reconstruction of a paleotemperature record from 0 3 3 7ka for subtropical south china using lacustrine branched gdgts from huguangyan maar abstract the concentrations of glycerol dialkyl glycerol tetraethers gdgts in catchment soils suspended particulate matter spm lake bottom sediments and sediment cores from huguangyan maar subtropical south china were investigated the distribution of isoprenoid gdgts has gdgt 0 crenachaol 2 and therefore the widely used tex 86 is precluded from being used for the calculation of lake water temperature in this lake the total concentration of branched gdgts br gdgts in the soils spm and lake bottom sediments ranged from 91 3 223 7 ng g 17 8 41 4 ng l and 864 2 2008 6 ng g respectively the molecular composition of br gdgts mbt values methylation of br gdgts and cbt values the cyclization ratio of br gdgts in the catchment soils differ from those in lake materials this difference indicates that br gdgts in the lake are largely produced in situ based on the global lake specific mbt cbt mat mean air temperature calibration the air temperature was reconstructed for lacustrine material in huguangyan maar the estimates fall in the range 23 2 23 8 c similar to the average value of local mat for the preceding 45 years the paleotemperature history of huguangyan maar was reconstructed using br gdgts extracted from a sediment core spanning the period 0 3 3 7 ka and ranged from 24 6 to 26 3 c the temperature pattern of huguangyan maar based on the global lake specific mbt cbt mat resembles those recorded in east china using numerous indicators the pattern consists of five cool and four warm periods including two distinct phases within the medieval warm period 900 1300 ad the coldest temperature in the little ice age 1550 1850 ad and reveals even finer temperature variations than other indicators this new method based on br gdgts produced in situ in the subtropical lacustrine environment provides a new sensitive and precise paleotemperature proxy for lacustrine sediments for which other gdgt based proxies are not applicable

planetary science a chunk of ancient mars analysis of a meteorite found in northwest africa prosaically named nwa 7533 indicates that it is the first sample of the regolith or soil of mars and is derived from the earliest martian igneous crust yet identified see letter p 513 this paper identifies the nwa 7533 meteorite from northwest africa as the first sample of martian highlands rock in the meteorite collection munir humayun and co authors show that nwa 7533 has a composition indicative of a highlands breccia it also contains zircons more than 4 4 billion years old implying that early crustal differentiation on mars occurred in the first 100 million years of its history coeval with earliest crust formation on the moon and the earth

the mediaeval warm period drought recorded in lake huguangyan tropical south china the geochemistry of dated sediment cores from lake huguangyan 21o9 n 110o17 e tropical south china reveals distinct stratigraphical patterns in total organic and inorganic carbon toc tic biogenic silica bs and total nitrogen tn over the past 1400 years in this hydrologically closed lake tic variations may reeect changes in the precipitation evaporation ratio which controls the evaporative enrichment of carbonate toc bs and tn in the sediment are proxy indicators of lake productivity and nutrient input which we believe are linked to local precipitation high tic content correlates with low concentrations of toc bs and tn and indicates two drought episodes dated to ad 670 760 and ad 880 1260 in the sediments of lake huguan gyan local historical chronicles support these data suggesting that the climate of tropical south china was dry during the mediaeval warm period mwp and wet during the little ice age lia the detected mwp drought is temporally correlated with evidence for lower precipitation on the guliya china and quelccaya peru ice caps and with increased salinity in moon lake us great plains

mid late holocene climate variations in southeast china inferred by the intermountain peat records from fujian china abstract the climate of southeastern china is strongly influenced by the easm and tcs which produce most of the precipitation in this area and sustain large scale industrial and agriculture activities however proxy climate records from this area are sparse because of the dense population and intensive human activities in this study a total of ten well dated peat cores collected from the intermountain basins in fujian province were evaluated to explore the initiation histories of the peat bogs and 13 c c of cellulose extracted from four cores were further analyzed to investigate the precipitation history over the last thousand years lithological characteristics of the peat sections show that coarse gravel and sands occur at the bottom of each core which implies that erosion may be the constraint for the initiation of these peat bogs the formation of intermountain peatlands indicates rapidly weakening erosion which in turn suggests a decline in intensive rainfall and or total rainfall based on ams ages three cores show consistent basal ages of approximately 4 2 ka bp whereas five cores exhibit consistent basal ages centered at approximately 1 2 ka bp this staged increasing trend of peat bogs distribution since the mid holocene coincides with the gradual decline in the intensity of the easm intensity suggested by the chinese stalagmite 18 o records which indicates that intensive rainfall in the fujian area has decreased as the easm has weakened during the late holocene this long term change on insolation scale may be connected to insolation and sst of the western north pacific ocean the 13 c c exhibits large variability in amplitude from 27 5 to 11 3 and the periods of heavier 13 c c and lighter 13 c c corresponded to the layers of gray muddy silt and black peat respectively we interpret the large amplitude variability in 13 c c as a reflection of changes in the proportions of submerged plant matter which is rich in 13 c heavier 13 c c indicates a higher proportion of submerged plants with more detritus input and suggests wetter hydrological conditions with higher precipitation the changes in 13 c c over time show that there was a rapid decreasing trend of 13 c c around 800 yr bp which indicated that precipitation decreased since 800 yr bp this decrease in precipitation was consistent with the decrease in temperature from the mwp to the lia which implies that there was a wetter climate during the mwp and a less wet during the lia in southeastern china

temperature trends over the past five centuries reconstructed from borehole temperatures for an accurate assessment of the relative roles of natural variability and anthropogenic influence in the earth s climate reconstructions of past temperatures from the pre industrial as well as the industrial period are essential but instrumental records are typically available for no more than the past 150 years therefore reconstructions of pre industrial climate rely principally on traditional climate proxy records each with particular strengths and limitations in representing climatic variability subsurface temperatures comprise an independent archive of past surface temperature changes that is complementary to both the instrumental record and the climate proxies here we use present day temperatures in 616 boreholes from all continents except antarctica to reconstruct century long trends in temperatures over the past 500 years at global hemispheric and continental scales the results confirm the unusual warming of the twentieth century revealed by the instrumental record but suggest that the cumulative change over the past five centuries amounts to about 1 k exceeding recent estimates from conventional climate proxies the strength of temperature reconstructions from boreholes lies in the detection of long term trends complementary to conventional climate proxies but to obtain a complete picture of past warming the differences between the approaches need to be investigated in detail

linkages between climate fire and vegetation in southwest china during the last 18 5ka based on a sedimentary record of black carbon and its isotopic composition abstract fires are sensitive to climate changes and in addition they have a major influence on the global carbon cycle land surface properties and chemical composition of the atmosphere which in turn can affect the climate system projecting the impacts of future climate changes on fire mediated biogeochemical processes requires understanding of how various climatic factors influence regional fire regimes however long term variations in fire activity and their controls are poorly known in this study we report the concentration of black carbon bc and its isotopic composition 13cbc in an upland lake sediment core from southwest china in order to elucidate linkages between changes in fire regime climate and vegetation over the past 18 5 ka the results show that the sedimentary bc content recorded variations in fire activity and exhibits a close negative correlation with the amount of precipitation delivered by the indian summer monsoon ism during heinrich event 1 18 5 15 0 cal ka bp the younger dryas 12 8 11 1 cal ka bp and the mid to late holocene the weakening of the ism led to greatly increased fire activity in southwest china in the last 1 0 ka the bc record may have been affected by human activity in the catchment which may have caused an increased influx of minerogenic material to the lake thereby diluting the sedimentary bc concentration the general trend of changing vegetation compositions inferred from the 13cbc values also tracks the variations of the ism suggesting a change from mixed c3 c4 plant ecosystems during the last glacial maximum to c3 plant dominated forest during the holocene however the abundance of c4 plants may be overestimated during the bolling allerod warm interval and the early holocene due to the fact that fires were probably limited to the savanna ecosystem in the valleys and low lying basins

the little ice age recorded by sediment chemistry in lake erhai southwest china on the basis of concentrations of 21 major and minor elements in a well dated sediment core from the deepwater part of lake erhai principal component analysis pca reveals three main factors cont

biogenic silica record in lake biwa of central japan over the past 145 000 years abstract the record of the biogenic silica flux bsf g cm 2 103yr 1 in lake biwa reflects changes in diatom productivity in the lake and provides information regarding changes in paleoclimatic conditions the bsf record of lake biwa demonstrates five periods over the past ca 145 000 yr when the bsf values were significantly greater than 7 5 g cm 2 103yr 1 and five intervals when they were lower the data imply that paleoclimatic conditions were warmer and wetter from ca 123 000 to 115 000 103 000 to 95 000 88 000 to 72 000 57 000 to 32 000 yr b p and around ca 6000 yr b p when the bsf values were greater and relatively dry and cold from ca 141 000 to 123 000 yr b p and during intervals between two of the five warm and wet episodes when the bsf values were lower time series of the bsf record can be correlated with the record of biogenic silica content in lake baikal and the marine oxygen isotope stages 1 through 6 furthermore the bsf values varied with much higher amplitude during the last interglaciation than during the last glaciation probably implying that the diatom productivity in lake biwa was likewise more variable and had a larger range under interglacial conditions than under glacial conditions

the wet little ice age recorded by sediments in huguangyan lake tropical south china abstract although temperature decreased in a similar trend in many regions around the word during the little ice age lia the reconstructed humidity is remarkably different from region to region the precipitation history during the lia is poorly understood as compared to the temperature history in tropical south china in this study a sediment core with a length of 117 5 cm was recovered in the central part of huguangyan lake in tropical south china total organic carbon toc total nitrogen tn inorganic carbon ic and non residual strontium sr were analyzed at approximately 1 cm intervals to study the regional precipitation changes during the lia generally sr containing minerals are sensitive to chemical weathering which is dominated by the precipitation in tropical south china thus the non residual sr in huguangyan sediments can be used as an indicator of precipitation changes which is also verified by the downcore variations of toc tn and ic in huguangyan lake the non residual sr correlated positively with toc and tn but negatively with ic in the sediment profile toc tn ic and the non residual sr jointly demonstrated a wet period from ad 1500 to 1750 which corresponds to the lia coincidently both the total solar irradiance tsi and northern hemisphere temperature have the lowest values between ad 1500 and 1750 over the past millennium therefore the wet lia in tropical south china was most likely caused by the low solar irradiation during the lia the low solar irradiation likely resulted in the decrease of the northern hemisphere temperature which weakened the intensity of the east asian summer monsoon easm and synchronously moved the north edge of the asian summer monsoon southward leading to an increase in the precipitation in tropical south china

stable isotope and ostracode species assemblage evidence for lake level changes of nam co southern tibet during the past 600 years abstract ostracode species assemblages and stable oxygen and carbon isotopes of shells from two 210 pb dated short cores of 78 cm and 47 cm length taken from lake nam co southern tibet provide information about lake level history of the past approximately 600 years at decadal resolution a transfer function is applied to reconstruct paleo water depths from modern ostracodes ostracode assemblages and isotope data from five species allow a subdivision into phases of lake level evolution before 1600 ad relatively low oxygen isotope values and high abundances of deep water 30 m ostracodes i e leucocythere dorsotuberosa leucocythere dorsotuberosa f postilirata suggest a lake level 10 m higher than today between 1600 ad and 1800 ad more positive oxygen isotope values and higher abundances of shallow water ostracodes i e ilyocypris cf mongolica candona xizangensis suggest a lake level approximately 40 m below modern level between 1800 ad and 1920 ad oxygen isotopes are characterized by a trend to more negative values followed by a trend to more positive ones these trends are interrupted by several short term fluctuations but overall oxygen isotope values suggest a drop in lake level a clearer lake level picture is provided by species assemblages that suggest a continuously increasing lake level since 1900 ad precipitation data from meteorological stations nearby show an increase in precipitation in the last 30 years the low lake level between 1600 ad and 1800 ad is contemporary to the little ice age during that cold period meltwater input into the lake decreased this underlines the sensitivity of the level of lake nam co to temperature changes on the tibetan plateau

the little ice age and medieval warm period in the sargasso sea sea surface temperature sst salinity and flux of terrigenous material oscillated on millennial time scales in the pleistocene north atlantic but there are few records of holocene variability because of high rates of sediment accumulation holocene oscillations are well documented in the northern sargasso sea results from a radiocarbondated box core show that sst was approximately 1 degree c cooler than today approximately 400 years ago the little ice age and 1700 years ago and approximately 1 degree c warmer than today 1000 years ago the medieval warm period thus at least some of the warming since the little ice age appears to be part of a natural oscillation 39 refs 4 figs 1 tab

hydroclimatic changes in china and surroundings during the medieval climate anomaly and little ice age spatial patterns and possible mechanisms abstract investigating hydroclimatic changes during key periods such as the medieval climate anomaly mca 1000 1300 ad and the little ice age lia 1400 1900 ad is of fundamental importance for quantifying the responses of precipitation to greenhouse gas induced warming on regional and global scales this study synthesizes the most up to date and comprehensive proxy moisture precipitation records during the past 1000 years in china and surroundings the proxy data collected include 34 records from arid central asia aca and 37 records from monsoonal asia our results demonstrate a pattern of generally coherent regional moisture variations during the mca and lia in mid latitude asia north of 30 n monsoonal northern china north china and northeast china was generally wetter while aca northwest china and central asia was generally drier during the mca than in the lia a west east mode the boundary between wetter northern china and drier aca was roughly consistent with the modern summer monsoon boundary in monsoonal china to the east of 105 e the northern part was generally wetter while the southern part was generally drier during the mca than in the lia a north south mode with a boundary roughly along the huai river at about 34 n these spatial patterns of moisture precipitation variations are also identified by instrumental data during the past 50 years in order to understand the possible mechanisms related to the moisture variations during the mca and lia we investigate the major sst and atmospheric modes e g the el nino southern oscillation enso the atlantic multidecadal oscillation amo and the north atlantic oscillation nao which affect the moisture precipitation variations in the study region using both the instrumental data and the reconstructed time series it is found that the enso may play an important role in determining hydroclimatic variability over china and surroundings on a multi centennial time scale and that the foregoing spatial patterns could be attributed to the la nina like el nino like condition during the mca lia in addition amo and nao may also have their own contributions

palaeovegetation and palaeoclimate in low latitude southern china during the last glacial maximum abstract the evolution of vegetation and climate changes in tropical regions during the last glacial maximum remains controversial a continuous high resolution terrestrial palynological data from 40 to 13 cal ka bp is recorded in sediments of huguangyan maar lake in southern china the biomization technique and pollen data are used to reconstruct the history of vegetation and climate changes during the last glacial maximum lgm the results suggest that the huguangyan area in the last glacial maximum was dominated by subtropical evergreen forest with some deciduous trees implying that the climate was drier and colder in southern china than at present grassland vegetation did not appear in this area a significant drop in temperature occurred at 18 5 cal ka bp and terminated at 15 5 cal ka bp and the annual mean temperature during the lgm was 2 3 c lower or even more than present this is in agreement with previous results from tropical low latitude regions

biologically induced calcite and its isotopic composition in lake ontario we studied water sediment trap and core samples from eastern lake ontario to reconstruct the factors controlling the biologically induced production and sedimentation of calcite during so called whiting events calcite accumulation and its isotopic composition are controlled by a complex set of interrelated factors including temperature primary productivity and the abundance of pica cyanobacteria during the stratified period calcite precipitation is highly correlated to lake temperature because physical and biological factors interact to produce conditions favorable for whitings during warm years when the lake stratifies early in the seasonal cycle carbonate stratigraphies in multiple cores from eastern lake ontario revealed similar patterns of historical variation in percent carbonate an exponential rise in carbonate accumulation occurred in nine cores after 1930 culminating in peak values in the early 1980s this rise was related to historic increases in primary productivity resulting from increased phosphorus loading to lake ontario superimposed upon this rise were four peaks centered on 1940 1942 1957 1961 1971 1977 and 1983 that correlate with maxima in summer air temperature anomalies from the great lakes region and with strong el niiio events these peaks are also associated with maxima in s c values and minima in s180 values of carbonate lending support to our model that more calcite is precipitated with higher 6 c values during warm years when thermal stratitication occurs early in the seasonal cycle beginning in the mid 1980s calcite accumulation and its 6 c ratio began to decrease suggesting a reduction in primary productivity in surface waters probably related to lower phosphate concentrations in epilimnetic waters of lake ontario during the stratified period reduced summer p loading may be explained either by a lagged response to p abatement measures that began in the late 1970s or by decreased p loading from upstream lake erie beginning in the late 1980s as a result of the establishment of filter feeding zebra mussels

environmental change controls of lacustrine carbonate cayuga lake new york dated sediment cores from cayuga lake new york state document that biologically mediated precipitation of calcite has been controlled by environmental change both natural and anthropogenic over the past 10 000 yr during the holocene hypsithermal 9 4 ka 14 c milankovitch forcing of summer insolation in the northern hemisphere resulted in a broad increase to 55 then decrease to 5 of calcite content in bottom sediment warmer summers resulted in earlier onset of thermal stratification of the water column which increased the duration of primary production as well as the abundance of picoplankton which in turn increased the amount of calcite precipitated at the end of the hypsithermal ca 3500 yr ago global cooling greatly reduced the amount of calcite precipitated however since a d 1940 calcite contents in cayuga lake sediments have risen up to 20 one hypothesis is that this recent increase in calcite is the result of cultural eutrophication nutrient loading however this rise in calcite also closely tracks the anthr opogenic rise of atmospheric carbon dioxide suggesting a possible link to global environmental change further research on hard water lake basins will be needed to test which of these two hypotheses is corr ect

late holocene indian summer monsoon variations recorded at lake erhai southwestern china in this study we report changes in indian summer monsoon ism intensity during the past 3500 yr inferred from proxy indices at lake erhai southwestern china both the pollen concentrations and other proxy indices including sediment grain size total organic carbon contents toc and elemental contents e g fe al clearly indicate a long term decreasing trend in ism intensity over the late holocene during the period from approximately ad 750 to ad 1200 pollen concentrations of conifer and broadleaf trees and herbs reached the lowest levels over the past 3500 yr while the pollen percentages of both herbs and broadleaf trees increased suggesting a significant medieval drought the grain size toc and elemental contents also support an arid climate during the medieval period the little ice age lia at lake erhai was characterized as cold and wet the medieval and lia climatic patterns at lake erhai were similar to those over most of the ism areas but anti phase with those over east asian summer monsoon easm areas we suspect that sea surface temperature variations in the indo pacific oceans and the related land sea thermal contrasts may be responsible for such hydroclimatic differences between easm and ism areas

westerlies asia and monsoonal asia spatiotemporal differences in climate change and possible mechanisms on decadal to sub orbital timescales abstract the westerlies dominated climatic regime wdcr in the present interglacial period was proposed because precipitation moisture variations between arid central asia and mid latitude monsoonal asia are out of phase or anti phased on different timescales during the holocene in this study we first review the development of the theoretical framework of the wdcr and then outline the boundary of its core area from the caspian sea in the west to the western hexi corridor in the east with the northern and southern limits coinciding with the domain of arid central asia next we present a synthesis of multiple lines of evidence for the occurrence of the wdcr on multi millennial sub orbital herein to decadal timescales during the holocene finally we examine the possible physical mechanisms responsible for the wdcr we find that external factors insolation changes induced by orbital factors generated the wdcr on a sub orbital timescale whereas a circum global teleconnection silk road pattern was the most significant factor responsible for the wdcr on centennial and decadal timescales the study provides a comprehensive summary of the development of our knowledge of the wdcr over the past several decades together with a tentative theoretical framework for understanding climatic and environmental changes within its region of influence in addition it forms a scientific basis for environmental management and ecological restoration in this arid region in the context of global warming

dust records from varved lacustrine sediments of two neighboring lakes in northeastern china over the last 1400 years dust storms are natural phenomena described in chinese historical documents as early as 1150 bc these documents provide a way to evaluate proxy data from different natural records the minerogenic clastic content and grain size from two closed maar lakes located a short distance apart in northeastern china were analyzed the area is located in the path of dust storms the minerogenic clastics in the studied maar lakes originate mainly from dust deposition general variations of the minerogenic clastic content in these two neighboring lakes show a good coincidence with dust concentration in a tibet ice core and dust events as recorded in historical documents the minerogenic clastic content in the lake sediments is linked with the climate conditions in the dust source regions and wind strength three periods of intensive dust events ad 1050 1330 ad 1590 1690 and the last 200 years have been identified during the past 1500 years the recent increasing pattern of clastic content could be linked to human activity in the dust source regions significantly most of the medieval warm period mwp was marked by a high frequency of dust storms

magnitude and significance of carbon burial in lakes reservoirs and peatlands globally lakes are currently accumulating organic carbon oc at an estimated annual rate of about 42 tg yr 1 most of the oc in all but the most oligotrophic of these lakes is autochthonous produced by primary production in the lakes the sediments of reservoirs accumulate an additional 160 tg annually and peatlands contribute 96 tg annually these three carbon pools collectively cover less than 2 of the earth9s surface and constitute a carbon sink of about 300 tg yr 1 although the oceans cover 71 of the earth9s surface they accumulate oc at a rate of only about 100 tg yr 1

severe drought in the early holocene 10 000 6800 bp interpreted from lake sediment cores southwestern alberta canada abstract six lake sediment vibracores from the foothills and mountain valleys of southwestern alberta were analysed on the basis of ams radiocarbon dates tephrochronology and sediment geochemistry from these results the magnitude timing and duration of the early holocene warm period are presented at about 10 000 bp immediately following the younger dryas cold period climate warmed dramatically precipitation decreased and surface evaporation increased previous research has identified this warm interval but new results have improved resolution of regional scale effects specific timing and severity sedimentation changed from extra basinal clastic to intra basinal organic between 10 000 and 9400 bp changes in subalpine lakes from sand silt deposition to biogenic carbonate precipitation suggest decreases in suspended sediment load caused by complete ablation of glacial sediment sources peat which formed in lakes of less than 4 m present depth indicates climate induced lake level lowering in the foothills water depth and stratigraphic position of the peat suggest that regional water table levels decreased by up to 6 5 m at cartwright lake an erosional unconformity 6 5 m below the modern lake surface indicates the lake had completely dried out either during or immediately after mazama tephra time 6800 bp

silicon isotope composition of diatoms as a paleoenvironmental proxy in lake huguangyan south china abstract silicon is essential for the growth of diatoms which utilize dissolved silicic acid in lake water and form opaline silica sio 2 n h 2 o during the uptake of dissolved silicic acid there is a preferential incorporation of light silicon isotope 28 si into biogenic silica resulting in the enrichment of heavy silicon isotope 30 si in dissolved silicic acid the silicon isotope composition of diatom silica 30 si diatom may thus record changes in the percentage utilization of dissolved silicic acid by diatoms which can be then related to other aspects of climate environment with the aim of exploring the potential of 30 si diatom as an indicator of lacustrine environment here we made the first measurements of 30 si diatom in the sediment core from lake huguangyan a closed crater lake in china the result shows that 30 si diatom varies from 0 6 to 1 1 and displays broad similarities to variations in contents of biogenic silica and organic carbon throughout the sediment core 30 si diatom is a reliable paleotemperature proxy in lake huguangyan which is supported by good correlation between 30 si diatom and available temperature records heavier 30 si diatom indicates greater dissolved silicic acid utilization at higher temperature while lighter 30 si diatom reflects decreased utilization at lower temperature the most negative 30 si diatom values in the sediment core occur between ad 1580 and 1920 which suggests ad 1580 1920 was the coldest period in lake huguangyan over the past 2000 years thus providing evidence for the existence of the lia in tropical south china there are few means by which to reconstruct the history of temperature changes in tropical terrestrial region 30 si diatom in this study has proven to be a new promising paleotemperature proxy in lacustrine sediments and may play important role in reconstructing past temperature changes at low latitude in the future detailed investigations on the silicon isotopes of diatoms in more lakes would be desirable in further research

hydrogeotechnical characterization of a metallurgical waste this paper presents the results of hydrogeotechnical characterization tests carried out on the metallurgical waste mw from a tailings impoundment located on the terraces of the moa river cuba characterization of the mw includes chemical and mineralogical analysis oedometer tests triaxial tests tensile strength tests determination of the water retention curve and shrinkage and permeability tests the mw which has a grain size distribution similar to that of a silt mainly contains iron and heavy metals minerals and has low plasticity consolidated undrained triaxial tests on remoulded samples indicate a dilative behaviour with a decrease in pore water pressure near failure the material is susceptible to liquefaction when subjected to a cyclic load in the triaxial test hydraulic conductivity soil stiffness and compressive and tensile strength of the mw have an important dependence on the degree of saturation and vary significantly during the drying process the results indicate that during t

panigarh cave stalagmite evidence of climate change in the indian central himalaya since ad 1256 monsoon breaks and winter southern jet depressions abstract variations in petrography stable isotopes reflectance and luminescence along the central growth axis of a 14 5 cm stalagmite from panigarh cave indicate cooler and slightly wetter conditions in the himalayan foothills of northern india during the little ice age lia which lasted from ad 1489 1889 based on deposition of calcite and ad 1450 1820 based on rapid changes in 18o values conditions were warmer and drier during the preceding medieval climate anomaly mca and also in the post lia periods as evidenced by deposition of aragonite a review of currently existing stalagmite and other proxy data from south and east asia reveals a broad spatial pattern in precipitation over south and east asia during the lia with northern areas showing generally increased precipitation and southern areas reduced precipitation during the mca and after the lia the records suggest this pattern was reversed weaker ism during the lia brought drought conditions to the core ism area but triggered more monsoon breaks that brought higher precipitation to the himalayas at the same time the weaker ism may also have pushed more depressions along the path of the southern winter jet which brought more winter precipitation to the himalayas and therefore a lia wetter in our study area

climatic fluctuations during the lia and post lia in the kumaun lesser himalaya india evidence from a 400 y old stalagmite record this paper presents the first stable isotope delta o 18 and delta c 13 data of a similar to 400 years 1590 2006 ad long annual to decadal resolution speleothem record collected from the indian lesser himalaya the data show a variation from 2 7 to 5 9 parts per thousand in delta o 18 and 5 3 to 8 8 parts per thousand in delta c 13 the isotopic analyses indicate that the climate during this period can be divided into two stages a wet phase during the little ice age lia 1590 1850 ad and comparatively dry phase during the post lia after 1850 ad however the record also documents the minor dry events during the lia and a wet episode after the lia within the age uncertainty the dry spells during the lia are linked with the historical drought events in the indian subcontinent and similar latitudes the isotopic record is consistent with a number of previous studies in the areas influenced by the westerlies but appears to be conflicting to the regions dominated by the indian summer monsoon ism this may be due to the possible changes in the strength of westerlies in the study area and added by negative anomaly of north atlantic oscillation nao during the lia c 2012 elsevier ltd and inqua all rights reserved

early interglacial carbonate dilution events in the south china sea implications for strengthened typhoon activities over subtropical east asia abstract a compilation of many late quaternary marine sediment records from the northern south china sea scs continental slope confirms 15 50 reductions in sedimentary calcium carbonate concentrations between 11 0 and 8 5 ka bp in the early holocene this low carbonate event occurred at a time when the regional sea level rose from 50 m to 10 m which drowned large areas of continental shelves especially those near and within the taiwan strait this event is associated with a significant increase in bulk sedimentation rates on the upper continental slope and the relative abundance of fine grained detritus sediment provenance analyses suggest a dominant terrigenous input from taiwan and a minor contribution from luzon during the low carbonate event similar to the background terrigenous deposition in other periods of the holocene two comparable low carbonate events respectively from the beginning of marine isotope stages 5 5 and 7 3 have also been recognized pointing to similar causal factors while carbonate dissolution and carbonate accumulation rate should not have been responsible increased terrigenous input and dilution is considered as the main cause for the recurrent low carbonate events in early interglacials we further hypothesize that during early interglacials fluvial sediment discharge from taiwan and luzon intensified due to stronger typhoon activities and massive fine grained sediments from these two end members may have been transported to the northern scs continental slope via surface and deep ocean currents the conjecture of strengthened typhoon activities over east asia during the early holocene is supported by high ocean heat contents in the west pacific warm pool area with the prevailing la nina like conditions

continental climate response to orbital forcing from biogenic silica records in lake baikal changes in insolation caused by periodic changes in the earth s orbital parameters provide the primary forcing for global ice ages1 6 but it is not clear to what extent the climates in continental interiors are controlled directly by regional variations in insolation and to what extent they are driven instead by the highly nonlinear response of the oceans and ice sheets here we investigate this question using the record of biogenic silica in lake baikal as a proxy for climate change in this high latitude mid continental region we find a good correlation between this record and that of marine oxygen isotopes4 over the past 250 kyr the baikal record exhibits both a strongly nonlinear component manifested in a 100 kyr periodicity and weaker direct insolation components manifested in the 41 kyr obliquity and 23 and 19 kyr precession orbital cycles these results show that even though extreme continental climates such as this are influenced directly by insolation variations they are dominated by the nonlinear rhythm of the oceans and ice sheets

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

new evidence for the presence of changbaishan millennium eruption ash in the longgang volcanic field northeast china abstract the changbaishan millennium eruption ad 940s produced a widely distributed tephra layer around northeast asia this tephra layer serves as a marker bed in greenland ice cores and in marine lake archeological and tsunami sediments in japan and the surrounding region however little attention has been paid to the widespread sediments west of changbaishan volcano here we present new stratigraphic geochemical varve chronology and 14c geochronological data from the varved sediments in lake sihailongwan longgang volcanic field northeast china extending the westerly margin of this eruption the distinctive geochemical characteristic of volcanic glass ranging from trachyte to rhyolite similar to those of proximal and distal tephra confirmed the occurrence of changbaishan millennium eruption ash in the lake illustrating the westward dispersal fan of the ash deposits the position of the peak concentration of glass shards of this tephra was dated to 953 37 ad by varve chronology and the radiocarbon samples immediately above this tephra gave a date of 940 1020 ad overlapping the most recent ages for this eruption the occurrence of changbaishan millennium eruption ash in this lake enables a direct and precise synchronization with other high resolution archives in northeast asia such as maar lakes and peat and marine sediments thus providing an isochronous marker for a range of sedimentary contexts

millennial scale asian summer monsoon variations in south china since the last deglaciation abstract characterizing spatiotemporal variability of the asian summer monsoon asm is critical for full understanding of its behavior dynamics and future impacts the present knowledge about asm variations since the last glaciation in south china largely relies on several precisely dated speleothem stable oxygen isotope 18 o records although these speleothem 18 o signals provide useful evidence for regional past environmental changes their validity for denoting asm intensity remains a great controversy the huguangyan maar lake hml provides one of the most complete archives of environmental and climatic changes in the tropical subtropical south and east asia since the last glaciation here we document a continuous centennial to millennial scale asm record over the past 16 ky bp from the high sedimentation rate hml sediments in contrast with the low amplitude variations of chinese speleothem derived 18 o signals and the chinese loess based monsoon precipitation proxy indexes our multi proxy records reveal a pattern of high amplitude regional climatic fluctuations including fine scale oscillations during the bolling allerod warming the 8 2 ka cooling event and an abrupt climate shift from 6 5 5 9 ka the existence of bond like cold dry events indicates a distinct influence of the north atlantic circulation on low latitude monsoon changes the broad comparability between the hml paleo proxies chinese speleothem 18 o records and the northern hemisphere summer insolation throughout the holocene suggests that solar insolation exerts a profound influence on asm changes these findings reinforce a model of combined insolation and glacial forcing of the asm

lacustrine organic fluxes and palaeoclimatic variations during the last 15 ka lac du bouchet massif central france to assess the influence of climatic changes on organic lacustrine sedimentation two cores recovered from the centre of the lac du bouchet were studied by petrographical palynofacies and geochemical methods only core ldb h was used for estimation of the organic fluxes the variation of these fluxes with climo stratigraphic periods showed low organic fluxes during the lateglacial an increase at the beginning of the holocene a minimum at the end of the atlantic period resulting from the climatic cooling and a maximum at the end of the sub boreal related to the installation of the present climatic conditions