late quaternary climate and landscape evolution in arid central asia a multiproxy study of lake archive bayan tohomin nuur gobi desert southern mongolia abstract a 7 m sediment core from the bayan tohomiin nuur dry lake located in southern mongolia was investigated by a multidisciplinary study to reconstruct the history of climate and paleoenvironmental conditions during the late quaternary the geochemical granulometric palynological and ostracod results show a graduation of at least nine climatic units during the last 15 ka cal bp the climate during the late glacial changed from wet towards more dry conditions representing the beginning of the younger dryas period at 11 ka cal bp a rise in temperature and precipitation could be reconstructed marking the onset of the holocene the humid period of the holocene lasted until about 4 ka cal bp interrupted by shorter dry cold reversals at 8 5 7 5 ka cal bp and 5 4 5 ka cal bp the aridity in southern mongolia increased afterwards accompanied by the strengthening of aeolian processes dune remobilization and lake desiccation

early holocene aeolian dust accumulation in northeast china recorded in varved sediments from lake sihailongwan abstract annually laminated sediments of lake sihailongwan shl in northeast china preserve a high resolution record of past climatic and environmental changes thin sections of varved early holocene sediments were analyzed using light optical and scanning electron microscopic methods sediment micro facies and geochemical analyses reveal two different seasonal clastic layer types spring snow melt and dust layers dust layers distinctly differ from snow melt layers through their finer grain size better sorting higher al and lower mg and ca contents in contrast to recent lake shl sediments during the early holocene silt sized dust has been deposited after spring snow melt and after pronounced spring diatom blooms for the time interval between 11 580 and 7060 varve years bp dust layers were quantified at annual resolution highest intensities and frequencies of dust accumulation are observed in the period from 11 100 to 8200 varve years bp in good agreement with dry conditions in this time interval documented by palaeoclimatic records derived from lake sediments and loess in central asia and northern china based on modern meteorological observation of dust storms in china the dust accumulation record mirrors mainly the variation in climatic conditions governing generation of cyclone and cold air surges in the arid and semi arid mid latitude regions of china and mongolia on multidecadal and centennial time scales solar activity might have been an additional forcing factor for dust accumulation frequency in the early holocene spectral analyses reveal 205 years and 88 years periodicities in variations of dust accumulation frequency that likely reflect the de vries suess and the gleissberg solar cycles

assessment for paleoclimatic utility of terrestrial biomarker records in the okhotsk sea sediments we measured terrestrial plant biomarker long chain n alkanes in the sediment cores taken from the sea of okhotsk to examine paleoclimatic utility of long chain n alkanes in marine sediments this study demonstrates that sedimentary record of n alkane in the sea has a high potential to provide important complementary paleo climate paleo environmental information molecular distributions of long chain n alkanes in marine sediments show a typical signature of terrestrial plant wax derived n alkanes with strong odd carbon number predominance from the last glacial to the present suggesting a source of long chain n alkanes in the okhotsk sea sediments has been terrestrial higher plants throughout the time the down core profiles of concentrations of c25 c35 n alkanes in xp07 c9 collected from the northwestern site revealed three events of enhanced terrestrial organic matter input during the last deglaciation the two pronounced events correspond to melt water pulse mwp events 1a 14 5 12 5 ka and 1b 11 6 5 ka these events possibly linked to increases in river discharge and erosion of submerged continental shelf due to drastic rise in sea level down core profiles of molecular distributions of n alkanes in the okhotsk sea sediments significantly vary over the last 25 kyr and are similar to that of a peat core sequence in the east russia and essentially consistent with pollen data from marine and peat core sequences

holocene vegetation and climate of the alashan plateau nw china reconstructed from pollen data a set of 55 recent pollen spectra from the alashan plateau and the qilian mountains qilianshan northwestern china has been analyzed the established relationships between the pollen spectra and modern vegetation and precipitation patterns of the studied area have been applied to 65 fossil pollen spectra from a 825 cm long sediment record collected in the topographic depression formerly occupied by eastern juyan palaeolake 41 89 n 101 85 e 892 m a s l several qualitative approaches e g indicator plant species artemisia chenopodiaceae and ephedra fragilis type s l ephedra distachya type pollen ratios and quantitative methods of vegetation and climate reconstruction have been tested with the surface pollen and then applied to the eastern juyan pollen record fossil pollen data reveal pronounced environmental changes in the studied area of the alashan plateau between ca 10 700 and 1700 cal yr b p desert taxa as chenopodiaceae nitraria calligonum reaumuria were abundant in the vegetation cover around the study site through the whole record pollen spectra dated to ca 10 700 5400 cal yr b p are characterised by highest values of chenopodiaceae e fragilis type and other desert indicating taxa suggesting rather dry climate most favourable conditions are reconstructed between 5400 and 3900 cal year b p on the basis of relative increase in abundance of artemisia pollen a return to dry conditions occurred at about 3900 cal yr b p the lake finally desiccated after 1700 cal yr b p reconstructed dry climate oscillations between 5900 and 5400 and 3100 cal yr b p correlate well with similar events found in the published records from northern and western china and central mongolia however eastern juyan record does not show the early holocene humidity maximum as suggested by the sedimentary data from monsoon influenced areas of china

climate change and cultural response around 4000 cal yr b p in the western part of chinese loess plateau new data suggest that dramatic environmental change in the western loess plateau of china corresponded with substantial changes in human demography ca 4000 cal yr b p these data demonstrate that a rapid climatic transition from wet to dry led to an ecologically devastated period between 4090 and 3600 cal yr b p the sudden reduction in the number of archaeological sites during this period namely a reduction in the total number of sites and a contraction of the areal distribution of sites points to declining agricultural productivity associated with widespread aridification beginning at 4000 cal yr b p 2005 published by university of washington

hydrogen isotopic ratios of plant wax n alkanes in a peat bog deposited in northeast china during the last 16 kyr abstract based on paleoclimatic reconstructions using various proxies the holocene climate optimum 10 5 6 ka has been characterized as a warmer and wetter period in most of east asia the summer monsoons associated with the east asian monsoon evidently intensified and extended further inland from the pacific ocean a source region of moisture a notable exception to this general pattern exists in northeast china where less wet conditions are recorded we determined molecular compositions of individual plant wax hydrocarbons and their hydrogen isotope compositions d values in a radiocarbon dated peat core recovered from the hani marsh in jilin province china and confirmed that the temperature dependent effective precipitation in northeast china decreased during the holocene climate optimum a combination of p aq an indicator of the relative contribution of aquatic to terrestrial plants and the difference in d between low c 23 c 25 and c 27 and high molecular weight c 31 n alkanes in the hani peat bog indicates a dramatic change in vegetation from the deglaciation to the holocene no significant differences were observed between the d values of low and high molecular weight n alkanes with relatively high d values and low p aq during the early holocene indicating that all n alkanes were produced by evapotranspiration sensitive terrestrial plants during that time however lower d values of mid chain n alkanes c 23 c 25 and c 27 relative to the long chain n alkane c 31 together with higher p aq values during the deglaciation 14 11 ka suggest an increase in the contribution of aquatic plants and a higher water level during the period the study demonstrates that northeast china was under a markedly wetter climate condition during the late deglaciation for the 16 kyr record in the hani peat sequence we infer that moisture delivery by the east asian monsoon was relatively invariable in northeast china but increased evaporation during the warmer holocene climate optimum reduced the effective precipitation defined by the balance between precipitation and evaporation

synoptic stability and anomalies in ne china inferred from dust provenance of sihailongwan maar sediments during the past 80 kyr abstract the paleo synoptic conditions that prevailed during the past 80 kyr in northeastern china are inferred from the elemental and sr nd isotopic compositions of lake sihailongwan maar sediments the detrital fraction in the lake sediments is dominated by aeolian input of felsic rock origin with little contribution of local volcanic material based on the isotopic sr nd composition of the lake core sediments we postulate that the deserts of northern china are the main source of allochthonous particles to the lake throughout the past 80 kyr northwesterly winds associated with the east asian winter monsoon and high latitude westerlies are the main carriers of dust from these deserts to the lake the deserts of central china are an additional minor dust source the episodic dust input from these deserts results from anomalous dry southwesterly winds these could be related to either el nino conditions or to delays in the onset of the east asian summer monsoon rains

anti phase oscillation of asian monsoons during the younger dryas period evidence from peat cellulose δ13c of hani northeast china abstract significant changes in the global atmospheric and oceanic circulation system occurred during the younger dryas cold period several researchers have demonstrated a weakening of intensity of the indian ocean summer monsoon during that period however the exact characteristics of the east asian summer monsoon still remain vague here we present a late glacial precipitation proxy record of the east asian summer monsoon based on the peat cellulose 13 c found in hani northeast china both the peat cellulose record and a pollen record from lake sihailongwan sediment indicate an abrupt increase in precipitation in the region during the younger dryas period these results support the occurrence of wet conditions in the north and of dry conditions in the south of the chinese mainland during that period by examining the activity of the east asian summer monsoon on an interannual timescale we propose a theory for the anomalous precipitation distribution that we attribute to the occurrence of an el nino like phenomenon in the equatorial pacific ocean during the younger dryas in this case the intensity of the western pacific subtropical high may strengthen and its position over the western pacific ocean may move northward this could cause an enhancement of the east asian summer monsoon and migration of a monsoonal rainbelt towards the northern region of the chinese mainland resulting in a precipitation distribution of wet conditions in the north and dry conditions in the south therefore this anomalous rainfall distribution should be considered to indicate the strengthening of the east asian summer monsoon in anti phase with the indian ocean summer monsoon that weakened during the same period this agrees with the previously revealed anti phase variations of the two monsoons during the ice rafted debris cold events of the north atlantic ocean it appears that in relation to the abrupt temperature drop in the northern hemisphere on centennial to millennial time scales anti phase variations of the two asian summer monsoons occurred

a 6000 year record of changes in drought and precipitation in northeastern china based on a δ13c time series from peat cellulose we report a new peat delta c 13 proxy record for humidity or precipitation based on c3 plants from northeastern china the record reveals two times of significant climate shift and eight severe drought periods during the past 6000 years all of which have the nature of widespread global occurrence the variability of precipitation shows periodicities of around 70 80 90 107 110 123 134 141 162 198 205 249 278 324 389 467 584 834 and 1060 years the occurrence and persistent times of drought and periodicities of precipitation show good correspondence with solar variability the remarkable correlations between peat delta c 13 peat delta o 18 and atmospheric delta c 14 suggest that on timescales of decades to centuries the changes in drought and precipitation are likely caused by variations of atmospheric circulation and atmosphere ocean interactions in large scale patterns that seem to be related to solar variability c 2001 elsevier science b v all rights reserved

abrupt variations of indian and east asian summer monsoons during the last deglacial stadial and interstadial abstract the phase relationship between the indian summer monsoon ism and the east asian summer monsoon easm during the last deglaciation remains controversial here we reconstruct a 15 000 year plant cellulose 13 c proxy record for the ism from the yuexi peat bog in southwestern china the record shows that the ism abruptly decreases during the younger dryas yd stadial and abruptly increases during the bolling allerod ba interstadial a comparison of the yuexi record with other related proxy climate records reveals two types of phenomena first the strengths of the two asian monsoons are inversely related during the yd stadial i e the ism strength decreases and the easm increases during this period the southern chinese mainland consisted of a wide arid zone while the northern chinese mainland was much wetter the arid zone in southern china resulted from two different types of monsoon processes the abnormal northward extension of the easm rain belt leading to less rainfall in southeast china or an illusion that the easm weakened the other process is a real weakening of the ism second during the ba interstadial the strengths of both the ism and easm clearly increased however the maximum strengths appear to have occurred in the allerod period during this period the entire chinese mainland both northern and southern experienced wet conditions the abnormal climate pattern of wet in the north and dry in the south during the yd stadial occurs because of the combined effects of the strengthened easm intensified westerlies and weakened ism which could be attributed to the response to the abrupt cooling in the high northern latitudes and to the el nino like activity in the equatorial pacific the widespread wet climate during the ba interstadial may be related to an abrupt increase in the greenhouse gases ghgs concentrations in the atmosphere and to the la nina like activity in the equatorial pacific these results contribute to a better understanding of the response of the asian monsoon to global changes and present a geo historical scenario for understanding the east asian hydrological variations in the current global warming phase

maar and crater lakes of the long gang volcanic field n e china overview laminated sediments and vegetation history of the last 900 years abstract maar and crater lakes have due to their specific formation and characteristic morphology a high potential for the development and preservation of seasonally laminated sediments varves within the long gang volcanic field lgvf in n e china eight maar or crater lakes with water depths between 15 and 127 m are located the seasonal climate with strong influence of the east asian summer and winter monsoon and the position of the lgvf at the northern margin of the east asian dust storm tracks make these lakes key archives for palaeoclimatic studies in the course of a site survey for a deep lake coring water samples and short sediment cores were investigated from all of these lakes detailed pollen investigations of the last 900 years from lake sihailongwan an ideally bowl shaped maar lake with 50 m water depth revealed a very stable vegetation cover except for the last 150 years which shows increasing anthropogenic influence no evidence could be found in the pollen record for a climatic deterioration comparable to the european little ice age however climatic variations can be revealed from high resolution geochemical and sedimentological investigations on a decadal to annual scale

oxygen isotopes in lacustrine carbonates of west china revisited implications for post glacial changes in summer monsoon circulation five lakes in the qinghai tibet plateau and north xinjiang have provided oxygen isotope records covering the past 17 11 cal kyr bp the modern lakes are first presented within the major atmospheric circulation and climate patterns of china with the climate related isotope composition of input water equations used to extract hydrological and climatic information from 18o in carbonates are then given after a discussion on potential causes for 18o changes each of the five isotope profiles is interpreted in the light of its specific environmental data the most significant event observed in all records occurred at 12 11 cal kyr bp an abrupt intensification of summer rainfall associated with an extremely rapid 1000 1500 km westward migration of the monsoon fronts the monsoon regime weakened in stages after 8 7 cal kyr bp holocene maximal aridity is recorded at all sites between about 4 5 and 3 5 cal kyr bp long term changes in monsoon strength as inferred from our isotopic interpretation are in good agreement with climate model reconstructions in the tibet qinghai plateau while observed hydrological changes in north xinjiang are not simulated by the models also the non linearity of the holocene monsoon variations cannot be accounted for by orbital forcing

the huguang maar lake a high resolution record of palaeoenvironmental and palaeoclimatic changes over the last 78 000 years from south china abstract a series of seven piston cores from the huguang maar lake situated near the south china sea coastline provides insight into regional palaeoenvironmental and palaeoclimatic changes in southern china over the last 78 000 years the data set comprises a high resolution record of magnetic susceptibility dry density and water content total organic carbon and inorganic carbon total nitrogen biogenic silica bsio2 and palynological results the time scale was developed by ams 14c dating of 17 terrestrial plant macro fossils during the last glacial the huguang record is characterised by an alternation of more temperate and humid periods from 78 to 58 and 48 to 40 5 ka bp and periods with predominance of grassland vegetation and possibly lowered lake level from 58 to 48 and ca 40 5 to 15 ka bp the huguang data have been compared to regional marine and terrestrial records in order to discuss variability of the south east asian monsoon system for most of the last glacial period the huguang proxies do not exhibit marked millennial scale variability as known from some long se asian and many north atlantic records this picture changes at about 15 cal ka bp when the huguang and greenland records appear to correlate well a short climatic reversal which is assumed to reflect a younger dryas type event is well recorded in the huguang record during the holocene the huguang multi proxy data show a much higher variability than during the last glacial stage probably reflecting at least for the early mid holocene fluctuations in monsoon activity however the last 4000 years of the sediment record are clearly influenced by enhanced human activity and thus difficult to interpret in terms of palaeoclimate change

environmental influences over the last 16 ka on compound specific δ13c variations of leaf wax n alkanes in the hani peat deposit from northeast china compound specific carbon isotope ratios 13c of leaf wax n alkanes c21 c33 odd carbon numbered n alkanes were measured in the hani peat sequence from northeast china these data were compared with lipid biomarker compositions to assess changes in local vegetation and paleoclimate for the last 16 ka the 13c values of n alkanes range between 36 6 and 30 7 showing that the compounds originate from c3 plants much larger variations 5 4 in the n alkane 13c values than those of atmospheric co2 during the last 16 ka 0 5 indicate that the isotopic values were affected by environmental factors in addition to the postglacial 13c variations in the atmospheric reservoir the stratigraphic records of 13c reveal decoupled fluctuations among the individual n alkanes particularly between 15 5 and 11 4 ka synchronous excursions in the 13c offsets among individual n alkanes 13c and lipid biomarker paleoplant proxies paq and c23 c31 and c27 c31 from 14 9 to 13 2 ka and 12 7 to 11 6 ka suggest that vegetational changes are the most likely causes for the decoupled 13c variations parallel fluctuations of the 13c values of terrestrial higher plant derived c29 and c31n alkanes and the n alkane average chain length acl from 11 to 6 ka indicate that the 13c variations responded to net evaporation changes negative shifts in the n alkane 13c values coinciding with the acl decreases at 10 5 9 3 ka and 8 1 ka indicate the short term onset and fluctuations of the summer monsoon strength in eastern china during the early holocene

volcanic eruptions in the longgang volcanic field northeastern china during the past 15 000 years the longgang volcanic field located in northeastern china is volcanically active with a number of eruptions during the quaternary but the chronology of the eruptions is poorly defined some tephra layers are well preserved in the annually laminated sediments of maar lakes in the region and facilitate the construction of a much improved chronological framework for the volcanic history of the area the results of our investigations reveal that three basaltic explosive eruptions occurred at ad 460 11460 cal yr bp and 14000 cal yr bp respectively the largest explosive basaltic eruption ad 460 produced a thick black scoria layer in the longgang volcanic field including lakes the tephra distribution and chronological data suggest that this eruption is likely to be from the jinlongdingzi volcano two basaltic flood eruptions occurred at jinlongdingzi the earlier basaltic eruption produced a lava flow that spread over a forest and encased standing trees two radiocarbon ages obtained from charcoal samples collected from the burned remains of these trees are 1828 1989 cal yr bp and 2164 2359 cal yr bp in the most recent stage of volcanism the lava flow extended only ca 2 km and flowed into lake dalongwan from the present status of the forest ecosystem which has not yet reached the fully mature successional stage we estimate that this lava is very young ca a few hundreds years old jinlongdingzi is a potentially dangerous volcano monitoring and assessment of the potential hazards in the longgang volcanic field should be carried out in the future

reply to comment on anti phase oscillation of asian monsoons during the younger dryas period evidence from peat cellulose δ13c of hani northeast china by b hong y t hong q h lin y shibata m uchida y x zhu x t leng y wang and c c cai palaeogeography palaeoclimatology palaeoecology 297 2010 214 222 abstract the intensity variation of the east asian summer monsoon during the younger dryas yd cold period remains an important scientific issue requiring clarification in our article published in palaeogeography palaeoclimatology palaeoecology 297 2010 214 222 based on the hani peat cellulose 13 c sequence from northeast china we have documented the abrupt strengthening of the east asian summer monsoon during that period our findings support the occurrence of wet conditions in the north and of dry conditions in the south of the chinese mainland and they indicate behavior in anti phase with the indian ocean summer monsoon that weakened during the same period this result agrees with the previously revealed anti phase variations of the two monsoons during the ice rafted debris ird cold events occurring in the north atlantic ocean we have also proposed a theory for the anti phase variations of the monsoons and for the anomalous distribution of precipitation we have attributed these events to the occurrence of an el nino like phenomenon in the equatorial pacific ocean during the yd g schettler has argued that this palaeo climatic interpretation cannot be substantiated by chemical data from the nearby lake sihailongwan or by biomarker studies of the hani peat the inferred inverse correlation between the summer monsoon strength in northeast and southern china during the younger dryas appears questionable however after carefully examining schettler s g schettler comment on anti phase oscillation of asian monsoons during the younger dryas period evidence from peat cellulose 13 c of hani northeast china by b hong y t hong q h lin y shibata m uchida y x zhu x t leng y wang and c c cai palaeogeography palaeoclimatology palaeoecology 297 2010 214 222 palaeogeography palaeoclimatology palaeoecology this issue water chemistry data from lake sihailongwan we find considerable accumulation ratios of biosilica during the yd period that clearly indicates abrupt strengthening of the east asian summer monsoon we point out that schettler referred incorrectly to zhou s research results zhou et al have clearly indicated that elevated n alkane p aq values and c 23 c 29 ratios serve to record an especially moist local climate in yd we also confirm that the influence of an increased relative contribution of sphagnum species to hani peat composition on peat cellulose 13 c is negligible therefore our conclusions that during the yd cold period the easm abruptly strengthened and that moreover an anti phase occurred between the two asian monsoons during the yd period are both in fact substantiated not only by biomarker studies of the hani peat but also by chemical data from the nearby lake sihailongwan we therefore consider schettler s statement to be untenable

co2 h2o and orbitally driven climate variability over central asia through the holocene small variations in earth s orbit have a direct impact on global climate with the greatest changes occurring over large land masses such as asia orbitally driven climate signals are therefore likely to be identifiable in climate proxy records derived from sediment sections in the continental interior proxy records derived from temperature dependent variables are also likely to display a signal due to temporal variability of atmospheric co2 and related climatic parameters such as water vapour content to determine the magnitude of climate anomalies associated with shortwave and longwave radiative forcing over asia a suite of numerical atmospheric simulations is performed that spans most of the holocene from 10 000 to 2500 years bp at 500 year intervals over central asia the amplitude of the summer winter seasonal cycle is greater than today in all simulations but exhibits two distinct maxima at 9000 and 6000 bp simulated precipitation and snow accumulation over central asia are markedly higher during the early mid holocene and are oscillatory exhibiting peaks at 8000 7500 and 4500 bp the atlantic and subboreal times respectively co2 h2o forcing and orbital forcing combine to drive temperature oscillations over central asia which in turn regulate relative humidity and changes in surface hydrology correlation between simulated results and proxy records from across asia suggest that co2 h2o and orbital forcing are dominant factors driving fluctuations of large scale central asian climate through the holocene

comment on anti phase oscillation of asian monsoons during the younger dryas period evidence from peat cellulose δ13c of hani northeast china by b hong y t hong q h lin y shibata m uchida y x zhu x t leng y wang and c c cai palaeogeography palaeoclimatology palaeoecology 297 2010 214 222

asynchronous holocene climatic change across china a review of holocene climatic variations in different parts of china shows that they were asynchronous proxy data from ice cores pollen loess lacustrine sediments and changes of sea and lake levels demonstrate that many warm and cold oscillations have occurred in china during the holocene including a most important climatic event known as the holocene optimum a milder and wetter period and that the duration and amplitude of the optimum period as well as its start and end times differed in different parts of china uplift of the tibetan plateau over the past millions of years led to the development of the monsoon climate and to complex atmospheric circulation over continental china during the holocene as a result the holocene optimum began and terminated earlier in high altitude regions of western china than at lower elevations in eastern china and the amplitude of the variations was lower in the east this suggests that the western higher altitude areas were more sensitive to climatic change than were the eastern lower altitude areas holocene climatic records in the dunde and guliya ice cores do not correspond inverse 18o variations between the two cores indicate that the effects of climate and atmospheric processes on the stable isotopes at the two sites differed the correlation between the isotopic composition of carbonates in lake deposits in western china and climatic variations is similar to that in the ice cores the climatic resolution in ice cores and lake sediments is higher than that in other media the lack of precise correspondence of climatic records constructed on the basis of proxy data from different parts of china is a result of the different locations and elevations of the sampling sites the different resolutions of the source material and the varied climatic conditions within china further work is needed to confirm both the conclusions and the inferences presented here

effective elastic thickness of zealandia and its implications for lithospheric deformation abstract zealandia was once located at the active gondwana margin and experienced complicated tectonic evolution from continental breakup to subduction and oblique slipping along the plate boundary here we investigate the lithospheric thermal and rheological properties via spatial variations in effective elastic thickness te using the topography sediment thickness and gravity data the fan wavelet coherence method is employed to recover te values the effects of dynamic topography and gravity in the subduction zone on the estimated te are considered and removed the final results reveal that the te variation pattern generally coincides well with the tectonic regimes relatively high te values up to 22 km are observed in north island and the southernmost part of south island while central and northern south island are dominated by smaller te values 15 km similar to those of the surrounding submerged plateaus we interpret the relatively high te values as indicating the combined lithospheric strength due to the contacting plates in the subduction zone to the north along the tonga kermadec subduction zone the lithosphere surprisingly exhibits anomalously high te values ranging from 22 to 36 km which contradicts the geological evidence of normal faults developed in the incoming pacific plate and the magmatism in the overlying australian plate that generally contribute to low lithospheric strength we speculate that the high te zone is related to the large bathymetry and gravity anomalies in the bending plate and controlled by non isostatic factors finally we find widespread low te values covering the entire arcs and oceanic basins in northern zealandia which may indicate that regional lithospheric thinning associated with delamination weakened the integrated strength of the lithosphere

atmospheric connections with the north atlantic enhanced the deglacial warming in northeast china variations in atmospheric circulation across the last deglaciation in the northernmost monsoon influenced regions of asia are not well constrained highlighting a fundamental gap in our understanding of asian climate here we reconstruct continental air temperatures for northeast china across the last deglaciation past 16 k y based on the distribution of bacterial branched glycerol dialkyl glycerol tetraethers in a sequence of the hani peat jilin province northeast china our results indicate large as much as 10 degrees c oscillations in temperature in northeast china across the deglaciation oscillations significantly larger than observed in other temperature records from low latitude or same latitude east asia but consistent with climate model simulations this enhanced magnitude as well as the timing of temperature variations provides evidence for atmospheric teleconnections with high latitudes in particular we suggest that highlatitude cooling associated with arctic ice expansion and changes in atlantic meridional overturning circulation enhanced the intensity and lowered the temperature of eurasian mid latitude westerlies and northwesterly winds over east asia during the last glacial delivering cold air masses to northeast china during the deglaciation the westerlies and therefore delivery of cold air masses weakened amplifying the deglacial warming in this region we conclude that changes in north atlantic climate had a particularly strong impact on the northernmost parts of the east asian monsoon influenced area

the variation of summer monsoon precipitation in central china since the last deglaciation abstract two stalagmites c996 1 and c996 2 collected from the jiuxian cave in the shaanxi province in central china have been studied with u series dating and stable isotope analysis thirty eight 230 th dating results showed that the stalagmite c996 1 was continuously deposited through the last 8 5 ka bp thousand years before present present 1950 ad and c996 2 was deposited through the last 19 ka bp excluding two growth hiatuses between 8 3 and 5 7 ka bp and 15 4 and 11 9 ka bp with a relatively stable boundary condition we interpret the 18 o of speleothem calcite as most indicative of the amount of summer monsoon precipitation although temperature and other factors might have some minor impact the 18 o records show notable changes within the last glacial maximum lgm resembling other east asian monsoon records such as those from the hulu and sanbao caves suggesting that significant monsoonal climate changes occurred in eastern asia as far north as the qinling mountains during the lgm interval a comparison of our records to precisely dated contemporaneous speleothem records from other caves shows that the increasing trend of 18 o during the holocene commenced as early as 7 5 ka bp in the low latitude monsoonal area i e the hoti cave while at higher latitudes this shift occurred later such as 7 0 ka bp in the dongge cave 5 3 ka bp in the heshang cave 4 7 ka bp in the sanbao cave and 4 5 ka bp in the jiuxian cave these results imply an asynchronous change of the summer monsoon precipitation occurred in east asia during the holocene the asynchrony may be related to the responses of a coupled tropical and subtropical monsoon system to changes of the insolation and the differences in thermal forcing which result from the complex geographical configuration the variation of sea surface temperature sst in the western tropical pacific may also have important impacts on the summer monsoon precipitation changes in central and northern china because it affects the northwestern pacific subtropical high a monsoon front regulator more robust tests are needed to confirm this phenomenon and to evaluate the contribution of different factors in detail

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

east asian monsoon variability between 15 000 and 2000 cal yr bp recorded in varved sediments of lake sihailongwan northeastern china long gang volcanic field a palaeohydrological reconstruction on decadal scale for the period 15000 2000 cal yr bp based on calculated net accumulation rates for biogenic silica f bsio2 and additional proxies sedimentol

evidence of centennial scale drought from southeastern massachusetts during the pleistocene holocene transition abstract a principal method for studying past hydroclimatic change is the reconstruction of paleo lake levels here we provide high resolution lake level records from new long pond and rocky pond in southeastern massachusetts which each contain evidence for multiple sub centennial to millennial scale low stands during the transition between the late pleistocene 15 0 ka and middle holocene ca 7 0 ka data from new long pond also demonstrate sedimentary evidence for a drop in water levels in the early to mid ad 20th century when long term trends in instrumental data show lower than average precipitation in the northeastern united states local data show the most precipitous declines in precipitation and groundwater levels are concurrent with the most severe drought in the ad 1960s which occurred during a period of low sea surface temperatures in the western north atlantic ground penetrating radar and sediment core data indicate five intervals with numerous paleo shoreline deposits between ca 15 0 and 7 0 ka similar to the layer deposited in the ad 1960s many of the intervals of low lake levels coincide with proposed meltwater release events or abrupt climate oscillations in the circum north atlantic for example we document at least three low stands during the younger dryas 12 9 11 6 ka and in association with the 9 2 and 8 2 ka events the combined evidence of 1 concurrent paleo droughts in southeastern new england with documented north atlantic abrupt cooling events and 2 recent drought with the modern association of low sea surface temperatures indicates that freshening and cooling of the western north atlantic is a viable mechanism for decreasing moisture within the region large scale changes in seasonality and ice sheet extent also may have increased the susceptibility of the northeast to dry conditions triggered by changes in the north atlantic

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

palaeoclimatic changes in the qinghai lake area during the last 18 000 years abstract multi proxy analysis of a sediment core from qinghai lake including pollen carbonate toc tn and 13 c of organic matter was used to document regional climatic changes during the last 18 000 years climate was very cold and dry before 16 9 cal kyr bp the warm and wet period which began at about 14 1 cal kyr bp culminated at 6 5 cal kyr bp and came to its end at about 4 5 cal kyr bp after that the climate gradually became colder and drier during the transitional period from the late glacial to the holocene the climate fluctuated frequently the short term climatic oscillations including the bolling allerod younger dryas and the cooling event at ca 8 2 cal kyr bp appear to be recorded in the qinghai lake sedimentary record the climatic evolution in the qinghai lake area during the past 18 000 years indicates that solar insolation changes on the ten thousand year scale are the likely driving force of the east asia monsoon

holocene cyclic climatic variations and the role of the pacific ocean as recorded in varved sediments from northeastern china we present an n alkane and compound specific carbon isotope record of the past 9 ka from the annually laminated sedimentary sequence of lake xiaolongwan northeastern china the n alkane distribution suggests that lake xiaolongwan has undergone a shift from an oligotrophic state with low algal production and little emergent submerged macrophytes in the early holocene to a eutrophic state with high algal production and abundant emergent submerged macrophytes since the middle holocene the pattern of variation observed in the biomarker proxies acl the n alkane average chain length paq aquatic macrophyte versus aquatic macrophyte and terrestrial plant ratio and lptp lake productivity terrigenous organic production is throughout the record similar to that of the total organic carbon the variation of compound specific carbon isotopic values in the middle and short chain alkanes was mainly regulated by lake productivity and the accumulating organic pool through time in this forested region where the vegetation is dominated by c 3 plants the long chain n alkanes c27ec31 are predominantly derived from leaf wax lipids the compound specific d 13 c27e31 value is sensitive to effective precipitation and therefore represents a useful indicator of regional monsoonal precipitation spectral analysis on the d 13 c27e31 time series reveals significant periodicities of 87e89 205e212 1020e1050 and 1750e2041 years on the centennial timescale the quasi periodicities around 88 and 210 years suggest a strong link between solar activity and monsoon rainfall the millennial monsoon cycle in northeastern china is associated with sea surface temperature sst variations in two active centers of the summer monsoon the western pacific subtropical high wpsh and the okhotsk high increasing sst in the subtropical sea may cause a northwards shift of the wpsh which extends the monsoon rain band meiyu to northeastern china and thus increasing rainfall in that region meanwhile decreasing sst in the okhotsk sea may strengthen the okhotsk high bringing more moisture into northeastern china we suggest that the pacific ocean is a main regulator for summer monsoon rainfall in northeastern china at present and at different time scales during the holocene

late holocene climatic variability south of the alps as recorded by lake level fluctuations at lake ledro trentino italy a lake level record for the late holocene at lake ledro trentino northeastern italy is presented it is based on the sediment and pollen analysis of a 1 75 m high stratigraphic section observed on the southern shore site ledro i and a 3 2 m long sediment core taken from a littoral mire on the southeastern shore site ledro ii the chronology is derived from 15 radiocarbon dates and pollen stratigraphy the late holocene composite record established from these two sediment sequences gives evidence of centennial scale fluctuations with highstands at c 3400 2600 1700 1200 and 400 cal bp in agreement with various palaeohydro logical records established in central and northern italy as well as north of the alps in addition high lake level conditions at c 2000 cal bp may be the equivalent of stronger river discharge observed at the same time in central italy s rivers in agreement with the lake level record of accesa tuscany the ledro record also suggests a relatively complex palaeohydrological pattern for the period around 4000 cal bp on a millennial scale sediment hiatuses observed in the lower part of the ledro i sediment sequence indicate that except for a high stand occurring just after 7500 cal bp lower lake levels generally prevailed rather before c 4000 cal bp than afterwards finally the lake level data obtained at lake ledro indicate that the relative continuity of settlements in humid areas of northern italy during the bronze age in contrast to their general abandonment north of the alps between c 3450 and 3150 cal bp does not reflect different regional patterns of climatic and palaeohy drological conditions in contrast the rise in lake level dated to c 3400 cal bp at ledro appears to coincide with a worldwide climate reversal observed in both the hemispheres while palaeoenvironmental and archaeological data collected at lake ledro may suggest as a working hypothesis a relative emancipation of proto historic societies from climatic conditions

a synthesis of abrupt changes in the asian summer monsoon since the last deglaciation we have compiled 36 previously published palaeoclimate records to determine the timing and spatial pattern of century scale abrupt changes in asian monsoon precipitation since the last deglaciation we identify abrupt events from 1 the interpretations of the authors of these records and 2 the more objective moving t test calculation our results indicate that abrupt climatic changes occurred at 11 5 cal ka 4 5 5 0 cal ka and ad 1300 at the start of the holocene 11 5 cal ka asian monsoon precipitation increased dramatically this climatic change is synchronous with an abrupt warming in the north atlantic during the middle holocene there was a time of preferred and widespread weakening in monsoon strength 4 5 5 0 cal ka this result contradicts previous notions of either a gradual trend towards drier conditions or a series of abrupt events that occurred in an unorganized fashion across space and time the middle holocene abrupt event could have been synchronous with an abrupt cooling event in the north atlantic as well as a warming and intensie cation of internannual variability in the tropical pacie c in contrast to previous periods precipitation changes at ad 1300 have a heterogeneous spatial pattern we e nd no conclusive evidence for a change in the asian monsoon at 8 2 cal ka as suggested by several previous studies more high resolution data may be needed to observe this short lived event overall our results attest to the potential for rapid and major shifts in asian monsoon precipitation that may be triggered by variations in other components of the climatic system

large changes in seasonal sea ice distribution and productivity in the sea of okhotsk during the deglaciations changes in the surface environment of the central sea of okhotsk were reconstructed using tex86 paleothermometry facilitated by the bit index in order to investigate paleoenvironmental changes during the glacial interglacial cycles the core top tex86 derived temperature is the same as the present day summer sea surface temperature sst suggesting that tex86 records seasonal rather than annually averaged ssts in this region the tex86 record reveals 3 c lower summer sst during glacial maxima than during interglacial periods and significant warming during the deglaciations 15 10 ka and 136 130 ka this is consistent with previous inferences of more expanded and persistent seasonal sea ice during the glacial periods than the present day and its substantial retreat during the deglaciation timing of the deglacial warming also coincided with a distinct increase in coccolithophorid productivity suggesting a causal relationship between sea surface warming and coccolithophorid blooms during the deglaciations the relationship could reflect an increase in the supply of fresh and warm water from the amur river during deglaciation which significantly impacted hydrology by facilitating sea surface stratification which in turn promoted production of coccolithophids

the significance of maar volcanoes for palaeoclimatic studies in china abstract the sediments of maar lakes often provide paleoenvironmental records which are highly suitable for palaeoclimatic studies the main advantages of the records from maar lakes compared with other lacustrine records are as follows first the presence of varves annually laminated layers and tephra layers as well as other materials like terrestrial plant macrofossils charcoals organic carbon organic shells suitable for isotopic dating like ams 14c 210pb 137cs 238u 230th 40ar 39ar provides the possibility of developing several independent chronologies enabling the development of robust high resolution chronologies second maars and maar lakes can provide continuous sedimentary records spanning tens of thousands of years tianyang maar in china is hosted the longest known record spanning at least 400 kyr bp that are ideal for the investigation of climate change on different timescales including orbital millennial centennial and annual decadal third recent studies of biomarkers based on long chain alkenones lcas and glycerol dialkyl glycerol tetraethers gdgts have demonstrated the potential of maar lakes for quantitative paleotemperature reconstruction in this study we review some of the more significant achievements of palaeoclimatic research based on maar lake sediment sequences from china with the focus on chronology multiple timescales and quantitative paleoclimatic reconstruction

structure and origin of holocene cold events abstract the present interglacial the holocene spans the period of the last 11 700 years it has sustained the growth and development of modern society the millennial scale decreasing solar insolation in the northern hemisphere summer lead to northern hemisphere cooling a southern shift of the intertropical convergence zone itcz and a weakening of the northern hemisphere summer monsoon systems on the multidecadal to multicentury scale periods of more stable and warmer climate were interrupted by several cold relapses at least in the northern hemisphere extra tropical area based on carefully selected 10 000 year long time series of temperature and humidity precipitation as well as reconstructions of glacier advances the spatiotemporal pattern of six cold relapses during the last 10 000 years was analysed and presented in form of a holocene climate atlas hoclat see http www oeschger unibe ch research projects holocene atlas a clear cyclicity was not found and the spatiotemporal variability of temperature and humidity precipitation during the six specific cold events 8200 6300 4700 2700 1550 and 550 years bp was very high different dynamical processes such as meltwater flux into the north atlantic low solar activity explosive volcanic eruptions and fluctuations of the thermohaline circulation likely played a major role in addition internal dynamics in the north atlantic and pacific area including their complex interaction were likely involved

asynchronous holocene optimum of the east asian monsoon abstract the spatial and temporal distribution of summer monsoon precipitation or effective moisture during the holocene has been reconstructed on the basis of geological data including lake levels pollen profiles and loess paleosol records in addition the summer july precipitation increment effective precipitation and monsoon strength index have been obtained from numerical modeling experiments both geological data and numerical modeling indicate that the holocene optimum as defined by peak east asian summer monsoon precipitation was asynchronous in central and eastern china reaching a maximum at different times in different regions e g ca 10 000 8000 yr ago in northeastern china 10 000 7000 yr ago in north central and northern east central china ca 7000 5000 yr ago in the middle and lower reaches of the yangtze river and ca 3000 yr ago in southern china in southwestern china the maximum appeared ca 11 000 yr ago but probably was related to the maximum landward extension of the indian summer monsoon the regional shift in the maximum precipitation belt from northwest to southeast over the past 10 000 yr is interpreted as a response to changing seasonality related to orbital forcing of the climate the southeastward shift of the east asian summer monsoon maximum is consistent with the progressive weakening of the summer monsoon as the summer solar radiation anomaly decreased progressively through the holocene and the east asian monsoon index declined while the early maximum in southwestern china matches the maximum of the indian monsoon index

the dry holocene megathermal in inner mongolia the paleoclimate since 14 kyr bp 14c age was reconstructed based on a 16 22 m long sediment core collected from lake yanhaizi a saline lake located near the northern limit of the east asian summer monsoon in inner mongolia coarse sediments were deposited there during a shrinkage phase of the lake when sand dunes reactivated these sediments have low organic carbon contents but high maturity indices indicating that they were deposited in an arid environment by contrast based on high organic contents and low maturity indices fine sediments were deposited during periods of high lake stand in a humid environment it was in general dry between 8 0 and 4 3 kyr bp the above dry and wet phases are consistent with those recovered from the arid semiarid transition zone elsewhere but are unlike the widely perceived humid holocene megathermal reported in east china and the newly reconstructed record in the alpine retreat lake in taiwan the discrepancy may be due to a relative insensitivity to humidity changes in these two areas since they have both been under the total influence of the summer monsoon on the other hand much enhanced evaporation over higher monsoon precipitation at lake yanhaizi reduces the effective humidity in the warm climate near the northern boundary of the summer monsoon this also accounts for the fact the high temperature holocene megathermal as revealed in the okinawa trough and the northern south china sea is correlated to the dry phases at lake yanhaizi conversely the 4 2 kyr bp coldest period in the holocene corresponds to a wet phase at lake yanhaizi

asynchronous evolution of the indian and east asian summer monsoon indicated by holocene moisture patterns in monsoonal central asia abstract the numerical meta analysis of 92 proxy records 72 sites of moisture and or temperature change confirms earlier findings that the dominant trends of climatic evolution in monsoonal central asia since the last glacial roughly parallel changes in northern hemisphere summer insolation i e the period following the last glacial maximum was characterized by dry and cold conditions until 15 cal kyr bp followed by a warm wet period coincident with the bolling allerod warm period and terminated by a cold dry reversal during the younger dryas period after an abrupt increase at the start of the holocene warm and wet conditions prevailed until ca 4 cal kyr bp when moisture levels and temperatures started to decrease ordination of moisture records reveals strong spatial heterogeneity in moisture evolution during the last 10 cal kyr the indian summer monsoon ism areas northern india tibetan plateau and southwest china exhibit maximum wet conditions during the early holocene while many records from the area of the east asian summer monsoon indicate relatively dry conditions especially in north central china where the maximum moisture levels occurred during the mid holocene we assign such phenomena to strengthened hadley circulation centered over the tibetan plateau during the early holocene which resulted in subsidence in the east asian monsoonal regions leading to relatively dry conditions our observations of the asynchronous nature of the two asian monsoon subsystems on millennial time scales have also been observed on annual time scales as well as implied through the spatial analysis of vertical air motion patterns after strong ascending airflows over the tibetan plateau area that were calculated from ncep ncar reanalysis data for the last 30 years analogous with the early holocene the enhancement of the ism in a future warming world will result in an increase in the asynchronous nature of the monsoon subsystems this trend is already observed in the meteorological data from the last 15 years

interdecadal variability of summer climate over east asia and its association with 500 hpa height and global sea surface temperature interdecadal variability of summer climate rainfall and temperature in east asia china and japan and its association with the anomalies of geopotential heights at 500 hpa over the northern hemisphere nh global sea surface temperature ssta and outgoing longwave radiation olr were examined an abrupt change was found in the middle and by the end of the 1970s in the variations of time coefficients of the second mode of singular value decomposition svd2 for the summer rainfall and temperature in china the rainfall anomaly around 1977 1979 changes from above normal to below normal and the temperature changes from below normal to above normal in the southern and southwestern parts of china a similar interdecadal variability was also found in the summer climate variations in the southwest islands of japan the 500 hpa height anomalies related to the spatial pattern of svd2 shows a clear dipole pattern the negative center is located in mongolia and northeastern china and the positive center is located in middle and southern china the abrupt change of summer climate in the middle and by the end of the 1970s over the subtropical regions of east asia is characterized with the intensification and westward and southward extension of the western pacific subtropical high wpsh it is also observed in geopotential height variations over eurasia around 1977 1978 an abrupt change of sst over the tropical indian ocean and tropical western pacific was also found around 1976 1977 it is indicated that interdecadal variability of summer rainfall and temperature over east asia is largely influenced by the change of ssta and convective activity in the tropical indian ocean and tropical western pacific the convective activity over the tropical indian ocean and tropical western pacific is usually enhanced when the sst is warmer than normal so the subtropical high anomalies over the subtropical regions of east asia are intensified through the enhancement of a hadley cell as a result the subtropical regions of east asia including southern and southwestern china and the southwest islands of japan are covered by a positive height anomaly at 500 hpa where the temperature is above normal and the rainfall is below normal

holocene vegetation and climate dynamics of ne china based on the pollen record from sihailongwan maar lake abstract high resolution palynological analysis on annually laminated sediments of sihailongwan maar lake shl provides new insights into the holocene vegetation and climate dynamics of ne china the robust chronology of the presented record is based on varve counting and ams radiocarbon dates from terrestrial plant macro remains in addition to the qualitative interpretation of the pollen data we provide quantitative reconstructions of vegetation and climate based on the method of biomization and weighted averaging partial least squares regression wa pls technique respectively power spectra were computed to investigate the frequency domain distribution of proxy signals and potential natural periodicities pollen assemblages pollen derived biome scores and climate variables as well as the cyclicity pattern indicate that ne china experienced significant changes in temperature and moisture conditions during the holocene within the earliest phase of the holocene a large scale reorganization of vegetation occurred reflecting the reconstructed shift towards higher temperatures and precipitation values and the initial holocene strengthening and northward expansion of the east asian summer monsoon easm afterwards summer temperatures remain at a high level whereas the reconstructed precipitation shows an increasing trend until approximately 4000 cal yr bp since 3500 cal yr bp temperature and precipitation values decline indicating moderate cooling and weakening of the easm a distinct periodicity of 550 600 years and evidence of a mid holocene transition from a temperature triggered to a predominantly moisture triggered climate regime are derived from the power spectra analysis the results obtained from shl are largely consistent with other palaeoenvironmental records from ne china substantiating the regional nature of the reconstructed vegetation and climate patterns however the reconstructed climate changes contrast with the moisture evolution recorded in s china and the mid latitude semi arid regions of n china whereas a clear insolation related trend of monsoon intensity over the holocene is lacking from the shl record variations in the coupled atmosphere pacific ocean system can largely explain the reconstructed changes in ne china

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

lake qinghai china closed basin like levels and the oxygen isotope record for ostracoda since the latest pleistocene abstract in 1985 a sino swiss limnogeological expedition to china s largest inland lake recovered seismic profiles and piston cores to help calibrate palaeoclimatic models of monsoon and insolation fluctuations over the northern tibet qinghai plateau since the last glacial maximum lake qinghai a perennial lake with an area of 4278 km2 1985 at 3194 m above sea level receives drainage from 30 000 km2 of catchment near the northwest corner of the plateau the 26 5 m deep terminal lake 1985 with brackish alkaline magnesium sulphate rich waters 14 g 1 1 tds has not overflowed since the last glacial but its levels have responded to climatic and hydrologic changes seismic reflection profiles for the sub bottom sediment structures revealed a complex topography with channels relict terraces tectonic tilting and deformation in deposits buried under a 4 6 m packet of mainly flat bedded sediments from which core samples were recovered the lowermost cored material 14 500 yr b p comprises mainly water lain loess deposited in a smaller flood plain lake of up a few metres depth under cold arid climatic conditions ams radiocarbon dating indicates average sedimentation rates for latest pleistocene and holocene deposits in central basin regions of 0 3 0 5 mm yr 1 the 18o values of fossil ostracod valves provide a record of changes in the isotopic chemistry of the lake waters that can be related to the precipitation evaporation budgets which have controlled the palaeo levels for lake qinghai the precipitation evaporation budget for the lake qinghai region is largely determined by the asian monsoon system the lake qinghai sediment record shows that there was no large influx of glacoer melt waters into the lake basin during the post glacial the regional climate remained arid until at least 12 500 yr b p when an incipient monsoon was possibly initiated river transported silts first reached the basin centre at 11 800 yr b p when the lake depth may have increased to 5 m possibly a monsoonal weakening for several centuries after 10 800 yr b p europe younger dryas caused a further period of aridity at 10 200 yr b p the basin began filling towards modern lake dimensions in response to a permanent strengthening of the asian monsoon substantial lake level rises probably characterised the periods 10 200 9800 9500 8500 8300 7200 yr b p and through perhaps a century at about 6800 yr b p decreasing levels probably characterised the intervening intervals short term lake level fluctuations through the mid holocene climatic optimum were minimal indicating a very stable climatic hydrologic regime an isotopic steady state for the lake waters since 3000 500 yr b p obscures the climatic hydrologic regime dependent 18o gradient but there is little stratigraphic evidence to suggest that the lake level has been significantly below its present level since that time three negative 18o excursions for the lake waters may correspond to known glacier advances on the plateau at 3000 2000 and 1500 yr b p during china s neoglacial

pacific sea surface temperature forcing dominates orbital forcing of the early holocene monsoon orbital forcing is known to play a primary role in regulating the strength of the south asian monsoon circulation in this study a comparison is made between orbital forcing and pacific sea surface temperature sst forcing of the monsoon through a sequence of atmospheric general circulation model experiments configured for 6 000 and 9 000 yr b p early mid holocene orbital parameters are shown to increase continental seasonality as well as the meridional mean the zonal mean and the summer monsoon circulations winds in the southeast asian monsoon are weakened by warm pacific sst to such an extent that the increase in strength caused by early holocene orbital parameters is offset these results imply that ssts are potentially as important as orbital parameters in governing the monsoon and that more data particularly from the equatorial pacific are crucial to deciphering holocene climate

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

deuterium excess in an east antarctic ice core suggests higher relative humidity at the oceanic surface during the last glacial maximum a continuous deuterium excess profile d d 8 18o was obtained from the dome c ice core spanning 32 000 yr it exhibits significant variations over this period in particular d was 4 5 lower around 18 000 yr bp than over the past 7 500 yr interpreted as reflecting higher relative humidity estimated 90 over the oceanic areas providing moisture for antarctic precipitation

mid late holocene maar lake mire transition in northeast china triggered by hydroclimatic variability abstract the density of maar lake type peatlands in the changbai mountain areas northeast ne china is among the highest in the world these deposition systems include both peat and limnic deposits providing valuable sites to study their evolutionary history shaped by their sensitivity to climate forced state shifts to investigate the maar lake mire shift in response to hydroclimatic variability we examined developmental history of the jinchuan peatland based on sedimentary facies grain size physical and chemical properites plant macrofossils and peat basal age the results indicate that the jinchuan peatland mainly originated from paludification in a maar lake from approximately 7000 cal bp its water level continuously increased since the middle holocene reaching the peak during the period of 5000 4000 cal yr bp the outward expansions of jinchuan peatland suggest a climate driven model based on which water level variability superimposes the underlying basin morphology the hydroclimatic variability and peatland development history can be divided into three periods from 12 to 7 ka cal bp the increasing east asian summer monsoon easm was the major water vapor source of jinchuan peatland the strong evaporation effects induced by the strong winter asian winter monsoon wawm and the maximum sea surface temperatures ssts of japan sea might have changed the jinchuan maar lake into dry upland from 7 to 4 ka cal bp the maximum easm and increasing westerly jet wj provided water vapor for the peatland the decreasing eawm and ssts of japan sea resulted in decreased evaporation effects the moisture and water level in jinchuan peatland gradually increased the peat covered 68 97 of the area during this period since 4 ka cal bp the decreased easm and the maximum wj provided water vapor for the jinchuan peatland the weak eawm and the lower ssts of japan sea induced lower evaporation effects the moisture and water level in the peatland reached the maximum subsequently peat area further expanded and covered the remaining 31 03 area this study reveals a remarkable link between the maar lake mire shift and hydroclimatic variability which is significant for future prediction of maar lake mire ecosystem shifts under global climate change

holocene east asian monsoonal precipitation pattern revealed by grain size distribution of core sediments of daihai lake in inner mongolia of north central china abstract two sediment cores recovered in the central part of daihai lake in north central china were analysed at 2 to 4 cm intervals for grain size distribution grain size distributions of the lake sediments are inferred to be a proxy for past changes in east asian monsoon precipitation such that greater silt size percentage and higher median grain size reflect increased monsoonal precipitation rates the grain size record of daihai lake sediments spanning the last ca 10 000 yr indicates that the monsoonal precipitation in the lake region can be divided into three stages the early middle and late holocene during the early holocene before ca 7900 cal yr bp the median grain size md and the silt fraction content were relatively low and constant suggesting relatively low precipitation over the lake region the middle holocene between ca 7900 and 3100 cal yr bp was marked by intensified and highly variable monsoonal precipitation as indicated by high and variable md values and silt contents of the lake sediments during this period average precipitation rate gradually increased from ca 7900 to 6900 cal yr bp displayed intense oscillations between ca 6900 and 4400 cal yr bp and exhibited a decreasing trend while fluctuating from ca 4400 to 3100 cal yr bp although generally high during the middle holocene both the md and the silt content assumed distinctly low values at the short intervals of ca 6500 6400 6000 5900 5700 5600 4400 4200 cal yr bp implying that monsoonal precipitation might have been significantly reduced during these intervals during the late holocene since ca 3100 cal yr bp grain size values suggest that precipitation decreased however during the late holocene relatively higher md values and silt contents occurring between ca 1700 to 1000 cal yr bp may denote an intensification of hydrological cycles in the lake area changes in the east asian monsoonal precipitation were not only directly linked with the changing seasonality of solar insolation resulting from progressive changes in the earth s orbital parameters but also may have been closely related to variations in the temperature and size of the western pacific warm pool in the intensity of the el nino southern oscillation and in the path and strength of the north equatorial current in the western pacific

paleoceanography of the last 500 kyrs in the central okhotsk sea based on geochemistry abstract analyses of geochemical constituents organic carbon nitrogen calcium carbonate and biogenic opal on core yk07 12 pc3b core pc3b provided detailed and useful information in biological productivity and paleoceanographic changes which occurred in the central okhotsk sea during the last 500 kyrs an age model for core pc3b was established based on changes in benthic foraminiferal 18 o the trend in organic carbon oc content represented the temporal change that can be correlated with the 18 o curve in core pc3b high during the interglacial periods mis 1 5 9 11 and 13 the trend in caco 3 content represented is similar to the trend seen in the oc content the high correlation between oc and caco 3 contents indicates an increase in coccolithophorid productivity during the early deglaciations the comparison between the changes in caco 3 and biogenic opal indicates that the dominant phytoplankton group was coccolithophorids during the early deglaciations which was subsequently replaced by diatoms during the late deglaciations it appears that such a temporal phytoplankton succession was caused by an increase in dissolved silicon supply to the euphotic layer possibly associated with a change in surface hydrography that subsequently caused an upward expansion of the intermediate layer such ecological changes probably played an important role in the uptake of atmospheric co 2

enhanced trapping of molybdenum by sulfurized marine organic matter of marine origin in mesozoic limestones and shales there have been many studies devoted to trace metals and their value in assessing the paleoredox conditions of ancient marine deposition among them molybdenum mo is frequently cited as an effective proxy for sediments and sedimentary rocks recently helz et al helz g r miller c v charnock j m mosselmans j l w pattrick r a d garner c d vaughan d j 1996 mechanisms of molybdenum removal from the sea and its concentration in black shales exafs evidences geochim cosmochim acta 60 3631 3642 and adelson et al adelson j m helz g r miller c v 2001 reconstructing the rise of recent coastal anoxia molybdenum in chesapeake bay sediments geochim cosmochim acta 65 237 252 suggested that mo does not behave conservatively in the water column when h2s reaches a threshold concentration above this concentration a switch operates and mo is scavenged by forming bonds with metal rich notably iron particles sulfur rich organic molecules and pyrite in this paper mo trapping by sulfur rich organic matter om in ancient marine deposits is emphasized the following mesozoic geological formations were selected for study because of their relatively high concentration of sulfurized om the akkuyu formation turkey the calcaires d orbagnoux france and kimmeridge clay uk and its timeequivalent in boulonnais france the kashpir oil shales russia and the la luna formation venezuela the sulfur rich om is identified by either measured organic s abundance or kerogen microscope observation our results show that mo is systematically more enriched relative to the other redox sensitive sulfide forming elements studied u v ni cu zn cr and mo enrichment is positively correlated with the amount of sulfurized om but not with pyrite abundance these results illuminate the role played by sulfurized om in geologic scale mo capture and retention but they also underline the role played by reactive iron significant om sulfurization is only possible when reactive iron is limited nevertheless pyrite formation though limited could act as an initial mo trap prior to mo uptake by om that is sulfurized after the pyritization step in future paleoenvironmental reconstructions attention must be paid to this enhanced mo enrichment in the presence of sulfurized organic matter in such cases the use of mo could lead to overestimation of the reducing conditions of the depositional environment

global nature of the younger dryas cooling event inferred from oxygen isotope data from sulu sea cores the younger dryas an approximately 1 000 year long return to near glacial conditions interrupted the glacial holocene climate transition during which most of the northern hemisphere ice sheets melted evidence for the younger dryas event has been found mainly in sediments from the north atlantic ocean and northwest europe and this has led to the idea that the event was caused by an injection of meltwater into the north atlantic ocean1 3 this model however has been recently questioned in the light of coral reef data on the rate of sea level changes during this transition4 here we present high resolution oxygen isotope records from benthic and planktonic foraminifera from two radiocarbon dated cores in the sulu sea showing that the younger dry as occurred synchronously in the surface and deep waters of the sulu sea and the northern atlantic ocean by combining our results with other palaeoclimate data we suggest that the younger dry as event was a global phenomenon and we believe it to have been caused by low atmospheric co2concentrations

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

three dimensional seismic monitoring of an enhanced oil recovery process seismic reflection data were used to monitor the progress of an in situ combustion enhanced oil recovery process three sets of three dimensional 3 d data were collected during a one year period in order to map the extent and directions of propagation in time acquisition and processing parameters were identical for each survey so that direct one to one comparison of traces could be made seismic attributes were calculated for each common depth point data set and in a unique application of seismic reflection data the preburn attributes were subtracted from the midburn and postburn attributes the resulting difference volumes of 3 d seismic data showed anomalies which were the basis for the interpretation shown in this case study profiles and horizon slices from the data sets clearly show the initiation and development of a bright spot in the reflection from the top of the reservoir and a dim spot in the reflection from a limestone below it interpretation of these anomalies is supported by informa

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

inverse phase oscillations between the east asian and indian ocean summer monsoons during the last 12 000 years and paleo el nino abstract the inverse phase variations between the east asian and indian ocean summer monsoons on the interannual timescale result from the el nino southern oscillation activity in the tropical pacific which potentially provides a new way for studying paleo enso here we reconstruct a 12 000 yr proxy record for the east asian summer monsoon from 13 c time series of the plant cellulose of the hani peat bog in the northeastern china the comparison of it with the peat proxy record of the indian ocean summer monsoon suggests that the el nino conditions are coincident with strong east asian summer monsoons weak indian summer monsoons and drift ice events in the north atlantic at both orbital and millennial time scales the orbital scale inverse phase relationships between the monsoons indicate the occurrence of a long term enso like pattern confirming the sensitivity of the monsoon systems associated with enso to insolation forcing the nine inverse phase variations on the millennial time scales may suggest the nine el nino like patterns superimposing the long term enso like pattern the inverse phase variations between the monsoons also show close correspondence to the drift ice events at high northern latitudes in every case when the abrupt ice rafted debris events occurred in the north atlantic the inverse phase relationship established and the el nino like pattern occurred in the tropical pacific correspondingly the discussions on the influence of ocean thermohaline circulation on these global linkages have been made

long chain alkenone inferred temperatures from the last deglaciation to the early holocene recorded by annually laminated sediments of the maar lake sihailongwan northeastern china abrupt temperature changes during the last deglaciation are well recognized in greenland ice cores and in deep sea sediment records on the continent of monsoonal asia however only a few terrestr

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

on the weakening relationship between the indian monsoon and enso analysis of the 140 year historical record suggests that the inverse relationship between the el nino southern oscillation enso and the indian summer monsoon weak monsoon arising from warm enso event has broken down in recent decades two possible reasons emerge from the analyses a southeastward shift in the walker circulation anomalies associated with enso events may lead to a reduced subsidence over the indian region thus favoring normal monsoon conditions additionally increased surface temperatures over eurasia in winter and spring which are a part of the midlatitude continental warming trend may favor the enhanced land ocean thermal gradient conducive to a strong monsoon these observations raise the possibility that the eurasian warming in recent decades helps to sustain the monsoon rainfall at a normal level despite strong enso events

evolution and variability of the asian monsoon system state of the art and outstanding issues the asian monsoon is comprised of the indian and east asian subsystems these two components are linked to one another in varying degrees by regions of strong sensible heating indo asian landmass and strong latent heat export the western pacific warm pool and the southern subtropical indian ocean variability within the indian and east asian subsystems interactions among them and the extent to which they interact with other climate phenomena e g enso are current topics of modern and paleoclimate research this work provides an overview of past and current paleomonsoon research on tectonic to interannual time scales with a primary focus on marine sediment records while past and current work has contributed greatly to our understanding of paleomonsoon variability at all time scales additional efforts are required to make further progress in two critical areas 1 additional efforts are needed in terms of proxy development and evaluation requiring concerted efforts at long term sediment trap deployments in key monsoon influenced regions as well as development of adequate and widely available core top databases these are necessary to assess the impact of modern oceanographic and seafloor processes on potential monsoon proxies 2 additional effort is also needed in acquiring a sufficient geographic distribution of downcore records to assess linkages among the subsystems and their role in the context of extratropical climate change these records should have high sedimentation rates including varved sections this requires substantial survey support to identify the most appropriate coring and drilling targets c 2004 elsevier ltd all rights reserved

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

14 kyr of atmospheric mineral dust deposition in north eastern china a record of palaeoclimatic and palaeoenvironmental changes in the chinese dust source regions a multi proxy record of holocene and late pleistocene aeolian mineral dust is reconstructed using a combination of geochemical trace elements mineralogical and grain size analyses on cores from