temperature seasonality and enso variability in the northern south china sea during the medieval climate anomaly interval derived from the sr ca ratios of tridacna shell abstract the nature of how the el nino southern oscillation enso and its seasonality respond to warmer climate is critical knowledge to predict future climates under the expected anthropogenic warming scenario in this study a sub fossil tridacna gigas specimen was collected from the northern scs and ams14c dating suggested that the animal lived around ad 1099 during the medieval climate anomaly mca interval the most recent natural warm period of the late holocene monthly sr ca ratios were determined by the icp oes measurements and a 30 year long sst record was calculated based on a sr ca sst calibration equation the results showed that the sst seasonality for this 30 year window around ad 1099 was about 3 11 c which is smaller than the modern warm period i e about 4 36 c for ad 1994 2005 interval this new result is consistent with another published tridacna gigas record that was dated around ad 990 from the northern scs the signals of enso activity were also extracted from the reconstructed sst record and statistical analyses yielded 9 el nino events and 8 la nina events within the 30 year record indicating that the frequency of enso activity around ad 1099 was similar to the modern instrumental period

profiles of trace elements and stable isotopes derived from giant long lived tridacna gigas bivalves potential applications in paleoclimate studies this study investigates the environmental and biological controls on trace element partitioning and stable isotope composition of modern giant long lived bivalves tridacna gigas with the aim to use these archives for paleoclimatic reconstructions firstly the intra shell variability is studied by measuring time equivalent profiles in the different shell layers characterised by different growth rates secondly the inter site variability is studied by comparing profiles derived from three modern specimens collected in sites across the indo pacific region characterised by different ranges of temperature and productivity these results show that 18o profiles are highly reproducible across the shell regardless of significantly different growth rates shell 18o is primarily controlled by water 18o and temperature comparison of intra shell mg ca profiles shows a clear and systematic partitioning where inner layer mg ca values are a least 2 3 times higher than outer layer and hinge areas inner layer mg ca shows seasonal oscillations but superimposed on an ontogenetic trend with increasing values and increasing amplitude mg ca oscillations with age the sr ca profiles do not show clear reproducible seasonal trends in the different shell zones it is concluded that mg ca and sr ca profiles appear to reflect a combination of biological and environmental controls that will need to be disentangled before using these proxies in paleoclimatic studies finally intra shell ba ca profiles are reproducible in great detail for all modern specimens studied inter site comparison shows that the amplitude and the timing of the ba ca peaks appear to reflect the timing and the amplitude of the chlorophyll peaks associated with phytoplankton blooms at each locality making this tracer a potential paleoproductivity indicator

fluctuations of caspian sea level beyond climatic variations the continued rising mode since about 1978 in the level of the caspian sea cannot be ascribed to a change in the hydrologic balance that is governed solely by runoff precipitation and evaporation such a change fails to explain some of the chemical links k cl rb cl ca cl sr cl and k rb between kara bogaz and caspian sea waters a more realistic model must include a tectono hydrodynamic factor that allows for subsurface addition of saline water to caspian sea and kara bogaz waters the subsurface water component could be akin to the coastal thermal springs in the area but must dissolve some evaporite deposits in the subsurface before addition to the waters of the inland sea a budget calculation gives an estimate of 2 to 9 subterranean addition of saline water to the seawater such an addition could cause a rise in the level of the caspian sea from 63 to as much as 225 cm within the past 20 yr

giant bivalves tridacna gigas as recorders of enso variability we compare monthly resolved oxygen isotope records derived from a giant bivalve shell tridacna gigas and massive parkes corals collected along the northern coast of papua new guinea this intercomparison study demonstrates that delta o 18 profiles obtained from these different aragonite secreting organisms collected from within a 30 km range are correlated in great detail and record the timing and amplitude of seasonal and interannual enso related variations in sea surface temperature sst and water isotopic composition which is closely related to rainfall furthermore the t gigas record is shown to be close to isotopic equilibrium with the local sea water in contrast to the corals which are approximately 4 parts per thousand offset these results reveal that living and fossil t gigas clam shells have the potential to yield reliable records of past changes in seasonality and enso variability as well as mean climate conditions in particular since the non porous shells are generally more resistant to diagenesis than coral skeletons they may provide robust estimates of past tropical climate for periods and locations where unaltered corals are absent crown copyright c 2011 published by elsevier b v all rights reserved

palaeolimnological approaches to climate change with special regard to the biological record abstract lakes systems respond physically chemically and biologically to changes in climate and these responses are registered in many various ways in lake sediment records this paper focuses principally on the biological record and describes recent research that aims to reconstruct i past variability in effective moisture and ii past variability in temperature changes in effective moisture are manifested especially by changes in lake water level in closed lake basins water level change can cause significant changes in water salinity that is registered in sediments by changes in the composition of fossil assemblages especially diatoms in open freshwater lake basins changes in water level are best reconstructed from the aquatic macrofossil record and potentially from the ratio of open water to littoral species of cladocera ostracods and diatoms the most promising biological method for reconstructing past temperature is chironomid analysis and a range of new chironomid temperature transfer functions are being developed however biological responses to changing temperature are usually indirect as a result of temperature effects on water column stratification nutrient cycling and alkalinity generation and in most cases a correct interpretation of the climatic significance of changes in the fossil record requires an understanding of the processes that are operating in the water column a multi proxy whole lake approach is advocated as the best way forward not only as a means of reconstructing past climate but also as a means of assessing the impact of climate change on lake systems

river inflow and salinity changes in the caspian sea during the last 5500 years abstract pollen spores and dinoflagellate cysts have been analysed on three sediment cores 1 8 1 4 m long taken from the south and middle basins of the caspian sea a chronology available for one of the cores is based on calibrated radiocarbon dates ca 5 5 0 8 cal ka bp the pollen and spores assemblages indicate fluctuations between steppe and desert in addition there are some outstanding zones with a bias introduced by strong river inflow the dinocyst assemblages change between slightly brackish abundance of pyxidinopsis psilata and spiniferites cruciformis and more brackish dominance of impagidinium caspienense conditions during the second part of the holocene important flow modifications of the uzboy river and the volga river as well as salinity changes of the caspian sea causing sea level fluctuations have been reconstructed a major change is suggested at ca 4 cal ka bp with the end of a high level phase in the south basin amongst other hypotheses this could be caused by the end of a late and abundant flow of the uzboy river now defunct carrying to the caspian sea either meltwater from higher latitudes or water from the amu daria a similar later clear phase of water inflow has also been observed from 2 1 to 1 7 cal ka bp in the south basin and probably also in the north of the middle basin

recent coastal evolution of the caspian sea as a natural model for coastal responses to the possible acceleration of global sea level rise abstract the caspian sea serves as an excellent natural laboratory for studies of coastal response patterns as it is highly variable in its water level over decadal and secular time scales coastal morphology presumably nearshore bottom slope and profiles of depositional coastal bodies or erosional scarps as well as rates and amplitudes of water level changes appear to be the most important factors of coastal response rates and patterns nearshore bottom slope determines not only shoreline retreat values according to the bruun rule but also the very patterns of coastal evolution for various morphological types of depositional coasts including deltaic coasts strict analytical prediction of coastal response to the accelerated sea level rise is yet to be solved analysis of every response pattern of depositional coasts to sea level changes requires a specific modification of the bruun rule however these equations should be regarded only as the means to estimate an order of magnitude of shoreline retreat or advance in many cases equations based on the bruun rule cannot be applied at all boundary conditions for each quantitative model should be thoroughly studied where possible longshore sediment drift sediment washover on to the landward slope of depositional coastal features and possible onshore or offshore aeolian sediment movement should be taken into account moreover applicability of the bruun rule based equilibrium approach will possibly diminish under the possible future acceleration of sea level rise

sefidrud delta and quaternary evolution of the southern caspian lowland iran abstract the southern caspian sea lowland in iran forms a thick sedimentary prism produced by interactions of marine deltaic and fluvial processes during the late neogene and quaternary deltaic and fluvial deposits have been developed mainly by the sefidrud which is the largest river of the country its drainage area ca 61 600 km 2 includes nearly the entire alborz mountain range and forms deep valleys gorges and a large delta at the southern coast of the caspian sea the sefidrud delta is so large that it covers one third of the large guilan mazanderan plain both from an aerial and volumetric point of view consequently the drainage network of the sefidrud represents the quaternary evolution of northern iran and can be used to test the hypothesized evolution of the region the sefidrud delta has been investigated using many short and long cores satellite images and lithofacies maps and the results show that this delta complex 1680 km 3 consists of a covered lower part and exposed upper deltaic sequences the lower and upper parts of the complex were formed during the early pleistocene and late pleistocene respectively the upper exposed alluvial and deltaic sediments represent a total progradation of approximately 50 km forming three separate delta subsequences d1 3 of which the last one d3 is the modern sefidrud delta the modern delta is a wave dominated blanket like sediment cover ca 30 m thick and 1550 km 2 produced during the last three millennia it was formed by 30 km progradation of six juxtaposed lobes each lobe corresponds to a long term sea level fluctuation of the caspian sea the active lobe ca 50 km 2 has been forming since 1550 ad late pleistocene deltaic sequences d1 3 particularly the modern one d3 were produced by relatively fast deposition due to high volume sediment load of the sefidrud it is suggested that they were produced after the opening of the rudbar gorge by river capture that in turn six times enlarged the drainage area previous deltaic progradation and marine transgressions were relatively slow and the development of the whole lowland at the southern caspian sea lasted ca 1 1 2 ma bp

comparison between instrumental observational and high resolution proxy sedimentary records of late holocene climatic change a discussion of possibilities abstract variability of the north atlantic region is a key factor in the workings of global climate changes related to orbital factors and to the thermohaline circulation thc occur on timescales ranging from 1000 to 100 000 years whereas subdecadal decadal and multidecadal trends are associated with changes in atmospheric circulation sea surface temperature sst and salinity long term changes are known only from proxies whereas shorter periodicities are identified in instrumental and other observational data between lies a range of less well known centennial periodicities too long to be recorded observationally and too short for all but the highest resolution proxy records such as tree rings atmospheric 14c and varved lake sediments numerous investigations of such periodicities involve comparisons between the proxy and the observational record however results depend on the length of the datasets being analysed the relative strength of the periodicities present whether data are stationary or non stationary the degree to which they have been smoothed in order to remove particular fluctuations and the methods of analysis employed ideally comparisons should be between datasets of equal length and of similar properties but these criteria are not always easy to fulfill a search for periodicities in a range of well known multidecadal datasets reveals that whilst some frequencies previously identified in the central england temperature cet record and in the koch sea ice index are statistically significant those found by several authors in the index of the north atlantic oscillation nao are not as the index approximates to white noise instead decadal periodicity of the nao described by several authors appears to be result of smoothing of the raw data periodicities of 6 1 33 9 and 213 years identified in a proxy record from laminated sediments from loch ness scotland appear respectively to be related to a subdecadal variations in sst and salinity in the north atlantic ocean b multidecadal interactions between the nao and the north atlantic thc and c a well known centennial solar periodicity

warming and cooling the medieval climate anomaly in africa and arabia the medieval climate anomaly mca is a well recognized climate perturbation in many parts of the world with a core period of 1000 1200 common era here we present a palaeotemperature synthesis for the mca in africa and arabia based on 44 published localities the data sets have been thoroughly correlated and the mca trends palaeoclimatologically mapped the vast majority of available afro arabian onshore sites suggest a warm mca with the exception of the southern levant where the mca appears to have been cold mca cooling has also been documented in many segments of the circum africa arabian upwelling systems as a result of changes in the wind systems which were leading to an intensification of cold water upwelling offshore cores from outside upwelling systems mostly show warm mca conditions the most likely key drivers of the observed medieval climate change are solar forcing and ocean cycles conspicuous cold spikes during the earliest and latest mca may help to discriminate between solar oort minimum and ocean cycle atlantic multidecadal oscillation amo influence compared to its large share of nearly one quarter of the world s landmass data from africa and arabia are significantly underrepresented in global temperature reconstructions of the past 2 000 years onshore data are still absent for most regions in africa and arabia except for regional data clusters in morocco south africa the east african rift and the levant coast in order to reconstruct land palaeotemperatures more robustly over africa and arabia a systematic research program is needed

a full sea level cycle in 65 years barrier dynamics along caspian shores abstract the caspian sea being a closed basin shows much higher rates of sea level change up to 340 mm yr than the oceans it experienced a full sea level cycle with an amplitude of 3 m between 1929 and 1995 its coasts therefore present an attractive physical model to test predicted changes along oceanic coasts as a result of expected eustatic sea level rise and to validate sequence stratigraphical interpretations of ancient sediments along the wave dominated coasts with intermediate shore face slopes in dagestan low onshore bars were formed during the 1929 1977 sea level fall they represent minor short lived 1 2 years transgressive oscillations within the major regressional trend after the 1977 lowstand a prominent barrier lagoon system was formed which during the first phase of sea level rise 1977 1988 encroached landwards about 18 m each year by washover during storms continuous retreat between 1988 and 1995 however barrier size diminished lagoons widened and deepened apparently due to lack of coarse grained sediment supply discontinuous retreat the 1995 highstand prevented the barriers from being overstepped altogether sea level fall after 1995 again produced low bars without lagoons the caspian sea barrier coast demonstrates that for the formation of barrier lagoon complexes the combination of transgression and storms is essential barriers may show either continuous or discontinuous development at constant rate of sea level rise and constant offshore slope depending essentially on the availability of coarse grained sediments the rate of sea level rise as a factor in barrier behaviour cannot be viewed independently from barrier dimensions which in turn depend on wave base depth and maximum storm wave height relations between para sequence thickness and frequency and amplitude of sea level change in closed basins with an independent sea level regime may differ markedly from those in basins influenced by eustasy

increased seasonality in the western mediterranean during the last glacial from limpet shell geochemistry the seasonal cycle is a fundamental aspect of climate with a significant influence on mean climate and on human societies assessing seasonality in different climate states is therefore important but outside the tropics very few palaeoclimate records with seasonal resolution exist and there are currently no glacial age seasonal resolution sea surface temperature sst records at mid to high latitudes here we show that both mg ca and oxygen isotope 18o ratios in modern limpet patella shells record the seasonal range of sst in the western mediterranean a region particularly susceptible to seasonal change analysis of a suite of fossil limpet shells from gibraltar shows that sst seasonality was greater during the last glacial by 2 c as a result of greater winter cooling these extra tropical seasonal resolution sst records for the last glacial suggest that the presence of large ice sheets in the northern hemisphere enhances winter cooling this result also indicates that seasonality in the mediterranean is not well represented in most palaeoclimate models which typically show little change in seasonal amplitude and provides a new test for the accuracy of climate models

sr ca profile of long lived tridacna gigas bivalves from south china sea a new high resolution sst proxy abstract high resolution 18o and sr ca ratio profiles of a modern live caught and a fossil dead collected giant bivalve shell tridacna gigas from northern south china sea were analyzed the high resolution 18o profiles as documented in most of previous studies showed pronounced seasonal cycles and recorded the combined influence of seawater 18o and sea surface temperature the sr ca ratio profiles derived from icp oes had well defined annual cycles and significant and negative correlation with sea surface temperature while the sr ca profiles derived from la icp ms did not reveal clear annual cycles this difference was likely caused by the organics contents in t gigas shells which had a chemical composition different than caco3 crystals and a heterogeneous distribution across the shell the sampling methods and the experimental errors two calibration equations between sr ca ratios determined by icp oes of modern t gigas shell and instrumental sst were calculated based on all monthly and extremum sst data and the equation from extremum data produced better sst predictions these results suggested that the high resolution icp oes derived sr ca ratios of t gigas in the south china sea had the potential of providing a good proxy of historical sst

delta o 18 sr ca and mg ca records of porites lutea corals from leizhou peninsula northern south china sea and their applicability as paleoclimatic indicators combined seasonal to monthly resolution coral skeletal delta 18 o sr ca and mg ca records are reported for one modem and two late holocene porites lutea corals from a fringing reef at leizhou peninsula the northern coast of the south china sea scs all the profiles for the period 1989 2000 reveal annual cycles well correlated with instrumental sea surface temperatures sst and display broad peaks in summer and narrow troughs in winter reflecting seasonal growth rate variations calibration against instrumental sst yields the following equations delta 18 o 0 174 0 010 xsst degrees c 1 02 0 27 mswd 5 8 sr ca mmol mol 0 0424 0 0031 xsst degrees c 9 836 0 082 mswd 8 6 and mg ca mmol mol 0 110 0 009 xsst degrees c 1 32 0 23 mswd 55 the scatter in the mg ca sst relationship is much larger than analytical uncertainties can account for suggesting the presence of sst unrelated components in the mg ca variation calculated sr ca sst values for two later holocene porites lutea samples u series ages similar to 541 bc and similar to 487 ad respectively from the same reef suggest that sst in the scs at similar to 541 bc was nearly as warm as in the 1990s the warmest decade of the last century but at similar to 487 ad it was significantly cooler this observation is consistent with climatic data reported in chinese historic documents confirming that the sr ca sst relationship is a reliable thermometer removing the sst component in the delta 18 o variation based on calculated sr ca sst values the residual delta 18 o reflects the deviation of the holocene seawater delta 18 o from the modem value which is also a measure of the holocene sea surface salinity sss or the summer monsoon moisture level in mainland china such residual delta 18 o was close to zero at similar to 541 bc and 0 3 parts per thousand at similar to 487 ad suggesting that it was as wet as in the 1990s at similar to 541 bc but significantly drier at similar to 487 ad in mainland china which are also consistent with independent historic records calculated mg ca sst values for the two late holocene corals are significantly lower than the sr ca sst values and are also in conflict with chinese historic records suggesting that coral mg ca is not reliable proxy for sst at comparable sr ca ranges fossil corals always display negative mg ca offsets if compared with the modem coral of the same site we interpret this observation as due to preferential loss of mg during meteoric dissolution of cryptic mg calcite bearing microbialites in the exposed fossil corals microbialites mgo up to 17 sr only 100 300 ppm are ubiquitous during reef building processes and their presence in only a trace amount will have a significant impact on coral mg ca ratios without detectable influence on coral sr ca ratios c 2004 elsevier b v all rights reserved

seasonal temperature variability of the neoglacial 3300 2500 bp and roman warm period 2500 1600 bp reconstructed from oxygen isotope ratios of limpet shells patella vulgata northwest scotland abstract seasonal sea surface temperature variability for the neoglacial 3300 2500 bp and roman warm period rwp 2500 1600 bp which correspond to the bronze and iron ages respectively was estimated using oxygen isotope ratios obtained from high resolution samples micromilled from radiocarbon dated archaeological limpet patella vulgata shells the coldest winter months recorded in neoglacial shells averaged 6 6 0 3 c and the warmest summer months averaged 14 7 0 4 c one neoglacial shell captured a year without a summer which may have resulted from a dust veil from a volcanic eruption in the katla volcanic system in iceland rwp shells record average winter and summer monthly temperatures of 6 3 0 1 c and 13 3 0 3 c respectively these results capture a cooling transition from the neoglacial to rwp which is further supported by earlier studies of pine history in scotland pollen type analyses in northeast scotland and european glacial events the cooling transition observed at the boundary between the neoglacial and rwp in our study also agrees with the abrupt climate deterioration at 2800 2700 bp also referred to as the subboreal subatlantic transition and therefore may have been driven by decreased solar radiation and weakened north atlantic oscillation conditions

natural and anthropogenic rapid changes in the kara bogaz gol over the last two centuries reconstructed from palynological analyses and a comparison to instrumental records abstract palynological analyses pollen and dinocysts of a sediment core taken in the kara bogaz gol have been used to reconstruct rapid and catastrophic environmental changes over the last two centuries chronology based on 210pb a natural cyclicity 65 years of water level changes in the caspian sea cs and in the kara bogaz gol kbg and anthropogenic factors building of a dam separating the cs and the kbg waters combine to induce rapid changes in water levels of the kbg in the salinity of its waters and in vegetation cover of its surroundings the impact of low water levels on the dinocysts is marked by a lower diversity and the survival of two species that are typical of the kbg the caspian sea species present in the kbg having disappeared during periods of higher water levels ad 1871 1878 the lake is surrounded by a steppe like vegetation dominated by artemisia whereas during periods of low water levels ad 1878 1913 and ad 1955 1998 the emerged shore are colonised by chenopodiaceae the period of ad 1913 1955 corresponding to decreasing water levels has an extremely low pollen concentration and a maximum of reworking of arboreal taxa during the last low level period humans responded by abandoning the shores of the bay what happened to the kbg can be used as an example of what may happen in the future for the aral sea a problem of reworking of tertiary dinocysts into modern deposits has been detected owing to the knowledge of the modern dinoflagellate assemblages recently made available through a water survey a comparison to modern surface pollen samples from central asia anzali caspian sea south and central basins aral sea lake balkhash lake issyk kul and the chinese tien shan range allows us to establish the potential reworking of at least five arboreal pollen taxa possibly by run off and dust storms

pacific east asian teleconnection how does enso affect east asian climate observational evidence is presented to show a teleconnection between the central pacific and east asia during the extreme phases of enso cycles this pacific east asian teleconnection is confined to the lower troposphere the key system that bridges the warm cold events in the eastern pacific and the weak strong east asian winter monsoons is an anomalous lower tropospheric anticyclone cyclone located in the western north pacific the western north pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures the anomalies persist until the following spring or early summer causing anomalously wet dry conditions along the east asian polar front stretching from southern china northeastward to the east of japan kuroshio extension using atmospheric general circulation and intermediate models the authors show that the anomalous philippine sea anticyclone results from a rossby wave response to suppressed convective heating which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central pacific warming the development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling both the anticyclone and the cooling region propagate slowly eastward the development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades the rapid establishment of the philippine sea wind and sst anomalies implies the occurrence of extratropical tropical interactions through cold surge induced exchanges of surface buoyancy flux the central pacific warming plays an essential role in the development of the western pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone sst interaction and midlatitude tropical interaction in the western north pacific

sr ca differences within and among three tridacnidae species from the south china sea implication for paleoclimate reconstruction abstract in this study eight tridacnidae specimens of three different species tridacna gigas tridacna derasa and hippopus hippopus were collected from xisha islands of south china sea the sr ca ratio which has been widely used as sea surface temperature sst proxy in coral samples was determined on these specimens using icp oes to examine their potential for paleoclimate reconstruction while within species differences were found to be insignificant the mean sr ca ratios of the three species 2 24 0 1 1 77 0 1 and 1 91 0 14 mmol mol for modern t gigas t derasa and h hippopus specimens respectively are statistically different species identification therefore is necessary before using tridacnidae sr ca ratios as paleoclimate recorders while the relationship between local sst and sr ca ratios of h hippopus was unclear the sr ca profiles of modern t gigas and t derasa specimens are significantly correlated to local sst implying that they can be used as sst proxies the range of sr ca ratios measured in this study is comparable to the tridacnidae sr ca measurements obtained in previous studies from other areas but there are also substantial differences in detail indicating that calibration for regional differences is also needed before paleoclimate reconstruction is attempted in addition although the mean sr ca values of t gigas t derasa and coral samples in xisha islands were significantly different their sr ca sst calibration slopes were comparable pointing to a similar thermodynamic fractionation and highlighting the potential of the combination of tridacnidae and coral samples for paleo sst seasonality reconstruction

record of little ice age sea surface temperatures at bermuda using a growth dependent calibration of coral sr ca 1 strontium to calcium ratios sr ca are reported for a massive brain coral diploria labyrinthiformis collected from the south shore of bermuda and are strongly correlated with both sea surface temperature sst and mean annual skeletal growth rate high sr ca ratios correspond with cold ssts and slow skeletal growth rate and vice versa we provide a quantitative calibration of sr ca to extension rate and sst along the axis of maximum growth and derive a growth dependent sr ca sst calibration equation to reconstruct western subtropical north atlantic ssts for the past 223 years when the influence of growth rate is excluded from the calibration sr ca ratios yield ssts that are too cold during cool anomalies and too warm during warm anomalies toward the end of the little ice age 1850 sst changes derived using a calibration that is not growth dependent are exaggerated by a factor of 2 relative to those from the growth corrected model that yields ssts 1 5 c cooler than today our results indicate that incorporation of growth rate effects into coral sr ca calibrations may improve the accuracy of ssts derived from living and fossil corals

a multi proxy approach to understanding complex responses of salt lake catchments to climate variability and human pressure a late quaternary case study from south eastern spain abstract this article focuses on a former salt lake in the upper vinalopo valley in south eastern spain the study spans the late pleistocene through to the late holocene although with particular focus on the period between 11 ka cal bp and 3000 ka cal bp which spans the mesolithic and part of the bronze age high resolution multi proxy analysis including pollen non pollen palynomorphs grain size x ray fluorescence and x ray diffraction was undertaken on the lake sediments the results show strong sensitivity to both long term and small changes in the evaporation precipitation ratio affecting the surrounding vegetation composition lake biota and sediment geochemistry to summarise the key findings the main general trends identified include 1 hyper saline conditions and low lake levels at the end of the late glacial 2 increasing wetness and temperatures which witnessed an expansion of mesophilic woodland taxa lake infilling and the establishment of a more perennial lake system at the onset of the holocene 3 an increase in solar insolation after 9 ka cal bp which saw the re establishment of pine forests 4 a continued trend towards increasing dryness climatic optimum at 7 ka cal bp but with continued freshwater input 5 an increase in sclerophyllous open woody vegetation anthropogenic and increasing wetness climatic is represented in the lake record between 5 9 and 3 ka cal bp 6 the holocene was also punctuated by several aridity pulses the most prominent corresponding to the 8 2 ka cal bp event these events despite a paucity of well dated archaeological sites in the surrounding area likely altered the carrying capacity of this area both regionally and locally particularly during the mesolithic neolithic transition in terms of fresh water supply for human animal consumption wild plant food reserves and suitable land for crop growth

a composite sea surface temperature record of the northern south china sea for the past 2500 years a unique look into seasonality and seasonal climate changes during warm and cold periods abstract high resolution late holocene climate records that can resolve seasonality are essential for confirming past climatic dynamics understanding the late 20th century global warming and predicting future climate here a new composite record of the sea surface temperature sst variation in the northern south china sea scs during the late holocene is constructed by combining seven seasonally resolved coral and tridacna gigas sr ca based sst time windows with the instrumental sst record from modern interval between 1990 and 2000 this composite multi proxy marine record together with the reconstructions from mainland china and tropical western pacific indicates that the late holocene warm periods the roman warm period rwp and medieval warm period mwp were prominently imprinted and documented in the climatic and environmental history of the east asia western pacific region meanwhile substantial and significant sst seasonality variations during the late holocene were observed in the composite record the observed increase in seasonality or amplitude of seasonal cycles during the cold periods around our study area was probably caused by the different amplitudes between winter versus summer sst variations in northern scs with much larger sst variation during winters than during summers for the late holocene in addition the distinctive warm cold and neutral climatic episodes identified in our northern scs composite sst record correspond well with other paleo reconstructions from mainland china and especially well with the northern hemisphere wide composites by moberg et al 2005 and ljungqvist 2010 the overall agreement however also calls for more information and insights on how seasonal temperatures and their ranges vary on decadal centennial timescales

high resolution saline lake sediments as enhanced tools for relating proxy paleolake records to recent climatic data series abstract lake level in an endorheic saline lake in southern europe has been inferred for the last 105 years 1889 1994 at an annual level of resolution using two independent methods first ordination analyses factor analysis fa correspondence analysis ca and detrended correspondence analysis dca have been used to point out the mineral successions of the sedimentary record these successions are evidenced by the arch disposition of both samples and mineral phases in the plane defined by the first two eigenvectors calculated by these analyses these temporal evolutions are the same as those obtained during the drying and refilling phases of saline lakes relay indices ri were obtained from distances to the first two eigenvectors which accurately reconstructed the lake level evolution during this period second an inferred lake level series was obtained using a multivariate time series model from the average maximum temperatures and total rainfall six main drought periods were found which coincided with known droughts in the area a high level of agreement was found between the two reconstructions which offered the possibility of directly extending the instrumental record back into the past therefore climatic changes could be reconstructed from saline lakes provided that an accurate chronological control of sedimentary processes is available

diatom based transfer functions for inferring past hydrochemical characteristics of african lakes abstract a new dataset of 282 modern diatom samples and associated environmental information has been created by merging existing regional datasets from north and east africa and niger the relationships between diatom species distributions and hydrochemistry are examined using canonical correspondence analysis cca and partial cca variables reflecting water conductivity ph and cation and anion composition account for significant and independent components of the total variation in the diatom data predictive models transfer functions are developed using the method of weighted averaging for conductivity r 2 0 87 ph r 2 0 77 and ratios between alkali and alkaline earth metals r 2 0 81 and carbonate bicarbonate and sulphate chloride ions r 2 0 82 prediction errors are estimated using the computer intensive method of jackknifing these transfer functions enlarge the potential domain for reconstruction of past hydrochemistry from fossil diatoms preserved in lake sediments

multi proxy reconstructions of northeastern pacific sea surface temperature data from trees and pacific geoduck abstract we demonstrate the potential for developing sea surface temperature sst reconstructions in the northeast pacific from combinations of tree ring and growth increment chronologies of the long lived marine bivalve the pacific geoduck six pacific geoduck chronologies developed from site along the washington british columbia coast are compared and combined with tree ring chronologies from california to alaska all chronologies are annually resolved and strongly relate to local to regional scale sst though differences in the response season as well as the spectral properties of the two proxies are observed both proxy types closely track sst and when used in combination yield a more robust sst reconstruction than tree ring or geoduck chronologies could provide alone in total variance explained in sst is 63 9 at the regional scale and 68 2 at a local scale providing sst estimates for more than 60 years prior to the start of continuous instrumental records in this region this study represents one of the few climate reconstructions where both proxies are annually resolved and is the first to integrate regional networks of geoduck chronologies and tree ring chronologies

seawater temperature seasonality in the south china sea during the late holocene derived from high resolution sr ca ratios of tridacna gigas temperature seasonality the difference between summer and winter temperature has significant influences on global terrestrial and marine ecosystems however most of proxy based climate records are of limited temporal resolution and thus insufficient to quantify the past temperature seasonality in this study high resolution sr ca ratios of modern live caught and fossil dead collected tridacna gigas shells from the south china sea scs were used to reconstruct the seawater temperature seasonality during the late holocene the averaged seawater temperature seasonality around 2165 75 bc 4 46 1 41 c derived from the data of 18 yr were similar to the seasonality of recent decade 4 41 0 82 c during ad 1994 2005 but the temperature seasonality around ad 50 40 3 69 1 37 c derived from the data of 48 yr and ad 990 40 3 64 0 87 c derived from the data of 11 yr was significantly lower than that during ad 1994 2005 the reduced seasonality around ad 990 40 was attributable to the unusually warm winter during the medieval times probably caused by the weakening of east asian winter monsoon our study highlighted the potential of t gigas shells in providing high resolution seasonality climate information during the late holocene

a high resolution sr ca and δ18o coral record from the great barrier reef australia and the 1982 1983 el nino abstract a high resolution near weekly sr ca and oxygen isotopic record is presented for a coral from the pandora reef in the great barrier reef gbr of australia during the period 1978 to 1984 the records are well correlated except for periods of high rainfall when river runoff has significantly modified the 18o value of seawater using the sr ca temperature calibration of de villiers et al 1994 the sr ca records exhibit seasonally controlled cyclical sst sea surface temperature variations of from 21 to 28 c during the very strong el nino of 1982 1983 the sr ca systematics indicate a sharp drop in the winter sst to 18 5 c this represents a temperature anomaly of 3 c which is approximately twice that given by the 18o variations suggesting an 2 amplification of the anomaly by the sr ca system possibly due to the increasing dominance of inorganically controlled aragoniteseawater fractionation the oxygen isotopic systematics show the combined effects of both temperature and changing seawater 18o values the latter reflecting the influx of 18o depleted runoff during periods of high rainfall due to the extremely low 10 3 sr and ca contents of river run off relative to seawater it is possible to use the sr ca thermometer to calculate temperatures independent of major floods and hence deconvolve the combined effects in the oxygen isotopic record of variable temperature and the 18o value of seawater using this approach it is possible to quantitatively reproduce the volume of runoff from the burdekin river during the periods of major flooding that occurred in early 1979 and 1981 the results of this study demonstrate that the combined use of high resolution sr ca and 18o systematics in scleractinian corals is a powerful tool for providing quantitative constraints on past climate

an image analysis technique to measure grain size variation in thin sections of soft clastic sediments this paper presents a simple and fast image analysis technique to measure grain size variation in thin sections of soft elastic sediments optical and backscattered electron microscope photographs are digitised from thin sections cut by freeze drying to avoid disturbing the sediments processing of the 256 grey scale images produces binary black and white images where white pixels represent the clay rich sedimentary matrix and black pixels represent elastic grains data measured include grain surface grain perimeter and centre of gravity two indices are defined to quantify grain size d 0 equivalent disk diameter and p phase percentages the technique is applied to silt and clay laminations attributed to the d division of a distal turbidite from lake baikal the data obtained using image analysis are similar to the conventional descriptions of such deposits indices calculated on very small samples e g on a single lamina allow for greater precision in interpretation of sedimentary processes compared to photomicrographs backscattered electron microscope images have better qualities and allow to quantify variations in the grain size along a sediment core the technique produces objective and quantified grain size observations in less time than conventional petrographic methods c 1998 elsevier science b v all rights reserved

the wandering of the volga delta a response to rapid caspian sea level change due to its very low gradient and absence of tide and surf the volga delta is an even more extreme example of the fluvially dominated type than the mississippi delta however it differs from all other large delta systems in that it borders a closed basin the caspian sea now at 26 m below global sea level caspian sea level is much more dynamic than that of the world oceans and rises at present about 1 5 cm yr a hundred time the eustatic rate within the quatemary sea level oscillations of at least 5 orders of magnitudes have been distinguished which seem grossly out of phase with eustatic sea level between the weichselian early khvalyn highstand of 50 m and the early holocene mangyshlak lowstand at 80 m the apex of the volga delta has wandered over 700 km alongstream the present day volga delta is not a highstand deposit but probably represents a minor transgression in a major regressional stage the delta does not show a coarsening upwards sedimentary sequence but consists of a weichselian transgressional fining upwards sequence topped by eolian deposits in which the delta distributary channels have been incised present day sedimentation is limited to a narrow fringe along the delta front and to deeper waters over 200 km offshore sea level changes outpaced aggradation to such an extent that volga sediment is spread over the whole north caspian plain sequence stratigraphical principles are difficult to apply because sea level cycles of five orders of magnitude are superimposed and because there is not enough sediment loading or tectonic subsidence to create sufficient accommodation space

cyclic water level oscillations of the karabogazgol caspian sea system abstract the karabogazgol kbg water level oscillations were reconstructed in the last 200 years using the geochemical evolution of the uppermost meter of its sedimentary infill high resolution studies of the mineralogical composition of the kbg sediments show alternating periods of high concentration brines followed by periods of more dilute waters the relative water level reconstruction was based on statistical models factor analysis fa correspondence analyses ca and detrended correspondence analyses dca whilst the chronological framework was established using the 210 pb technique this reconstruction was compared with the instrumental water level record of the caspian sea showing a high degree of correlation r 2 0 83 the agreement between the reconstructed and the measured water level oscillations of the caspian sea indicates that environmental changes can be reconstructed from closed lakes provided that an accurate chronological control of sedimentary processes is available the water level reconstruction shows that the caspian sea water level fluctuations follow a cyclical pattern rather than an erratic one as has been suggested in the literature two main periodicities of 62 5 and 38 46 years have been found

the high sensitivity of the palynological record in the vico maar lacustrine sequence latium italy highlights the climatic gradient through europe for the last 90 ka the palynological study of the vice maar lacustrine sequence italy is realized from the correlation of three drillholes the time span covers a period from the end of oxygen isotope substage 5b till the beginning of stage 1 from ca 90 to ca 10 ka bp at the base of the pollen diagram pollen zone 0 a younger dryas like fluctuation is observed after pollen zone 1 which is a well developed forest period substage 5a the forests of pollen zones 3 and 5 correspond to extensive climate improvements these last two zones are correlated to the ognon complex of the grande pile france and to interstadial periods 20 and 19 defined in the grip ice core greenland 72 6 66 2 ka before the stage 5 4 transition these two interstadial periods are global events found in the greenland and antarctica ice sheets as well as in north atlantic marine cores in other pollen records from north of the alps changes have been recorded but they are less pronounced than in vico pollen zone 7 stage 3 shows ca 7 warm humid fluctuations that might have a link to the dansgaard oeschger events greenland during zone 9 the lateglacial interstadial is recorded as well as the younger dryas event the localization of vice near plant refugia and far from the ice cap enables its pollen diagram to record abrupt and intense response to climate changes possibly through a link to the atlantic ocean via westerly winds c 1996 elsevier science ltd

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

climate variability in central china over the last 1270 years revealed by high resolution stalagmite records oxygen and carbon isotopic variations in the upper section of a stalagmite sf 1 from buddha cave 33 40 n 109 05 e dated by 230th 234u 210pb and lamination counting to a time resolution as fine as 1 3 years have recorded climate changes in central china for the last 1270 years the changes include those corresponding to the medieval warm period little ice age and 20th century warming lending support to the global extent of these events the isotopic records also show cycles of 33 22 11 9 6 and 7 2 years the 33 year cycle could well represent the 35 year periodicity of climate fluctuations previously recognized in china and europe cycles of 22 11 and 9 6 years have often been associated with the sunspot or lunar orbit variations the 7 2 year cycle was recently identified also in tree ring records from an area close to buddha cave these cycles suggest that external forcing e g solar irradiance may affect the summer monsoon over eastern china the general consistency between the climate characteristics inferred from the stable isotope records of sf 1 and those from other proxy records underscores the value of stalagmites as recorders of paleoclimate

seismic velocity and q anisotropy in fractured poroelastic media a fluid saturated poroelastic isotropic medium with aligned fractures behaves as a transversely isotropic and viscoelastic tiv medium when the predominant wavelength is much larger than the average distance between fractures a planar fracture embedded in a fluid saturated poroelastic background medium can be modeled as a extremely thin and compliant porous layer p waves traveling in this type of medium induce fluid pressure gradients at fractures and mesoscopic scale heterogeneities generating fluid flow and slow diffusion biot waves causing attenuation and dispersion of the fast modes mesoscopic loss a poroelastic medium with embedded aligned fractures exhibits significant attenuation and dispersion effects due to this mechanism which can properly be represented at the macroscale with an equivalent tiv medium in this work we apply a set of compressibility and shear harmonic finite element fe experiments on fractured highly heterogeneous poroelastic samples to determine the five complex and frequency dependent stiffnesses characterizing the equivalent medium the experiments consider brine or patchy brine co 2 saturated samples and a brine saturated sample with a heterogeneous fractal skeleton with fractures we show that fractures induce strong seismic velocity and q anisotropy both for qp and qsv waves enhanced either by patchy saturation or frame heterogeneity

gulf of maine shells reveal changes in seawater temperature seasonality during the medieval climate anomaly and the little ice age article i nfo in this study we use subannually resolved oxygen isotope values of fossil dead collected and modern live caught bivalve shells arctica islandica l from the northwestern atlantic gulf of maine usa to reconstruct past seasonal changes in seawater temperature our results indicate decreased seasonal temperature amplitude of about 1 6 c or 21 during medieval times ca ad 1033 1062 compared to shells from the early little ice age ca ad 1321 1391 and during the late 19th century ad 1864 1886 additionally seasonal oxygen isotope data suggest that summers were cooler and winters were warmer in the gulf of maine during the 11th century compared to summers and winters in the 14th century and the late 19th century the inferred decreased seasonality during medieval times likely resulted from increased stratification of the coastal waters due to warmer seawater temperatures as seawater cooled during the little ice age we suggest that increased vertical mixing of the coastal surface waters was a major driving factor for the observed increase in the amplitude of the seasonal seawater temperature cycle