variations in monsoonal rainfall over the last 21 kyr inferred from sedimentary organic matter in tung yuan pond southern taiwan abstract changes in paleorainfall intensity linked to the strength of the east asian ea summer monsoon since 21 cal kyr bp are inferred from the organic matter contents of a 15 m sediment core from tung yuan pond in southern taiwan high total organic carbon total nitrogen toc tn values in association with increased toc content suggest that more soil derived material containing terrestrial organic matter om was delivered to the lake during periods of increased runoff associated with extensive precipitation that resulted from intensified summer monsoons whereas low values indicate om possessing a dominant algal origin during weakened summer monsoons rainfall intensity in terms of the proportion of terrestrial om was high in four periods the last deglaciation 17 2 to 12 2 ka the early holocene 10 6 to 8 6 ka the middle holocene thermal optimum 7 7 to 5 ka and the late holocene 4 2 to 2 ka whereas it was low in the intervening time periods high toc tn values coincide with peak values of summer insolation and thus the strongest ea summer monsoon during the early and middle holocene small drops in these ratios correspond to increasing and decreasing solar radiation in the deglacial period and the late holocene respectively the four intervals with low toc tn ratios as well as episodic drops of the ratios during the deglaciation and the early and late holocene are concordant with the late last glacial 21 to 17 2 ka the oldest 14 8 ka the older 13 3 ka and the younger dryas 13 to 11 5 ka the 8 2 cold event 8 6 7 7 ka and a late holocene cold event 5 4 2 ka and suggest a weakened ea summer monsoon during these times moreover high frequency hydrological variability occurred during the early holocene heavy rainfall persisted during the middle holocene and precipitation intensity generally diminished after 5 ka the tung yuan pond sediment record indicates that the toc tn ratio can be used as a paleorainfall intensity proxy to trace variations in the ea summer monsoon strength in other small lakes

pollen and diatom inferred climatic and hydrological changes in sumxi co basin western tibet since 13 000 yr b p although the tibetan plateau greatly influences the atmospheric circulation of the nortbern hemisphere few continuous paleoclimatic records are available from the plateau a 13 000 yr pollen and diatom record from the sumxi longmu co basin in western tibet gives information on major changes both in regional vegetation and in local hydrology after the basin first filled ca 13 000 yr b p a dry spell occurred about 10 500 yr b p within the interval spanned by the european younger dryas chronozone a major environmental change occurred suddenly at 10 000 yr b p with the establishment of wet conditions and was followed by a long term trend toward maximum aridity which lasted approximately 6000 yr short term oscillations are superimposed on this general climatic change with a major reversal event about 8000 yr b p and a second wet pulse leading to a maximum lake volume ca 7500 6000 yr b p maximum aridity occurred 4300 yr b p the major environmental fluctuations recorded at sumxi longmu co appear in phase with climatic changes recognized in north tropical africa suggesting that the 8000 to 7000 yr b p event was caused by an abrupt disequilibrium in the climatic system as was the younger dryas and possibly the 4300 yr b p event

the latest post variscan fluids in the spanish central system evidence from fluid inclusion and stable isotope data abstract the spanish central system has been subjected to repeated fluid incursions which were responsible for a variety of mineralizing episodes including w sn cu zn pb as ag f ba and barren quartz veins these hydrothermal fluids occurred over a 200 ma time period and the latest hydrothermal event is recorded in barren quartz veins this study is a multidisciplinary approach leading to the characterization of the hydrothermal fluids preserved in barren quartz veins which are spatially but not temporally related to hercynian upper crustal granites the veins were dated by the 39 ar 40 ar method and the fluids were examined using petrographic microthermometric chemical and isotopic methods fluid inclusions in barren quartz veins indicate that two fluids were related to this hydrothermal event the main part of the quartz veins were formed from an early low salinity 2 o nacl fluid this fluid was trapped at around 270 25 c and 0 1 1 kbar under sublithostatic to hydrostatic conditions 18 o 9 to 2 and d 70 to 34 5 values indicate a meteoric origin for water with significant water rock interactions the latest h 2 o nacl cacl 2 fluid is found in two types of fluid inclusions a primary liquid vapour type 16 24 wt nacl and 1 12 wt cacl 2 and secondary hypersaline type 7 15 wt nacl and 21 27 wt cacl 2 significant li concentrations in this fluid were confirmed this late ca bearing fluid formed quartz crystals in the central part of the veins and was trapped at 70 140 c at a maximum pressure of 0 5 kbar the low 18 o 20 to 6 and d 137 to 116 values suggest a meteoric origin for this fluid however its high salinity probably requires a source from triassic evaporite basins located in the ne tip of the spanish central system anomalously low isotopic values have been previously reported from kaolinites of lower cretaceous age anomalous climatic conditions during the cretaceous appear to be the main reason to explain this very negative meteoric water strong isotopic depletion in meteoric water has been observed in modern areas with monsoonal climates the hydrothermal evolution of barren quartz veins in the spanish central system is comparable to other hydrothermal post variscan events in central and south western europe related to the opening of the north atlantic during cretaceous time

detecting holocene movements of the woodland steppe ecotone in northern china using discriminant analysis discriminant functions link vegetation zones and surface pollen along the woodland steppe ecotone in northern china these links were utilised to reconstruct palaeovegetation using fossil pollen data from four lake sediment sites within the ecotone holocene movements of the vegetation zones were derived from the above results and were interpreted as the results of climatic topographic and edaphic factors this study shows that climatic change was the driving factor for ecotonal movement but that the positions of vegetational zones were nevertheless controlled by topographical and edaphic conditions and consequently boundaries between different vegetational zones responded individualistically copyright 2001 john wiley sons ltd

reconstruction of winter monsoon strength by elemental ratio of sediments in the east china sea abstract the east asian winter monsoon eawm transports cold air from the high northern latitudes to the mid and low latitudes thus investigations on its variation pattern and mechanism are essential for acquiring further knowledge on the interplay across the high and low latitudes proxies such as grain size and foraminiferal 18o in marine sediments and elemental ratios in the chinese loess have been used for the reconstruction of eawm strength however more high resolution reconstructions for eawm are required for further understanding the mechanism of climate systems and predicting climate change in this study we present a high resolution time series of the late holocene eawm strength reconstructed by element method comparisons of element concentrations elemental ratios and mean grain size mgs of environment sensitive components in a sediment core from the shelf of the east china sea indicate that k ti ratio is an appropriate proxy for the reconstruction of the eawm strength k ti ratio exhibits similar trends with proxies of sea surface temperature and eawm strength in different regions influenced by the eawm warm and cold periods such as the roman warm period medieval warm period and little ice age are identified in the reconstructed results total solar irradiance anomaly tsi and k ti ratios exhibit comparable tendencies in the last two millennia and frequency spectrum analysis exhibits similar periodicities in the time series of tsi and k ti which confirm that solar irradiance has a significant impact on the easm on centennial time scale

tree ring δd as an indicator of asian monsoon intensity oxygen and hydrogen isotopic compositions of meteoric water are known to correlate with surface air temperature except in tropical areas this relationship has been described using a number of terms corresponding to specific observations such as latitude altitude and seasonal effects however these temperature effects do not seem to apply to precipitation in monsoonal areas of asia questions have been raised as to whether the isotopic composition of meteoric water can be used to reconstruct paleomonsoon intensity tree rings of two modern spruce trees picea meyeri and a 10 000 yr old timber picea jezoensis were analyzed for hydrogen isotopic composition on average the older tree is depleted in deuterium by 45 compared to the modern trees we attribute this isotopic depletion to the strength of summer monsoons which were more intense in the early holocene than at present although this study is not definitive it suggests that paleomonsoon intensity can be reconstructed by direct or proxy methods that yield the oxygen or hydrogen isotopic composition of meteoric water

cyclic quaternary alluviation and terracing in a nonglaciated drainage basin on the north flank of the qinling shan central china abstract pleistocene alluvial terraces of the nonglaciated ba river drainage basin on the north flank of the qinling shan are capped by a succession of loess units and paleosols that correlate with the standard marine isotope chronology and are used to date the subjacent alluvial gravels alluvial fills were deposited during isotope stages 2 6 8 12 and 16 whereas terracing occurred during interglacial stages 1 5 7 11 and 15 the apparent absence of terraces dating to stage 14 and stage 4 may be due to the lesser intensity of these glaciations compared to that of stage 2 although disruption of the alluvial regime by local tectonism is a likely alternative for the lack of a stage 4 terrace a stage 10 terrace was not positively identified from available exposures its possible absence could be related to post stage 12 uplift aggradational episodes correlate with glaciations and loess deposition whereas degradational episodes correlate with interglaciations or interstades and soil formation implying that climate is the primary control on quaternary paleohydrology this in turn points to variations in the earth s orbital geometry as the major factor that modulates both climate and ultimately the fluvial system in the qinling shan in this region glaciations were dominated by a cold dry winter monsoon climate whereas during interstades and interglaciations a warmer and wetter climate prevailed implying strengthening of the summer monsoon both the loess paleosol and the alluvial records are consistent with climate model simulations spanning the last 18 000 yr that show a change from cold dry conditions during the last glacial maximum to a climate warmer and wetter than present during the first half of the holocene

oxygen and carbon isotope patterns archived in shells of the aquatic gastropod radix hydrologic and climatic signals across the tibetan plateau in sub monthly resolution abstract the tibetan plateau tp including its surrounding mountain ranges represents the largest store of ice outside the polar regions it hosts numerous lakes as well as the head waters of major asian rivers on which billions of people depend and it is particularly sensitive to climate change the moisture transport to the tp is controlled by the indian and pacific monsoon and the westerlies understanding the evolution of the interaction of these circulation systems requires studies on climate archives in different spatial and temporal contexts the objective of this study is to learn more about the interannual variability of precipitation patterns across the tp and how different hydrologic systems react to different climatic factors aragonite shells of the aquatic gastropod radix which is widely distributed in the region may represent suitable archives for inferring hydrologic and climatic signals in particularly high resolution therefore sclerochronological studies of 18 o and 13 c ratios in radix shells from seven lakes were conducted each representing a different hydrologic and climatic setting on a transect from the pamirs across the tp the shell patterns exhibit an increasing influence of precipitation and a decreasing influence of evaporation on the isotope compositions from west to east 18 o values of shells from lakes on the eastern and central tp donggi cona yamdrok yumco tarab co mirror monsoon signals indicated by more negative values and higher variabilities compared to the more western lakes karakul bangong nyak manasarovar in yadang co located on the central southern tp the monsoon rains did not reach the lake in the sampling year although it is located in a region which is usually affected by monsoon circulation the 18 o values are used to differentiate the annual hydrological cycle into ice cover period melt water period precipitation period and evaporation period 13 c compositions in the shells particularly depend on specific habitats which vary in biological productivity and in carbon sources 18 o and 13 c patterns show a positive covariance in shells originating from large closed basins the results show that radix shells mirror general climatic differences between the seven lake regions these differences reflect both regional and local climate signals in sub seasonal resolution without noticeable dependence on the particular lake system

dynamics of retreating slabs 1 insights from two dimensional numerical experiments from the effects of mantle flux part 2 therefore in this paper we apply forces to the slab using simple analytical functions related to buoyancy and viscous forces in order to isolate the role of rheology on slab dynamics we analyze parameters for simplified elastic viscous and nonlinear viscoelastoplastic single layer models of slabs and compare them with a stratified thermomechanical viscoelastoplastic slab embedded in a thermal solution the near surface behavior of slabs is summarized by assessing the amplitude and wavelength of forebulge uplift for each rheology in the complete thermomechanical solutions vastly contrasting styles of slab dynamics and force balance are observed at top and bottom bends however we find that slab subduction can be modeled using simplified rheologies characterized by a narrow range of selected benchmark parameters the best fit linear viscosity ranges between 5 10 22 pa s and 5 10 23 pa s the closeness of the numerical solution to nature can be characterized by a deborah number 0 5 indicating that elasticity is an important ingredient in subduction index terms 8120 tectonophysics dynamics of lithosphere and mantle general 8159 tectonophysics rheology crust and lithosphere 8160 tectonophysics rheology general keywords subduction numerical models lithospheric rheology

on the connexion of vegetation dynamics with climatic changes in high asia abstract within the scope of research on environmental changes in high asia indications of desiccation and thermal oscillations are described they refer to different periods and are caused by different climatic factors distribution patterns of forest constituents with disjunctions in the central and eastern himalayas are explained with changes in monsoonal rainfall presumably during the holocene in southern tibet the plant relicts of one of the younger holocene phases of higher humidity kobresia pygmaea age have been widely destroyed by the himalaya fohn giving way to semiarid alpine steppe on stone pavements field observations of a recent intensification of gelifluction processes in the southeastern part of the tibetan plateau is in accordance with a cooling period between the late 1950s and the late 1970s the obviously decreased vigour and lacking regeneration of the climax vegetation in the alpine belt becomes conceivable under the presumption that the respective cover of alpine turf is a relict of the climatic optimum which slowly but increasingly deteriorated since then a decrease of plant vigour at climatically sensitive vegetation borders upper treeline drought limit of forests transition zone between alpine cyperaceae mats and the free gelifluction belt transition zone between humid alpine mats and alpine steppe gives evidence of diminishing winter precipitation during the last 30 to 40 years in the karakorum

holocene environmental changes in lake bangong basin western tibet part 1 chronology and stable isotopes of carbonates of a holocene lacustrine core abstract a 12 4 m core collected from the eastern part of lake bangong is analyzed for mineralogy radiometric chronology and stable isotope contents of authigenic inorganic carbonate isotopic compositions of the modern lake waters and of its major tributaries are first presented radiocarbon activity of these waters show that equilibrium with the atmospheric co2 is not reached because of admixture of dead carbon in solution in the system a model is thus developed to correct the radiocarbon ages of fossil material of aquatic origin for this ageing the core provides a continuous holocene record changes in mineralogy of bulk sediments and in 13c and 18o contents of authigenic carbonates reveal extremely large changes in environmental conditions induced by climate changes and or local hydrological factors e g closure opening of the lake system controlled by the altitude of the outflow sill the eastern basin of lake bangong was closed before 9 6 and after 1 2 ka b p in response to aridity on the catchment wet warm conditions attributed to the monsoon influence were established suddenly at 9 6 ka b p and maintained until 6 2 ka b p although minor reversal events occurred between 8 6 and 7 7 ka b p the return towards aridity is non linear dry spells at 6 2 3 9 3 2 and 1 3 ka b p are alternated with short term periods with positive precipitation evaporation balance

late pleistocene climatic change in the french jura gigny recorded in the δ18o of phosphate from ungulate tooth enamel oxygen isotope compositions of phosphate in tooth enamel from large mammals i e horse and red deer were measured to quantify past mean annual air temperatures and seasonal variations between 145 ka and 33 ka in eastern france the method is based on interdependent relationships between the delta 18 o of apatite phosphate environmental waters and air temperatures horse equus caballus germanicus and red deer cervus elaphus remains have delta 18 o values that range from 14 2 to 17 2 indicating mean air temperatures between 7 degrees c and 13 degrees c oxygen isotope time series obtained from two of the six horse teeth show a sinusoidal like signal that could have been forced by temperature variations of seasonal origin intra tooth oxygen isotope variations reveal that at 145 ka winters were colder 7 2 degrees c than at present 3 1 degrees c while summer temperatures were similar winter temperatures mark a well developed west east thermal gradient in france of about 9 degrees c much stronger than the 4 degrees c difference recorded presently negative winter temperatures were likely responsible for the extent and duration of the snow cover thus limiting the food resources available for large ungulates with repercussions for neanderthal predators c 2011 university of washington

monsoon influenced variation in productivity and lithogenic sediment flux since 110 ka in the offshore mahanadi basin northern bay of bengal abstract the indian monsoon drives seasonal changes in precipitation and weathering across india as well as circulation and productivity in the northern indian ocean variation in paleo monsoon intensity and its effect on productivity and lithogenic fluxes is poorly constrained in the bay of bengal in this paper we present analysis of a sediment record from the offshore mahanadi basin recovered during the indian national gas hydrate program expedition 01 site nghp 01 19b we reconstruct variation in biogenic and lithogenic components during the last 110 kyr using measurements of total organic carbon toc total nitrogen tn toc tn caco3 biogenic silica bsi 13toc 15tn bulk mineralogy from x ray diffraction bulk and lithogenic grain size distribution magnetic susceptibility bulk density and ca br and zr rb from x ray fluorescence xrf the mass accumulation rate mar of caco3 a function of marine productivity drastically increased between 70 and 10 ka and is correlated to previously documented elevated asian dust fluxes and increased bay of bengal salinity during a weakened southwest monsoon decreased freshwater input over this period likely diminished stratification allowing for increased mixing and nutrient availability thus enhancing productivity despite weaker southwest monsoon winds the mar of lithogenic material is highest during the holocene suggesting that sediment supply driven by monsoon intensity is a stronger control on margin sedimentation than sea level at the mahanadi basin over the entire record magnetic susceptibility and xrf zr rb are strongly correlated with caco3 suggesting higher primary mineral input under a weakened southwest monsoon toc tn and 13toc also increase under glacial conditions suggesting higher relative input of terrestrial c4 organic matter these results highlight the mahanadi basin as a supply dominated margin where terrigenous sedimentation is strongly influenced by monsoon intensity and that productivity is limited by variation in monsoon driven stratification on glacial interglacial timescales rather than a direct response to monsoon winds

the effects of different methods of preparing cellulose nitrate on the determination of the d h ratios of non exchangeable hydrogen of cellulose abstract cellulose nitrate prepared by different methods was subjected to elemental isotopic and spectroscopic analysis cellulose nitrate prepared by nitration of wood powder was contaminated most likely by nitrated lignin cellulose nitrate prepared by nitration of wood cellulose did not contain this component and thus provides a more accurate measure of the d h ratios of non exchangeable hydrogen of cellulose however cellulose nitrate prepared directly from cellulose contained trace amounts of hemicellulose nitrates and was not completely nitrated these conditions will not cause significant errors in the d h ratios measured for most samples analysis of aliquots of the same samples nitrated by the two methods suggests that published d values of cellulose nitrate from wood may be in error by 6 8 in many cases and occasionally by as much as 15

pollen evidence of changing holocene monsoon climate in sichuan province china pollen evidence from lake shayema mianning county was obtained to examine postglacial vegetation and climatic change in southwestern sichuan china the sclerophyllous character of the region s warm temperate vegetation today is a reflection of extreme drought in spring before the onset of the asian monsoons the pollen record displays several changes in the vegetation over the last 11 000 yr from 11 000 to 9100 yr b p cold tolerant species such as abies betula and deciduous oaks dominated the vegetation between 9100 and 7800 yr b p the abundance of deciduous oaks decreased and evergreen oaks increased as did tsuga and mesic deciduous species this change suggests a warming climate with increased precipitation from 7800 to 4000 yr b p sclerophyllous species increased at the expense of mesic deciduous species an indication that precipitation was becoming more seasonal except for increased disturbance starting ca 1000 yr b p the predominance of sclerophyllous vegetation continued until today the pollen results are compatible with proposed global circulation hypotheses of a strengthened monsoon system during the early to mid holocene

spatial and temporal reconstructions of changes in the asian palaeomonsoon a new mineral magnetic approach abstract a new quantitative approach is proposed for estimating palaeoprecipitation across the chinese loess plateau at present there is a strong rainfall gradient across the plateau from 300 mm yr in the near desert conditions in the northwest to over 750 mm yr in the southeast just 700 km distant we find that the concentration of ferrimagnetic iron oxide minerals in nine modern soil types represented by 37 individual soil profiles is strongly correlated with this contemporary rainfall gradient the ferrimagnetic concentration rises along this gradient from 0 01 in the northwest to over 0 2 in the southeast the nine modern soil types have been used in the construction of a rainfall vs magnetic susceptibility least squares regression climofunction past variations of loess soil iron oxide content are easily established through magnetic susceptibility measurements and so can be used to reconstruct the rainfall of former interglacial and glacial periods the physical and pedological basis of the rainfall vs susceptibility relationship is discussed and potential limitations of our rainfall reconstruction method are explored our palaeoclimate reconstructions indicate dramatic changes in rainfall due to variations in the structure of the asian monsoon the rainfall variations are about four times greater than has been suggested for this region by atmospheric general circulation modelling our data indicate increased rainfall throughout central china both in interglacial periods and in the early holocene the increases in monsoonal rain were particularly pronounced at our westernmost sites adjacent to the northeastern edge of the tibetan plateau in contrast for glacial periods a reduction in rainfall is found across the whole loess area with the greatest decreases in the southeast

east asian summer monsoon variability during marine isotope stage 5 based on speleothem δ18o records from wanxiang cave central china abstract speleothems from wanxiang cave china 33 19 n 105 00 e located near the northern limit of the east asian summer monsoon provide high resolution records of paleomonsoon variability we present a simple model for interpreting 18o shifts in speleothems from this region in which the 18o of speleothem calcite is inversely related to monsoon intensity in contrast to observations at higher latitudes atmospheric temperature has little effect on 18o of precipitation near wanxiang cave furthermore the temperature dependence of calcite water 18o fractionation acts in the opposite sense most likely canceling out the effect of local temperature variations on speleothem 18o given this the maximum 18o shift that could occur due only to changes in the composition of the oceanic source region the amount of rainfall and the amount of evaporation between full glacial conditions with a weak summer monsoon and full interglacial conditions with a strong summer monsoon is 5 5 accordingly it is necessary to invoke changes in past atmospheric circulation patterns and in the ratio of summer to winter precipitation to explain the nearly 7 range observed in fossil wanxiang cave speleothems two stalagmites wxsm 51 and wxsm 52 exhibit more positive 18o during stadial periods marine isotope stages mis 8 6 5d 5b and 2 than during interstadial periods mis 9 5a 5c 5e thus east asian summer monsoon intensity is generally decreased during globally cooler periods and increased during globally warmer periods we present detailed 18o records from mis 5a 5b and 5c 5d during the mis 5d 5c transition summer monsoon intensity increased steadily from 117 6 ka with a peak in intensity occurring at 106 8 ka concurrent with greenland interstadial 24 during the mis 5b 5a transition monsoon intensity increased abruptly at about 85 7 ka when 18o decreased by approximately 4 in 200 years monsoon variability inferred from the mis 5c 5d and mis 5a 5b records closely coincides with global climate changes observed in the gisp2 vostok and specmap records and with the northern hemisphere insolation curve this suggests that east asian summer monsoon intensity varies in phase with global climate fluctuations and is largely controlled by variations in northern hemisphere incident solar radiation the mis 5a 5b and 5c 5d paleomonsoon records from wanxiang cave also agree well with other records of asian monsoon variability indicating that 18o of speleothems from wanxiang cave is a valid proxy for past changes in monsoon intensity

the southwest indian monsoon over the last 18 000 years previously published results suggest that the strength of the sw indian monsoon can vary significantly on century to millenium time scales an observation that has important implications for assessments of future climate and hydrologic change over densely populated portions of asia we present new well dated multi proxy records of past monsoon variation from three separate arabian sea sediment cores that span the last glacial maximum to late holocene to a large extent these records confirm earlier published suggestions that the monsoon strengthened in a series of abrupt events over the last deglaciation however our data provide a somewhat refined picture of when these events took place and suggest the primacy of two abrupt increases in monsoon intensity one between 13 and 12 5 ka and the other between 10 and 9 5 ka this conclusion is supported by the comparisons between our new marine data and published paleoclimatic records throughout the african asian monsoon region the comparison of data sets further supports the assertion that maximum monsoon intensity lagged peak insolation forcing by about 3000 years and extended from about 9 5 to 5 5 ka the episodes of rapid monsoon intensification coincided with major shifts in north atlantic european surface temperatures and ice sheet extent this coincidence coupled with new climate model experiments suggests that the large land sea thermal gradient needed to drive strong monsoons developed only after glacial conditions upstream of and on the tibetan plateau receded cold north atlantic sea surface temperatures european ice sheets and extensive asian snow cover it is likely that abrupt changes in seasonal soil hydrology were as important to past monsoon forcing as were abrupt snow related changes in regional albedo our analysis suggests that the monsoon responded more linearly to insolation forcing after the disappearance of glacial boundary conditions decreasing gradually after about 6 ka our data also support the possibility that significant century scale decreases in monsoon intensity took place during the early to mid holocene period of enhanced monsoon strength further highlighting the need to understand paleomonsoon dynamics before accurate assessments of future monsoon strength can be made

reconstruction of holocene monsoon history from the pearl river estuary southern china using diatoms and carbon isotope ratios this study employs a multiproxy approach in the reconstruction of holocene monsoon history from sedimentary sequences obtained from the pearl river estuary southern china a set of modern surface sediment samples were collected within and outside the estuary and a sediment core was obtained from the mouth of the estuary a range of modern environmental variables were recorded including water salinity summer winter and annual average and water depth the diatom results show a good relationship with water salinity with marine diatoms dominating the more distal samples from outside the main estuary and freshwater diatoms dominating the proximal samples influenced by higher freshwater flux this pattern is matched by the bulk organic carbon isotopes the isotope values vary between 21 1 0 3 0 for samples from the fully marine environment between 23 2 0 8 and 23 7 0 8 for samples from the mid to outer estuary brackish water environment and less than 24 7 1 3 for samples from the inner estuary close to the freshwater sources similarly the c n ratios vary from below 7 0 6 in the marine end members to over 14 8 3 0 in the freshwater end members both the diatom and carbon data from the sediment core reveal a significant increase in freshwater flux from 8500 cal yr bp resulting from the enhanced summer monsoon regime in early holocene the strength of freshwater flux reached its highest between 7500 and 6000 cal yr bp in the last 6000 years freshwater flux decreased towards present reflecting a gradual weakening of the summer monsoon

dating the onset of lgm ice surface lowering in the high alps abstract the general chronological outline of the last glacial maximum lgm in the alps is well known after more than two centuries of ice age research in europe current studies focus on resolving the details of the deglaciation process after the lgm particularly few data in this context are available from the high alps here we report chronological constraints on the onset of deglaciation in two different study areas from the western and eastern alps the mont blanc italy and zillertal alps austria we sampled 32 bedrock and boulder surfaces from high elevation ridges beneath the glacial trimline the oldest 10 be exposure ages of 18 5 ka correspond to the initiation of lowering of the lgm ice surface identical ages from both study areas suggest synchronous decay of the lgm glaciers in the accumulation zones of the western and eastern alps thus the high alpine ice surface lowered roughly synchronously to the downwasting of the glacier tongues in the forelands that was completed 19 18 ka in both study areas ages of numerous samples that are consistently 2 3 ka younger than 18 5 ka suggest the persistance of remnant ice patches at high elevations in the lateglacial accumulation zones approximately until the bolling allerod interstadial

lake evolution in the tengger desert northwestern china during the last 40 000 years climatic changes inferred from lacustrine deposits and lake level fluctuations in northwestern and central china are mainly based on paleoclimatic records from the tibetan plateau while there is still a lack of data relating to the semiarid arid desert regions of inner mongolia in the tengger desert different paleolake levels at baijian hu are documented by six paleoshorelines and stratified lake carbonates the highest lake level occurred ca 39 000 14c yr b p and prevailed over about 16 000 km2 from sediment structure geochemical composition and ostracods we infer humid cool conditions until 23 000 14c yr b p in the northern badanjilin desert at gaxan nur sogu nur high lake levels can be deduced from mollusc bearing paleobeaches and lake carbonates which have been dated to 34 000 14c yr b p and indicate a lake that covered some 32 000 km2 after ca 20 000 yr b p the climate became dry with increased eolian activity and decreasing lake levels reestablishment of wet conditions occurred ca 13 000 yr b p the holocene is represented by stratified lake deposits that alternate with fluvial and eolian deposits indicating a longterm oscillating trend toward arid conditions the existence of widespread freshwater lakes during the late pleistocene indicates a semihumid climate without an accompanying fall in temperature to arctic conditions

modulation and amplification of climatic changes in the northern hemisphere by the indian summer monsoon during the past 80 k y high frequency suborbital variations dansgaard oeschger cycles characterize the climatic history of the northern hemisphere as observed in greenland ice cores deep sea sediments of the north atlantic the californian borderland the arabian sea the south china sea and the chinese loess area paleoceanographic data from core kl126 from the bay of bengal in combination with data from the other asian monsoonal areas indicate that the feedback processes involving snow and dust of the tibetan plateau vary the summer monsoon capacity to transport moisture into central south asia and into the atmosphere we postulate that the summer monsoon initiates amplifies and terminates these cycles in the northern hemisphere

holocene variability of the east asian summer monsoon from chinese cave records a re assessment oxygen isotope records from stalagmites in caves in southern china interpreted as proxy rainfall records reflecting the intensity of the east asian summer monsoon indicate gradual monsoon weakening for the last 9000 years as also documented for the indian monsoon coupled with high precision dating the speleothem proxy records have been used to test monsoon links with orbital forcing solar changes iceberg discharges in the north atlantic ocean currents and atmospheric methane however these benchmark cave records do not match other published dated e asian proxy rainfall record specifically here independently calibrated rainfall records from loess palaeosol magnetic properties and cave oxygen isotope intercomparisons which show variable e asian monsoon intensity through the entire holocene the strong correlation of the cave records with the extraregional indian monsoon record yet their mismatch with these other dated chinese rainfall records might be reconciled if the speleothem isotope variations reflect not changes in holocene rainfall amount but in rainfall source declining holocene influence of isotopically lighter indian monsoon sourced moisture over china would have resulted in increasing proportions of isotopically heavier rainfall sourced from the more oceanic e asian monsoon individual speleothems may thus regionally record holocene changes in indian monsoon intensity and isotopic influence conversely the other chinese proxy records described here reflect changes in rainfall amount and thus in e asian summer monsoon intensity for the holocene the e asian and the indian monsoon responses to orbital forcing are likely to have differed specifically due to e asian internal feedbacks and the seasonal contrasts between the two monsoon systems

holocene environmental changes in bangong co basin western tibet part 2 the pollen record abstract a better knowledge of environmental variations in key regions such as the tibetan plateau which plays a fundamental role in the indian monsoon dynamics and thus on the whole northern hemisphere atmospheric circulation is of great importance we present here a detailed paleoenvironmental study based on pollen analyses of a sediment core from lake bangong results on the modern pollen rain are also discussed as they give valuable information for the interpretation of the fossil pollen data the pollen results of the bangong sequence and their paleoclimatic interpretation are integrated into a chronological framework on the basis of palynostratigraphical methods because of dead carbon in the lake system it has been difficult to establish a reliable chronology of the bangong sequence using a geochemical model for correcting measured 14c ages the pollen record from lake bangong compares well with the record from lake sumxi in western tibet lake bangong core provides a continuous holocene pollen record before 9600 yr b p the dominance of desertic elements in the pollen record reflects an arid environment at about 9600 yr b p an abrupt shift to steppe vegetation suggests the onset of moister conditions and from 9500 to 6200 yr b p proxy data indicate conditions warmer and wetter than today proxy data also indicate short term changes during this interval climate instability is suggested by the development of a local palustral flora which peaks at 7700 yr b p and is interpreted as a lake regression in phase with increase in the percentage of littoral and saline water diatom species between 8600 and 7700 yr b p the first humid pulse culminating at 9000 8500 yr b p is thus followed by drier conditions around 8000 7700 yr b p the interval between 7200 and 6500 yr b p regarded as optimal for vegetation growth from the pollen record corresponds to a second humid pulse a trend towards aridity is observed during the following period with dry events centered around 5500 3900 3200 and 700 yr b p

hydrometeorological reconstructions for northeastern mongolia derived from tree rings 1651 1995 reconstructions of annual prior august current july precipitation and streamflow 345 yr in length 1651 1995 are presented for northeastern mongolia based on tree ring width data these precipitation and streamflow reconstructions account for 54 and 48 of the respective variance in instrumental data over the past 50 years variations in instrumental precipitation and streamflow are within the range of those reconstructed over the length of tree ring records however there appear to be more frequent extended wet periods during the twentieth century multitaper spectral analysis revealed statistically significant peaks at 10 8 and 12 8 yr for the precipitation reconstruction and at 12 8 and 20 3 23 8 yr for the streamflow reconstruction similarly singular spectrum analysis identified spectral modes of variation at 12 and 21 yr for both series these spectra resemble those found for tree ring based precipitation reconstructions in central china as well as the western united states and may reflect solar influences on the climate of mongolia

coherent response of arabian sea upwelling and pollen transport to late quaternary monsoonal winds the indian summer monsoon causes large seasonal changes in the environments of both eastern africa and the arabian sea here we compare time series 140 kyr long of selected pollen types and foraminiferal upwelling faunas preserved in marine sediments to identify the frequencies of their variability and the coherence and phase of the terrestrial and marine responses to monsoonal circulation during interglacial intervals the pollen and upwelling records of the western arabian sea indicate stronger monsoons and are both coherent and in phase at periodicities near the precession of the earth s rotational axis 23 kyr we conclude that the strength of the monsoonal southwesterlies accounts for this high coherence of marine and terrestrial records during interglacial intervals low correlation during glacial phases indicates weaker monsoons and some decoupling of these two records these data indicate that two distinct modes of monsoon variability may exist an interglacial mode with strong monsoons and effective coupling of terrestrial and marine records and a glacial mode with both weaker monsoons and decreased linkage between arabian sea pollen and upwelling records

distinct climate change synchronous with heinrich event one recorded by stable oxygen and carbon isotopic compositions in stalagmites from china abstract uranium series dating of oxygen and carbon isotope records for stalagmite sj3 collected in songjia cave central china shows significant variation in past climate and environment during the period 20 10 ka stalagmite sj3 is located more than 1000 km inland of the coastal hulu cave in east china and more than 700 km north of the dongge cave in southwest china and despite minor differences displays a clear first order similarity with the hulu and dongge records the coldest climatic phase since the last glacial maximum which is associated with the heinrich event 1 in the north atlantic region was clearly recorded in sj3 between 17 6 and 14 5 ka in good agreement in timing duration and extent with the records from hulu and dongge caves and the greenland ice core the results indicate that there have been synchronous and significant climatic changes across monsoonal china and strong teleconnections between the north atlantic and east asia regions during the period 20 10 ka this is much different from the holocene optimum which shows a time shift of more than several thousands years from southeast coastal to inland china it is likely that temperature change at northern high latitudes during glacial periods exerts stronger influence on the asian summer monsoon relative to insolation and appears to be capable of perturbing large scale atmospheric oceanic circulation patterns in the northern hemisphere and thus monsoonal rainfall and paleovegetation in east asia climatic signals in the north atlantic region propagate rapidly to east asia during glacial periods by influencing the winter land sea temperature contrast in the east asian monsoon region

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

spatial and temporal variability in the stable isotope systematics of modern precipitation in china implications for paleoclimate reconstructions the stable isotopic composition of materials such as glacial ice tree rings lake sediments and speleothems from low to mid latitudes contains information about past changes in temperature t and precipitation amount p however the transfer functions which link 18op to changes in t or p d 18op dt and d 18op dp can exhibit significant temporal and spatial variability in these regions in areas affected by the southeast asian monsoon past variations in 18o and d of precipitation have been attributed to variations in monsoon intensity storm tracks and or variations in temperature proper interpretation of past 18op variations here requires an understanding of these complicated stable isotope systematics since temperature and precipitation are positively correlated in china and have opposite effects on 18op it is necessary to determine which of these effects is dominant for a specific region in order to perform even qualitative paleoclimate reconstructions here we evaluate the value of the transfer functions in modern precipitation to more accurately interpret the paleorecord the strength of these transfer functions in china is investigated using multiple regression analysis of data from 10 sites within the global network for isotopes in precipitation gnip 18op is modeled as a function of both temperature and precipitation the magnitude and signs of the transfer functions at any given site are closely related to the degree of summer monsoon influence 18op values at sites with intense summer monsoon precipitation are more dependent on the amount of precipitation than on temperature and therefore exhibit more negative values in the summer in contrast 18op values at sites that are unaffected by summer monsoon precipitation exhibit strong relationships between 18op and temperature the sites that are near the northern limit of the summer monsoon exhibit dependence on both temperature and amount of precipitation comparison with simple linear models 18op as a function of t or p and a geographic model 18op as a function of latitude and altitude shows that the multiple regression model is more successful at reproducing 18op values at sites that are strongly influenced by the summer monsoon the fact that the transfer function values are highly spatially variable and closely related to the degree of summer monsoon influence suggests that these values may also vary temporally since the southeast asian monsoon intensity is known to exhibit large variations on a number of timescales annual to glacial interglacial and the magnitude and sign of the transfer functions is related to monsoon intensity we suggest that as monsoon intensity changes the magnitude and possibly even the sign of the transfer functions may vary therefore quantitative paleoclimate reconstructions based on 18op variations may not be valid