lateglacial vegetation development in denmark new evidence based on macrofossils and pollen from slotseng a small scale site in southern jutland abstract this paper presents the first unambiguous terrestrial palaeoecological record for the late glacial bolling warming in denmark pollen and macrofossil stratigraphies from pre bolling to 10 800 cal yr bp are presented from a small kettle hole in southwest denmark during which the lake basin developed from an immature stage after the deglaciation to complete infilling in the early holocene results show that the recently deglaciated landscape bore a discontinuous vegetation of pioneer plants after the bolling warming an open dryas octopetala betula nana community developed with helianthemum oelandicum subarctic species were dominant and local successions were probably delayed by relatively unstable and infertile soils there is no indication of a climate cooling during the period corresponding to the older dryas but the occurrence of several drought tolerant and steppe species indicates that the period was relatively dry in the allerod period the dryas b nana vegetation was initially replaced by an open salix and grass dominated vegetation and some 400 years later the first tree birches were documented presumably occupying moist and sheltered soils while drier land remained open in the younger dryas period trees disappeared and the vegetation became open again and dominated by subarctic species following climate warming at the younger dryas holocene transition a shrub community of empetrum and juniperus developed after approximately 200 years it was replaced by birch forest overall the late glacial vegetation cover had a more open and patchy character than inferred from previous pollen studies as assessment of the vegetation succession based on macrofossil evidence is essential the inferred general vegetation development corresponds well with results of other studies in the region canonical ordinations rda indicate that vegetation changes at the landscape scale during the lateglacial period were driven by changes in climate soils and competition for light

review and test of reproducibility of subdecadal resolution palaeoenvironmental reconstructions from microfossil assemblages abstract very high even annual resolution quantitative palaeoenvironmental reconstructions have been generated from microfossil assemblage data using transfer functions evidence of the utility of some of these reconstructions is given by the high correlations between the reconstructions and instrumental records such performance is despite several ecological and taphonomic issues that can become more problematic at subdecadal resolution than at multidecadal resolution this paper explores these timescale dependent issues and tests the reproducibility of the several of published reconstructions it demonstrates that the previously reported exceptionally good performance of several published chironomid based reconstructions is not reproducible

millennial scale fluctuations of the european ice sheet at the end of the last glacial and their potential impact on global climate abstract reconstructing northern hemisphere ice sheet oscillations and meltwater routing to the ocean is important to better understand the mechanisms behind abrupt climate changes to date research efforts have mainly focused on the north american laurentide ice sheets lis leaving the potential role of the european ice sheet eis and of the scandinavian ice sheet sis in particular largely unexplored using neodymium isotopes in detrital sediments deposited off the channel river we provide a continuous and well dated record for the evolution of the eis southern margin through the end of the last glacial period and during the deglaciation our results reveal that the evolution of eis margins was accompanied with substantial ice recession especially of the sis and simultaneous release of meltwater to the north atlantic these events occurred both in the course of the eis to its lgm position i e during heinrich stadial hs 3 and hs2 31 29 ka and 26 23 ka respectively and during the deglaciation i e at 22 ka 20 19 ka and from 18 2 0 2 to 16 7 0 2 ka that corresponds to the first part of hs1 the deglaciation was discontinuous in character and similar in timing to that of the southern lis margin with moderate ice sheet retreat from 22 5 0 2 ka in the baltic lowlands as soon as the northern summer insolation increase from 23 ka and an acceleration of the margin retreat thereafter from 20 ka importantly our results show that eis retreat events and release of meltwater to the north atlantic during the deglaciation coincide with amoc destabilisation and interhemispheric climate changes they thus suggest that the eis together with the lis could have played a critical role in the climatic reorganization that accompanied the last deglaciation finally our data suggest that meltwater discharges to the north atlantic produced by large scale recession of continental parts of northern hemisphere ice sheets during hs could have been a possible source for the oceanic perturbations i e amoc shutdown responsible for the marine based ice stream purge cycle or so called he s that punctuate the last glacial period

methodology of the last climatic cycle reconstruction in france from pollen data abstract a numerical method has been devised to reconstruct the climate of the last climatic cycle from pollen data reliable annual reconstructions have been published recently for the two french long sequences of la grande pile and les echets covering the last 140 millennia this paper gives more details on the method used it proposes new reconstructions based on an extended modern pollen data base these reconstructions are consistent with the previous ones especially detailed information is obtained on the seasonal characteristics of climate computations of gcm on the climate variations from 125 kyr to 115 kyr b p are confirmed for western europe the insolation variations have induced at that time a decrease of seasonality accompanied by an increased cyclonic activity in winter this has been the beginning of the first ice growth after the last interglacial other glacier growth phases are detected at the end of substage 5c and particularly at the end of substage 5a

magnetic investigations of framboidal greigite formation a record of anthropogenic environmental changes in eutrophic lake st moritz switzerland magnetic minerals found in sediments can either be transported to the basin from the catchment area or can be authigenically formed in the sediments sem studies x ray diffraction spectra and magnetic mineralogical analyses performed on magnetic extracts from freeze dried sediments of lake st moritz switzer land undoubtedly identified the presence of greigite the occurrence of this magnetic iron sulphide fe3s4 is associated with changing environmental conditions that can be interpreted from historical data available for the area results of the combined xrd and sem study show that authigenically formed greigite in lake st moritz sediments displays a predominant framboidal crystal arrangement amorphous irregular shapes and spherical aggregates most often associated with this mineral are present in lower concentration these results provide a natural example of framboidal iron sulphide formation and support previous experimental results that have shown that oxidation state and iron availability ar

lateglacial early holocene fluvial reactions of the jeetzel river elbe valley northern germany to abrupt climatic and environmental changes abstract mechanisms of climatic control on river system development are still only partially known palaeohydrological investigations from river valleys often lack a precise chronological control of climatic processes and fluvial dynamics which is why their specific forces remain unclear in this multidisciplinary case study from the middle elbe river valley northern germany multiple dating of sites palynostratigraphy radiocarbon and osl dating and high resolution analyses of environmental and climatological proxies pollen plant macro remains and ostracods reveal a continuous record of the environmental and fluvial history from the lateglacial to the early holocene biostratigraphical correlation to northwest european key sites shows that river system development was partially out of phase with the main climatic shifts the transition from a braided to an incised channel system predated the main phase of lateglacial warming 14 6 ka bp and the meandering river did not change its drainage pattern during the cooling of the younger dryas period environmental reconstructions suggest that river dynamics were largely affected by vegetation cover as a vegetation cover consisting of herbs dwarf shrubs and a few larger shrubs seems to have developed before the onset of the main lateglacial warming and pine forests appear to have persisted in the river valley during the younger dryas in addition two phases of high fluvial activity and new channel incision during the middle part of the younger dryas and during the boreal were correlated with changes from dry towards wet climatic conditions as indicated by evident lake level rises lateglacial human occupation in the river valley which is shown by numerous palaeolithic sites forming one of the largest settlement areas of that period known in the european plain is assigned to the specific fluvial and environmental conditions of the early allerod

multiple causes of the younger dryas cold period the last deglaciation was interrupted by a cool period known as the younger dryas numerical simulations suggest that the cold interval was the result of a combination of changes in ocean and atmospheric circulation and reduced radiative forcing

lateglacial insect assemblages from the palaeolithic site slotseng new evidence concerning climate and environment in sw denmark the site slotseng represents paleolithic settlements of the havelte phase of the hamburgian culture c 15 to 14 cal yr bp the lateglacial sediment stratigraphy of an adjacent kettle hole was stu

present day temperatures in northern scandinavia during the last glaciation scandinavia is generally considered to have been covered extensively with ice throughout marine isotope stages mis 4 2 between 75 and 10 ka here we present evidence for ice free warm conditions in the central area of the scandinavian glaciations during mis 3 our multiproxy data obtained from a lacustrine sequence in northern fin land reveal not only significant response in the northeastern sector of the scandinavian ice sheet to warming during the early part of mis 3 but also indicate rapid climate warming to present day temperatures in this ice free period new climate model simulations for interstadial conditions in mis 3 confirm the high mean july temperatures northeast of the scandinavian ice sheet in response to the high insolation values and the presence of the ice sheet during mis 3

kuroshio extension bimodality and the north pacific oscillation a case of intrinsic variability paced by external forcing abstracta previous north pacific ocean circulation model forced by climatological winds is extended here to include a time dependent north pacific oscillation npo forcing the kuroshio extension ke decadal bimodal cycle which is a self sustained intrinsic relaxation oscillation in the climatologically forced case is now excited by the npo forcing both the timing of the cycles and the rossby wave teleconnection mechanism that is found to govern the synchronization from 1993 to 2012 are in good agreement with altimeter observations sensitivity numerical experiments are carried out by varying the zonal location and amplitude of the npo forcing and the lateral eddy viscosity the emergence of the ke bimodality with a correct timing is found to be extremely sensitive to changes in the dissipative parameterization the implications of such sensitivity for deficiencies found in more realistic north pacific ocean general circulation models are discussed the dynamical mechanism that emerges from this stu

a comparison between the generalized digital environmental model and levitus climatologies two ocean climatologies of temperature and salinity the generalized digital environmental model gdem and the climatological atlas of the world ocean are compared dynamic height fields are computed by season from each climatology for the north atlantic north pacific and indian oceans and are compared on a 1 latitude longitude grid large scale oceanographic features are generally found to be similarly represented in both climatologies gdem appears to render better representations of seasonal variability and regions of high current shear such as the gulf stream because of a different smoothing method and a finer grid spacing maps of dynamic heights from both climatologies are presented and their similarities and differences are discussed the methodology for the construction of gdem is also described in detail

a laboratory study of the zonal structure of western boundary currents abstract the zonal structure of strongly nonlinear inertial western boundary currents wbcs is studied experimentally along a straight meridional coast in a 5 m diameter rotating basin by analyzing the zonal profile of the meridional velocity field as a function of transport intensity and other dynamical parameters the return flow that is generated by the surface wind stress curl in the oceanic interior is forced in the rotating basin by the motion of a piston in the absence of any surface stress the laboratory setup consists of two parallel rectangular channels separated by an island and linked by two curved connections in the first channel a piston is forced at a constant speed up ranging from 0 5 to 3 cm s 1 over a distance of 2 5 m producing a virtually unsheared current at the entrance of the second channel in the latter a linear reduction of the water depth provides the topographic beta effect that is necessary for the development of the westward intensification nearly steady currents

reinvestigation of the classic late glacial bolling so sequence denmark chronology macrofossils cladocera and chydorid ephippia the late glacial bolling period was first identified by johs iversen on the basis of pollen results from lake bolling so in denmark because there were no radiocarbon dates from the sequence the bolling chronozone 12 000 13 000 14c yr bp was later established on the basis of dates from other sites a new project is reinvestigating the sediments from the bolling so sequence with ams radiocarbon dating and multiproxy analyses here we present results of ams radiocarbon dating macrofossil analyses cladoceran analyses cladocera concentrations and chydorid ephippia and pediastrum analyses concentrations the ams dates on land plant remains show that the lower part of the sequence is around 12 500 14c yr bp and thus clearly pre dates the allerod chronozone however construction of a chronology for the sequence was problematic partly because of reworking of macroscopic plant remains the climate ameliorated after glacial conditions to such an extent that growth of plants could begin at ca 12 500 14c yr bp but the results of multiproxy analyses show little evidence for a further warming period during the pre allerod part of the sequence lake productivity was low and tree birch rare or maybe absent this may reflect widespread occurrence of dead ice unstable soils heavy in wash of minerogenic matter to the lake resulting in turbid water and rapid sedimentation the early pioneer vegetation was characterised by salix polaris and dryas octopetala and by herbs the allerod chronozone and especially its initial part appears to have been relatively warm but reduced cladoceran concentrations and increased proportion of chydorid ephippia suggest that climate cooled in the middle allerod and that the late allerod was colder than the early part the early younger dryas was probably colder than the late younger dryas clear warming is apparent at the beginning of the holocene where the first macrofossil evidence of trees betula pubescens populus tremula is found copyright 2004 john wiley sons ltd

climatic changes in areas adjacent to the north atlantic during the last glacial interglacial transition 14 9 ka bp a contribution to igcp 253 this paper presents a summary of the evidence for climatic changes during the last glacial interglacial transition 14 9 ka bp in land areas adjacent to the north atlantic it is a synthesis of the results of the 12 regional summaries compiled by contributors to the north atlantic seaboard programme of igcp 253 that are published separately in this issue of journal of quaternary science eighteen palaeotemperature curves are compared and arranged in three transects one from southern europe to spitsbergen a second from ireland to poland and the third from southern new england to the labrador baffin shelf area ten maps are presented that summarise the synoptic climatic conditions of the region in 500 year time periods the purpose of the exercise is to examine the extent to which any emerging patterns support the ruddiman and mclntyre model of large scale shifts in the position of the oceanic polar front during the last glacial interglacial transition some broad agreement emerges although the influence of oceanic changes is diminished in areas that lay in close proximity to the laurentide and fennoscandian ice sheets attention is drawn to limitations in the compilations and to the potential for improved models in the future

southwest scandinavia 40 15 kyr bp palaeogeography and environmental change twelve palaeogeographical reconstructions illustrate environmental changes at the southwest rim of the scandinavian ice sheet 40 15 kyr bp synchronised land sea and glacier configurations are based on the lithostratigraphy of tills and intertill sediments dating is provided by optically stimulated luminescence and calibrated accelerator mass spectrometry radiocarbon an interstadial sequence ca 40 30 kyr bp with boreo arctic proglacial fjords and subarctic flora and occasional glaciation in the baltic was succeeded by a last glacial maximum sequence ca 3020 kyr bp with the closure of fjords and subsequent ice streams in glacial lake basins in kattegat and the baltic steadily flowing ice from sweden bordered the norwegian channel ice stream a deglaciation sequence ca 20 15 kyr bp indicates the transgression of arctic waters retreat of the swedish ice and advance of baltic ice streams succeeded by a return to interstadial conditions when ameliorated ice free conditions prevailed in maritime regions glaciers advanced through the baltic and when interstadial regimes dominated the baltic glaciers expanded off the norwegian coast the largest glacier extent was reached in the north sea around 29 kyr bp about 22 kyr bp in denmark and ca 18 kyr bp in the baltic our model provides new data for future numerical and qualitative landform based models copyright c 2003 john wiley sons ltd less

global bifurcation of shilnikov type in a double gyre ocean model abstract the dynamics of an idealized wind driven double gyre circulation in an ocean basin are studied from a dynamical systems point of view in an effort to better understand its variability while previous analyses of this circulation have mostly dealt with local bifurcations of steady states and limit cycles this study demonstrates the importance of considering global bifurcations as well in one case a coherent picture of the global dynamics spanning a range of parameters from where there are only stable steady state solutions to where there is chaotic eddy shedding is presented a simple but novel use of power spectra along with dynamical projections of the dynamics suggests that just beyond the regime in which there are only stable steady states the system exhibits a complicated global bifurcation known as the shilnikov phenomenon

the recent eutrophication of baldeggersee switzerland as assessed by fossil diatom assemblages diatom analyses with an annual resolution were carried out on varves of the hypertrophic baldeg gersee central swiss plateau for the timespan ad 1885 to 1993 they reveal seven major changes in the dominant planktonic diatoms as a result of progressive nutrient enrichment baldeggersee changed in the 1910s from a cyclotella to a tabellaria fenestrata dominated assemblage and eventually in the 1950s to a stephanodiscus parvusdominated diatom assemblage the timing and direction of diatom assemblage changes in the varved sediment compare well with sedimentological and limnological observations partitioning of the variance in the diatom data revealed that tp is a stronger explanatory variable than temperature for these changes a diatom inferred total phosphorus tp reconstruction indicates three major steps in eutrophication occurring at 1909 the mid 1950s and the mid 1970s comparison with tp measurements in the water column demonstrates that the diatom tp inference model used is able to hindcast past tp concentrations reliably the major steps in eutrophication led to decreases in diatom diversity and also resulted in a progressive increase of calcite grain size the lake restoration programme established since 1982 shows no direct impact on the composition of the diatom assemblages however the decrease in phosphorus loads since the mid 1970s is reflected in the diatom assemblages and in decreasing diatom inferred tp concentrations

decadal scale autumn temperature reconstruction back to ad 1580 inferred from the varved sediments of lake silvaplana southeastern swiss alps a quantitative high resolution autumn september november temperature reconstruction for the southeastern swiss alps back to ad 1580 is presented here we used the annually resolved biogenic silic

suspended sediment and phosphorus in proglacial rivers bioavailability and potential impacts upon the p status of ice marginal receiving waters this paper adopts standard tests developed in temperate catchment research to determine the total phosphorus tp and the algal available base extractable phosphorus naoh p content of a wide range of glaciofluvial sediments from the northern hemisphere we find that the tp content of these sediments is broadly similar to the p content of major rock types in earth s crust 230 670 gp g and so the tp yields of glacier basins may be high owing to the efficacy of suspended sediment evacuation by glacial meltwaters we show that this is best achieved where subglacial drainage systems are present the naoh p pool of the sediments is found to be low 1 23 gp g relative to the tp pool and also to the naoh p pool of suspended sediments in temperate non glacierized catchments this most probably reflects the restricted duration of intimate contact between dilute meltwaters and glacial suspended sediments during the ablation season thus despite the high surface area volume ratio of glacial suspended sediments the potential for p adsorption to mineral surfaces following release by dissolution is also low further sorption experiments and sequential extraction tests conducted using glacial suspended sediments from two svalbard catchments indicate that the generation of reactive secondary minerals e g fe and other hydroxides with a strong capacity to scavenge p from solution and thereby promote the continued dissolution of p may also be limited by the short residence times most p is therefore associated with poorly weathered calcite apatite rich mineral phases however we use examples from the svalbard glacier basins austre broggerbreen and midre lovenbreen to show that the high sediment yields of glaciers may result in appreciable naoh p loading of ice marginal receiving waters again the importance of subglacial drainage is highlighted as it produces a major episodic release of naoh p at midre lovenbreen that results in a yield 8 2 kg naoh p km2 year more than one order of magnitude greater than that at austre broggerbreen where subglacial drainage is absent and the yield is 0 48 kg naoh p km2 year therefore as since both detrimental and beneficial effects of sediment bound p loading in ice marginal receiving waters are possible i e either reduced primary productivity owing to increased turbidity or p fertilization following desorption there is a pressing need to assess the ambient p status of such environments and also the capacity for ice marginal ecosystems to adapt to such inputs copyright 2004 john wiley sons ltd

a nonlinear theory of the kuroshio extension bimodality abstract the kuroshio extension ke flow in the north pacific ocean displays a very distinctive decadal variability of bimodal character involving two completely different states a large meander elongated state and a small meander contracted state connected by very asymmetric temporal transitions although such a flow has been widely studied by means of a suite of mathematical models and by using several observational platforms a satisfactory theoretical framework answering quite elementary questions is still lacking the main question being whether such variability is induced by a time varying wind forcing or rather by intrinsic oceanic mechanisms in this context the chaotic relaxation oscillation produced by a process oriented model of the ke low frequency variability with steady climatological wind forcing was recently recognized to be in substantial agreement with altimeter data here those model results are further compared with a comprehensive altimeter dataset the positive result of

palaeoecology of two lake basins from disko west greenland the macrofossils lithology and chronology of two lake basins on disko in central west greenland have been investigated both lakes were isolated from the sea in the mid holocene as a result of relative land uplift a marine brackish limnic sequence was recovered from the qivittut lake the marine fauna is unusually diverse whereas the brackish water fauna consists only of few species immediately after isolation the lake passed through a short lived eutrophic phase after which stable mesotrophic conditions were established from the second lake basin the fortunebay lake only limnic sediments were recovered this lake record demonstrates that rather stable conditions have persisted since mid holocene times both lakes show anomalously high accumulation rates

last glacial maximum environmental conditions at andoya northern norway evidence for a northern ice edge ecological hotspot abstract andoya on the nw coast of norway is a key site for understanding the last glacial maximum lgm in northern europe controversy has arisen concerning the local conditions especially about the timing and extent of local glacial cover maximum july temperatures and whether pine and or spruce could have grown there we reviewed all existing data and add newly analysed ancient sedimentary dna sedadna pollen macrofossils geochemistry and stable isotopes from three lake sediment cores from ovre aerasvatnet a total of 23 new dates and age depth modelling suggests the lake has been ice free since gi2 14 7 cal ka bp data recorded 94 vascular plant taxa of which 38 have a northern limit in shrub tundra or more southern vegetation zones this unusual assemblage likely stems from a combination of proximity to ice free water in summer geographical isolation linked with stochastic long distance dispersal events and the presence of bird fertilized habitats the environmental reconstruction based on all records from the area does not preclude local growth of tree species as the local climate combined with high nutrient input may have led to periodically suitable environmental hotspot conditions

on the timing of retreat of the loch lomond younger dryas readvance icefield in the sw scottish highlands and its wider significance abstract it has long been assumed that the last glacier expansion in the scottish highlands the loch lomond readvance llr resulted from a cold reversal that was broadly coeval with the younger dryas episode this view has recently been challenged with the suggestion that glacier ice had disappeared from rannoch moor one of the main ice accumulation centres in the sw scottish highlands by as early as 12 5 ka i e within the first half of the younger dryas here we present new radiocarbon tephrostratigraphical and pollen stratigraphical evidence from one of the key sites on rannoch moor the results of an experiment designed to test this hypothesis our results not only contradict that concept but are fully compatible with other evidence from the sw scottish highlands that suggests that the llr glaciers in this area continued to expand until towards the end of the younger dryas period and may have persisted in some places after the onset of the holocene we consider the possible reasons for this marked divergence in chronology a matter that is crucial to resolve because the precise timing of the demise of the llr glaciers has important palaeoclimatic and other implications in the wider context we also draw attention to problems with the general use of the term younger dryas and why we regard the greenland stratotype unit and term greenland stadial 1 gs 1 a more secure stratigraphic comparator

diatom response to climatic warming over the last 200 years a record from gonghai lake north china abstract annual monitoring data and centennial and millennial scale paleolimnological records have revealed an increase in small celled planktonic diatom species relative to heavier tycho planktonic and small benthic diatoms in many high altitude lakes presumably in response to recent climatic warming in addition to changes in the composition and structure of lacustrine diatom assemblages there have also been changes in diatom biodiversity however these changes are not regionally consistent in this study we chose a temperate mid latitude lake to explore the response of changes in diatom assemblages and biodiversity to recent climatic warming the diatom record spans the past ca 200 years and reveals that since 1966 ce the small celled cyclotella ocellata stelligera has replaced the previously dominant large celled phytoplankton cyclotella schroeteri these changes are in accordance with the increasing trend in global mean surface temperature biodiversity increased remarkably from 1966 ce but began to decline after 1990 ce presumably in response to rapid climatic warming our findings indicate that the response of diatom biodiversity to climate change was a nonlinear process

quantitative summer temperature reconstruction derived from a combined biogenic si and chironomid record from varved sediments of lake silvaplana south eastern swiss alps back to ad 1177 abstract high resolution quantitative temperature records are needed for placing the recent warming into the context of long term natural climate variability in this study we present a quantitative high resolution 9 year summer june august temperature reconstruction back to ad 1177 for the south eastern swiss alps this region is a good predictor for summer temperatures in large parts of western and central europe our reconstruction is based on a combination of the high frequency component of annually resolved biogenic silica bsi flux data and the low frequency component of decadal chironomid inferred temperatures from annually laminated well dated sediments varves from proglacial lake silvaplana eastern swiss alps for the calibration period ad 1760 1949 we assess systematically the effects of six different regression methods type i regressions inverse regression ir inverse prediction ip generalised least squares gls type ii regressions major axis ma ranged major axis rma and standard major axis sma with regard to the predicted amplitude and the calibration statistics such as root mean square error of prediction rmsep reduction of error re and coefficient of efficiency ce we found a trade off in the regression model choice between a good representation of the amplitude and good calibration statistics the band pass filtered bsi flux record is in close agreement both in the structure and the amplitude with two fully independent reconstructions spanning back to ad 1500 and ad 1177 respectively all known pulses of negative volcanic forcing are represented as cold anomalies in the bsi flux record volcanic pulses combined with low solar activity sporer and maunder minimum are seen as particularly cold episodes around ad 1460 and ad 1690 the combined chironomid and bsi flux temperature record rmsep 0 57 c is in good agreement with the glacier history of the alps the warmest ad 1190 and coldest decades 17th century 1680 1700 of our reconstruction coincide with the largest anomalies in the alpine tree ring based reconstruction both records show in the decadal variability an amplitude of 2 8 c between ad 1180 and 1950 which is substantially higher than the amplitude of hemispheric reconstructions our record suggests that the current decade is slightly warmer than the warmest decade in the pre industrial time of the past 800 years

anomalously mild younger dryas summer conditions in southern greenland the first late glacial lake sediments found in greenland were analyzed with respect to a variety of environmental variables the analyzed sequence covers the time span between 14400 and 10500 calendar yr b p and the data imply that the conditions in southernmost greenland during the younger dryas stadial 12800 11550 calendar yr b p were characterized by an arid climate with cold winters and mild summers preceded by humid conditions with cooler summers climate models imply that such an anomaly may be explained by local climatic phenomenon caused by high insolation and fohn effects it shows that regional and local variations of younger dryas summer conditions in the north atlantic region may have been larger than previously found from proxy data and modeling experiments

a kuroshio extension system model study decadal chaotic self sustained oscillations abstract a model study of the kuroshio extension system in which forcing is provided by a time independent climatological wind yields a mean meandering path and a decadal variability of the jet in significant agreement with in situ and altimetric measurements a reduced gravity primitive equation ocean model is implemented in a box spanning the whole north pacific including a schematic coastline at the western side and an analytical wind forcing is determined according to the ecmwf and comprehensive ocean atmosphere data set coads climatologies the modeled time averaged kuroshio extension shows meanders northern and southern recirculation regions and a jet penetration that are in good agreement with the corresponding observed climatological features this result suggests that intrinsic nonlinear mechanisms are likely to play a major role in determining the meander pattern of the mean flow the internal low frequency variability is found to be a chaotic bimodal self sustained oscillation between a

on the crucial role of basin geometry in double gyre models of the kuroshio extension abstract the decadal chaotic relaxation oscillation obtained in a recent double gyre model study of the kuroshio extension intrinsic low frequency variability was found to compare surprisingly well with the real variability of the jet as revealed by altimeter data despite the high degree of idealization of the model in this note it is shown that elements of realism in the basin geometry present in that study and absent in previous double gyre models applied to the kuroshio extension play a crucial role in shaping the low frequency variability of the jet and can explain the good performance of the model a series of numerical experiments with different basin geometries of increasing degrees of simplicity are analyzed if the schematic western boundary representing the coastline south of japan is removed the strong decadal variability completely disappears and only a very weak periodic oscillation about an elongated state of the jet is found if the large zonal width of the basin representing correct

a laboratory study of nonlinear western boundary currents with application to the gulf stream separation due to inertial overshooting various dynamical aspects of nonlinear western boundary currents wbcs have been investigated experimentally through physical modeling in a 5 m diameter rotating basin the motion of a piston with a velocity up that can be as low as up 5 0 5 mm s 21 induces a horizontally unsheared current of homogeneous water that flowing over a topographic beta slope experiences westward intensification first the character of wbcs for various degrees of nonlinearity is investigated by varying up flows ranging from the highly nonlinear inertial charney regime down to a weakly nonlinear regime can be simulated in the first case the dependence of zonal length scales on up is found to be in agreement with charney s theory for weaker flows a markedly different functional dependence emerges describing the initial transition toward the linear viscous case this provides an unprecedented coverage of nonlinear wbc dependence on an amplitude parameter in terms of experimental data wbc separation from a wedge shaped continent past a cape simulating cape hatteras due to inertial overshooting is then analyzed by increasing current speed a critical behavior is identified according to which a very small change of up marks the transition from a wbc that follows the coast past the cape to a wbc nearly dynamically similar to a full scale gulf stream that separates from the cape without any substantial deflection as with the gulf stream extension the important effect of the deflection angle of the continent is analyzed as well finally the qualitative effect of a sloping sidewall along a straight coast is considered the deflection of the flow away from the western wall due to the tendency to preserve potential vorticity clearly emerges

how stable are twentieth century calibration models a high resolution summer temperature reconstruction for the eastern swiss alps back to ad 1580 derived from proglacial varved sediments we found a significant positive correlation between local summer air temperature may september and the annual sediment mass accumulation rate mar in lake silvaplana 46 n 9 e 1800 m a s l during the twentieth century r 0 69 p 0 001 for decadal smoothed series sediment trap data 2001 2005 confirm this relation with exceptionally high particle yields during the hottest summer of the last 140 years in 2003 on this base we developed a decadal scale summer temperature reconstruction back to ad 1580 surprisingly the comparison of our reconstruction with two other independent regional summer temperature reconstructions based on tree rings and documentary data revealed a significant negative correlation for the pre 1900 data ie late little ice age this demonstrates that the correlation between mar and summer temperature is not stable in time and the actualistic principle does not apply in this case we suggest that different climatic regimes modern little ice age lead to changing state conditions in the catchment and thus to considerably different sediment transport mechanisms therefore we calibrated our mar data with gridded early instrumental temperature series from ad 1760 1880 r 0 48 p 0 01 for decadal smoothed series to properly reconstruct the late lia climatic conditions we found exceptionally low temperatures between ad 1580 and 1610 0 75 c below twentieth century mean and during the late maunder minimum from ad 1680 to 1710 0 5 c below twentieth century mean in general summer temperatures did not experience major negative departures from the twentieth century mean during the late little ice age this compares well with the two existing independent regional reconstructions suggesting that the lia in the alps was mainly a phenomenon of the cold season

a late weichselian stable isotope stratigraphy compared with biostratigraphical data a case study from southern sweden late weichselian lake sediments from a site in southern sweden were analysed for stable carbon and oxygen isotopes as well as plant macrofossils and insect remains by comparison of independent d

early weichselian interstadial mis 5c summer temperatures were higher than today in northern fennoscandia abstract only fragmentary biostratigraphical interstadial data exist from northern european high latitudes the palaeoenvironmental interpretations for the early part of the last glaciation in northern fennoscandia are mainly based on palynological evidence that suggests open birch woodland and a sub arctic climate plant macrofossils from the sokli sediment sequence in finnish lapland provide different evidence of interstadial climate conditions the assemblage includes several species that currently have considerably more southern distribution ranges this indicates that ca 100 000 years ago summer temperatures were warmer than today the mean minimum july temperature may have been as high as 16 c and the effective temperature sum may have been 1000 in day degree units d d the modern values being 13 c and 650 d d respectively the contemporary astronomical forcing mechanisms may have resulted in a weaker north south temperature gradient and a longer growing period creating more favourable climate conditions compared with today

a spatially restricted younger dryas plateau icefield in the gaick scotland reconstruction and palaeoclimatic implications considerable research has been conducted in scotland to reconstruct younger dryas glaciers and palaeoclimatic conditions but our understanding remains incomplete in this contribution we examine the gaick a dissected plateau that extends over 520 km 2 in the central grampians scotland the extent and style of younger dryas glaciation in the gaick has been repeatedly contested although a model of extensive plateau icefield glaciation has become generally accepted this is despite well documented issues with key elements of the plateau icefield reconstruction we synthesise the results of recent geomorphological mapping in the gaick and recognise a distinct morphostratigraphic signature in the upper parts of the western catchments this differs markedly from sediment landform associations in other parts of the area and we argue this provides a strong indication of spatially restricted younger dryas 12 9 11 7 ka glaciation in the gaick our interpretation is independently supported by glacierisation threshold analysis which implies that the eastern gaick was unable to nourish younger dryas ice we therefore contest the accepted paradigm of extensive younger dryas glaciation in this area based on the geomorphological evidence and glacier surface profile modelling we reconstruct a 42 km 2 plateau icefield that yields an equilibrium line altitude of 751 46 m using this value a sea level precipitation value of 826 331 mm a 1 is inferred for the younger dryas which suggests considerably drier conditions than at present using recalculated glacier derived precipitation estimates from scotland we present regional climate analysis that corroborates arguments for a strong west east precipitation gradient across scotland

floral evidence for high summer temperatures in southern scandinavia during 15 11 cal ka bp abstract the global climate transition from the lateglacial to the early holocene is dominated by a rapid warming trend driven by an increase in orbital summer insolation over high northern latitudes and related feedbacks the warming trend was interrupted by several abrupt shifts between colder stadial and warmer interstadial climate states following instabilities of the atlantic meridional overturning circulation amoc in response to rapidly melting ice sheets the sequence of abrupt shifts between extreme climate states had profound impacts on ecosystems which make it challenging to reliably quantify state variables like july temperatures within a non analogue climate envelope for europe there is increasing albeit inconclusive evidence for higher stadial summer temperatures than initially thought here we present a comprehensive floral compilation of plant macrofossils from lake sediment cores of 15 sites from s scandinavia covering the period 15 to 11 ka bp we find evidence for a continued presence of plant species indicating high july temperatures throughout the last deglaciation the presence of hemiboreal plants in close vicinity to the southern margin of the fennoscandian ice sheet implies a strong thermal summer forcing for the rapid ice sheet melt consistent with some recent studies we do not find evidence for a general stadial summer cooling which indicates that other reasons than summer temperatures caused drastic setbacks in proxy signals possibly driven by extreme winter cooling and or shorter warm seasons

archaeal community changes in lateglacial lake sediments evidence from ancient dna the lateglacial early holocene sediments from the ancient lake at hasseldala port southern sweden provide an important archive for the environmental and climatic shifts at the end of the last ice age and the transition into the present interglacial the existing multi proxy data set highlights the complex interplay of physical and ecological changes in response to climatic shifts and lake status changes yet it remains unclear how microorganisms such as archaea which do not leave microscopic features in the sedimentary record were affected by these climatic shifts here we present the metagenomic data set of hasseldala port with a special focus on the abundance and biodiversity of archaea this allows reconstructing for the first time the temporal succession of major archaea groups between 13 9 and 10 8 ka bp by using ancient environmental dna metagenomics and fossil archaeal cell membrane lipids we then evaluate to which extent these findings reflect physical changes of the lake system due to changes in lake water summer temperature and seasonal lake ice cover we show that variations in archaeal composition and diversity were related to a variety of factors e g changes in lake water temperature duration of lake ice cover rapid sediment infilling which influenced bottom water conditions and the sediment water interface methanogenic archaea dominated during the allerod and younger dryas pollen zones when the ancient lake was likely stratified and anoxic for large parts of the year the increase in archaeal diversity at the younger dryas holocene transition is explained by sediment infilling and formation of a mire peatbog

holocene temperature history of northwest greenland with new ice cap constraints and chironomid assemblages from deltaso abstract arctic temperature shifts drive changes in carbon cycling sea ice extent and greenland ice sheet mass balance all of which have global ramifications paleoclimate data from past warm periods provide a unique means for assessing the sensitivity of these systems to warming climate but the magnitude and timing of past temperature changes in many parts of the arctic are poorly known here we assess orbital scale holocene temperature change in northwest greenland near the margin of the ice sheet using subfossil insect assemblages from lake deltaso based upon sedimentation history in this currently proglacial lake we also place constraints on holocene extents of the adjacent north ice cap a large independent ice cap reconstructed summer temperatures were warmer than present at the onset of lacustrine sedimentation following regional deglaciation by the greenland ice sheet sometime between 10 8 and 10 1 ka bp deltaso experienced the warmest summer temperatures of the holocene between 10 and 6 2 ka bp followed by progressive cooling that continued through the late holocene as summer insolation declined culminating in the lowest temperatures during the pre industrial last millennium deltaso chironomids indicate peak early holocene summer temperatures at least 2 5 3 c warmer than modern and at least 3 5 4 c warmer than the pre industrial last millennium we infer based upon lake sediment organic and biogenic content that in response to declining temperatures north ice cap reached its present day size 1850 ad having been smaller than present through most of the preceding holocene our synthesis of paleoclimate evidence from northwest greenland ellesmere island and northern baffin bay supports the timing of temperature trends inferred at deltaso and suggests that quantitative temperature reconstructions from deltaso may represent a minimum bound on regional early holocene warming collectively records from the region indicate 4 c summer cooling through the holocene intense early holocene warmth around northwest greenland argues against delayed onset of warmer than present conditions due to the influence of the nearby waning laurentide ice sheet and has implications for understanding the greenland ice sheet s sensitivity to climate change

interactions of climate and land use documented in the varved sediments of seebergsee in the swiss alps this paper presents a multiproxy high resolution study of the past 2600 years for seebergsee a small swiss lake with varved sediments at the present tree line ecotone the laminae were identieed as varves by a numerical analysis of diatom counts in the thin sections the hypothesis of two diatom blooms per year was corroborated by the 210 pb and 137 cs chronology a period of intensive pasturing during the little ice age between ad 1346 and ad 1595 is suggested by coprophilous fungal spores as well as by pollen indicators of grazing by the diatom inferred total phosphorus by geochemistry and by documentary data the subsequent re oligotrophication of the lake took about 88 years as determined by the timelag between the decline of coprophile fungal spores and the restoration of pre eutrophic nutrient conditions according to previous studies of latewood densities from the same region cold summers around ad 1600 limited the pasturing at this altitude this demonstrated the socio economic impact of a single climatic event however the variance partitioning between the effects of land use and climate which was applied for the whole core revealed that climate independent of land use and time explained only 1 32 of the diatom data while land use independent of climate and time explained 15 7 clearly land use ineuenced the lake but land use was not always driven by climate other factors beside climate such as politics or the introduction of fertilizers in the seventeenth and eighteenth centuries also ine uenced the development of alpine pasturing

the 1 5 ka varved record of lake montcortes southern pyrenees ne spain abstract the karstic lake montcortes sedimentary sequence spanning the last 1548 yr constitutes the first continuous high resolution multi proxy varved record in northern spain sediments consist of biogenic varves composed of calcite organic matter and detrital laminae and turbidite layers calcite layer thickness and internal sub layering indicate changes in water temperature and seasonality whereas the frequency of detrital layers reflects rainfall variability higher temperatures occurred in lake montcortes in ad 555 738 825 875 1010 1322 and 1874 present lower temperatures and prolonged winter conditions were recorded in ad 1446 1598 1663 1711 and 1759 1819 extreme and multiple precipitation events dominated in ad 571 593 848 922 987 1086 1168 1196 1217 1249 1444 1457 1728 1741 and 1840 1875 indicating complex hydrological variability in ne spain since ad 463 the sedimentary record of lake montcortes reveals a short term relation between rainfall variability and the detrital influx pronounced during extended periods of reduced anthropogenic influences in pre industrial times during warm climate episodes population and land use increased in the area after the onset of the industrialization the relationship between climate and human activities decoupled and population dynamics and landscape modifications were therefore mostly determined by socio economic factors

warm younger dryas summers and early late glacial spread of temperate deciduous trees in the pannonian basin during the last glacial termination 20 9 kyr cal bp abstract this paper focuses on the last glacial termination vegetation and climate reorganization of the eastern pannonian plain via the multi proxy paleoecological analysis of kokad mire in eastern hungary grains size sediment chemistry and magnetic susceptibility records are compared with the pollen and plant macrofossil records on the basis of which biome and quantitative summer mean temperature reconstructions are provided and discussed with other climate records of the region biome assignments indicated graminoid and forb tundra vegetation from 19 440 cal yr bp with the local presence of betula pendula b pubescens b nana and pinus sylvestris a rapid biome shift to cool coniferous forest took place at 16 200 cal yr bp and a second biome shift was identified at 14 740 cal yr bp when cool mixed forest developed and persisted into the early holocene the most prominent feature of the record was the early post last glacial maximum lgm establishment 17 700 cal yr bp and expansion 14 700 cal yr bp of elm ulmus and hazel corylus supporting the phylogeographical evidence for extra mediterranean refugia in the pannonian basin the fungal spore record indicated the presence of large grazing mammals locally after the lgm until 16 780 cal yr bp their disappearance predated the biome shift to cold coniferous forest and the final increase of forest fires pollen based summer temperature reconstruction suggested relatively warm summers 14 5 c by 19 440 cal yr bp and buffered july mean temperature fluctuations throughout the last glacial termination in this region with

variability of the kuroshio extension jet recirculation gyre and mesoscale eddies on decadal time scales abstract twelve years of sea surface height ssh data from multiple satellite altimeters are used to investigate the low frequency changes and the interconnections of the kuroshio extension ke jet its southern recirculation gyre and their mesoscale eddy field the dominant signal is characterized by the steady weakening of the ke jet recirculation gyre from 1993 to 1996 followed by a gradual strengthening after 1997 during the weakening period of 1993 96 the ke path migrated southward in general and this path migration reversed in direction during the strengthening period of the ke jet and recirculation gyre after 1997 by hindcasting the ssh signals using linear vorticity dynamics it was found that weakening strengthening in the ke jet and recirculation gyre is consistent with westward propagation of negative positive ssh anomalies generating in the eastern north pacific and strengthening during their westward propagation when the ke jet and recirculation gyre were in a weak mode during 19

dating the trollesgave site and the bromme culture chronological fix points for the lateglacial settlement of southern scandinavia abstract the bromme culture belongs to the lateglacial the period when people settled in the recently deglaciated southern scandinavia until now there have been only a few imprecise fix points relating to the chronological position of this archaeological culture this situation can now be improved with the aid of research results from a bromme culture settlement at trollesgave in se denmark using pollen and plant macrofossil data lateglacial lacustrine deposits containing waste material from the settlement can be assigned to the end of the climatically mild allerod period a series of 14 c dates establishes the age of the settlement as c 10 826 49 14 c years bp 12 871 12 590 cal yr bp by correlation with climate data from the greenland ice cores the occupation can be assigned to the early part of the cold climatic zone gs 1 thus demonstrating that the global ice core climate zones are not absolutely synchronous with the regional division into biozones

flora fauna and climate of scotland during the weichselian middle pleniglacial palynological macrofossil and coleopteran investigations thin lenses of organic rich material on the upper surface of a layer of glacio fluvial deposits have been studied in an open cast coal mine near sourlie western scotland radiocarbon dates on antler fragments plant debris and bulk organic matter from silt showed that the sediments accumulated between ca 33 500 and 29 000 14c yr bp during a period when this part of western scotland was free of glaciers the organic rich sediments yielded a very rich flora and fauna and in total about 160 plant taxa and 61 coleopteran taxa were recorded together with other invertebrates the sourlie flora is one of the richest late middle weichselian floras yet studied within the british isles leg bones of coelodonta antiquitatis woolly rhinoceros and rangifer tarandus reindeer were also found at the site during this period the landscape was treeless and the vegetation could be characterised as an intermediate between a low shrub tundra and sedge grass moss tundra both the flora and arthropod fauna suggest that during formation of the organic rich layers at sourlie mean july temperatures were 9 10 c the flora suggests also that at the beginning of formation of these layers minimum mean july temperatures increased from 7 to 9 10 c but later dropped again to 7 8 c a possible time correlation with one of the warmer periods of the dansgaard oeschger cycles in the stable oxygen isotope record of the greenland ice cores during this period is proposed the arthropod fauna suggests that mean january temperatures were somewhere between 34 and 11 c mean annual temperatures lay probably between 1 and 10 c which implies the possible presence of discontinuous or continuous permafrost in the area during winter a protective snow cover of varying thickness probably enabled perennial plants especially shrubs to survive

paleocean circulation during the last deglaciation a bipolar seesaw hughen et al 1998 have documented that during the first 200 years of younger dryas time the 14c content of atmospheric co2 increased by 50 and that during the remainder of this 1200 year duration cold event it steadily declined the initial increase in 14c c was likely the result of a reduction in the atlantic s conveyor circulation however were the subsequent radiocarbon decline due to the rejuvenation of this potent heat pump then it is difficult to understand why the climate conditions in the northern atlantic basin remained cold throughout the younger dryas modeling exercises by stocker and wright 1996 mikolajewicz 1998 and schiller et al 1998 show that if the conveyor is terminated the transfer of radiocarbon into the deep sea shifts to the southern ocean thereby stabilizing the atmospheric 14c c ratio paleoclimatic evidence from the antarctic continent suggests that this model based scenario might have been played out in the real world while the younger dryas cooling has been documented in many places around the world including new zealand denton and hendy 1994 sowers and bender 1995 using their 18o in o2 based correlation between the ice core 18o in ice records for antarctica and greenland have demonstrated that in antarctica the younger dryas was a time of maximum warming the point of this paper is that the steep rise in 18o rise in antarctic ice which commenced close to the onset of the younger dryas might have been caused by heat released to the atmosphere in response to an increase in deep sea ventilation in the southern ocean

deglaciation of fennoscandia abstract to provide a new reconstruction of the deglaciation of the fennoscandian ice sheet in the form of calendar year time slices which are particularly useful for ice sheet modelling we have compiled and synthesized published geomorphological data for eskers ice marginal formations lineations marginal meltwater channels striae ice dammed lakes and geochronological data from radiocarbon varve optically stimulated luminescence and cosmogenic nuclide dating this is summarized as a deglaciation map of the fennoscandian ice sheet with isochrons marking every 1000 years between 22 and 13 cal kyr bp and every hundred years between 11 6 and final ice decay after 9 7 cal kyr bp deglaciation patterns vary across the fennoscandian ice sheet domain reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins for example the ice sheet margin in the high precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and other ice marginal deposits in many fjords and coastal valleys retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern sweden and rapid retreat of the calving ice margin in the baltic basin our reconstruction is consistent with much of the published research however the synthesis of a large amount of existing and new data support refined reconstructions in some areas for example the lgm extent of the ice sheet in northwestern russia was located far east and it occurred at a later time than the rest of the ice sheet at around 17 15 cal kyr bp we also propose a slightly different chronology of moraine formation over southern sweden based on improved correlations of moraine segments using new lidar data and tying the timing of moraine formation to greenland ice core cold stages retreat rates vary by as much as an order of magnitude in different sectors of the ice sheet with the lowest rates on the high elevation and maritime norwegian margin retreat rates compared to the climatic information provided by the greenland ice core record show a general correspondence between retreat rate and climatic forcing although a close match between retreat rate and climate is unlikely because of other controls such as topography and marine versus terrestrial margins overall the time slice reconstructions of fennoscandian ice sheet deglaciation from 22 to 9 7 cal kyr bp provide an important dataset for understanding the contexts that underpin spatial and temporal patterns in retreat of the fennoscandian ice sheet and are an important resource for testing and refining ice sheet models

mean july temperatures during the younger dryas in northwestern and central europe as inferred from climate indicator plant species abstract we estimated minimum mean july temperatures in northwestern and central europe during the younger dryas 10 950 10 15014c yr b p from distributions of climate indicator plant species which were reconstructed from 140 pollen and plant macrofossil diagrams paleobotanical records mainly from the central and eastern part of the study area show that the coldest conditions occurred early in the younger dryas before 10 55014c yr b p for this phase mean july temperatures at sea level of around 10 c are suggested for the northern part of the british isles and for ice free scandinavia we estimated a mean july temperature of 12 c for central england the netherlands and northern germany the 13 c mean july isotherm largely based on the modern distribution oftypha latifolia was most probably located in southern england belgium central germany and poland the reappearance of thermophilous elements in the records after 10 55014c yr b p suggests a summer warming at least temporarily of 1 to 2 c in the study area the reconstructed temperatures are comparable with temperature estimates based on beetle data however they appear rather high when compared with estimates based on glaciological evidence

synchronized terrestrial atmospheric deglacial records around the north atlantic on the basis of synchronization of three carbon 14 c 14 dated lacustrine sequences from sweden with tree ring and ice core records the absolute age of the younger dryas preboreal climatic shift was determined to be 11 450 to 11 390 80 years before the present a 150 year long cooling in the early preboreal associated with rising delta 14 c values is evident in all records and indicates an ocean ventilation change this cooling is similar to earlier deglacial coolings and box model calculations suggest that they all may have been the result of increased freshwater forcing that inhibited the strength of the north atlantic heat conveyor although the younger dryas may have begun as an anomalous meltwater event

pronounced summer warming in northwest greenland during the holocene and last interglacial projections of future rates of mass loss from the greenland ice sheet are highly uncertain because its sensitivity to warming is unclear geologic reconstructions of quaternary interglacials can illustrate how the ice sheet responded during past warm periods providing insights into ice sheet behavior and important tests for data model comparisons however paleoclimate records from greenland are limited early holocene peak warmth has been quantified at only a few sites and terrestrial sedimentary records of prior interglacials are exceptionally rare due to glacial erosion during the last glacial period here we discuss findings from a lacustrine archive that records both the holocene and the last interglacial lig from greenland allowing for direct comparison between two interglacials sedimentary chironomid assemblages indicate peak july temperatures 4 0 to 7 0 c warmer than modern during the early holocene maximum in summer insolation chaoborus and chironomids in lig sediments indicate july temperatures at least 5 5 to 8 5 c warmer than modern these estimates indicate pronounced warming in northwest greenland during both interglacials this helps explain dramatic ice sheet thinning at camp century in northwest greenland during the early holocene and for the lig aligns with controversial estimates of eemian warming from ice core data retrieved in northern greenland converging geologic evidence for strong lig warming is challenging to reconcile with inferred greenland ice sheet extent during the lig and the two appear incompatible in many models of ice sheet evolution an increase in lig snowfall could help resolve this problem pointing to the need for hydroclimate reconstructions from the region

climatic and environmental changes in north western russia between 15 000 and 8000 cal yr bp a review multi proxy palaeoenvironmental studies of nine sediment sequences from four areas in north western russia reveal significant changes in climate lake productivity and vegetation during the lateglacial and early holocene that show some degree of correlation with changes reconstructed from sites throughout the north atlantic region at lake nero in the rostov jaroslavl area which is outside the maximum limit of the scandinavian ice sheet sedimentation recommenced shortly after 15 cal ka bp in response to increases in temperature and humidity during greenland interstadial 1 gi 1 bolling allerod however climatic amelioration during gi 1 was slow to increase lake organic productivity or trigger large scale changes in much of northwestern russia in general this region was characterised by long lasting lake ice cover low lake productivity soil erosion and dwarf shrub and herb tundra until the end of greenland stadial 1 gs 1 younger dryas at some sites distinct increases in lake organic productivity mean summer temperatures and humidity and the expansion of forest trees coincide with rapid warming at the beginning of the holocene and the increasing influence of warm air masses from the north atlantic at other sites particularly on the karelian isthmus but also in russian karelia the delayed response of limnic and terrestrial environments to early holocene warming is likely related to the cold surface waters of the baltic ice lake the proximity of the scandinavian ice sheet and associated strengthened easterlies and or extensive permafrost and stagnant ice these multi proxy studies underscore the importance of local conditions in modifying the response of individual lakes and their catchments while lateglacial vegetation was dominated by betula nana and salix shrubs and various herbs pollen and plant macrofossils suggest that betula pubescens trees became established as early as 14 13 cal ka bp in the rostov jaroslavl area in general our data sets suggest that trees migrated from the southeast to the west and then spread later to the northeast and northwest paralleling the direction of ice retreat with betula pubescens immigrating first followed by pinus sylvestris and picea abies however palaeoecological records from lake terebenskoye in the valdai highlands suggest that the arrival of picea abies preceded other trees in that area and that it colonised tundra communities as early as 12 cal ka bp since lateglacial vegetation change in north western russia was time transgressive independent measures of palaeoclimate e g chironomid based palaeotemperature estimates are needed for this region r 2007 elsevier ltd all rights reserved

high resolution chironomid inferred temperature history since ad 1580 from varved lake silvaplana switzerland comparison with local and regional reconstructions chironomids were used to reconstruct mean july air temperatures between c ad 1580 and 2001 at lake silvaplana a varved lake located in the engadine eastern swiss alps the goal of this study was to reconstruct temperature changes at near annual resolution and validate the reconstruction by comparison with records based on early instrumental data documentary proxy evidence dendrochronology geochemical biogenic silica bsi and mineralogical data quartz mica ratios at local and regional scales warmer than the climate normal ad 1961 1990 mean july air temperatures were inferred between c ad 1610 and 1662 ad 1710 and 1740 ad 1790 and 1866 ad 1940 and 1960 and ad 1990 and 2001 colder than the climate normal july air temperatures were reconstructed between c ad 1662 and 1710 ad 1740 and 1790 ad 1866 and 1919 and ad 1970 and 1990 the 420 year chironomid inferred mean july air temperature record was significantly p 0 01 related to june september jjas temperatures reconstructed from e

quantifying human induced eutrophication in swiss mountain lakes since ad 1800 using diatoms sedimentary diatom assemblages from three lakes in the southeastern swiss alps were analysed at high temporal resolution since ad 1800 altered land use patterns increasing population and exploitation through tourism are clearly reflected in annually laminated sediments of lej da san murezzan lake st moritz and lej da silvaplauna lake silvaplana diatom assemblages originally dominated by cyclotella taxa are replaced by taxa indicating higher total phosphorus tp concentrations such as asterionella formosa fragilaria crotonensis and stephanodiscus parvus in lej da la tscheppa located well above the treeline in a catchment that was hardly exposed to human impact cyclotella comensis prevails throughout the entire sediment sequence quantitative estimates of past tp concentrations were inferred using a newly developed regional diatom tp inference model based on 119 modern samples in lej da la tscheppa diatoms imply stable low tp concentrations 10 g l which can be considered as natural background concentration elevated tp levels are inferred for lej da san murezzan max 60 g l since ad 1910 and for lej da silvaplauna max 40 g l since ad 1950 corroborated by changes in sedimentary biogenic silica concentration and organic carbon content since ad 1970 improved waste water management led to a considerable reduction in tp loading in lej da silvaplauna and lej da san murezzan

chironomidae insecta diptera succession in żabieniec bog and its palaeo lake central poland through the late weichselian and holocene abstract subfossil chironomidae assemblages were studied in a sediment sequence from abieniec bog in central poland the climate history and habitat changes in the palaeo lake were reconstructed from these assemblages currently no chironomid based climate calibration set is available from poland and so past mean july air temperatures were inferred from chironomid climate calibration data sets from norway russia and switzerland during the late weichselian the three calibration functions from these data sets provided similar temperature inferences but there was some divergence in the reconstructions for the younger dryas and holocene in the late pleniglacial inferred summer air temperature was relatively low 8 12 c and the lake was oligotrophic at about 16 5 ka bp temperature rapidly rose to 15 c and assemblage diversity substantially increased during the interstadial temperature stayed at this level in the younger dryas july air temperature was only 1 2 c lower than in the interstadial as inferred from the norwegian calibration data set whereas the russian and swiss calibration functions did not indicate any temperature decrease from the beginning of the holocene taxa typical of meso eutrophic conditions dominated there was an increased abundance of phytophilous species and the assemblage composition was also influenced by changes in water level palaeotemperature reconstructions differed in their values from 8 0 to 8 7 ka bp inferences based on the swiss and russian data sets indicated a cold oscillation while reconstructions based on the norwegian data set did not show any temperature decrease after 2 5 ka bp assemblage diversity and head capsule concentrations decreased in the last millennium semi terrestrial taxa dominated except from late medieval to early modern times when shallow water species reappeared

measuring the impact of observations on the predictability of the kuroshio extension in a shallow water model abstractin this paper sequential importance sampling is used to assess the impact of observations on an ensemble prediction for the decadal path transitions of the kuroshio extension this particle filtering approach gives access to the probability density of the state vector which allows the predictive power an entropy based measure of the ensemble prediction to be determined the proposed setup makes use of an ensemble that at each time samples the climatological probability distribution then in a postprocessing step the impact of different sets of observations is measured by the increase in predictive power of the ensemble over the climatological signal during one year the method is applied in an identical twin experiment for the kuroshio extension using a reduced gravity shallow water model this study investigates the impact of assimilating velocity observations from different locations during the elongated and the contracted meandering states of the kuroshio extension optimal observation lo

temperature gradients in northern europe during the last glacial holocene transition 14 914c kyr bp interpreted from coleopteran assemblages late glacial and early holocene climatic conditions have been reconstructed for northern europe using the mutual climatic range mcr palaeoclimate method based on fossil coleopteran assemblages altogether beetle faunas from 77 sites have been analysed ranging from ireland in the west to poland and finland in the east and mcr estimates calculated the results are plotted on 16 maps each representative of a selected time slice covering the period from 14 5 14c kyr bp to 9 0 14c kyr bp eight of the maps show the mcr estimates of tmax mean temperature of the warmest month derived from each site for which data are available while the remainder show estimated tmax isotherms interpolated from these values it can be demonstrated that at times the thermal climate was fairly uniform throughout the study area whereas at others temperature gradients were much steeper than they are in the region today there also appears to be a distinct contrast between cold periods when contours trended nw se and warmer periods when contours trend w e or even ne sw the pattern of climatic changes that emerges is shown to be very different from the traditional view that has been used up to now as a template for classifying late glacial climatic events on a wide even global scale the suddenness and intensity of changes in the thermal climate may have been partially responsible for an apparent lack of equilibrium between the flora and fauna of the time and the physical environment in which they lived 1998 john wiley sons ltd

a diatom inference model for nutrients screened to reduce the influence of background variables application to varved sediments of greifensee and evaluation with measured data abstract palaeoenvironmental reconstructions of lake sediment records have been greatly facilitated by statistical comparisons with microfossil assemblages from the surface sediments of modern lakes these modern sub fossil assemblages from different lakes which are often referred to as training sets attempt to incorporate gradients of environmental parameters such as e g temperature and phosphorus are of interest for paleoenvironmental reconstruction one major assumption of quantitative palaeoenvironmental reconstructions requires that the environmental variable to be reconstructed is or is linearly related to an ecologically important determinant in the ecological system of interest and that the joint distribution with other variables in the fossil set is the same as in the training set the motivation for this paper is that present day diatom species abundances in surface sediment samples are often influenced by several environmental gradients partial least squares pls or weighted averaging partial least squares wa pls regression methods can be used to adjust species optima if the additional pls components which are orthogonal to previous pls components are included this paper tests a reproducible approach for reducing the influence of background variables within a diatom training set to produce a screened training set which focuses on the variable of interest in our example total phosphorus tp is the variable of interest the initial training set consists of modern swiss lakes along an elevation gradient spanning 2005 m 334 to 2339 m a s l which follows a tp gradient from 522 to 3 g l 1 however high elevation lakes are not distributed equally along the tp gradient they are meso oligotrophic because high elevation eutrophic lakes are rare in switzerland this leads to a potential confounding effect between the elevation and the nutrient gradients these higher elevation lakes were selectively excluded using monte carlo permutation tests until the conditional effect with respect of covariables of elevation was no longer significantly related to the relative abundance of diatoms the initial and screened inference models for log tp were applied to fossil assemblages from varved sediments at greifensee switzerland which cover the past century the evaluation of the reconstructions with measured tp 1954 1994 demonstrates that the smaller screened subset performs better than the larger more heterogeneous initial data set when the same number of components are included the slope of the relation between measured and inferred log tp changed significantly for the reconstructions using partial least squares with one and two components and for reconstruction using weighted averaging partial least squares with two components according to our interpretation the accuracy of the reconstructions improved because modern diatom abundances of the smaller subset are controlled mainly by log tp and lakes are more equally distributed along the log tp gradient this approach of reducing the influence of background variables is applicable to other heterogeneous training sets such as merged training sets in order to homogenise the background variables and to maintain the gradient of interest

delayed hydrological response to greenland cooling at the onset of the younger dryas in western europe during the younger dryas cold event about 12 800 years ago environmental change in western europe seems to occur 170 years after cooling over greenland lake sediment analyses confirm this delay and suggest european hydrological and vegetation change occurred only after the build up of sea ice in the north atlantic pushed the westerly wind system south

late weichselian environmental change in southern sweden and denmark a synthesis is presented of the envronmental and climatic variations that are inferred to have occurred in southern sweden up to latitude 59 n and denmark during the weichselian late glacial 14 9 ka bp the chronology and characteristics of the main phases of deglaciation sea level change periglacial activity soil development vegetation cover and climate change are summarised a curve representing the main changes in temperature including quantitative estimates based upon beetle data and using the mutual climatic range method is presented

direct comparison of uk temperatures and greenland snow accumulation rates 15000 12000 yr ago a palaeotemperature record based on fossil coleopteran evidence and dated by accelerator mass spectroscopy ams 14c determinations on plant macrofossils has been obtained for the last glacial interglacial transition from the site of gransmoor in eastern england calibration of the radiocarbon measurements enabled a direct comparison to be made between this palaeotemperature curve and the snow accumulation record from the gisp 2 greenland ice core the similarity between the two data sets suggests a degree of correspondence in the pattern and timing of climatic change in greenland and the british isles at the end of the last cold stage

temperature and effective moisture variability in southern finland during the holocene quantified with midge based calibration models effective moisture and temperature dynamics during the late glacial and holocene were reconstructed from fossil midge diptera nematocera assemblages in lake hirvijarvi southern finland quantitative inferences were performed using midge based transfer functions for water depth and mean july air temperature the aim was to identify major trends in holocene climate development the results were generally consistent with patterns found in previous investigations from nearby regions and indicated some distinct differences in palaeoclimate between southern and northern finland the results indicate that the region was characterised by a very cold late pleistocene cool and moist but drying early holocene warm and moist mid holocene and cool and moist late holocene a progressive trend of increasing lake levels from the early holocene towards the present was evident the results of this study provide implications for regional differences in effective moisture between southern and northern finland during the holocene copyright 2010 john wiley sons ltd

holocene changes in atmospheric circulation recorded in the oxygen isotope stratigraphy of lacustrine carbonates from northern sweden the oxygen isotope composition of local precipitation delta 18 o p is reconstructed from carbonate lake sediment components in a sediment core covering the last 10000 calendar years from lake tibetanus a small hydrologically open groundwater fed take in the abisko area northern sweden comparison of the delta 18 o p history with a pollen based palaeotemperature record from the same core clearly reveals pronounced deviations from the normally expected temporal delta 18 o p temperature relation so called dansgaard relation that may be a function of changing oceanicity the transition from relatively moist maritime conditions in the early holocene to a much drier climate after 6500 cal bp is reflected by major changes in forest extent and composition as recorded by pollen and plant macrofossil data at the time of maximum influence of westerly air mass circulation high zonal index c 9500 cal bp brought about by high summer insolation and enhanced meridional pressure gradients delta 18 o p at lake tibetanus was about 2 higher than would be predicted by the modem isotope temperature relation the occurrence of long term changes in delta 18 o p temperature relations which are more sensitive measures of palaeoclimate than either delta 18 o p or temperature alone needs to be taken into account when extracting palaeoclimatic information from continental oxygen isotope records less

quantitative multiproxy assessment of long term patterns of holocene environmental change from a small lake near abisko northern sweden quantitative reconstructions are made of holocene changes in climatic and environmental conditions from analyses of pollen chironomids and diatoms in identical stratigraphic levels of a sediment c

thousand years of climate change reconstructed from chironomid subfossils preserved in varved lake silvaplana engadine switzerland abstract fossil chironomids non biting midges from varved lake silvaplana switzerland were used to reconstruct climate mean july air temperatures during the last millennium at the beginning of the record corresponding to the last part of the medieval climate anomaly mca here the period between ca 1032 and 1262 ad the chironomid inferred mean july air temperatures were 1 c warmer p

a review of the history of the baltic sea 13 0 8 0 ka bp abstract the dynamic history of the baltic sea during the millennia following the last deglaciation has been one of the main topics for many generations of quaternary geologists around the baltic sea based on the present state of knowledge and certain hypotheses a model for the development during the baltic ice lake yoldia sea and ancylus lake stages are presented the oresund strait was the threshold of the initial stage of the baltic ice lake and was eroded down to bedrock as a result of the isostatic uplift the emerging threshold forced the baltic ice lake to rise above sea level at ca 12 0 ka bp this gradual up damming ended at ca 11 2 ka bp when the large glacial lake was lowered 5 10m by possible subglacial drainage at mt billingen a glacial readvance during the younger dryas ended a ca 400 year long land bridge between sweden and the continent by blocking the former drainage route once again the baltic ice lake had to rise above sea level to be drained over the oresund strait at ca 10 5 ka bp a gradual ice recession began and 200 years later when the receding ice sheet could not withhold the up dammed water masses the final drainage of the baltic ice lake occurred which rapidly lowered the water level within the baltic basin with ca 25 m and ended the baltic ice lake stage the next stage the yoldia sea was characterized by a complex pattern of relative sea level changes with large differences within the baltic basin a very restricted baltic sea in the south and thus an extensive landbridge at ca 9 9 ka bp a short 100 200 years saline ingression is seen in the baltic sediment records from stockholm in the north to the southernmost parts of the yoldia sea the gradually shallower strait in south central sweden the narke strait ended the saline influence 300 400 years later the two remaining outlets west of lake vanern gota alv and otteid steinselva had become too shallow to swallow the outflowing yoldia sea waters at this stage the baltic lake vanern level could thus not fall in pace with the relative sea level fall outside the outlet areas this was the isolation of lake vanern and the baltic from the sea and the beginning of the ancylus lake since the water depth of the larger gota alv outlet had to be more or less maintained the ancylus lake level had to rise in pace with the uplift of the outlet region this caused a significant and rapid transgression 10 30 m in ca 300 years in the southern baltic which flooded large areas with recently immigrated pine forests since the oresund strait during the yoldia sea stage had been uplifted more than southerly areas the ancylus transgression ended with a new drainage pathway at ca 9 2 ka bp through the darss sill area in the southern baltic and northwards through the store belt strait this so called dana river had cut off the former large land bridge the quaternary deposits of this new threshold were eroded and a fairly rapid regression set in at ca 9 0 ka bp the dana river had eroded down to the sea level which isolated lake vanern from the ancylus lake and created a land bridge between southern sweden and northwards ca 800 years later when the sea level rose above the oresund threshold marine water could enter the baltic and at ca 8 0 ka bp brackish water characterized the southern baltic this marks the end of the ancylus lake

elevation changes of the fennoscandian ice sheet interior during the last deglaciation the dynamics of ice sheet interiors during the last deglaciation are poorly constrained hindering evaluation of ice sheet models we provide direct evidence of fennoscandian ice sheet fis interior behaviour during deglaciation through surface exposure dating our results demonstrate early thinning of the fis prior to the younger dryas yd 12 8 11 7 ka interior thinning in central norway was concurrent with retreat along the coastline exposing ice free mountainous tracts potentially as early as 20 15 ka the fis then formed moraines in these ice free tracts during the yd this is contrary to current hypotheses advocating a landscape fully covered by cold inactive ice during this period present empirical and model reconstructions fail to capture rapid interior down wastage increasing uncertainties in ice sheet volume estimates and sea level contributions

timing and east west correlation of south swedish ice marginal lines during the late weichselian abstract the retreat of the late weichselian ice sheet over the southern part of sweden is marked along the southwest coast by distinct marginal moraine ridges their timing can directly and indirectly be assessed based on a number of radiocarbon dates and pollen stratigraphic investigations on lake sediment sequences adjacent to the ice marginal lines along the southeastern side of the peninsula the ice recession has been reconstructed based on a combination of clay varve chronology pollen and radiocarbon stratigraphy a morphological correlation of ice marginal lines between the west and east coast is problematic since the distinct west coast moraines cannot be followed through the central part of the peninsula towards the east coast this paper is an attempt to reconstruct an age equivalent west east extension of the ice recession lines on the basis of existing data sets for our correlation we use calibrated radiocarbon ages for ice marginal deposits on the west coast and compare these with a partly radiocarbon dated clay varve chronology on the east coast we conclude that the two oldest moraines on the west coast formed at 18 000 16 000 and 15 400 14 500 cal yr bp respectively during the following rapid deglaciation which may have coincided with the beginning of the bolling pollen zone large parts of southernmost sweden became ice free except for higher elevated areas where stagnant ice remained for another 400 500 yr a best guess is that the formation of the next younger ice marginal lines may have occurred at 14 400 14 200 14 200 and 13 400 cal yr bp and during the younger dryas cold event

similarities and discrepancies between chironomid and diatom inferred temperature reconstructions through the holocene at lake 850 northern sweden similarities and discrepancies between chironomid and diatom inferred temperature reconstructions through the holocene at lake 850 northern sweden

interannual variability of the kuroshio extension system and its impact on the wintertime sst field altimetry data from the first 7 yr topex poseidon t p mission october 1992 september 1999 are analyzed to investigate the interannual variability in regions of the kuroshio extension and its southern recirculation gyre large scale interannual changes of the kuroshio extension system are characterized by the oscillation between an elongated state and a contracted state in the elongated state the kuroshio extension has a larger eastward surface transport a greater zonal penetration and a more northerly zonal mean path all these characteristics are closely connected to the presence of an intense zonally elongated southern recirculation gyre in its contracted state the kuroshio extension has a smaller eastward surface transport a more southerly mean path and is accompanied by a weaker southern recirculation gyre during the t p period the kuroshio extension changed from the elongated state in 1992 93 to the contracted state in 1996 97 and back to the elongated state since late 1997 in addition to these large scale changes the mesoscale eddy field also exhibited prominent interannual changes in the kuroshio extension region in the upstream region between the izu ridge and the shatsky rise the eddy kinetic energy level was generally low while the kuroshio extension was in its elongated state and high while in the contracted state downstream of the shatsky rise on the other hand the eke level was high low when the kuroshio extension was in the elongated contracted state the large scale interannual changes in the kuroshio extension system have a significant impact on the regional wintertime sst anomaly field the warm cold wintertime sst anomalies tend to persist in years when the kuroshio extension is in its elongated contracted state a diagnostic analysis of the surface ocean heat balance indicates that the nonseasonal geostrophic advection by the ocean circulation works to reduce increase the wintertime sst anomalies when the kuroshio extension changes from an elongated contracted state to a contracted elongated state the sst anomalies associated with the large scale changes of the kuroshio extension have an area averaged peak topeak amplitude of 18c and appear independent of the interannual sst changes in the tropical pacific ocean

late glacial and early holocene environmental and climatic change at lake tambichozero southeastern russian karelia abstract high resolution lithostratigraphy mineral magnetic carbon pollen and macrofossil analyses and accelerator mass spectrometry 14c measurements were performed in the study of a sediment sequence from lake tambichozero southeastern russian karelia to reconstruct late glacial and early holocene aquatic and terrestrial environmental changes the lake formed ca 14 000 cal yr b p and the area around the lake was subsequently colonized by arctic plants forming patches of pioneer communities surrounded by areas of exposed soil a minor rise in lake productivity and the immigration of betula pubescens occurred ca 11 500 cal yr b p the rise in summer temperatures probably led to increased melting of remnant ice and enhanced erosion the distinct increase in lake productivity and the development of open betula populus forests which are reconstructed based on plant macrofossil remains indicate stable soils from 10 600 cal yr b p onward pinus and picea probably became established ca 9900 cal yr b p

the role of seasonality in abrupt climate change abstract a case is made that seasonality switches dominated by wintertime were instrumental in abrupt climate changes in the north atlantic region during the last glaciation and into the holocene the primary evidence comes from mismatches between mean annual temperatures from greenland ice cores in comparison with snowline changes in east greenland northern europe and north america the most likely explanation is a shutdown or reduction in strength of the conveyor this allows the spread of winter sea ice across the north atlantic thus causing the northern region to experience much colder winters because they mimic the greenland temperature rather than the snowline signal changes in the atlantic intertropical convergence zone and the asian monsoon may also share a winter linkage with greenland thus the paleoclimate record is consistent with the notion that a huge continental sector of the northern hemisphere stretching from greenland to asia was close to an extreme winter threshold during much of the last glaciation winter climate crossed this threshold repeatedly with marked changes in seasonality that may well have amplified and propagated a signal of abrupt change throughout the hemisphere and into the tropics

multiple equilibria and low frequency variability of the wind driven ocean circulation abstract the link between low frequency time dependent variability and the existence of multiple unstable steady state solutions in a reduced gravity quasigeostrophic ocean model for the midlatitude wind driven circulation is investigated it is shown that a sequence of successive symmetry breaking pitchfork bifurcations lead to multiple equilibria that differ from each other primarily in the elongation of the recirculation cell in the amount of meandering present in the intergyre jet and in a north south shift in the eastward jet the elongation of the recirculation cells and the meandering of the jet play compensating roles in the establishment of the global energy and vorticity balance the solutions also have distinct energy levels but general agreement between them and the bumps in a histogram of the total energy obtained from a 1200 yr time dependent simulation is not found nevertheless a substantial fraction of the variance 30 can be accounted for by four coherent structures that capture th