evolution of the indian summer monsoon and terrestrial vegetation in the bengal region during the past 18 ka the indian summer monsoon ism is a major global climatic phenomenon long term precipitation proxy records of the ism however are often fragmented and discontinuous impeding an estimation of the magnitude of precipitation variability from the last glacial to the present to improve our understanding of past ism variability we provide a continuous reconstructed record of precipitation and continental vegetation changes from the lower ganges brahmaputra meghna catchment and the indo burman ranges over the last 18 000 years 18 ka the records derive from a marine sediment core from the northern bay of bengal nbob and are complemented by numerical model results of spatial moisture transport and precipitation distribution over the bengal region the isotopic composition of terrestrial plant waxes dd and d13c of n alkanes are compared to results from an isotope enabled general atmospheric circulation model isocam for selected time slices pre industrial mid holocene and heinrich stadial 1 comparison of proxy and model results indicate that past changes in the dd of precipitation and plant waxes were mainly driven by the amount effect and strongly influenced by ism rainfall maximum precipitation is detected for the early holocene climatic optimum ehco 10 5 6 ka bp whereas minimum precipitation occurred during the heinrich stadial 1 hs1 16 9 15 4 ka bp the isocam model results support the hypothesis of a constant moisture source i e the nbob throughout the study period relative to the pre industrial period the model reconstructions show 20 more rain during the mid holocene 6 ka bp and 20 less rain during the heinrich stadial 1 hs1 respectively a shift from c4 plant dominated ecosystems during the glacial to subsequent c3 c4 mixed ones during the interglacial took place vegetation changes were predominantly driven by precipitation variability as evidenced by the significant correlation between the dd and d13c alkane records when compared to other records across the ism domain precipitation and vegetation changes inferred from our records and the numerical model results provide evidence for a coherent regional variability of the ism from the last glacial to the present

palaeo moisture evolution in monsoonal central asia during the last 50 000 years abstract the late quaternary climate history of monsoonal central asia was inferred from 75 palaeoclimatic records which provide information about moisture conditions in the last 50 ka or part of this period wet conditions occurred during middle and late marine isotope stage 3 while the last glacial maximum lgm was characterized by dry climate conditions in the region a stepwise climate amelioration is suggested by the climate records following the lgm several climate signals of this period which were reported from high latitude ice core records are preserved in archives from monsoonal central asia as well during the early holocene high effective moisture was inferred from most records from the area dominated by the indian monsoon e g the tibetan plateau suggesting that holocene optimal climate conditions occurred there during this period in contrast areas which are dominated by the south east asian monsoon se monsoon and the westerlies in north western and north central china mongolia do not uniformly show an early holocene climate optimum for this area optimal conditions prevailed during the mid holocene these apparent contradictions can possibly be explained by the regional uplift and descent of air masses in the holocene during the early holocene strengthened insolation possibly caused an enhanced low level convergence over the tibetan plateau which led to the intensification of the summer monsoon the strong air uplift caused intensified precipitation and air divergence in the upper troposphere over the tibetan plateau the areas adjacent to the north therefore experienced an intensified descent of air masses and consequently increased aridity the majority of the palaeoclimatic records suggest reduced effective moisture since the late holocene in the region

striding athabasca mylonite zone complex archean deep crustal deformation in the east athabasca mylonite triangle northern saskatchewan the geophysically defined snowbird tectonic zone is manifested in northernmost saskatchewan as a deep crustal multistage mylonitic structure the east athabasca mylonite triangle the triangle located at the northeastern apex of a stiff crustal scale lozenge is composed of mid archean annealed mylonites and late archean ribbon mylonites formed during two granulite facies events 850 1000 c 1 0 gpa the flow pattern in the mylonites is geometrically and kinematically complex and corresponds to that expected adjacent to the apex of a stiff elliptical volume subjected to subhorizontal regional extension parallel to its principal axis the late archean mylonites are divided into an upper structural deck entirely occupied by a dip slip shear zone and an underlying lower deck the latter is divided into two upright conjugate strike slip shear zones separated by a low strain septum which deformed by progressive coaxial flow the flow pattern in the mid archean mylonites is compatible with that of

biomarkers as proxies for plant inputs to peats an example from a sub boreal ombrotrophic bog lipid distributions in modern peat forming plants were determined and compared to biomarkers recovered from a ca 2800 year old peat deposited in a dutch ombrotrophic bog the peat section spans a well constrained shift in local hydrology and vegetation and potential molecular proxies for plant inputs were directly tested against the macrofossil record based on the analyses of modern plants low molecular weight lmw n alkanes c23 c25 and high molecular weight n alkanes c33 are proposed as potential biomarkers for sphagnum and non sphagnum inputs respectively consistent with this in the bargerveen peat core lmw n alkane abundances increase and hmw n alkane abundances decrease coincident with the shift to sphagnum dominated peat additional potential proxies include the abundances of c22 alkanedioic acid and phytenyl phytenoate as sphagnum indicators and the abundances of the triterpenoids taraxer 14 ene and taraxast 20 ene as biomarkers for ericaceae rootlets

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

development and refinement of proxy climate indicators from peats peat especially from acidic mires bogs is a natural archive of past environmental change reconstructions of past climate from bogs commenced in the 19th century through examination of visible peat stratigraphy and later formed the basis for a postglacial climatic scheme widely used in northwest europe nevertheless misconceptions as to how bogs grow led to a 50 year lacuna in peat climate study before the concept of cyclic regeneration in bogs was refuted in recent decades research using proxy climate indicators from bogs has burgeoned a range of proxies for past hydrological change has been developed as well as use of pollen bog oaks and pines and other data to reconstruct past temperatures most of this proxy climate research has been carried out in northern europe but peat based research in parts of asia and north america has increased particularly during the last decade while research has also been conducted in australia new zealand and south america this paper reviews developments in proxy climate reconstructions from peatlands chronicles use of a range of palaeo proxies such as visible peat stratigraphy plant macrofossils peat humification testate amoebae and non pollen palynomorphs and explains the use of wiggle match radiocarbon dating and relationship to climate shifts it details other techniques being used increasingly such as biomarkers stable isotopes inorganic geochemistry and estimation of dust flux and points to new proxies under development although explicit protocols have been developed recently for research on ombrotrophic mires it must be recognised that not all proxies and techniques have universal applicability owing to differences in species assemblages mire formation topographic controls and geochemical characteristics

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

paleoenvironmental implications of molecular and carbon isotopic distributions of n alkanes in the hominoid bearing upper miocene sediments from the zhaotong basin southwestern china abstract it is crucial to understand the relationship between hominoid primates and their living environment located at the southeastern margin of the tibetan plateau the shuitangba stb outcrop from the zhaotong basin is famous for bearing the remains of the youngest known ape fossil in the terminal miocene 6 2 ma in this study the molecular and carbon isotope compositions of n alkanes together with the loss on ignition and the bulk carbon isotope composition of total organic matter were investigated in the stb outcrop to infer the paleoenvironmental conditions in this uppermost miocene sedimentary sequence with the emphasis on the habitat of the stb hominoid in the hominoid bearing peaty clay layer and the surrounding lignite layers the n alkane molecular and carbon isotope compositions support a primary contribution from terrestrial higher plants in contrast n alkanes in the upper shallow lake sediments are derived from multiple origins mainly from aquatic plants and bacteria both carbon preference index cpi and average chain length acl vary closely with the lithology but the cpi record shows the larger amplitude of change than the acl and varies sharply during the lithological boundary it is notable that the changes of the molecular and carbon isotope compositions of long chain n alkanes do not parallel with the abrupt increase of poaceae pollen percentage during the stb hominoid appearing stage such an inconsistency between herb pollen percentage and n alkane ratios may result from the different sources our results clearly support that these organic matter based ratios have the potential to record the paleoenvironmental changes in ancient lacustrine sediments

tectonic entrapment and its role in the evolution of continental lithosphere an example from the precambrian of western canada new geophysical data acquired over the buried crystalline basement of western canada provide constraints on the history of tectonic assembly of the western canadian shield in the interval 1 75 1 85 ga specifically these data provide new perspectives on the evolution of an archean continental fragment heame province that was trapped in a tectonic vise between coeval orogenic belts that dipped beneath the hearne province the trans hudson orogen developed along the southeastern margin of the hearne province as a series of ocean floor oceanic arc and arc marginal basins were telescoped and thrust obliquely beneath the hearne along the northwest edge of the hearne collapse and subduction of a narrow marginal basin now marked by the subsurface extension of the snowbird tectonic zone led to formation of magmatic arc and collision of older proterozoic terranes the hearne province itself is characterized by regional granulite grade metamorphism and evidence of extensive and pervasive partial melting of the crust the internal character of the hearne province seen on crustal seismic reflection profiles is that of a crustal scale structural fan with reflection fabrics that verge toward the bounding orogens the deformation of the hearne is predominantly of paleoproterozoic age and constitutes a thorough reworking of this formerly archean crustal domain over a distance of more than 600 km across strike entrapment and thermal weakening of the hearne resulted from mechanical coupling of inferred buoyant subduction collision zones and removal of or modification of archean lithospheric mantle that may have originally formed the keel to the hearne long period magnetotelluric profiles show that anomalously conductive mantle lithosphere underlies the present day hearne province which is attributed to metasomatic modification of the subcontinental lithosphere following collisional thickening and delamination convective removal of thickened lithosphere in the proterozoic tectonic entrapment as illustrated by the proterozoic structural and thermal evolution of the hearne province crust and subcontinental mantle may be an example of the lithospheric consequences of opposing collisional polarity during assembly of continents

geochronological constraints on the legs lake shear zone with implications for regional exhumation of lower continental crust western churchill province canadian shield the legs lake shear zone marks the southeastern boundary of an extensive region 20 000 km2 of high pressure 0 8 1 5 gpa granulite facies rocks in the western churchill province canada the shear zone is one of the largest exhumation related structures in the canadian shield and coincides with the central segment of the 2 800 km long snowbird tectonic zone the movement history of this shear zone is critical for the development of models for the exhumation history of the high pressure region we used electron microprobe u th pb dating of monazite with supplemental id tims u pb geochronology to place constraints on the timing of shear zone activity combining these and other data we suggest that regional exhumation occurred during at least three distinct phases over an 150 million year period the first phase involved high temperature decompression from 1 0 to 0 8 0 7 gpa shortly following 1 9 ga peak metamorphism possibly under an extensional regime the second phase involved rock uplift and decompression of the hanging wall to 0 5 0 4 gpa during east vergent thrusting across the legs lake shear zone at ca 1 85 ga this phase was likely driven by early collision related convergence in the trans hudson orogen the final phase of regional exhumation involving the removal of 15 20 km of overburden from both footwall and hanging wall likely occurred after 1 78 ga and may have been related to regional extensional faulting

paleoclimate influence on early diagenesis of plant triterpenes in the dajiuhu peatland central china abstract aromatic derivatives of vascular plant triterpenoids are common in recent and ancient sediments coal and petroleum understanding their early diagenetic alterations and their relation with environmental conditions can facilitate their applications in paleoenvironmental reconstructions here we present a high resolution record of aromatic triterpenes in a holocene peat core collected in the dajiuhu peatland central china these aromatic triterpenes are derivatives of plant triterpenoids with oleanane ursane and lupane carbon skeletons and exist in three different structural groups aromatic des a triterpenes aromatic pentacyclic triterpenes and c ring cleaved aromatic triterpenes such a high diversity of aromatic triterpenes in a young peat deposit is compelling evidence for rapid microbial mediation of these important degradation pathways during very early diagenesis of particular importance is the occurrence of c ring cleaved aromatic triterpene and aromatic des a triterpenes in the dajiuhu peat samples which until now have not been identified in recent sediments the downcore profile shows that the microbial aromatization process of oleanoids positively correlates with paleoclimate change during dry or warm intervals highly aromatized products such as tetraaromatic triterpenes become predominant over their triaromatic homologs in contrast triaromatic triterpenes become dominant during wet or cold intervals in addition this study provides further evidence to support that the climate pattern in the middle reaches of the yangtze river is different from that in north china during 13 9 4 ka these findings suggest that aromatic triterpenes can be valuable tools for holocene paleoenvironmental reconstructions

impact of early diagenesis on distributions of sphagnum n alkanes in peatlands of the monsoon region of china abstract sphagnum species are important peat forming plants in wetlands the world over their n alkane distributions are typically characterized by a predominance of mid chain c 23 and c 25 alkanes a property that has been employed in paleoclimatic reconstruction based on peat sequences however knowledge of the fate of sphagnum derived n alkanes during the very early stage of diagenesis remains limited this study compares the n alkane differences between samples of fresh plants and litter collected from four peatlands across the monsoon region of china the results clearly show that the distributions of sphagnum derived n alkanes differ between the plants and the litter with proportional decreases in c 23 and c 25 n alkanes and increases in c 29 and c 31 homologs in the litter other than the influence of species shifts changes in the n alkane distributions between the fresh plants and litter samples may be caused by preferential degradation of mid chain n alkanes c 23 and c 25 relative to their longer chain homologues c 29 and c 31 during the early diagenesis of sphagnum n alkanes this hypothesis is supported by decreases in cpi values and positive excursions of 13 c values of c 23 and c 29 n alkanes from the plant to the litter samples regardless of what the exact mechanisms for the changes may be the p aq ratio should be applied with caution as a paleoclimatic proxy in peat deposits especially those located in warmer climates or deposited during former warmer stages relatively low p aq values may result from elevated microbial degradation of sphagnum alkanes in such conditions and hence fail to record the former plant assemblages accurately

geochronological constraints on metamorphism magmatism and exhumation of deep crustal rocks of the kramanituar complex with implications for the paleoproterozoic evolution of the archean western churchill province canada u pb and sm nd geochronology establishes an important paleoproterozoic 1 9 ga history for the kramanituar complex located in the interior of the archean western churchill province and provides further insight into the snowbird tectonic zone a crustal scale 2000 km feature whose role during precambrian time remains controversial the kramanituar complex is a window of deep crustal rocks dominated by a granulite facies metagabbroic suite of 1902 ma age with minor supracrustal rocks and charnockite these yield peak equilibrium conditions of 12 15 kbar and 850 900 c which are bracketed between 1910 ma the age of prograde metamorphic monazite in sillimanite and kyanite bearing paragneiss and 1901 ma the cooling ages of titanite and rutile in gabbroic and paragneissic rocks although mineral assemblages reflecting peak metamorphic conditions are widespread some rocks record near isothermal decompression to 8 kbar and 800 c the timing of uplift and exhumation is tightly bracketed between magmatic crystallization of gabbroic anorthosite under granulite facies conditions at 1902 ma and widespread rutile cooling ages of 1901 ma time averaged cooling rates of 100 c ma are estimated for gabbroic anorthosite and leucogranite rocks surrounding the kramanituar complex are mainly amphibolite facies archean plutonic and supracrustal rocks those to the north were at deep crustal conditions coeval with the complex whereas those to the south appear to preserve a record of older mainly neoarchean tectonometamorphic assemblages and fabrics the southern boundary of the complex is inferred to be a normal fault that accommodated tectonic unroofing of the kramanituar complex at 1 9 ga this geochronological data set highlights the protracted history of a segment of the geophysically defined snowbird tectonic zone a structure along which latest significant magmatism and tectonometamorphism has been interpreted as either 2600 or 1800 ma penetrative 1900 ma activity in the east trending chesterfield segment as documented at the kramanituar complex suggests that the complex may have represented a favorably oriented segment of a crustal scale archean fault that was reactivated during paleoproterozoic time possibly in response to collision between the slave and churchill cratons thelon orogen at 1 97 1 9 ga

different altitude effect of leaf wax n alkane δd values in surface soils along two vapor transport pathways southeastern tibetan plateau abstract here we present 76 hydrogen isotope values for leaf wax derived n alkanes d wax being the abundance weighted average d values of c 29 and c 31 n alkanes in surface soils along two vapor transport pathway transects running across the southeastern tibetan plateau tp the first is the south himalayan sh transect with an altitude range of 1660 5050 m above sea level and representing the southern himalayan air mass and the second a combination of the zayu bomi zb altitude 1468 4800 m and bayi lhasa bl altitude 3050 4970 m transects together representing the brahmaputra yarlung zangbo river valley air mass d wax values and their relation to altitude did exhibit some variability nonetheless altitude was the predominant factor in determining soil d wax values with a lapse rate of 2 2 100 m r 2 0 78 n 76 based on overall soil d wax values despite changes in precipitation amount relative humidity rh and vegetation type furthermore our e wax rw values the isotopic fractionation between the d wax and d values of river water d rw remained approximately constant at 104 5 ranging between 99 and 110 confirming that the relation between altitude and isotopic hydrology river water and precipitation controls the n alkane d wax altitudinal gradients for all of the sample localities in the southern himalaya sh and the southern tp this endorses the efficacy of using d wax to reconstruct paleoelevation along the sh transect soil d wax values varied from 151 to 264 with an altitudinal lapse rate of 2 4 100 m r 2 0 84 n 32 this was due to the significant change in altitude over short distances along the zb transect soil d wax values varied from 174 to 263 with a lower lapse rate of 1 9 100 m r 2 0 68 n 29 the altitudinal lapse rate was 3 3 100 m above 3000 m r 2 0 63 n 19 and 1 35 100 m below 3000 m r 2 0 64 n 10 in the lower sub transect the latitudinal effect significantly counteracted the altitude effect along the bl transect soil d wax values varied from 205 to 244 with an altitudinal lapse rate of 1 4 100 m r 2 0 74 n 15 the lower lapse rate for soil d wax reflects a combination of local continental and altitudinal effects the differences we observed in soil d wax altitudinal lapse rates along the two vapor transport pathways imply that they are affected by subtle local environmental conditions moisture sources latitude and topography this should be considered fully during any reconstruction of paleoelevation

crustal evolution and age of thermotectonic reworking in the western hinterland of the trans hudson orogen northern saskatchewan abstract the hearne province in northern saskatchewan forms the western hinterland of the trans hudson orogen it is a fault bounded terrane lying structurally and geographically between the rae province to its west and the wathaman batholith and orogenic internides to its east the hearne province is comprised primarily of high grade metamorphic archean rocks structurally overlain by archean or proterozoic metasedimentary rocks and intruded by paleoproterozoic granites whereas the rae terrane on its west boundary is comprised primarily of still higher grade archean rocks the calc alkaline wathaman batholith was intruded at ca 1 855 ga and the orogenic internides to the east of it include mostly high grade mafic and intermediate volcanic rocks crystallized between 1 92 and 1 86 ga terminal collision and orogenesis in the internides have been constrained to be later than 1 82 ga and earlier than 1 78 ga mineral u pb data presented here unequivocally demonstrate that high grade metamorphism and large volume anatexis across the southern hearne province were approximately synchronous with terminal collision and high grade metamorphism across the trans hudson orogen zircon data for most samples form complex arrays in concordia space but demonstrate a high grade metamorphic overprint at 1810 1800 ma zircons typically have inherited components of archean age suggesting the presence of extremely old material in the hearne and a potential archean connection with the rae province sm nd data indicating ca 3500 ma model ages for similar parageneses in both terranes further support the proposed archean connection between hearne and rae province and the great antiquity of hearne crust sm nd data also elucidate the similarity of the ca 1 80 ga anatectic granites of the hearne to the 1 82 ga junction granite which intruded the virgin river shear zone and constrains the timing of final motion on that structure monazite 207 pb 206 pb ages are not older than 1812 ma or younger than 1769 ma and rutile 207 pb 206 pb ages and u pb ages are tightly constrained at about 1750 ma these data in combination with results of standard thermobarometric analysis permit determination of post orogenic cooling and denudation rates high cooling 7 c ma and denudation 240 m ma rates suggest fault accomodated uplift during post orogenic collapse

quaternary ecological responses and impacts of the indian ocean summer monsoon at nam co southern tibetan plateau the transition from the last glacial to the current interglacial the holocene represents an important period with climatic and environmental changes impacting ecosystems in this study we examined the interplay between the indian ocean summer monsoon iosm and the westerlies at lake nam co southern tibet to understand the climatic effects on the ecosystem different organic geochemical proxies n alkanes glycerol dialkyl glycerol tetraethers d 13corg 15n are applied to reconstruct the environmental and hydrological changes on one of the longest available paleorecords at the tibetan plateau based on our paleohydrological d proxies the aquatic signal lags the terrestrial one due to specific ecological thresholds which in addition to climatic changes can influence aquatic organisms the aquatic organisms response strongly depends on temperature and associated lake size as well as ph and nutrient availability because the terrestrial vegetation reacts faster and more sensitively to changes in the monsoonal and climatic system the d of n c29 and the reconstructed inflow water signal represent an appropriate iosm proxy in general the interplay of the different air masses seems to be primarily controlled by solar insolation in the holocene the high insolation generates a large land ocean pressure gradient associated with strong monsoonal winds and the strongest iosm in the last glacial period however the weak insolation promoted the westerlies thereby increasing their influence at the tibetan plateau our results help to elucidate the variable iosm and they illustrate a remarkable shift in the lake system regarding ph 13corg and 15n from the last glacial to the holocene interglacial period

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

hydrogen isotope ratios of terrestrial leaf wax n alkanes from the tibetan plateau controls on apparent enrichment factors effect of vapor sources and implication for altimetry abstract empirical evidence suggested that the altitudinal dependence of hydrogen isotope ratios of leaf wax n alkanes d wax can be used to estimate paleoaltitudinal changes however the application of d wax based paleoaltimetry remains difficult as the impacts of evaporative transpirative and biosynthetic processes on hydrogen isotope fractionations in changing environments and the influence of likely changing water vapor sources are not well explored for this study we sampled stream waters soils and plant leaves along two transects spanning large gradients of altitude precipitation amount vapor source temperature and vegetation type on the tibetan plateau tp d values of stream water as an approximation for d p soil water d sw and plant leaf water d lw as well as leaf wax n alkanes were measured in order to quantify isotopic fractionations in the formation of leaf waxes most interestingly we found a strong negative correlation between the evapotranspirative enrichment of leaf water against precipitation e lw p which combines the effects of soil evaporation and leaf transpiration and the biosynthetic hydrogen isotope fractionation e wax lw which describes isotopic enrichment between leaf wax and leaf water the relationship yields a steady apparent isotopic enrichment factor e wax p between leaf wax and precipitation which is independent from climatic parameters and has an average value of 107 26 for grasses monocotyledons and 77 22 for trees dicotyledons since the terrestrial n alkanes especially n c 27 and n c 29 in sediments are derived from trees and grasses the likely change of the vegetation type in the uplift of mountains can change the isotopic estimates by about 30 which corresponds to an altitudinal change of 1600 m we therefore suggest that hydrogen isotope ratio of sedimentary n c 31 alkane which is mainly derived from grasses might be better proxies to reconstruct paleoaltitudes our large dataset of d wax from trees and grasses that aimed to mirror the variability of environmental factors over geological time frames showed the lapse rates were significant but much smaller than in previous studies most importantly our result demonstrated that the lapse rate significantly differed for both transects p 0 0068 i e 0 87 0 71 100 m r 2 0 28 p 0 2841 n 6 and 2 28 0 82 100 m r 2 0 34 p 0 0135 n 17 for indian monsoon and westerly dominated areas respectively this suggests that different moisture sources might strongly affected the observed lapse rates in consequences altitude reconstructions are strongly complicated in areas with likely changing air masses like the tibetan plateau

soil n alkane δd vs altitude gradients along mount gongga china the altitude effect on the isotopic composition of precipitation and its application to paleoelevation reconstruction using authigenic or pedogenic minerals have been intensively studied however there are still no studies on variations in biomarker d along altitude transects to investigate its potential as a paleoelevation indicator although it has been observed that d of higher plant lipid may record changes in precipitation d dp here we present d values of higher plant derived c27 c29 and c31n alkanes from surface soil along the eastern slope of mount gongga china with great changes in physical variables and vegetation over a range from 1000 to 4000 m above sea level the weighted mean d values of these n alkanes dwax show significant linear correlations with predicted dp values r2 0 76 with an apparent isotopic enrichment ewax p of 137 9 indicating that soil dwax values track overall dp variation along the entire altitudinal transect leaf dwax is also highly correlated with mountain altitude by a significant quadratic relationship r2 0 80 evapotranspiration is found declining with altitude potentially lowering dwax values at higher elevations however this evapotranspiration effect is believed to be largely compensated by the opposing effect of vegetation changes resulting in less varied ewax p values over the slope transect this study therefore confirms the potential of using leaf dwax to infer paleoelevations and more generally to infer the d of precipitation

hydroclimatic variability in loess δd wax records from the central chinese loess plateau over the past 250 ka abstract this study reports hydrogen isotopic records from the central chinese loess plateau clp over the past 250 ka after eliminating the influence of ice and local temperatures the dwax records extracted from two loess sites at xifeng and luochuan can be taken to represent arid humid alternations in the hydrological environment in this marginal asian summer monsoon asm region they also contain integrated information on summer precipitation patterns and the corresponding responses to these changes by predominant vegetation cover types these arid humid alternations show 100 ka 40 ka and 20 ka cycles an increase in precipitation in association with an enhanced summer monsoon has historically been taken to be the major factor driving a humid environment in the central clp however hydroclimatic changes in dwax records differ for the central clp central china and southern china over a 20 ka cycle the influence of solar insolation on hydroclimatic changes can be shown to be consistent throughout the central clp however changes in the relative location of the land and sea may have caused different hydroclimatic responses between southern china and the central clp on a glacial interglacial scale the hydroclimatic variability in the central clp would suggest that an enhanced summer monsoon due to climatic warming is the key to understanding decreased drought degree in this marginal monsoonal region

multistage exhumation and juxtaposition of lower continental crust in the western canadian shield linking high resolution u pb and 40ar 39ar thermochronometry with pressure temperature deformation paths 1 new u pb titanite apatite rutile and 40ar 39ar hornblende muscovite biotite data are linked with existing pressure temperature deformation paths to impose detailed temporal constraints on the juxtaposition and unroofing of domains in an extensive 20 000 km2 region of exhumed lower crust in the east lake athabasca region of the western canadian shield in the 200 m y between circa 1 9 ga high pressure granulite facies metamorphism and circa 1 7 ga unconformable deposition of athabasca basin sediments on the exhumed rocks our analysis reveals at least three distinct phases of unroofing at different rates specifically we distinguish 1 an early phase of extensional unroofing in the chipman domain at rates of 1 5 2 0 km m y from 1 0 gpa to 0 8 gpa associated with mafic magmatism and metamorphism 2 an episode of regional contractional uplift and associated unroofing along the legs lake shear zone at circa 1850 ma from 0 7 0 8 gpa to 0 4 0 5 gpa and 3 a final period of extensional unroofing at rates of 0 2 0 3 km m y from 0 4 to 0 5 gpa that culminated in transport of current exposures to near surface conditions the cooling patterns and retrograde assemblages are consistent with pauses between exhumational phases the apparent convergence of disparate higher temperature histories in several deep crustal domains at circa 1 89 1 88 ga implies their juxtaposition at 0 7 0 8 gpa conditions regional east directed thrusting of the deep crustal domains as a coherent unit at 1 85 ga juxtaposed the granulites with middle crustal hearne domain rocks at 0 4 0 5 gpa conditions the detailed exhumational history allows correlation with changing regional tectonic regimes associated with the amalgamation of laurentia the temporal and spatial heterogeneity of exhumation patterns in the east lake athabasca region may be a common feature of the unroofing histories of lower crustal rocks

reconstruction of a large deep crustal terrane implications for the snowbird tectonic zone and early growth of laurentia the 2800 km long snowbird tectonic zone is a well recognized but still enigmatic feature in the western canadian shield it has been interpreted as a paleoproterozoic continental suture or an archean strike slip fault system but here we suggest that the distinctive geometry of the central snowbird tectonic zone is primarily due to the interaction of crosscutting paleoproterozoic intracontinental thrust and strike slip shear zones having a length of hundreds of kilometers first a major zone of thrust sense shearing coeval with early continent continent collision between the superior and western churchill provinces accommodated uplift of a large exposure of granulite facies lower continental crust younger strike slip shear zones perhaps analogous to asian fault systems behind the himalayan orogen offset the thrust zone thus the current geometry and distribution of deep crustal rocks in this region represent a relatively late stage in the tectonic evolution of the western churchill province rather than an accretionary one earlier structures oriented at a high angle to the snowbird tectonic zone may record the fundamental accretionary history in this part of laurentia

asynchronous evolution of the isotopic composition and amount of precipitation in north china during the holocene revealed by a record of compound specific carbon and hydrogen isotopes of long chain n alkanes from an alpine lake both the timing of the maximum east asian summer monsoon easm intensity in monsoonal china and the environmental significance of the chinese stalagmite oxygen isotopic record delta o 18 have been debated here we present a ca 120 year resolution compound specific carbon delta c 13 and hydrogen sd isotopes of terrestrial long chain n alkanes extracted from a well dated sediment core from an alpine lake in north china our delta c 13 data together with previously reported pollen data from a parallel core demonstrate a humid mid holocene from ca 8 5 ka bp assuming that the climatic humidity of north china is an indicator of the easm intensity then the maximum easm intensity occurred in the mid holocene our sd data reveal a similar long term trend to the delta o 18 record from nearby lianhua cave indicating that the synchronous sd and delta o 18 records faithfully record the sd and delta o 18 of precipitation respectively the most negative sd and delta o 18 values occur in t he early mid holocene from ca 11 5 ka bp this contrast in the timing of isotopic variations demonstrates a complex relationship between the isotopic composition of precipitation and precipitation amount or easm intensity further comparisons indicate a possible linkage between the precipitation amount in north china and the west east thermal gradient in the equatorial pacific in addition the temperature of the moisture source area may play an important role in determining the isotopic composition of precipitation in monsoonal china c 2016 elsevier b v all rights reserved

structure of peat soils and implications for water storage flow and solute transport a review update for geochemists abstract global peatlands are a valuable but vulnerable resource they represent a significant carbon and energy reservoir and play major roles in water and biogeochemical cycles peat soils are highly complex porous media with distinct characteristic physical and hydraulic properties pore sizes in undecomposed peat can exceed 5 mm but significant shrinkage occurs during dewatering compression and decomposition reducing pore sizes the structure of peat soil consists of pores that are open and connected dead ended or isolated the resulting dual porosity nature of peat soils affects water flow and solute migration which influence reactive transport processes and biogeochemical functions advective movement of aqueous and colloidal species is restricted to the hydrologically active or mobile fraction of the total porosity i e the open and connected pores peat may attenuate solute migration through molecular diffusion into the closed and dead end pores and for reactive species also through sorption and degradation reactions slow diffusion limited solute exchanges between the mobile and immobile regions may give rise to pore scale chemical gradients and heterogeneous distributions of microbial habitats and activity in peat soils while new information on the diversity and functionalities of peat microbial communities is rapidly accumulating the significance of the geochemical and geomicrobial study on peat stands to benefit from a basic understanding of the physical structure of peat soils in this paper we review the current knowledge of key physical and hydraulic properties related to the structure of globally available peat soils and briefly discuss their implications for water storage flow and the migration of solutes this paper is intended to narrow the gap between the ecohydrological and biogeochemical research communities working on peat soils

lacustrine source rock deposition in response to co evolution of environments and organisms controlled by tectonic subsidence and climate bohai bay basin china three paleogene syn rift intervals from the bohai bay basin the most petroliferous basin in china were analyzed with sedimentological and geochemical techniques to characterize the lateral source rock heterogeneities to reveal the environmental and ecological changes through geologic time and to construct depositional models for lacustrine source rocks under different tectonic and climatic conditions the third es3 and first es1 members of the eocene shahejie formation and the oligocene dongying formation ed display widely variable total organic carbon contents hydrogen indices and visual kerogen compositions suggesting changes in organic facies from deep to marginal sediments carefully selected deep lake facies samples from any interval however display fairly uniform biomarker composition these three intervals have distinctly different biomarker assemblages which indicate weakly alkaline freshwater lakes with a moderately deep thermocline during es3 deposition alkaline saline lakes with shallow chemocline during es1 deposition and acidic freshwater lakes with deep unstable thermocline during the deposition of the dongying formation such environmental changes corresponded to changes in subsidence rate and paleoclimate from rapid subsidence and wet climate during es3 deposition through slow subsidence and arid climate during es1 deposition to rapid subsidence and wet climate during ed deposition and resulted in synchronous changes in terrigenous organic matter input phytoplankton community and primary productivity the co evolution of environments and organisms controlled by tectonic subsidence and climate accounted for the deposition and distribution of high quality lacustrine source rocks with distinctly different geochemical characteristics most rift basins experienced changes in subsidence rates and possibly changes in climates during their syn rift evolutions the models constructed in this paper may have important implications for source rock prediction in other lacustrine rift basins

paleoclimate variability in central taiwan during the past 30 kyrs reflected by pollen δ13ctoc and n alkane δd records in a peat sequence from toushe basin abstract a total of 233 samples from the upper 16 m of the toushe peat core retrieved in central taiwan were measured for toc and 13ctoc values from these samples 17 selected samples with large 13ctoc fluctuations were analyzed for n alkane and d of the c27 and c29 n alkanes combining with the detailed high resolution pollen and geochemical records this study reveals more detailed climatic variations in terms of temperature and precipitation as well as abrupt climatic events during the past 30 kyrs before the last glacial maximum lgm climate was cold and damp with predominantly woodland vegetation in toushe basin and turned to cold and dry after 25 kyr bp climatic conditions there were the worst during lgm over the past 30 kyrs especially around 23 and 18 kyr bp when the woodland was diminished and c4 grass was dominated although short durations of relatively wet conditions could be found at 17 16 and 14 kyr bp cold and dry climates were prevailing during 29 5 28 24 22 17 15 and 13 11 5 kyr bp corresponding to heinrich h events 3 2 1 and younger dryas yd respectively during the early holocene dry climate occurred at 11 10 9 7 9 2 and 8 kyr bp whereas wet condition appeared at 10 3 9 8 9 7 5 kyr bp in the middle holocene climate kept warm and moderate wet in the first half period but many dry events existed in the second half following a cold and dry event at 6 kyr bp after a sharply warm peak at 5 2 kyr bp the climate in toushe turned to cold quickly and tree shrub vegetation disappeared completely with the replacement of c3 grasses in the late holocene climate was relatively wetter with predominant c3 grasses in the basin our climatic interpretations based on the peat records agree well with the greenland ice core and chinese speleothem records on millennium time scales during the last glacial period dry climates corresponding to weakening of the east asian summer monsoon easm during the heinrich events and younger dryas in central taiwan and eastern china demonstrate the climatic forcing on such long time scales in concert with regional monsoon climate however the discrepancies exist between our peat record and the dongge hulu stalagmite record on 1 the age of h2 2 climate intensities of lgm and h1 and 3 wetness condition during holocene these observations call for further study on high resolution climatic changes especially on moisture budget in the east asian monsoonal region

u pb monazite xenotime and titanite geochronological constraints on the prograde to post peak metamorphic thermal history of paleoproterozoic migmatites from the grand canyon arizona the petrology and u pb geochronology of pelitic migmatite and calc silicate gneiss reveal a detailed prograde to post peak metamorphic thermal history for a single outcrop of paleoproterozoic supracrustal rocks in the eastern part of the grand canyon metamorphic monazite from paleosomal pelitic schist grew on the prograde path beginning at about 1708 ma and continued to grow until about 1697 ma the u pb dates for magmatic xenotime and monazite from peraluminous granite and pegmatite leucosomes indicate that partial melting which involved the breakdown of muscovite to sillimanite commenced at about 1702 ma prior to the metamorphic peak partial melting continued until about 1690 ma the youngest u pb date from magmatic monazite in the leucosomes field and petrographic evidence as well as inheritance patterns in monazites from the leucosomes suggest that some of the leucosomes appear to represent in situ partial melts that did not escape the source region between 1702 and 1690 ma the migmatite package heated to peak metamorphic conditions of about 720 c and 6 kbar cooled to about 675 c at a cooling rate 30 c million years and decompressed to about 4 kbar the u pb geochronological data for metamorphic titanite from a calc silicate gneiss exhibit a clear relationship between grain size and the 207pb 206pb date indicating that the titanite crystals record cooling ages these data combined with the titanite pb diffusion data of cherniak 1993 yield a cooling rate of 5 4 0 9 1 7 c million years integrated over the interval 1690 to 1676 ma and suggest that by 1675 ma the cooling rate slowed to less than 2 c million years the rapid decompression during the peak of metamorphism and the change in cooling rate immediately following peak metamorphism are interpreted to reflect large scale tectonic processes associated with the accretion of juvenile crust to the margin of laurentia juvenile arc crust appears to have been assembled accreted and stabilized into laurentian lithosphere in less than 30 million years

investigating the long term palaeoclimatic controls on the δd and δ18o of precipitation during the holocene in the indian and east asian monsoonal regions abstract this paper aims to achieve an improved understanding of the long term change trends of precipitation d and 18 o values d p and 18 o p in the asian monsoonal region and their relationship with the corresponding humidity trends during the holocene to do this we first review the observed modern spatial pattern of summer precipitation distribution in the east asian summer monsoon easm region under different easm intensities and the relationship between modern observed 18 o p values and corresponding precipitation amounts on monthly and inter annual timescales in the easm and indian summer monsoon ism regions second we compare holocene lacustrine and marine compound specific hydrogen isotopic records of n alkanes n alkanoic acid d n lacustrine authigenic carbonate and cave stalagmite oxygen isotopic records 18 o c and 18 o s from the asian monsoonal region all of which are closely related to d p and 18 o p variations the results demonstrate that in both the ism and easm regions all of these isotopic records exhibit roughly similar long term characteristics i e they were all more negative during the early holocene and early mid holocene ca 11 6 ka b p b p means before present present 1950 ad and then became more positive towards the late holocene third we compare representative paleo humidity records from the asian monsoonal region the results confirm that in the ism region a humid interval occurred in the early holocene and early mid holocene ca 11 6 ka b p and subsequently the climate became more arid towards the late holocene this indicates an enhanced ism during the early holocene and early mid holocene ca 11 6 ka b p and an ism of decreasing intensity towards the late holocene on a holocene orbital scale both 18 o p and d p appear to be controlled by an amount effect in the ism region consistent with the region s inter annual modern 18 o p data this evidence indicates that both 18 o p and d p paleo records are significantly related to paleo humidity in the ism region in contrast holocene humidity variations in the easm region exhibit clear spatial differences a humid mid holocene interval ca 8 3 ka b p occurred in southern and northern china but an arid interval from ca 7 3 ka b p occurred in central china in the middle reaches of the yangtze river based on precipitation distribution patterns under different easm intensities in the easm region over the past few decades we conclude that easm intensity was enhanced during the mid holocene ca 8 3 ka b p relative to the ism intensity the response of easm intensity to summer insolation was relatively slow in the easm region the relationship between climate and 18 o p and d p is more complex consistent with analyses of regional inter annual modern 18 o p data this evidence demonstrates that both 18 o p and d p paleo records cannot be used directly as paleo humidity i e precipitation amount or easm intensity indicators in the easm region further comparison and analyses demonstrate that the coupled variations in west east equatorial pacific temperature gradients and the west pacific subtropical high wpsh played an important role in determining easm intensity during the holocene

paleoclimate significance of n alkane molecular distributions and δ2h values in surface peats across the monsoon region of china abstract leaf wax molecular distributions and isotopic values are generally considered paleohydrologic proxies here we evaluate the sensitivity of alkane chain length distributions and compound specific hydrogen isotopic compositions 2halk in surface peats to environmental parameters across the monsoon region of china the alkane average chain length acl carbon predominance index cpi and 2halk values show relatively large variations in multiple samples from a single site highlighting the complexity of the processes affecting these ratios at small spatial scales nonetheless the site averaged cpi values correlate significantly with the mean annual temperature r 0 57 p

a 13 000 year peatland palaeohydrological response to the enso related asian monsoon precipitation changes in the middle yangtze valley abstract quantitative reconstructions of the depth to water table dwt of ombrotrophic rain fed peatlands are important for understanding the palaeohydrological responses of peatlands to past climate changes this understanding can provide insights into projecting peatlands future variability and evolution however the postglacial dwt reconstruction of peatlands in china is challenging due to complications of the atmospheric circulation system the scarcity of hydrological proxies and the site specific nature of hydrological signals here we present a postglacial quantitative dwt reconstruction based on the analysis of fossil phytoliths from the dajiuhu peatland central china the reconstructions were based on a phytolith dwt calibration model using a weighted averaging partial least squares regression analysis of peatland topsoil calibration datasets three shallow dwt wet periods at 13 000 11 500 cal yr bp 9 600 7 500 cal yr bp and 3 000 cal yr bp present and two extended deep dwt dry periods at 11 500 9600 cal yr bp and at 7 500 3 000 cal yr bp are found based on the cluster analysis of phytolith assemblages and reconstructed dwt changes these five documented hydrological periods are consistent with regional precipitation reconstructions from independent records in the middle yangtze valley myv we interpret these changes as mostly reflecting changes in enso at various timescales an amplified enso forced a southward western pacific subtropical high and caused the persistence of the meiyu front in the mid lower yangtze valley consistent with the intense rainfall periods in our study region our results indicate that phytolith records are a reliable and sensitive proxy for the calibration of water table models and the quantitatively palaeo dwt reconstruction of peatlands and reveal a remarkable link between the local hydrological variations and the coupled atmospheric oceanic circulation which is significant for the prediction of future hydrological changes in the asian monsoon region under the background of global warming

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

changes in dominant moisture sources and the consequences for hydroclimate on the northeastern tibetan plateau during the past 32 kyr abstract lake qinghai located on the northeastern tibetan plateau north of the modern maximum summer monsoon extent is well situated to record northward advances of the summer monsoon existing paleoclimate records contain conflicting evidence for the timing of summer monsoon advance into this region an early arrival pre younger dryas or a late arrival at the beginning of the holocene a 30 kyr long leaf wax hydrogen isotope n alkanoic acid 2 h wax record from lake qinghai helps to address this discrepancy by elucidating changes in the three main moisture sources in this region southerly summer monsoon northwesterly and local precipitation lake qinghai 2 h wax indicates that the arid glacial period was dominated by northwesterly moisture extremely arid conditions prevailed from 15 to 14 ka likely because westerly winds were weakening and the summer monsoon had not yet reached this region this arid period ended by 13 6 ka when small amounts of summer monsoon precipitation reached lake qinghai summer monsoon moisture subsequently retreated off of the northeastern tibetan plateau during the younger dryas and re advanced in the early holocene summer monsoon precipitation decreased progressively throughout the holocene in response to decreasing summer insolation and the modern northwesterly and local dominated moisture regime was attained ca 2 6 ka lake qinghai 2 h wax demonstrates that the summer monsoon extent was dynamic during the past 30 kyr responding dramatically to insolation and north atlantic circulation changes moreover lake qinghai 2 h wax demonstrates that local and northwesterly air masses are important moisture sources to the northeastern tibetan plateau and should be considered when reconstructing past hydroclimate in this region

the distribution of long chain n alkan 2 ones in peat can be used to infer past changes in ph abstract long chain c21 c33 n alkan 2 ones are biomarkers ubiquitous in peat deposits however their paleoenvironmental significance lacks constraints here we evaluate the influence ph exerts on the occurrence of long chain n alkan 2 ones in chinese peats a comparison of the distribution in a collection n 65 of modern peat samples with different ph ph values 4 4 8 6 from china demonstrates that their distribution is significantly different in acid compared to alkaline peat this difference can be explained by the ph control on the conversion of n alkan 2 one precursor compounds n alkanes and fatty acids transfer functions between ph and n alkan 2 one ratios were established using linear and logarithmic regression models we then applied these proxies to reconstruct variations of paleo ph in the dajiuhu peat sequence to identify the history of peatland acidification over the last 13 kyr we find significant changes in paleo ph during the deglaciation early holocene and relate these to times of dry climate in the region the drought induced peat acidification is supported by observations from modern drying events in the peatland we propose that long chain n alkan 2 ones in peats have potential to trace paleo ph changes across the deglaciation and holocene although further research from different peatlands and time periods is still needed

geology and thermotectonic evolution of the western margin of the trans hudson orogen evidence from the eastern sub athabasca basement saskatchewan in the cree lake zone of northern saskatchewan reworked archean orthogneisses are overlain by a highly deformed supracrustal sequence the paleoproterozoic wollaston group this package of rocks was deformed and metamorphosed during the ca 1 8 ga continent continent collision of the trans hudson orogen tho forming the wollaston fold thrust belt that underlies the eastern athabasca basin the hudsonian structural metamorphic and magmatic evolution of the wollaston fold thrust belt in the eastern athabasca area involved six major stages 1 early collisional stage dp1 at 1860 1835 ma involved burial of wollaston group metasediments from surface to depths equivalent to 3 5vkbar 1 kbar 100 mpa by thrust pile stacking or imbrication tectonics prograde metamorphism with garnet growth and development of early leucosomes and emplacement of ca 1840 ma grey granite suite 2 collisional stage dp2a at 1835 1820 ma involved continued deeper burial of wollaston group metasediments along a prograde

assessing paleohydrologic controls on the hydrogen isotope compositions of leaf wax n alkanes in chinese peat deposits abstract the high concentrations of lipid biomarkers in peat and the close relation between peatland development and hydrological conditions merit further assessment of the paleohydrological proxy potential of the 2h 1h ratio of leaf wax n alkanes 2halk in peat deposits in the context of the dynamics of the east asian summer monsoon detailed investigation of modern processes is an important way to improve our understanding of the controls on 2halk records from chinese peat deposits this review first synthesizes the results of investigations of modern processes in the dajiuhu peatland of central china complemented by results from other peatlands and nearby non peatland sites to evaluate how the 2h 1h ratio changes from source water to leaf water and then to lipids in leaf waxes and ultimately to peat deposits the results reveal that the precipitation 2h values and the peatland plant types are the two major factors that control the 2halk signals preserved in peat at dajiuhu comparison of results from holocene 2halk sequences from other chinese peat deposits illustrates how peat 2halk values respond to paleoclimate changes on centennial to millennial timescales throughout the east asian summer monsoon region finally proposed incubations of peat forming plants in controlled chambers that could assess the response of plant 2halk values to environmental stresses are described as an example responses of the compound specific biomarker 2h and 13c values of sphagnum the dominant plant in the dajiuhu peatland could provide important information on the symbiotic relation between sphagnum and microbes it is expected that experiments such as these that combine the carbon and hydrogen isotope compositions of multiple lipids will yield important new insights into the responses of peatland ecosystems to climate changes

pb diffusion in monazite a combined rbs sims study abstract we report measurements of pb diffusion in both synthetic cepo4 and natural monazites run under dry 1 atm conditions powdered mixtures of prereacted cepo4 and pbzro3 were used as the source of pb diffusant for in diffusion experiments conducted in sealed pt capsules for durations ranging from a few hours to several weeks following the diffusion anneals pb concentration profiles were measured with rutherford backscattering spectroscopy rbs and supplemented by measurements with secondary ion mass spectrometry sims in order to evaluate potential compositional effects upon pb diffusivity and simulate diffusional pb loss that might occur in natural systems we also conducted out diffusion experiments on pb bearing natural monazites in these experiments monazite grains were surrounded by a synthetic zircon powder to act as a sink monazites from these experiments were analyzed with sims over the temperature range 1100 to 1350 c the arrhenius relation determined for in diffusion experiments on synthetic monazite is given by d 0 94 exp 592 39 kj mol 1 rt m 2 s 1 diffusivities for synthetic and natural monazites are similar as are results of measurements made on the same samples using both rbs and sims the activation energy for pb diffusion we determined is more than three times that for natural monazite reported previously with pb diffusivities at

eclogites of the snowbird tectonic zone petrological and u pb geochronological evidence for paleoproterozoic high pressure metamorphism in the western canadian shield eclogite occurs within the southern domain of the east athabasca mylonite triangle in northern saskatchewan situated at the boundary between the archean rae and hearne provinces of the western canadian shield the east athabasca mylonite triangle is a fundamental exposure of the 3 000 km long snowbird tectonic zone the eclogite occurs in association with a variety of lower crustal high pressure granulites that record a complex metamorphic history from 2 6 to 1 9 ga temperatures of the eclogite facies metamorphism are constrained by garnet clinopyroxene exchange thermometry at 920 1 000 c minimum pressure conditions are recorded by the jadeite quartz albite geobarometer at 1 8 2 0 gpa a near isothermal decompression path to granulite facies conditions is inferred from retrograde reaction textures involving the formation of granulite facies assemblages such as orthopyroxene plagioclase and pargasite plagioclase u pb idtims zircon geochronology of the eclogite yields a weighted mean 207pb 206pb date of 1 904 0 0 3 ma which we interpret as the time of peak eclogite facies metamorphism shrimp in situ analyses of metamorphic zircons included within omphacitic clinopyroxene support this interpretation with a weighted mean 207pb 206pb date of 1 905 19 ma inclusion suites of high pressure phases and the petrographic setting of zircon are a direct link between zircon growth and eclogite facies metamorphism zircon from one eclogite sample has older cores that are 2 54 ga which is a minimum age for the emplacement or earliest metamorphism of the gabbroic protolith u pb rutile data indicate slow cooling at 1 c ma below 500 c from 1 88 to 1 85 ga the formation and exhumation of the eclogites at ca 1 9 ga has important implications for the tectonic significance of the snowbird tectonic zone during the paleoproterozoic the eclogites described here are consistent with transport of continental crust to mantle depths during the paleoproterozoic followed by rapid buoyancy driven exhumation to normal lower crustal depths

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

electron microprobe age mapping of monazite high resolution x ray maps of th u pb and y in monazite can be used to construct age maps which reveal the continuous spatial distribution of ages in a single grain of monazite the age mapping algorithm and three examples are presented to illustrate the capabilities and applications of this mapping technique the insights it can provide into monazite geochronology in general and its limitations compared to electron microprobe emp quantitative dating and other in situ geochronologic techniques age maps offer critical information for unraveling metamorphic and tectonic histories and for interpreting results from other geochronologic techniques and they are a valuable aid for rigorously locating in situ analytical points age mapping also can be used to better understand the behavior of the u th pb system in monazite during metamorphism deformation and s uid circulation events age maps presented in this paper reveal unsuspected age heterogeneities on the micrometer scale like a now healed fracture not visible in back scattered electron bse images or young domains less than 5 m in width located inside an older core in both cases using age maps as a template for locating in situ analysis points will minimize the peril of age mixing and erroneous geological interpretations in addition to providing critical information for illustrating and interpreting the history of complex polygenetic monazite age mapping may ultimately lead to a better understanding of the processes involved with monazite growth and recrystallization and thus even more powerful applications of the monazite geochronometer the agemap program is available in a windows version and can be downloaded from the internet at the following address http www geo umass edu probe agemap

east asian hydroclimate modulated by the position of the westerlies during termination i speleothem oxygen isotope records have revolutionized our understanding of the paleo east asian monsoon yet there is fundamental disagreement on what they represent in terms of the hydroclimate changes we report a multiproxy speleothem record of monsoon evolution during the last deglaciation from the middle yangtze region which indicates a wetter central eastern china during north atlantic cooling episodes despite the oxygen isotopic record suggesting a weaker monsoon we show that this apparent contradiction can be resolved if the changes are interpreted as a lengthening of the meiyu rains and shortened post meiyu stage in accordance with a recent hypothesis model simulations support this interpretation and further reveal the role of the westerlies in communicating the north atlantic influence to the east asian climate

striding athabasca mylonite zone implications for the archean and early proterozoic tectonics of the western canadian shield study of the northern saskatchewan district of mackenzie segment of the snowbird tectonic zone suggests that fragments of relatively stiff mid archean crust possibly arc related have controlled the localization shape and complex kinematics of the multistage striding athabasca mylonite zone during the archean as well as the geometry of the early proterozoic rifted margin of the western churchill continent by the late archean the striding athabasca mylonite zone was located in the interior of the western churchill continent well removed from the contemporaneous plate margins except for the alberta segment the snowbird tectonic zone was not the site of an early proterozoic plate margin we suggest that the geometry of the archean early proterozoic boundary in the western canadian shield represents a jagged continental margin composed of a pair of reentrants defined by rifted and transform segments these segments were inherited from early proterozoic breakup and controlled by the archean structure

time transgressive onset of the holocene optimum in the east asian monsoon region abstract the east asian summer monsoon affects precipitation and hence vegetation in the densely populated northwest pacific region yet a long standing controversy exists concerning the spatial and temporal dynamics of the holocene optimum ho in the east asian monsoon region here we use a detailed 14 000 year record reconstructing vegetation variations from a strategically selected crater lake from northeast china as well as a compilation of previous paleoclimatic studies to show that the ho began around 6 000 cal a bp in northeast china significantly later than generally recognized by comparing our paleoenvironmental data with holocene vegetation records from other regions of east asia we identified a marked northward shift for the onset of the ho from 10 260 cal a bp in south china to 6 000 cal a bp in northeast china the gradual northward transgression of the vegetation change could be caused by both the temperature and precipitation changes in different regions finally we fitted a regression model of the start of the ho period versus latitude which allowed us to make predictions for the beginning of the ho at different geographical locations this study reveals a strong relationship between latitude and the initiation of the ho and provides a window towards better understanding the forcing of vegetation changes in the east asian monsoon region

lipid stratigraphy of a flandrian peat bed northumberland uk comparison with the pollen record a flandrian peat bed near low hauxley northumberland uk was studied both optically and geochemically to compare the pollen and lipid records of changing plant input during its accumulation a pr

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

differential hydrogen isotopic ratios of sphagnum and vascular plant biomarkers in ombrotrophic peatlands as a quantitative proxy for precipitation evaporation balance abstract we have developed a new approach to quantitatively reconstruct past changes in evaporation based on compound specific hydrogen isotope ratios of vascular plant and sphagnum biomarkers in ombrotrophic peatland sediments we show that the contrast in h isotopic ratios of water available to living sphagnum top 20 cm and in the rooting zone of peatland vascular plants can be used to estimate the fraction of water remaining after evaporation vascular plant leaf waxes record h isotopic ratios of acrotelm water which carries the d h ratio signature of precipitation and is little affected by evaporation whereas the sphagnum biomarker c 23 n alkane records h isotopic ratios of the water inside its cells and between its leaves which is strongly affected by evaporation at the bog surface evaporation changes can then be deduced by comparing h isotopic ratios of the two types of biomarkers we calibrated d h ratios of c 23 n alkane to source water with lab grown sphagnum we also tested our isotopic model using modern surface samples from 18 ombrotrophic peatlands in the midwestern united states finally we generated a 3000 year downcore reconstruction from minden bog michigan usa our new record is consistent with records of other parameters from the same peatland derived from different proxies and allows us to differentiate precipitation supply and evaporative loss

syntectonic generation and segregation of tonalitic melts from amphibolite dikes in the lower crust striding athabasca mylonite zone northern saskatchewan vapor absent melting in a swarm of amphibolite dikes in the lower crust has produced segregations of tonalitic and trondhjemitic composition in a variety of textures and structures that dramatically illustrate the mechanisms of melt segregation during deformation the 3 2 ga chipman dikes intrude the mylonitized chipman tonalite within the striding athabasca mylonite zone of northern saskatchewan dike emplacement spans a major sinistral transpressive ductile deformation and granulite facies metamorphic event older dikes are intensely folded and sheared younger dikes are undeformed major and trace element analyses indicate that the dikes are tholeiitic basalts similar in composition to midocean ridge basalt thermobarometry finds conditions of 750 850 c 1 0 gpa the youngest most pristine dikes contain hornblende and plagioclase with minor clinopyroxene and garnet older migmatitic dikes have tonalitic to trondhjemitic segregations spatially associated with garnet crystals where small the segregations occupy tails or strain shadows on every garnet crystal where garnets and segregations are large leucosomes form an interconnected network that extends into the host tonalite tonalitic pools probably of dike origin collect in boudin necks and fold hinges the chipman dikes are interpreted to have been emplaced solidified and partially melted during ductile shearing in the lowermost crust perhaps near the base of an archean island arc they appear to offer an exceptional view of magma genesis where underplated mantle derived mafic magmas provide not only heat but also a component of material to new felsic magmas deformation is essential to the process allowing access of mafic magma into the lower crust and facilitating the segregation of the new felsic melts from their source rocks

influence of the indian monsoon and the subtropical jet on climate change on the tibetan plateau since the late pleistocene abstract precipitation atop the tibetan plateau tp is delivered by the indian summer monsoon the asian summer monsoon and weather systems associated with the subtropical westerly jet variations in the relative importance of the monsoon systems and the westerly jet are hypothesized to have occurred at decadal millennial and glacial interglacial scales however paleoclimate observations based on explicit climate proxies are still scarce limiting our understanding of the mechanisms of holocene climate variability on the tibetan plateau tp here we present three independently dated compound specific hydrogen isotope records of sedimentary leaf waxes from lakes on the tp bangong co lake qinghai and linggo co the leaf wax d records reflect isotopes in precipitation and we combine these observations with existing isotopic and hydrological data to investigate variations in the influence of the summer monsoon and the westerly jet on the moisture budget of the tp since the late pleistocene d values of precipitation at all three lakes were relatively positive during the late pleistocene indicating a weakened summer monsoon during the early and mid holocene d values of precipitation at the three lakes were relatively negative suggesting the importance of summer monsoon during the middle to late holocene d values at bangong co and lake qinghai gradually increased with superimposed episodes of short term of d variability however at linggo co in the northern tp periods of more positive d values of precipitation correspond to wetter intervals inferred from lake level high stands and likely reflect variations in moisture associated with the westerly jet thus the d records at linggo co imply the lesser importance of summer monsoon moisture in the hydrologic budget of the northern tp collectively the hydrogen isotope records at these three lakes document millennial and centennial scale variations in the strength of the summer monsoon systems and concurrent changes in the westerly jet furthermore millennial scale fluctuations in the d records at the three lakes during the middle to late holocene suggest episodes of reduced summer monsoonal moisture delivery to these regions and correspond with intervals of cool sea surface temperatures in the north atlantic

formation of the maturin foreland basin eastern venezuela thrust sheet loading or subduction dynamic topography 1 the maturin basin in eastern venezuela is considered a good example of a peripheral foreland basin earthquake and tomographic data indicate that eastern venezuela is affected by the oblique subduction of the south american plate underneath the caribbean plate new forward flexural isostatic modeling of eastern venezuela has been carried out in order to determine whether the maturin basin was generated purely by thrust sheet loading from the serrania and monagas foreland thrust belts a sequence of forward models from middle miocene to present was generated for 3 profiles across the serrania del interior thrust belt the monagas foreland thrust belt and the maturin foreland basin the predictions of these models are constrained using seismic reflection and well data the flexural isostatic modeling shows that thrust sheet loading associated with the serrania del interior and monagas foreland thrust belts is insufficient to generate the observed subsidence within the maturin basin dynamic fluid flow modeling of subduction related dynamic topography of eastern venezuela has been used to investigate the influence of south american plate subduction on the generation of the accommodation space observed in the maturin basin fluid flow modeling of subduction related dynamic topography suggests that the subduction of the south american lithospheric mantle caused downward deflection of the south american crust affecting the maturin basin and the serrania thrust belt this modeling suggests that the maturin basin subsidence has two components 55 related to thrust sheet loading and 45 driven by continental subduction

compound specific δd values of long chain n alkanes derived from terrestrial higher plants are indicative of the δd of meteoric waters evidence from surface soils in eastern china the stable carbon and hydrogen isotope composition of higher plant derived long chain n alkanes 13cn alkanes and dn alkanes from 45 surface soil samples within well characterized vegetation zones from eastern china 18 n 50 n are reported the weighted average dn alkanes value for n c27 n c29 and n c31 in the samples and the annual average d of meteoric water recorded at 12 weather stations proximal to the sampling sites show similar spatial variations the d of n alkanes shows a gradual depletion in value with increasing latitude the results demonstrate that on a large spatial scale the d values of long chain n alkanes derived from higher plants have the potential to record the d of meteoric water although many other factors can also influence the isotope values there appears to be no apparent relationship between the d of the n alkanes extracted from the surface soil and the overlying vegetation type i e forest grassland or c3 c4 composition therefore palaeoenvironmental studies utilizing dn alkanes from higher plant derived material in geological samples have the potential to provide additional information with regard to the past hydrological cycle

palaeoclimate records in compound specific δd values of a lipid biomarker in ombrotrophic peat compound specific d values recorded by means of gas chromatography thermal conversion isotope ratio mass spectrometry gc tc irms of the biomarker n alkane n tricosane n c23 representative of the dominant sphagnum species in a 40 cm peat profile from bolton fell moss cumbria uk correlate with vegetation changes in the past 200 years age depth model based on 210pb dating the bog vegetation is sensitive to climate change correlating with the global scale cooler period of the later 19th and early 20th centuries the correlation with meteorological records suggests compound specific d values of lipid biomarkers have potential for use as a new climate proxy

u pb systematics of monazite and xenotime case studies from the paleoproterozoic of the grand canyon arizona monazite is accepted widely as an important u pb geochronometer in metamorphic terranes because it potentially preserves prograde crystallization ages however recent studies have shown that the u pb isotopic system in monazite can be influenced by a variety of processes that partially obscure the early growth history in this paper we attempt to interpret complex monazite and xenotime u pb data from three paleoproterozoic granite dikes exposed in the grand canyon single crystal monazite analyses from an unfoliated granite dike spread out along concordia from the crystallization age of the dike defined by u pb zircon data to be 1685 1 ma to 1659 2 ma a span of 26 million years back scattered electron bse imaging reveals that magmatic domains within most crystals from this sample are truncated by secondary domains associated with prominent embayments at the grain margin fragments of a single crystal yield contrasting concordant dates and fragments from the edges and tips of crystals yield the youngest dates based on these observations we suggest that the secondary domains formed at least 26 million years after the crystal formed monazite and xenotime dates from the second sample a sheared dike that cross cuts the previous dike spread out along concordia over 16 million years and range up to 2 4 normally discordant again bse imaging reveals secondary domains that truncate both magmatic zoning and xenocrystic cores fragments sliced from specific domains of a previously imaged monazite crystal demonstrate that the secondary domain is 13 million years younger than the core domain textures revealed in bse images suggest that the secondary domains formed by fluid mineral interaction normal discordance appears to result from both radiation damage accumulated at temperatures below 300 c and water mineral interaction monazite data from the third sample exhibit dispersion in both the 207pb 206pb dates 1677 1690 ma and discordance 1 6 to 3 1 reverse discordance in these monazites cannot be explained by incomplete dissolution or excess thorogenic 206pb sliced fragments from several crystals reveal dramatic intragrain u pb disequilibrium that does not correlate with either th or u concentration or position within the crystal we suggest that reverse discordance resulted from mechanisms that involve exchange or fractionation of elemental u or elemental pb and that neither the u pb dates nor the 207pb 206pb dates are reliable indicators of the rock s crystallization age given the large number of processes proposed in the recent literature to explain monazite u pb systematics from rocks of all ages our results can be viewed as another cautionary note for single crystal and multi crystal monazite geochronometry however we suggest that because individual crystals can preserve a temporal record of primary and secondary monazite growth micro sampling of individual monazite crystals may provide precise absolute ages on a variety of processes that operate during the prograde peak and or retrograde history of metamorphic terranes

plant wax hydrogen isotopic evidence for postglacial variations in delivery of precipitation in the monsoon domain of china the asian monsoon is a key component of the earth s climate system that directly affects the livelihood of 60 of the world population reliable reconstruction of changes in monsoon precipitation during the holocene is required to better understand the present climate conditions and to predict future climate processes in the asian monsoon domain reconstruction of changes in holocene monsoon precipitation has been done in various regions of this domain using a variety of paleoclimate proxies however different proxies have yielded different paleoclimate records of long term monsoon rainfall variability we apply compound specific stable hydrogen isotope compositions of the plant wax n alkanes isolated from the hongyuan peat sequence in eastern tibet to reevaluate the regional carbonate oxygen isotopic and lake level records the d h ratios of the n alkanes resolve the apparent discrepancy among the different paleoclimate proxies our result indicates that lake level fluctuation is a reliable recorder of changes in the amount of summer monsoonal precipitation while long term isotope records largely reflect large scale changes in the source of water vapor rather than a local precipitation signal combining lake level biomarker and carbonate isotopic records we conclude that the early holocene monsoon precipitation in southwest china has been greatly influenced by the indian monsoon

compound specific d h ratios and molecular distributions of higher plant leaf waxes as novel paleoenvironmental indicators in the chinese loess plateau abstract we measured d h ratios of individual long chain leaf wax n alkanes isolated from a loess profile spanning the last 130 ka from xifeng china the d values show large variation 140 to 200 for the past 130 ka and are highly correlated with changes in magnetic susceptibility ms an accepted proxy for past monsoon circulation in the chinese loess plateau peaks in high d values 140 to 160 coincide with low ms values for loess sections formed under relatively dry conditions marine isotope stages miss 2 and 4 whereas peaks in low d values 190 to 200 coincide with high ms values for paleosol sections formed under relatively wet conditions miss 1 3 and 5 we attribute the isotopic variations to the combined effects of varying aridity which controls the soil and leaf water evaporation and temperature and monsoon intensity which alter the d h ratios of precipitation we also discovered a strong negative correlation between the molecular distributions ratios of c31 c29 and c31 c27 n alkanes and the d values of n alkanes based on studies of modern plants and the xifeng loess sequence the complex relationship between ms and monsoon circulation has been difficult to understand mechanistically however the climatic controls on the d h ratios of individual long chain n alkanes and c31 c29 n alkane ratios can be readily demonstrated and calibrated from modern plants and surface soils therefore these new molecular and isotopic proxies have potential as quantitative proxies for paleoenvironmental reconstruction in the chinese loess plateau