palaeo moisture evolution in monsoonal central asia during the last 50 000 years abstract the late quaternary climate history of monsoonal central asia was inferred from 75 palaeoclimatic records which provide information about moisture conditions in the last 50 ka or part of this period wet conditions occurred during middle and late marine isotope stage 3 while the last glacial maximum lgm was characterized by dry climate conditions in the region a stepwise climate amelioration is suggested by the climate records following the lgm several climate signals of this period which were reported from high latitude ice core records are preserved in archives from monsoonal central asia as well during the early holocene high effective moisture was inferred from most records from the area dominated by the indian monsoon e g the tibetan plateau suggesting that holocene optimal climate conditions occurred there during this period in contrast areas which are dominated by the south east asian monsoon se monsoon and the westerlies in north western and north central china mongolia do not uniformly show an early holocene climate optimum for this area optimal conditions prevailed during the mid holocene these apparent contradictions can possibly be explained by the regional uplift and descent of air masses in the holocene during the early holocene strengthened insolation possibly caused an enhanced low level convergence over the tibetan plateau which led to the intensification of the summer monsoon the strong air uplift caused intensified precipitation and air divergence in the upper troposphere over the tibetan plateau the areas adjacent to the north therefore experienced an intensified descent of air masses and consequently increased aridity the majority of the palaeoclimatic records suggest reduced effective moisture since the late holocene in the region

biomarker based reconstructions of holocene lake level changes at lake gahai on the northeastern tibetan plateau holocene hydrological changes in regions dominated by the westerlies significantly differ from those by the asian summer monsoon the high elevated northeastern tibetan plateau located in between is likely influenced by the interactions of both circulation systems here we attempt to use biomarkers n alkanes and alkenones to reconstruct holocene lake level changes at lake gahai in the qaidam basin we choose a sediment core drilled at the lake shore where biomarkers would be sensitive to lake level changes the n alkane records show high average chain length acl high carbon preference index cpi and low proportion of aquatic macrophyte paq values at 7 2 kyr thousand calibrated years ago with peaked values around 6 kyr whereas low acl low cpi and high paq values occurred after 2 kyr and before 7 kyr no alkenones were detected at 7 2 kyr suggesting that lake level at this period was incapable of constantly reaching to the coring site therefore combined results provide unambiguous evide

formation of coastline features by large scale instabilities induced by high angle waves along shore sediment transport that is driven by waves is generally assumed to smooth a coastline this assumption is valid for small angles between the wave crest lines and the shore as has been demonstrated in shoreline models but when the angle between the waves and the shoreline is sufficiently large small perturbations to a straight shoreline will grow here we use a numerical model to investigate the implications of this instability mechanism for large scale morphology over long timescales our simulations show growth of coastline perturbations that interact with each other to produce large scale features that resemble various kinds of natural landforms including the capes and cuspate forelands observed along the carolina coast of southeastern north america wind and wave data from this area support our hypothesis that such an instability mechanism could be responsible for the formation of shoreline features at spatial scales up to hundreds of kilometres and temporal scales up to millennia

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

the east asian monsoon during mis 2 expressed in a speleothem δ18o record from jintanwan cave hunan china abstract stalagmite j1 from jintanwan cave hunan china provides a precisely dated decadally resolved 18o proxy record of paleoclimatic changes associated with the east asian monsoon from 29 5 to 14 7 ka and from 12 9 to 11 0 ka at the time of the last glacial maximum lgm the east asian summer monsoon weakened and then strengthened in response to changes in northern hemisphere insolation as the ice sheets retreated the east asian summer monsoon weakened especially during heinrich event h1 when atmospheric and oceanic teleconnections transferred the climatic changes around the north atlantic to the monsoonal regions of eastern asia a depositional hiatus between 14 7 and 12 9 ka leaves the deglacial record incomplete but an abrupt shift in 18o values at 11 5 ka marks the end of the younger dryas and the transition into the holocene comparisons of the j1 record to other chinese speleothem records indicate synchronous climatic changes throughout monsoonal china further comparisons to a speleothem record from western asia socotra island and to greenland ice cores support hemispherical scale paleoclimatic change spectral and wavelet analyses reveal centennial and decadal scale periodicities that correspond to solar frequencies and to oscillations in atmospheric and oceanic circulation

biomarkers as proxies for plant inputs to peats an example from a sub boreal ombrotrophic bog lipid distributions in modern peat forming plants were determined and compared to biomarkers recovered from a ca 2800 year old peat deposited in a dutch ombrotrophic bog the peat section spans a well constrained shift in local hydrology and vegetation and potential molecular proxies for plant inputs were directly tested against the macrofossil record based on the analyses of modern plants low molecular weight lmw n alkanes c23 c25 and high molecular weight n alkanes c33 are proposed as potential biomarkers for sphagnum and non sphagnum inputs respectively consistent with this in the bargerveen peat core lmw n alkane abundances increase and hmw n alkane abundances decrease coincident with the shift to sphagnum dominated peat additional potential proxies include the abundances of c22 alkanedioic acid and phytenyl phytenoate as sphagnum indicators and the abundances of the triterpenoids taraxer 14 ene and taraxast 20 ene as biomarkers for ericaceae rootlets

branched gdgt based paleotemperature reconstruction of the last 30 000 years in humid monsoon region of southeast china abstract the use of bacterial branched glycerol dialkyl glycerol tetraethers brgdgts to reconstruct mean annual air temperatures maats and environmental ph from soils has sparked significant interest in the terrestrial paleoclimate community however the reconstruction of these climate proxies from peat bogs is rare in monsoonal regions of the east asia this research was carried out on a core from the shuizhuyang szy peat bog located in fujian province branched gdgt brgdgt indexes were used for reconstructing the paleoclimate of the last 30 cal ka the aim was to evaluate quantitatively the maat and ph values since the last glacial maximum lgm in the subtropical zone of china results show that the cbt mbt derived maat at mis 3 is about 15 6 c on average which is followed by a significant fall at the lgm 11 7 12 1 c the temperature difference between the lgm and the present day value is as high as 5 8 c the synchronous variation of biomarker and pollen proxies indicates that replacement of subtropical evergreen broadleaved forests by cold tolerant deciduous broadleaved forests was driven by the significant drop in air temperature our results also indicate that the younger dryas event lasted from about 12 9 to about 11 3 cal ka and cooling event at 3 2 cal ka in the late holocene was detected showing the sensitivity of peat bogs to rapid cooling our ph reconstructions indicate that the ph of the bog rose during heinrich 1 and bolling allerod periods probably due to low precipitation and were lowest in the holocene thermal maximum between 8 ka and 2 5 ka probably due to higher precipitation the decoupling of reconstructed maat and ph during particularly deglaciation and yd periods supports the hypothesis that the variations in temperature and precipitation are not always synchronous

wave current interaction in willapa bay 1 this paper describes the importance of wave current interaction in an inlet estuary system the three dimensional fully coupled coupled ocean atmosphere wave sediment transport coawst modeling system was applied in willapa bay washington state from 22 to 29 october 1998 that included a large storm event to represent the interaction between waves and currents the vortex force method was used model results were compared with water elevations currents and wave measurements obtained by the u s army corp of engineers in general a good agreement between field data and computed results was achieved although some discrepancies were also observed in regard to wave peak directions in the most upstream station several numerical experiments that considered different forcing terms were run in order to identify the effects of each wind tide and wave current interaction process comparison of the horizontal momentum balances results identified that wave breaking induced acceleration is one of the leading terms in the inlet area the enhancement of the apparent bed roughness caused by waves also affected the values and distribution of the bottom shear stress the pressure gradient showed significant changes with respect to the pure tidal case during storm conditions the momentum balance in the inlet shares the characteristics of tidal dominated and wave dominated surf zone environments the changes in the momentum balance caused by waves were manifested both in water level and current variations the most relevant effect on hydrodynamics was a wave induced setup in the inner part of the estuary

paleoenvironmental implications of molecular and carbon isotopic distributions of n alkanes in the hominoid bearing upper miocene sediments from the zhaotong basin southwestern china abstract it is crucial to understand the relationship between hominoid primates and their living environment located at the southeastern margin of the tibetan plateau the shuitangba stb outcrop from the zhaotong basin is famous for bearing the remains of the youngest known ape fossil in the terminal miocene 6 2 ma in this study the molecular and carbon isotope compositions of n alkanes together with the loss on ignition and the bulk carbon isotope composition of total organic matter were investigated in the stb outcrop to infer the paleoenvironmental conditions in this uppermost miocene sedimentary sequence with the emphasis on the habitat of the stb hominoid in the hominoid bearing peaty clay layer and the surrounding lignite layers the n alkane molecular and carbon isotope compositions support a primary contribution from terrestrial higher plants in contrast n alkanes in the upper shallow lake sediments are derived from multiple origins mainly from aquatic plants and bacteria both carbon preference index cpi and average chain length acl vary closely with the lithology but the cpi record shows the larger amplitude of change than the acl and varies sharply during the lithological boundary it is notable that the changes of the molecular and carbon isotope compositions of long chain n alkanes do not parallel with the abrupt increase of poaceae pollen percentage during the stb hominoid appearing stage such an inconsistency between herb pollen percentage and n alkane ratios may result from the different sources our results clearly support that these organic matter based ratios have the potential to record the paleoenvironmental changes in ancient lacustrine sediments

reconstruction of late glacial and holocene climate evolution in southern china from geolipids and pollen in the dingnan peat sequence we have carried out a multi proxy analysis of a radiocarbon dated peat core that records the history of paleoclimate change dating from 18 ka in the dingnan region of southern china fatty acid and hydrocarbon distributions total organic carbon toc concentrations pollen assemblages and sediment lithology reveal a succession of three major paleoclimate intervals plant waxes are the predominant origin of the n alkanoic acid and n alkane compositions of this sedimentary sequence contributions of these geolipid components vary relative to toc and with changes in lithology and help to refine a pollen based reconstruction of local paleoclimate evolution a period of cool and fairly wet climate 15 630 10 450 cal abp follows accumulation of coarse fluvial sediments under relatively dry deglacial conditions the second period 10 450 6040 cal abp experienced the warmest climate and the highest precipitation indicated by a minimum c18 1 c18 0 ratio together with the low cpi values of n alkanes and high acl values the third time interval 6040 3800 cal abp was a moderately dry and cool period the climate record of the most recent period 3800 cal abp is obscured by agricultural disturbance the younger dryas 12 900 11 600 cal abp appears in this record as a period of variable and very wet climate during the interval 10 450 6040 cal abp both temperature and the precipitation evaporation ratio maximized therefore we consider this period to represent the holocene optimum which coincides with that of the northern hemisphere moreover our results do not fit the spatially asynchronous pattern of the east asian monsoon holocene optimum in china suggested by previous studies they instead parallel the pattern of global paleoclimate change and consequently show that the evolution of holocene paleoclimate in southern china is consistent with changes in northern hemisphere solar radiation

an asymptotic theory for the interaction of waves and currents in coastal waters a multi scale asymptotic theory is derived for the evolution and interaction of currents and surface gravity waves in water of finite depth under conditions typical of coastal shelf waters outside the surf zone the theory provides a practical and useful model with which wave current coupling may be explored without the necessity of resolving features of the flow on space and time scales of the primary gravity wave oscillations the essential nature of the dynamical interaction is currents modulating the slowly evolving phase of the wave field and waves providing both phase averaged forcing of long infra gravity waves and wave averaged vortex and bernoulli head forces and hydrostatic static set up for the low frequency current and sea level evolution equations analogous relations are derived for wave averaged material tracers and density stratification that include advection by horizontal stokes drift and by a vertical stokes pseudo velocity that is the incompressible companion to the horizontal stokes velocity illustrative solutions are analysed for the special case of depth independent currents and tracers associated with an incident surface wave field and a vortex with o 1 rossby number above continental shelf topography

paleoclimate influence on early diagenesis of plant triterpenes in the dajiuhu peatland central china abstract aromatic derivatives of vascular plant triterpenoids are common in recent and ancient sediments coal and petroleum understanding their early diagenetic alterations and their relation with environmental conditions can facilitate their applications in paleoenvironmental reconstructions here we present a high resolution record of aromatic triterpenes in a holocene peat core collected in the dajiuhu peatland central china these aromatic triterpenes are derivatives of plant triterpenoids with oleanane ursane and lupane carbon skeletons and exist in three different structural groups aromatic des a triterpenes aromatic pentacyclic triterpenes and c ring cleaved aromatic triterpenes such a high diversity of aromatic triterpenes in a young peat deposit is compelling evidence for rapid microbial mediation of these important degradation pathways during very early diagenesis of particular importance is the occurrence of c ring cleaved aromatic triterpene and aromatic des a triterpenes in the dajiuhu peat samples which until now have not been identified in recent sediments the downcore profile shows that the microbial aromatization process of oleanoids positively correlates with paleoclimate change during dry or warm intervals highly aromatized products such as tetraaromatic triterpenes become predominant over their triaromatic homologs in contrast triaromatic triterpenes become dominant during wet or cold intervals in addition this study provides further evidence to support that the climate pattern in the middle reaches of the yangtze river is different from that in north china during 13 9 4 ka these findings suggest that aromatic triterpenes can be valuable tools for holocene paleoenvironmental reconstructions

a numerical study of the roles of subgyre scale mixing and the western boundary current on homogenization of a passive tracer a numerical model integrated the steady advection diffusion equation by using a kinematic circulation with characteristics of a subtropical gyre i e closed streamlines and western intensification homogenization of the interior concentration increased and the gradients were forced to the boundaries as mixing parameterized as eddy diffusion decreased as the western boundary current intensified the value of the homogenized interior became closer to the southern boundary value this indicated that cross stream mixing was enhanced within the western boundary current tongues of high and low tracer concentration spiraled across streamlines toward the center of the gyre these simulations will be helpful in the interpretation of lateral distributions of geochemical tracers which are being generated by programs such as tto 9 references 6 figures 2 tables

impact of early diagenesis on distributions of sphagnum n alkanes in peatlands of the monsoon region of china abstract sphagnum species are important peat forming plants in wetlands the world over their n alkane distributions are typically characterized by a predominance of mid chain c 23 and c 25 alkanes a property that has been employed in paleoclimatic reconstruction based on peat sequences however knowledge of the fate of sphagnum derived n alkanes during the very early stage of diagenesis remains limited this study compares the n alkane differences between samples of fresh plants and litter collected from four peatlands across the monsoon region of china the results clearly show that the distributions of sphagnum derived n alkanes differ between the plants and the litter with proportional decreases in c 23 and c 25 n alkanes and increases in c 29 and c 31 homologs in the litter other than the influence of species shifts changes in the n alkane distributions between the fresh plants and litter samples may be caused by preferential degradation of mid chain n alkanes c 23 and c 25 relative to their longer chain homologues c 29 and c 31 during the early diagenesis of sphagnum n alkanes this hypothesis is supported by decreases in cpi values and positive excursions of 13 c values of c 23 and c 29 n alkanes from the plant to the litter samples regardless of what the exact mechanisms for the changes may be the p aq ratio should be applied with caution as a paleoclimatic proxy in peat deposits especially those located in warmer climates or deposited during former warmer stages relatively low p aq values may result from elevated microbial degradation of sphagnum alkanes in such conditions and hence fail to record the former plant assemblages accurately

variability of shore and shoreline evolution shore and shoreline evolution both due to natural and human induced causes or factors can be variable over a wide range of different temporal and or spatial scales our capability to understand and especially predict this variability is still limited this can lead to misinterpretation of coastal change information which hampers informed decision making and the subsequent design and implementation of soft engineering interventions collecting and describing example observations of shore and shoreline variability is one way to support and improve such human intervention this paper describes causes and factors for the variability and the resulting possible evolutions of wave dominated shores and shorelines which are illustrated by a number of case studies the new element of this work is that the variability is described in terms of a range of different time and space scales which helps to structure such analysis however it is difficult to generalise the results for arbitrary situations especially on decadal time scales scientific and engineering improvements require more quantitative insight into the physical mechanisms behind the free and forced shore behaviour responsible for the variability

possible reverse trend in asian summer monsoon strength during the late holocene holocene climate change is characterized as generally cooling in high latitudes and drying in tropical and asian summer monsoonal regions following the gradual decrease in northern hemisphere summer insolation over the last 12 000 years however some recent high resolution well dated monsoon reconstructions seem to suggest an abnormal increase in asian summer monsoon strength during the late holocene against the generally weakening holocene trend here we synthesize marine and terrestrial moisture records from asian monsoonal regions that span most of the holocene period late holocene strengthening of asian summer monsoon identified from a wealth of the synthesized monsoon records appears to be a robust feature which warrants further consideration of its possible causes the possible reverse trend in asian summer monsoon strength preceding insolation minima seems to have also occurred during previous interglacial periods based on speleothem records we further show a similar late holocene reverse trend in tropical hydrological changes suggesting that the asian summer monsoon behavior might be internally linked to the movement of the average position of the itcz and enso variability during the late holocene on the other hand we suggest that even though several holocene temperature records indeed show a reverse trend in the late holocene the overall evidence for a link between the late holocene reverse trend in asian summer monsoon and global temperature changes is insufficient the reverse trend in asian summer monsoon during the late holocene is difficult to be explained with the traditional boreal insolation driven view we suggest that this phenomenon might be linked to austral summer insolation changes and or greenhouse gas increase however we caution that additional paleoclimate reconstructions and model simulations are needed to systematically study the spatial pattern and understand underlying mechanism of the late holocene reverse trend in asian summer monsoon strength

peatland development and climate changes in the dajiuhu basin central china over the last 14 100 years abstract peatlands are one of the optimal archives for paleoclimate research and their records contain a detailed history of climatic and environmental variations during their formation here we collected a peat profile from the dajiuhu basin in central china and analyzed several geochemical proxies such as total organic carbon toc total nitrogen tn titanium ti and aluminum al to investigate the history of peat development the results show that the peat growth was initiated after around 12 8 cal ka bp at the sampling site and the toc and tn contents kept stable during the holocene except during the periods of 10 5 9 0 cal ka bp and recent 1 5 cal ka bp however compared with other toc records in the dajiuhu basin the history of peat development varied greatly in different sampling sites indicating that the peat development in the dajiuhu basin probably responds to both climate changes and local geological and hydrological conditions investigations of the interactions between climate change and peat development record in this study suggest that peat development presented significant responses to the large and rapid decreases in east asian summer monsoon intensity such as the 9 2 ka monsoon weakening event however the obvious long term decreasing trend of monsoon precipitation during the mid late holocene did not lead to the degradation of the dajiuhu peat probably resulting from relatively stable temperature in addition the sharp decrease of toc and tn values in the surface 15 cm of dajiuhu peat was probably attributed to increased human activity

variation of the asian summer monsoon since the last glacial interglacial recorded in a stalagmite from southwest china abstract a number of studies proposed a close link between the climate changes in the asian summer monsoon asm the southern hemisphere sh and high latitudes of the northern hemisphere nh but the mechanisms is still an open question although speleothems 18o records have displayed excellent values in the reconstruction of paleoclimate change at centennial millennial to orbital timescales the significance of speleothems 18o and 13c is still debatable here a high precise 230th dated stalagmite from southwestern china was used to reconstruct the changes of asm and regional hydrological conditions since the last interglacial 3 6 118 1 ka bp by the coupled 18o and 13c we found 1 the easm and ism are synchronous changing on the orbital timescale responding to the change of north hemisphere summer insolation nhsi and high latitude climate change there is a teleconnection between antarctic temperature change and asm through the mascarene high and the somali jet 2 during mis 5d the stalagmite 18o in yangzi cave is nearly 1 5 higher than that in mis 2 the maximum of last glacial this should be attributed to the different isotopic compositions in moisture source of ism and easm and the dynamic changes of monsoon circulations 3 from mis 3 to mis 2 the asm showed a stepped pattern in weakening consistent with the decreasing nhsi and increasing global ice volume 4 the changes in stalagmite 13c indicated the changes of local hydrological conditions and closely correlated with climate changes revealed by stalagmite 18o the effective humidity which determined by temperature evaporation and precipitation dominated the regional hydrological conditions the change of effective humidity recorded in stalagmite 13c by influencing surface biomass and soil co2 production

paleotemperature variability in central china during the last 13 ka recorded by a novel microbial lipid proxy in the dajiuhu peat deposit the asian summer monsoon is a very important climatic component affecting the land ecosystem on the eastern asian continent here we assess microbe derived lipid biomarker evidence from a well date

short term to decadal scale onshore bar migration and shoreline changes in the vicinity of a megatidal ebb delta 1 swash bar development has been well documented from coasts with low to moderate tidal ranges while studies of the effects of these forms on the morphology and dynamics of the adjacent shore in large tide range environments are rare the analysis of sequential vertical aerial photographs was combined with field work in order to highlight the effects of swash bar development on the adjacent shoreline in the vicinity of a megatidal inlet mean spring tidal range of 11 m swash bars are observed to form on the ebb tidal delta and to migrate landward before welding onto the coast a close relationship was noticed between the position of the swash bar and shoreline dynamics the bar protects the shore against wave attack in a sedimentary system controlled by longshore transport this protective role is however modulated by the large tidal range as the bar migrates upward toward the high tide level and the subaerial beach it develops morphologically into a transverse form that acts as a cross shore obstacle to longshore sediment transport thus resulting in shoreline accretion updrift and in strong erosion downdrift this disturbance may persist for years because of the relatively slow speed of movement of the bar at this stage an aspect characteristic of large tide range environments this pattern of behavior differs fundamentally from that documented in the literature where the perturbation of the longshore sediment transport occurs over shorter periods an original conceptual model of swash bar morphodynamics and repercussions on the adjacent shoreline for this megatidal environment is proposed

the role of morphology and wave current interaction at tidal inlets an idealized modeling analysis the outflowing currents from tidal inlets are influenced both by the morphology of the ebb tide shoal and interaction with incident surface gravity waves likewise the propagation and breaking of incident waves are affected by the morphology and the strength and structure of the outflowing current the 3 d coupled ocean atmosphere wave sediment transport coawst modeling system is applied to numerically analyze the interaction between currents waves and bathymetry in idealized inlet configurations the bathymetry is found to be a dominant controlling variable in the absence of an ebb shoal and with weak wave forcing a narrow outflow jet extends seaward with little lateral spreading the presence of an ebb tide shoal produces significant pressure gradients in the region of the outflow resulting in enhanced lateral spreading of the jet incident waves cause lateral spreading and limit the seaward extent of the jet due both to conversion of wave momentum flux and enhanced bottom friction the interaction between the vorticity of the outflow jet and the wave stokes drift is also an important driving force for the lateral spreading of the plume for weak outflows the outflow jet is actually enhanced by strong waves when there is a channel across the bar due to the return current effect for both strong and weak outflows waves increase the alongshore transport in both directions from the inlet due to the wave induced setup over the ebb shoal wave breaking is more influenced by the topography of the ebb shoal than by wave current interaction although strong outflows show intensified breaking at the head of the main channel

lipid biomarkers in the zoige hongyuan peat deposit indicators of holocene climate changes in west china abstract lipid biomarkers extracted from a peat core obtained from the northeast edge of the tibetan plateau have provided a 13 kyr record of regional climate change a period of warmer climate corresponding to the holocene optimum between 9 ka and 5 ka is evident in greater alteration of n alkanoic acids and n alkanols and in the appearance of biomarkers indicative of greater microbial activity concomitant increases in local precipitation that raised the water level of the peat bog are recorded by increases in the proportions of c23 and c25 n alkanes that are mainly derived from submerged floating plants alternations in submergent and emergent plant n alkane proxies reveal multi decimeter scale rises and falls in the bog water level that relate to variation in precipitation on the tibetan plateau during the holocene major low water level events occurred around 12 6 11 3 10 7 9 4 8 3 6 0 4 5 3 1 2 1 and 1 0 ka these events correlate well with cold dry events recorded in same region from other climatic proxies that reflect millennial scale holocene instability in the asian monsoon system our biomarker results also indicate that peat accumulation and preservation on the tibetan plateau are more sensitive to variability in monsoonal precipitation than in annual temperature

a review of molecular organic proxies for examining modern and ancient lacustrine environments molecular organic geochemical proxies are increasingly being utilized to reconstruct past environmental conditions as new tools continue to be discovered and developed to date organic geochemical proxies have been developed mainly for use in marine systems and are widely used in paleoceanography in contrast organic proxies have been less commonly used on lacustrine sedimentary records one reason for this is that the wide range in the physical and chemical properties of lakes complicates application of some organic geochemical proxies in lacustrine settings furthermore in comparison to marine studies presently only a small number of studies have conducted or are currently conducting fundamental research aimed at developing organic geochemical proxies for use in lacustrine settings despite this an increasing number of paleo limnological studies are currently applying organic geochemical techniques to examine present and past environmental conditions in this manuscript we review the use of a number of commonly utilized organic geochemical and isotopic proxies and discuss their potential for environmental reconstruction in quaternary lacustrine deposits

pressure gradient driven nearshore circulation on a beach influenced by a large inlet tidal shoal system 1 the nearshore circulation induced by a focused pattern of surface gravity waves is studied at a beach adjacent to a major inlet with a large ebb tidal shoal using a coupled wave and wave averaged nearshore circulation model it is found that the nearshore circulation is significantly affected by the heterogeneous wave patterns caused by wave refraction over the ebb tidal shoal the model is used to predict waves and currents during field experiments conducted near the mouth of san francisco bay and nearby ocean beach the field measurements indicate strong spatial variations in current magnitude and direction and in wave height and direction along ocean beach and across the ebb tidal shoal numerical simulations suggest that wave refraction over the ebb tidal shoal causes wave focusing toward a narrow region at ocean beach due to the resulting spatial variation in nearshore wave height wave induced setup exhibits a strong alongshore nonuniformity resulting in a dramatic change in the pressure field compared to a simulation with only tidal forcing the analysis of momentum balances inside the surf zone shows that under wave conditions with intensive wave focusing the alongshore pressure gradient associated with alongshore nonuniform wave setup can be a dominant force driving circulation inducing heterogeneous alongshore currents pressure gradient forced alongshore currents can exhibit flow reversals and flow convergence or divergence in contrast to the uniform alongshore currents typically caused by tides or homogeneous waves

transient tidal circulation and momentum balances at a shallow inlet an analysis of transient momentum balances is carried out to elucidate circulation dynamics and exchange mechanisms at shallow barotropic tidal inlets circulation is computed using a depth integrated fully nonlinear time stepping finite element model with variably spaced grids having horizontal resolution down to 50 m velocity and elevation fields from the model are used to directly evaluate the contribution of each term in the momentum equations to the overall momentum balance a transformation of the x y momentum terms into an s n coordinate system is used to simplify the interpretation of the dynamics and provide vivid illustrations of the forces and resulting accelerations in the flow the analysis is conducted for an idealized inlet and contrasted with a highly detailed model of beaufort inlet north carolina results show that momentum balances in the immediate vicinity of these inlets vary significantly in time and space and oscillate between two dynamical states near maximum ebb or flood the alongstream momentum balances are dominated by advective acceleration pressure gradient and bottom friction cross stream balances are dominated by centrifugal acceleration and pressure gradients near slack balances more closely follow linear wave dynamics with local accelerations balancing pressure gradients and to a lesser degree coriolis comparisons between the idealized inlet and beaufort inlet show broad similarities in these momentum balances however natural inlet geometry and bottom topography as well as the tidal transmission characteristics of the sounds behind beaufort inlet produce strong asymmetries moreover momentum balances are highly localized often with subkilometer length scales the dynamics are used to explain the physical mechanisms for inlet exchange in particular the results indicate that the cross stream dynamics generate a wall along the length of an inlet during the stronger phases of the tide the wall is established by opposing cross inlet pressure gradients and centrifugal forces and it poses a significant barrier to cross inlet exchange during the stronger phases of the tide but is absent near slack

paleoclimate significance of n alkane molecular distributions and δ2h values in surface peats across the monsoon region of china abstract leaf wax molecular distributions and isotopic values are generally considered paleohydrologic proxies here we evaluate the sensitivity of alkane chain length distributions and compound specific hydrogen isotopic compositions 2halk in surface peats to environmental parameters across the monsoon region of china the alkane average chain length acl carbon predominance index cpi and 2halk values show relatively large variations in multiple samples from a single site highlighting the complexity of the processes affecting these ratios at small spatial scales nonetheless the site averaged cpi values correlate significantly with the mean annual temperature r 0 57 p

the history and variability of the east asian paleomonsoon climate abstract changes in the east asian paleomonsoon reflect interactions between the global atmosphere ocean land and ice systems and are also an expression of their combined effect within the boundary conditions imposed by the east asian continent and solar radiation the history of the east asian monsoon is an alternation between dominance by the dry cold winter and warm humid summer monsoons high resolution eolian sequences preserved in the chinese loess plateau reveal that the east asian monsoon may have commenced at least 7 2 ma ago they also provide evidence indicating that the pulsed uplift of the tibetan plateau at about 3 4 and 7 2 ma may have played an important role in inducing climate change the palaeoclimatic records of the last glacial cycle show high frequency variability on time scales of 1000 year or even shorter and instability of the east asian paleomonsoon system the high frequency variability could be due to a non linear response to orbital forcing or a result of the coupling processes between different components of the global system cold air activity in northern high latitudes the trans equatorial air streams from the southern hemisphere and possibly enso may have played an important role in east asian monsoon variability the synchroneity of all the palaeoclimatic events along the polar equator polar pep transect is still an open question correlation of limited palaeoclimatic records for the last 30 kyr obtained from east asia and australia suggests that the trans equatorial air streams driven by the monsoon and trade winds may have had an influence on opposite hemispheres

the 9 2 ka event in asian summer monsoon area the strongest millennial scale collapse of the monsoon during the holocene numerous holocene paleo proxy records exhibit a series of centennial millennial scale rapid climatic events unlike the widely acknowledged 8 2 ka climate anomaly the likelihood of a significant climate excursion at around 9 2 cal ka bp which has been notably recognized in some studies remains to be fully clarified in terms of its magnitude and intensity as well as its characteristics and spatial distributions in a range of paleoclimatic records in this study a peat sediment profile from the dajiuhu basin in central china was collected with several geochemical proxies and a pollen analysis carried out to help improve understanding of the climate changes around 9 2 cal ka bp the results show that the peat development was interrupted abruptly at around 9 2 cal ka bp when the chemical weathering strength decreased and the tree pollen declined this suggests that a strong drier regional climatic event occurred at around 9 2 cal ka bp in central china which was in turn probably connected to the rapid 9 2 ka climate event co developing worldwide in addition based on the synthesis of our peat records and the other holocene hydrological records from asian summer monsoon asm region we further found that the 9 2 ka event probably constituted the strongest abrupt collapse of the asian monsoon system during the full holocene interval the correlations between asm and the atmospheric 14c production rate the north atlantic drift ice records and greenland temperature indicated that the weakened asm event at around 9 2 cal ka bp could be interpreted by the co influence of external and internal factors related to the changes of the solar activity and the atlantic meridional overturning circulation amoc

sub weekly to interannual variability of a high energy shoreline abstract sixty one global positioning system gps sub aerial beach surveys were completed at 7 km long ocean beach san francisco ca usa between april 2004 and march 2009 the five year time series contains over 1 million beach elevation measurements and documents detailed changes in beach morphology over a variety of spatial temporal and physical forcing scales results show that seasonal processes dominate at ocean beach with the seasonal increase and decrease in wave height being the primary driver of shoreline change storm events while capable of causing large short term changes in the shoreline did not singularly account for a large percentage of the overall observed change empirical orthogonal function eof analysis shows that the first two modes account for approximately three quarters of the variance in the data set and are represented by the seasonal onshore offshore movement of sediment 60 and the multi year trend of shoreline rotation 14 the longer term trend of shoreline rotation appears to be related to larger scale bathymetric change an eof based decomposition technique is developed that is capable of estimating the shoreline position to within one standard deviation of the range of shoreline positions observed at most locations along the beach the foundation of the model is the observed relationship between the temporal amplitudes of the first eof mode and seasonally averaged offshore wave height as well as the linear trend of shoreline rotation this technique while not truly predictive because of the requirement of real time wave data is useful because it can predict shoreline position to within reasonable confidence given the absence of field data once the model is developed at a particular site

dynamics of a wave dominated tidal inlet and influence on adjacent beaches currumbin creek gold coast australia currumbin creek on the australian gold coast is a wave dominated tidal inlet which exhibits a particularly active morphology the recent history of currumbin creek entrance has seen rapid growth of the entrance for access to the ocean by fishermen as a world class surfing site and as a recreational area before the construction of two groynes in the 70 s currumbin creek entrance was highly variable in terms of inlet location and sand bar characteristics due to a cyclical behaviour of spit migration nowadays the entrance is stabilised however natural processes continue with the entrance infilling causing flood and navigation issues resulting in a regular dredging program to maintain an open entrance and for regular beach nourishment plans this paper investigates the behaviour of the entrance and adjacent beaches from aerial photographs and numerical modelling before groyne construction sand by passing was intense resulting in channel migration and sometimes the closure of the mouth after training works the longshore drift is diverted further north from the mouth leading to new circulation patterns behind the headland during fair weather conditions the sand transported by the longshore current is trapped by currumbin rock groyne resulting in a negative sediment budget in palm beach for high energy conditions the diverted longshore current splits in the southern palm beach resulting in a circulation cell the sediment of the southern beaches is stirred up and transported both northward and toward the inlet

beach morphodynamics influenced by an ebb tidal delta on the north florida atlantic coast tidal inlets interrupt longshore sediment transport thereby exerting an influence on adjacent beach morphology to investigate the details and spatial extent of an inlet s influence we examine beach topographic change along a 1 5 km coastal reach adjacent to matanzas inlet on the florida atlantic coast analyses of beach morphology reveal a behavioral change between 0 64 and 0 86 km from the inlet channel centerline interpreted to represent the spatial extent of inlet influence beyond this boundary the beach is narrow exhibits a statistically significant inverse correlation of shoreline position with offshore wave conditions and has a uniform alongshore pattern in temporal behavior as determined from empirical orthogonal function eof analysis on the inlet side of the boundary the beach experiences monotonic widening with proximity to the inlet lacks spatial consistency in correlation between shoreline position and wave conditions and exhibits an irregular pattern in spatial eof modes we augment the field observations with numerical modeling that provides calculations of wave setup and nearshore current patterns near the inlet highlighting the effects of the ebb tidal delta on the assailing waves the modeling results are verified by a natural experiment that occurred during may 2009 when a storm produced sedimentary mass accreted to the lower beach then subsequently split into two oppositely directed waves of sediment that migrated away from the initial accretion site in the subsequent months our results suggest that the ebb tidal delta produces a pattern of wave setup that creates a pressure gradient driving an alongshore flow that opposes the longshore currents derived from breaking of obliquely oriented incident waves the resulting recirculation pattern on the margin of the ebb tidal delta provides a mechanism through which the inlet influences adjacent barrier island beach morphology copyright 2016 john wiley sons ltd

shoreline variability via empirical orthogonal function analysis part i temporal and spatial characteristics empirical orthogonal functions eofs or principal components were used to extract the significant modes of shoreline variability from several data sets collected at three very different locations although eofs have proven to be a valuable tool in the analysis of nearshore data most applications have focused on the ability of the technique to describe cross shore or profile variability here however eofs were used to help identify the dominant modes of longshore shoreline variability at duck north carolina the gold coast australia and at several locations within the columbia river littoral cell in the u s pacific northwest in part one of this analysis characteristic patterns of shoreline variability identified by the eof analysis are described in detail at each site the dominant modes consisting of the first four eigenfunctions were found to describe nearly 95 of the total shoreline variability at both duck and the gold coast several interesting longshore periodic features suggestive of sand waves were identified while boundary effects related to natural headlands and navigational structures entrances dominated the pacific northwest data sets

quantitative assessment of precipitation seasonality and summer surface wetness using ombrotrophic sediments from an arctic norwegian peatland article i nfo article history received 18 april 2008 available online xxxx seasonality of precipitation is an important yet elusive climate parameter in paleoclimatological reconstructions this parameter can be inferred qualitatively from pollen and other paleoecological methods but is difficult to assess quantitatively here we have assessed seasonality of precipitation and summer surface wetness using compound specific hydrogen and carbon isotope ratios of vascular plant leaf waxes and sphagnum biomarkers extracted from the sediments of an ombrotrophic peatland bostad bog nordland norway our reconstructed precipitation seasonality and surface wetness are consistent with regional vegetation reconstructions during the early holocene 11 5 7 5 ka fennoscandia experienced a cool moist climate the middle holocene 7 5 5 5 ka was warm and dry transitioning towards cooler and wetter conditions from the mid holocene to the present changes in seasonality of precipitation during the holocene show significant coherence with changes in sea surface temperature in the norwegian sea with higher sst corresponding to greater percentage of winter precipitation both high sst in the norwegian sea and increased moisture delivery to northern europe during winter are correlated with a strong gradient between the subpolar low and subtropical high over the north atlantic positive north atlantic oscillation

δd values of individual n alkanes from terrestrial plants along a climatic gradient implications for the sedimentary biomarker record abstract the compound specific hydrogen isotope composition d of sedimentary n alkanes is increasingly used as a palaeoclimate proxy to explore the origin of the hydrogen isotope signal of n alkanes from higher terrestrial plant biomass in sedimentary organic matter of small lakes we have analysed the n alkane composition and d values of 31 plant biomass samples birch betula beech fagus oak quercus alder alnus hornbeam carpinus and myrtle myrtus as well as non stomata containing sphagnum cladonia and moss from 14 sites along a climatic gradient from northern finland to southern italy eleven of the sites were previously investigated for the n alkane d values in adjacent lake sediments and are compared to the leaf wax n alkane d values the distribution of terrestrial n alkanes in lake sediments was not found to be characteristic of the dominant vegetation around the lake evidently n alkane distributions within the same species at different sites were found to be variable these findings complicate the use of certain n alkane distributions in sediments as a palaeoenvironmental indicator d values of plant biomass n alkanes show a significant positive correlation with the precipitation d values biomass n alkane d values are in general less negative than the associated sedimentary n alkanes of terrestrial origin possibly due to the stronger evapotranspiration during the summer when sampling took place this suggests that n alkanes in leaves show seasonal variations and the sedimentary organic matter receives the lighter isotope signal of the autumn when most leaves are incorporated into the sediment the variability of the d values from non stomata containing plants is much higher than for broadleaf trees since stomata can regulate water loss through evapotranspiration the average chain length acl of n alkanes from deciduous tree leaves increases from north to south with increasing acl the hydrogen isotopic fractionation e between source water and n alkanes also increases our results prove that terrestrial n alkane d values record the d value of precipitation modified by the amount of isotope enrichment in the leaf water due to plant anatomy stomata vs no stomata and site specific meteorological conditions such as evapotranspiration relative humidity and soil moisture therefore terrestrial n alkanes in lake sediments can deliver information on changes in these parameters over geological timescales in lake sediments where aquatic n alkanes such as n c 17 record the lake water d value the isotopic difference between terrestrial and aquatic n alkanes could therefore be used to reconstruct changes in evapotranspiration

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

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

concordant monsoon driven postglacial hydrological changes in peat and stalagmite records and their impacts on prehistoric cultures in central china asian monsoon records are widely documented but specific proxies of monsoonal rainfall are limited we present here two new independent proxy records from peatland and stalagmite archives that indicate a high degree of concordance between monsoon driven hydrological changes occurring since the last deglaciation in a broad region of central china the wet periods elevated the water table in the dajiuhu peatland as recorded by reduced mass accumulation rates of hopanoids biomarkers for aerobic microbes confirmed by molecular phylogenic analyses the hopanoid based reconstruction is supported by the first report of the environmental magnetism parameter arm sirm anhysteretic remanent magnetization saturation isothermal remanent magnetization ratio of fine magnetic particles to total ferrimagnetic particles in a stalagmite from heshang cave in central china heavy rainfall resulted in the enhanced transport of coarse particles to the cave and thus low arm sirm values in the stalagmite the hydrological conditions inferred from the two records reveal three relatively long wet periods in central china 13 11 5 k y ago 9 5 7 0 k y ago and 3 0 1 5 k y ago archaeological evidence for the hydrological impacts on regional populations comes from the observation that temporal shifts among six distinctive cultures of the neolithic period to the iron age in central china occurred during wet periods or flood episodes spatiotemporal distributions of 1600 prehistoric settlement sites correlate with the proxy inferred fluctuating hydrological conditions with enhanced flooding risk forcing major relocations of human settlements away from riparian zones

peatland evolution and associated environmental changes in central china over the past 40 000 years central china has experienced stronger summer monsoon during warm periods such as marine isotope stages mis 1 and 3 and weaker summer monsoon during cool periods such as mis 2 the evolution history of dajiuhu subalpine peatland in central china can help investigate how the expansion and shrinkage of peatland were associated with monsoonal strength over the last glacial interglacial cycle here we apply bulk organic carbon and molecular biomarkers hopane and n alkane to reconstruct the evolution history for the dajiuhu peatland over the past 40 000 yr the results indicate fluctuations between lacustrine and peat like deposition during mis 3 steady lacustrine deposition during mis 2 and peatland initiation and expansion during mis 1 in the dajiuhu peatland therefore at the glacial interglacial scale warmer summer and cooler winter conditions in interglacial periods are crucial to trigger peat deposition whereas reduced evaporation in glacial period instead of decreased monsoonal driven precipitation would have played a predominant role in the regional effective moisture balance however within the holocene mis 1 monsoonal precipitation changes appear to be the main controller on millennial scale variations of water table level of the dajiuhu peatland

molecular proxies for paleoclimatology we summarize the applications of molecular proxies in paleoclimatology marine molecular records especially are proving to be of value but certain environmentally persistent compounds can also be measured in lake sediments loess deposits and ice cores the fundamentals of this approach are the molecular parameters the compound abundances and carbon hydrogen nitrogen and oxygen isotopic contents which can be derived by the analysis of sediment extracts these afford proxy measures which can be interpreted in terms of the conditions which control climate and also reflect its operation we discuss two types of proxy those of terrigenous and those of aquatic origin and exemplify their application in the study of marine sediments through the medium of ten case studies based in the atlantic mediterranean and pacific oceans and in antarctica the studies are mainly for periods in the present the holocene and particularly the last glacial interglacial but they also include one study from the cretaceous the terrigenous proxies which are measures of continental vegetation are based on higher plant leaf wax compounds i e long chain circa c30 hydrocarbons alcohols and acids they register the relative contributions of c3 vs c4 type plants to the vegetation in the source areas the two marine proxies are measures of sea surface temperatures sst the longer established one u37k is based on the relative abundances of c37 alkenones photosynthesized by unicellular algae members of the haptophyta the newest proxy tex86 is based on c86 glycerol tetraethers gdgts synthesized in the water column by some of the archaeal microbiota the crenarchaeota

postglacial climate change record in biomarker lipid compositions of the hani peat sequence northeastern china abstract the peat sequence at hani in northeastern china accumulated over the past 16 cal kyr in a percolation mire in which rain water and ground water seeped through the peat system the molecular compositions of n alkanes n alkanols and n alkanoic acids extracted from the hani peat sequence reveal different responses to the progressive evolution of climate and changes in the nature of the peat forming vegetation long chain length components that originate from the waxy coatings of subaerial vascular plants dominate the n alkane distributions throughout the hani peat sequence the paleoclimate integrity of these biomarker molecules appears to be well preserved most of the n alkanol distributions are similarly dominated by long chain components that indicate their origins from subaerial plants in contrast n alkanoic acid distributions are dominated by secondary components that record the importance of post depositional microbial activity in this peat sequence which evidently can be extensive in a percolation mire elevated n alkane paq values and c23 c29 ratios which are both molecular proxies for water loving plants record an especially moist local climate in the bolling allerod 14 5 to 12 9 ka younger dryas 12 9 to 11 5 ka and pre boreal 11 5 to 10 5 ka portions of the hani peat sequence depressed paq values and c23 c29 ratios and larger n alkane average chain length values indicate that the holocene climatic optimum 10 5 to 6 ka was a period of warmer climate with lower effective precipitation which contrasts with evidence of wetter climates in most of east asia

systematic monthly morphologic variation of assawoman inlet nature and causes assawoman inlet virginia u s a representative of small mesotidal barrier island tidal inlets exhibits systematic variations of sediment volume among certain of its morphologic elements sediment volume variations were calculated from topographic bathymetric maps of the inlet system as surveyed on 11 occasions at approximately monthly intervals by a fathometer and plane table and alidade of 36 pairings among nine morphologic elements seven show statistically significant pearson product moment correlation coefficients the southern ramp margin shoals are negatively correlated with the southern beach face and the northern ramp margin shoals are negatively correlated with the northern beach face on the northern spit the southern and northern ramp margin shoals themselves are negatively correlated the southern ramp margin shoals are negatively correlated with the fore flood tidal delta which is negatively correlated with a tidal channel on its landward side the back flood tidal delta is positively correlated with the northern ramp margin shoals and negatively correlated with the back side of wallops spit these associations may be qualitatively explained using wave and tidal climate data during the sampling year plus megaripple and bedding orientations constructive waves tend to transfer sediment from the ramp margin shoals landward building up the adjacent beach faces destructive waves tend to move sediment back to the ramp margin shoals waves striking the coast obliquely promote asymmetric growth of the shoals causing the ebb jet to erode into whichever is the smaller shoal

interaction between wave and tide generated processes at the mouth of a microtidal estuary matanzas river florida u s a abstract the zone of transition between the wave dominated open coast and tide dominated mouth of estuaries is complicated a time series study of wave parameters longshore currents and tidal parameters at the mouth of an estuary on the northeast coast of florida has demonstrated that tidal influence on nearshore processes is modest and localized tidal currents are nearly undetectable less than 0 5 km from the estuary mouth along the open coast tidal currents reach 80 cm s in the throat of the main ebb channel but immediately seaward of the terminal lobe of the ebb delta the tidal component is barely detectable with longshore currents predominating lateral flood channels adjacent to the estuary mouth show that tidal currents are significant and dominate longshore currents near low tide stage but are suppressed by longshore currents near high tide weather patterns may have an important effect on tidal processes at the estuary mouth because they control wave impingement and therefore longshore current speed and direction longshore currents may reinforce or suppress tidal currents particularly in lateral flood channels

millennial scale east asian monsoon variability of the last glacial deduced from annually laminated sediments from lake sihailongwan n e china abstract lake sihailongwan in jilin province ne china provides the first continuous and almost entirely seasonally laminated sediment record on the east asian mainland comprising the complete holocene the late glacial period and large parts of the last glacial sediment and palynological proxy data provide a finely resolved regional environmental history of the east asian monsoon a varve based chronology shl vc2 has been established for the last 65 000 years and allows a detailed comparison with other long regional and global palaeoclimate records vegetation density of the study area depends on the long run on precessionally forced insolation changes with superimposed millennial scale variability during the last glacial periodic increase of organic carbon content and thermophilous tree species like ulmus and fraxinus and contemporary decrease of shrub alnus precisely mirror millennial scale climatic variations primarily known from greenland ice cores as dansgaard oeschger cycles as well as late glacial period climate changes percentages of trees shrubs pollen and in particular lake productivity related data reveal substantial differences between interstadial intensities with those between 50 and 60 ka bp being more pronounced than the following ones