sedimentary rhythm of mn carbonate laminae induced by east asian summer monsoon variability and human activity in lake ohnuma southwest hokkaido northern japan abstract past and ongoing precipitations of mn carbonate rhodochrosite have occurred in the freshwater lake ohnuma which is situated about 8 km south of the hokkaido komagatake volcano southwest hokkaido northern japan lake sediments from a surface and a longer 4 m core contain the sedimentary rhythms of rhodochrosite laminae and volcanic deposits which were identified by nondestructive micro xrf fluorescence analyses the three tephra ash layers from the hokkaido komagatake volcano characterized by peaks of al si k ca and ti correspond to regionally recognized tephras 1640 1929 and 1996 ce based on ashfall isopachs and 137cs 210pb and 14c ages determined from the two cores the sedimentation rate showed a drastic change around 1929 ce 0 3 cm yr for 1640 1929 ce and 2 7 cm yr for 1929 2012 ce the mn content record of lake ohnuma sediments composed of rhodochrosite laminae showed a periodic variation with a decadal centennial scale over the interval 1640 2012 ce sediment petrography and hydrochemical measurements suggest that the metastable phase of rhodochrosite was deposited during summer after being precipitated followed by the crystal growth of rhodochrosite within the anoxic sediments on the basis of these results high mn content is interpreted as an indicator of strengthened summer stratification associated with reduced rainfall runoff the ti si ratios are representative of the relative abundance of detrital inputs from the watershed the combined signals of elevated mn content and ti si ratio for 1935 2012 ce indicate eutrophication and hypoxia in the lake and enhanced land erosion in the watershed associated with the post 1970s intensive land use such as livestock farming for 1640 1935 ce the lake ohnuma record shows an antiphase relationship between the mn content and ti si ratio which implies that the detrital inputs reflected the strength of the east asian summer monsoon easm and the reduced rainfall runoff resulted in weaker mixing followed by depleted o2 in the water column the antiphase variation in mn content and ti si ratio suggest weak easm during the little ice age 1850 ce followed by strong easm between 1860 and 1929 ce

regulation of the monsoon climate by two different orbital rhythms and forcing mechanisms the east asian monsoon is responsible for transferring huge amounts of heat and moisture between the land and the adjacent ocean significant changes in its capacity to do this will have direct impacts on regional climatic gradients and global atmospheric circulation determining the mechanisms that force long term variation in monsoon behavior is therefore important for understanding global climate change competing theories vary in the degree of importance attached to glacial forcing other orbital rhythms and internal feedback mechanisms as primary drivers of change there is however no convincing explanation as to why different proxy records from closely neighboring regions are tuned to different orbital rhythms here we present quantitative climatic reconstructions for the past 450 k y based on a long pollen record from lake biwa in japan the data suggest that continental and oceanic air mass temperatures respond predominantly to the 100 k y orbital rhythm whereas the land ocean temperature gradient and monsoon vigor oscillate mainly at the 23 k y insolation cycle we suggest that the mechanisms for this behavior lie in the differential response of land and ocean to solar forcing and conclude that the 100 k y signal dominates monsoon intensity only when the amplitude of solar forcing falls below a threshold level

flooding history of lake nakaumi western japan inferred from sediment records spanning the past 700 years management of flood risk can benefit from a knowledge based approach to flooding history however the data on such events are often insufficient for an objective evaluation of flooding characteristics such as their intensity therefore we analyzed a 14c dated sediment core recovered from near the iinashi river mouth in lake nakaumi western japan and reconstructed flooding records over the past 700 years from rock magnetism grain size distribution and sediment geochemistry the sediment core contained three black layers characterized by high magnetic susceptibility low anhysteretic remanent magnetization to saturation isothermal remanent magnetization ratio high total organic carbon toc to total nitrogen ratio and coarse mean grain size which we identified as possible flooding event deposits moreover the chemical index of alteration was low and the toc to total sulfur ratio was high in these layers indicating intensified erosion associated with more freshwater inflow due to the flood events we tentatively correlated the three event deposits with historical floods along the iinashi river in ad 1596 1666 and 1826 the variations in rock magnetic and geochemical properties suggest that the flooding in ad 1666 may have been the least extreme of the events detected in the core

anatomy of extremely thin marine sequences landward of a passive margin hinge zone neogene calvert cliffs succession maryland u s a abstract detailed examination of neogene strata in cliffs 25 35 m high along the western shore of chesapeake bay maryland reveals the complexity of the surviving record of siliciclastic sequences 150 km inland of the structural hinge zone of the atlantic passive margin previous study of the lower to middle miocene calvert plum point member and choptank formations documented a series of third order sequences 7 10 m thick in which lowstand deposits are entirely lacking transgressive tracts comprise a mosaic of condensed bioclastic facies and regressive highstand tracts are present but partially truncated by the next sequence boundary smaller scale fourth order cyclic units could not be resolved together these sequences constitute t e transgressive and early highstand tracts of a larger second order miocene composite sequence the present paper documents stratigraphic relations higher in the calvert cliffs succession including the upper miocene st marys formation which represents late highstand marine deposits of the miocene second order sequence and younger neogene fluvial and tidal inlet deposits representing incised valley deposits of the succeeding second order cycle the st marys formation consists of a series of tabular units 2 5 m thick each with an exclusively transgressive array of facies and bounded by stranding surfaces of abrupt shallowing these units which are opposite to the flooding surface bounded regressive facies arrays of model parasequences are best characterized as shaved sequences in which only the transgressive tract survives and are stacked into larger transgressive highstand and forced regression sets biostratigraphic analyses by others indicate that this onshore record contains the same number of third order 1 my duration units as present offshore and so thinning landward of the hinge zone was accomplished not by omission or erosion of entire cycles of deposition but instead by omission of some subsidiary elements e g lowstand tracts by erosional shaving of sequence tops removing the entire regressive tract in some sequences by a reduced number of component high order cycles surviving per larger set and by qualitative changes in the anatomy or composition of elements e g condensed transgressive tracts shaved sequences rather than parasequences all of these differences can be attributed to limited accommodation ut preservation of an onshore record of each baselevel cycle was probably also favored by the large amplitude and rapidity of eustatic fluctuations during the miocene

the effect of north pacific sea surface temperature anomalies on the january climate of a general circulation model abstract four perpetual january integrations of an atmospheric general circulation model have been performed in each of which a different sea surface temperature sst anomaly was specified in the north pacific the observed sst anomaly for the 1976 77 winter was chosen as the basic anomaly and 1200 day runs were carded out in which this anomaly was multiplied by 1 and 2 a fifth run was performed which combined the basic midlatitude sst anomaly from 1976 77 with a tropical pacific sst anomaly representative of the mature phase of a warm el nino southern oscillation enso episode an ensemble of eight independent 90 day averaged realizations was extracted from each simulation maps of ensemble mean differences from the model climatology are presented in this paper together with estimates of the statistical significance of some of the features which appear on these maps the model response to the basic sst anomaly and to twice the basic sst anomaly is a midiatitude teleconnection pattern the pacifi

late holocene asian monsoon variations recorded in lake rara sediment western nepal the himalayas are a key location for understanding centennial to millennial scale variations in the asian monsoon yet few studies of the late holocene have been conducted in this sensitive area direct evidence for shifts in monsoonal wind strength is often limited to marine proxy records while terrestrial reconstructions e g lake levels and spleothems focus on precipitation here we present the first evidence of terrestrial summer monsoon wind strength changes from lake rara western nepal based on mn ti ratios a proxy for lake stratification these data indicate a link between the arabian sea and the himalayas suggesting that centennial to millennial scale changes in wind strength occurred synchronously distinct similarity is also observed between lake rara and the southern part of china which may support previous suggestions that the southern part of china is influenced by indian summer monsoon copyright 2012 john wiley sons ltd

variations of east asian summer monsoon since the last deglaciation based on mg ca and oxygen isotope of planktic foraminifera in the northern east china sea 1 variations in mg ca based sea surface temperature and oxygen isotope ratio 18o of the surface water in the northern east china sea ecs were reconstructed with high resolution during the last 18 kyr using planktic foraminifera millennial scale variations between warmer more saline surface water and cooler less saline surface water were recognized during the early deglacial period and the holocene suggesting changes in the mixing ratio between the kuroshio water and the changjiang diluted water stronger east asian summer monsoon easm precipitation events in south china are identified at 10 5 8 8 7 0 5 3 4 7 2 9 1 7 and 0 5 ka based on sea surface salinity sss records of the northern ecs weaker easm precipitation events are also detected at 9 3 8 3 7 3 6 0 3 3 2 3 0 7 and 0 4 ka during the holocene these events agree with the maxima in 18o records of stalagmites from various parts of the changjiang yangtze river drainage this agreement supports that our sss record properly captures the millennial scale dry less easm precipitation events over the drainage basin of the changjiang river during the holocene these dry events are also in good agreement with north atlantic ice rafted events suggesting a teleconnection between north atlantic climate and the easm during the holocene

sequence stratigraphy in active extensional basins implications for the interpretation of ancient basin fills abstract systematic variations in sequences their component units and their stacking patterns exist within rift basins these variations can be related to displacement gradients associated with the large scale 12 50 km segmentation of normal fault zones which control accommodation sediment supply and basin physiography sediment supply is also strongly influenced by the nature of pre rift drainage networks and variations in bedrock lithology high rates of hangingwall subsidence close to the centre of normal fault segments may cancel out the effects of glacio eustatic sea level fall so that accommodation development is normally characterized by the continual addition of new space the resulting sequences lack type 1 sequence boundaries and lowstand systems tracts and stack into aggradational sequence sets the adjacent footwall is subject to uplift which may lead to subaerial exposure and incision generating a composite type 1 sequence boundary away from the fault zone and near segment boundaries slip rates are much lower and hence relative sea level change is dominated by eustasy here falls in relative sea level are important resulting in type 1 sequences sequence stacking patterns reflect not only eustasy and local fault controlled subsidence but also the interaction of these with adjacent uplifting footwalls and or regional uplift tectonic influence on sequence development will be more pronounced during greenhouse times than icehouse times

holocene stalagmite δ18o records in the east asian monsoon region and their correlation with those in the indian monsoon region we compare well dated holocene stalagmite delta o 18 records from the east asian summer monsoon easm region and from the indian summer monsoon ism region we found that the pattern of latitudinal change of speleothem delta o 18 values from the indian monsoon region to the east asian monsoon region is almost identical to that of modern precipitation this suggests that the modern moisture transport route from the indian ocean to the east asian monsoon region has existed since at least the early holocene the delta o 18 records from both regions exhibit a remarkably similar trend of variation in that the values are more negative during the early holocene rapidly become heavy from the mid holocene and are heaviest during the late holocene the stalagmite delta o 18 changes in the east asian monsoon region are statistically well correlated with those in the indian monsoon region both over the entire holocene and in detail over the last 2000 years however in contrast to the obvious consistency of the delta o 18 values in all of the speleothem records both instrumental and historical climate records indicate significant spatial variations in rainfall over eastern china the early holocene strong easm pattern referred from speleothem delta o 18 in the east asian monsoon region is quite different to that of other paleoclimatic records such as holocene paleosol development in the chinese loess plateau eolian activity in the northern chinese sandlands and lake sediments in easm dominated region in china in which the strongest easm was documented during the mid holocene these findings suggest that the speleothem delta o 18 record from the east asian monsoon region may not record easm variability but rather that it is controlled by variations in the isotopic composition of precipitation which is determined mainly by rainfall variability in the ism region

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

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

a general circulation model study of january climate anomaly patterns associated with interannual variation of equatorial pacific sea surface temperatures abstract a general circulation model has been run in the perpetual january mode to produce several long term simulations each distinguished by a different imposed equatorial pacific sea surface temperature from each of them simulations we have extracted an eight member ensemble of 90 day averaged fields ensemble mean difference maps are presented in this paper together with an estimate of the statistical significance of features which appear in thee maps these results are compared with observational studies in the literature that present difference maps of northern hemisphere winter fields composited according to some index related to the two extremes of equatorial pacific sea surface temperature variation the results show many anomaly patterns of high statistical significance that are also in good agreement with those observed in the tropics them include 990 mb wind sea level pressure and rainfall anomalies constituting the southern oscillation as well as a 200 mb height anomaly at all longitud

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

compaction corrected paleomagnetic paleolatitudes for late cretaceous rudists along the cretaceous california margin evidence for less than 1500 km of post late cretaceous offset for baja british columbia the paleolatitudinal distribution of bivalve rudists has important significance for the baja british columbia baja bc hypothesis that western canadian superterranes from british columbia have been displaced 3000 km since cretaceous time rudists are not observed in baja bc sedimentary rocks yet they are common in late cretaceous strata in california and baja california which have the same paleomagnetically determined paleolatitudes approximately 25 n as baja bc rocks of late cretaceous age in order to resolve this contradiction and to delimit more exactly the southern paleolatitudes of baja bc paleomagnetic inclinations corrected for the effects of burial compaction were used to determine the paleolatitudinal distribution of rudists along the california margin compaction corrected paleomagnetic data from the peninsular ranges and salinia terranes indicate that rudists were restricted to paleolatitudes between 34 and 40 n evidence of coastal upwelling in the latest cretaceous marca shale may explain the northern limit of the rudist distribution these data suggest that baja bc was no farther south than 40 n in the late cretaceous thus limiting its post cretaceous displacement to less than 1500 km and that burial compaction has also affected the paleomagnetism of nanaimo group sedimentary rocks from vancouver island this result also helps resolve the conflict between paleomagnetic results which show 1500 km of post late cretaceous offset between the insular coast plutonic complex superterrane and the intermontane superterrane and geologic observations which can allow only tens of kilometers of offset between these terranes in the methow tyaughton basin

solar forcing of centennial scale east asian winter monsoon variability in the mid to late holocene abstract centennial scale variability of the east asian winter monsoon during the holocene is poorly understood because suitable archives and proxies are lacking here we present a high resolution 30 yr spacing planktonic foraminiferal o 18 record of neogloboquadrina incompta dextral form which reflects sea surface temperature during the winter season for the last 6000 yrs from marine sediments in the western north pacific stronger winter monsoons indicated by cooler winter ssts correspond to weaker summer monsoons indicated by the cave oxygen isotopes in centennial scale variability the variability also shows good correlation with o 18 records in lake sediments and ice cores from the yukon territory canada spanning the last 4500 yrs suggesting east west climate coupling across the north pacific furthermore the climate changes across the north pacific co vary over widespread regions such as the eastern tropical pacific and the northern red sea and the reconstructed solar activity the cross spectral and wavelet analyses show that the east asian winter monsoon shares some cyclicity with the solar variability our results suggest that the solar activity is a fundamental forcing producing the centennial scale eawm variability mediated by the large scale climate linkages

petrologic evolution and paleogeography of the late cretaceous nanaimo basin washington and british columbia implications for cretaceous tectonics systematic variations in sandstone petrofacies of the upper cretaceous nanaimo group are related to basin evolution and uplift of surrounding tectonic provinces a subaerially exposed horst partially separated southern and northeastern portions of the nanaimo basin volcaniclastic and arkosic sediment was derived from this horst the horst subsided below wave base during very early evolution of the nanaimo basin but it controlled sediment dispersal throughout basin development lower units of the nanaimo group in the southern nanaimo basin are chert rich and were derived largely from terranes of the san juan islands and north cascades basaltic and plutonic debris from the insular belt was deposited into the northwestern nanaimo basin during early basin development minor deposition of arkosic debris from the coastal plutonic belt also occurred upper units of the nanaimo group contain abundant plagioclase rich sediment derived from the coastal plutonic belt rocks along the southeastern margin of the basin however reflect continued sedimentation from terranes of the san juan islands and north cascades arkosic and dacitic debris from insular belt sources is recognized in the northwestern nanaimo basin the nanaimo basin may have developed as a pull apart basin within a broad zone of normal and transcurrent faulting in response to oblique convergence or transform faulting between the kula plate and the pacific margin of washington and british columbia

tepees in peritidal carbonates origin via earthquake induced deformation with example from the middle cambrian of western canada abstract tepee structures are common in many ancient carbonate tidal flat successions and because analogues are known from tropical coastal areas they are well established as evidence for synsedimentary lithification of subaerially exposed carbonate sediment existing explanations involving desiccation thermal expansion and contraction fluctuating groundwater pore pressure or diagenetic force of crystallization do not adequately account for the style and degree of deformation seen in some examples such as those in the middle cambrian cathedral formation of the southern rocky mountains western canada these tepees provide evidence for essentially instantaneous events causing brittle failure of decimetre thick crusts of ooidal and pisoidal grainstone followed by their dilation rupturing separation tilting and shingling they can be explained as breccias generated by sporadic episodes of strong ground motion from earthquakes that emanated from a syndepositionally active fault system nearby variably directed tensile and compressive stresses broke crusts shifted them upwards and shuffled them laterally subsequent microbial encrustation and vigorous flushing by seawater in the resulting shelter cavities led to rapid stabilization by cementation recognition of the role of seismically induced deformation in explaining some tepee structures furnishes a proxy for synsedimentary tectonism and adds another member to the family of seismites which reflect a range of rheological properties of unlithified and lithifying sediments

an improved real time global sea surface temperature analysis abstract the monthly global sea surface temperature sst analysis of reynolds using real time in situ and satellite sst data has now been improved by using sea ice data to simulate ssts in ice covered regions the simulated ssts now become the external boundary condition for the analysis solution this technique eliminates any high latitude satellite biases and extends the analysis to the ice edge the analysis with the ice data has been computed for the period january 1982 to present

a conceptual model for the preservation of thick transgressive shoreline successions examples from the forearc nanaimo basin british columbia canada abstract sequence stratigraphic models derived from passive margins and foreland basins characterize transgressive shorelines excluding incised valleys as recording periods of sediment starvation and are commonly represented as thin 10 m are more likely to be developed in active tectonic settings e g forearc and rift basins which generally experience high sedimentation rates and relatively rapid changes in base level settings with high sedimentation rates and moderate base level rise lead to progradational trends despite overall transgression of the shoreline in settings where changes in eustatic sea level mainly control the resulting stratigraphic architecture e g passive margins thin transgressive successions 1 10 m are more likely to be produced finally in settings defined by relatively slow base level change e g foreland basins the resultant transgressive succession typically comprises a lag 1 m overlain by offshore mudstones this conceptual model highlights the importance of the interplay between sedimentation rates and base level rise and is intended as a guide for the predictive modeling of sedimentary basins

compositions of sandstones in circum pacific subduction complexes and fore arc basins arc trench systems of the circum pacific orogenic belt contain voluminous sandstones within fore arc terranes that include complexly deformed subduction complexes and relatively undeformed fore arc basins of several types turbidites incorporated within subduction complexes include not only axially transported trench fill but also abyssal plain sediments deposited on the sea floor beyond the trench and slope basin deposits perched on the accretionary trench slope mean framework modes of circum pacific sandstone suites can be expressed adequately by the use of qfl and qmflt plots supplementary qmpk and qplvls plots depict partial modes of mineral grains alone and polycrystalline lithic fragments respectively source rocks were mainly volcanic and plutonic terranes of he circum pacific magmatic arcs although some recycled sedimentary and metasedimentary debris is also present analysis of point counts for 2 587 rocks grouped into 104 suites from california the pacific northwest southern alaska southwest japan and new zealand indicates that the characteristic fore arc sandstones display similar compositional ranges everywhere and can be termed the circum pacific volcano plutonic graywacke suite knowledge of their petrology may aid the recognition of analogous tectonic settings in the geologic past frameworks vary across a compositional spectrum that ranges chiefly from feldspatholithic sands derived mainly from volcanic cover in undissected magmatic arcs to lithofeldspathic sands derived largely from plutonic batholiths in dissected magmatic arcs quartz contents are typically intermediate and the feldspar to quartz ratio is semiconstant plagioclas is the dominant feldspar and volcanic rock fragments are commonly the most abundant lithic fragments interpretations of compositional trends within subduction complexes and adjacent fore arc basins imply that simple transverse delivery of sediment from the arc orogene to the fore arc region is not the rule instead sand evidently is distributed along subduction zones by longitudinal turbidity currents initiated at widely spaced sediment delivery points where sediment derived from tectonic culminations along the arc trench system can bypass the sediment traps of fore arc basins moreover turbidites shed from dormant or transform segments of arc orogenes are locally spread far into the ocean basin as abyssal plains which are later rafted bodily into the subduction zone finally no sedimentologic explanations of compositional contrasts across fore arc graywacke terranes can be acce ted without considering the alternative of postdepositional tectonic transport by strike slip

influence of the intertropical convergence zone on the east asian monsoon a palaeoclimate record spanning the past 16 000 years with nearly annual time resolution has been obtained from lake huguang maar in china the magnetic properties and titanium content of the lake sediments are thought to reflect changes in the east asian winter monsoon strength thus providing a complement to palaeoclimate archives that record the strength of the rain bearing summer monsoon the records point to an anti correlation between winter and summer monsoon strength best explained by migration of the intertropical convergence zone itcz a belt of low pressure air at the equator interestingly the decline of china s tang dynasty and the mayan civilization broadly coincide with drought periods recorded in lake huguang maar and cariaco basin sediments respectively did major shifts in the position of the itcz catalyse simultaneous events in civilizations on opposite sides of the pacific ocean the asian australian monsoon is an important component of the earth s climate system that influences the societal and economic activity of roughly half the world s population the past strength of the rain bearing east asian summer monsoon can be reconstructed with archives such as cave deposits1 2 3 but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct here we present high resolution records of the magnetic properties and the titanium content of the sediments of lake huguang maar in coastal southeast china over the past 16 000 years which we use as proxies for the strength of the winter monsoon winds we find evidence for stronger winter monsoon winds before the bolling allerod warming during the younger dryas episode and during the middle and late holocene when cave stalagmites suggest weaker summer monsoons1 2 3 we conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone similar migrations of the intertropical convergence zone have been observed in central america for the period ad 700 to 900 refs 4 6 suggesting global climatic changes at that time from the coincidence in timing we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the tang dynasty in china and the classic maya in central america

role of the tibetan plateau thermal forcing in the summer climate patterns over subtropical asia the mechanism of the tibetan plateau tp thermal forcing in influencing the summer climate patterns over subtropical asia is investigated by means of ncep ncar reanalysis diagnosis results show that since the tp is a huge elevated heating source with the strongest heating in the surface layers in summer the thermal adaptation results in a shallow cyclonic circulation near the surface and a deep anticyclonic circulation above it according to the steady barotropic vorticity equation for large scales airflow must converge in the lower layers and diverge in the higher layers over the eastern side of the tp however the western side of the tp is characterized by a reversed structure i e divergence in lower layers but convergence in higher layers hence pumping and sucking processes bring in upward and downward movement over the east and west sides of the tp respectively such a circulation is embedded in the large scale circulation that is forced by the eurasian continental heating because the tp together with iran plateau are located at the central and eastern parts of the continent and because the orography induced circulation is in phase with the continental scale circulation the role of the tp thermal forcing is to intensify the east asian monsoon to its east and the dry and hot desert climate in mid asia to its west the summertime thermal forcing of the rockies and andes can generate similar circulations along the two subtopics as the tp does since they are located near the western coasts but the lower troposphere poleward flow that is induced by orographic thermal forcing does not coincide with the poleward flows over the eastern coastal region that is induced by continental heating and the monsoon rainfall in north and south america is not as strong as in east asia however the equatorward flow and the associated subsidence induced by the two mountain ranges along the western coasts of both north and south america are in phase with those induced by continental heating these contribute to the formation of the stable low stratus clouds and strong long wave radiative cooling over the eastern subtropical pacific regions just off the western coast of the continent

variation of east asian monsoon precipitation during the past 21 k y and potential co2 forcing paleoclimatic research can provide critical insight on causes of change in the east asian monsoon which influences the lives of 1 6 billion people today in this study we use paleoclimatic indexes from chinese loess deposits which have clear climatic implications and are independently dated to reconstruct the monsoon precipitation since 21 ka our results show that monsoon precipitation persistently decreased from 21 ka to ca 8 ka and increased after ca 8 ka with a precipitation peak at 8 3 ka these changes in east asian summer monsoon precipitation are synchronous with changes in high northern latitude ice volume ice cover and atmospheric co2 these new data suggest that variation of the monsoon precipitation was probably driven by co2 forced high northern latitude temperature changes shifting the location of the intertropical convergence zone that dominates monsoon precipitation our trace 21000 modeling experiment supports this interpretation

seasonally specific responses of the east asian monsoon to deglacial climate changes the deglacial meltwater pulse in the north atlantic that induced the younger dryas event also prompted climate cooling in east asian monsoon regions such as japan and coastal mid latitude china however very little is understood about the mechanism that can transmit changes in the north atlantic to the far east here we show that the shutdown of the north atlantic thermohaline circulation brought about significantly lower temperatures and higher precipitation in the japanese winter whereas the change in the japanese summer climate was considerably smaller the cooling of the siberian air mass seems to have caused an increased pressure gradient between siberia and the west pacific in winter intensifying the winter monsoon the mongolian high pressure system and the westerly jet stream played an important role in the teleconnection in contrast the warming at the onset of the late glacial interstadial gi 1 bolling allerod in the west pacific did not have season specific features implying that the principal driving mechanism of this warming event may lie in a pan hemispheric or global factor such as insolation changes

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

sensitivity of the systematic error of extended range forecasts to sea surface temperature anomalies abstract the sensitivity of the systematic error of extended range forecasts to sea surface temperature sst anomalies is investigated general circulation model gcm experiments were performed to quantify error patterns for warm normal and cold sst anomalies in the equatorial central pacific the model underestimates the strength of tropical convection during warm el nino southern oscillation enso episodes and has large zonal mean errors in midlatitudes the model captures the negative pacific north american teleconnection pna pattern during the cold enso episodes but the simulated amplitude is too weak the time mean errors during warm and cold enso events bear little resemblance to the errors estimated from a 10 yr integration which includes both warm and cold episodes the time mean error of a 10 yr integration is a good estimate of the systematic model error only for those years when ssts are close to climatology

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

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

characteristics of the east asian summer monsoon in the south sea of korea during the little ice age abstract the sediment record of a drilled core ssdp 103 and four ams 14 c datings were used to generate oxygen and carbon isotope data over the last 2000 years of the benthic foraminifer cibicides lobatulus in the south sea of korea high sedimentation rates facilitated a decadal resolution throughout the study period significant periodicities of 316 249 144 and 88 years were observed in the 18 o record of the benthic foraminifera similar periodicities of 310 220 143 and 120 years were identified in the 13 c record these periodicities were close to those of solar origin which are related to changes in the oceanic and atmosphere circulation in east asia the three point smoothed 18 o curve of benthic foraminifera in the study area was closely correlated with the stalagmite 18 o record from chinese caves for the last 2000 years except during the dramatic cooling interval of the little ice age lia during the cooling period the benthic foraminifera 18 o values significantly increased while stalagmite 18 o values decreased such an inverse relationship during the lia reflects synchronous strengthening of the east asian summer monsoon easm and weakening of the indian summer monsoon ism under the present climatic system an inverse relationship between these two asian monsoons has frequently occurred when an el nino event developed the results suggest that late holocene cold events are associated with el nino like climatic patterns

linkages between 200 mb tropical and extratropical circulation anomalies during the 1986 1989 enso cycle abstract nmc operational wind analyses have been used to document the 200 mb circulation anomalies during the solstice seasons of the 1987 1989 enso cycle using the one level vorticity balance diagnostic approach the 200 mb rossby wave anomalous source distribution was derived as departures from a three year mean for the single warm phase season january march 1987 the effective rossby wave anomaly sources were found to be generally quite small within 15 of the equator poleward of about 15 the anomalous 200 mb divergence through the planetary vorticity divergence anomaly stretching term is the dominant factor in determining the anomalous 200 mb vorticity source distribution its jfm standard deviation around 30 35 n was an order of magnitude larger than that found in the deep tropics the january march and june august 200 mb circulation differences between the warm and cold phase of the 1987 1989 enso cycle are described the enso cycle linkages between the equatorial pacific convection anomali

holocene east asian summer monsoon records in northern china and their inconsistency with chinese stalagmite δ18o records abstract monsoon precipitation over china exhibits large spatial differences it has been found that a significantly enhanced east asian summer monsoon easm is characterized by increased rainfall in northern china and by reduced rainfall in southern china and this relationship occurs on different time scales during the holocene this study presents results from a diverse range of proxy paleoclimatic records from northern china where precipitation variability is traditionally considered as an easm proxy our aim is to evaluate the evolution of the easm during the holocene and to compare it with all of the published stalagmite 18 o records from the asian monsoon region in order to explore the potential mechanism s controlling the chinese stalagmite 18 o we found that the intensity of the easm during the holocene recorded by the traditional easm proxy of moisture or precipitation records from northern china is significantly different from the chinese stalagmite 18 o records the easm maximum occurred during the mid holocene challenging the prevailing view of an early holocene easm maximum mainly inferred from stalagmite 18 o records in eastern china in addition all of the well dated holocene stalagmite 18 o records covering a broad geographical region exhibit a remarkably similar trend of variation and are statistically well correlated on different time scales thus indicating a common signal however in contrast with the clear consistency in the 18 o values in all of the cave records both instrumental and paleoclimatic records exhibit significant spatial variations in rainfall on decadal to centennial time scales over eastern china in addition both paleoclimatic records and modeling results suggest that holocene east asian summer monsoon precipitation reached a maximum at different periods in different regions of china thus the stalagmite 18 o records from the easm region should not be regarded as a reliable indicator of the strength of the east asian summer monsoon furthermore modern observations indicate that the moisture for precipitation in the east asian monsoon region is mainly derived from the indian ocean the moisture transport route from the indian ocean to the east asian monsoon region during the holocene is almost identical to that of modern precipitation therefore the strong correlation of 18 o records in the easm and indian summer monsoon ism regions and the similarity of the pattern of latitudinal changes in 18 o values in stalagmites and in modern meteoric precipitation along the water vapor transport route further suggests that the stalagmite 18 o records from the easm region are essentially a signal of the isotopic composition of precipitation which is determined mainly by changes in the 18 o of atmospheric vapor in the upstream source region over the indian ocean and indian monsoon region via the upstream depletion mechanism finally the main trends of the stalagmite 18 o records are strongly correlated with the known evolution of the ism and therefore these records reflect the history of the ism rather than that of the easm our findings support the conclusion that easm variability is mainly controlled by northern hemisphere summer insolation and was strongly modulated by ice volume during the last deglaciation and early holocene which delayed the response of the easm maximum to peak insolation forcing

canadian cordilleran tectonics from geosynclines to crustal collage the major contributions by the geological survey of canada in the canadian cordillera systematic mapping and definition of the regional geological framework led directly to tectonic syntheses that attempted to explain its origin from the late 1800 s until the 1960 s cordilleran mountain building was viewed as the end result of geosynclinal deposition early workers felt that a connection existed between mountain building and the pacific basin but its nature was never clear because little was known about ocean basins and their relationships to continental margins in the 1950 s the nature of the oceanic lithosphere and ocean continent relationships became better known the knowledge led to formulation of the plate tectonic hypothesis in the 1960 s a time fortuitously coinciding with completion by the survey of most of the regional geological mapping scale 1 250 000 geosynclinal rock units were reinterpreted in terms of their possible modern analogues oceanic island arc continental shelf slo

siliciclastic sequence stratigraphic patterns in foreland ramp type basins stratal patterns within shelf depositional sequences are dependent on tectonically controlled subsidence rates and their regional patterns in active tectonic basin settings regional subsidence patterns can be very different from passive continental margin settings resulting in substantial modifications of the basic sequence stratigraphic model in ramp type foreland basins on the tectonically active side subsidence rates decrease seaward in contrast with passive continental margins where the opposite subsidence pattern exists analysis of the interplay between eustasy and subsidence suggests the existence of two tectono stratigraphic zones occurring proximally and distally with respect to the basin margin zone a is defined as the region within which the rate of subsidence always exceeds the rate of eustatic fall consequently relative sea level rises continuously during a eustatic cycle albeit at varying rates zone b is defined as the region within which the rate of eustatic fall periodically exceeds the rate of subsidence resulting in an interval of relative sea level fall during a eustatic cycle on the tectonically active sides of foreland basins zone a lies on the landward side of the basin margin proximal to the orogenic belt and zone b lies seaward off zone a away from the orogenic belt where subsidence rates are lower on passive continental margins because of the opposite subsidence patterns zone a lies seaward of zone b where subsidence rates are greater the location of the shoreline relative to these zones determines the stacking patterns and stratal discontinuities within a depositional sequence if the shoreline remains in zone a then only type 2 sequence boundaries will occur if sufficient sediment flux is available allowing the shoreline to prograde into zone b then type 1 sequence boundaries can occur in foreland basins these type 1 sequence boundaries would become type 2 sequence boundaries updip in zone a the pattern of seaward decreasing subsidence on the tectonically active sides of foreland basins results in characteristic longitudinal facies and stratal patterns when the two zones occur the updip region of the basin proximal to the orogenic belt is characterized by nearly continuous nonmarine deposition albeit at varying rates the downdip region is characterized by forced regressions and deposition primarily of lowstand and transgressive systems tracts a transitional region containing deposits of all three systems tracts commonly occurs between the updip and downdip areas

centennial scale east asian summer monsoon intensity based on δ18o values in ostracode shells and its relationship to land ocean air temperature gradients over the past 1700 years centennial scale variations in the east asian summer monsoon easm remain ambiguous in the present study the 18o of shells from the ostracode bicornucythere bisanensis from lake nakaumi japan were examined to identify the bottom salinity changes caused by easm variations over the past 1700 yr four weak easm periods were identified in lake nakaumi at a d 600 1000 1350 and 1900 we detected discordance among the centennial scale easm variations in japan and the 18o of stalagmites 18ostalagmite in southern china furthermore both total solar irradiance and atmospheric 14c concentration which were previously considered to be linked with the centennial scale easm variations were asynchronous with the easm variations conversely we observed significant positive and negative correlations between the easm from japan and the 18ostalagmite in north central china and the relationship was associated with the asia pacific oscillation apo index centennial scale easm periods dominated during the high apo period these synchronous variations imply that the strength of the easm variations is tied to temperature gradients between east china and the north central pacific ocean

a synchronized dating of three greenland ice cores throughout the holocene as part of the effort to create the new greenland ice core chronology 2005 gicc05 a synchronized stratigraphical timescale for the holocene parts of the dye 3 grip and ngrip ice cores is made by using volcanic reference horizons in electri cal conductivity measurements to match the cores the main annual layer counting is carried out on the most suited records only exploit ing that the three ice cores have been drilled at locations with different climatic con ditions and differences in ice flow however supplemental counting on data from all cores has been performed between each set of reference horizons in order to verify the valid ity of the match after the verification the main dating is transferred to all records us ing the volcanic reference horizons as tie points an assessment of the mean annual layer thickness in each core section confirms that the new synchronized dating is consistent for all three cores the data used for the main annual layer counting of the past 7900 years are the dye 3 grip and ngrip stable isotope records as the high accumulation rate at the dye 3 drill site makes the seasonal cycle in the dye 3 stable isotopes very resistant to firn diffusion an effort has been made to extend the dye 3 holocene record the new syn chronized dating relies heavily on this record of 75 000 stable isotope samples the dat ing of the early holocene consists of an already established part of gicc05 for grip and ngrip which has now been transferred to the dye 3 core gicc05 dates the younger dryas termination as defined from deuterium excess to 11 703 b2k 130 years earlier than the previous grip dating

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

sequence stratigraphic hierarchy of the upper devonian foreknobs formation central appalachian basin usa evidence for transitional greenhouse to icehouse conditions abstract the foreknobs formation upper devonian upper frasnian to basal famennian comprises the uppermost marine strata of the progradational catskill clastic wedge of the south central appalachian mountains virginia west virginia usa the foreknobs formation consists of 14 lithofacies arranged in four facies associations which record the following depositional settings 1 storm dominated distal to proximal offshore to shoreface facies association a 2 sharp based conglomeratic shoreface facies association b 3 fluvial redbed facies association c and 4 incised valley fill ivf facies association d vertical juxtaposition and stacking patterns of lithofacies and facies associations permit recognition of a hierarchy of three scales of cyclicity up to 70 short term 5th order cycles each averaging 65 kyr consist of coarsening upward parasequences of storm dominated offshore marine facies in the distal setting which correspond to high frequency unconformity bound sequences hfs of fluvial redbed strata overlain by offshore marine strata in the proximal setting these facies relationships are a consequence of 10 15 m of sea level fluctuations up to 12 intermediate term 4th order cycles each averaging 375 kyr consist of stacked 5th order cycles the 4th order cycles are bounded by regressive surfaces of marine erosion rsme at the base of sharp based conglomeratic shoreface sandstones in the distal setting that correspond with paleosols in the proximal setting in some cases the 5th order cycles within each 4th order cycle exhibit stacking patterns indicative of increasing or decreasing accommodation space these facies relationships are a consequence of 25 35 m of sea level fluctuations three complete and portions of two additional 3rd order cycles each averaging 1 12 myr consist of stacked 4th order cycles the 3rd order sea level trends reflected in the foreknobs formation are nearly identical to published eustatic sea level curves incised valley fills are present at one of the 3rd order cycle boundaries and are a consequence of a 35 45 m sea level fluctuation the amplitudes of the inferred sea level fluctuations are comparable to the expansion and contraction of ice volumes within the current greenland and antarctic ice sheets which suggests glacioeustasy was the primary control on sea level fluctuations and cyclicity within the foreknobs formation such an interpretation is consistent with knowledge of devonian climate transitioning from middle devonian greenhouse to late devonian icehouse as indicated by evidence of glaciation during parts of the late devonian in south america and the appalachians