nocturnal low level jet and atmospheric streams over the rain shadow region of indian western ghats spatial and temporal characteristics of a nocturnal low level jet llj on the east side of the western ghat mountain range over india s west coast and processes leading to the formation of the jet are discussed the boundary layer jet has a regional scale extent as revealed by high resolution advanced research weather research and forecasting arw model simulations and contributes to the formation of atmospheric streams of water vapor over the selected land regions simulations indicate that the formation of llj is mainly attributed to the baroclinicity of the valley atmosphere due to the gently rolling terrain which is assisted by the persistence of an unstable residual layer above the developing stable boundary layer in the valley and cooling over the slopes prior to the formation of llj the boundary layer is dominated by deep roll circulations the llj followed a gust front zone associated with a mountain wave the low level flow below the jet is decoupled from the upper level flow as a result of strong vorticity below the jet and suppression of turbulence at the jet core a conceptual model for the boundary layer interactions dynamics of the mountain wave llj etc are proposed for western ghat region

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

vegetation and climate history of northern japan inferred from the 5500 year pollen record from the oshima peninsula sw hokkaido this study reconstructs middle and late holocene vegetation and climate dynamics in the oshima peninsula sw hokkaido using the published method of biome reconstruction and modern analogue technique applied to the yakumo pollen record 42 17 03 n 140 15 34 e spanning the last 5500 years two previously published matrices assigning japanese plant pollen taxa to the major vegetation types biomes are tested using a newly compiled dataset of 78 surface pollen spectra from hokkaido with both matrices showing strengths and weaknesses in reconstructing cool mixed and temperate deciduous forests of hokkaido the results suggest the necessity to consider the whole list of identified terrestrial pollen taxa for generating robust vegetation reconstructions for northern japan applied to the fossil pollen data both biome reconstruction approaches demonstrate consistently that oak dominated cool mixed forest spread in the study region between 5 5 and 3 6 cal ka bp and was subsequently replaced by beech dominated temperate deciduous forest the pollen based climate reconstruction suggests this change in the vegetation composition was caused by a shift from cooler and drier than present climate to warmer and wetter similar to modern conditions about 3 6 cal ka bp comparing the pollen based reconstruction results with the published marine records from the nw pacific the reconstructed vegetation and climate dynamics can be satisfactorily explained by the greater role played by the warm tsushima current in the sea of japan and in the tsugaru strait during the middle and late holocene an increase in sea surface temperatures west and south of the study site would favour air temperature rise and moisture uptake and cause an increase in precipitation and snow accumulation in the western part of hokkaido during the late holocene

gravity wave excitation during the coastal transition of an extreme katabatic flow in antarctica abstractthe offshore extent of antarctic katabatic winds exerts a strong control on the production of sea ice and the formation of polynyas in this study we make use of a combination of ground ba

nocturnal meso beta basin and katabatic flows on a midlatitude island abstract a mesoscale simulation for the island of majorca spain in the western mediterranean sea is used to study the nocturnal system of winds under weak synoptic pressure gradients a very high vertical resolution is used in the first 500 m above ground level to characterize with large detail the thin circulations close to ground namely basin and katabatic flows it is found that the island the basin and the slope scales interact strongly especially when a quasi steady state is reached in the second part of the night a high mountain range creates a high pressure area upwind where local winds can develop katabatic flows converge to the valleys where they interact with a cold pool which is advected slowly to sea by the land sea night breeze effect combined with a topographic forcing the katabatic flows experience small entrainment at the top and have well defined characteristics the results are partially confirmed by the observations and some satellite images

atmospheric radiocarbon calibration to 45 000 yr b p late glacial fluctuations and cosmogenic isotope production more than 250 carbon 14 accelerator mass spectrometry dates of terrestrial macrofossils from annually laminated sediments from lake suigetsu japan provide a first atmospheric calibration for almost the total range of the radiocarbon method 45 000 years before the present the results confirm the recently revised floating german pine chronology and are consistent with data from european and marine varved sediments and combined uranium thorium and carbon 14 dating of corals up to the last glacial maximum the data during the glacial show large fluctuations in the atmospheric carbon 14 content related to changes in global environment and in cosmogenic isotope production

application of two new stereographic projection techniques to slope stability problems abstract slope instabilities were observed in the benches of the alipasa open pit albite mine in the menderes massif forming one of the tectonic zones of the anatolides in turkey tension crack patterns observed in the berms were formed depending on the discontinuity planes cutting each other in the orthogneiss rock unit two new stereographic projection methods in the stability analyses were applied by considering two cases the first one that used the overlay linear element process based on the geometrical conditions relating to the ground movement directions on the survey monuments dip direction lines of the foliation planes and sloped bench faces and the second one that based on the determination of relationships between tension cracks on the upper slope face and discontinuity sets into the slope forming release and lower surfaces of the sliding blocks it is kinematicly investigated with the overlay linear element process whether an agreement among these parameters is presence or not if there is this case is indicated that the planar sliding was occurred on the foliation plane beforehand or in a critical balance in terms of the planar sliding of a slope the proposed method will be useful to determine quickly and efficiently whether the relationships between the discontinuity sets into the rock masses and tension cracks on the berms or upper slope faces in an open pit or not in addition whether the angular values from the kinematic analysis are in agreement with the ones directly measured from the field was also investigated this study involved making stability assessment of the already failed and standing sloped bench faces in the open pit using the stereographic projection techniques and software

the impact of the north atlantic ocean on the younger dryas climate in northwestern and central europe the main results of multiproxy climate reconstructions for the younger dryas and experiments carried out with an atmospheric general circulation model are discussed quantitative temperature inferences for northwestern and central europe show that winter conditions were remarkably extreme with values of 20 30 c below that of today annual temperature ranges with a continental signature 30 34 c were reconstructed for the entire study area compared with today the greatest cooling was experienced in the seaboard area the comparison of the climate reconstructions and simulation experiments indicates that sea ice in the north atlantic ocean played a decisive role in the climate of the study area by cooling the surface air temperatures and by controlling the position of the storm track surface air circulation was westerly even during younger dryas winters a slight northward shift of the mean atlantic sea ice margin during winter may explain the proposed subdivision of the younger drays into a phase of maximum cold and humidity succeeded by a less cold and relatively dry phase 1998 john wiley sons ltd

some aspects of the variation with time of katabatic flow over a simple slope features of the variations in katabatic flow along a simple slope in athens greece are examined both observationally and from a simplified theoretical basis when undisturbed periods of established flows are selected it is observed that the velocity and temperature fluctuations reveal characteristics which are in agreement with the theory proposed by fleagle interesting implications of the theory are discussed such as the effects of prescribing a decreasing cooling rate throughout the night or of taking into account the vertical structure of the katabatic layer

transient cold air drainage down a shallow valley abstractdrainage of cold air down a small valley and associated near surface wind maxima are examined from 20 stations with sonic anemometers at 1 m and from a 20 m tower that includes six sonic anemometers in the lowest 5 m deployed in the shallow cold pool experiment scp the small valley is about 270 m wide and 12 m deep with a downvalley slope of 2 3 the momentum budget indicates that the flow is driven by the buoyancy deficit of the flow and opposed primarily by the stress divergence while the remaining terms are estimated to be at least an order of magnitude smaller this analysis also reveals major difficulties in quantifying such a budget due to uncertainties in the measurements sensitivity to choice of averaging time and sensitivity to measurement heights wind maxima occur as low as 0 5 m in the downvalley drainage flow the lowest observational level the downvalley cold air drainage and wind maxima are frequently disrupted by transient modes that sometimes lead to significant vertical mi

analysis of gravity waves generated at the top of a drainage flow abstract drainage or katabatic flows are common mesoscale circulations established as a result of differential radiative cooling of near surface air masses in sloping terrain the initial irruption of these flows with sudden shifts in wind speed and direction may result in vertical displacements of air parcels from their equilibrium position which prove to be a common source of internal gravity waves this paper illustrates this mechanism and describes the main features of the oscillations following the study of observational data gathered throughout one night during the stable atmospheric boundary layer experiment in spain 2006 sables2006 field campaign pressure differences measured by microbarometers set at different levels of a tower help to interpret the evolution of other atmospheric variables provide a detailed picture of the irruption of a drainage current and reveal the formation of gravity waves at its top the main parameters of the waves are derived from wavelet cross correlation of p

climatic variability in the southwest pacific during the last termination 20 10 kyr bp the degree to which palaeoclimatic changes in the southern hemisphere co varied with events in the high latitude northern hemisphere during the last termination is a contentious issue with conflicting evidence for the degree of teleconnection between different regions of the southern hemisphere the available hypotheses are difficult to test robustly however because there are few detailed palaeoclimatic records in the southern hemisphere here we present climatic reconstructions from the southwestern pacific a key region in the southern hemisphere because of the potentially important role it plays in global climate change the reconstructions for the period 20 10 kyr bp were obtained from five sites along a transect from southern new zealand through australia to indonesia supported by 125 calibrated c 14 ages two periods of significant climatic change can be identified across the region at around 17 and 14 2 cal kyr bp most probably associated with the onset of warming in the west pacific warm pool and the collapse of antarctic ice during meltwater pulse 1a respectively the severe geochronological constraints that inherently afflict age models based on radiocarbon dating and the lack of quantified climatic parameters make more detailed interpretations problematic however there is an urgent need to address the geochronological limitations and to develop more precise and quantified estimates of the pronounced climate variations that clearly affected this region during the last termination c 2005 elsevier ltd all rights reserved

tracking aquatic change using chlorin specific carbon and nitrogen isotopes the last glacial interglacial transition at lake suigetsu japan joint carbon and nitrogen isotope measurements were made from chlorins chlorophyll a phaeophytin a and pyrophaeophytin a extracted from the last glacial interglacial transition sediments of lake suigetsu central japan these data highlight both the potential and difficulty of using chlorin specific isotopes to track aquatic change from lake sediments 13c and 15n of the three chlorins show coherent patterns with time supporting the theory that phaeophytin a and pyrophaeophytin a are early diagenetic products of chlorophyll a and that despite this transition their isotopic signatures remain intact however our data suggest that the isotopic composition of phaeophytin a and pyrophaeophytin a can be imprecise proxies for the isotope composition of chlorophyll a possibly owing to the complex array of factors which affect the synthesis transformation and sedimentation of these phaeopigments in nature the total accumulation of organic matter in lake suigetsu appears to be controlled by the balance of allocthonous and authocthonous material as reflected by the c n ratio however both bulk organic and chlorin specific 13c show similar changes suggesting that the first order variability in bulk organic 13c reflects aquatic change by contrast there is no similarity between chlorin and bulk 15n suggesting that interpretation of bulk 15n in this setting is compromised by diagenetic alteration the isotopic composition of chlorins are interpreted to reflect the response of aquatic primary productivity to post glacial environmental change however further research into the synthesis and transformation of chlorins in the modern environment is required in order to facilitate a more rigorous approach to interpreting isotope ratios in chlorins extracted from sediments

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

unstable younger dryas climate in the northeast north atlantic the younger dryas stadial greenland stadial 1 has long been recognized in proxy records throughout the north atlantic region as a stable cool period that started and ended abruptly however modeling experiments in which the younger dryas cooling was forced by meltwater predict much more unstable climatic conditions compared to the proxy records here we present evidence of a climatically unstable younger dryas based on a decadal resolution marine proxy record from the norwegian continental shelf this record shows that the north atlantic was characterized in the early younger dryas by arctic water and an increasing accumulation of fresh surface water that peaked at 12 500 calendar yr b p for 300 yr during the late younger dryas the sea surface temperatures fluctuated between glacial values 2 c and interglacial values 10 c on a subdecadal to multidecadal time scale this period of extreme instability preceded the more stable and warm holocene starting ca 11 500 calendar yr b p these results are consistent with modeling experiments that link the younger dryas climate changes to fluctuations of the north atlantic thermohaline circulation

evidence for last interglacial chronology and environmental change from southern europe establishing phase relationships between earth system components during periods of rapid global change is vital to understanding the underlying processes it requires records of each component with independent and accurate chronologies until now no continental record extending from the present to the penultimate glacial had such a chronology to our knowledge here we present such a record from the annually laminated sediments of lago grande di monticchio southern italy using this record we determine the duration 17 70 0 20 ka and age of onset 127 20 1 60 ka b p of the last interglacial as reflected by terrestrial ecosystems this record also reveals that the transitions at the beginning and end of the interglacial spanned only 100 and 150 years respectively comparison with records of other earth system components reveals complex leads and lags during the penultimate deglaciation phase relationships are similar to those during the most recent deglaciation peaks in antarctic warming and atmospheric methane both leading northern hemisphere terrestrial warming it is notable however that there is no evidence at monticchio of a younger dryas like oscillation during the penultimate deglaciation warming into the first major interstadial event after the last interglacial is characterized by markedly different phase relationships to those of the deglaciations warming at monticchio coinciding with antarctic warming and leading the atmospheric methane increase diachroneity is seen at the end of the interglacial several global proxies indicate progressive cooling after 115 ka b p whereas the main terrestrial response in the mediterranean region is abrupt and occurs at 109 50 1 40 ka b p

the development of antarctic katabatic winds and implications for the coastal ocean the influence of katabatic winds on the antarctic coastal waters is examined by using simple models of the ocean and atmosphere a katabatic flow model incorporating coriolis dynamics is solved analytically and another with nonlinear friction is solved numerically to provide wind stress to a two layer coastal ocean model the resulting solutions are evidently the first to incorporate coriolis terms with a thermodynamic equation that includes compressional warming effects the emphasis in this paper is on delineating the parameters that control the relative adjustment of the katabatic wind into alongshore and offshore components by including nonlinear friction it is shown that steeper slopes and weaker stratification tend to direct the wind more toward the ocean it is further demonstrated that the katabatic forcing supports the strong polar easterlies winds from the east along the periphery of the continent and that the offshore extent should be dependent on the atmospheric rossby deformation radius the ocean model shows that significant downwelling occurs at the coast while upwelling is predicted at a distance of the order of the ocean rossby radius an alongshore coastal jet from the east is found in the model and is evidently the manifestation of the east wind drift the upwelling offshore may be a significant aspect of polynya formation and maintenance of the antarctic divergence zone and contribute to the biological productivity of the region

asynchronous climate change between new zealand and the north atlantic during the last deglaciation climatic fluctuations recorded in antarctica and greenland during the last deglaciation 18 10 ka differ markedly in their timing it remains controversial whether local climate fluctuations recorded in southern mid latitudes relate primarily to northern or southern polar records we present multiproxy results from new zealand that show strong evidence for a minor cooling or slowdown in the rate of warming at the time of the north atlantic late glacial interstadial the younger dryas chronozone in new zealand was a period of resumed warming and increased westerly airflow differences between the hemispheres at this time were probably due to a reorganization of the thermohaline circulation system and associated changes in the meridional temperature gradient

the structure of katabatic flows down a simple slope an analysis of the katabatic flow structure is presented based on data collected along a simple slope over a two month period four meteorological stations were deployed along the nearly two dimensional east slope of mt hymettos in greece the study focuses on the momentum and energy budgets of the flows during carefully selected stationary periods with negligible ambient winds in order to achieve a proper selection the mean features of the observed flows are presented along with their response to external winds the observed profiles are successfully compared with the theoretical prandtl profiles bulk quantities of the katabatic layer are compared with proposed experimental values in order to check the representativity of the observed flows these comparisons offer a further test of theoretical considerations and assist in discussions of processes affecting mean flow features the flows were 20 m deep with velocities 1 2 m s 1 during steady state periods the katabatic acceleration was mainly balanced by the surface friction the contribution of advective terms being small the estimated interfacial drag was less important than the surface drag which proved large compared with usually suggested values within the experimental uncertainties values of the drag coefficient of the order of 10 2 seem appropriate the steady state energy balance showed that the downslope advection balanced the turbulent heat flux to the ground surface

last glacial interglacial vegetation and environmental dynamics in southern siberia chronology forcing and feedbacks abstract radiocarbon dated pollen and diatom records from lake kotokel in southern siberia help to reconstruct the environmental history of the area since 47 kyr bp pollen spectra composition and reconstructed biome scores suggest predominance of a tundra steppe vegetation and variable woody cover 5 20 between 47 and 30 kyr bp indicating generally a harsh and unstable climate during this interval conventionally regarded as the interstadial within the last glacial the short term climate amelioration episodes in the glacial part of the records are marked by the peaks in taiga and corresponding minima in steppe biome scores and appear synchronously with the hemispheric temperature and precipitation changes recorded in the greenland ice cores and chinese stalagmites transition to full glacial environments occurred between 32 and 30 kyr bp the interval at 30 24 kyr bp was probably the driest and coldest of the whole record as indicated by highest scores for steppe biome woody coverage

vegetation and climate changes around the lama lake taymyr peninsula russia during the late pleistocene and holocene a continuous lacustrine sequence from the western part of lama lake 69 32 n 90 12 e complemented by a peat sequence from the lake catchment provides the first detailed environmental reconstruction for the late glacial and holocene on the taymyr peninsula scarce steppe like communities with artemisia poaceae and cyperaceae dominated during the late glacial tundra like communities with betula nana dryas and salix grew on more mesic sites there are distinct climatic signals which may be correlated with the bolling and allerod warming and middle and younger dryas cooling the late glacial preboreal transition at about 10 000 14c yr bp was characterized by changes from predominantly open herb communities to shrub tundra ones larch forest might have been established as early as 9700 9600 14c yr bp whilst shrub alder came to the area ca 9500 9400 14c yr bp and spruce did not reach area before ca 9200 14c yr bp spruce larch forests with shrub alder and tree birch dominated the vegetation around the lama lake from ca 9000 14c yr bp dwarf birch communities were also broadly distributed the role of spruce in the forest gradually decreased after 4500 14c yr bp the vegetation cover in the lama lake area became similar to the modern larch spruce forest ca 2500 14c yr bp a pollen based biome reconstruction supports a quantitative interpretation of the pollen spectra climate reconstructions obtained with information statistical and plan functional type methods show very similar trends in reconstructed july temperature since ca 12 300 14c yr bp while precipitation anomalies are less coherent especially during the late glacial holocene transition

pollen event stratigraphy of the varved sediment of lake suigetsu central japan from 15 701 to 10 217 sg vyr bp suigetsu varve years before present description interpretation and correlation with other regions high resolution pollen data average interval between samples 15 years are reported on part of a varved sediment core from lake suigetsu japan spanning the interval 15 701 to 10 217 sg vyr bp suigetsu varve years before present this new record is compared with a previously proposed event stratigraphy based on pollen based reconstructed changes of mean annual temperature the deglacial climate history reconstructed at lake suigetsu resembles that observed in the north atlantic although the major boundaries of pollen zones are asynchronous with those in the north atlantic event stratigraphy by several centuries the onset of the late glacial interstadial occurred earlier in japan than in the north atlantic this demonstrates that the climate in japan was closely linked to the low latitude pacific sea surface temperatures that first reacted to orbital forcing conversely the onset of the subsequent cold reversal phase in japan lagged that of the north atlantic younger dryas by several centuries the duration of this cold phase was about the same as the younger dryas event but the amplitude was much reduced 4 2 c in mean annual temperature these findings support the hypothesis that this pan hemispheric cooling event was triggered by north atlantic forcing most probably by a meltwater pulse and an associated change in the north atlantic thermohaline circulation however the mechanism which transmitted the change in the north atlantic to the far east is unknown

climate shift at 4400 years bp evidence from high resolution diatom stratigraphy effingham inlet british columbia canada abstract diatom paleoecology and climatic interpretations were assessed from a 15 cm long laminated sediment slab extracted from an anoxic fjord in southwest british columbia the slab spans at least 62 years of deposition determined from counting varves and is dated at approximately 4400 years bp the slab shows a sedimentation pattern where thick diatom rich varves at the bottom become thinner and more silty toward the top thin section analysis reveals that the thicker varves contain a distinct succession of diatoms representing seasonal deposition throughout each year annual scale subsampling shows that the abundance of coastal marine diatoms namely a weakly silicified form of skeletonema costatum decreased over the 62 year period while benthic and brackish water diatoms such as planothidium delicatulum and achnanthes minutissima increased with the concomitant increase in silt the increase in such benthic species and silt along with the presence of 1 cm thick nonlaminated intervals is interpreted to represent deposition during progressively increasing precipitation over time these sedimentation patterns and changes in diatom assemblages may signify a change in the relative intensities of the aleutian low al and north pacific high nph atmospheric pressure systems thicker diatomaceous varves at the bottom of the slab reflect a stronger nph system with associated coastal upwelling and enhanced diatom production the thinner silty varves at the top of the slab suggest that the al system was prevalent resulting in greater amounts of precipitation and reduced upwelling the findings of this study show that significant natural environmental change can occur within a twenty year time frame and can provide a basis for the study of modern change in the ocean atmosphere system over the northeast pacific ocean

an extended and revised lake suigetsu varve chronology from 50 to 10 ka bp based on detailed sediment micro facies analyses abstract lake suigetsu japan is a key site for radiocarbon 14c calibration and palaeo environmental reconstruction in east asia here we present a description of the sediment micro facies which in combination with a new approach to varve interpolation allows construction of a revised varve based chronology that extends the previous 2012 varve based chronology by 10 ka back to 50 ka bp challenges in varve counting and interpolation which were previously discussed in detail only for the last glacial interglacial transition are described here back to 50 ka bp furthermore the relative merits of varve counting by xrf scanning and by thin section microscopy are discussed facies analysis reveals four facies zones their transitions driven by both local and climatic controls the lamination quality of the sediment is highly variable and varve interpolation reveals that in the analysed time interval on average only 50 of the annual cycles are represented by seasonal layers in the remaining years seasonal layers are indistinguishable i e either did not form or were not preserved for varve interpolation an advanced version of the varve interpolation program was used which enabled the construction of the longest purely varve dated chronology published despite long intervals of poor lamination quality the calculated interpolation uncertainty is 8 9 and 4 6 which is well within expectations considering the high degree of interpolation and the length of the record

review of wave turbulence interactions in the stable atmospheric boundary layer flow in a stably stratified environment is characterized by anisotropic and intermittent turbulence and wavelike motions of varying amplitudes and periods understanding turbulence intermittency and wave turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans the stable atmospheric boundary layer sabl commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces or even daytime over snow and ice surfaces and when warm air is advected over cold surfaces intermittent turbulence intensification in the sabl impacts human activities and weather variability yet it cannot be generated in state of the art numerical forecast models this failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random turbulence generation in a stably stratified flow in which wave turbulence interaction is a potential mechanism for turbulence intermittency a workshop on wave turbulence interactions in the sabl addressed the current understanding and challenges of wave turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent turbulence from the perspectives of theory observations and numerical parameterization there have been a number of reviews on waves and a few on turbulence in stably stratified flows but not much on wave turbulence interactions this review focuses on the nocturnal sabl however the discussions here on intermittent turbulence and wave turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general

seasonally specific responses of the east asian monsoon to deglacial climate changes the deglacial meltwater pulse in the north atlantic that induced the younger dryas event also prompted climate cooling in east asian monsoon regions such as japan and coastal mid latitude china however very little is understood about the mechanism that can transmit changes in the north atlantic to the far east here we show that the shutdown of the north atlantic thermohaline circulation brought about significantly lower temperatures and higher precipitation in the japanese winter whereas the change in the japanese summer climate was considerably smaller the cooling of the siberian air mass seems to have caused an increased pressure gradient between siberia and the west pacific in winter intensifying the winter monsoon the mongolian high pressure system and the westerly jet stream played an important role in the teleconnection in contrast the warming at the onset of the late glacial interstadial gi 1 bolling allerod in the west pacific did not have season specific features implying that the principal driving mechanism of this warming event may lie in a pan hemispheric or global factor such as insolation changes

an idealized modeling study of nocturnal cooling processes inside a small enclosed basin 1 the advanced regional prediction system is utilized to examine the evolution of the nocturnal boundary layer observed within arizona s meteor crater a small enclosed basin on quiescent nights during the 2006 meteor crater experiment field campaign two aspects of the observed basin atmosphere are investigated a quasi steady state three layer temperature structure including an isothermal layer away from the basin floor and the intrusion of a regional scale cold air drainage flow into the basin in general the two dimensional numerical simulations are able to reproduce the salient features of the nocturnal boundary layer inside meteor crater a combination of increasingly cold air intruding into the basin and pooling near the basin floor and compensating adiabatic ascent yield an isothermal layer over a large depth of the basin atmosphere a series of experiments are then conducted in order to examine the sensitivity of basin thermal structure to upstream terrain slope basin width and the presence of a rim surrounding the basin in the case of a large basin of o 10 km in diameter the cold air intrusion process remains but the larger basin volume yields greater dilution of the cold air intruding into the basin and a weak inversion develops inside the basin away from the floor in the case of a small basin with the same dimensions as meteor crater but with flat upstream terrain the influence of the surrounding terrain on basin cooling is negligible last the presence of a rim surrounding the basin is found to not be necessary for isothermal layer development

quasi steady katabatic winds on slopes in wide valleys hydraulic theory and observations theoretical and field observational studies on mean velocity and temperature fields of quasi steady nocturnal downslope katabatic flows on sloping surfaces are reported for the case of very wide valleys in the presence of weak synoptic winds because of the lateral constraints on the flow coriolis effects are considered negligible the layer averaged equations of manins and sawford were used for the analysis it is shown that i in the absence of significant turbulent entrainment into the current i e at large richardson numbers ri h cos u 2 the downslope flow velocity u is related to the slope length lh slope angle and the buoyancy jump between the current and the background atmosphere a su u lh sin 1 2 where u is a constant and h is the flow depth ii on very long slopes h is proportional to lh tan 1 2 and iii under highly stable conditions i e ri 1 the katabatic flow exhibits pulsations with period t0 2 n sin where n is the buoyancy frequency of the background atmosphere these predictions are verified principally using observations made during the vertical transport and mixing experiment vtmx conducted in salt lake city utah in october 2000 by assuming the flow follows a straight line trajectory to the nearest ridgeline a good agreement was found between the predictions and observations over appropriate richardson number ranges for ri 1 5 u 0 2 although u was a decreasing function of ri at lesser stabilities oscillations with period t0 are simply alongslope critical internal wave oscillations with a slope normal wavenumber which are liable for degeneration into turbulence during their reflection these critical internal waves may be responsible at least partly for weak sustained turbulence often observed in complex terrain nocturnal boundary layer flows

the evolution and sensitivity of katabatic flow dynamics to external influences through the evening transition data collected over an arid shallow slope 2 4 during the mountain terrain atmospheric modeling and observations materhorn program are used to study the katabatic structure and onset of katabatic flow through the evening transition an unprecedented suite of instrumentation including a transect of five turbulence towers with 29 sonic anemometers is used for the investigation fifteen transition periods with well defined katabatic flow and relatively little synoptic forcing are used in the study the katabatic onset jet velocity and jet height all show a large degree of interdiurnal and intersite variance the slope aligned budgets of momentum and potential temperature are used to define time scales that describe the evolution of the katabatic flow composite wind velocity time series are used to show that 30 min elapses from the time when the katabatic flow initializes at 0 5 m to the point of initialization at 20 m a simple katabatic model utilizing surface energy budget modeling is developed and used to model the interdiurnal katabatic variance finally uni and multi variate statistical analysis are used to diagnose the influence of specific external variables valley wind speed turbulence structure soil moisture and shadow front speed are all found to influence the katabatic dynamics to varying degrees

varved lacustrine sediments and diatom assemblages of lake fukami central japan abstract a sediment core taken from lake fukami in southern nagano prefecture in the summer of 1999 contained alternating light and dark colored laminae diatom microstratigraphy was determined for the succession between 60 and 68 cm core depth the frequency of synedra spp varied from more than 40 in the light colored laminae to less than 10 in the dark laminae aulacoseira spp or cyclotella spp were dominant in the dark laminae in which the proportion of synedra spp was relatively low the correlation of these diatom assemblages with alternating lamina color indicates a seasonal succession within the diatom biota each couplet of light and dark colored laminae in the sediment is therefore considered to be an annual sedimentation increment

a diatom record for the past 400 ka from lake biwa in japan correlates with global paleoclimatic trends abstract detailed diatom records from a 140 m sediment core with a time resolution of approximately 1000 1500 yr were obtained from lake biwa to examine possible correlations between diatom concentrations and paleoclimatic changes during the last approximately 400 ka in the sediments the diatom assemblages are generally dominated by planktonic diatoms the diatom stratigraphy is characterized by four zones with distinctly higher concentration values and 12 horizons with low concentration values diatom records from the 140 m core and another core indicate that these changes were not local phenomena but occurred throughout the lake basin comparison of diatom concentration records with pollen records from lake biwa sediments indicates that higher diatom concentrations represent warmer and wetter climatic conditions and that lower concentrations represent colder and drier climatic conditions comparison of diatom records from lake biwa with marine oxygen isotopic records shows that the number of peaks and their relative amplitudes are similar in both profiles therefore peaks and drops in diatom concentration profile might correlate with most oxygen isotopic events this finding indicates that during approximately the last 400 ka the changes in diatom concentration represented as diatom productivity in lake biwa correlate closely with global paleoclimatic changes at the scale of the milankovitch cycle precession cycles of 23 and 19 ka and that diatom concentration was higher during warm events and lower during cold or cooling events

optimal control of katabatic flows within canopies what slope angle favours the development of katabatic flow is still an open question some studies have clarified that katabatic winds are stronger on steep slopes while others have demonstrated that katabatic winds are stronger on gentle slopes here we explore the control mechanisms of katabatic flow using a simplified theoretical model in an attempt to clarify the causes of the paradoxical findings our results indicate that optimal conditions for katabatic flows within canopies are synergistically controlled by terrain angle canopy structure and thermal condition through a simple equation where is terrain slope lc 1 cda is canopy length scale cd is drag coefficient a is leaf area density vt rc is a thermal factor rc is a cooling rate is ambient lapse rate and b is a constant this theoretical prediction implies that gentle slopes are optimal for katabatic flow developments in stably stratified air while steep slopes are optimal in weak or near neutral stratification canopy effect is significant in the control of katabatic flows only on gentle slopes copyright 2012 royal meteorological society

varved lacustrine sediments of lake tougou ike western japan with reference to holocene sea level changes in japan abstract eighteen metres of laminated sediments were recovered in a holocene sediment core taken from lake tougou ike in 1992 the lamination evident from the alternation of light and dark coloured laminae records cyclic deposition of biochemical sediments annual environmental changes in and around the lake caused seasonal variations in sediment flux to the lake floor explaining these cyclic variations in sedimentary facies ams 14 c dating of organic remains from 40 horizons in the succession supports the interpretation of each light to dark couplet as an annual increment each laminated couplet is identified as a non glacial varve formed mainly by seasonal changes in diatom productivity varve counting and 14 c dating provide a detailed holocene chronological framework with time resolution on the order of individual years within which to reconstruct paleoenvironmental changes recorded in the sediment core holocene relative sea level changes at lake tougou ike were estimated with 10 yr precision using the variable authigenic iron mineral content of the sediment as a proxy the results demonstrate that the relative sea level at lake tougou ike rose abruptly at about 8900 7700 5600 4000 3600 and 2700 cal yr bp and decreased gradually in the intervening intervals these relative rises in sea level are demonstrated to be coeval with ice sheet discharge events recorded in sediment cores from the north atlantic ocean abrupt coastal environmental changes caused by sea level changes likely took place throughout the japanese islands and will probably be identified in both the holocene and the last glacial interval the latter being a time when dansgaard oeschger cycles were clearly active in the north atlantic region

diatom responses to limnological and climatic changes at ribains maar french massif central during the eemian and early wurm abstract high resolution diatom analysis was carried out to assess the limnological and climatic changes that took place at ribains maar french massif central during the late pleistocene 131 105 ka bp with a focus on the eemian interglacial in particular numerical analyses were used to show that most of the variability in the fossil diatom assemblages was due to climate independently from the changes in the lake catchment vegetation as represented by pollen data diatom based quantitative reconstructions of the past limnological conditions as well as a comprehensive literature review on the auto ecological requirements for the principal diatom taxa were used to interpret the record an absolute time scale for the sequence was derived by matching the major pollen shifts with the radiometrically dated changes in oxygen isotopes observed in italian stalagmites this study shows that at ribains maar the transition from the riss saalian glacial to the eemian interglacial was marked by a gradual increase in the contribution of spring blooming diatom species indicating a longer growing season and milder winter spring conditions at that time a short cooling event interrupts this trend and may correspond to a stadial at the start of the eemian a peak in benthic taxa and the suppression of spring blooming flora probably reflects the effects of deglaciation on the catchment during the eemian interglacial itself three main phases were distinguished within the diatom record the first phase 8000 years in duration was dominated by stephanodiscus minutulus which suggests that intense mixing in the water column took place during spring the pollen record was simultaneously dominated by quercus and corylus that typify this phase as the climatic optimum of the eemian the second phase almost equal in duration to the first phase 7000 years is generally dominated by cyclotella taxa and suggests a less productive lake and much reduced period of spring mixing compared with the first phase in the pollen diagram this corresponds to an interval dominated by carpinus picea abies that indicates a cooler and wetter climate the third and last phase of the eemian 2000 year long saw the return to stephanodiscus dominated assemblages indicating a warming that may correspond to the dansgaard oeschger event 25 identified in the greenland ice core record in the early stage of the wurm glacial weichselian assemblages in the melisey i stadial 3000 year long were dominated by either aulacoseira subarctica or asterionella formosa which suggest colder spring conditions than during the late eemian but not as cold as the ones indicated by the pollen record stephanodiscus spp again dominate during the saint germain ia interstadial 5000 year long suggesting a return to the conditions that prevailed before the melisey stadial in agreement with the pollen record the record ends with the montaigu cold event which is characterised by a pinus peak in the pollen record and corresponds to a large abundance of a subarctica in the diatom sequence throughout the eemian the abundance of stephanodiscus spp which is thought to be driven by winter conditions show cyclic fluctuations that most likely match the cooling events identified in a pollen record from germany variation in insolation throughout the eemian may have been the driving factor behind the species succession observed in the diatom sequence while this study demonstrates that diatom analysis of lake sediment can provide very detailed information on long term climate change a review of the few other diatom investigations published on european eemian deposits shows that this technique has been so far seldom used to its full potential in this context in central and southern europe

diatom inferred climatic and environmental changes over the last 9000 years from a low arctic nunavut canada tundra lake abstract diatom assemblage changes over the holocene were examined from a 14c dated sediment core retrieved from lake tk 2 a small low arctic lake located ca 200 km north of the forest tundra ecotone in mainland nunavut canada notable changes in the diatom assemblages were recorded throughout the core suggesting that the holocene epoch in this region has been environmentally and climatically dynamic the earliest diatom assemblages ca 9000 cal yr bp were dominated by taxa that are atypical of post glacial assemblages commonly recorded throughout the arctic and may suggest that early holocene conditions at lake tk 2 were relatively warmer a shift to dominance by small benthic opportunistic fragilaria taxa followed after ca 8550 cal yr bp more typical of arctic assemblages during initial lake ontogeny suggesting the onset of cooler more alkaline conditions an abrupt and short lived marked decrease in diatoms between ca 8550 and 8500 cal yr bp with corresponding changes in physical and chemical indicators e g sedimentation rate siliciclastic content organic matter content provides potential evidence for the 8 2 k cooling anomaly an event rarely recognized from other paleolimnological studies in the canadian north following ca 7000 cal yr bp a substantial shift occurred to a more complex and diverse diatom assemblage that now included more acidophilic taxa this compositional change is likely indicative of a natural long term loss of alkalinity in the lake and marks the onset of the holocene thermal maximum consistent with the timing of this warm period for this region the relatively stable diatom assemblage composition during the neoglacial period was punctuated by fluctuations in key species potentially correlative with the so called medieval warm period and little ice age in the most recent sediments the post industrial expansion of the small planktonic cyclotella stelligera complex and a concurrent decline in the heavily silicified aulacoseira lirata complex are similar to shifts that are increasingly being recognized as geographically widespread diatom responses to recent climate warming the lake tk 2 diatom record provides important insights into the holocene environmental history of this understudied region of the canadian arctic furthermore it is one of the few arctic lakes in which the 8 2 k cold event is possibly expressed

a new opportunity to detect paleo earthquake events dating back to the past 10 millennia a record from lacustrine sediment bulk density and grain density profiles of the uppermost 90 cm portion of lacustrine sediment from lake suigetsu one of the five major lakes of lake mikatagoko located in central japan indicate the occurrence of at least 10 depositional events characterized by anomalously high density spikes two events are accompanied by turbidites the dates of the sedimentary events estimated here are correlated with the occurrence of destructive earthquakes since 1100 a d close examination of the sedimentological signatures recorded in the lake sediment and historical literature describing destructive earthquake phenomena provides a new opportunity to detect paleo earthquake events in a high seismic area having a long history

younger dryas to mid holocene environmental history of the lowlands of nw transylvania romania pollen micro charcoal and total carbon analyses on sediments from the turbuta palaeolake in the transylvanian basin of nw romania reveal younger dryas to mid holocene environmental changes the chronostratigraphy relies on ams 14c measurements on organic matter and u th tims datings of snail shells results indicate the presence of pinus and betula open woodlands with small populations of picea ulmus alnus and salix before 12 000 cal yr bp a fairly abrupt replacement of pinus and betula by ulmus dominated woodlands at ca 11 900 cal yr bp likely represents competition effects of vegetation driven by climate warming at the onset of the holocene by 11 000 cal yr bp the woodlands were increasingly diverse and dense with the expansion of quercus fraxinus and tilia the establishment of corylus and the decline of upland herbaceous and shrubs taxa the marked expansion of quercus accompanied by tilia between 10 500 and 8000 cal yr bp could be the result of low effective moisture associated with both low elevation of the site and with regional change towards a drier climate at 10 000 cal yr bp corylus spread across the region and by 8000 cal yr bp it replaced quercus as a dominant forest constituent with only little representation of picea abies carpinus became established around 5500 cal yr bp but it was only a minor constituent in local woodlands until ca 5000 cal yr bp results from this study also indicate that the woodlands in the lowlands of turbuta were never closed

diatom based inference of variations in the strength of asian winter monsoon winds between 17 500 and 6000 calendar years b p 1 we present a continuous record of fossil diatoms from huguang maar lake hml in southeastern china spanning the time interval 17 500 to 6000 calendar years cal years b p the seasonal change in relative abundance of the dominant diatom taxa aulacoseira and cyclotella species can be used as a proxy of the strength of winter monsoon winds wmw which is supported by the results of a sediment trap experiment in hml and by an extensive review of the literature on the autoecologies of these species in the sediment high c stelligera abundance and high diatom concentration which indicate warm conditions and low wind driven turbulence of the water column characterize an interval equivalent to the greenland interstadial 1 this is followed by an interval with low diatom concentration and with assemblages dominated by aulacoseira species which suggests high wind driven turbulence and therefore strong wmw this interval corresponds with the greenland stadial 1 during the early and middle holocene another two episodes with strong wmw are evident from the data between 10 000 and 8500 and between 7000 and 6000 cal years b p the diatom record implies that strong winter monsoon episodes not only occurred during the last glacial holocene transition but also during the holocene thermal maximum

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

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

tracing the north atlantic decadal scale climate variability in a late holocene pollen record from southern siberia abstract this paper presents a new palynological record from a 146 cm long finely laminated sediment core obtained in 2009 from the deep water meromictic lake shira 54 30 38 n 90 12 09 e ca 353 m a s l situated in the khakassian steppe region of southern siberia between the rivers ob and yenisei the area is rich in lakes and represents an exceptionally well preserved sequence of bronze and iron age archeological cultures little is known about the changes in vegetation and climate of the region during the holocene the palynological analysis of the core allows us to partly fill up this gap in current knowledge the record of pollen and non pollen palynomorphs presented here covers the past 2450 year interval with an average resolution of 22 years the results obtained support the interpretation that the late holocene vegetation changes around lake shira are mainly associated with large scale atmospheric circulation processes controlling the regional water balance rather than with human activities an attempt to trace human impact in the pollen assemblages provides no clear evidence for anthropogenic activity except for the last few decades since ca 1955 though the region has a long history of mobile pastoralists for explanation of decadal scale changes in the regional vegetation cover the artemisia chenopodiaceae a c pollen ratio proved to be a reliable indicator of effective moisture availability using available fossil and published instrumental data our study suggests a link between the north atlantic warmer colder temperatures and higher lower atmospheric precipitation or moisture availability in southern siberia at multi decadal to centennial scales

can a simple dynamical system describe the interplay between drag and buoyancy in terrain induced canopy flows abstractunder nonneutral stratification and in the presence of topography the dynamics of turbulent flow within a canopy is not yet completely understood this has among other consequences serio

an abrupt wind shift in western europe at the onset of the younger dryas cold period the younger dryas cold reversal during the last glacial termination is one of the most abrupt climate change events observed in the northern hemisphere analyses of varved lake sediments from western germany suggest that storminess in the north atlantic region increased within a single year at this time providing a mechanistic link between a decrease in the meridional overturning circulation and western european cooling the younger dryas cooling 12 700 years ago is one of the most abrupt climate changes observed in northern hemisphere palaeoclimate records1 2 3 4 annually laminated lake sediments are ideally suited to record the dynamics of such abrupt changes as the seasonal deposition responds immediately to climate and the varve counts provide an accurate estimate of the timing of the change here we present sub annual records of varve microfacies and geochemistry from lake meerfelder maar in western germany providing one of the best dated records of this climate transition5 our data indicate an abrupt increase in storminess during the autumn to spring seasons occurring from one year to the next at 12 679 yr bp broadly coincident with other changes in this region we suggest that this shift in wind strength represents an abrupt change in the north atlantic westerlies towards a stronger and more zonal jet changes in meridional overturning circulation alone cannot fully explain the changes in european climate6 7 we suggest the observed wind shift provides the mechanism for the strong temporal link between north atlantic ocean overturning circulation and european climate during deglaciation

sg06 a fully continuous and varved sediment core from lake suigetsu japan stratigraphy and potential for improving the radiocarbon calibration model and understanding of late quaternary climate changes abstract the high potential of the varved sediments of lake suigetsu central japan to provide a purely terrestrial radiocarbon calibration model and a chronology of palaeoclimatic changes has been widely recognised for the last two decades however this potential has not been fully realised since the only available long sediment core from the lake sg93 was extracted from a single bore hole and was therefore interrupted by gaps of unknown duration between successive core sections in the summer of 2006 a new sediment core sg06 was recovered from the lake four separate boreholes were drilled and the parallel sets of cores recovered were found to overlap completely without gaps between segments this new record provides the ability to test existing atmospheric radiocarbon calibration models as well as to assess the scale of inter regional leads and lags in palaeoclimatic changes over the last glacial interglacial cycle multi disciplinary analyses from sg06 are still ongoing but a reliable description of the sedimentary sequence needs to be provided to the wider science community before major outputs from the project are released thereby allowing fully informed critical evaluation of all subsequent releases of data based on the sg06 record in this paper we report key litho stratigraphic information concerning the sg06 sediment core highlighting changes in the clarity of annual laminations varves with depth and possible implications for the mechanism of the climate change we also discuss the potential of the sg06 record to meet the fundamental goals of the inqua intimate project

quantitative pollen based climate reconstruction in central japan application to surface and late quaternary spectra abstract climate reconstruction in japan by the best modern analogues method was tested with 285 surface pollen spectra and then applied to the 47 000 years pollen profile from lake mikata central japan both pollen taxa percentages and plant functional type affinity scores were used in the reconstruction of six climate variables the reconstructed values were compared with the estimated modern climate at each surface pollen site in order to evaluate the accuracy of the pollen based reconstruction the reconstruction of thermal parameters is very reliable correlation coefficient r between 0 86 and 0 89 the reconstruction of annual precipitation is less accurate r 0 7 we also proposed a new technique to calibrate reconstructed values into both probability distribution and or confidence regions of observed values the specialized programs for this calibration polcalib and polhist are available at qsr website http www elsevier nl locate quascirev the reconstruction of the late quaternary climate changes around lake mikata shows that the summer and winter temperatures were 5 c lower than present around 40 uncal kyr bp reached a minimum around 20 uncal kyr bp 10 c lower than present and became similar to present day at 8 uncal kyr bp the estimates for annual precipitation show that it was driest around 20 uncal kyr bp

onset and termination of the late glacial climate reversal in the high resolution diatom and sedimentary records from the annually laminated sg06 core from lake suigetsu japan high resolution diatom sediment and pollen analyses of two sections from the annually laminated sg06 core from lake suigetsu were used to study the onset and termination of the late glacial climate reversal in central japan its broadly recognised counterpart is the younger dryas or greenland stadial 1 ca 12 85 11 65 cal kyr bp based on the ngrip ice core records our study suggests that accumulation of the analysed late glacial sediments occurred in a deep and relatively cold water meso eutrophic lake with a strong mixing regime and relatively high silica content combining these results together with available pollen based environmental reconstructions we suggest that climate cooling together with an intensified winter monsoon and thicker snow cover could influence changes in regional vegetation sedimentation processes and trophic status of the lake during the transition from the last interstadial to stadial around lake suigetsu a decrease in total pollen concentration and increase in fagus pollen percentage indicate local vegetation stress disturbances and suggest that cooling started at least 2 3 decades prior to the major shift in the inorganic sediment accumulation of detrital layers and in diatom assemblages change from aulacoseira ambigua to aulacoseira subarctica dominance which took about 10 years the transition from the last stadial to the holocene again shows that vegetation in the lake catchment area reacted first to the regional climate change i e to the weakening of the winter monsoon and decrease in winter snow accumulation the increase in the vegetation cover density and reduced volume of surface runoff associated with the decrease in melt water supply is likely responsible for the reduced soil erosion activity which caused the cessation in detrital layer accumulation and consequent decrease in the amount of nutrients brought to the lake and lowering of the water nutrient status the latter process finally influenced changes in the diatom assemblages including the return to dominance of a subarctica ca 30 years after the virtual disappearance of detrital layers from the sediment our results demonstrate the rapid response of the lake suigetsu system to the global cooling and subsequent warming and allow clear definition of the onset and termination of the late glacial climate reversal despite the fact that the lake system shows a more abrupt shift from the warm to cold and cold to warm environments than terrestrial records of vegetation demonstrate we do not see any delayed response of local vegetation to the climate change this last conclusion is of particular importance for application of the sg06 pollen record for quantitative climate reconstruction

timing duration and transitions of the last interglacial asian monsoon thorium 230 ages and oxygen isotope ratios of stalagmites from dongge cave china characterize the asian monsoon and low latitude precipitation over the past 160 000 years numerous abrupt changes in 18o 16o values result from changes in tropical and subtropical precipitation driven by insolation and millennial scale circulation shifts the last interglacial monsoon lasted 9 7 1 1 thousand years beginning with an abrupt less than 200 years drop in 18o 16o values 129 3 0 9 thousand years ago and ending with an abrupt less than 300 years rise in 18o 16o values 119 6 0 6 thousand years ago the start coincides with insolation rise and measures of full interglacial conditions indicating that insolation triggered the final rise to full interglacial conditions

a high resolution diatom inferred palaeoconductivity and lake level record of the aral sea for the last 1600 yr formerly the world s fourth largest lake by area the aral sea is presently undergoing extreme desiccation due to large scale irrigation strategies implemented in the soviet era as part of the intas funded climan project into holocene climatic variability and the evolution of human settlement in the aral sea basin fossil diatom assemblages contained within a sediment core obtained from the aral sea have been applied to a diatom based inference model of conductivity r2 0 767 rmsep 0 469 log10 s cm 1 this has provided a high resolution record of conductivity and lake level change over the last ca 1600 yr three severe episodes of lake level regression are indicated at ca ad 400 ad 1195 1355 and ca ad 1780 to the present day the first two regressions may be linked to the natural diversion of the amu darya away from the aral sea and the failure of cyclones formed in the mediterranean to penetrate more continental regions human activity however and in particular the destruction of irrigation facilities are synchronous with these early regressions and contributed to the severity of the observed low stands

deposition models for chronological records abstract long term sedimentary sequences provide a wealth of useful information for research into the palaeo environment especially in relation to past climate change shorter records provide similar information in many archaeological contexts however if such records are to be used to provide precise timing of events and more critically the relative timing between different records methods are needed to provide accurate and precise age depth models for these sequences given the imprecision of individual calibrated radiocarbon determinations it is necessary to use the information we have about the deposition process to refine our chronologies and also to provide interpolation between dated levels in any sequence even with layer counted chronologies the uncertainties are sometimes hard to quantify this paper outlines a range of bayesian models for deposition which have been implemented in the computer programme oxcal these models can be used to combine information from the sediments themselves with radiocarbon or other direct dating information such models have the potential to integrate information between different records and provide a coherent chronology on which to base environmental or archaeological research