indian ocean summer monsoon iosm dynamics within the past 4 ka recorded in the sediments of lake nam co central tibetan plateau china abstract in september 2008 several cores 68 cm 115 cm length water depth 93 m were retrieved from lake nam co southern central tibetan plateau 4718 m a s l this study focuses on the interpretation of high resolution partly 0 2 cm data from three gravity cores and the upper part of a 10 4 m long piston core i e the past 4000 cal bp in terms of lake level changes hydrological variations in the catchment area and consequently variations in monsoon strength a wide spectrum of sedimentological geochemical and mineralogical investigations was carried out results are presented for xrf core scans grain size distribution xrd measurements and sem image analyses these data are complemented by an age depth model using 210pb and 137cs analyses as well as eleven ams 14c ages this model is supported by excellent agreement between secular variations determined on one of the gravity cores to geomagnetic field models this is a significant improvement of the chronology as most catchments of lacustrine systems on the tibetan plateau contain carbonates resulting in an unknown reservoir effect for radiocarbon dates the good correlation of our record to the geomagnetic field models confirms our age depth model and indicates only insignificant changes in the reservoir effect throughout the last 4 ka high summer monsoonal activity i e moist environmental conditions was detected in our record between approximately 4000 and 1950 cal bp as well as between 1480 and 1200 cal bp accordingly lower monsoon activity prevails in periods between the two intervals and thereafter this pattern shows a good correlation to the variability of the indian ocean summer monsoon iosm as recorded in a peat bog 1000 km in ne direction from lake nam co this is the first time that such a supra regional homogenous monsoon activity is shown on the tibetan plateau and beyond finally our data show a significant lake level rise after the little ice age lia in lake nam co which is suggested to be linked to glacier melting in consequence of rising temperatures occurring on the whole tibetan plateau during this time

stable isotope and radiocarbon balances of two tibetan lakes sumxi co longmu co from 13 000 bp hydrologic and climatic changes in western tibet since 13 000 bp are inferred from mineralogical and isotopic analyses of lacustrine sediments from the sumxi longmu co basin the interpretation is based on isotope data from the modern system carbon isotope chemistry is complex because of the presence of old limestones on the watershed sediments contain detrital and authigenic calcites the proportions of which are quantitatively estimated by x ray diffractometry stable isotope contents of the authigenic calcite are reconstructed from mass balance equations the high 13c contents up to 6 are attributed to an enhancement of calcite precipitation from water surface during freezing periods the 18o content is related to residence time and evaporation the validity of 14c dates obtained from different types of material is discussed our record in good agreement with paleobiological data from the same material shows the sudden establishment of wet warm conditions at 10 000 bp which culminated at 7500 6000 bp after a brief reversal event at 7900 bp maximum aridity for the whole holocene is recorded at 4300 bp

the inorganic geochemistry of a peat deposit on the eastern qinghai tibetan plateau and insights into changing atmospheric circulation in central asia during the holocene abstract peat records enable the reconstruction of changes in the global biogeochemical mineral dust cycle and the detection of variations in atmospheric circulation patterns during the holocene they can therefore provide a key tool for understanding the relationship between the geochemical dust cycle and past climate change here we present the first detailed study of the inorganic geochemistry of a peat core collected at an altitude of 3500 m from the hongyuan peatland on the eastern qinghai tibetan plateau and test its potential as an archive of atmospheric dust deposition we find that the low accumulation rates of the peat and the presence of the extensive dust sources of northern china in the vicinity of the study site lead to approximately five times higher concentrations of mineral matter compared to temperate ombrotrophic peats a detailed geochemical assessment of the core and surface samples from local and non local dust sources as well as of the hydrology and hydrochemistry of the surrounding waters suggests that external and internal post depositional processes have not affected the record of lithogenic elements including the rare earth elements ree sc y and th changes in ti normalized major element profiles la yb y tb and the eu anomaly identify seven major shifts among the dominant dust sources and therefore potential changes in atmospheric circulation patterns bivariate plots using the ree based tracers la yb y tb la th y er sc la th sc and th ree suggest that the taklamakan desert and the chinese loess plateau in northern china were the dominant non local dust sources to the peat local dust input dominated throughout the early holocene until 4 9 kyr bp increased dust input from the non local sources thereafter suggests an enhanced influence of winds associated with the east asian winter monsoon and the westerly jet throughout most of the late holocene sharp increases in non local dust fluxes between 3 1 2 7 and between 1 3 0 9 kyr bp suggest a particular strengthening of these wind systems during these times in agreement with the organic characteristics of the core our results show that the hongyuan peat is a reliable archive to study dust deposition in central asia and allows the identification of changes in atmospheric circulation patterns and in the larger climatic arrangements of the monsoon system in this region during the holocene

exchange of neodymium and its isotopes between seawater and small and large particles in the sargasso sea the concentrations and isotopic ratios of nd were measured in small 1 53 m and large 53 m in situ filtered particles sediment trap material sediment and aerosol samples collected during oligotrophic and productive conditions in the sargasso sea atmospheric input is the main source of exogeneous nd into the sargasso sea based on ndal ratios in trapped material we suggest that up to 50 of atmospheric nd could dissolve at the air sea interface the concentration and isotopic composition of nd vary with both depth and the particle size neodymium concentrations of small and large particles increase with depth from 2 9 12 g g and 5 8 11 8 g g respectively at 40 m the nd signature of large particles is significantly more negative nd 0 13 1 0 2 than that of the small ones nd 0 11 7 0 3 and the particles filtered deeper below 237 m the nd 0 values for small particles match the seawater whereas the nd 0 values of large particles remain less radiogenic these differences are related to the different behaviors of the particulate fractions small particles apparently exchange nd with seawater and then sink rapidly to depth as biologically formed aggregates large particles these aggregates isolate the small particles slowing the exchange with the water to produce different signatures between large particles and seawater since these exchange processes modify the particulate nd signature the shallow radiogenic nd 0 signature observed in the surface and subsurface waters in the nw atlantic is not due to external contributions and is likely of advective origin at depth below 800 m the magnitude of the aggregation disaggregation process varies significantly with season the fraction of small particles repackaged into large aggregates can vary from 0 8 to 80 100 in productive and oligotrophic conditions respectively this seasonal variation may correspond to sinking particles of different zooplanktonic origin vertical fluxes of nd into and out of the sargasso sea as well as exchange fluxes in the water column are examined about 50 of the particulate flux from the surface is remineralized at depth a net scavenging flux of 0 8 10 4 g m2 y is required this value corresponds to a scavenging nd residence time of 1900 y considerably longer than previous estimates of global oceanic residence time of nd on the order of 400 y

the influence of climate hydrology and permafrost on holocene peat accumulation at 3500 m on the eastern qinghai tibetan plateau peatland of the eastern qinghai tibetan plateau lies at the convergence of the east asian and indian monsoon systems in eastern asia to understand the evolution of this peatland and its potential to provide new insights into the holocene evolution of the east asian monsoon a 6 m peat core was collected from the undisturbed central part of a peat deposit near hongyuan the age depth profile was determined using 16 14c ams age dates the peat analysed for a range of environmental variables including carbon nitrogen and hydrogen concentration bulk density 13c and the associated spring water analysed for hydrogen and oxygen isotopes the age depth profile of the recovered peat sequence covers the period from 9 6 to 0 3 kyr bp and is linear indicating that the conditions governing productivity and decay varied little over the holocene using changes in carbon density organic carbon content and its 13c cold dry periods of permafrost characterised by low density and impeded surface drainage were identified the low 18o and d values of the spring water emanating around the peat deposit down to 13 8 and 102 vsmow respectively with an inverse relationship between electrical conductivity and isotopic composition indicate precipitation under colder and drier conditions relative to the present day in view of the current annual mean air temperature of 1 c this suggests conditions in the past have been conducive to permafrost inferred periods of permafrost correspond to independently recognised cold periods in other holocene records from across china at 8 6 8 2 7 8 5 6 4 2 3 1 and 1 8 1 5 kyr bp the transition to a cold dry climate appears to be more rapid than the subsequent recovery and cold dry periods at hongyuan are of longer duration than equivalent cold dry periods over central and eastern china light dark banding peat on a scale of 15 30 years from 9 6 to 5 5 kyr bp may indicate a strong influence of decadal oscillations possibly the pacific decadal oscillation and a potential link between near simultaneous climatic changes in the northwest pacific enso movement of the intertropical convergence zone and the east asian monsoon

environmental changes since 8 4 ka reflected in the lacustrine core sediments from nam co central tibetan plateau china the tibetan plateau induces and enhances the asian monsoon that influences the plateau itself east china and even the whole of asia pursuing the changing monsoon history and its impact in this environment sensitive area is a key for understanding the climatic changes here we present the initial results from core sed iments in nam co central tibet to elucidate the holocene environment changes in this area the studied lake nam co is the second largest lake with an elevation of 4718 m water area of 2015 km 2 and catchment area of 10 610 km 2 by using echo seismic profiling and hydro echosounding we investigated the bathymetric dis tribution of the whole lake one 332 cm long piston core was successfully taken in the east part of the lake at 60 m water depth twelve ams 14 c dates from top to bottom of this core established a good time sequence toc tn n alkanes grain size clay minerals fe mn sr ba and caco3 content were analysed with sampling intervals from 1 cm to 10 cm results showed that since 8400 yr bp the environment changes in this region indicate three stages the early stage 8400 6900 yr bp was characterized by slight shifting from warm to cold with a cold dry interval at 8100 7800 yr bp the middle stage was from 6900 to 2900 yr bp during which cli mate changed from warm humid to cold dry however around 2900 yr bp the climate once was slightly cold but strongly dry the late stage from 2900 yr bp to present was characterized by a general tendency toward cold dry the first temperature decline was around 1700 1500 yr bp following which temperature increased once before decreasing again around 600 300 yr bp which might be the result of the little ice age

variations in the nd isotopic composition of foraminifera from atlantic ocean sediments 143nd 144nd ratios have been measured in recent core top foraminifera from 25 sites throughout the atlantic ocean the average nd 0 value from this study agrees well with previous estimates of the average nd isotopic composition of the atlantic based on analyses of ferromanganese deposits and seawater samples however the larger data base and the nature of the samples have allowed us to identify distinct provenances of nd isotopes in the atlantic

the evolution of el nino past and future abstract we review forecasts of the future of el nino and the southern oscillation enso a coupled instability of the ocean atmosphere system in the tropical pacific with global impacts enso in the modern world is briefly described and the physics of the enso cycle is discussed particular attention is given to the bjerknes feedback the instability mechanism which figures prominently in enso past and future our knowledge of enso in the paleoclimate record has expanded rapidly within the last 5 yr the enso cycle is present in all relevant records going back 130 kyr it was systematically weaker during the early and middle holocene and model studies indicate that this results from reduced amplification in the late summer and early fall a consequence of the altered mean climate in response to boreal summer perihelion data from corals shows substantial decadal and longer variations in the strength of the enso cycle within the past 1000 yr it is suggested that this may be due to solar and volcanic variations in solar insolation amplified by the bjerknes feedback there is some evidence that this feedback has operated in the 20th century and some model results indicate that it will hold sway in the greenhouse future but it is very far from conclusive the comprehensive general circulation models used for future climate projections leave us with an indeterminate picture of enso s future some predict more enso activity some less with the highly uncertain consensus forecast indicating little change

a general cooling trend on the central tibetan plateau throughout the holocene recorded by the lake zigetang pollen spectra abstract a 741 cm long laminated sediment core covering the last 10 800 years was collected from lake zigetang central tibetan plateau 90 9 e 32 0 n 4560 m a s l and analysed palynologically at 69 horizons biome reconstruction suggests a dominance of temperate steppe vegetation mainly artemisia and poaceae on the central tibetan plateau during the first half of the holocene 10 8 4 4 cal ka bp while alpine steppes with desert elements mainly cyperaceae poaceae chenopodiaceae and characteristic high alpine herb families tend to dominate the second half 4 4 0 cal ka bp the artemisia cyperaceae ratio a semi quantitative measure for summer temperature indicates a general cooling trend throughout the holocene dense temperate steppe vegetation and maximum desert plant withdrawal however indicate that a suitable balance of wet and warm conditions for optimum vegetation growth likely occurred during the middle holocene 7 3 4 4 cal ka bp severe early holocene cold events have been reconstructed for 8 7 8 3 and 7 4 cal ka bp

reduced north atlantic deep water flux to the glacial southern ocean inferred from neodymium isotope ratios the global circulation of the oceans and the atmosphere transports heat around the earth broecker and denton1 suggested that changes in the global ocean circulation might have triggered or enhanced the glacial interglacial cycles but proxy data for past circulation taken from sediment cores in the south atlantic ocean have yielded conflicting interpretations of ocean circulation in glacial times 13c variations in benthic foraminifera2 3 4 5 6 support the idea of a glacial weakening or shutdown of north atlantic deep water production whereas other proxies such as cd ca ba ca and 231pa 230th ratios show little change from the last glacial maximum to the holocene epoch7 8 9 here we report neodymium isotope ratios from the dispersed fe mn oxide component of two southeast atlantic sediment cores both cores show variations that tend towards north atlantic signatures during the warm marine isotope stages 1 and 3 whereas for the full glacial stages 2 and 4 they are closer to pacific ocean signatures we conclude that the export of north atlantic deep water to the southern ocean has resembled present day conditions during the warm climate intervals but was reduced during the cold stages an increase in biological productivity may explain the various proxy data during the times of reduced north atlantic deep water export

empirical relationships between elevation and the stable isotope composition of precipitation and surface waters considerations for studies of paleoelevation change a compilation of 68 studies from throughout many of the world s mountain belts reveals an empirically consistent and linear relationship between change in elevation and change in the isotopic composition of precipitation along altitudinal transects the isotopic composition of precipitation decreases linearly with increasing elevation in most regions of the world except in the himalayas and at elevations 5000 m there are no significant differences in isotopic lapse rates from most regions of the world 0 28 permil 100 m except at the extreme latitudes where isotopic lapse rates are higher given information on past changes in the isotopic composition of precipitation preserved in pedogenic or authigenic minerals this global isotopic lapse rate can be used to place numerical constraints on the topo graphic development of some ancient mountain belts or plateaus there are many complicating factors that can confound interpretation of paleoel evation change based on stable isotopes and many of these are unique to specific mountain belts or time periods relevant to all stable isotope based paleoelevation change studies is the temperature dependent isotope fractionation between a pedo genic or authigenic mineral and the water from which it forms in cases where isotopic proxy minerals are sampled from localities where temperature will change simulta neously with elevation change the apparent change in the isotopic composition of precipitation may be dampened by several permil this suggests that samples taken from the rainshadow side of an emerging orographic barrier may be more likely to preserve isotopic changes resulting from mountain uplift than samples taken from atop a rising mountain range or plateau

last glacial to holocene evolution of semi arid rangelands in southeastern australia pollen sequences from playa lakes in the darling anabranch dunefields of southwestern new south wales record vegetation changes over the last glacial period and into the holocene this interval was one of marked taxonomic and structural reorganization with the plant communities that became established after the last glacial maximum lgm 24 18 ka distinct from those that had prevailed over the build up to full glacial conditions 70 24 ka the glacial period was characterized by a gradual reduction of woodland and tall shrubland cover recolonization of the dunefields involved a similar gradual succession from herbfields and low shrublands to tall shrublands and finally woodlands these changes are likely to have been driven by climatic change particularly fluctuations in temperature precipitation and atmospheric co2 as global climate systems entered and emerged from the last glaciation

evolution of chaka salt lake in nw china in response to climatic change during the latest pleistocene holocene abstract the late pleistocene and holocene hydrologic balance of chaka salt lake in the eastern qaidam basin of nw china was studied based on the analysis of lithostratigraphy mineralogy total organic carbon and total nitrogen from a 9 0 m long sediment core an age depth model for the lake sediments is based on eight accelerator mass spectrometry ams 14 c measurements of organic matter and a 1700 year radiocarbon reservoir correction the pitzer model was used to calculate the sequence of minerals precipitated as a function of salinity assuming that the initial lake water was recharged from adjacent rivers and springs lake salinity values were derived from a good match between the calculated and observed mineral sequences our multi proxy based hydrologic reconstruction of chaka lake indicates that it was a clastic dominated freshwater lake between 17 2 and 11 4 cal ka bp which may have resulted from the input of glacial water into the lake at that time during the lateglacial and holocene a warm climatic regime predominated between 13 9 and 12 7 cal ka bp and then a cold climatic regime prevailed between 12 7 and 11 4 cal ka bp these warm and cold periods correlate with the bolling allerod and younger dryas events in the region beginning at 11 4 cal ka bp a saline or hypersaline lake developed which may have resulted from increased summer insolation and temperatures these conditions persisted throughout the holocene modeling indicates that lake salinity fluctuated between 66 and 223 ppt from 11 4 to 7 2 cal ka bp and then increased to 223 322 ppt between 7 2 and 6 0 cal ka bp when most regions of china recorded high moisture availability i e the so called mid holocene climatic optimum lake salinity decreased to 66 223 ppt during a short time period between 6 0 and 5 3 cal ka bp possibly caused by reduced evaporation subsequently salinity values rapidly increased to 223 322 ppt between 5 3 and 5 2 cal ka bp and a hypersaline lake with a salinity higher than 324 ppt similar to modern chaka salt lake became established around 5 2 cal ka bp this establishment may have been related to the weakening of asian monsoon regional comparisons of paleoclimatic records indicate that large temporal and spatial variations exist in the occurrence and intensity of drought over western china since the lateglacial

reconstruction of late glacial and holocene climate evolution in southern china from geolipids and pollen in the dingnan peat sequence we have carried out a multi proxy analysis of a radiocarbon dated peat core that records the history of paleoclimate change dating from 18 ka in the dingnan region of southern china fatty acid and hydrocarbon distributions total organic carbon toc concentrations pollen assemblages and sediment lithology reveal a succession of three major paleoclimate intervals plant waxes are the predominant origin of the n alkanoic acid and n alkane compositions of this sedimentary sequence contributions of these geolipid components vary relative to toc and with changes in lithology and help to refine a pollen based reconstruction of local paleoclimate evolution a period of cool and fairly wet climate 15 630 10 450 cal abp follows accumulation of coarse fluvial sediments under relatively dry deglacial conditions the second period 10 450 6040 cal abp experienced the warmest climate and the highest precipitation indicated by a minimum c18 1 c18 0 ratio together with the low cpi values of n alkanes and high acl values the third time interval 6040 3800 cal abp was a moderately dry and cool period the climate record of the most recent period 3800 cal abp is obscured by agricultural disturbance the younger dryas 12 900 11 600 cal abp appears in this record as a period of variable and very wet climate during the interval 10 450 6040 cal abp both temperature and the precipitation evaporation ratio maximized therefore we consider this period to represent the holocene optimum which coincides with that of the northern hemisphere moreover our results do not fit the spatially asynchronous pattern of the east asian monsoon holocene optimum in china suggested by previous studies they instead parallel the pattern of global paleoclimate change and consequently show that the evolution of holocene paleoclimate in southern china is consistent with changes in northern hemisphere solar radiation

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

temperature responses to quasi 100 yr solar variability during the past 6000 years based on δ18o of peat cellulose in hongyuan eastern qinghai tibet plateau china abstract during the past 6000 years the temperature variation trend inferred from 18o of peat cellulose in a peat core from hongyuan eastern qinghai tibet plateau southwestern china is similar to the atmospheric 14c concentration trend and the modeled solar output trend the general trend of hongyuan 18o during the past millennium also coincides well with the atmospheric 14c concentration trend the 10be concentration trend in an ice core from the south pole the reconstructed total solar irradiance trend as well as the modeled solar output trend in addition temperature events also correspond well to solar perturbations during the past 6000 years therefore the driving force of holocene temperature variations should be properly ascribed to solar activity the spectrum analysis further illustrates that quasi 100 yr fluctuation of solar activity was probably responsible for temperature variations in northeast qinghai tibet plateau during the past 6000 years

microscale neodymium distribution in sedimentary planktonic foraminiferal tests and associated mineral phases neodymium isotopic ratios recorded in calcareous foraminiferal tests shells and associated authigenic minerals were used to trace past water masses although the origin of preserved nd signals is still a matter of debate we determined for the first time the microscale nd distribution in two planktonic foraminifera species globigerinoides ruber and neogloboquadrina dutertrei and coexisting authigenic minerals from two selected time slices 15 6 and 129 kyr of a marine sediment core in the panama basin elemental mapping of nd ca fe mn and si was performed using nanosims ion probe and electron probe microanalysis epma on uncleaned tests together with scanning electron microscopy sem imagery epma and sem images revealed the presence of fe rich framboidal minerals inside test pores and inner chambers particularly in the old samples the young sample presented fe and mn rich patches on the inner test wall the nd intensity in fe mn rich patches and in some framboids was much higher than in foraminiferal calcite where the nd distribution was randomly heterogeneous with no systematic features such as an ontogenic nd rich layer or species specific differences the relationship between nd fe and mn confirmed a significant role of fe mn oxides as a nd carrier the high nd enrichment in some framboids could be explained by nd adsorption onto oxidized surface of fe sulfides particles rather than direct incorporation since the authigenic precipitates are major nd carrier phases the nd isotopic signals in sedimentary foraminiferal tests likely reflect bottom pore water values rather than surface water ones

holocene peatland initiation lateral expansion and carbon dynamics in the zoige basin of the eastern tibetan plateau the zoige basin on the eastern tibetan plateau has the largest area of highland peatlands in china however the development history of these peatlands is still poorly understood understanding how these carbon rich ecosystems responded to change in the asian summer monsoons during the holocene will provide insight into the peatland carbon accumulation processes under different climate boundary conditions here we document the timing of initiation and expansion histories of these peatlands using 59 new basal peat ages across the zoige basin with 29 ages for initiation analysis and 30 additional ages for lateral expansion analysis also we synthesized basal ages from 26 sites and carbon accumulation records at four sites from previous studies in this region the results show that the peatland initiation is widespread at 11 5 10 and 7 6 kyr 1 kyr 1000 cal yr bp and the minimum initiation periods occurred after 5 kyr our multiple basal ages along eight transects show that slopes are a dominant control on peatland lateral expansion rates with very slow and less variable rates at slopes 0 4 degrees furthermore we found a significant relationship between peatland basal ages and peat depths from 85 sites suggesting relatively uniform peat properties carbon accumulation rates from detailed downcore analysis at four sites and on the basis of peat depth basal age relationship show similar patterns with a peak carbon accumulation at 10 8 kyr on the basis of estimated mean values of bulk density and carbon content from the region the holocene average c accumulation for the zoige basin is 31 1 g c m 2 yr the widespread peatland initiation and rapid accumulation in the early holocene were likely in response to higher temperature and stronger summer monsoon intensity while the slowdown of peatland development during the late holocene might have been caused by climate cooling and drying

a new approach to the nd residence time in the ocean the role of atmospheric inputs concentrations of rare earth elements ree and nd isotopic ratios were analyzed for seawater filtered suspension and sediment trap samples collected in the tropical atlantic ocean eumeli program eutrophic mesotrophic and oligotrophic sites 20 n 18 21 w this is the first ree nd dataset on solution and different sized particles collected at the same site we present direct evidence of the nd isotopic exchange between particulate lithogenic fraction and seawater without significant mass transfer this exchange is probably one of the main factors that simultaneously constrains the nd concentration and isotopic ratio budget we propose a new approach to estimate the residence time of nd in the ocean nd based on isotopic exchange 200 yr nd 1000 yr the exchange requires a partial dissolution of lithogenic nd we estimate that the fraction of soluble nd proportion in atmospheric dust is of the order of 20 based on the isotopic ratios we suggest that the partial dissolution of atmospheric fallout is probably one of the main ree sources of the ocean

application of a chemical leach technique for estimating labile particulate aluminum iron and manganese in the columbia river plume and coastal waters off oregon and washington in order to determine the total concentration of bioavailable trace metals in seawater measurement of both the dissolved and labile particulate fractions is necessary comparison of labile particulate metal concentrations from various researchers is limited because of differing definitions of the fraction that is potentially available to phytoplankton on a time frame of generations a comparison experiment was conducted on coastal and riverine suspended particulate matter to determine the difference between several commonly used techniques that operationally define the labile particulate trace metal fraction furthermore we compared two leach techniques for surface transect samples from within the columbia river plume and water offshore of oregon and washington united states the particulate trace metal concentration in the leachate was determined by high resolution inductively coupled plasma mass spectrometry from this comparison one chemical leach was chosen to best define the labile particulate fraction of al fe and mn a weak acid leach 25 acetic acid at ph 2 with a mild reducing agent 0 02 m hydroxylamine hydrochloride and a short heating step 10 min 90 95 c this leach was applied to three surface transects within the columbia river plume these coastal waters were found to be rich in labile particulate trace metals that are directly delivered from the columbia river and indirectly supplied via resuspension from upwelling over a broad continental shelf

distinct modes of the east asian winter monsoon two distinct modes of the east asian winter monsoon eawm have been identified and they correspond to real and imaginary parts of the leading mode of the eawm respectively analyses of these modes used the national centers for environment prediction ncep and national center for atmospheric research ncar monthly mean reanalysis datasets for the period 1968 2003 as well as the southern oscillation index soi north atlantic oscillation index and eastern equatorial pacific sea surface temperature sst data results were obtained by resolving a complex hermite matrix derived from 850 hpa anomalous wind fields and determining the resulting modes associations with several climate variables the first distinct mode m1 is characterized by an anomalous meridional wind pattern over east asia and the western north pacific mode m1 is closely related to several features of the atmospheric circulation including the siberian high east asian trough east asian upper tropospheric jet and local hadley circulation over east asia thus m1 reflects the traditional eawm pattern revealed in previous studies the second distinct eawm mode m2 which was not identified previously displays dominant zonal wind anomalies over the same area mode m2 exhibits a closer relation than m1 to sea level pressure anomalies over the northwestern pacific southeast of japan and with the soi and equatorial eastern pacific sst unlike m1 m2 does not show coherent relationships with the siberian high east asian trough and east asian upper tropospheric jet since atmospheric circulation anomalies relevant to m2 exhibit a quasibarotropic structure its existence cannot simply be attributed to differential land sea heating el nino events tend to occur in the negative phase of m1 and the positive phase of m2 both corresponding to a weakened eawm the arctic oscillation does not appear to impact the eawm on interannual time scales although the spatial patterns for the two modes are very different the two distinct modes are complementary with the leading eawm mode being a linear combination of the two the results herein therefore demonstrate that a single eawm index may be inappropriate for investigating and predicting the eawm

a dry episode during the younger dryas and centennial scale weak monsoon events during the early holocene a high resolution stalagmite record from southeast of the loess plateau china 1 a high resolution stalagmite oxygen isotope record from dongshiya cave located southeast of the chinese loess plateau reveals detailed climatic oscillations between 12 7 and 9 0 ka bp on centennial and decadal timescales with a temporal resolution of 1 to 20 years the early younger dryas is characterized by a gradual increase in 18o values which is followed by a depositional hiatus for the remainder of the younger dryas between 12 1 and 11 5 ka bp implying a weak east asian monsoon or a dry climate during the younger dryas eight weak monsoon events between 11 5 and 9 0 ka bp punctuate the early holocene east asian monsoon and are likely tied to cold events in greenland including the pre boreal oscillation and the 9 2 ky event the spectral analysis of the dongshiya 18o time series yields peaks at frequencies that have been linked to solar frequencies indicating that solar changes may be at least partially responsible for changes in the intensity of the east asian monsoon during the early holocene

lead atmospheric deposition rates and isotopic trends in asian dust during the last 9 5 kyr recorded in an ombrotrophic peat bog on the eastern qinghai tibetan plateau a full understanding of the atmospheric pb cycle in asia during the holocene is key to palaeoclimate studies of past atmospheric circulation patterns as well as to assess the impact of increasing industrial activities in this region however long term records of atmospheric pb isotopic trends in asia are still sparse consequently we study changes in the concentrations fluxes and isotopic signature of deposited pb contained in a 14c dated peat core from the eastern qinghai tibetan plateau dating back to 9 5 kyr bp and present the first peat record of the changing isotopic composition of atmospheric pb in dust in asia during this time lead concentrations and fluxes vary between 2 96 21 58 lg g 1 and 0 06 3 52 mg m 2 y 1 respectively with an average pb baseline of 6 80 4 18 lg g 1 these values agree with other pb studies of lake and peat archives in china but are one order of magnitude larger than early and mid holocene values measured in europe lead isotopic variability throughout the core is small varying between 206pb 207pb 1 190 1 197 206pb 204pb 18 648 18 786 207pb 204pb 15 666 15 694 and 208pb 204pb 38 890 39 090 the application of bayesian trans dimensional changepoint modelling to the pb dataset enabled the identification of eight significant changes in the isotopic composition of the deposited pb such changes mark different phases of atmospheric pb deposition and hence variations in atmospheric circulation patterns and environmental conditions temporal variations in the potential natural and or anthropogenic pb sources are assessed based on the 206pb 207pb 208pb and 204pb isotopic composition and the 1 pb ratio of the peat samples our results suggest that pb deposition throughout the holocene was governed by local deposition and long range input from natural dust sources in northwestern taklamakan desert and qaidam basin and northern china badain jaran and tengger deserts input from the northern sources seems to have been particularly important between 3 1 2 7 kyr bp and 1 7 0 9 kyr bp suggesting a possible strengthening of the east asian winter monsoon in agreement with previous reconstructions in asia based on the pb sc and isotopic composition profiles we do not note any evidence for anthropogenic pb derived from the thriving mining or smelting activities in northern and eastern china in the last few millennia suggesting that atmospheric deposition to this region of the eastern tibetan plateau was dominated by natural pb fluxes these can serve as a true asian background value against which anthropogenic impacts can be quantified our results confirm that the combination of radiogenic isotopes pb and trace elements in peat bogs enables observational reconstructions of changes in past regional atmospheric circulation such records will enable more refined interpretations of marine and terrestrial palaeorecords in asia and the pacific and consequently provide further constraints for changes in ocean and atmospheric circulation and for the testing of palaeoclimate models of circulation patterns

reactivity of neodymium carriers in deep sea sediments implications for boundary exchange and paleoceanography the dissolved neodymium nd isotopic distribution in the deep oceans is determined by continental weathering inputs water mass advection and boundary exchange between particulate and dissolved fractions reconstructions of past nd isotopic variability may therefore provide evidence on temporal changes in continental weathering inputs and or ocean circulation patterns over a range of timescales however such an approach is limited by uncertainty in the mechanisms and importance of the boundary exchange process and the challenge in reliably recovering past seawater nd isotopic composition end from deep sea sediments this study addresses these questions by investigating the processes involved in particulate solution interactions and their impact on nd isotopes a better understanding of boundary exchange also has wider implications for the oceanic cycling and budgets of other particle reactive elements sequential acid reductive leaching experiments at ph 2 5 on deep sea sediments from the western indian ocean enable us to investigate natural boundary exchange processes over a timescale appropriate to laboratory experiments we provide evidence that both the dissolution of solid phases and exchange processes influence the end of leachates which suggests that both processes may contribute to boundary exchange we use major element and rare earth element ree data to investigate the pools of nd that are accessed and demonstrate that sediment leachate end values cannot always be explained by admixture between an authigenic component and the bulk detrital component for example in core wind 24b acid reductive leaching generates end values between 11 and 6 as a function of solution solid ratios and leaching times whereas the authigenic components have end 11 and the bulk detrital component has end 15 we infer that leaching in the mascarene basin accesses authigenic components and a minor radiogenic volcanic component that is more reactive than madagascan derived clays the preferential mobilisation of such a minor component demonstrates that the nd released by boundary exchange could often have a significantly different end composition than the bulk detrital sediment these experiments further demonstrate certain limitations on the use of acid reductive leaching to extract the end composition of the authigenic fraction of bulk deep sea sediments for example the detrital component may contain a reactive fraction which is also acid extractible while the incongruent nature of this dissolution suggests that it is often inappropriate to use the bulk detrital sediment elemental chemistry and or end composition when assessing possible detrital contamination of leachates based on the highly systematic controls observed and evidence from ree patterns on the phases extracted we suggest two approaches that lead to the most reliable extraction of the authigenic end component and good agreement with foraminiferal based approaches either i leaching of sediments without a prior decarbonation step or ii the use of short leaching times and low solution solid ratios throughout

the distribution of neodymium isotopes and concentrations in the eastern equatorial pacific water mass advection versus particle exchange the radiogenic isotope composition of the rare earth element ree neodymium nd is a powerful water mass proxy for present and past ocean circulation the processes controlling the nd budget of the global ocean are not quantitatively understood and in particular source and sink mechanisms are still under debate in this study we present the first full water column data set of dissolved nd isotope compositions and nd concentrations for the eastern equatorial pacific eep where one of the globally largest oxygen minimum zones omz is located this region is of particular interest for understanding the biogeochemical cycling of rees because anoxic conditions may lead to release of rees from the shelf whereas high particle densities and fluxes potentially remove the rees from the water column data were obtained between 1 40 n and 16 s along a nearshore and an offshore transect near surface zonal current bands such as the equatorial undercurrent euc and the subsurface countercurrent sscc which are supplying oxygen rich water to the omz are characterized by radiogenic nd isotope signatures end 2 surface waters in the northernmost part of the study area are even more radiogenic end 3 most likely due to release of nd from volcanogenic material deep and bottom waters at the southernmost offshore station 14 s are clearly controlled by advection of water masses with less radiogenic signatures end 7 originating from the southern ocean towards the equator however the deep waters show a clear trend towards more radiogenic values of up to end 2 the northernmost station located in the panama basin shows highly radiogenic nd isotope signatures in the entire water column which indicates that particle scavenging downward transport and release processes play an important role this is supported by relatively low nd concentrations in deep waters 3000 6000 m in the eep 20 pmol kg compared to locations in the northern and central pacific 40 60 pmol kg which suggests enhanced removal of nd in the eep

testing the extraction of past seawater nd isotopic composition from north atlantic deep sea sediments and foraminifera neodymium isotopes provide a paleoceanographic proxy for past deep water circulation and local weathering changes and have been measured on various authigenic marine sediment components including fish teeth ferromanganese oxides extracted by acid reductive leaching cleaned foraminifera and foraminifera with fe mn oxide coatings here we compare nd isotopic measurements obtained from ferromanganese oxides leached from bulk sediments and planktonic foraminifera as well as from oxidatively reductively cleaned foraminiferal shells from sediment cores in the north atlantic sedimentary volcanic ash contributes a significant fraction of the nd when the ferro manganese fe mn oxide coatings are leached from bulk sediments reductive leachates of marine sediments from north atlantic core tops near iceland or directly downstream from iceland scotland overflow waters record nd values that are significantly higher than seawater indicating that volcanic material is easily leached by acid reductive methods the nd values from sites more distal to iceland are similar to modern seawater values showing little contamination from iceland derived volcanogenic material in all comparisons core top planktonic foraminifera nd values more closely approximate modern deep seawater than the bulk sediment reductive leached value suggesting that the foraminifera provide a route toward quantifying the nd isotopic signature of deep north atlantic water masses

tectonically driven changes in the indian ocean circulation over the last 25 ma neodymium isotope evidence abstract changes in ancient oceanic current patterns have been strongly influenced by plate tectonics particularly by the opening or closing of gateways between different oceans such modifications of oceanic circulation have important consequences on climate we studied the nd seawater isotopic composition of indian and pacific ocean cores using nd isotopes which are good paleo oceanographic tracers we focused on the past 25 ma which are marked by the closure of the indonesian gateway as well as the mediterranean connection we show that a strong westerly oceanic surface current which we refer to the miocene indian ocean equatorial jet miojet linked the eastern and western indian ocean from 14 ma to 3 ma and infer that this major change in oceanic circulation probably induced important variations of global climate

new insights into the origin of kabbaldurga charnockites karnataka south india abstract a detailed study of the structure and petrology of the rocks bordering the kabbaldurga type charnockites provides important constraints on the origin of these charnockites the structural elements register three phases of deformation and show a uniform pattern in the larger area a pattern consistent with the regional structure of the precambrian of southern karnataka in the kabbaldurga area however some of the earlier structures are poorly preserved yet there are vestiges of early folds described by banded layered charnockites as in the neighbouring kodamballi area and a consistent development of dilatant structures which can be related to the kinematics of deformation in the larger terrain at kabbaldurga the pegmatitic charnockites occur as veins of diverse orientation but they rarely follow the shear generated structures the metamorphic reactions invoked by previous workers to explain in situ transformation of gneiss to charnockite were based on chemical similarity of some close pairs but the petrographic and chemical variations in the pegmatitic charnockites and the peninsular gneisses at kabbaldurga quarry are compelling features which cannot be explained by the hypothesis of in situ transformation we have argued on the basis of rock and mineral chemistry that derivation of the pegmatitic charnockites by dehydration melting in metabasites offers a better explanation pressure temperature values at least 850 to 900 c 7 kbar obtained by us for the granulites of this area viewed against the results of experimental dehydration melting in basic rocks with hornblende and or biotite provide strong support for this model in the field leucosomes within the basic granulites of kabbaldurga are not uncommon the compositions of the pegmatitic charnockites tonalitic and granitic match those of the melts produced in experiments further the pattern of variation in the composition of hornblende and plagioclase in the basic granulites of the kabbaldurga area is compatible with extraction of melts this alternative model for the origin of the kabbaldurga charnockites is petrologically feasible and does not require either in situ transformation or structurally controlled growth which incidentally are not ubiquitous at kabbaldurga

determination of easily accessible metal fractions in rocks by batch leaching with acid cation exchange resin the easily accessible fraction of metals in rocks is derived from leaching experiments aliquots of rock powders are mixed with ion exchange resin and distilled water the ph self adjusts to a value of 3 after batch leaching times of 2 48 hr at 70 c the resin is quantitatively separated from the rock powder and eluted with 4 n hno3 the metal contents of the leachates are determined and related to the respective contents of the whole rock the leaching kinetics of each element is related to that of a reference element aluminium is most commonly chosen as a reference element because it is considered to represent the dissolution behaviour of the main rock forming minerals the easily accessible trace element fraction eat is given as the percentage of leached element at 1 al dissolution these eat values are reproducible and independent from grain size and sample resin ratio the procedure is tested on basaltic glass and variably altered gneisses the glass shows congruent release of all metals a slightly crystalline glass of the same chemical composition displays heterogeneous leaching behaviour the leaching kinetics of variably altered gneisses provide insight into the mineralogical siting of elements and their accessibility to fluids consequences for rb sr dating of rocks are discussed

rare earth elements in foraminifera tests abstract the concentrations of nine rare earth elements ree la ce nd sm eu gd dy er and yb have been determined in mixed species assemblages of foraminifera tests taken from atlantic ocean sediment core tops reductive cleaning techniques have revealed that ree are present in three phases in foraminifera tests collected from sea floor sediments ree included in the foraminiferal calcite matrix termed lattice ree ree associated with an authigenic femn rich phase adsorbed onto the surface of the test following the death of the organism termed coating ree and ree associated with alumino silicate detritus termed detrital ree which commonly infills the test chambers after burial in the sediment the concentrations of ree in the nondetrital lattice plus coating and lattice phases have been measured in this study approximately 90 of the ree measured in the non detrital phase reside in the coating phase the remainder being present in the lattice phase these data have been used to investigate the relationship between the distribution of dissolved ree in the ocean and in the coating and lattice phases in addition to the ree the concentrations of mn fe cu al and po4 have been measured as an aid to characterisation of the various phases

porewater ph and authigenic phases formed in the uppermost sediments of the santa barbara basin abstract in this paper porewater and solid phase analyses are used in combination with in situ o 2 and ph microelectrode measurements to characterize early diagenetic processes in the uppermost sediments of the santa barbara basin california rapid reduction of dissolved oxygen nitrate solid phase manganese and iron and dissolved sulfate is observed between sediment depths of 0 and 2 cm reductive solubilization of ferric iron phases releases fe 2 adsorbed phosphate and fluoride to the porewaters and contributes to a sharp increase in porewater ph between 2 and 4 cm sulfate reduction rates peak ph levels off and acid volatile sulfides and pyrite become the dominant forms of solid phase iron saturation state calculations which depend largely on ph indicate that the porewaters of the santa barbara basin become saturated with respect to carbonate fluorapatite and calcite within the first 0 25 mm of the sediment and are highly supersaturated by and below 2 cm in spite of this result porewater evidence of phosphate and fluoride removal into a solid phase is observed only in the first 5 cm of some cores whereas dissolved ca profiles suggest dispersed calcite precipitation throughout the sediment column this finding is interpreted as an indication of the nonsteady state nature of the surface reactions that may given sufficient nucleation sites and time lead to carbonate fluorapatite genesis in anoxic sediments finally microelectrode ph profiles from two other basins in the california borderlands are presented these demonstrate that the porewaters of the santa barbara basin are more alkaline than those of other basins this outcome is attributed to the lack of particle mixing and a unique interplay between fe liberation and fes precipitation reactions in the santa barbara basin

peatland development and climate changes in the dajiuhu basin central china over the last 14 100 years abstract peatlands are one of the optimal archives for paleoclimate research and their records contain a detailed history of climatic and environmental variations during their formation here we collected a peat profile from the dajiuhu basin in central china and analyzed several geochemical proxies such as total organic carbon toc total nitrogen tn titanium ti and aluminum al to investigate the history of peat development the results show that the peat growth was initiated after around 12 8 cal ka bp at the sampling site and the toc and tn contents kept stable during the holocene except during the periods of 10 5 9 0 cal ka bp and recent 1 5 cal ka bp however compared with other toc records in the dajiuhu basin the history of peat development varied greatly in different sampling sites indicating that the peat development in the dajiuhu basin probably responds to both climate changes and local geological and hydrological conditions investigations of the interactions between climate change and peat development record in this study suggest that peat development presented significant responses to the large and rapid decreases in east asian summer monsoon intensity such as the 9 2 ka monsoon weakening event however the obvious long term decreasing trend of monsoon precipitation during the mid late holocene did not lead to the degradation of the dajiuhu peat probably resulting from relatively stable temperature in addition the sharp decrease of toc and tn values in the surface 15 cm of dajiuhu peat was probably attributed to increased human activity

enso tropical extratropical climate teleconnections and mechanisms for holocene debris flows along the hyperarid coast of western south america 17 24 s abstract el nino the warm phase of the enso cycle involves ocean climate anomalies in the tropical pacific ocean and in the extratropics which frequently result in heavy rainfall episodes along the equatorial and subtropical regions of western south america here we investigate meteorological mechanisms producing heavy rains floods and debris flows along the less known hyperarid coasts of southern peru and northern chile to evaluate the paleoclimate significance of holocene debris flow deposits our results reveal that heavy rainfall over the coast of southernmost peru occurs either during austral summer at the mature stage of el nino in connection with warmer sea surface temperatures and anomalous jet streams off northern chile or during the previous austral winter spring associated with equatorward shifted pacific south america psa atmospheric teleconnection patterns at antofagasta in northern chile such events occur almost exclusively in the latter season when deeper psa related anomaly poles extend their influence equatorwards beyond central chile during non el nino conditions short lived heavy rainfall episodes in southernmost peru can be associated with similar albeit weaker or less persistent circulation anomalies in addition to that a seasonally enhanced low level southerly flow provides orographic uplift rainfall favourable conditions by the andes at the 18 s coastal bend ultimately the trigger for rainfall events in all seasons and phases of the enso cycle was invariably connected with mid troposphere wave disturbances from mid latitudes the chronostratigraphy of debris flow deposits from both areas and its comparison with other paleoclimate records at the western side of the andes suggests that the enso related teleconnection patterns operated only during the second half of the holocene supporting an onset of modern el nino manifestations at 5300 5500 cal bp and increased frequency of major events during recent times we suggest that several debris flows dated between 12 900 and 8400 cal bp in southernmost peru previously interpreted as an indication of strong el nino events were associated with short and intense heavy rainfall episodes similar to those described here during the late winter spring season in non el nino conditions concomitant with stronger low level southerlies strengthened south eastern pacific subtropical anticyclone and intensified coastal upwelling

multidecadal drought and holocene climate instability in the rocky mountains time series analysis of a diatom inferred drought record suggests that holocene hydroclimate of the northern rocky mountains has been characterized by oscillation between two mean climate states the dominant climate state was initiated at the onset of the holocene ca 11 ka under this climate state drought was strongly cyclic recurring at frequencies that are similar to twentieth century multidecadal phase changes of the pacific decadal oscillation this pattern remained consistent throughout much of the midholocene continuing until ca 4 5 ka after this time the mean climate state changed and drought recurrence became unstable periods of cyclic drought alternated with periods of less predictable drought the timing of this shift in climate was coincident with widespread severe drought in the mid continent of north america overall the strongest periodicity in severe drought occurred during the mid holocene when temperatures in the northern rocky mountains were warmer than today

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

lipid biomarkers in the zoige hongyuan peat deposit indicators of holocene climate changes in west china abstract lipid biomarkers extracted from a peat core obtained from the northeast edge of the tibetan plateau have provided a 13 kyr record of regional climate change a period of warmer climate corresponding to the holocene optimum between 9 ka and 5 ka is evident in greater alteration of n alkanoic acids and n alkanols and in the appearance of biomarkers indicative of greater microbial activity concomitant increases in local precipitation that raised the water level of the peat bog are recorded by increases in the proportions of c23 and c25 n alkanes that are mainly derived from submerged floating plants alternations in submergent and emergent plant n alkane proxies reveal multi decimeter scale rises and falls in the bog water level that relate to variation in precipitation on the tibetan plateau during the holocene major low water level events occurred around 12 6 11 3 10 7 9 4 8 3 6 0 4 5 3 1 2 1 and 1 0 ka these events correlate well with cold dry events recorded in same region from other climatic proxies that reflect millennial scale holocene instability in the asian monsoon system our biomarker results also indicate that peat accumulation and preservation on the tibetan plateau are more sensitive to variability in monsoonal precipitation than in annual temperature

continuous 150 k y monsoon record from lake eyre australia insolation forcing implications and unexpected holocene failure our reconstructed history of lake eyre provides the first continuous continental proxy record of australian monsoon intensity over the past 150 k y this continental record s broad correspondence to the marine isotope record demonstrates that this very large catchment with its hydrology dependent on a planetary scale climate element responds to milankovitch scale climate forcing abrupt transitions from dry phases to wet phases ca 125 and 12 ka coincide with northern hemisphere winter insolation minima rather than southern hemisphere summer insolation maxima indicating that northern hemi sphere insolation exerts a dominant control over the intensity of the australian monsoon stratigraphic and dating uncertainties of other wet phases preclude conclusive correlation to specific insolation signals but within the uncertainties are consistent with northern hemisphere forcing regardless of the hemispheric forcing the low intensity of the early holocene australian monsoon by comparison with the last interglacial and particularly the last high level lacustrine event at 65 60 ka when all forcing elements were modest is an enigma that can be explained by a change in boundary conditions within australia

nd isotopic composition in the central north pacific three vertical profiles of seawater concentration and isotopic composition of nd were determined for the western to central north pacific ocean in the subarctic oceanic region at depths greater than 500 m one vertical profile of nd isotopic composition was indistinguishable from most previously reported profiles from here the data indicate a rather homogeneous nd isotopic composition in the subarctic oceanic region at middle to deep depths 500 m two stations in the subtropical oceanic region exhibited similar nd isotopic composition profiles to those previously reported the maxima end values at depths of 800 1000 m end 3 4 to 2 7 which correspond to the north pacific intermediate water npiw are found at both subtropical stations this implies a ubiquitous distribution of npiw showing a radiogenic end value in the north pacific the subsurface minimum at a depth of 200 m which indicates the penetration of the north pacific tropical water nptw with an unradiogenic nd isotopic signal was observed at one station in the western pacific this station had much lower end than the central station at depths around 5000 m suggesting the greater prominence of antarctic bottom water aabw in the western subtropical pacific than in the central to eastern subtropical pacific results of a model calculation assuming boundary exchange indicate that the hawaiian islands play an important role in supplying radiogenic nd to the central pacific similar to some continental margins we show that nd isotopic composition is a versatile tracer for ocean circulation and the geochemical cycle of nd in the north pacific further studies on the distribution of nd isotopic composition in the pacific ocean including the southern pacific will better elucidate the circulation and geochemical cycle of nd in the pacific

holocene climate development on the central tibetan plateau a sedimentary record from cuoe lake abstract we present a climate record for central tibet spanning the time between 10500 and 1600 cal years bp from a 5 3 m long sediment core from cuoe lake the analyses show that high sr concentration high toc content high c n ratio and enriched 13c of lake sediments corresponded to stronger chemical weathering high productivity high lake level and warmer wetter climate and vice versa as revealed by the variations of these proxies the climatic evolution during this period can be divided into five stages and several substages these are a cold dry stage before 10140 cal years bp a transition stage from 10140 to 8560 cal years bp an optimum stage warm wet from 8560 to 5750 cal years bp a cool dry stage from 5750 to 4000 cal years bp a transition stage from 4000 to 3000 cal years bp and a drying up stage after 3000 cal years bp these changes are presumably reflections of variations in indian monsoon intensity which according to that interpretation should have been enhanced from 8560 cal years bp slightly weakened after 5750 cal years bp and gradually diminished since 3000 cal years bp in this region

a synthesis of abrupt changes in the asian summer monsoon since the last deglaciation we have compiled 36 previously published palaeoclimate records to determine the timing and spatial pattern of century scale abrupt changes in asian monsoon precipitation since the last deglaciation we identify abrupt events from 1 the interpretations of the authors of these records and 2 the more objective moving t test calculation our results indicate that abrupt climatic changes occurred at 11 5 cal ka 4 5 5 0 cal ka and ad 1300 at the start of the holocene 11 5 cal ka asian monsoon precipitation increased dramatically this climatic change is synchronous with an abrupt warming in the north atlantic during the middle holocene there was a time of preferred and widespread weakening in monsoon strength 4 5 5 0 cal ka this result contradicts previous notions of either a gradual trend towards drier conditions or a series of abrupt events that occurred in an unorganized fashion across space and time the middle holocene abrupt event could have been synchronous with an abrupt cooling event in the north atlantic as well as a warming and intensie cation of internannual variability in the tropical pacie c in contrast to previous periods precipitation changes at ad 1300 have a heterogeneous spatial pattern we e nd no conclusive evidence for a change in the asian monsoon at 8 2 cal ka as suggested by several previous studies more high resolution data may be needed to observe this short lived event overall our results attest to the potential for rapid and major shifts in asian monsoon precipitation that may be triggered by variations in other components of the climatic system

a boundary exchange influence on deglacial neodymium isotope records from the deep western indian ocean the use of neodymium nd isotopes to reconstruct past water mass mixing relies upon the quasi conservative behaviour of this tracer whereas recent studies in the modern oceans have suggested that boundary exchange involving the addition of nd from ocean margin sediments may be an important process in the nd cycle here we suggest that the relative importance of water mass advection versus boundary exchange can be assessed where the deep western boundary current in the indian ocean flows past the madagascan continental margin a potential source of highly unradiogenic nd foraminiferal coatings and bulk sediment reductive leachates are used to reconstruct bottom water nd isotopic composition end in 8 holocene age coretops with excellent agreement between the two methods these data record spatial variability of 4 end units along the flow path of circumpolar deep water end 8 8 in the deep southern inflow upstream of madagascar which evolves towards end 11 5 offshore northern madagascar whereas end 7 3 where deep water re circulates in the eastern mascarene basin this variability is attributed to boundary exchange and together with measurements of detrital sediment end an isotope mass balance suggests a deep water residence time for nd of 400 yr along the madagascan margin considering deglacial changes a core in the deep inflow upstream of madagascar records end changes that agree with previous reconstructions of the circumpolar deep water composition in the southern ocean consistent with a control by water mass advection and perhaps indicating a longer residence time for nd in the open ocean away from local sediment inputs in contrast sites along the madagascan margin record offset end values and reduced glacial interglacial variability underlining the importance of detecting boundary exchange before inferring water mass source changes from nd isotope records the extent of madagascan boundary exchange appears to be unchanged between the holocene and late glacial periods while a consistent shift towards more radiogenic end values at all sites in the late glacial compared to the holocene may represent a muted signal of a change in water mass source or composition

the use of foraminifera as a record of the past neodymium isotope composition of seawater 1 we present new isotopic data for sedimentary planktonic foraminifera as well as for potential water column and sedimentary sources of neodymium nd which confirm that the isotopic composition of the foraminifera is the same as surface seawater and very different from deep water and sedimentary nd the faithfulness with which sedimentary foraminifera record the isotopic signature of surface seawater nd is difficult to explain given their variable and high nd ca ratios ratios that are often sedimentary foraminifera ratios that are often much higher than is plausible for direct incorporation within the calcite structure we present further data that demonstrate a similarly large range in nd ca ratios in plankton tow foraminifera a range that may be controlled by redox conditions in the water column cleaning experiments reveal in common with earlier work that large amounts of nd are released by cleaning with both hydrazine and diethylene triamine penta acetic acid but that the nd released at each step is of surface origin while further detailed studies are required to verify the exact location of the surface isotopic signature and the key controls on foraminiferal nd isotope systematics these new data place the use of planktonic foraminifera as recorders of surface water nd isotope ratios and thus of variations in the past supply of nd to the oceans from the continents via weathering and erosion on a reasonably sure footing

late quaternary variability of mediterranean outflow water from radiogenic nd and pb isotopes mediterranean outflow water mow is characterised by higher temperatures and salinities than other ambient water masses mow spreads at water depths between 500 and 1500 m in the eastern north atlantic and has been a source of salinity for the atlantic meridional overturning circulation in the north atlantic we used high resolution nd and pb isotope records of past ambient seawater obtained from authigenic ferromanganese coatings of sediments in three gravity cores at 577 1745 and 1974 m water depth in the gulf of cadiz and along the portuguese margin complemented by a selection of surface sediments to reconstruct the extent and pathways of mowover the past 23 000 years the surface and downcore nd isotope data from all water depths exhibit only a very small variability close to the present day composition of mowbut do not reflect the present day nd isotopic stratification of the water column as determined from a nearby open ocean hydrographic station in contrast the pb isotope records show significant and systematic variations which provide evidence for a significantly different pattern of the mow pathways between 20 000 and 12 000 years ago compared with the subsequent period of time

reconstructing deglacial north and south atlantic deep water sourcing using foraminiferal nd isotopes during the last few decades neodymium isotopes have been increasingly used as a paleoceanographic and paleoclimate proxy on million year through millennial time scales the widespread use of the nd isotope proxy depends on whether the nd isotopic composition of past seawater can be reliably extracted from authigenic sediment phases here we show evidence that planktonic foraminifera with authigenic coatings preserve a deep water nd isotopic signature and thus can be used to reconstruct past deep water nd isotopes applying this method downcore on south atlantic deep cape basin core tno57 21 41 1 s 7 9 e 4981 m the nd isotopic composition of the planktonic foraminiferal fe mn oxide coatings is identical with and confirms that of the reductively leached bulk sediment fraction piotrowski et al 2004 2005 2008 as reflecting changes in bottom water sourcing in the case of northeastern north atlantic core bofs 8k 52 5 n 22 1 w 4045 m the planktonic foraminiferal fe mn oxide coatings have different nd isotopes from reductive sediment leaches clearly acid reductive leaching must be tested in more detail we observe that the nd isotopic composition of the deep northeastern atlantic core shifted during the deglaciation from glacial values similar to the south atlantic cape basin towards holocene values similar to the bermuda rise roberts et al 2010 taken as a whole the nd isotope record from foraminiferal authigenic coatings suggests large scale changes in the proportion of northern and southern deep water sources occurred throughout the atlantic ocean with substantial chemical gradients at times during the last deglaciation

rare earth elements and neodymium isotopes in ferromanganese oxide coatings of cenozoic foraminifera from the atlantic ocean abstract an evaluation has been made of the method of establishing the ree contents and patterns and nd isotopic compositions of sea water over cenozoic time from their record in the femn oxide coatings of foraminiferal calcite using 0 60 ma samples from the rio grande rise dsdp site 357 it has been established that the ree contents of the coatings are generally similar to those of recent samples however in the cenozoic samples the surface coatings have been diagenetically modified under suboxic conditions resulting in a distinctly different ree pattern although the original 143 nd 144 nd ratios appear to have been preserved the nd isotopic curve for cenozoic sea water in the s atlantic shows clear temporal trends although these are not so extreme as to show 143 nd 144 nd ratios outside the range observed in modem sea water with the principal exception of the oldest samples there is an approximate inverse relationship between the nd and sr isotopic compositions of the foraminifera it is suggested that the changes reflect both global changes in the relative proportions of nd and sr derived from continental input and from the weathering of volcanic debris together with short term and local variations to which the sr curve is insensitive reflecting the different response times of the two elements to changes in oceanic input functions the nd isotope curve appears to be a potentially useful tracer of ocean palaeochemistry

manganese carbonate overgrowths on foraminifera tests below the zone where manganese is remobilized as mn2 aq reductively cleaned foraminifera in deep sea sediments have much higher mnca than those in core tops and sediment traps mnca ranges from less than 20 10 6 in and above the mno2 maximum to as high as 700 10 6 in reducing panama basin sediments the most plausible explanation for this enrichment is that the tests are coated with mn carbonate overgrowths these coatings can account for a significant proportion of the mn in reduced deep sea sediments uptake of manganous ion by carbonate may explain the absence of mn nodules in areas of high carbonate accumulation extreme degrees of overgrowth can alter foram trace element values but this artifact can be avoided by avoiding foraminifera with high mn ca

origin of negative ce anomalies in mixed hydrothermal hydrogenetic fe mn crusts from the central indian ridge abstract layered fe mn crusts from the off axis region of the first segment of the central indian ridge north of the rodrigues triple junction were studied geochemically and mineralogically vernadite mno2 is the main mineral oxide phase 230thxs and co concentrations suggest high growth rates of up to 29 mm myr and a maximum age of the basal crust layer of 1 ma whereas most of the major and minor elements show concentrations which are typical of hydrogenetic formation co pb ni and ti concentrations are strikingly lower concentrations and distribution of the strictly trivalent rare earths and yttrium rey are typical of hydrogenetic ferromanganese oxide precipitates but in marked contrast the crusts are characterized by negative cesn shale normalized anomalies and ce pr sn ratios less than unity profiles through the crusts reveal only minor variations of the rey distribution and ce pr sn ratios range from 0 45 to 0 68 compared to ratios of up to 2 for typical hydrogenetic crusts from the central indian basin the apparent bulk partition coefficients between the crusts and seawater suggest that for the strictly trivalent rey the adsorption desorption equilibrium has been reached positive ce anomalies in the partition coefficient patterns reveal preferential uptake of ce but to a lesser extent than in normal hydrogenetic crusts a new parameter excess ce cexs to quantify the degree of decoupling of ce from rey iii is established on the basis of partition coefficients cexs cebulk ratios suggest that the cir crusts formed by precipitation of fe mn oxides from a hydrothermal plume and that in hydrothermal plumes and normal seawater the enrichment of ce results from the same oxidative sorption process the growth rates calculated with 230thxs data as well as with the co formula are inversely related to cexs

diatom based inference of variations in the strength of asian winter monsoon winds between 17 500 and 6000 calendar years b p 1 we present a continuous record of fossil diatoms from huguang maar lake hml in southeastern china spanning the time interval 17 500 to 6000 calendar years cal years b p the seasonal change in relative abundance of the dominant diatom taxa aulacoseira and cyclotella species can be used as a proxy of the strength of winter monsoon winds wmw which is supported by the results of a sediment trap experiment in hml and by an extensive review of the literature on the autoecologies of these species in the sediment high c stelligera abundance and high diatom concentration which indicate warm conditions and low wind driven turbulence of the water column characterize an interval equivalent to the greenland interstadial 1 this is followed by an interval with low diatom concentration and with assemblages dominated by aulacoseira species which suggests high wind driven turbulence and therefore strong wmw this interval corresponds with the greenland stadial 1 during the early and middle holocene another two episodes with strong wmw are evident from the data between 10 000 and 8500 and between 7000 and 6000 cal years b p the diatom record implies that strong winter monsoon episodes not only occurred during the last glacial holocene transition but also during the holocene thermal maximum

neodymium isotopes in the mediterranean sea comparison between seawater and sediment signals nine depth profiles of dissolved nd concentrations and isotopic ratios epsilon nd were obtained in the levantine basin the ionian the aegean the alboran seas and the strait of gibraltar thirteen core top sediments and nile river particle samples were also analyzed leached with 1 n hcl acetic acid or hydroxylamine hydrochloride the seawater epsilon nd values become more radiogenic during the eastward circulation in the mediterranean sea the relationship between salinity and the seawater epsilon nd shows that the nd isotopic signature is more conservative than salinity in the mediterranean sea the water mass with the highest epsilon nd 4 8 is found at about 200 m in the easternmost levantine basin the average epsilon nd value for deep waters is 7 0 in the eastern basin 2 5 epsilon units higher than in the western basin by examining the sensitivity of seawater epsilon nd to nd inputs from the nile we conclude that the most significant radiogenic nd source is partially dissolved nile river particles the nd flux from the nile river water has a minor influence on the mediterranean seawater end except for the easternmost levantine basin the leachate epsilon nd values are consistent with the seawater values in the easternmost levantine basin the leachate end values obtained with hcl leaching are systematically higher than the seawater values the relationship between leachate and residual epsilon nd values indicates that the hcl leaching partially dissolves lithogenic nd so the dissolution of nile river particles is the cause of the observed shift some end values obtained with hydroxylamine hydrochloride leaching are higher than those obtained with hcl leaching although the reason for this shift is not clear sr 87 sr 86 successfully detects the presence of a nonmarine component in the leachate our results suggest that leaching performance may vary with the mineralogy of marine sediments at least in the case of the mediterranean sea copyright c 2004 elsevier ltd

modeling the distribution of nd isotopes in the oceans using an ocean general circulation model nd isotopic compositions of authigenic phases in marine archives are increasingly used as a tracer of past changes in ocean circulation such applications assume that water masses are tagged with distinct nd isotope compositions in source regions and that away from these regions the nd isotope ratios observed in deep waters mainly reflect water mass mixing however the degree to which the simple assumption of quasi conservative mixing reflects the complicated reality of general circulation in the oceans is not well understood here we present numerical simulations of the nd isotope distribution in seawater using an offline ocean general circulation model ogcm treating the nd isotopic composition of seawater as a conservative tracer nd isotope data from modern surface waters are used to generate an interpolated map of nd isotope compositions for the entire surface ocean this map is treated as a fixed surface boundary condition that is propagated into the interior ocean by the advective diffusive transport of the ocean model until a steady state is reached this treatment of nd isotopes was chosen because it mimics the behavior of well known and well understood conservative tracers such as potential temperature and salinity the model results for all non surface grid points are then compared to published data this simple approach produces nd isotope estimates for north atlantic deep water that are consistent with observations but produces values lower than observed in the deep pacific and southern oceans indicating the need for a source of radiogenic nd directly to the deep pacific ocean sensitivity tests show this to be a robust result by fixing the return flow of the pacific ocean to the southern ocean with nd isotope ratios that are consistent with modern observations the model results are brought into close agreement with a majority of the available data with the addition of a deep pacific source of radiogenic nd more than half of the simulated values from the interior ocean fall within one e unit of the corresponding observations our results thus indicate that the deep pacific ocean requires a source of radiogenic nd in addition to inputs to the surface ocean and that when the deep waters of the north atlantic and north pacific are set with realistic values a majority of intermediate areas are consistent with quasi conservative mixing of these two end members

early arrival of southern source water in the deep north atlantic prior to heinrich event 2 the atlantic meridional overturning circulation amoc plays an important role in the northern hemisphere climate system significant interest went into the question of how excessive freshwater input through melting of continental ice can affect its overturning vigor and hence heat supply to higher northern latitudes such forcing can be tested by investigating its behavior during extreme iceberg discharge events into the open north atlantic during the last glacial period the so called heinrich events he here we present neodymium nd isotope compositions of past seawater a sensitive chemical water mass tag extracted from sediments of ocean drilling program site 1063 in the western north atlantic bermuda rise covering the period surrounding he 2 the last glacial maximum and the early deglaciation these data are compared with a record of the kinematic circulation tracer 231pa 230th xs extracted from the same sediment core both tracers indicate significant circulation changes preceding intense ice rafting during he 2 by almost 2 kyr moreover the nd isotope record suggests the presence of deeply ventilating north atlantic deep water early during marine isotope stage 2 until it was replaced by southern source water at 27 ka the early switch to high pa th xs and radiogenic nd in relation to intensified ice rafting during he 2 suggests that ice rafting into the open north atlantic during major he 2 was preceded by an early change of the amoc this opens the possibility that variations in amoc contributed to or even triggered the ice sheet instability rather than merely responding to it

modeling the neodymium isotopic composition with a global ocean circulation model abstract for the first time modeling of the neodymium nd isotopic composition expressed as end is performed in an ocean global circulation model opa orca2 0 model in the interest of simplicity nd concentration is not explicitly included and end is modeled as a passive tracer recent studies suggest that dissolved particulate exchanges between continental margin sediments and seawater termed boundary exchange be could be the dominant source sink terms that determine the distribution of neodymium isotopes in the global ocean to test this hypothesis we only included this be source sink term in the model be was parameterized as a relaxing term that forces end of seawater to the isotopic composition of the continental margin over a characteristic exchange time sensitivity tests were made using different exchange times and parameterizations the model reproduces most of the general trends of end composition in seawater at global scale inter basin gradient composition of some of the main water masses these results suggest that be process may account for the major sources and sinks of oceanic nd while indicating that the characteristic time of interaction between seawater and margins varies from about half a year in surface waters to several years at depth the disparities between the model and observations might reflect the typical shortcomings of utilizing a coarse resolution ocean model circulation fields or neglected sources of neodymium such as dissolution of aeolian inputs or dissolved river loads

postglacial climate change record in biomarker lipid compositions of the hani peat sequence northeastern china abstract the peat sequence at hani in northeastern china accumulated over the past 16 cal kyr in a percolation mire in which rain water and ground water seeped through the peat system the molecular compositions of n alkanes n alkanols and n alkanoic acids extracted from the hani peat sequence reveal different responses to the progressive evolution of climate and changes in the nature of the peat forming vegetation long chain length components that originate from the waxy coatings of subaerial vascular plants dominate the n alkane distributions throughout the hani peat sequence the paleoclimate integrity of these biomarker molecules appears to be well preserved most of the n alkanol distributions are similarly dominated by long chain components that indicate their origins from subaerial plants in contrast n alkanoic acid distributions are dominated by secondary components that record the importance of post depositional microbial activity in this peat sequence which evidently can be extensive in a percolation mire elevated n alkane paq values and c23 c29 ratios which are both molecular proxies for water loving plants record an especially moist local climate in the bolling allerod 14 5 to 12 9 ka younger dryas 12 9 to 11 5 ka and pre boreal 11 5 to 10 5 ka portions of the hani peat sequence depressed paq values and c23 c29 ratios and larger n alkane average chain length values indicate that the holocene climatic optimum 10 5 to 6 ka was a period of warmer climate with lower effective precipitation which contrasts with evidence of wetter climates in most of east asia

modelling nd isotopes with a coarse resolution ocean circulation model sensitivities to model parameters and source sink distributions the neodymium nd isotopic composition nd of seawater is a quasi conservative tracer of water mass mixing and is assumed to hold great potential for paleoceanographic studies here we present a comprehensive approach for the simulation of the two neodymium isotopes 143nd and 144nd using the bern3d model a low resolution ocean model the high computational efficiency of the bern3d model in conjunction with our comprehensive approach allows us to systematically and extensively explore the sensitivity of nd concentrations and nd to the parametrisation of sources and sinks previous studies have been restricted in doing so either by the chosen approach or by computational costs our study thus presents the most comprehensive survey of the marine nd cycle to date our model simulates both nd concentrations as well as nd in good agreement with observations nd covaries with salinity thus underlining its potential as a water mass proxy results confirm that the continental margins are required as a nd source to simulate nd concentrations and nd consistent with observations we estimate this source to be slightly smaller than reported in previous studies and find that above a certain magnitude its magnitude affects nd only to a small extent on the other hand the parametrisation of the reversible scavenging considerably affects the ability of the model to simulate both nd concentrations and nd furthermore despite their small contribution we find dust and rivers to be important components of the nd cycle in additional experiments we systematically varied the diapycnal diffusivity as well as the atlantic to pacific freshwater flux to explore the sensitivity of nd concentrations and its isotopic signature to the strength and geometry of the overturning circulation these experiments reveal that nd concentrations and nd are comparatively little affected by variations in diapycnal diffusivity and the atlantic to pacific freshwater flux in contrast an adequate representation of nd sources and sinks is crucial to simulate nd concentrations and nd consistent with observations the good agreement of our results with observations paves the way for the evaluation of the paleoceanographic potential of nd in further model studies

paleoenvironmental significance of compound specific δ13c variations in n alkanes in the hongyuan peat sequence from southwest china over the last 13 ka abstract compound specific 13c 12c ratios of the c23 c25 c27 c29 and c31 n alkanes in the hongyuan peat sequence from southwest china were measured to decipher paleoenvironmental information recorded in the 13c variations over the last 13 ka the 13c values of the n alkanes range between 35 4 and 30 5 falling within the range of those from modern c3 peat forming vegetation however the vertical trends do not match with those of the 13c value for the c3 peat forming plant cellulose such a discrepancy between the 13c profiles implies that the n alkane 13c values are unlikely to reflect signals from emerged aquatic plants in the bog because submerged floating aquatic plants are major contributors of mid chain c23 and c25 n alkanes in the sequence the decoupling between the c23 and c25 n alkanes and the peat cellulose likely reflects the situation that these mid chain homologues primarily record the isotopic signals of submerged floating aquatic plants the stratigraphic profile of 13c values of submerged floating aquatic plant n alkanes c23 and c25 reveals two prominent positive excursions 0 8 2 4 during the early to middle holocene the excursions coincide with peat accumulation maxima and stronger indian monsoon activity in southwest china indicating that the 13c variations in submerged floating aquatic plants are closely related to changes in bog primary productivity controlled by the asian monsoon activity

the enso asian monsoon interaction in a coupled ocean atmosphere gcm abstract in this study the authors evaluate the el nino southern oscillation enso asian monsoon interaction in a version of the hadley centre coupled ocean atmosphere general circulation model cgcm known as hadcm3 the main focus is on two evolving anomalous anticyclones one located over the south indian ocean sio and the other over the western north pacific wnp these two anomalous anticyclones are closely related to the developing and decaying phases of the enso and play a crucial role in linking the asian monsoon to enso it is found that the hadcm3 can well simulate the main features of the evolution of both anomalous anticyclones and the related sst dipoles in association with the different phases of the enso cycle by using the simulated results the authors examine the relationship between the wnp sio anomalous anticyclones and the enso cycle in particular the biennial component of the relationship it is found that a strong el nino event tends to be followed by a more rapid decay and i

neodymium budget in the modern ocean and paleo oceanographic implications the oceanic nd budget is calculated using a steady state 10 box model and a compilation of field data this is the first attempt to propose consistent estimates of the nd fluxes entering the ocean as well as indicating possible nd sources and the proportion of nd fluxes exchanged between dissolved and particulate fractions with presently available nd data the best estimates give a total nd influx of 9 x 10 9 g yr which leads to an oceanic nd residence time of 500 years from modeling tests we suggest that the authigenic nd scavenged by particulates is 100 remineralized in the deep ocean the total exchanged nd flux may be as high as 2 x 10 10 g yr the epsilon nd 0 values of the influxes are 22 11 1 and 4 for the north atlantic surface atlantic north pacific and surface indo pacific regions respectively atmospheric and riverine nd fluxes are insufficient to explain the magnitude and regional variability of calculated nd influxes and epsilon nd 0 we propose continental margins as an additional source supplying nd to the ocean using the model calibrated for nd we examine the sensitivity of deep water epsilon nd 0 to variations of nd inputs to the ocean deep water nd concentrations and epsilon nd 0 vary with the changes in nd influxes and their epsilon nd 0 as nd sources to the ocean may change during glacial interglacial periods the epsilon nd 0 shifts recorded in ferromanganese nodules and crusts do not necessarily reflect changes in paleoceanic circulation the effects of continental erosion should be considered in reconstructing patterns of ocean circulation using nd isotopes

proxy value of n alkan 2 ones in the hongyuan peat sequence to reconstruct holocene climate changes on the eastern margin of the tibetan plateau abstract n alkan 2 ones in the hongyuan peat core from the eastern margin of the tibetan plateau were investigated to assess the paleoclimate proxy value of variations in their compositions over the last 13 500 cal years a homologous series of these compounds that ranged from c 19 to c 31 was identified throughout the peat sequence maximizing at c 23 and showing a strong odd over even carbon chain length predominance to help evaluate the possible paleoclimatic value of the n alkan 2 ones in the hongyuan peat core we compared our molecular results with the pollen records from the same sequence results show that past changes in monsoon precipitation amounts as revealed by the ratio of abies cyperaceae firs sedges are also recorded in the n alkan 2 one c 23 c 25 c 27 c 29 c 31 ket ratio and cpi ket carbon preference index value stratigraphic variations of n alkane and n alkanoic acid ratios suggest that changes in the moisture sensitive microbial oxidation of odd chain n alkanes and decarboxylation of even chain length n alkanoic acids is recorded in the abundance of n alkan 2 ones changes in the monsoon rain intensity on millennial scales are also evident in the n alkan 2 one proxies indicating that their variations in the peat sequence are correlative with changes in microbial activity controlled by the asian monsoon

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

the influence and chronological uncertainties of the 8 2 ka cooling event on continental climate records in china a compilation of early holocene terrestrial records from lacustrine sediments ice cores peat bog palaeosols stalagmites and flood sediments from china indicates that the early holocene climate was unstable and characterized by at least one centennial scale 500 200 years cooling event between 9 0 and 7 6 ka bp the cold period recorded in different settings has been previously linked to the 8 2 ka event suggested by 18o ice from greenland ice cores but the differences in time duration and regional climate conditions have been attributed to monsoon systems inadequate age control and sampling resolution and complex topography in china however our compilation indicates that it is premature to attribute the cold periods recorded at different locations in china simply to the 8 2 ka event let alone to attribute the cause of those anomalies to a freshening of the north atlantic ocean circulation whether there was one synchronous event or not in china where the climate is mainly affected by the mons