during the early holocene

orbitally driven insolation forcing on holocene climate trends evidence from alkenone data and climate modeling a global spatial pattern of long term sea surface temperature sst trends over the last 7000 years is explored using a comparison of alkenone derived sst records with transient ensemble climate simulations with a coupled atmosphere ocean circulation model under orbitally driven insolation forcing the spatial trend pattern both in paleo sst data and in model results shows pronounced global heterogeneity generally the extratropics cooled while the tropics experienced a warming during the middle to late holocene we attribute these divergent holocene climate trends to seasonally opposing insolation changes furthermore climate mode changes similar to the arctic north atlantic oscillation are superimposed on the prevalent pattern it is concluded that nonlinear changes in the entire seasonal cycle of insolation played a dominant role for the temporal evolution of holocene surface temperatures for understanding of marine proxy data apart from the dominance of summer insolation in high latitudes a notable shift in the maximum insolation of the year in low latitudes has to be taken into account which may influence timing of phytoplankton production and thus alters the seasonal origin of temperature signals recorded in the proxies

mid holocene nao a pmip2 model intercomparison 1 the mid holocene 6000 years before present north atlantic oscillation nao from nine models in the paleoclimate modeling intercomparison project phase 2 is studied primarily through principal component analysis of winter time north atlantic sea level pressure slp modeled mid holocene nao and mean slp show small changes compared to pre industrial control runs with a shift in mean state towards a more positive nao regime for three of the models modeled nao variability shows little change with a small increase for some models in the fraction of time spent in the nao negative phase during the mid holocene proxy based reconstructions of the nao indicate a more positive nao regime compared to present day during the mid holocene we hypothesise that there was a small nao like shift in mean state during the mid holocene

a long hard road reviewing the evidence for environmental change and population history in the eastern adriatic and western balkans during the late pleistocene and early holocene the eastern adriatic and western balkans are key areas for assessing the environmental and population history of europe during the late pleistocene and early holocene it has been argued that the balkan region served as a late glacial refugium for humans animals and plants much like iberia and the italian peninsula and in contrast to the harsh conditions of eastern and central europe as post glacial amelioration occurred and sea level rose these regions to the north and west of the balkan mountains became forested and were populated by mesolithic forager fishers meanwhile to the south the domestication of plants and animals in the near east began to cause large scale environmental as well as lifestyle changes even as the balkan peninsula was a likely crossroads on the route for the spread of agriculture and herding from southwest asia into europe issues such as pre neolithic settlement the discussion of human environment interactions and the role of climate events such as the 11 4 9 3 and 8 2 ka cal bp in this critical landscape are often overlooked efforts to counter this challenge have been hampered by an apparent lack of data so that the region hardly occurs in distribution maps in part this is due to patchy research and a complicated political history which have contributed to a fragmented archaeological and paleoecological record yet as we show here there is in fact plenty of evidence available for review we present a survey of different proxies for environment and settlement throughout the late pleistocene and into the early holocene combining radiocarbon data with zooarchaeological lithic and palynological records by mapping this evidence we are able to discuss the impact of climate change during the pleistocene holocene transition and consider the role of environment and landscape on human population distribution at this crossroads in place and time

seasonal sea surface temperature contrast between the holocene and last glacial period in the western arabian sea ocean drilling project site 723a modulated by monsoon upwelling 1 annual summer and winter sea surface temperatures ssts in the western arabian sea were reconstructed through the last 22 kyr using artificial neural networks anns based on quantitative analyses of planktic foraminifera down core sst estimates reveal that annual summer and winter ssts were 2 1 2 and 2 6 c cooler respectively during the last glacial period than in the holocene a 2 5 c sst increase during termination 1a hereinafter referred as glacial to holocene transition in the western arabian sea the study reveals a strong seasonal sst contrast between winter and summer from 18 to 14 calendar kyr owing to the combined effect of weak upwelling and strong cold northeasterly winds minor or no seasonal sst changes were noticed within the holocene period which is attributed to the intense upwelling during the summer monsoon this causes a lowering of sst to values similar to those of the winter season in analogy with the present day a 3 c rise in winter ssts during the glacial to holocene transition coincides with a strengthening of the monsoon suggesting a link between winter sst and monsoon initiation from the beginning of the holocene strikingly annual summer and winter ssts show a cooling trend from 8 ka to the present day implying tropical cooling in the late holocene

high resolution alkenone sea surface temperature variability on the north icelandic shelf implications for nordic seas palaeoclimatic development during the holocene the palaeoceanography of the northern icelandic shelf for the holocene period was reconstructed from alkenone indices measured in core jr51 gc35 this contains a continuous record of holocene sedimentation spanning 0 10 2 cal kyr bp with a resolution of 20 yr cm we have identified a general holocene cooling trend that has superimposed millennial scale oscillations of 28c their timing is in close agreement with the timing of glacier advances in northern iceland for the later half of the holocene the alkenone sea surface temperature sst record from jr51 gc35 correlates with proxy data for the strength of nadw formation recorded in cores south of iceland this is interpreted as evidence of a close connection existing between north icelandic sea surface temperatures and the north atlantic meridonal overturning circulation the timing of the millennial scale sst variability in our core off north iceland is found to be out of phase or anti phased with the sst variability of a record in the eastern nordic seas md952011 this suggests that the evolution of holocene climate in the nordic seas was more complex than previously proposed and it is likely to be caused by differential responses of the irminger and norwegian currents and modulated by changes in atmospheric circulation analogous to the north atlantic oscillation

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

a persistent holocene wetting trend in arid central asia with wettest conditions in the late holocene revealed by multi proxy analyses of loess paleosol sequences in xinjiang china abstract there are significant differences in the interpretation of the moisture precipitation history of arid central asia aca during the holocene as inferred on one hand from speleothem oxygen isotope records and on the other from lake sediments here we present the results of measurements of climatically sensitive magnetic properties and soil color from four well dated loess paleosol sequences from the northern slopes of the tienshan mountains and the yili river valley xinjiang china in the core area of aca our results demonstrate that the characteristic holocene paleosol indicating relatively moist conditions generally formed after 6 ka 1 ka 1000 cal yr bp in the study region and that the accumulation of unweathered loess prevailed during the early holocene indicating a dry climate at that time the magnetic proxies further reveal a trend of generally increasing moisture since the last glacial maximum with the wettest climate occurring during the late holocene this trend of increasing moisture during the holocene is representative of the xinjiang region and possibly of the whole of the core area of aca and is in marked contrast both to the mid holocene moisture maximum observed in the east asian summer monsoon region and to the general decrease in the strength of the indian summer monsoon since the early holocene our findings are supported by the results of a climate simulation which indicate a trend of increasing summer and winter precipitation during the holocene in the core area of aca caused mainly by an increase in the strength of the westerlies effected by an increasing latitudinal insolation gradient and by a negative trend of the arctic oscillation ao or north atlantic oscillation nao

seasonal cycle as template for climate variability on astronomical timescales 1 we propose a new concept for insolation driven temperature variability on orbital timescales it relies on the modern relationship between insolation and temperature throughout the year the method consists of 1 estimating empirical transfer functions between daily insolation and daily temperature and 2 applying these transfer functions on the long term insolation to model the late quaternary temperature evolution on the basis of the observed insolation temperature relationship different temperature response regimes across the earth are identified linear relationships dominate extratropical land areas whereas in midlatitude oceans the seasonally varying mixed layer depth renders the temperature more sensitive to summer than to winter insolation the temperature in monsoon regions and regions of seasonal sea ice cover also shows a seasonally varying response to insolation these transfer functions characterize the shape of the seasonal cycle in temperature and influence the temperature evolution on orbital timescales by rectifying the insolation signal on the basis of our seasonal template model we estimate the temperature evolution of the last 750 000 years the model largely reproduces the holocene temperature trends as simulated by a coupled climate model in the frequency domain significant temperature variability in the eccentricity and semiprecession frequency band in the tropics is found midlatitudes are dominated by precession and high latitudes are dominated by obliquity further it is found that the expected frequency response highly depends on the location our local time independent approach complements the global milankovitch hypothesis climate variations are driven by northern summer insolation in explaining observed climate variability and potentially offers new insights in interpreting paleoclimate records

millennial scale holocene hydrological changes in the northeast atlantic new insights from la grande vasiere mid shelf mud belt a mid to late holocene paleohydrological reconstruction from the northeast atlantic is proposed through the study of a high resolution sedimentary record from the northern continental shelf of the

pollen based palaeoclimate reconstructions over long glacial interglacial timescales methodological tests based on the holocene and mis 5d c deposits at sokli northern finland palaeoclimatic reconstructions over long glacial interglacial timescales present major methodological challenges as calibration methods based on modern climate and vegetation patterns may yield biased reconstructions from non analogue palaeoclimates such as severely continental glacial periods in this work we present pollen based summer temperature reconstructions based on holocene and early weichselian marine isotope stages mis 5d c deposits at sokli northern finland we attempt to improve the robustness of reconstructions of continental palaeoclimates by using two calibration sets with one located in the region surrounding the fossil site and another in a more continental region in northwestern russia we assess the reliability of the reconstructions by estimating the compositional fit between fossil and calibration samples and by comparison with independent plant macrofossil based reconstructions we find the fossil samples to fit the extra regional high continentality calibration set better during the early holocene and mis 5d c especially in mis 5d c however even the high continentality calibration set fits the fossil samples poorly compared to the fit achieved in the mid and late holocene thus our results highlight the problem of finding applicable calibration data for pre holocene periods we finally discuss the relative strengths and vulnerabilities of different calibration methods in reconstruction of non analogue palaeoclimates copyright 2013 john wiley sons ltd

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

mid late holocene maar lake mire transition in northeast china triggered by hydroclimatic variability abstract the density of maar lake type peatlands in the changbai mountain areas northeast ne china is among the highest in the world these deposition systems include both peat and limnic deposits providing valuable sites to study their evolutionary history shaped by their sensitivity to climate forced state shifts to investigate the maar lake mire shift in response to hydroclimatic variability we examined developmental history of the jinchuan peatland based on sedimentary facies grain size physical and chemical properites plant macrofossils and peat basal age the results indicate that the jinchuan peatland mainly originated from paludification in a maar lake from approximately 7000 cal bp its water level continuously increased since the middle holocene reaching the peak during the period of 5000 4000 cal yr bp the outward expansions of jinchuan peatland suggest a climate driven model based on which water level variability superimposes the underlying basin morphology the hydroclimatic variability and peatland development history can be divided into three periods from 12 to 7 ka cal bp the increasing east asian summer monsoon easm was the major water vapor source of jinchuan peatland the strong evaporation effects induced by the strong winter asian winter monsoon wawm and the maximum sea surface temperatures ssts of japan sea might have changed the jinchuan maar lake into dry upland from 7 to 4 ka cal bp the maximum easm and increasing westerly jet wj provided water vapor for the peatland the decreasing eawm and ssts of japan sea resulted in decreased evaporation effects the moisture and water level in jinchuan peatland gradually increased the peat covered 68 97 of the area during this period since 4 ka cal bp the decreased easm and the maximum wj provided water vapor for the jinchuan peatland the weak eawm and the lower ssts of japan sea induced lower evaporation effects the moisture and water level in the peatland reached the maximum subsequently peat area further expanded and covered the remaining 31 03 area this study reveals a remarkable link between the maar lake mire shift and hydroclimatic variability which is significant for future prediction of maar lake mire ecosystem shifts under global climate change

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

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

temperature and salinity variations of mediterranean sea surface waters over the last 16 000 years from records of planktonic stable oxygen isotopes and alkenone unsaturation ratios alkenone unsaturation ratios and planktonic d18o records from sediment cores of the alboran ionian and levantine basins in the mediterranean sea show pronounced variations in paleo temperatures and salinities of surface waters over the last 16 000 years average sea surface temperatures ssts are low during the last glacial averages prior to 13 000 years 11 15 c vary rapidly at the beginning of the holocene and increase to 17 18 ca t all sites during s1 formation dated between 9500 and 6600 calendar years the modern temperature gradient 2 3 c between the mediterranean sub basins is maintained during formation of sapropel s1 in the eastern mediterranean sea after s1 ssts have remained uniform in the alboran sea at 18 c and have fluctuated around 20 c in the ionian and levantine basin sites the d18o of planktonic foraminifer calcite decreases by 2 from the late glacial to s1 sediments in the ionian basin and by 2 8 in the levantine basin in the alboran sea the decrease is 1 7 of the 2 8 decrease in the levantine basin the evect of global ice volume accounts for a maximum of 1 05 and the temperature increase explains only a maximum of 1 3 the remainder is attributed to salinity changes we use the temperature and salinity estimates to calculate seawater density changes they indicate that a reversal of water mass circulation is not a likely explanation for increased carbon burial during s1 time instead it appears that intermediate and deep water formation may have shifted to the ionian sea approximately 2000 years before onset of s1 deposition because surface waters were as cold but saltier than surface water in the levantine basin during the younger dryas sapropel s1 began to form at the same time when a significant density decrease also occurred in the ionian sea 2000 elsevier science b v all rights reserved

north pacific and north atlantic sea surface temperature variability during the holocene holocene climate variability is investigated in the north pacific and north atlantic realms using alkenone derived sea surface temperature sst records as well as a millennial scale simulation with a coupled atmosphere ocean general circulation model aogcm the alkenone sst data indicate a temperature increase over almost the entire north pacific from 7 cal kyr bp to the present a dipole pattern with a continuous cooling in the northeastern atlantic and a warming in the eastern mediterranean sea and the northern red sea is detected in the north atlantic realm similarly sst variations are opposite in sign between the northeastern pacific and the northeastern atlantic a 2300 year long aogcm climate simulation reveals a similar sst seesaw between the northeastern pacific and the northeastern atlantic on centennial time scales our analysis of the alkenone sst data and the model results suggests fundamental inter oceanic teleconnections during the holocene

impacts of the north atlantic gyre circulation on holocene climate off northwest africa we present well dated high resolution holocene records of sea surface temperature sst and upwelling intensity off northwest nw africa we identify long term cooling trends over the holocene in the subtropical north atlantic in response to boreal summer insolation a pronounced cooling event of similar to 1 degrees c ca 8 5 cal ka indicates a large scale reorganization of the ocean current system possibly induced by meltwater from the northern north atlantic our alkenone sst record off cape ghir provides strong evidence for the impact of ocean circulation changes on subtropical north atlantic ssts it is likely that cold waters were propagated to the subtropics via the canary current in a way similar to heinrich events and the younger dryas off cape blanc we find 2 3 k y periodic variations in sst and upwelling intensity off nw africa superimposed on the cooling trend such a cycle has been documented in various paleoclimate archives in phase with solar forcing we show that these variations on millennial time scales are linked to the north atlantic subtropical gyre circulation and the northern hemisphere atmospheric circulation and in particular to changes in the pressure gradient between the icelandic low and the azores high this suggests that oceanic circulation in response to solar forcing played a more important role in the generation of 2 3 k y cyclicity than has been previously considered

a multi proxy palaeolimnological study to reconstruct the evolution of a coastal brackish lake lough furnace ireland during the late holocene abstract this study examines the evolution of lough furnace a coastal brackish lake in the west of ireland using high resolution sensors in the water column and palaeolimnological examination of the sediment archive palaeoenvironmental reconstructions suggest that meromixis formed as a result of sea level rise prior to ca 4000 cal yr bp increased seawater inflow has progressively led to permanent water stratification which caused the onset of anoxia making the monimolimnion a harsh environment for biological life diatom floristic interpretations suggest a progressive upcore increase in salinity which is paralleled by a reduction in cladocera remains diagenetic processes have not altered the sediment organic matter signature organic matter mainly derives from freshwater doc and appears to be linked to the presence of peat bogs in the catchment as confirmed by the c n ratio upcore variations in the c n ratio with a ca 800 year periodicity have been interpreted as the result of alternating dry and wet climatic phases during the late holocene which appear synchronous with the nao and long term solar cycles the current hydrology is largely controlled by freshwater inflow which determines permanent meromictic conditions overturns are rare requiring a specific combination of factors such as exceptionally dry and warm summers followed by cool autumns according to the climate projections for the next century in ireland permanent meromictic conditions will probably continue

arctic oscillation during the mid holocene and last glacial maximum from pmip2 coupled model simulations abstract changes in the arctic oscillation ao during the mid holocene and the last glacial maximum were compared to preindustrial pi simulations using four coupled ocean atmosphere models i e community climate system model ccsm third climate configuration of the met office unified model hadcm3 met office surface exchanges scheme version 2 moses2 l institut pierre simon laplace ipsl and model for interdisciplinary research on climate 3 2 miroc3 2 from the second phase of the paleoclimate modeling intercomparison project results show that the amplitude of the simulated ao during the mid holocene is a little smaller than that of the preindustrial simulation although the ao pattern and vertical structures are similar to those in the preindustrial simulation the polar westerlies are slightly weakened and displaced downward to the lower stratosphere accompanied by weakening of the polar vortex and warming of the cold polar cap region during the last glacial maximum when the northern

subpolar north atlantic sea surface temperature since 6 ka bp indications of anomalous ocean atmosphere interactions at 4 2 ka bp abstract atmospheric circulation may change with future climate change in response to modification of meridional temperature gradients but the potential influence on ocean circulation is as yet unclear over the mid late holocene atmospheric circulation in the north atlantic region has fluctuated on millennial timescales therefore the ocean response to these changes can be investigated using the paleoceanographic records that have been developed in the north eastern subpolar north atlantic here we present a diatom based sea surface temperature reconstruction from the iceland basin south of iceland the reconstruction shows the warmest temperatures of the record at 6 1 4 ka bp cooler temperatures at 4 2 ka bp and warmer temperatures thereafter inter record comparisons indicate that the cold period at c 4 2 ka bp may have resulted from a strengthened east greenland current and or melting of the greenland ice sheet in response to a negative north atlantic oscillation the findings highlight that atmospheric circulation changes are likely to cause pronounced variations in the latitudinal exchange of heat which may have consequences for deep water formation and global ocean circulation

on the hydrological cycle under paleoclimatic conditions as derived from agcm simulations the atmospheric hydrological cycle is compared for different time slices of the late quaternary simulations have been conducted with an atmospheric circulation model at t42 resolution and we have performed a global evaluation of the atmospheric water vapor transport the water export from the atlantic catchment area important for driving the large scale thermohaline ocean circulation is analyzed in detail for the last glacial maximum lgm we examine the model s sensitivity with respect to tropical cooling relative to the climap reconstruction which is motivated by recent data we find that the lgm experiment with tropical cooling is in better agreement with proxy data available our experiments indicate that the water vapor transport is strongly affected by three mechanisms continental drying eddy moisture transport and changes in the tropical circulation except for the continental drying and the blocking effect of the laurentide ice sheet the hydrological cycle is substancially different for both lgm experiments we find that the hydrological system is rather sensitive to tropical temperature change which is important to understand paleoclimate and future climate changes

mid to late holocene changes in tropical atlantic temperature seasonality and interannual to multidecadal variability documented in southern caribbean corals proxy reconstructions of tropical atlantic sea surface temperature sst that extend beyond the period of instrumental observations have primarily focused on centennial to millennial variability rather than on seasonal to multidecadal variability here we present monthly resolved records of sr ca a proxy of sst from fossil annually banded diploria strigosa corals from bonaire southern caribbean sea the individual corals provide time windows of up to 68 years length and the total number of 295 years of record allows for assessing the natural range of seasonal to multidecadal sst variability in the western tropical atlantic during snapshots of the mid to late holocene comparable to modern climate the coral sr ca records reveal that mid to late holocene sst was characterised by clear seasonal cycles persistent quasi biennial and prominent interannual as well as inter to multidecadal scale variability however the magnitude of sst variations on these timescales has varied over the last 6 2 ka the coral records show increased seasonality during the mid holocene consistent with climatemodel simulations indicating that southern caribbean sst seasonality is induced by insolation changes on orbital timescales whereas internal dynamics of the climate system play an important role on shorter timescales interannual sst variability is linked to ocean atmosphere interactions of atlantic and pacific origin pronounced interannual variability in the western tropical atlantic is indicated by a 2 35 ka coral possibly related to a strengthening of the variability of the el nino southern oscillation throughout the holocene prominent inter to multidecadal sst variability is evident in the coral records and slightly more pronounced in the mid holocene we finally argue that our coral data provide a target for studying holocene climate variability on seasonal and interannual to multidecadal timescales when using further numerical models and high resolution proxy data

holocene climate change in arctic canada and greenland abstract this synthesis paper summarizes published proxy climate evidence showing the spatial and temporal pattern of climate change through the holocene in arctic canada and greenland our synthesis includes 47 records from a recently published database of highly resolved holocene paleoclimate time series from the arctic sundqvist et al 2014 we analyze the temperature histories represented by the database and compare them with paleoclimate and environmental information from 54 additional published records mostly from datasets that did not fit the selection criteria for the arctic holocene database combined we review evidence from a variety of proxy archives including glaciers ice cores and glacial geomorphology lake sediments peat sequences and coastal and deep marine sediments the temperature sensitive records indicate more consistent and earlier holocene warmth in the north and east and a more diffuse and later holocene thermal maximum in the south and west principal components analysis reveals two dominant holocene trends one with early holocene warmth followed by cooling in the middle holocene the other with a broader period of warmth in the middle holocene followed by cooling in the late holocene the temperature decrease from the warmest to the coolest portions of the holocene is 3 0 1 0 c on average n 11 sites the greenland ice sheet retracted to its minimum extent between 5 and 3 ka consistent with many sites from around greenland depicting a switch from warm to cool conditions around that time the spatial pattern of temperature change through the holocene was likely driven by the decrease in northern latitude summer insolation through the holocene the varied influence of waning ice sheets in the early holocene and the variable influx of atlantic water into the study region

comparison of alkenone estimates with other paleotemperature proxies 1 to a certain degree all sea surface temperature sst proxies suffer from uncertainty due to signal preservation problems and to perturbations by other environmental variables however a multiproxy reconstruction is justified because most biases should in principle cancel out as they are specific to the biological groups and or to the analyzed chemical species such a multiproxy strategy has proven crucial for calibrating these proxies and is also useful in assessing downcore profiles until now there have been only a dozen deep sea cores where it is possible to compare directly alkenone based ssts with other paleotemperature records from this still limited data set the broad picture is of general agreement for the amplitude of changes at low and middle latitudes the few observed discrepancies suggest that alkenone based temperatures are more comparable to those based on mg ca ratios than those obtained through statistical analysis of the foraminiferal distribution more systematic differences are noted at higher latitudes where alkenones indicate warmer temperatures during the glacial period than transfer functions based on foraminifera or diatoms several reasons have been invoked to resolve the mismatch but more ground truthing work is needed before deciding which temperature changes are the most accurate

climate conditions in the westernmost mediterranean over the last two millennia an integrated biomarker approach abstract climate conditions in the westernmost mediterranean alboran sea basin over the last two millennia have been reconstructed through integration of molecular proxies applied for the first time in this region at such high resolution two temperature proxies one based on isoprenoid membrane lipids of marine thaumarchaeota tex 86 h tetraether index of compounds consisting of 86 carbons and the other on alkenones produced by haptophytes u 37 k ratio were applied to reconstruct sea surface temperature sst both records reveal a progressive long term decline in sst over the last two millennia and an increased rate of warming during the second half of the 20th century this is in accord with previous temperature reconstructions for the northern hemisphere tex 86 h temperature values are higher than those inferred from u 37 k probably due to differences in the bloom season of haptophytes and thaumarchaeota and reflect summer sst the branched vs isoprenoid tetraether index bit index suggests a low contribution of soil organic matter om to the sedimentary om the stable carbon isotopic composition of long chain n alkanes indicates a predominant c3 plant contribution with no major change in vegetation over the last 2000 yr the distribution of long chain 1 14 diols most likely sourced by proboscia spp in this setting provides insight into variation in upwelling conditions during the last 2000 yr and depicts a correlation with the north atlantic oscillation nao index providing evidence of enhanced wind induced upwelling during periods of a persistent positive mode of the nao

holocene sea surface conditions in the western north atlantic spatial and temporal heterogeneities 1 holocene records of sea surface conditions in the western nordic seas were obtained from quantitative reconstructions based on dinoflagellate cyst assemblages two sediment cores from the east greenland and the north iceland shelves provide a detailed account of the long and short term dynamics of the opposing flows of arctic versus atlantic waters both marker species and quantitative reconstructions depict an overall trend toward warmer winter temperatures saltier surface waters and decreased sea ice extent the latter is supported by a close relationship between relative abundances of an atlantic dinocyst species nematosphaeropsis labyrinthus and ice rafted debris ird records we propose that the late holocene increased ird delivery in the denmark strait region was primarily induced by a combination of less extensive sea ice cover under increased atlantic water inflow and sustained iceberg calving tied to the readvance of the greenland ice sheet our records thus suggest diminishing polar water supplies throughout the holocene although the timing of regime changes differs between the western and eastern sides of the denmark strait finally comparison of our records with a core from southern greenland points to very heterogeneous sea surface conditions in the western north atlantic which could be explained by the decoupled dynamics of the two irminger current branches similarities between the southern greenland marine record and a continental record nearby suggest a close coupling with atmospheric processes reminiscent of a north atlantic oscillation like climate pattern

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

evolution of subpolar north atlantic surface circulation since the early holocene inferred from planktic foraminifera faunal and stable isotope records abstract past changes in the surface flow regime of two main eastern north atlantic warm water pathways toward the nordic seas were reconstructed based on faunal analyses in combination with carbon and oxygen stable isotope measurements in planktic foraminifera the investigated sites in the surroundings of the faroe islands are located in the transitional area where surface waters of subpolar and subtropical origin mix before entering the arctic mediterranean in these areas large amplitude millennial variability in the characteristics of the upper water column appears modulated by changes in the intensity of the subpolar gyre circulation from 7 8 to 6 ka bp faunal records indicate a deep mixed layer which in conjunction with lighter 18 o values suggest that the inflowing atlantic waters were dominated by a relatively cooler and fresher water mass reflecting a strengthening of the subpolar gyre under conditions of enhanced positive nao like forcing and reduced meltwater input a shift in the hydrographic conditions occurred during the mid holocene centered at 5 ka bp at this time increasing upper water column stratification and the incipient differentiation of the stable isotopic signal of the iceland faroe and faroe shetland surface water masses suggest increasing influx of warmer more saline surface waters from the subtropical gyre as subpolar gyre circulation weakened the mid holocene decline in subpolar gyre strength is presumably related to a shift toward a low state of the nao like forcing associated with decreased solar irradiance later in the holocene from 4 ka bp to present the increased frequency and reduced amplitude of the surface hydrographic changes reflect corresponding fluctuations in subpolar gyre circulation these high frequency oscillations in subpolar gyre strength suggest increased surface circulation sensitivity to moderate freshwater fluxes to the labrador irminger sea basin highlighting the importance of the salinity balance in modulating subpolar gyre dynamics particularly under conditions of low nao atmospheric forcing

north western alps holocene paleohydrology recorded by flooding activity in lake le bourget france abstract a 14 m long piston core was retrieved from lake le bourget nw alps france in order to provide a continuous record of flooding events of the rhone river during the holocene the selection of the coring site was based on high resolution seismic profiling in an area with limited mass wasting deposits and accumulated proximal rhone river inter and underflow deposits the age depth model of this core is based on i 14 ams radiocarbon dates ii radionuclide dating 137cs and iii the identification of historical data flood events eutrophication of the lake the sedimentary record dates back to 9400 cal bp and includes a thin mass wasting event deposited around 4500 cal bp a multi proxy approach was used to track the evolution and origin of clastic sedimentation during the holocene in order to identify periods of higher hydrological activity in the catchment area spectrophotometry was used to detect fluctuations in clastic supply and the study of clay minerals especially the illite crystallinity index allowed locating the main source area of fine grained clastic particles settling at the lake after flood events this dataset highlights up to 12 periods of more intense flooding events over the last 9400 years in lake le bourget and shows that the main source area of clastic particles during this period is the upper part of the arve river drainage basin this part of the catchment area drains several large glaciers from the mont blanc massif and fluctuations in rhone river flood supply in lake le bourget is interpreted as resulting essentially from mont blanc glacier activity during the holocene the comparison of clastic sedimentation in lake le bourget with periods of increasing land use and periods of alpine glacier and mid european lake level fluctuations suggest that the core ldb04 clastic record in lake le bourget is a continuous proxy of the holocene hydrological history of the nw alps

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

holocene climatic changes in greenland different deuterium excess signals at greenland ice core project grip and northgrip 1 water stable isotope measurements d and 18o have been conducted on the holocene part of two deep greenland ice cores greenland ice core project grip and northgrip located 320 km apart these combined measurements provide the first two continuous greenland holocene deuterium excess profiles d d 8 18o a parameter strongly influenced by changes in moisture sources we discuss here temporal and regional fluctuations of the deuterium excess within central to north greenland with a mean temporal resolution of 4 years although grip and northgrip exhibit similar annual mean surface temperatures and 18o levels a significant offset of modern deuterium excess is observed between the two sites we attribute this offset to a different mix of modern moisture sources pointing to regional scale differences in moisture advection toward greenland the common long term deuterium excess holocene increasing trend is probably related to the increased relative contribution of low latitude moisture to greenland snowfall in response to the change in the earth obliquity as symmetrically observed in antarctica three abrupt declines punctuate the grip excess record 8 2 4 5 and 0 35 ka bp suggesting associated reorganizations of the northern high latitudes hydrological cycle the 8 2 ka bp event is characterized by 1 a rapid cooling followed by a progressive warming and 2 a deuterium excess cooling restricted to grip therefore totally different from rapid events during glacial times by contrast the northgrip deuterium excess record is more stable we propose that a slightly larger proportion of moisture supplied by local storm tracks to grip induces an isotopic compensation mechanism between simultaneous site and source temperature coolings resulting in a rather temperature insensitive 18o profile together with well marked deuterium excess amplitudes northgrip 18o seems less biased by isotopic processes and should provide a more reliable past temperature record

holocene climate variability as derived from alkenone sea surface temperature and coupled ocean atmosphere model experiments holocene climate modes are identified by the statistical analysis of reconstructed sea surface temperatures ssts from the tropical and north atlantic regions the leading mode of holocene sst variability in the tropical region indicates a rapid warming from the early to mid holocene followed by a relatively weak warming during the late holocene the dominant mode of the north atlantic region sst captures the transition from relatively warm cold conditions in the eastern north atlantic and the western mediterranean sea the northern red sea to relatively cold warm conditions in these regions from the early to late holocene this pattern of holocene sst variability resembles the signature of the arctic oscillation north atlantic oscillation ao nao the second mode of both tropical and north atlantic regions captures a warming towards the mid holocene and a subsequent cooling the dominant modes of holocene sst variability emphasize enhanced variability around 2300 and 1000 years the leading mode of the coupled tropical north atlantic holocene sst variability shows that an increase of tropical sst is accompanied by a decrease of sst in the eastern north atlantic an analogy with the instrumental period as well as the analysis of a long term integration of a coupled ocean atmosphere general circulation model suggest that the ao nao is one dominant mode of climate variability at millennial time scales