formal definition and dating of the gssp global stratotype section and point for the base of the holocene using the greenland ngrip ice core and selected auxiliary records the greenland ice core from northgrip ngrip contains a proxy climate record across the pleistocene holocene boundary of unprecedented clarity and resolution analysis of an array of physical and chemical parameters within the ice enables the base of the holocene as reflected in the first signs of climatic warming at the end of the younger dryas greenland stadial 1 cold phase to be located with a high degree of precision this climatic event is most clearly reflected in an abrupt shift in deuterium excess values accompanied by more gradual changes in d 18 o dust concentration a range of chemical species and annual layer thickness a timescale based on multi parameter annual layer counting provides an age of 11 700 calendar yr b2 k before ad 2000 for the base of the holocene with a maximum counting error of 99 yr a proposal that an archived core from this unique sequence should constitute the global stratotype section and point gssp for the base of the holocene series epoch quaternary system period has been ratified by the international union of geological sciences five auxiliary stratotypes for the pleistocene holocene boundary have also been recognised copyright 2008 john wiley sons ltd

geology and petrogenesis of the edgecumbe volcanic field se alaska the interaction of basalt and sialic crust the edgecumbe volcanic field is a holocene volcanic province located on kruzof island se alaska exposed within the 260 km2 field are basalt andesitic basalt andesite dacite and rhyodacite the rhyodacites were erupted after the basalts and before the andesites the volcanics which are al rich 14 18 wt and lack an iron enrichment trend range from tholeiites 47 wt sio2 through rhyodacites 72 but a compositional gap of approximately 9 wt separates the dacites and rhyodacites initial 87sr 86sr ranges from 0 70297 in the basalts to 0 70440 in a pyroxene andesite 18o increases across the suite 5 8 to 7 9 plagioclase an32 86 is the dominant phenocryst in all but one lava olivine fo58 86 occurs in the basic lavas 53 wt sio2 but is replaced by orthopyroxene en43 73 and clinopyroxene en31wo41 en48wo40 in the more siliceous volcanics in the basalts and rhyodacites plagioclase is weakly zoned but extreme zoning 30 mole an is characteristic of phenocrysts in the intermediate lavas fractionation of the observed phenocryst assemblages could not have produced the more silicous volcanics instead they were generated by partial melting of intrusive basement 87sr 86sr 0 70487 18o 8 7 9 3 by basaltic magma and subsequent assimilation mass balance calculations show the rhyodacites are almost pure partial melt 5 basaltic component whereas the intermediate lavas contain between 30 and 60 partial melt

bulk organic δ13c and c n ratios as palaeosalinity indicators within a scottish isolation basin microfossils in isolation basin sediments are frequently used to reconstruct sea level change but preservation problems and non analogue situations can limit their usefulness here we investigate the potential of stable carbon isotopes 13c and c n ratios from bulk organic matter as an alternative proxy of salinity within isolation basin sediments from a basin in northwest scotland within the holocene sediment 13c and c n are determined largely by the mean weighted values of the predominant source of the organic material analysis of modern materials and comparison with the diatom record shows that the marine parts of the sequence are dominated by high 13c and variable c n in the fresh water sequences the organic material is a mixture of both freshwater aquatic and terrestrial plant input that have relatively low 13c and high c n the application of 13c and c n ratios in the studied basin in general follow the environmental change recorded by the diatoms and shows the potential of bulk organic matter in the investigation of salinity change in isolation basins copyright 2005 john wiley sons ltd

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

mineral magnetism of lacustrine sediments and holocene palaeoenvironmental changes in dali nor area southeast inner mongolia plateau china mineral magnetic measurements and analysis of total organic carbon toc and carbon nitrogen c n were performed on two ams 14c dated lacustrine sequences recovered from xiaoniuchang and jiangjunpaozi 42 n 117 e the two sites lie in the dali nor area of southeast inner mongolia plateau where the semi humid climate transforms into a semi arid one sirm low frequency magnetic susceptibility lf irm20mt hirm and irm20mt sirm may largely reflect the erosion of catchment materials and dilution effect of organic matter on deposited magnetic minerals irm 100mt sirm and irm 300mt sirm likely indicate the aeolian activities sirm lf positively correlated to sand percentage of sediments is diagnostic of changes of lake levels or effective humidity complemented by the data of toc and c n and of previously accomplished analyses of grain size loss on ignition loi and pollen the variations in mineral magnetism reveal holocene palaeoenvironmental changes conditions were quite dry and cool before 9970 years bp and then humidified in jiangjunpaozi the effective humidity maximised prior to 8000 years bp and subsequently declined in the two sites the less wet but warmer conditions persisted in jiangjunpaozi until 6600 years bp and xiaoniuchang until 5600 years bp deterioration occurred since then and culminated during 4300 1300 years bp in jiangjunpaozi and 3000 730 years bp in xiaoniuchang which was followed by a moderate but probably very short amelioration in the two sites

forty million years of magmatic evolution in the mariana arc the tephra glass record tephra glasses retrieved from 10 deep sea drilling project dsdp cores around the mariana arc system make up a remarkable record of explosive volcanism in the marianas over the past 40 m y major element compositions for approximately 1800 tephra glasses from basalt through rhyolite are reported and used to examine the nature and history of this activity three maxima of volcanic explosivity presumably related to especially vigorous volcanism in the mariana arc are identified with the biggest maximum at around 18 11 ma and two other maxima at 35 24 and 6 0 ma the two younger maxima are contemporaneous with peaks in explosive volcanism observed for other western pacific arcs explosive arc volcanism has been predominantly tholeiitic since shortly after arc inception no boninitic glasses were found the tephra glasses belong to the low to medium k suite except during an enigmatic phase of medium to high k explosive volcanism during the late miocene 11 7 ma even though mariana tephra glasses are largely similar in composition to mariana arc lavas the tephra show a much larger compositional range than that found for subaerial mariana arc lavas which totally lack dacitic to rhyolitic volcanic products the tephra glasses define a bimodal population in terms of silica content with a pronounced minimum or daly gap around 65 66 sio2 mariana tephra glasses are fractionated with the least evolved glass being fe rich and having a magnesium number mg 100mg mg fe 2 of 55 basaltic tephra glasses contain 16 a1203 average 14 3 a1203 and are not high alumina basalts this contrasts with the observation that modern mariana arc lavas contain 15 21 average 17 4 a1203 the high alumina basalt lavas of the mariana arc probably reflect plagioclase accumulation and not liquid compositions all tephra glasses plot near low pressure cotectics and reaction curves on the subprojection olivine clinopyroxene quartz mafic and felsic samples define distinct trends the mafic trend reflects fractional crystallization of mantle derived basaltic magma whereas the felsic trend may be due either to anatexis of mariana arc crust or to fractionation of mafic melts the tephra glass data reinforce the model that the magmatic evolution of the mariana arc has been dominated by low pressure fractionation perhaps accompanied by anatexis episodic changes in melting regime to generate miocene potassic tephra may be related to changing mantle sources and processes related to episodes of back arc basin spreading these episodic changes are superimposed on a long term increase in potassium that reflects progressive metasomatism of the mantle source long term increases in k20 contents for mariana arc magmas inferred from the tephra glass record are 0 004 wt m y mafic 0 011 wt m y intermediate and 0 023 wt m y felsic

evolving geographic patterns of cenozoic magmatism in the north american cordillera the temporal and spatial association of magmatism and metamorphic core complexes four maps are presented here that show the location and extent of magmatic fields between eastern alaska and northern mexico during the successive time intervals of 55 40 40 25 25 10 and 10 0 ma and four others show the distribution of metamorphic core complexes during the same cenozoic time intervals the maps are based on u s geological survey and canadian cordilleran data bases contining about 6000 isotopic dates and extensive literature review for nearly 60 ma the development of metamorphic core complexes has coincided with the locus of a really extensive and voluminous intermediate composition magmatic fields the association is suggestive of a close link between magmatism and core complex formation namely that magma directly and indirectly lowers the strength of the crust magmatism thus controls the location and timing of core complex formation the stresses responsible may be inherited from mesozoic crustal thickening locally created by uplift and magmatic thickening of the crust and imposed by the global pattern of plate motions and driving forces since the miocene rates of magmatism extension and core complex formation have declined the modern basin and range province is not a suitable model for the situation that existed during major magmatic culminations the singular event of early miocene time the merging of two large magmatic fields extinguishing the laramide magmatic gap explains several disconnected observations the hyperextension episode of the colorado river corridor rapid reorientation of stress patterns across much of western north america and subsequent rapid tectonic movements in california magma triggered breakup of western north america lithosphere coincided with development of the san andreas transform system thermal destruction of the laramide magmatic gap created a california microplate about 22 ma ago that moved rapidly away from north america thus two plate tectonic processes thermal destruction of the lithosphere bridge and northward growth of a transform system interacted to produce miocene and later tectonic patterns and events

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

comparison of truly undrained and constant volume direct simple shear tests the paper describes a chamber for the norwegian geotechnical institute s direct simple shear device that enables undrained tests with pore pressure measurements to be run the results of undrained

fluvial incision by the qingyijiang river on the northern fringe of mt huangshan eastern china responses to weakening of the east asian summer monsoon abstract this paper focuses on climatic and tectonic controls to determine their relative importance to the quaternary fluvial incision by the qingyijiang river eastern china the qingyijiang which is one of longest tributaries of the lower yangtze river drains the northern piedmont of mt huangshan a field survey focused on three natural sections of the qingyijiang in the jingxian basin where a well preserved sequence of one alluvial platform p and three fluvial terraces t3 t2 and t1 is presented the heights of the platform and the terraces above river level are 65 40 20 and 7 m respectively in this study electron spin resonance esr optical stimulated luminescence osl and palaeomagnetic dating were applied to reconstruct the fluvial incision history of the qingyijiang and evaluate the possible influence of tectonic uplift and or climate change on the fluvial incision the main results show that 1 the ages of p t3 t2 and t1 were determined to be 1300 900 600 and 1 5 ka respectively corresponding to four incision events in the qingyijiang 2 the east asian summer monsoon easm experienced four significant weakening events at 1300 900 600 and 1 5 ka according to previous research correspondingly we propose that four significant increased periods of regional precipitation occurred at 1300 900 600 and 1 5 ka in the study area because of the negative correlation between the intensity of the easm and regional precipitation from 1960 to 2012 and 3 fluvial incision by the qingyijiang arose as a result of the weakening of the easm in combination with tectonic uplift determined by matching fluvial incision history of the qingyijiang with tectonic movement and easm change in addition the weakening of the easm climatically triggered fluvial incision by the qingyijiang this study supports the conclusion that major fluvial incision has been climatically triggered however it also suggests that the mechanism of river incision may be regionally distinctive in different climatic zones

a 5500 year proxy climate and vegetation record from blanket mire at talla moss borders scotland a monolith of peat taken from an upland blanket mire at talla moss southern scotland was sub jected to peat humification and pollen analyses to produce both a proxy climate record and a vegetational history covering the last 5500 years while the peat showed little visible stratigraphy with no intimation of major peat humification changes colorimetric data indicate a markedly oscillatory climate record which is apparently largely independent of or out of phase with major vegetational changes the raw data imply particular wet shifts in climate at c 3455 bp c 2600 bp c 1930 bp c 1095 bp with a markedly wet or cool and wet episode commencing at c 540 bp these are central age estimates and should not be regarded as precise dates for the inferred climate shifts other wet shifts apparently date from c 3070 bp c 2265 bp and c 1700 bp although the first of these corresponds with pollen evidence for significant prehistoric human activity in the locality spectral analysis of the peat h

cyclic pore water pressure generation and stiffness degradation in compacted clays abstractcyclic hollow cylinder torsional tests were performed in undrained conditions on 12 compacted clay specimens collected from two types of dams an earth core rock filled dam and an earth zone dam in thailand the cyclic degradation cyclic pore water pressure generation and volumetric cyclic threshold shear strain were studied via multistage strain controlled tests the testing program encompassed five overconsolidation ratios ocrs 1 1 5 2 3 5 and 4 where six to eight cyclic strain controlled stages were applied in each test with frequency f 2 hz the results reveal that the volumetric threshold shear strain amplitude of these compacted clays ranged between approximately 0 009 and 0 025 and generally increased substantially with the plasticity index pi the cyclic pore water pressures normalized by c are consistently lower than previous ones using other types of clays tested with other types of devices at comparable cyclic shear strain amplitudes the cyclic degradation and cyclic p

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

hydrological changes in the european midlatitudes associated with freshwater outbursts from lake agassiz during the younger dryas event and the early holocene abstract recent studies of lake level fluctuations during the last deglaciation in eastern france jura mountains and pre alps and on the swiss plateau show distinct phases of higher water level developing at the beginning and during the latter part of greenland stade 1 i e younger dryas event and punctuating the early holocene period at 11 250 11 050 10 300 10 000 9550 9150 8300 8050 and 7550 7250 cal yr b p the phases at 11 250 11 050 and 8300 8050 cal yr b p appear to be related to the cool preboreal oscillation and the 8200 yr event assumed to be associated with deglaciation events a comparison of this mid european lake level record with the outbursts from proglacial lake agassiz in north america suggests that between 13 000 and 8000 cal yr b p phases of positive water balance were the response in west central europe to climate cooling episodes which were induced by perturbation of the thermohaline circulation due to sudden freshwater releases to oceans this probably was in response to a southward migration of the atlantic westerly jet and its associated cyclonic track moreover it is hypothesized that during the early holocene varying solar activity could have been a crucial factor by amplifying or reducing the possible effects of lake agassiz outbursts on the climate

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

middle holocene environmental change in central korea and its linkage to summer and winter monsoon changes to trace the surficial responses of lowlands to past climate change we investigated 13c in total organic carbon toc c n ratios magnetic susceptibility ms and silicon si intensity directly proportional to concentration in wetland sediments collected from the gimpo area of central korea covering 6600 4600 cal yr bp two organic layers with high toc negatively depleted 13ctoc values 27 to 29 low ms values and low si intensities were found at 6200 5900 and 5200 4800 cal yr bp respectively these middle holocene wet periods corresponded to relatively intensified summer monsoon and solar activity periods the intervening dry period 5900 5200 cal yr bp with high ms high si and low toc corresponded to an intensified dust activity interval and stronger winter monsoon this multi centennial climatic fluctuation of wet periods 6200 5900 cal yr bp and 5200 4800 cal yr bp and an intervening dry period 5900 5200 cal yr bp in central korea was more synchronous with climate change in the arid inner part of china than with that in south china suggesting possible strong high latitude driven climatic influences e g north atlantic cooling events during the middle holocene

holocene moisture variations across china and driving mechanisms a synthesis of climatic records based on the review of 33 holocene moisture reconstructions that passed quality scrutiny temporal and spatial patterns of regional moisture variations are delineated the regionally averaged moisture index from xinjiang demonstrates that the moisture index has been persistently climbing since 10 ka cal bp and that the period between 4 and 0 ka cal bp is the holocene moisture optimum comparison of the moisture index of xinjiang region with the winter climate of northern europe leads us to propose that the holocene moisture variations in xinjiang region have been controlled by the winter temperature variations in the north atlantic region the regionally averaged moisture index from the tibetan plateau shows that the moisture has been persistently declining since 11 ka cal bp and that the period between 11 5 and 7 5 ka cal bp was the holocene moisture optimum the parallel trends between the moisture level in the tibetan plateau and the indian summer monsoon strength retrieved from the arabian sea suggest that the tibetan plateau has been under influence of the indian summer monsoon throughout the holocene the regionally averaged moisture index curves from northern china and southern china are the delayed reflections of the east asian summer monsoon strength to the solar radiation that is the peak insolation was responded by the holocene oceanic thermal optimum with significant time lags and the oceanic thermal optimum was then responded by the holocene moisture optimum in southern china and northern china also with some time lags the differences in the moisture index curve shapes and in the durations of the holocene moisture optimum between northern china and southern china suggest that the strength of the east asian summer monsoon had gradually transgressed northward in the early holocene and gradually regressed southward in the late holocene

distal volcanic impacts on peatlands palaeoecological evidence from alaska abstract despite the fact that volcanic ash tephra layers are found preserved in peat deposits around the world comparatively little research has investigated the impacts of distal volcanic emissions on peatlands this study investigates the impacts of several late holocene volcanic eruptions on five peatlands in southern alaska using a palaeoecological approach testate amoebae analysis peat humification analysis and a basic analysis of plant macrofossil components were applied across 11 tephra layers changes in macrofossil and testate amoebae assemblages occur across several of the tephra layers the humification results were considered unreliable because of a methodological problem a finding which may have implications for other studies using this technique redundancy analyses on testate amoebae data show statistically significant changes associated with two tephras the most likely causes of the impacts are volcanic gases acidic precipitation or tephra derived leachates the finding that some tephras are associated with impacts whereas others are not may relate to the season of the eruption or meteorological conditions at the time of ash fall these results suggest the sensitivity of peatlands and peatland microbial communities to distal volcanic products and imply that changes in key palaeoclimatic proxies may be caused by a mechanism independent of climate change implications of the results for peat based palaeoclimatic studies are discussed as are possible directions for future research

rare earth element fractionations of the northwestern south china sea sediments and their implications for east asian monsoon reconstruction during the last 36 kyr abstract rare earth elements rees fractionations in siliciclastic marine sediments are related to the parent rock properties weathering degree grain size and heavy minerals the relations between marine sediment ree compositions and regional paleoclimate are not fully understood here the rees for detrital components of a core retrieved from the northwestern south china sea scs were measured results show the ree lree hree la yb n and light ree la sm n fractionation degrees have good responses to the regional paleoclimate over the past 36 kyr sea level played a key role in ree fractionations during 36 24 kyr bp manifesting as lower ree and lree fractionation degrees correspond to the decreased sea level the entire trends for lree hree la yb n and la sm n over the past 20 5 kyr are almost in phase with the regional east asian summer monsoon easm records because rees are mainly concentrated in heavy minerals the density difference of heavy minerals is probably the main controlling factor on ree fractionations clay minerals and feldspars released during the weathering process have a high content of light rees lrees in the warm wet periods holocene optimum and bolling allerod more precipitation promoted weathering and strengthened the estuarine hydrodynamic force which respectively resulted in high content of clay minerals and feldspars and high density heavy minerals e g monazite the process led to lree enrichment because the enriched minerals contain higher contents of the lrees in contrast the dry cold climate conditions during the periods heinrich 1 younger dryas and last glacial maximum resulted in the reversed ree fractionations as the weak hydrodynamic force can only carry the low density heavy minerals e g zircon that are enriched in hrees this model does not seem to apply to 36 24 kyr bp probably because of the re transport of ancient shelf sediments the study facilitates the understanding of ree application in paleoclimate reconstruction within slope sediments

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

sedimentary responses to the east asian monsoon and sea level variations recorded in the northern south china sea over the past 36 kyr abstract sediment grain size is an important proxy to detect sedimentary process and record paleoenvironmental variations in continental slopes grain size measurements were performed for 298 samples of the 5 96 m long core pc338 spanning the past 36 kyr recovered from the northern south china sea scs results show that sea level and climatic influences on grain size distributions are crucial a turbidite formed during the last glacial maximum lgm is ascribed to the favorable topography close to the red river estuary induced by the low sea level four end member em components for the normal sediment layers were unmixed using a lognormal parametric end member modeling emm with the sea level decreasing more em4 15 100 m and less em1 0 2 m supplied the scs slope because em2 2 10 m consisted of fluvial suspension is dominated by the east asian summer monsoon easm precipitation it has the potential to substitute for the easm intensity em2 varied in phase with many south china paleoclimate records and the 30 n july insolation over the past 36 kyr and cooling climate events including the lgm heinrich events h1 and h3 younger dryas 8 2 ka and 10 3 ka lowered the em2 content our results further confirm the synchronous easm evolution in the south china continent mainly forced by the northern hemisphere summer insolation

pyroclastic deposits of the mount edgecumbe volcanic field southeast alaska eruptions of a stratified magma chamber abstract the mount edgecumbe volcanic field in southeastern alaska consists of 5 6 km 3 dre of postglacial pyroclasts that overlie pleistocene lavas all eleven pyroclast vents align with the long axis of the field implying that the pyroclast magma conduits followed a crustal fissure most of these vents had previously erupted lavas that are compositionally similar to the pyroclasts so a persistent magma system chamber had likely evolved by the onset of the pyroclastic eruptions the pyroclastic sequence was deposited in about a millennium and is remarkable for a wide range of upward increasing silica contents 51 72 sio 2 which is consistent with rise of coexisting magmas at different rates governed by their viscosity basaltic and andesitic lava flows have erupted throughout the lifetime of the field rhyolite erupted late we infer that it formed early but was hindered from rising by its high viscosity most of the magmas and all siliceous ones erupted from vents on the central fissure basalt has not erupted from the center of the field during at least the latter part of its lifetime thus the field may illustrate basalt underplating heat and mass flux are concentrated at the center of a stratified magma chamber in which a cap of siliceous melt blocks the rise of basalt major element strontium isotope and mineral compositions of unaltered pyroclasts are broadly similar to those of older lavas of similar sio 2 content slightly fewer phenocrysts inherited grains and trace amphibole in pyroclastic magmas may be due simply to faster rise and less undercooling and degassing before eruption relative to the lavas dacite occurs only in the youngest deposits the magma formed by mixing of andesitic and rhyolitic magmas erupted shortly before by the dacitic vents

fractional crystallization and magma mixing in the tigalak layered intrusion the nain anorthosite complex labrador the tigalak intrusion is a dominantly dioritic layered body about 80 km2 in area which ranges in composition from norite to granodiorite local areas of the layered rocks display upward fractionation from norite to ferrodiorite periodic reversals of mineral composition trends record the emplacement of less fractionated dioritic magma heterogeneous mixtures of dioritic and granodioritic rocks occur widely in mappable lenses and layers that alternate up section and along the strike with more uniformly layered rocks in these mixtures chilled dioritic pillows occur abundantly in a hybrid cumulate matrix of granodiorite to diorite composition cross cutting granodioritic dikes grade upward into stratigraphically bound lensoid masses of the hybrid cumulates it appears that the hybrid rocks formed as a result of the emplacement of the granodioritic magma through lower cumulates into the dioritic magma chamber and that the dioritic pillows represent chilled bodies of ferich dioritic magma that commingled with cooler granodioritic magma and settled to the floor of the tigalak magma chamber

sedimentology dating and palaeoclimatic interpretation of a 76 3 ka record from lago grande di monticchio southern italy abstract detailed sedimentological and microstratigraphical investigations of lacustrine sediments from lago grande di monticchio southern italy provide a time scale based on rates of sedimentation obtained from annual laminations although not annually laminated throughout a time scale covering the last 76 3 ka is available by interpolation of sedimentation rates results of this chronology agree with radiocarbon dates and with ar ar dates on tephra layers from the same lacustrine sediment sequence occurrence of varves in combination with physical and geochemical properties are related to variations in the trophic state of the lake and to changing runoff both controlled by palaeoclimatic conditions water depth was relatively shallow with dominating bioturbation and only few varves preserved for most of the pleniglacial a marked increase in precipitation and related runoff characterises the early last glacial maximum when water depth reached a maximum and clastic varves were deposited subsequently water depth was shallower again a drastic change towards nutrient rich conditions occurred at the pleistocene holocene transition during the holocene organic varves were deposited two periods with higher organic productivity were recognised prior to the last glacial maximum around 50 ka and 73 ka these intervals are interpreted as the result of interstadial conditions the oldes of the two events shows laminations comparable to those at the glacial holocene transition the periods with increased minerogenic influx may be characterised as stadial conditions lasting from 14 40 ka and from 50 73 ka

lacustrine record of centennial and millennial scale rainfall variability of the east asian summer monsoon during the last deglaciation multi proxy evidence from taiwan abstract situated at the border between the southeast asian continent and the northwestern pacific taiwan s climate is primarily influenced by the east asian summer monsoon easm and episodic tropical cyclones formed in the western pacific the lake sediments in taiwan thus potentially archive the information of typhoon events and past monsoon variability a high resolution multi proxy total carbon mass accumulation rate of total carbon weight percent of wood fragments 13 c of the organic carbon magnetic susceptibility chemical weathering index and well dated lacustrine record from dongyuan lake 22 10 n 120 50 e 360 m above sea level in southern taiwan was used to reconstruct centennial to millennial timescale easm oscillations specifically for the transition from the last deglaciation to the early holocene 17 9 ka bp the temporal patterns of proxies on both timescales in our records broadly agree with those in the greenland ice core which shows enhanced easm during the warm period and weakened monsoon during the cold period different from northern high latitude climates we found two phases in the mystery interval opposite bolling allerod ba trend with maximum monsoonal rainfall in the allerod period and more gradual transition to younger dryas event in our record likely other climate forcings beyond the north atlantic climate jointly modulated the easm changes of sea surface temperature in the western tropical pacific also might have exerted synergistic control on easm precipitation in taiwan on the centennial timescale during the last deglaciation in addition several high sedimentation events accompanied by significant amounts of wood fragments were observed and coincide with the paleo record of mass wasting events identified on various downstream floodplains in taiwan since mass wasting processes were rainfall driven and threshold triggered such coherence possibly indicated an intensification of typhoon activity during the early holocene more high resolution lacustrine records are required to decipher the hydrological variation and climate dynamics that were co influenced by the intertropical convergence zone itcz and typhoon activity in southeast asia

postglacial floral and climate changes in southeastern china recorded by distributions of n alkan 2 ones in the dahu sediment peat sequence abstract long chain n alkane 2 ones occur widely in lacustrine and peat depositional settings however their paleobotanical and paleoclimate implications are less understood compared with their n alkyl counterparts n alkanes n fatty acids in this study we have performed a molecular stratigraphic investigation of changes in the plant contributions and depositional conditions using n alkan 2 ones in the dahu lacustrine peat sequence spanning the last 17 kyr a series of n alkan 2 ones ranging from c23 to c33 with a maximum at c29 appears to be contributed by microbial oxidation of both n alkanes and n alkanoic acids the values of the average chain length acl and the ratios of mid to long chained n alkan 2 ones display a trend comparable with the abundance of trees relative to herbs and ferns in addition the carbon predominance index cpi of n alkan 2 ones varied in pace with lithology paleoenvironment with higher values seen in peat deposits the alternating layers represent a succession of shallow lakes and peatlands that filled the depositional basin in response to paleoclimate changes between wetter and less wet conditions the succession of paleohydrologic conditions is responsible for the variation of ketone cpi values in this peat sediment sequence

effect of frequency and vertical stress on cyclic degradation and pore water pressure in clay in the ngi simple shear device abstractthe effects of the frequency of cyclic shearing and vertical consolidation stress on the cyclic degradation and cyclic pore water pressure in normally consolidated kaolinite clay having pi 28 were investigated with the help of the cyclic strain controlled norwegian geotechnical institute ngi simple shear test the testing program encompassed three cyclic shear strain amplitudes c 0 1 0 25 and 0 5 two vertical effective consolidation stresses vc 220 and 680 kpa and three frequencies f 0 001 0 01 and 0 1 hz the results reveal that the cyclic degradation parameter t which measures the rate of cyclic degradation with the number of cycles increases substantially with f and decreases with vc if f is increased 10 times t may increase by 20 50 if vc is increased from 220 to 680 kpa the t parameter may decrease by 20 38 the cyclic pore water pressure normalized by vc decreases with f and vc

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

freshwater outbursts to the oceans from glacial lake agassiz and their role in climate change during the last deglaciation abstract lake agassiz was the largest lake in north america during the last deglaciation as the laurentide ice sheet lis retreated large volumes of water stored in this proglacial lake were episodically released into the oceans these waters were variably routed to the gulf of mexico arctic ocean north atlantic ocean and hudson bay during this period the three largest cooling events in the northern hemisphere closely followed 4 of the 5 largest outbursts from lake agassiz 1 the younger dryas which was preceded by a release of 9500 km 3 2 the preboreal oscillation preceded by releases of 9300 km 3 and 5900 km 3 and 3 the 8 2 ka cold event preceded by a 163 000 km 3 outburst these are respectively fluxes of 0 30 sv 0 29 sv 0 19 sv and 5 2 sv if released in 1 year because the influx of freshwater reaching the north atlantic ocean can inhibit thermohaline circulation partly depending on whether the ocean was in a glacial interglacial or transitional mode of circulation we believe that at least these large outbursts from lake agassiz may have provided the triggers for changes in ocean circulation and in turn for widespread climate change

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

δ13c of loess organic matter as a potential proxy for paleoprecipitation paleoprecipitation reconstructions on the basis of pollen are well known but they do not provide high temporal resolution for glacial periods high resolution paleoprecipitation reconstructions for the last glaciation based on the isotopic record organic matter in loess from nussloch rhine valley germany are consistent with paleoprecipitation inferred from peat in the same area using an independant method thus 13c of loess organic matter can be used as a proxy for paleoprecipitation

a 15 400 year record of climate variation from a subalpine lacustrine sedimentary sequence in the western nanling mountains in south china abstract multi proxy records of a subalpine lacustrine sequence in daping swamp in the western nanling mountains provide evidence for exploring climate variability in the past 15 400 yr two dry and cool 15 400 14 500 and 13 000 11 000 cal yr bp and one humid and warm interval 14 500 13 200 cal yr bp which we correlate to heinrich event 1 the younger dryas and the bolling allerod event respectively are revealed the early holocene climate 11 000 8000 cal yr bp was characterized by less humid and warm conditions suggesting a weaker asian summer monsoon asm intensity our findings indicate that the holocene optimum occurred between 8000 and 4500 cal yr bp and the most intensified asm appears from 8000 to 7000 cal yr bp after 4500 cal yr bp climate shifted to relatively cool and dry conditions we speculate that five short dry and cool events centered at 11 000 9000 8400 6000 and 3500 cal yr bp were linked to the holocene ice rafting events detected in the north atlantic migration of the itcz and the oceanic atmospheric circulations particularly sst changes in the tropical pacific may play a pivotal role in climate variation of the study region

petrological evolution of the crust and mantle in its simplest form crust mantle evolution can be thought of as a study of the processes by which material is lost from the mantle and forms new crust the overall goal is achievement of mass balance between the average composition of material known to have been added to the crust and the estimated average composition of the entire crust attainment of this goal for the earth has been elusive primarily because the materials available for study have generally been involved in several stages of evolution including fractionation within both the crust and mantle and recycling of material from crust to mantle thereby complicating the interpretation of available data although the overall composition of the continental crust generally has been modelled as andesitic taylor and mclennan 1981a the present upper continental crust is granodioritic and requires a more mafic lower crust it has been proposed taylor and mclennan 1981a that originally the archean crust had an andesitic composition throughout its volume and that partial melting in the lower crust developed more felsic melts that rose to enrich the upper crust leaving a more mafic residuum of lower crust this concept has been challenged by weaver and tarney 1981a who argue that the granulites of presumed lower crustal origin do not have the correct compositions for this model if one considers more recent additions to the crust from the mantle over the past several hundred million years it appears that these latest additions are basaltic with very little if any granitic additions in fact barker 1981 in his introduction to a special issue of jgr on granites and rhyolites states to date no one has demonstrated that such magmas may form in the mantle indeed much experimental and geochemical work indicates that such siliceous liquids cannot originate there therefore such magmas must be generated in the crust in island arc environments where the average composition of added material normally is thought to be andesitic a anderson 1982 has shown that the parent melt is basaltic not andesitic in addition kay 1980 has shown that the k content of the newly added material is less than the average k content of the previously existing crust in the oceanic crust the additions from the mantle are basaltic and according to o hara 1982 probably are derived from very mafic picritic melts as parents continental flood basalts which have also added material from mantle to crust also are clearly derived from basaltic parental melts basaltic volcanism study project 1981 thus the evidence for the nature of material subtracted from the mantle and added to the crust for the past several hundred million or perhaps a billion years points to very mafic melts this contrasts significantly with the overall andesitic composition of continental crust it implies furthermore that if the overall archean crustal composition was andesitic as estimated by taylor and mclennan 1981a then additions to the crust have become more mafic with time a concept in direct conflict with most models in which secular trends are from mafic to felsic with time veizer and jansen 1979 and mclennan et al 198o a question which is beginning to appear either explicitly or implicitly is whether crustal volcanic rocks or the crust as a whole really represents the parent melt that formed in the mantle a anderson 1982 o hara 1982 and nisbet and walker 1982

tropical climate instability the last glacial cycle from a qinghai tibetan ice core an ice core record from the guliya ice cap on the qinghai tibetan plateau provides evidence of regional climatic conditions over the last glacial cycle 36 cl data suggest that the deepest 20 meters of the core may be more than 500 000 years old the 18 o change across termination i is 5 4 per mil similar to that in the huascaran peru and polar ice cores three guliya interstadials stages 3 5a and 5c are marked by increases in 18 o values similar to that of the holocene and eemian 124 000 years ago the similarity of this pattern to that of ch 4 records from polar ice cores indicates that global ch 4 levels and the tropical hydrological cycle are linked the late glacial stage record contains numerous 200 year oscillations in 18 o values and in dust nh 4 and no 3 levels

threshold shear strain for cyclic pore water pressure in cohesive soils threshold shear strain for cyclic pore water pressure t is a fundamental property of fully saturated soils subjected to undrained cyclic loading at cyclic shear strain amplitude c larger than t residual cyclic pore water pressure changes rapidly with the number of cycles n while at c t such changes are negligible even at large n to augment limited experimental data base of t in cohesive soils five values of t for two elastic silts and a clay were determined in five special cyclic norwegian geotechnical institute ngi type direct simple shear ngi dss constant volume equivalent undrained tests threshold t was also tested on one sand with the results comparing favorably to published data the test results confirm that t in cohesive soils is larger than in cohesionless soils and that it generally increases with the soil s plasticity index pi for the silts and clay having pi 14 30 t 0 024 0 06 was obtained limited data suggest that t in plastic silts and clays practically

holocene monsoon climate documented by oxygen and carbon isotopes from lake sediments and peat bogs in china a review and synthesis there has been much recent debate about holocene climate variation in the monsoon region of china especially the temporal pattern of variations in precipitation the time transgressive nature of the holocene precipitation maximum and the extent to which variations in regions influenced by the indian summer monsoon ism and the east asian summer monsoon easm have been synchronous we summarize and compare carbonate oxygen isotope records delta o 18 carb from ten lakes within the present day ism region we discuss their paleoclimate significance considering the present day moisture source isotopic composition of precipitation and the hydrological setting the delta o 18 carb records are controlled mainly by the isotopic composition of lake water which in turn is a function of regional precipitation evaporation p e balance and the proportion of precipitation that is monsoon derived we normalized the delta o 18 carb data and used these records to generate an integrated moisture index this index along with oxygen isotope records from speleothems and carbon isotope records delta c 13 org from peats within the monsoon region suggests that holocene climate was broadly synchronous across the monsoon region and within the limits of accuracy of the existing age models provides no strong evidence for previously proposed anti phasing of the ism and the easm stable isotope records from lake sediments and peat bogs have excellent potential for providing high quality paleoclimate data for monsoon asia and complement high resolution speleothem sequences which are only found in certain localities c 2011 elsevier ltd all rights reserved

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

paleohydrological records from peat profiles and speleothems in sutherland northwest scotland abstract paleohydrological changes during the late holocene are inferred from humification testate amoebae and pollen evidence from three blanket peat profiles in northwest scotland replicate peat humification records from the traligill basin share the same patterns of change for a 600 yr period of overlap between 1800 and 2400 cal yr b p the shared patterns inferred from samples with a resolution of 5 13 yr represent basinwide hydrological changes in a nearby but hydrologically separate area with caves beneath peat the luminescence emission wavelength measured in two speleothem samples correlated with the humification record in the overlying peat this correlation implies that speleothem luminescence emission wavelength depends primarily on decay rates in the soils from which drip waters are derived as long as there is no major change in soil or vegetation the peat and speleothem records from the cave site further correlate with the peat records from the traligill basin taken together the records thus represent a regional climatic signal peaks in surface wetness replicated in two or more records occur at ca 2300 2090 2030 1820 1600 and 1440 cal yr b p further peaks occur at 800 570 and 115 cal yr b p in the humification and stalagmite records that extend to the present day correlative changes have been observed not only in other peat records from scotland but also in ice accumulation at gisp2 these further correlations imply that precipitation regimes in scotland and greenland were in phase during the late holocene

threshold shear strains for cyclic degradation and cyclic pore water pressure generation in two clays abstractcyclic threshold shear strains are fundamental cyclic soil properties that have not been fully investigated to learn more about the threshold shear strains for cyclic degradation td and cyclic pore water pressure generation tp in fully saturated clays nine multistage cyclic strain controlled ngi direct simple shear tests are conducted on laboratory made kaolinite clay pi 28 and kaolinite bentonite clay pi 55 three levels of vertical effective consolidation stress vc 113 kpa approximately 216 kpa and approximately 674 kpa three ocrs 1 4 and 7 8 and two cyclic loading frequencies f 0 01 and 0 1 hz were applied in three tests on the normally consolidated nc kaolinite clay td varied between 0 012 and 0 014 and tp between 0 014 and 0 034 in two tests on the overconsolidated oc kaolinite clay with ocr 4 td was 0 013 and tp 0 016 and 0 017 in two tests on the nc kaolinite bentonite clay td was 0 013 and 0 016 and tp 0 052 and 0 078 in the test on oc kao

moisture changes in northeast china since the last deglaciation spatiotemporal out of phase patterns and possible forcing mechanisms abstract there is a strong chance that the 21 st century warming will cause differences in precipitation distribution over the globe northeast ne china is a unique area whose atmospheric circulation is still a controversial subject and is likely to be strongly impacted by global warming thus a good understanding of the past variations in effective moisture in ne china will be benefit for the prediction of future hydrological changes in this study we use basal peat ages and published paleoclimate records to evaluate the spatial and temporal patterns and possible forcing mechanisms for the moisture changes in ne china over the past 16 000 years basal peat ages suggest that the moisture conditions in different regions of ne china show as a spatiotemporal out phase pattern in addition the paleoclimate records of 17 sites also indicate that ne china experienced a spatiotemporal out phase pattern of moisture changes along northwest southeast direction since the last deglaciation the moisture in southern ne china experienced increasing trend during the period of 16 8 cal ka bp with the maximum moisture occurring 8 3 cal ka bp and decreasing trend after 3 cal ka bp the moisture pattern in western ne china is similar to that in southern ne china it experienced increasing trend during the period of 16 8 cal ka bp the maximum moisture during the period 8 4 cal ka bp and decreasing trend from 4 cal ka bp to present the moisture in eastern ne china experienced wet conditions from 16 cal ka bp to 4 cal ka bp and decreasing trend after 4 cal ka bp in central ne china two relatively wet periods occurred during the periods of 13 8 cal ka bp and 6 3 cal ka bp respectively in addition two wet periods occurred during the periods of 14 11 cal ka bp and 7 1 cal ka bp in northern ne china respectively the moisture patterns between ne china and other regions of china are also compared in this study we propose that the possible forcing mechanisms for the moisture changes in ne china were different for each 4000 year interval during the period of 16 12 cal ka bp the weak east asian summer monsoon easm and strong northeast monsoon nem were the major water vapor sources of ne china during the period of 12 8 cal ka bp the increasing easm and strong nem were still the major water vapor sources of ne china during the period of 8 4 cal ka bp the strongest easm was the major water vapor sources of the whole ne china furthermore the increasing westerlies slightly penetrated into northern ne china during this period from 4 cal ka bp to present the decreasing easm provided precipitation for the most regions of ne china the westerlies reached the maximum and further penetrated into the whole northern ne china during this period

a high resolution sediment record of east asian summer monsoon from the northern south china sea spanning the past 7500 years high resolution holocene marine sediment records are limited which hampers our understanding of paleomonsoon evolution continental shelf sediment records are derived mainly from terrestrial weath

high resolution multi proxy climate records from chinese loess evidence for rapid climatic changes over the last 75 kyr the loess paleosol sequence in loess layer l1 malan loess is investigated in three regions of the western chinese loess plateau nine pedogenic layers are found in l1 and three proxy climate indices magnetic susceptibility ms grain size gs and caco3 content are measured at intervals of 0 2 kyr in order to recover records of monsoon climate variations time series of ms gs and caco3 content document the high resolution history of summer and winter monsoon climate variations over the last 75 kyr the records show a high degree of similarity to the warm interstadials recorded in ice cores from greenland and the antarctic and with heinrich events in the north atlantic during the last glacial cycle bond cycles are also recorded by the chinese loess records overall our results indicate that numerous rapid changes in climate occurred in china during the last glacial cycle but that the range of climate variations was smaller than recorded in greenland

climatic changes since the last deglaciation inferred from a lacustrine sedimentary sequence in the eastern nanling mountains south china two sediment cores recovered from dahu swamp which is located in eastern nanling mountains in south china were selected for investigation of palaeoclimatic changes multi proxy records of the two cores including lithological variation organic carbon isotope ratio dry bulk density organic matter content magnetic susceptibility humification degree median grain size and geo chemical proxies reveal that during the last deglaciation three drier phases correspond to the oldest older and younger dryas cooling events and the intercalated two wetter phases synchronise with the bolling and allerod warming events the holocene optimum which was resulted from a strengthen ing of the east asian ea summer monsoon occurred in the early and mid holocene ca 10 6 cal ka bp in the mid and late holocene ca 6 3 cal ka bp a prevailing dry climate suggested a weakening of the ea summer monsoon the general trend of holocene climatic changes in this study agrees with the 258 n summer solar insolation suggesting that orbitally induced insolation may have played an important role in the holocene climate in the study region copyright 2010 john wiley sons ltd

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

holocene climate changes inferred from peat humification a case study from the daiyun mountains southeast china abstract the investigation of two profiles dys1 and dys5 from the daiyun mountains in southeastern china sheds new light on the history of regional climate changes and the variability of the intensity of the east asian summer monsoon easm over the past 10350 years based on the degree of peat humification loss on ignition loi magnetic susceptibility ms and geochemical rb zr and zr rb data the records indicate that three main climatic regimes have occurred over the past 10350 years 1 relatively warm and wet conditions from 10350 to 8800 cal bp 2 a warmer and wetter climate from 8800 to 3000 cal bp that was interrupted by four cold episodes at 7500 6400 5400 and 4400 cal bp and 3 a dry and cool climate after 3000 cal bp these climatic changes were probably associated with a weak easm which was related to the latitudinal movement of the intertropical convergence zone itcz other important influences include solar radiation etc

evidence for magma mixing within the laacher see magma chamber east eifel germany abstract the final pyroclastic products of the late quaternary phonolitic laacher see volcano east eifel w germany range from feldspar rich gray phonolite to dark olivine bearing rocks with variable amounts of feldspar and al augite megacrysts petrographically and chemically homogeneous clasts occur along with composite lapilli spanning the compositional range from phonolite mgo 0 9 to mafic hybrid rock mgo 7 0 for all major and trace elements both a basanitic and a phonolitic phenocryst paragenesis occur within individual clasts the phonolite derived phenocrysts are characterized by glass inclusions of evolved composition rare inverse zoning and strong resorption indicating disequilibrium with the mafic hybrid matrix basanitic magnesian clinopyroxene and olivine in contrast show skeletal normally zoned overgrowths indicative of post mixing crystallization in accord with petrographical and other chemical evidence mass balance calculations suggest mixing of an evolved laacher see phonolite containing variable amounts of mineral cumulates and a megacryst bearing basanite magma magma mixing occurred just prior to eruption hours of the lowermost magma layer of the laacher see magma chamber but did not trigger the volcanic activity

palaeoclimatic changes deduced from 13c 12c and c n ratios of karewa lake sediments india most long palaeoclimatic records based on isotope studies have come from deep sea cores however in order to obtain information on regional climatic variations it is essential to study continental deposits the chief limitation has been the lack of well preserved datable geological records with the exception of cave formations we report here values for the stable carbon isotope ratio 13c 12c and the elemental carbon to nitrogen c n ratio of the organic fraction of the palaeomagnetically and radiometrically dated pleistocene karewa lake sediments from kashmir india together the two ratios which are anticorrelated provide an excellent marker of the source of organic matter in the lake the karewa sediments indicate at least three major episodes of shallower than normal levels these episodes of shallow lake levels and hence a cold dry climatic regime are broadly correctable with deep sea records

history of moisture change indicated by aeolian deposit in the horqin sandy land northeastern china since the last glacial maximum abstract the horqin sandy land located in the monsoonal boundary of northeastern china is sensitive to the vicissitudes of the asian monsoon am the aeolian sand paleosol sequences in this area especially since the last glacial maximum lgm have preserved valuable geological archives indicating the history of humidity changes in the region however existing studies on the local humidity rhythms have not been sufficient to reach a consensus in a relatively in depth study of the forcing mechanism we present the results of a systematic optically stimulated luminescence osl chronology and detailed multi proxy analyses of the grain size geochemical elements magnetic susceptibility and organic matter since the lgm the results demonstrate that the humidity gradually increased from the lgm to the middle holocene reaching optimum humidity around 9 3 ka despite intense oscillations occurring during 6 5 ka that is largely consistent with other paleoenvironmental records from ne china it is suggested that the variation in the humidity is basically controlled by the solar driven monsoonal precipitation which is the most dominant moisture source the coupled atmosphere pacific ocean system and the westerlies could have both disturbed the monsoon precipitation thus indirectly affecting the humidity of the sandy land during the late holocene human occupation also played a significant role in the re activation of dunes

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

sediment geochemistry of dahu swamp in the nanling mountains south china implication for catchment weathering during the last 16 000 years this study emphasizes to testify the potential of geochemical proxies of lacustrine sediments as indicative of past climatic changes since the last deglaciation over the catchment of a small closed lake in south china based on the study on the core k02 from dahu swamp a small lake in the eastern nanling mountains we inferred that chemical features of clastic materials which were mainly derived from the granite weathering crust and transported by surface runoff into this lake possibly had played an important role in affecting chemical characteristics of the sediments wetter climatic conditions would lead to stronger chemical weathering intensity cwi resulting in more soluble and mobile elements being easily leached downward in granite weathering crusts and the insoluble ones being enriched in the top materials of the weathering crusts in contrast dry conditions would exert a converse influence although this study presents a different climatic implication of geochemistry from lacustrine sediments in south china from that in north central china the results demonstrate that chemical elements of sediments in the small lake in south china can be utilized to reflect the cwi which was closely in association with variations in temperature and precipitation in the lake catchment

normalized behavior of offshore clay under uniform cyclic loading a method for characterization of normally consolidated and overconsolidated clay subjected to undrained constant shear strain amplitude cyclic loading is presented and verified the method is based

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

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

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

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

synchronous tropical south china sea sst change and greenland warming during deglaciation the tropical ocean plays a major role in global climate it is therefore crucial to establish the precise phase between tropical and high latitude climate variability during past abrupt climate events in order to gain insight into the mechanisms of global climate change here we present alkenone sea surface temperature sst records from the tropical south china sea that show an abrupt temperature increase of at least 1 c at the end of the last glacial period within the recognized dating uncertainties this sst increase is synchronous with the bolling warming observed at 14 6 thousand years ago in the greenland ice sheet project 2 ice core

evidence for wetter climate recorded in the jingxian red clay section since approximately 840 ka ago and its relationship with the east asian summer monsoon intensity abstract the quaternary red clay qrc is one of the typical terrestrial sediments in southern china which contains abundant palaeoclimatic information a natural qrc outcrop named the jingxian red clay section jrcs was developed in jingxian city on the northern piedmont of mt huangshan offering a valuable archive for long term palaeoclimatic study from a southern china perspective the objective of this study is to reveal palaeoclimatic information of regional precipitation from the jrcs and its correlation with the east asian summer monsoon easm intensity using grain size measurements combined with dating via electron spin resonance esr and palaeomagnetism the results indicate that 1 ten palaeoclimatic wetter periods pwps designated as pwpi to pwpx from top to bottom were detected from the grain size analysis results of the upper 9 4 m jrcs these pwps span a period from approximately 840 ka ago to present 2 three pwps pwpviii to pwpx were basically determined to approximately 612 690 720 762 and 792 822 ka ago basically corresponding to china loess layers of l6 l7 and l8 and deep sea isotope stages of mis16 mis18 and mis20 respectively data suggests that the pwps in the study area were observed mainly during glaciations 3 regional precipitation in the study area should be negatively related to the easm intensity since approximately 840 ka ago as a result of variations in north hemisphere solar insolation and uplifts of the tibetan plateau 4 the modern anti phase of monsoonal rainfall at glacial interglacial timescales seemed to have existed between northern china and southern china since the late early pleistocene approximately 840 ka ago

composition gaps critical crystallinity and fractional crystallization in orogenic calc alkaline magmatic systems the recognition of a three way correlation between magmatic sio2 content critical crystallinity and the size magnitude of crystal fractionation generated composition gaps in calc alkaline magmatic systems suggests an important control of magmatic critical crystallinity on the formation of such composition gaps to explain this correlation it is proposed that fractionation generated composition gaps are caused by 1 simultaneous interior i e non substrate crystallization and vigorous chamberwide convection which leads to progessive crystal suspension 2 cessation of convection when the percentage of suspended crystals reaches the critical crystallinity of the magma and 3 eventual buoyancy driven crystal liquid segregation producing a discrete body of fractionated magma which is separated from the initial magma by a composition gap this mechanism implies that many if not most magma bodies are characterized by interior crystallization and vigorous convection conditions which are not universally agreed upon at present given that such conditions characterize natural magma bodies fractional crystallization through crystal settling in low velocity boundary layers should be an important mechanism of fractional crystallization in a crystallizing and convecting body of magma composition gap formation should represent one endmember of a complete spectrum of possible evolutionary paths governed by the relative rates of crystal settling and crystal retention as a given volcanic plumbing system matures with time average settling retention ratios within individual magma bodies should increase due to higher average wall rock temperatures it follows that within a given volcanic center early stage volcanism should be more likely to display fractionation generated composition gaps than later stage volcanism such a temporal evolution has been documented at at least two aleutian calc alkaline volcanic centers

timing duration and transitions of the last interglacial asian monsoon thorium 230 ages and oxygen isotope ratios of stalagmites from dongge cave china characterize the asian monsoon and low latitude precipitation over the past 160 000 years numerous abrupt changes in 18o 16o values result from changes in tropical and subtropical precipitation driven by insolation and millennial scale circulation shifts the last interglacial monsoon lasted 9 7 1 1 thousand years beginning with an abrupt less than 200 years drop in 18o 16o values 129 3 0 9 thousand years ago and ending with an abrupt less than 300 years rise in 18o 16o values 119 6 0 6 thousand years ago the start coincides with insolation rise and measures of full interglacial conditions indicating that insolation triggered the final rise to full interglacial conditions

mass balance calculations with end member compositional variability applications to petrologic problems although end member compositional variability is quite common most quantitative mass balance procedures cannot accommodate this variability in a systematic manner by rearranging the traditional mass balance relations a series of equations can be derived to account for such heterogeneity while this approach can be applied ton component systems the results are difficult to represent graphically accordingly the procedure is most useful for two and three component systems for two components the concentration of an element in a mixture is cpm chmx 1 1x c1 and the isotopic signature is epmc pm ehmc hmx 1 1x e1c 1 where pm hm and 1 refer to parental magma hybrid magma and component 1 respectively x is the proportion of parental magma c is concentration is isotopic ratio and c the concentration of the denominator isotope in the particular isotopic ratio of interest these equations describe straight lines termed isoproportional or ip lines of fixed mixing proportion in the cpm c1 concentration or epmc pm e1c 1 planes only those ip lines intersecting the rectangle defined by observed end member compositions represent viable mixing proportions for three component systems the mass balance equations are y chm c2 x cpm c2 c1 c2 and y c hmehm c 2e2 x c pmepm c 2e2 c 1e1 c 2e2 where y is now the proportion of component 1 and the proportion of component 2 z is simply 1 x y using major trace and rare earth element as well as isotopic data a region of the x y plane representing possible mixing combinations can be defined due to the compositional variability of most magmatic end members this new mass balance procedure should be applicable to a diverse range of petrologic problems this procedure has been applied to three different petrologic processes aleutian parental magma genesis assimilation contamination and crust mantle differentiation