quantification of holocene asian monsoon rainfall from spatially separated cave records abstract a reconstruction of holocene rainfall is presented for southwest china an area prone to drought and flooding due to variability in the east asian monsoon the reconstruction is derived by comparing a new high resolution stalagmite 18 o record with an existing record from the same moisture transport pathway the new record is from heshang cave 30 27 n 110 25 e 294 m and shows no sign of kinetic or evaporative effects so can be reliably interpreted as a record of local rainfall composition and temperature heshang lies 600 km downwind from dongge cave which has a published high resolution 18 o record wang y j cheng h edwards r l he y q kong x g an z s wu j y kelly m j dykoski c a li x d 2005 the holocene asian monsoon links to solar changes and north atlantic climate science 308 854 857 by differencing co eval 18 o values for the two caves secondary controls on 18 o e g moisture source moisture transport non local rainfall temperature are circumvented and the resulting 18 o signal is controlled directly by the amount of rain falling between the two sites this is confirmed by comparison with rainfall data from the instrumental record which also allows a calibration of the 18 o proxy the calibrated 18 o record provides a quantitative history of rainfall in southwest china which demonstrates that rainfall was 8 higher than today during the holocene climatic optimum 6 ka but only 3 higher during the early holocene significant multi centennial variability also occurred with notable dry periods at 8 2 ka 4 8 4 1 ka 3 7 3 1 ka 1 4 1 0 ka and during the little ice age this holocene rainfall record provides a good target with which to test climate models the approach used here of combining stalagmite records from more than one location will also allow quantification of rainfall patterns for past times in other regions

sedimentary record of environmental evolution off the yangtze river estuary east china sea during the last 13 000 years with special reference to the influence of the yellow river on the yangtze river delta during the last 600 years abstract a 35 60 m long core ecs 0702 recovered from a water depth of 22 m in the muddy area off the yangtze river estuary was analyzed for sedimentary characteristics clay and detrital mineral components and element geochemistry as well as by ams 14 c dating to document sediment provenance changes and environmental evolution during the postglacial period in the study area on the basis of the lithology the benthic foraminiferal and ostracod assemblages and the ams 14 c ages we divided the core into four depositional units du1 du4 in descending order representing the postglacial sedimentary sequence during the last 13 000 years du 4 was deposited in a littoral to tidal flat environment during 13 000 11 500 cal yr bp du 3 in a nearshore subtidal environment upwards to the nearshore shelf with tidal influence in response to the postglacial sea level rise during 11 500 7400 cal yr bp du 2 in a tide affected nearshore shallow sea environment during 7400 540 cal yr bp on the delta front of the yangtze river when the delta was actively prograding and du 1 in a nearshore shallow sea environment during the last 540 years on the delta front under modern marine conditions in du 1 the depositional rate was much higher than in the underlying units and the sediment composition reflects more influence from the yellow river this unit can therefore be logically linked to the period when the yellow river last discharged into the south yellow sea from ad 1128 to 1855 according to historical records this period can be divided into an early stage ad 1128 1494 when the shoreline near the yellow river mouth was advancing slowly eastward and a late stage 1495 1855 when the shoreline was advancing rapidly the initiation of du 1 deposition corresponds to the latter part of the early stage suggesting that since that time a relatively large amount of sediment from the old yellow river mouth area has been transported to the offshore area of the yangtze river mouth our study has identified a high resolution sedimentary signature associated with the last course shift of the yellow river in the yangtze river delta front thus highlighting the intricate relationship between sediment sources and sinks in coastal areas a significant contribution of the old yellow river sediments to the yangtze subaqueous delta during the last 600 years must be considered when the evolutional history of the yangtze delta is examined and especially when the influence of the three gorge dam construction on the future changes of the yangtze estuary and ecological environments in the east china sea is estimated

yangtze delta eastern china 1 geometry and subsidence of holocene depocenter abstract stratigraphic analysis of 59 borings serves to define the subsurface configuration of late quaternary deposits of the outer yangtze delta including both subaerial lower plain and its contiguous submerged sector isopachous maps of the holocene sediment section reveal a linear thickened trend parallel to the lower yangtze estuary chongming island which extends seaward southeast to the mid shelf maps depicting depths of the holocene to late pleistocene contact also highlight this thickened northwest to southeast trend and a deep downward bowing depression formed by the sedimentary sequence seaward of the yangtze mouth radiocarbon dated facies in the cores serve to calculate long term averaged subsidence rates for the holocene section 0 1 to 3 0 mm year on land and 1 6 to 4 4 mm year at sea this preliminary information is vital for planning coastal protection erosion salt water intrusion in this densely populated low lying region vulnerable to marine inundation

late holocene 2 ka east asian monsoon variations inferred from river discharge and climate interrelationships in the pearl river estuary a sediment core from the pearl river estuary pre was analyzed for grain size and organic geochemistry parameters toc and delta c 13 org the results showed that high mean grain size value and increased sand content were correlated with the high toc and negative delta c 13 org these results indicated high river runoff in the pre area peak river discharge occurred during the periods 1900 1750 1500 1600 1400 1200 1000 900 and 750 600 cal yr bp the main changes recorded in grain size distributions toc contents and delta c 13 org variations appear to be directly related to monsoon precipitation in the sediment source area an increased east asian summer monsoon rainfall easm and or an enhanced east asian winter monsoon rainfall could result in the increasing of monsoon rainfall typhoon related rainfalls could act as positive influence on precipitation levels the study of the correlations between the rainfall records and enso activities revealed a close relationship between the monsoon rainfall in the pre and the tropical pacific variations the frequent occurrence of enso might result in the southern migration of the easm rain belt and lead to more typhoon derived rainfall in the prd during the late holocene c 2013 university of washington published by elsevier inc all rights reserved

sedimentary facies of the tide dominated paleo changjiang yangtze estuary during the last transgression abstract a large estuary was formed by marine inundation of the paleo changjiang yangtze incised valley during the transgression after the last glacial maximum this paper presents the sedimentary facies and architecture of the estuary fill based on the analysis of three sediment cores cm97 js98 and hq98 obtained from the present changjiang delta plain estuary fill deposits showing an upward fining succession were grouped into five depositional facies tidal river distributary channel muddy intertidal to subtidal flats transgressive lag and estuary front based on sedimentary textures lithology and physical sedimentary structures sand mud couplets are common in these deposits indicating that tides played a significant role in producing these sedimentary structures and that the estuary type was tide dominated some of the successive sand mud couplets probably recorded neap spring cycles as well as semidiurnal tidal cycles the nature of the estuary was very different from other representative tide dominated estuaries in sediment facies its distribution and sediment source for estuarine fill unlike the other estuaries that receive sediments mainly from the sea the paleo changjiang estuarine fill deposits were supplied largely from the river this difference would also have a great influence on the sedimentological and morphological component in the estuary the sediment distribution of the estuary showed fining seaward and estuary mouth sand bodies fed by marine source sand were absent the architecture model of tide dominated estuaries should be divided into two types by the degree of fluvial sediment supply the paleo changjiang estuary shows a good example for an estuary of large rivers

dynamical response of the tropical pacific ocean to solar forcing during the early holocene we present a high resolution magnesium calcium proxy record of holocene sea surface temperature sst from off the west coast of baja california sur mexico a region where interannual sst variability is dominated today by the influence of the el nino southern oscillation enso temperatures were lowest during the early to middle holocene consistent with documented eastern equatorial pacific cooling and numerical model simulations of orbital forcing into a la nina like state at that time the early holocene ssts were also characterized by millennial scale fluctuations that correlate with cosmogenic nuclide proxies of solar variability with inferred solar minima corresponding to el nino like warm conditions in apparent agreement with the theoretical ocean dynamical thermostat response of enso to exogenous radiative forcing

significant effect of sediment cohesion on delta morphology delta morphology is thought to be controlled by factors such as river discharge tides and waves numerical modelling shows that sediment cohesion also strongly influences the development of a delta s characteristics the morphologies of the world s deltas are thought to be determined by river discharge tidal range and wave action 1 more recently sea level rise 2 3 and human engineering4 have been shown to shape delta evolution the effects of factors such as sediment type and the overall amount of sediment carried by rivers are considered secondary4 5 6 in particular the role of sediment cohesion which is controlled by sediment size and type of vegetation is unclear here we use a numerical flow and transport model7 8 9 10 to show that sediment cohesiveness also strongly influences the morphology of deltas we find that holding all other factors constant highly cohesive sediments form bird s foot deltas with rugose shorelines and highly complex floodplains whereas less cohesive sediments result in fan like deltas with smooth shorelines and flat floodplains in our simulations sediment cohesiveness also controls the number of channels that form within the deltas and the average angle of bifurcation of those channels as vegetation generally acts as a cohesive agent we suggest that deltas that formed before the expansion of land plants in the devonian period should show fan like characteristics a finding consistent with the limited data from the sedimentological record11

asymmetric vegetation responses to mid holocene aridity at the prairie forest ecotone in south central minnesota abstract the mid holocene ca 8000 4000 cal yr bp was a time of marked aridity throughout much of minnesota and the changes due to mid holocene aridity are seen as an analog for future responses to global warming in this study we compare the transition into ca 9000 7000 yr ago and out of ca 5000 2500 yr ago the mid holocene mh period at kimble pond and sharkey lake located along the prairie forest ecotone in south central minnesota using high resolution 5 36 yr sampling of pollen charcoal sediment magnetic and loss on ignition properties changes in vegetation were asymmetrical with increasing aridity being marked by a pronounced shift from woodland forest dominated landscape to a more open mix of grassland and woodland savanna in contrast at the end of the mh grassland remained an important component of the landscape despite increasing effective moisture and high charcoal influxes median 2 7 4 0 vs 0 6 1 7 mm 2 cm 2 yr 1 at start of mh suggest the role of fire in limiting woodland expansion asymmetric vegetation responses variation among and within proxies and the near absence of fire today suggest caution in using changes associated with mid holocene aridity at the prairie forest boundary as an analog for future responses to global warming

influence of provenance weathering and sedimentary processes on the elemental ratios of the fine grained fraction of the bedload sediments from the vembanad lake and the adjoining continental shelf southwest coast of india abstract geochemical studies comprising twelve major elements and twenty four trace elements including the rare earth elements ree have been carried out on the concentrations normalized to the average upper continental crust ucc show that the sediments studied are depleted in rb k ba ta hf na and ca and enriched in cs u th rees sc fe co and cr ucc normalized patterns are strikingly similar for all the three sediment types probably because of efficient mixing of sedimentary material during weathering transport and deposition the depletion of na k ca and ba in sediments relative to ucc could be attributed to their mobility during weathering the depletion of ta and hf and enrichment of th ree and sc are probably related to provenance characteristics and enrichment of u is attributed to oxidation reduction processes shale normalized ree values reveal steep hree patterns tbsample tbshale ybsample ybshale lasample lashale smsample smshale and flat lree patterns the shale normalized patterns for all the three types of sediments are remarkably similar with variations in the magnitude of lree enrichment lan ybn varies between 1 72 to 2 57 times that of paas lree enrichment and steep hree patterns are attributed to felsic source rock characteristics other geochemical characteristics such as high la th and low la sc and th sc ratios compared to ucc also support a felsic provenance eu eu values for all the three types are little more than 1 which is also a characteristic feature of archean crust furthermore data plotted on discrimination diagrams of la th vs hf and la th sc cluster closer to granite and away from basalt and komatiite and are consistent with source rock geology geochemical data have also helped in ascertaining the weathering trends the chemical index of alteration cia has been used to quantify the degree of weathering cia values range between 81 and 94 on a scale of 40 100 indicating a high degree of alteration fluvial sediments seem to be more altered on an a cn k diagram the data fall closer to the compositional fields of highly weathered minerals kaolinite gibbsite and chlorite a high degree of weathering is also indicated by other plots such as k2o fe2o3 al2o3 and log k vs log rb the geochemical data are consistent with the studies on clay mineralogy higher kaolinite carried out by other authors on the sediments of the same area secondary processes seem to affect other geochemical discriminants such as co cr ni and u as revealed by plots of 1 la sc vs co th and 2 th hf co and co th cr th ratios and makes them unsuitable for determining provenance and tectonic setting

yangtze delta eastern china 2 late quaternary subsidence and deformation abstract late quaternary deposits examined on high resolution seismic profiles provide evidence of recent subsidence of the outer yangtze delta in the east china sea deformed late pleistocene strata and mud diapirs tilted bedding and gas deformed structures in holocene sequences record remobilization of underconsolidated sediment within and adjacent to the yangtze depocenter deformation types and their specific position relative to the depocenter record displacement of sediment as a result of quaternary overburden and probable compaction and deep seated tectonic motion the configuration of depositional sequences demonstrates that subsidence in the outer yangtze delta has continued from the late pleistocene to the present

correlation between indian ocean summer monsoon and north atlantic climate during the holocene there has been a number of investigations for the correlation between the asia monsoon and the north atlantic climate for the last glacial however little research has been done for the present interglacial the holocene here we present for the first time a high resolution composite proxy record for the indian ocean summer monsoon spanning around 12 000 years based on the 13c time series of both a single plant species carex mulieensis remains cellulose and the total plant assemblage cellulose in the hongyuan peat bog from the tibet plateau the records show that the strength of the indian ocean summer monsoon had abrupt variations during the last 12 000 years the weakest monsoon occurred in the younger dryas period following rapid strengthening from around 11 200 to 10 800 a bp the monsoon kept a generally strong level for around 5300 years from around 5500 a bp onwards the monsoon strength tended to gradual decrease in addition there are a series of abrupt variation events of the monsoon strength on centennial to millennial time scales which superimpose the general tendency of the monsoon variation in every case when the ice rafted debris events in the north atlantic occurred the summer monsoon strength decreased correspondingly these evidences show that teleconnection between the indian ocean summer monsoon and the north atlantic climate is present not only in the last glacial but also in the holocene which may be linked to abrupt reorganizations of the ocean thermohaline circulation leading to redistribution of energy changing temperature and moisture gradient over the southern subtropical indian ocean and eventually controlling the variability of the indian ocean summer monsoon

stratigraphy and paleoenvironmental changes in the yangtze delta during the late quaternary the yangtze delta area may be subdivided into paleo valley and paleointerfluves of the last glaciation the postglacial transgressive sedimentary cycle ptsc on the front zones of the paleointerfluves is composed of marsh nearshore and barrier lagoon shallow marine and nearshore tidal flat units with a basement in stiff clay the ptsc in back zones of the paleointerfluves consists of lacustrine marsh deposits the ptsc in the incised valley contains river channel floodplain estuary estuarine shallow marine and deltaic units with an erosional surface at its bottom the stiff clay and the erosional surface constitute the ptsc lower boundary the stiff clay consisting of a paleosol experienced deposition alternating with pedogenesis during the falling of sea level during 18o stage 3 ongoing pedogenesis in the sea level lowstand of 18o stage 2 and early diagenesis after paleointerfluve inundation by the sea level rise of 18o stage 1 the climate during the paleosol formation was temperate with more than 500 mm a 1 rainfall and frequently fluctuating groundwater the yangtze river incised its course during falling sea level of stage 3 and a huge incised valley was formed during the sea level lowstand stage 2 the filling of the incised valley took place during the postglacial sea level rise and delta formation occurred at a late stage of ptsc development

flux and fate of yangtze river sediment delivered to the east china sea numerous cores and dating show the yangtze river has accumulated about 1 16 x 10 12 t sediment in its delta plain and proximal subaqueous delta during holocene high resolution seismic profiling and coring in the southern east china sea during 2003 and 2004 cruises has revealed an elongated similar to 800 km distal subaqueous mud wedge extending from the yangtze river mouth southward off the zhejiang and fujian coasts into the taiwan strait overlying what appears to be a transgressive sand layer this distal clinoform thins offshore from similar to 40 in thickness between the 20 and 30 m water depth to 1 2 in between 60 and 90 m water depth corresponding to an across shelf distance of less than 100 km total volume of this distal mud wedge is about 4 5 x 10 11 m 3 equivalent to similar to 5 4 x 10 11 t of sediment most of the sediment in this mud wedge comes from the yangtze river with some input presumably coming from local smaller rivers thus the total yangtze derived sediments accumulated in its deltaic system and east china sea inner shelf have amounted to about 1 7 x 10 12 t preliminary analyses suggest this longshore and across shelf transported clinoform mainly formed in the past 7000 yrs after postglacial sea level reached its mid holocene highstand and after re intensification of the chinese longshore current system sedimentation accumulation apparently increased around 2000 yrs bp reflecting the evolution of the yangtze estuary and increased land erosion due to human activities such as fanning and deforestation the southward flowing china coastal current the northward flowing taiwan warm current and the kuroshio current appear to have played critical roles in transporting and trapping most of yangtze derived materials in the inner shelf and hence preventing the sediment escape into the deep ocean c 2006 elsevier b v all rights reserved

strong coherence between solar variability and the monsoon in oman between 9 and 6 kyr ago variations in the amount of solar radiation reaching the earth are thought to influence climate but the extent of this influence on timescales of millennia to decades is unclear a number of climate records show correlations between solar cycles and climate1 but the absolute changes in solar intensity over the range of decades to millennia are small2 and the influence of solar flux on climate is not well established the formation of stalagmites in northern oman has recorded past northward shifts of the intertropical convergence zone3 whose northward migration stops near the southern shoreline of arabia in the present climate4 here we present a high resolution record of oxygen isotope variations for the period from 9 6 to 6 1 kyr before present in a th u dated stalagmite from oman the 18o record from the stalagmite which serves as a proxy for variations in the tropical circulation and monsoon rainfall allows us to make a direct comparison of the 18o record with the 14c record from tree rings5 which largely reflects changes in solar activity6 7 the excellent correlation between the two records suggests that one of the primary controls on centennial to decadal scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation

high resolution evidence from southern china of an early holocene optimum and a mid holocene dry event during the past 18 000 years abstract computer models suggest that the holocene optimum for east asian summer monsoon precipitation occurred at different times in different regions of china previous studies indicate that this time transgressive holocene optimum should have been experienced about 3000 yr ago in southern china in this study we describe a section which allows us to test this timing directly we have closely examined high resolution eutrophic peat mud sequences covering the past 18 000 cal yr at dahu jiangxi on the southern boundary of the mid subtropical zone in china late pleistocene successions in the dahu record indicate cooler and much wetter conditions relative to synchronous events in north central china our results indicate that the holocene optimum occurred between ca 10 000 and 6000 cal yr ago in southern china consistent with the global pattern conditions were relatively dry and cold from 6000 to 4000 cal yr ago our data also support the conclusion that the last deglaciation to early holocene in the south was much wetter resulting in the formation of dense broad leaved forests which could have acted to moderate land temperature 10 000 to 6000 cal yr ago yielding a stable early holocene climate after 6000 cal yr forest reduction led to unstable land temperatures and possibly to a northerly shift of the subtropical high pressure system whatever the mechanism these changes resulted in decreased precipitation between 6000 and 4000 cal yr b p in southern china

weathering and global denudation a negative correlation between sediment yield and weathering history as measured by the chemical alteration cia of the suspended sediment is observed for many of the world s major rivers and other regions of denudation the weathering history is a first order control on the sediment yield of such areas termed equilibrium denudation regions for other areas data scatter with either apparent increases or decreases of sediment yield for given cia values these areas are termed nonequilibrium denudation regions low sediment yields can be attributed to moderated erosion either natural or human induced and or the incorporation of unweathered glacial debris accelerated erosion resulting in high sediment yield is primarily human induced and results from cultivation and other land use each of these effects has a profound influence on global sediment discharge from the continents pre human suspended sediment discharge from the continents is estimated to be 12 6 times 10 15 g yr or about 0 6 the

link between east asian summer monsoon and sedimentation in river mouth sandbars since the early holocene preserved in the yangtze river subaqueous delta front this paper presents geochemical and grain size records since the early holocene in core ecs0702 with a fine chronology frame obtained from the yangtze river subaqueous delta front since 9500 cal yr bp the proxy records of chemical weathering from the yangtze river basin generally exhibit a holocene optimum in the early holocene a weak east asian summer monsoon easm period during the middle holocene and a relatively strong easm period in the late holocene the 8 2 and 4 4 cal ka bp cooling events are recorded in core ecs0702 the flooding events reconstructed by the grain size parameters since the early holocene suggest that the floods mainly occurred during strong easm periods and the yangtze river mouth sandbar caused by the floods mainly formed in the early and late holocene the yangtze river mouth sandbars since the early holocene shifted from north to south affected by tidal currents and the coriolis force and more importantly controlled by the easm our results are of great significance for enriching both the record of holocene climate change in the yangtze river basin and knowledge about the formation and evolution progress of the deltas located in monsoon regions

initiation of the changjiang yangtze delta and its response to the mid holocene sea level change abstract the changjiang yangtze delta in eastern china is one of the largest tide dominated deltas in the world to obtain a more detailed information on its initiation we drilled three sediment cores pk01 hg01 and xj03 from the uppermost region of the delta plain on the basis of sedimentary facies and ams 14c dating we identified three depositional systems 1 a fluvial system 2 an estuarine system and 3 a deltaic system including an initial delta estuary delta transition and a typical delta the maximum flooding surface separates the estuarine and deltaic systems and occurred at ca 8 0 cal kyr bp when brackish water intruded landward and reached the nanjing area the changjiang delta was initiated at the area between nanjing and yizheng when the sea level rise decelerated after the rapid rise in sea level during 9 0 8 2 cal kyr bp the subsequent evolution of the changjiang delta has been shown as a seaward development model of river mouth bars with shoreline migration the oldest river mouth bar called hongqiao sand body which is located most landward was dated at 6 0 5 5 cal kyr bp in this study nearly one thousand years younger than the previous estimates a tide dominated funnel shaped estuary was formed at 8 0 cal kyr bp and lasted until the hongqiao sand bar became exposed this stage is regarded as an aggradation dominated initial stage of the changjiang delta followed by a progradation dominated stage that is characterized by the formation of a series of seaward migrating river mouth bars a relative sea level highstand in the mid holocene may be associated with glacio hydro isostatic tilting

10 000 yr record of extreme hydrologic events well dated lacustrine sediments provide a hydrologic record indicating that the frequency and magnitude of runoff events and by inference storms have varied over the past 10 k y in northern new england we used five sediment cores and radiocarbon dating to develop a chronology of holocene hydrologic events for the ritterbush pond basin northern vermont chemical and physical analyses allow us to identify 52 distinct layers of predominately inorganic sediment that represent terrestrially derived material delivered to the pond by runoff events the thickness of some layers suggests hydrologic events at least equal in size to and probably much larger than any storm or flood recorded during nearly 300 yr of written regional history layer thickness and frequency and by analogy storm size and recurrence change through the holocene the largest events occurred 2620 6840 and 9440 calibrated 14c years before present cal 14c yr b p the most frequent hydrologic events occurred in three periods 1750 to 2620 6330 to 6840 and 8600 cal yr b p the recurrence interval of layer deposition during stormy periods averages 130 100 cal yr whereas the recurrence interval during less stormy periods is longer 270 170 cal yr the ritterbush pond event record illustrates the potential of inorganic lacustrine sediment to serve as a proxy record for estimating paleoflood frequency and deciphering climate change

el nino southern oscillation extrema in the holocene and last glacial maximum 1 the el nino southern oscillation enso is the largest engine of interannual climate variability on the planet yet its past behavior and potential for future change are poorly understood and vigorously contested reconstructions of past enso are indispensable for testing climate models tasked with predicting future enso activity in a warming world but suitable geologic archives are scarce especially for the last glacial period here we reconstruct mean climate and enso variability in the holocene and last glacial maximum lgm from oxygen isotopic ratios 18o of individual foraminifera retrieved from deep sea sediments our results document coordinated adjustments of the tropical pacific enso system between two diametrically opposite states an amplified enso state in the lgm associated with a reduced zonal temperature gradient and a damped enso state in the mid holocene with enhanced gradient orbital precession provided the switch between these states and acted as the dominant external driver of the tropical pacific enso system in the past 25 000 years the linked response of the mean state and variability to orbital forcing provides an integrated framework for testing enso theory and models

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

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

geodynamical implications from the correlation of surface geology and seismic tomographic structure abstract we have investigated the relationship between the lateral seismic structure in the mantle and the geological features associated with major mantle upwellings the oceanic ridge system and hotspots using the technique of correlation analysis we have identified that these features extend quite deeply into the mantle to a depth of around 1300 km this finding is surprising for the ridges because it indicates that the style of upwelling is rather active and is somewhat two dimensional in character the confidence level of the correlation between ridges and slow seismic regions is maintained at a level of greater than 90 to a depth of 1300 km this is followed by a sharp decrease to 50 at 1700 km a similar correlation pattern is found for the hotspots in both cases the correlation maxima lie close to a depth of 1000 km where remnants of old slabs have recently been revealed by correlation analysis these findings suggest that dynamical processes at a depth of around 1000 km can be linked with surface tectonic activity this correlation disappears at a depth of around 1500 1700 km certain features of the surface tectonic pattern can again be recognized around a depth of 2000 km and in the deepest mantle where major hotspot plumes and the remnant old lithosphere are the dominant features there may be some dynamical relationship between the ridge system and the two megaplumes we have proposed a physical mechanism based on viscous heating within megaplumes to explain the two peaks in the correlation between the hotspots and the seismic heterogeneities

episodic gullying and paleomonsoon cycles on the chinese loess plateau buried gullies exposed in road excavations along the margin of a loess tableland on the loess plateau of central china lie within a thick loess paleosol succession that spans 780 000 years constraining ages for gully cutting and filling are provided by dates of loess and soil units cut by and capping the paleogullies an episode of gully cutting begins at the onset of an interglaciation and ceases as the gullies begin to fill with colluvium and airborne dust during the transition to full glacial conditions the episodic cutting and filling of gullies implies a basic astronomical orbital control of gully evolution involving cyclic changes in dominant summer and winter monsoon climates surface hydrology and vegetation cover

environmental change in the yangtze river delta since 12 000 years b p abstract a 52 m core from qidong at the tip of the yangtze river chang jiang delta provides a history of sea level change deltaic development and vegetational and climatic changes during the last 12 000 yr about 12 000 yr ago when sea level was about 60 m below the present level the coring site was situated in the innermost part of the exposed continental shelf the late pleistocene vegetation on the uplands of the lower yangtze river valley was a mixed forest of deciduous and broadleaved evergreen trees in which betula ulmus tsuga and cupressaceae were slightly more abundant than at present abies and picea were probably present as relict populations on mountains bordering the region rapidly rising sea level converted the qidong area to a coastal or estuarine environment between 11 000 and 10 800 yr b p leading to widespread development of wetlands dominated by gramineae and cyperaceae during the next 2500 yr coastal erosion due to marine transgression obliterated the sedimentary record deltaic sedimentation predominated from 8300 to 3800 yr b p as the yangtze river delta prograded by successively building a series of estuarine sand bars during the mid holocene the climate was slightly warmer and more humid than at present allowing the subtropical broadleaved evergreen trees to increase their populations pinus and quercus became more abundant after 3800 yr b p in response to climatic cooling the present deltaic plain in qidong formed less than 200 yr ago

variability in terrigenous sedimentation processes off northwest africa and its relation to climate changes inferences from grain size distributions of a holocene marine sediment record variations in deposition of terrigenous fine sediments and their grain size distributions from a high resolution marine sediment record offshore northwest africa 30 51 0 n 10 16 1 w document climate changes on the african continent during the holocene end member grain size distributions of the terrigenous silt fraction which are related to fluvial and aeolian dust transport indicate millennial scale variability in the dominant transport processes at the investigation site off northwest africa as well as recurring periods of dry conditions in northwest africa during the holocene the terrigenous record from the subtropical north atlantic reflects generally humid conditions before the younger dryas during the early to mid holocene as well as after 1 3 kyr bp by contrast continental runoff was reduced and arid conditions were prevalent at the beginning of the younger dryas and during the mid and late holocene a comparison with high and low latitude holocene climate records reveals a strong link between northwest african climate and northern hemisphere atmospheric circulation throughout the holocene due to its proximal position close to an ephemeral river system draining the atlas mountains as well as the adjacent saharan desert this detailed marine sediment record which has a temporal resolution between 15 and 120 years is ideally suited to enhance our understanding of ocean continent atmosphere interactions in african climates and the hydrological cycle of northern africa after the last deglaciation

controls on river delta formation insights from numerical modelling abstract primary hydraulic and sedimentary controls on river deltas were previously postulated in classification schemes in the field of sedimentary geology based on many field observations however detailed mechanistic models were restricted to the river dominated delta class analogous to the concept of morphological conditioning here we show that antecedent stratigraphy controls morphometrics of prograding river dominated delta distributary networks under steady sea level further we use coupled hydrodynamic morphodynamic stratigraphic detailed numerical modelling to assess the influence of wind generated waves and tides on clastic river delta formation our synthetic simulations show that deltas forming under mere riverine forcing prograde via sequences of mouth bar induced flow bifurcation and upstream channel shifting windwave action suppresses sequestration of fine sediments on the developing delta plain entailing relatively smooth shorelines perturbed by a limited number of distributary channels in contrast tide influenced river deltas are found to prograde mainly via lengthening of initially formed relatively stable distributaries as well as being characterized by cyclicity in deposits interbedding of sands and silts these results provide a framework for physics based river delta modelling under various environmental conditions particularly our findings suggest that relatively low energetic basin conditions can already significantly impact morphological and stratal patterns of prograding river deltas

influence of steady base level rise on channel mobility shoreline migration and scaling properties of a cohesive experimental delta 1 here we describe results from an alluvial delta physical experiment with and without steady base level rise using a unique cohesive sediment mixture that promotes the development of persistent channels and a rugose shoreline we quantitatively characterize channel network properties as a function of base level rise in a distributary system that reproduces many aspects of the geometry of natural deltas analysis of the experimental data shows clear dynamical differences between the predominantly progadational and aggradational phases of the experiment the experiment was conducted in two phases a first in which the delta prograded into standing water of constant depth in the absence of base level rise and a second during which steady base level rise was imposed on the system forcing a twofold increase in topset aggradation due to greater sediment retention in the fluvial reach the shift in sediment mass balance to enhanced fluvial deposition in the second phase caused channel network mobility to increase reducing the autogenic channel time scale from 23 5 to 12 5 h and supporting a positive correlation between deposition and channel avulsion frequency an independent shoreline time scale that characterizes the dominant time over which shoreline regression is persistent closely correlates with measurements of the channel network 28 3 h during fan progradation and 9 5 h during fan aggradation these metrics suggest a strong coupling between channel network and shoreline kinematics and a more active fluvial surface during fan aggradation by a factor of 2 to 3 similar to the increase in aggradation rate spatial scaling of shoreline roughness reveals that maximum shoreline variability is set by the scale of distributary lobes strong coupling exists between delta growth and shoreline geometry during progradation during aggradation however shoreline variability is not solely due to distributary lobe growth but is also set by shoreline transgression over inactive portions of the delta illustrating a decoupling between fan kinematics and fan geometry this decoupling together with the matched increase in channel network mobility and fluvial aggradation suggest the stratigraphic architecture may not be a strong geometric signal of different fluvial surface conditions either

simulations of magma ascent and pyroclast dispersal at vulcano aeolian islands italy abstract two phase flow models of magma ascent in volcanic conduits and pyroclast dispersal in the pressure and temperature stratified atmosphere were employed to study the consistency of the palizzi pumice fall eruption phase and the last eruption of vulcano with modeling predictions the input data for magma ascent modeling were constrained by the limited availability of petrological volcanological and geophysical data and consisted of magma composition crystal content conduit geometry and pressure and temperature of magma in the magma chamber the magma ascent model was used to establish the locations of magma exsolution and fragmentation levels gas and pyroclast velocities pressure and pyroclast volumetric fractions at the exits of conduits of different diameters and lengths the vent exit conditions of gas and pyroclasts corresponding to different magma compositions and conduit geometry were employed in the pyroclastic dispersion modeling to establish the distribution of gas and pyroclasts in the atmosphere and along the slopes of the volcano during the first few minutes of the eruptions in order to determine the volcanic column and flow behavior along the slopes of the volcano the results from simulations showed that the palizzi pumice fall eruption phase and the last eruption of vulcano which produced bread crust bombs are consistent with magma ascent and pyroclastic dispersion models using the available volcanological petrological and geophysical data as well as the modeling results an eruptive scenario of each cycle of vulcano was hypothesized where the chemical characteristics of new magma supply into the volcanic system and magma remaining in the system after preceding eruptions mechanical characteristics of the magma ascent pathways and the conditions of aquifers surrounding these pathways determine the duration of phreatic phreatomagmatic magmatic and lava flow activities within each cycle the modeling results also suggested that the palizzi pumice fall eruption phase ejected magma with a dissolved water content of about 2 wt from a vent diameter of about 30 m and that the dissolved water content in magma during the last eruption of vulcano ranged between 1 and 2 wt detailed modeling of various eruptive phases and adequate volcanic hazard assessment at vulcano not only requires the development of magma water interaction and hydrothermal circulation models but also the collection of modeling oriented volcanological petrological and geophysical data

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

holocene late pleistocene climatic ice core records from qinghai tibetan plateau three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau of china provide a detailed record of holocene and wisconsin wurm late glacial stage lgs climate changes in the subtropics the records reveal that lgs conditions were apparently colder wetter and dustier than holocene conditions the lgs part of the cores is characterized by more negative 18 o ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes than the holocene part these changes occurred rapidly 10 000 years ago in addition the last 60 years were apparently one of the warmest periods in the entire record equalling levels of the holocene maximum between 6000 and 8000 years ago

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