identification of multivariate geochemical anomalies using spatial autocorrelation analysis and robust statistics abstract multivariate geochemical anomaly identification is one of the most important tasks in exploration geochemical data analysis this paper proposes a new approach to identify multivariate geochemical anomalies which accounts for the degree of spatial autocorrelation among observations this method is a combination of robust mahalanobis distance rmd spatial autocorrelation analysis and robust statistics the minimum covariance determinant mcd estimator based rmds were first used to reduce the dimension of geochemical data sets spatial correlogram and local moran s i statistics were then applied to determine the spatial variability spatial scales and to measure the degree of spatial autocorrelation at global and different local scales respectively negative and positive anomalies were finally separated from a set of local moran s i values using robust statistics the median 1 5 iqr iqr interquartile range rule we illustrated the proposed method by using a data set of 1842 stream sediment samples associated with cu au mo and sn mineralizations in the jiurui ore district jiangxi province southeastern china the results showed that i the maximum spatial variability of rmds were 12 km in which strong positive spatial autocorrelation was detected at the first three spatial scales ranging from 0 to 6 km ii both of negative and positive multivariate geochemical anomalies were strongly correlated with 13 known cu au mo and cu mo deposits especially at spatial scales where high degrees of positive spatial autocorrelation were measured iii weak anomalies associated with a magmatic hydrothermal related sn and polymetallic mineralization were successfully identified in the zengiialong and jianfengpo sn deposits which were not detected in previous studies we demonstrate the combination of spatial autocorrelation analysis and robust statistics allows for improved identification of significant multivariate geochemical anomalies of the deposit type sought from stream sediment geochemical data

calcite dissolution in sediments of the ceara rise in situ measurements of porewater o2 ph and co2 aq in situ electrode measurements of porewater oxygen and ph from four sites on the ceara rise in the western tropical atlantic unequivocally demonstrate that calcite dissolution driven by metabolic co2 produced within the sediments is a significant part of the diagenesis of sedimentary calcite dissolving at least 20 of the calcite rain to the seafloor the first ever in situ absorbance based measurements of porewater co2 aq support the dissolution estimates based on models of the observed ph distributions and are incompatible with scenarios excluding metabolic co2 driven dissolution our dissolution estimates are consistent with those estimated by an independent study of porewater calcium and alkalinity profiles martin and sayles 1996 at this location the consistency of these disparate porewater measurements and our ability to interpret them with simple models of respiration and dissolution implies that no special mechanism is required to describe this process the calcite dissolution rate constant in the sediments of the deepest station in this study is significantly higher than determined by in situ studies at other locations values approach those determined by early laboratory measurements the dissolution rate constant here must be at least two orders of magnitude higher than for calcite in sediments on the ontong java plateau based on in situ electrode measurements there hales and emerson 1996 the calcite solubility consistent with these data is not compatible with that consistent with the ontong java data the reason for this difference is currently unresolved but may be due to the high order of the empirical dissolution rate law assumed in this study

reconstruction of millennial changes in dust emission transport and regional sea ice coverage using the deep epica ice cores from the atlantic and indian ocean sector of antarctica continuous sea salt and mineral dust aerosol records have been studied on the two epica european project for ice coring in antarctica deep ice cores the joint use of these records from opposite sides of the east antarctic plateau allows for an estimate of changes in dust transport and emission intensity as well as for the identification of regional differences in the sea salt aerosol source the mineral dust flux records at both sites show a strong coherency over the last 150 kyr related to dust emission changes in the glacial patagonian dust source with three times higher dust fluxes in the atlantic compared to the indian ocean sector of the southern ocean so using a simple conceptual transport model this indicates that transport can explain only 40 of the atmospheric dust concentration changes in antarctica while factor 5 10 changes occurred accordingly the main cause for the strong glacial dust flux changes in antarctica must lie in environmental changes in patagonia dust emissions hence environmental conditions in patagonia were very similar during the last two glacials and interglacials respectively despite 2 4 c warmer temperatures recorded in antarctica during the penultimate interglacial than today 2 3 times higher sea salt fluxes found in both ice cores in the glacial compared to the holocene are difficult to reconcile with a largely unchanged transport intensity and the distant open ocean source the substantial glacial enhancements in sea salt aerosol fluxes can be readily explained assuming sea ice formation as the main sea salt aerosol source with a significantly larger expansion of summer sea ice in the weddell sea than in the indian ocean sector during the penultimate interglacial our sea salt records point to a 50 reduction of winter sea ice coverage compared to the holocene both in the indian and atlantic ocean sector of the so however from 20 to 80 ka before present sea salt fluxes show only very subdued millennial changes despite pronounced temperature fluctuations likely due to the large distance of the sea ice salt source to our drill sites

present antarctic aerosol composition a memory of ice age atmospheric dust the data obtained from the chemical analysis na al and ca concentrations of deep antarctic ice cores has been reexamined the correlations found between the concentrations of these elements suggest that the patagonian continental shelf was the dominant aerosol source during the last ice age the dust being an intimate mixture of marine clay and carbonates in addition it is proposed that sea salt deposited on the continental shelf sediments during drop in sea level was emitted and transported jointly with this dust the present antarctic aerosol composition is very similar to the one deduced from ice core studies for glacial climatic conditions it is concluded that present antarctic aerosol originates mainly from ice age aeolian deposits in south american cold deserts

a continuous 770 year record of volcanic activity from east antarctica a 100 m ice core from site g 15 accumulation rate 0 1 m water yr 1 mean annual temperature 38 c on the mizuho plateau dronning maud land east antarctica has been analysed using the dielectric profiling dep technique the capacitance and conductance of the core were measured at ac frequencies 20 hz 300 khz the high frequency conductivity profile shows variations that are primarily related to the strong acids derived from volcanic activity the tambora 1815 eruption can be identified with the aid of an approximate chronology based on the firn densification rate other historic eruptions can then be recognised beyond about 300 years historical observations are very few however if a constant overall accumulation rate is assumed a well known eruption of 1259 a d can be found near the bottom of the core other peaks in the conductivity profile can then be assigned dates accurate to within a few years using the conductivity profile it is possible to estimate the relative acid deposition fluxes produced by the main eruptions with reasonable accuracy the estimated acid deposisition fluxes realtive to the tambora 1815 eruption of agung 1963 is 27 krakatoa 1883 25 the signal of 1601 28 and that of 1259 53

inter hemispheric transport of volcanic ash from a 1259 a d volcanic eruption to the greenland and antarctic ice sheets a strong volcanic sulfuric acid signal corresponding to an age of 1259 a d has been reported in ice cores from greenland antarctica and arctic canada tiny 5 m volcanic glass shards were reported previously in samples from this layer in an ice core from the south pole here we report the discovery of volcanic glass shards from a contemporaneous layer in an ice core from summit greenland the major element composition of the glass shards in the greenland sample are identical to those from the south pole confirming the assumption that has been made previously that the sulfuric acid signal in the ice cores is an inter hemispheric time stratigraphic marker the composition of these glass shards is similar to those produced by a 550 700 yrs b p eruption of el chichon volcano in mexico suggesting that it may be the source of the widely dispersed material

compositional data analysis in the geosciences from theory to practice since karl pearson wrote his paper on spurious correlation in 1897 a lot has been said about the statistical analysis of compositional data mainly by geologists such as felix chayes the solution appeared in the 1980s when john aitchison proposed to use iogratios since then the approach has seen a great expansion mainly building on the idea of the natural geometry of the sample space statistics is expected to give sense to our perception of the natural scale of the data and this is made possible for compositional data using iogratios this publication will be a milestone in this process this book will be of interest to geologists using statistical methods it includes the intuitive justification of the methodology convincing through case studies and presenting user friendly software which includes a section for those who need to see the proof of the mathematical consistency of the methods used

major features and forcing of high latitude northern hemisphere atmospheric circulation using a 110 000 year long glaciochemical series the greenland ice sheet project 2 glaciochemical series sodium potassium ammonium calcium magnesium sulfate nitrate and chloride provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid low latitudes of the northern hemisphere interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants volcanic and biomass burning events storminess over marine surfaces continental aridity and biogenic source strength plus information related to the controls on both high and low frequency climate events of the last 110 000 years climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long term behavior of atmospheric circulation patterns through changes in ice volume sea level events such as the heinrich events massive discharges of icebergs first identified in the marine record that are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics and rapid climate change events massive reorganizations of atmospheric circulation that are demonstrated to operate on 1450 year cycles changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events explanation for the exact timing and global synchroneity of these events is however more complicated preliminary evidence points to possible solar variability climate associations for these events and perhaps others that are embedded in our ice core derived atmospheric circulation records

high resolution ammonium ice core record covering a complete glacial interglacial cycle high resolution ammonium measurements were performed along the greenland ice core program grip deep ice core covering a complete climatic cycle no overall anthropogenic increase is observed over the last 300 years however springtime concentrations have roughly doubled since 1950 biomass burning is estimated to be a major source for ammonia emissions for preindustrial times it contributes between 10 to 40 to the total ammonium deposited on the central greenland ice sheet during the holocene no correlation is found between the ammonium summer concentrations recorded over the last 100 years and the area burned in northern north america which is considered to be the main source area for ammonium deposited on the central greenland ice sheet this suggests that the meteorological factor is predominant for the pattern of ammonium spikes observed in the ice core if unchanged meteorological conditions are assumed for the holocene as indicated by the 18o ice record a decreasing biomass burning activity toward present time can be derived from the ammonium ice record soil and vegetation emissions are responsible for the ammonium background concentrations in the ice the record therefore may be used to trace back the biomass history of the north american continent a pronounced decreasing trend in background ammonium is found during the holocene reflecting decreasing temperature and therefore lower nh3 emissions in the source region variations in the ammonium concentration during the glacial age are discussed in terms of changes in transport and deposition mechanisms and changes in source strength which can be related to the extent of the laurentide ice sheet the data suggest that the laurentide ice sheet was built up immediately after the last interglacial and went through several large fluctuations during the last ice age

porphyry cu mo au deposits related to melting of thickened mafic lower crust examples from the eastern tethyan metallogenic domain abstract most porphyry cu deposits in the world occur in magmatic arc settings and are formed in association with calc alkaline arc magmas related to subduction of oceanic lithosphere this contribution reviews a number of significant porphyry cu deposits in the eastern tethyan metallogenic domain they widely occur in a variety of non arc settings varying from post late collisional transpressional and extensional environments to intracontinental extensional environments related to orogenic and anorogenic processes their spatial temporal localization is controlled by strike slip faults orogen transverse normal faults lineaments and their intersections in these non arc settings these deposits are dominated by porphyry cu mo deposits with minor porphyry cu au and epithermal au deposits and exhibit a broad similarity with those in magmatic arcs the associated magmas are generally hydrous relatively high fo2 high k calc alkaline and shoshonitic and show geochemical affinity with adakites they are distinguished from arc magmas and or oceanic slab derived adakites by their occurrence as isolated complexes high k2o contents 1 2 8 5 and much wider range of end t values 10 to 3 and positive ehf t values 4 6 to 6 9 these potassic magmas are most likely formed by partial melting of thickened juvenile mafic lower crust or delaminated lower crust but also involving various amounts of asthenospheric mantle components key factors that generate hydrous fertile magmas are most likely crust mantle interaction processes at the base of thickened lower crust in non arc settings rather than oceanic slab dehydration as in arc settings breakdown of amphibole in thickened lower crust e g amphibole eclogite and garnet amphibolite during melting is considered to release fluids into the fertile magmas leading to an elevated oxidation state and higher h2o content necessary for development of porphyry cu mo au systems copper and au in hydrous magmas are likely derived from mantle derived components and or melts which either previously underplated and infiltrated at the base of the thickened lower crust or were input into the primitive magmas by melt mantle interaction in contrast mo and part of the s in the fertile magmas are probably supplied by old crust during melting and subsequent ascent

spatio temporal variability in volcanic sulphate deposition over the past 2 kyr in snow pits and firn cores from amundsenisen antarctica in the framework of the european project for ice coring in antarctica epica a comprehensive glaciological pre site survey has been carried out on amund senisen dronning maud land east antarctica in the past decade within this survey four intermediate depth ice cores and 13 snow pits were analyzed for their ionic compos ition and interpreted with respect to the spatial and temporal variability of volcanic sul phate deposition the comparison of the non sea salt nss sulphate peaks that are related to the well known eruptions of pinatubo and cerro hudson in ad1991 revealed sulphate depositions of comparable size 15 8 3 4 kg km 2 in 11 snow pits there is a tendency to higher annual concentrations for smaller snow accumulation rates the combination of seasonal sodium and annually resolved nss sulphate records allowed the establishment of a time scale derived by annual layer counting over the last 2000 years and thus a detailed chronology of annual volcanic sulphate deposition using a robust outlier detection algo rithm 49 volcanic eruptions were identified between ad165 and 1997 the dating uncer tainty is 3 years between ad1997 and 1601 around 5 years between ad1601 and 1257 and increasing to 24 years at ad165 improving the accuracy of the volcanic chronology during the penultimate millennium considerably abstract in the framework of the european project for ice coring in antarctica epica a comprehensive glaciological pre site survey has been carried out on amund senisen dronning maud land east antarctica in the past decade within this survey four intermediate depth ice cores and 13 snow pits were analyzed for their ionic compos ition and interpreted with respect to the spatial and temporal variability of volcanic sul phate deposition the comparison of the non sea salt nss sulphate peaks that are related to the well known eruptions of pinatubo and cerro hudson in ad1991 revealed sulphate depositions of comparable size 15 8 3 4 kg km 2 in 11 snow pits there is a tendency to higher annual concentrations for smaller snow accumulation rates the combination of seasonal sodium and annually resolved nss sulphate records allowed the establishment of a time scale derived by annual layer counting over the last 2000 years and thus a detailed chronology of annual volcanic sulphate deposition using a robust outlier detection algo rithm 49 volcanic eruptions were identified between ad165 and 1997 the dating uncer tainty is 3 years between ad1997 and 1601 around 5 years between ad1601 and 1257 and increasing to 24 years at ad165 improving the accuracy of the volcanic chronology during the penultimate millennium considerably

mapping mineral prospectivity using an extreme learning machine regression abstract in this research we conduct a case study of mapping polymetallic prospectivity using an extreme learning machine elm regression a quad core cpu 1 8 ghz laptop computer served as hardware platform almeida s python program was used to construct the elm regression model to map polymetallic prospectivity of the lalingzaohuo district in qinghai province in china based on geologic metallogenic and statistical analyses of the study area one target and eight predictor map patterns and two training sets were then used to train the elm regression and logistic regression models elm regression modeling using the two training sets spends 61 4 s and 65 9 s whereas the logistic regression modeling using the two training sets spends 1704 0 s and 1628 0 s the four trained regression models were used to map polymetallic prospectivity based on the polymetallic prospectivity predicted by each model the receiver operating characteristic roc curve was plotted and the area under the curve auc was estimated the roc curves show that the two elm regression based models somewhat dominate the two logistic regression based models over the roc performance space and the auc values indicate that the overall performances of the two elm regression based models are somewhat better than those of the two logistic regression based models hence the elm regression based models slightly outperform the logistic regression based models in mapping polymetallic prospectivity polymetallic targets were optimally delineated by using the youden index to maximize spatial association between the delineated polymetallic targets and the discovered polymetallic deposits the polymetallic targets predicted by the two elm regression based models occupy lower percentage of the study area 2 66 2 68 compared to those predicted by the two logistic regression based models 4 96 but contain the same percentage of the discovered polymetallic deposits 82 therefore the elm regression is a useful fast learning data driven model that slightly outperforms the widely used logistic regression model in mapping mineral prospectivity the case study reveals that the magmatic complexes which intruded into the baishahe formation of the paleoproterozoic jinshuikou group or the carboniferous dagangou and shiguaizi formations and which were controlled by northwest western east western trending deep faults are critical for polymetallic mineralization and need to be paid much attention to in future mineral exploration in the study area

glaciochemistry of polar ice cores a review human activities have already modified the chemical composition of the natural atmosphere even in very remote regions of the world the study of chemical parameters stored in solid precipitation and accumulated on polar ice sheets over the last several hundred thousand years provides a unique tool for obtaining information on the composition of the preindustrial atmosphere and its natural variability over the past this paper deals with the chemistry of polar ice focused on the soluble mineral na nh4 k ca mg h f cl no3 so4 and h2o2 and organic methanesulfonate ch3so3 formate hcoo acetate ch3coo and formaldehyde hcho species and their interpretation in terms of past atmospheric composition aerosols and water soluble gaseous species we discuss ice core dating the difficulties connected with trace measurements and the significance of the ionic composition of snow we examine temporal from the last decades back to the last climatic cycle and spatial including examples from coastal as well as central areas of greenland and antarctica variations in the ionic budget of the precipitation and evaluate ice core studies in terms of the chemical composition of our past atmosphere we review 1 how greenland and antarctic ice cores that span the last few centuries have provided information on the impact of human activities and 2 how the chemistry of deep ice cores provides information on various past natural phenomena such as climatic variations glacial interglacial changes el nino volcanic eruptions and large boreal forest fires

cornucopia of ice core results polar ice cores contain records of earth s climate the deeper the core the further back in time the records go early last year a drilling project at the vostok station in antarctica reached a depth of 3 623 m or around 420 000 years ago that means that the ice core climate record now extends back across four glacial interglacial cycles

aerosol deposited in east antarctica over the last glacial cycle detailed apportionment of continental and sea salt contributions 1 the major ions sodium na calcium ca2 and chloride cl deposited in central antarctica and preserved in ice cores originate from both marine and continental sources they provide important proxy records helping to reconstruct past climatic processes however it is difficult to clearly separate the individual contributions from the two sources particularly the continental one during glacial periods on the basis of na and ca2 records at an unprecedented resolution from the european project for ice coring in antarctica epica dome c ice core back to the penultimate glacial period mean ion mass ratios were deduced for the continental and the sea salt aerosol body over east antarctica the sea salt ion mass ratios are in the range predicted for both wind induced bubble bursting of breaking waves on the open ocean and sea ice brine derived aerosols respectively thus allowing no clear decision on the contribution of sea ice to the central antarctic sea salt aerosol the continental ion mass ratios point to a substantial contribution by halide aerosols which is in agreement with the source properties in southern south america although these ratios do not rule out the continental shelf exposed during glacial stages as an additional source while during cold glacial periods continental sources accounted for more than 90 of the total ca2 input this contribution was highly variable during the remaining glacial periods covarying with the antarctic warm events during the holocene it was less than 50 but it was significantly higher during the last interglacial period the sea salt aerosol contribution to the total na input which was mostly dominant and higher than 90 was reduced to only two thirds during the last two glacial maxima and the period around 60 ka thus the glacial continental na contribution appears to be more important than previously assumed implying that na records not corrected for continental na do not represent a pure marine signal at the east antarctic plateau during glacial times

timescales for dust variability in the greenland ice core project grip ice core in the last 100 000 years the calcium representing dust concentration record of the last 100 000 years from the greenland ice core project grip ice core shows a huge dynamic range factor 100 the relationship between dust concentrations and temperature represented by the oxygen isotope ratio is not a simple one as has often been assumed a rapid alternation factor of 5 10 between low concentrations during the dansgaard oeschger interstadial periods and high levels in colder periods is superimposed on a long term trend encompassing a further factor of 5 10 within climate periods there is only a very weak relationship between ca concentration and temperature previous authors biscaye et al 1997 have suggested that the most likely source for the increased dust is eastern asia for the first time we consider each possible cause of both rapid and slow increases from source to deposition we suggest that to account for the size and rapidity of the fast changes significantly higher wind speed in the source area is required although changes in atmospheric residence time could also play a role for the slower long term variability changes in transport speed or possibly route are probably also involved changes in the size of the source area could give some change on longer time periods the probable importance of changes in source area wind speed almost simultaneous with greenland temperature changes confirms that climatic parameters in high and low latitudes were strongly coupled through the atmosphere during glacial climatic changes this adds to evidence that the atmospheric circulation system underwent almost instantaneous large scale changes during the last glacial period

using local moran s i to identify contamination hotspots of rare earth elements in urban soils of london abstract rare earth elements rees in urban soils are receiving more attention because of their increased use in modern technology up to now there is little information about the spatial patterns of rees and their influencing factors in urban soils in this study based on the british geological survey london earth geochemical survey data containing a total of 6467 soil samples collected from the urban area of london the spatial distributions of ce la nd sc sm yb and y and their influencing factors were investigated the element sc is included in this study as related element urban samples were collected at a depth of 0 20 cm and total concentrations of 48 chemical elements were determined in the

imprint of large scale atmospheric transport patterns on sea salt records in northern greenland ice cores the decadal to interannual variability of sea salt aerosol concentrations in northern greenland ice cores is investigated and contrasted to meteorological reanalysis data over the time span 1959 1993 correlation analysis with average data on sea level pressure and geopotential height at the 500 mbar level identifies the eastern and northeastern pacific region as the most important center of action responsible for variations in sea salt aerosol export onto the greenland ice sheet which is related to the pacific north american teleconnection pattern the atlantic region however appears to be of secondary importance only correlation coefficients are highest during the first quarter of the year but also significant for annual pressure data explaining 20 of the sea salt variance in the ice cores furthermore higher storm activity in the pacific center of action as well as in the northern atlantic leads to higher sea salt concentrations in northern greenland explaining about 40 and 17 of the ice core variance a 30 increase during the nineteenth century in a 600 year sea salt record from northeastern greenland may be interpreted at least in part as an enhancement of sea salt export from the pacific region during that time

preferential dissolution of carbonate shells driven by petroleum seep activity in the gulf of mexico abstract authigenic carbonates are common at deep sea petroleum seeps as a result of excess bicarbonate production during microbial degradation of hydrocarbons coupled to sulfate reduction consequently these seep environments are supersaturated with respect to carbonates this finding conflicts with taphonomic data that dissolution is the most pervasive mode of shell alteration at seeps we provide here the first study linking the preservational process with the chemical characterization of the taphonomically active zone at petroleum seep sites this characterization is made possible using fine scale porewater carbonate chemistry data and skeletal material deployed for 8 years at petroleum seep sites in the northwestern gulf of mexico microelectrode measurements of ph and pco2 identify a very restricted zone of caco3 undersaturation immediately below the sediment water interface in otherwise supersaturated environments i e sandwiched between supersaturated bottom seawater and sediment porewater this zonation characterizes the taphonomically active zone and is a result of a highly compressed redox front between acid generating aerobic oxidation of reduced chemical species including hydrocarbons h2s and planktonic and terrestrial organic carbon and base generating sulfate reduction coupled to ch4 oxidation porewater geochemistry is spatially variable at seep sites and produces variable shell dissolution signatures shells deployed at seep sites have moderate to severe dissolution that is consistent with a much higher flux of total dissolved inorganic carbon dic from the porewater to the bottom water therefore a mosaic of preservational conditions is directly related to the spatially and chemically varying taphonomically active zones found at seep sites these findings support the variability of carbonate preservation reported for globally distributed phanerozoic fossil seeps and the view that data from field taphonomy can significantly upgrade and validate carbonate destruction rates used in geochemical and climatic models carbon mass balance analyses also lead to an important conclusion that carbonate dissolution forms a very important mechanism for benthic carbon recycling possibly accounting for 50 of the benthic dic flux to the bottom water in northern gulf of mexico petroleum seep sediments

prevalence of the antarctic circumpolar wave over the last two millenia recorded in dronning maud land ice 1 the influence of atmospheric circulation patterns on sea salt aerosol deposition in the study area of the new epica european project for ice coring in antarctica deep drilling in dronning maud land dml antarctica has been investigated comparison of ice core records with reanalysis data showed that recent sea salt concentrations are strongly influenced by the occurrence of a blocking high pressure ridge over the eastern and enhanced storm activity over the western atlantic sector of the southern ocean so leading to marine intrusions thus enhanced sea salt export into dml these variations occur with periods of 4 5 and 12 14 yr the prior being associated with the antarctic circumpolar wave acw the prevalence of these periodicities in a 2000 year ice core record from dml shows for the first time that the acw is a prevalent feature of so atmosphere dynamics over the last two millennia

the role of seasonality of mineral dust concentration and size on glacial interglacial dust changes in the epica dronning maud land ice core we present a record of particulate dust concentration and size distribution in subannual resolution measured on the european project for ice coring in antarctica epica dronning maud land edml ice core drilled in the atlantic sector of the east antarctic plateau the record reaches from present day back to the penultimate glacial until 145 000 years b p with subannual resolution from 60 000 years b p to the present mean dust concentrations are a factor of 46 higher during the glacial 850 4600 ng ml compared to the holocene 16 112 ng ml with slightly smaller dust particles during the glacial compared to the holocene and with an absolute minimum in the dust size at 16 000 years b p the changes in dust concentration are mainly attributed to changes in source conditions in southern south america an increase in the modal value of the dust size suggests that at 16 000 years b p a major change in atmospheric circulation apparently allowed more direct transport of dust particles to the edml drill site we find a clear in phase relation of the seasonal variation in dust mass concentration and dust size during the glacial r conc size 0 8 but no clear phase relationship during the holocene 0 r conc size 0 4 with a simple conceptual 1 d model describing the transport of the dust to the ice sheet using the size as an indicator for transport intensity we find that the effect of the changes in the seasonality of the source emission strength and the transport intensity on the dust decrease over transition 1 can significantly contribute to the large decrease of dust concentration from the glacial to the holocene

firn accumulation records for the past 1000 years on the basis of dielectric profiling of six cores from dronning maud land antarctica this paper presents an overview of firn accumulation in dronning maud land dml antarctica over the past 1000 years it is based on a chronology established with dated volcanogenic horizons detected by dielectric profiling of six medium length firn cores in 1998 the british antarctic survey retrieved a medium length firn core from western dml during the nordic epica european project for ice coring in antarctica traverse of 2000 01 a 160 m long firn core was drilled in eastern dml together with previously published data from four other medium length ice cores from the area these cores yield 50 possible volcanic horizons all six firn cores cover a mutual time record until the 29th eruption this overlapping period represents a period of approximately 1000 years with mean values ranging between 43 and 71 mm w e the cores revealed no significant trend in snow accumulation running averages over 50 years averaged over the six cores indicate temporal variation in the order of 5 all cores display evidence of a minimum in the mean annual firn accumulation rate around ad 1500 and maxima around ad 1400 and 1800 the mean increase over the early 20th century was the strongest increase but the absolute accumulation rate was not much higher than around ad 1400 in eastern dml a 13 increase is observed for the second half of the 20th century

calcite dissolution driven by benthic mineralization in the deep sea in situ measurements of ca 2 ph pco 2 and o 2 abstract in situ measured microprofiles of ca 2 pco 2 ph and o 2 were performed to quantify the caco 3 dissolution and organic matter mineralization in marine sediments in the eastern south atlantic a numerical model simulating the organic matter decay with oxygen was used to estimate the calcite dissolution rate from the oxygen microprofiles measured at four stations along a 1300 m isobath of the eastern african margin and one in front of the river niger at a water depth of 2200 m the diffusive oxygen uptake dou and oxygen penetration depth opd was calculated dou rates were in the range of 0 3 to 3 mmol m 2 d 1 and showed a decrease with increasing water depth corresponding to an increase in opd the calculated amount of degradated organic matter is in the range of 1 to 8 5 gc m 2 a 1 the metabolic co 2 released from mineralization of the organic matter drives calcite dissolution in these sediments overlain by calcite supersaturated water fluxes across the sediment water interface calculated from the in situ ca 2 microprofiles were 0 6 mmol m 2 d 1 for two stations at a water depth of 1300 m the ratio of calcite dissolution flux and organic c degradation is 0 53 and 0 97 respectively the microprofiles indicate that co 2 produced within the upper oxic sediment layer dissolves up to 85 of the calcite rain to the seafloor modeling our o 2 ph and ca 2 profiles from one station predicted a calcite dissolution rate constant for this calcite poor site of 1000 mol kgw 1 a 1 mol per kg water and year which equals 95 d 1 this rate constant is at the upper end of reported in situ values

effects of misclassification costs on mapping mineral prospectivity abstract mineral prospectivity mapping is a classification process because in a given study area a specific region is classified as either a prospective or non prospective area the cost of false negative errors differs from the cost of false positive errors because false positive errors lead to wasting much more financial and material resources whereas false negative errors result in the loss of mineral deposits traditional machine learning algorithms using for mapping mineral prospectivity are aimed to minimize classification errors and ignore the cost sensitive effects in this study the effects of misclassification costs on mapping mineral prospectivity are explored the cost sensitive neural network csnn for minimizing misclassification costs is applied to map fe polymetallic prospectivity in china s southwestern fujian metalorganic belt sfmb a csnn with a different cost ratio ranging from 1 10 to 10 1 was used to represent various misclassification costs the cross validation results indicated a lower misclassification cost compared to traditional neural networks through a threshold moving based csnn the csnn s predictive results were compared to those of a traditional neural network and the results demonstrate that the csnn method is useful for mapping mineral prospectivity the targets can be used to further explore undiscovered deposits in the study area

spatial analysis and visualization of exploration geochemical data abstract this paper briefly reviews the application of geoinformatics in exploration geochemistry from the perspective of spatial analysis and visualization and demonstrates the advantages of geoinformatics in exploring geochemical patterns and identifying geochemical anomalies in particular the application of geoinformatics to geochemical mapping recognition of geochemical anomalies and simulation of geochemical patterns are discussed the benefits of geoinformatics include 1 overlay of geochemical data on a geological map which helps geochemists to understand spatial geochemical patterns and visualize geochemical anomalies 2 local neighbourhood spatial analysis which considers the local spatial structure of geochemical patterns as a powerful tool to identify weak geochemical anomalies and 3 geochemical patterns simulation based on geological constrains which helps to understand geological processes future researches should focus on development and application of various functions for processing geochemical data in a gis to promote the progress of geoinformatics in both geochemical exploration and environmental studies

calcium carbonate dissolution in deep sea sediments reconciling microelectrode pore water and benthic flux chamber results abstract we report the benthic fluxes of o2 titration alkalinity ta ca2 no3 po43 and si oh 4 from in situ benthic flux chamber incubations on the ceara rise and cape verde plateau and compare them to previously published results we find within analytical uncertainty that the ta flux is twice the calcium flux suggesting that dissolution precipitation of caco3 is the principal mechanism controlling benthic ta and ca2 fluxes at sites where the sediments contain significant 35 caco3 and the overlying waters are supersaturated with respect to caco3 the ratios of the total dissolution rate to the remineralization rate are significantly less than at all other study sites we propose that these observations can be explained by precipitation of fresh caco3 at the supersaturated sediment surface followed by redissolution deeper in the sediments because of metabolically produced co2 a numerical simulation is presented to demonstrate the feasibility of this explanation in addition surface exchange reactions in high caco3 sediments coupled with high rates of particle mixing may also impact rates of metabolic dissolution and depress chamber derived estimates of carbonate alkalinity and calcium benthic fluxes these results suggest that at supersaturated high caco3 locations previous models of sediment diagenesis may have overestimated the impact of metabolic dissolution on the preservation of caco3 deposited on the sea floor

dissolution of calcite in deep sea sediments ph and o2 microelectrode results abstract we present microelectrode profiles of oxygen ph and porosity measured at in situ depth across the sediment water interface from stations above and below the calcite saturation horizon in the equatorial atlantic resistivity electrode data indicate that the diffusion coefficient for solutes is attenuated by nearly a factor of two within the top centimeter of the sediment lattice oxygen and porosity data are used to estimate that the organic carbon respiration rate of the sediment is 10 15 mol cm 2 yr 1 in these locations comparison of the ph data with numerical model results reveals that sedimentary calcite dissolves in response to respiration in the top few centimeters of sediment even above the saturation horizon we calculate that the effective in situ dissolution rate constant for calcite required to explain these data is the neighborhood of 10 100 d 1 although more data are needed to confirm this result it appears to be at least an order of magnitude less than the rate observed in laboratory stirred reactor experiments

volcanic forcing of climate over the past 1500 years an improved ice core based index for climate models 1 understanding natural causes of climate change is vital to evaluate the relative impacts of human pollution and land surface modification on climate we have investigated one of the most important natural causes of climate change volcanic eruptions by using 54 ice core records from both the arctic and antarctica our recently collected suite of ice core data more than double the number of cores ever used before reduces errors inherent in reconstructions based on a single or small number of cores which enables us to obtain much higher accuracy in both detection of events and quantification of the radiative effects we extracted volcanic deposition signals from each ice core record by applying a high pass loess filter to the time series and examining peaks that exceed twice the 31 year running median absolute deviation we then studied the spatial pattern of volcanic sulfate deposition on greenland and antarctica and combined this knowledge with a new understanding of stratospheric transport of volcanic aerosols to produce a forcing data set as a function of month latitude and altitude for the past 1500 years we estimated the uncertainties associated with the choice of volcanic signal extraction criteria ice core sulfate deposition to stratospheric loading calibration factor and the season for the eruptions without a recorded month we forced an energy balance climate model with this new volcanic forcing data set together with solar and anthropogenic forcing to simulate the large scale temperature response the results agree well with instrumental observations for the past 150 years and with proxy records for the entire period through better characterization of the natural causes of climate change this new data set will lead to improved prediction of anthropogenic impacts on climate the new data set of stratospheric sulfate injections from volcanic eruptions for the past 1500 years as a function of latitude altitude and month is available for download in a format suitable for forcing general circulation models of the climate system

bipolar changes in atmospheric circulation during the little ice age annually dated ice cores from siple dome west antarctica and central greenland indicate that meridional atmospheric circulation intensity increased in the polar south pacific and north atlantic at the beginning 1400 a d of the most recent holocene rapid climate change event the little ice age lia as deduced from chemical concentrations at these core sites the lia was characterized by substantial meridional circulation strength variability and this variability persists today despite strong evidence for an end to lia cooling thus increased late 20th century storm variability may be in part a result of the continuation of these climatic fluctuations

calcite dissolution in sediments of the ontong java plateau in situ measurements of pore water o2 and ph we present in situ electrode measurements of sediment resistivity pore water oxygen and pore water ph from three stations between 2300 and 3000 m depth on the ontong java plateau in the western equatorial pacific one of these stations is also the site of a concurrent benthic chamber incubation experiment jahnke et al 1994 the pore water oxygen data and a steady state diffusion and reaction model constrain the depth dependent rate of oxic respiration in the sediments and imply a diffusive flux of oxygen to the sediments of 10 21 mol cm 2 yr 1 given these respiration rates the pore water ph data cannot be explained without calcite dissolution driven by metabolically produced co2 the dissolution necessary to explain the observations quantified by a statistical approach is 3 5 6 mol cm 2 yr 1 which corresponds to at least 20 40 of the calcite rain to these sediments over 65 of the total dissolution is driven by metabolic co2 oxygen fluxes and net calcite dissolution constrained by the electrode data are compatible with the benthic chamber measurements of jahnke et al 1994 the dissolution flux while a significant part of the early diagenesis of calcite in these sediments is less than would be predicted by earlier models of dissolution and jahnke et al 1994 probably could not distinguish it from zero with the benthic chamber technique the dissolution rates found in this study are lower than previous estimates because the respiration reaction is concentrated near the sediment water interface and the calcite dissolution rate constants are very small the statistical evaluation of the pore water ph data and model constrain the calcite dissolution rate constant to 0 005 0 16 d 1 following the general trend of lower values determined by in situ techniques rather than by laboratory methods

upwelling in the taiwan strait during the summer monsoon detected by satellite and shipboard measurements the taiwan strait is located at the confluence of the east china sea and the south china sea in the west pacific ocean several upwelling zones in the taiwan strait are noted for their high fisheries production these upwelling zones have been studied in the past decade but we have no overall picture on the size and temporal changes of these upwelling zones due to only limited in situ observation over short periods of time the present paper investigates upwelling in the taiwan strait with satellite remote sensing data of noaa derived sea surface temperature sst and seawifs derived chlorophyll a chl a and shipboard measurements during summer 1998 results reveal five upwelling zones 1 coastal upwelling near pingtan island ptu 2 coastal upwelling between meizhou and xiaman mxu 3 big coastal upwelling near dongshan island dsu sometimes extending to offshore 4 small occasional upwelling near the penghu island phu and 5 an intensive upwelling in the taiwan bank tbu tbu was extensively studied over summer 1998 results showed that the tbu looks like a banana in shape in the southern edge of the taiwan bank it intensifies in its southeastern edge the size of tbu was about 2500 3000 km 2 with a mean value of 2796 km 2 the temperature difference between the upwelling and non upwelling areas was about 2 5 3 5 jc for early august with a mean value of 2 3 jc on july to october series of images indicated a short term variation of tbu and showed that high chl a concentrations up to 0 8 2 mg m 3 zones coincided with low sst 25 26 jc zones in terms of location time and shape these upwelling zones change with size and intensity center from time to time field measurements of water temperature salinity and chl a in 1998 are consistent with satellite measurements d 2002 elsevier science inc all rights reserved

sulphate record from a northeast greenland ice core over the last 1200 years based on continuous flow analysis a 150 m deep ice core from the low accumulation area of northeast greenland was analyzed for sulphate calcium sodium and electrolytical meltwater conductivity at a depth resolution of approximately 1 cm by continuous flow analysis cfa the calcium and sodium profiles are used to establish a relatively precise ice core chronology by annual layer counting back to ad 830 inspection of the novel cfa method for sulphate revealed relative errors typically around 15 but at least 20 ng g 1 for concentrations 5130 ng g 1 and a current detection limit for routine ice core analyses of 40 ng g 1 annual sulphate peaks are shown to occur over almost the entire core with only a small shift in seasonality between the modern and pre industrial sections inspection of volcanic horizons allowed more accurate timing of these peaks and clear identification of calcium rich events disregarding clear volcanic peaks significant long term changes of sulphate are only seen over the industrial period however a higher frequency of important volcanic inputs was identified around ad 1200

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

ammonium and non sea salt sulfate in the epica ice cores as indicator of biological activity in the southern ocean sulfate so42 and ammonium nh4 flux records over the last 150 000 years from both antarctic epica ice cores european project for ice coring in antarctica are presented the ice core record from dome c is influenced by the indian sector of the southern ocean so whereas dronning maud land is facing the atlantic sector generally they reflect the past atmospheric aerosol load and thus potentially reveal the fingerprint of marine biogenic sources from the so the most important feature of both the nssso 4 2 as well as nh4 flux records is the absence of any significant glacial cycles in contrary to the distinct transitions for mineral dust and sea salt aerosol over the last 150 000 years this finding challenges the iron fertilization hypothesis on long time scales as the significant changes in dust e g from the last glacial maximum toward the holocene have neither an impact on nssso 4 2 nor on nh4 fluxes found in interior antarctica the inter site correlation of both species is weak r 2 0 42 for the nssso 4 2 flux and r 2 0 12 for the nh4 flux respectively emphasizing the local source characteristics of biogenic aerosol from the so millennial variability in nh4 and nssso 4 2 is within the uncertainty of our flux estimates correlation with mineral dust and sea ice derived sodium shows only a very weak influence of dust deposition on those insignificant changes in nssso 4 2 flux for the atlantic sector of the southern ocean but also small transport changes or terrigeneous sulfate contributions may contribute to those variations at edml c 2009 elsevier ltd all rights reserved

molybdenite re os and albite 40ar 39ar dating of cu au mo and magnetite porphyry systems in the yangtze river valley and metallogenic implications abstract the area of the middle lower yangtze river valley eastern china extending from wuhan hubei province to western zhenjiang jiangsu province hosts an important belt of cu au mo and fe deposits there are two styles of mineralization i e skarn porphyry stratabound cu au mo fe deposits and magnetite porphyry deposits in several nne trending cretaceous fault bound volcanic basins the origin of both deposit systems is much debated we dated 11 molybdenite samples from five skarn porphyry cu au mo deposits and 5 molybdenite samples from the datuanshan stratabound cu au mo deposit by icp ms re os isotope analysis nine samples from the same set were additionally analyzed by ntims on re os results from the two methods are almost identical the re os model ages of 16 molybdenite samples range from 134 7 2 3 to 143 7 1 6 ma 2 the model ages of the five samples from the datuanshan stratabound deposit vary from 138 0 3 2 to 140 8 2 0 ma with a mean of 139 3 2 6 ma their isochron age is 139 1 2 7 ma with an initial os ratio of 0 7 8 1 mswd 0 29 these data indicate that the porphyry skarn systems and the stratabound deposits have the same age and suggest an origin within the same metallogenic system albite 40 ar 39 ar dating of the magnetite porphyry deposits indicates that they formed at 123 to 125 ma i e 10 20 ma later both mineralization styles characterize transitional geodynamic regimes i e the period around 140 ma when the main ns trending compressional regime changed to an ew trending lithospheric extensional regime and the period of 125 115 ma of dramatic ew trending lithospheric extension

multi scale modeling of the north pacific ocean assessment and analysis of simulated basin scale variability 1996 2003 1 a primitive equation ocean general circulation model is used to investigate climate impacts in the north pacific ocean in the 1996 to 2003 period the objective is to assess the model ability to reproduce observed modes of variability and study their impact in the northeast pacific this work is done within the framework of the u s global ecosystem globec northeast pacific program studying the links between climate variability and ecosystem dynamics three large scale events are considered the 1997 1998 el nino the 1999 regime shift and the 2002 cold fresh subsurface anomalous water mass that was observed in the gulf of alaska and off the coast of oregon the circulation model is shown to generate the correct seasonal to interannual large scale variability and is able to represent the climatic signals of interest in the eastern pacific we show that the influence of the 1997 1998 el nino reached the coastal gulf of alaska and induced an increase in the upper ocean heat content along the coast of north america an analysis of the sea surface temperature for the model years shows agreement between model and data in the representation of the 1999 shift to a cold phase in the eastern and northern north pacific finally using the model results we speculate that the origin of the 2002 cold fresh anomaly in the northeast pacific was due to enhanced mixing during the preceding winter in the center of the alaska gyre owing to anomalous changes in the density structure of the upper ocean this water was able to move geostrophically toward the coast and it persisted in the northeast pacific below the mixed layer the following year

two dimensional ph distributions and dynamics in bioturbated marine sediments the seafloor is the site of intense biogeochemical and mineral dissolution precipitation reactions which generate strong gradients in ph near the sediment overlying water interface these gradients are usually measured in one dimension vertically with depth two dimensional ph distributions in marine sediments were examined at high resolution 65 65 m pixel and analytical precision over areas of 150 to 225 cm2 using a newly developed ph planar fluorosensor dramatic three dimensional gradients complex heterogeneity and dynamic changes of ph occur in the surficial zone of deposits inhabited by macrofauna ph can vary by 2 units horizontally as well as vertically over millimeter scales ph minima zones often form in association with redoxclines within a few millimeters of inner burrow walls and become more pronounced with time if burrows remain stable and irrigated for extended periods microenvironmental ph minima also form locally around decaying biomass and relict burrow tracks and dissipate with time 5 d h concentrations and fluxes in sandy mud show complex acid base reaction distributions with net h fluxes around burrows up to 12 nmol cm 2 d 1 and maximum net reaction rates varying between 90 consumption to 120 production m d 1 90 nmol cm 1 d 1 burrow length acid producing zones that surround irrigated burrows are largely balanced by acid titration zones along inner burrow walls and outer radial boundaries the geometry and scaling of ph microenvironments are functions of diagenetic reaction rates and three dimensional transport patterns determined by sediment properties such as diffusive tortuosity and by benthic community characteristics such as the abundance mobility and size of infauna previously undocumented biogeochemical phenomena such as low ph regions associated with in filled relict biogenic structures and burrowing tracks are readily demonstrated by two dimensional and time dependent images of ph and sedimentary structure

spatial and seasonal variations of the snow chemistry at the central filchner ronne ice shelf antarctica the chemical stratigraphy of the surface firn of the central filchner ronne ice shelf was determined in conjunction with stable isotopes from shallow firn cores and snow pit samples collected at 1 1 widely distributed sites and covering a time period of at least 20 years the chemical analysis included ecm profiling and the determination of chloride non sea salt nss sulphate methanesulphonate msa nitrate and partly sodium and bromide throughout the investigated area winter time nss sulphate levels are found to be substantially negative indicating that the sulphate to sodium ratio in airborne sea salt particles is depleted by a factor of 5 approximately in relation to the bulk sea water ratio while winter firn layers appear to be marked by episodic events of large sea salt inputs pronounced annual cycles with maxima in summer firn layers are commonly observed for the ecm signal and for nss sulphate nitrate and msa at all sites for msa however this phase relation is almost reversed for depths greater than 3 4m the mean impurity levels consistently are strongly depleted with increasing distance from the ice edge by about 30 100 km for sea salt 25 100 km for msa and only 10 100 km for nss sulphate however no substantial trend is observed for nitrate it is concluded therefore that the sea salt and the biogenic sulphur compounds deposited on the filchner ronne ice shelf mainly originate from the adjacent weddell sea further important implications of the continental effects are a an atmospheric residence time of nss sulphate apparently exceeding that of msa probably due to the supplementary sulphate production on the ice shelf from biogenic so 2 and b a substantial limitation of the potential of deep ice cores already drilled on the filchner ronne ice shelf in extracting reliable net temporal changes of sea salt and biogenic sulphur species

the transition from the last glacial period in inland and near coastal antarctica recent studies suggested that during the transition out of the last glacial period one near coastal site in antarctica showed a response similar to that of greenland and unlike that of central antarctica here we present a new high resolution record of calcium from dome c antarctica changes in flux of calcium an indicator of dust input from other continents should be synchronous across the region and probably the continent using ca to synchronise records we find that the main warming at the near coastal site of taylor dome was slower than suggested previously and similar to that of central antarctica until there is further evidence it is still a reasonable hypothesis that antarctic climate behaved more or less as a single unit during the transition

temporal variations and sources of elements in the south pole atmosphere 1 nonenriched and moderately enriched elements high volume particle samples were collected from 1979 to 1983 from the south pole atmosphere and analyzed by nuclear methods the new results are combined with similar studies at the south pole there is no trend of concentrations during 12 years of sampling but concentrations of elements fluctuate through seasonal cycles concentrations of elements associated with crustal dust and sea salt showed opposite seasonal variations concentrations of most crustal elements are low during winters but double during summers concentration of marine elements are low in the summers and high in winters enrichment factors of some crustal elements such as ba la ce yb and hf are higher in the winter than summer indicating the presence of a second crustal component with a different chemical composition in the south pole atmosphere a similar difference in the crustal enrichment factor of co is due to the influence of volcanic or anthropogenic sources sulfate seasalt meteoritic particles volatiles and two different types of crustal particles are found to be components of the south polar aerosols the relative contribution of each component to total aerosol mass is as follows crustal 4 0 in summer 2 5 in winter marine elements 16 6 in summer 78 6 in winter sulfate 77 5 in summer 18 0 in winter meteoritic particles 0 1 in summer 0 1 in winter volatiles 0 9 in summer 0 5 in winter crustal component ii 0 8 in summer 0 7 in winter

layering of surface snow and firn at kohnen station antarctica noise or seasonal signal the density of firn is an important property for monitoring and modeling the ice sheet as well as to model the pore close off and thus to interpret ice core based greenhouse gas records one feature which is still in debate is the potential existence of an annual cycle of firn density in low accumulation regions several studies describe or assume seasonally successive density layers horizontally evenly distributed as seen in radar data on the other hand high resolution density measurements on firn cores in antarctica and greenland showed no clear seasonal cycle in the top few meters a major caveat of most existing snow pit and firn core based studies is that they represent one vertical profile from a laterally heterogeneous density field to overcome this we created an extensive dataset of horizontal and vertical density data at kohnen station dronning maud land on the east antarctic plateau we drilled and analyzed three 90 m long firn cores as well as 160 one meter long vertical profiles from two elongated snow trenches to obtain a two dimensional view of the density variations the analysis of the 45 m wide and 1 m deep density fields reveals a seasonal cycle in density however the seasonality is overprinted by strong stratigraphic noise making it invisible when analyzing single firn cores our density dataset extends the view from the local ice core perspective to a hundred meter scale and thus supports linking spatially integrating methods such as radar and seismic studies to ice and firn cores

gis based prospectivity mapping based on geochemical multivariate analysis technology a case study of mvt pb zn deposits in the huanyuan fenghuang district northwestern hunan province china abstract this paper demonstrates a partial least squares regression pls method for geochemical modelling and then uses the models and geological favourable features to obtain mineral potential maps the pls is one of multivariate analysis technologies which can identify variations in associations and correlations among geochemical elements and mineralisation the method is here used to calculate principal components as well as to identify correlations between pb zn mineralization and 25 stream sediment elements for constructing geochemical models in the huayuan fenghuang district of northwestern hunan province china the models showing the distribution of geochemical anomaly are useful in interpreting the distribution of faults and the cambrian qingxudong formation ore bearing formation and to better define the architecture on mineralisation in the study area in addition the models and other favourable features proxies are easily integrated into single possibility map by boost weights of evidence boost wofe approach for targets

age scale of the air in the summit ice implication for glacial interglacial temperature change the air occluded in ice sheets and glaciers has in general a younger age defined as the time after its isolation from the atmosphere than the surrounding ice matrix because snow is first transformed into open porous firn in which the air can exchange with the atmosphere only at a certain depth firn ice transition the pores are pinched off and the air is definitely isolated from the atmosphere the firn ice transition depth is at around 70 m under present climatic conditions at summit central greenland the air at this depth is roughly 10 years old due to diffusive mixing whereas the ice is about 220 years old this results in an age difference between the air and the ice of 210 years this difference depends on temperature and accumulation rate and did thus not remain constant during the past we used a dynamic firn densification model to calculate the firn ice transition depth and the age of the ice at this depth and an air diffusion model to determine the age of the air at the transition past temperatures and accumulation rates have been deduced from the 18o record using time independent functions we present the results of model calculations of two paleotemperature scenarios yielding a record of the age difference between the air and the ice for the greenland ice core project grip and the greenland ice sheet project two gisp2 ice cores for the last 100 000 years during the holocene the age difference stayed rather stable around 200 years while it reached values up to 1400 years during the last glaciation for the colder scenario the model results are compared with age differences obtained independently by matching corresponding climate events in the methane and 18o records assuming a very small phase lag between variations in the greenland surface temperature and the atmospheric methane the past firn ice transition depths are compared with diffusive column heights obtained from 15n of n2 measurements the results of this study corroborate the large temperature change of 20 to 25 k from the coldest glacial to holocene climate found by evaluating borehole temperature profiles

origin of the granites and related sn and pb zn polymetallic ore deposits in the pengshan district jiangxi province south china constraints from geochronology geochemistry mineral chemistry and sr nd hf pb s isotopes the pengshan sn and pb zn polymetallic deposits are located in the south margin of the jiujiang ruichang jiurui district of the middle lower yangtze river metallogenic belt in south china four large deposits include huangjinwa zengjialong jianfengpo and zhangshiba the former three are sn dominant deposits which occur as stratiform orebodies in the contact zones of the pengshan granites and within the country rock strata whereas zhangshiba consists of stratiform pb zn orebodies within the precambrian metasedimentary strata in this study we present results on zircon u pb ages major and trace elements and mineral chemistry as well as sr nd hf isotope data of the granites pb and s isotopes of both the sn dominant and pb zn dominant deposits and u pb dating of cassiterite from the pengshan district shrimp and la icp ms zircon u pb dating shows that the pengshan granites were emplaced in the early cretaceous 129 128 ma which is in good agreement with the u pb dating 130 128 ma of cassiterite from the jianfengpo sn deposit the pengshan granites consist mainly of weakly peraluminous highly fractionated i type affinity granitic rocks detailed elemental and isotopic data suggest that the granites formed by partial melting of mesoproterozoic metamorphic basement materials with minor input of mantle derived melts the mineral chemistry of biotite demonstrates that the pengshan granitic magma had a low oxygen fugacity thereby precluding the tin dominantly partitioning into the rock forming silicate minerals and favoring accumulation in the exsolved residual liquid during magma crystallization stages sulfur isotopes show a relatively heavy sulfur isotopic composition from 5 8 to 17 6 and no difference for sulfur isotopes between the sn deposits 5 8 13 4 huangjinwa zengjialong jianfengpo and the pb zn deposit mostly 7 1 13 0 except for one 17 6 zhangshiba the sulfur isotope data of pyrite from the host sedimentary rocks show relatively higher 34s values of 22 7 28 7 lead isotopes indicate that the granites have higher 206pb 204pb 207pb 204pb and 208pb 204pb ratios than the host precambrian metasedimentary rocks and the sulfide minerals from the orebodies fall in between them again there is no difference for pb isotopes between the sn deposits huangjinwa zengjialong jianfengpo and the zhangshiba pb zn deposit the coincidence in s and pb isotope compositions for sn and pb zn deposits suggests that similar sources for these mineralization possibly derived from a mixed source of the granitic magmas and the precambrian metasedimentary rocks these data therefore favor of a magmatic hydrothermal origin for both the sn and pb zn polymetallic mineralization in the pengshan district

respiration dissolution and the lysocline 1 here i synthesize the results of several types of measurements of organic carbon respiration and calcium carbonate dissolution rates in pelagic seafloor sediments measurements of pore water oxygen demonstrate that most of the respiration takes place very near the sediment water interface with a scale depth of a few millimeters the remainder of the oxic respiration occurs much deeper in the sediments with a scale depth of several centimeters all measures of respiration from locations as disparate as the tropical pacific and atlantic and the subtropical north atlantic agree that pelagic seafloor rates of oxic respiration of organic carbon are relatively independent of depth and location with the exception of sediments beneath the pacific eastern equatorial upwelling zone calcite dissolution in seafloor sediments requires forcing by respiration produced co2 and rates are consistent with a first order dependence on pore water undersaturation solubility as determined by mucci 1983 at atmospheric pressure and locally variable mass specific dissolution rate constants respiration driven calcite dissolution fluxes predicted by this combination of respiration and dissolution rate expressions are significantly lower than many previous estimates comparison of dissolution fluxes in the oligotrophic open ocean measured by other researchers with benthic chamber incubation techniques with those predicted by this combination of rate expressions is within stated uncertainties in agreement in all but one case questioning the need for complicated mechanisms such as surface buffering or authigenic precipitation to explain seafloor calcite diagenesis applying these kinetics to a simple one dimensional steady state model of the bulk calcite content and sediment accumulation rates of the sediment mixed layer yields results consistent with observations of the seafloor lysocline the region of transition from high calcite to low calcite sediments on the ceara rise in the western tropical north atlantic and the ontong java plateau in the western equatorial pacific scenarios ignoring dissolution driven by respiration produced co2 in pore waters and using the high order dependence on undersaturation and very large dissolution rate constants implied by some earlier laboratory studies do not simulate these observations while the scheme represented here does in fact imply a strong shift in the locus of carbonate dissolution toward the sediment water interface as bottom water saturation decreases as implied by the observations of martin et al 2000 no simple combination of sediment transport coefficients and reaction kinetics can reproduce the observation of increasing 14c age as dissolution progresses these results emphasize the importance of accurate knowledge of the kinetics of respiration and dissolution to interpretation of either the present day or paleolysocline

the 800 year long ion record from the lomonosovfonna svalbard ice core we present a high resolution record of water soluble ion chemistry from a 121 m ice core spanning about 800 years the core is well dated to 2 3 depth using cycle counting and reference horizons and a simple but close fitting model for the lower 1 3 of the core this core suffers from modest seasonal melt and so we present concentration data in decadal running means to minimize percolation effects sea salt ions na cl mg2 and k account for more than 70 of all ions in general sea salt ion concentrations are rather variable and have no clear association with climatic variations sulfate with 74 being from non sea salt sources has higher concentrations than seen on vestfonna ice cap but lower than in ny alesund aerosols suggesting central spitsbergen receives more marine westerly air masses than ny alesund but more sulfate enriched easterly air masses than nordaustlandet clear anthropogenic impacts are found for sulfate nitrate and ammonium and probably excess chloride after the mid twentieth century with sulfate showing a significant rise by the end of the nineteenth century sulfate and methanesulfonate concentrations correlate well during the twentieth century and it is clear that most of the preindustrial sulfate is of biogenic origin terrestrial component ca2 has the highest concentrations in the coldest part of the little ice age suggesting more windy conditions transporting local terrestrial dust to the ice cap all ion concentrations decrease at the end of the twentieth century which reflects loss of ions by runoff with non sea salt magnesium being particularly sensitive to melting

the lower changjiang yangzi yangtze river metallogenic belt east central china intrusion and wall rock hosted cu fe au mo zn pb ag deposits abstract the lower valley of changjiang from wuhan of the hubei province in the west to zhenjiang of the jiangsu province in the east contains more than 200 polymetallic cu fe au mo zn pb ag deposits and is one of the most important metallogenic belts in china this metallogenic belt situated at the northern margin of the yangzi craton and bordered by the dabieshan ultrahigh pressure metamorphic belt to the north consists mainly of cambrian triassic marine clastic sedimentary rocks and carbonate and evaporite rocks which overlay a precambrian basement and are intruded by yanshanian 205 to 64 ma granitoid intrusions and subvolcanic complexes repeated tectonism from late proterozoic to triassic resulted in extensively developed networks of faults and folds involving the cambrian triassic sedimentary strata and the precambrian basement the yanshanian granitoid intrusions and subvolcanic complexes in the lower changjiang metallogenic belt are characterized by whole rock 18 o of 8 to 10 initial 87 sr 86 sr of 0 704 to 0 708 and ndt from 10 to 17 and have been interpreted to have originated from mixing between juvenile mantle and old crustal materials also the yanshanian granitoids exhibit eastward younging and increase in alkalinity i e from older calc alkaline in the west to younger subalkaline alkaline in the east which are related to oblique collision between the yangzi and sino korean cratons and tectonic evolution from early compressional to late extensional or rifting regimes most polymetallic deposits in the lower changjiang metallogenic belt are clustered in seven districts where the yanshanian magmatism is particularly extensive from west to east edong jiurui anqing guichi luzhong tongling ningwu and ningzhen mineralization is characterized by the occurrence of three distinct types of orebodies in individual deposits orebodies in yanshanian granitoid intrusions skarn orebodies at the contact zones between the yanshanian intrusions and late paleozoic early mesozoic sedimentary rocks and stratabound massive sulfide orebodies in the late paleozoic early mesozoic sedimentary strata the most important host sedimentary strata are the middle carboniferous huanglong formation lower permian and lower middle triassic carbonate and evaporite rocks the intrusion hosted and skarn orebodies exhibit well developed zonation in alteration assemblages metal contents and isotopic compositions within individual deposits and apparently formed from hydrothermal activities related to the yanshanian magmatism the stratabound massive sulfide orebodies in the late paleozoic early mesozoic sedimentary strata have long been suggested to have formed from sedimentary or volcano sedimentary exhalative processes in shallow marine environments however extensive research over the last 40 years failed to produce unequivocal evidence for syngenetic mineralization on the basis of geological relationships and isotope geochemical characteristics we propose a carbonate hosted replacement deposit model for the genesis of these stratabound massive sulfide orebodies and associated skarn orebodies this model suggests that epigenetic mineralization resulted from interactions between magmatic fluids evolved from the yanshanian intrusions with carbonate and evaporite wall rocks mineralization was an integral but distal part of the larger hydrothermal systems that formed the proximal skarn orebodies at the contact zones and the intrusion hosted orebodies the stratabound massive sulfide deposits of the lower changjiang metallogenic belt share many features with the well studied high temperature carbonate hosted replacement deposits of northern mexico and western united states particularly with respect to association with small shallow granitoid complexes structural and stratigraphic controls on mineralization alteration assemblages geometry of orebodies metal association metal zonation and isotopic systematics

on the impact of impurities on the densification of polar firn abstract understanding polar firn densification is crucial for reconstructing the age of greenhouse gas concentrations extracted from ice cores and for the interpretation of air in ice as a dating tool or as a climate proxy firn densification is generally modeled as a steady burial and sintering process of defined layers where the structure of the layering is maintained along the whole firn and ice column however available high resolution density data as well as firn air samples question this picture and point to a lack of understanding of firn densification based on analysis of high resolution density and calcium concentration records from antarctic and greenland ice cores we show for the first time that also impurities may have a significant impact on the densification analysis of firn cores shows a correlation between density and the calcium ion ca concentration and this correlation increases with depth the existence of this relationship is independent of the local climatic conditions at the core sites analyzed the strong positive correlation between the density and the logarithm of ca concentration indicates that impurities induce softening and lead to faster densification over a wide range of concentrations in one core the impurity effect manifests itself so strongly that the density develops a seasonal cycle closely following the seasonal cycle of ca our results clearly show that the structure of the firn layering changes with depth and suggest that the increased variability in density observed in deep firn recently described as a universal feature of polar firn may arise from the influence of ca and or other impurities the impurity effect is likely to have direct implications on our understanding of glacial firn densification and on glacial gas age estimates

a new continuous high resolution detection system for sulphate in ice cores sulphate so4 2 is a major ion found in polar ice cores and is related to different aerosol sources and processes explosive volcanic eruptions even far away can cause distinct sulphate peaks in ice core records thus a robust sulphate detection system which is suitable for fieldwork and which enables the measurement of sulphate at high temporal resolution is of great interest in this study we present the adaptation of a new continuous flow analysis system for sulphate that is based on a spectrophotometric method using dimethylsulfonazo iii and an inline reactor column containing barium sulphate particles the method shows a detection limit of 70 ng g 1 and a linear range up to at least 3000 ng g 1 it is simple robust and less prone to interferences compared to the previously used method

deepwater overflow through luzon strait 1 this study examines water property distributions in the deep south china sea and adjoining pacific ocean using all available hydrographic data our analysis reveals that below about 1500 m there is a persistent baroclinic pressure gradient driving flow from the pacific into the south china sea through luzon strait applying hydraulic theory with assumptions of zero potential vorticity and flat bottom to the luzon strait yields a transport estimate of 2 5 sv 1 sv 106 m3 s 1 some implications of this result include 1 a residence time of less than 30 years in the deep south china sea 2 a mean diapycnal diffusivity as large as 10 3 m2 s 1 and 3 an abyssal upwelling rate of about 3 10 6 m s 1 these quantities are consistent with residence times based on oxygen consumption rates the fact that all of the inflowing water must warm up before leaving the basin implies that this marginal sea contributes to the water mass transformations that drive the meridional overturning circulation in the north pacific density distributions within the south china sea basin suggest a cyclonic deep boundary current system as might be expected for an overflow driven abyssal circulation

a 10 century comparison of prominent bipolar volcanic events in ice cores measurements of key chemical and physical parameters made along continuous and selected long sections of polar ice cores provide reliable past snow accumulation rates and other environmental records the prime accumulation indicators include variations found in the stable isotopes ionic constituents and acidity concentration levels and physical changes in the strata and structure cross correlations of the time series curves resulting from multiparameter analyses of ice cores from antarctica nby89 sp78 bs68 and greenland cr74 d3 81 d3 18c have been made the results permit construction of a bipolar chemical stratigraphy chronology of volcanic events that is coherent with the 18 o and electrical conductivity method data sets and consistent back in time with historically recorded volcanic activity a bihemispheric comparison of high non sea salt so 4 2 peaks shows strong correlation at 1885 1836 1816 1810 1459 1346 1287 1278 1259 1228 and 1168 a d at time of snow deposit the prominent 1259 a d volcanic signal appears to be a significant bipolar ice core index horizon

mineral composition of host sediments influences the fossilization of soft tissues cambrian lagerstatten host rocks are frequently composed of kaolinite and chlorite in varying amounts accordingly our goal was to study the preservation potential of crustaceans in these two clays we conducted long term experiments 12 18 months the longest duration of actualistic taphonomy experiments from published literature on the decay of artemia salina in these clay sediments the degree of preservation transformed mineralogical composition of the sediments and the elemental composition of the nauplial remains were examined we demonstrate that the kaolinite and chlorite sediment enhanced the preservation in the kaolinite the effect was considerably higher than in the chlorite compared with the sediment free control ph inside the sediments dropped to 6 5 7 1 and was even lower 4 around the buried carcasses facilitating the dissolution of clays this phenomenon was confirmed by mineralogical analyses of the experimental sediments which showed mineralogical signatures of such dissolutio

glacial interglacial changes in mineral dust and sea salt records in polar ice cores sources transport and deposition 1 sea salt and mineral dust records as represented by na and ca2 concentrations respectively in greenland and antarctic ice cores show pronounced glacial interglacial variations for the last glacial maximum lgm mineral dust sea salt concentrations in greenland show an increase of a factor of approximately 80 15 compared to the holocene and significant shifts by a factor of 15 5 during dansgaard oeschger events in antarctica the dust sea salt flux is enhanced by a factor of 15 3 during the lgm compared to the holocene and variations by approximately a factor of 8 1 2 exist in parallel to antarctic warm events primary glacial dust sources are the asian deserts for greenland and patagonia for antarctica ice core evidence and model results show that both changes in source strength as well as atmospheric transport and lifetime contributed to the observed changes in greenland ice cores in antarctica changes in ice core fluxes are in large parts related to source variations both for sea salt and dust where the formation of sea salt aerosol from sea ice may play a pivotal role summarizing our latest estimates on changes in sources transport and deposition these processes are roughly able to explain the glacial increase in sea salt in both polar regions while they fall short by at least a factor of 4 7 for mineral dust future improvements in model resolution and in the formulation of source and transport processes together with new ice core records e g on dust size distributions will eventually allow convergence of models and observations

a glacio chemical characterization of the new epica deep drilling site on amundsenisen dronning maud land antarctica in the framework of the european project for ice coring in antarctica epica a glacio chemical pre sitesurvey was carried out in dronning maud land dml antarctica up to now three intermediate deep icecores and twelve snow pits have been analysed by ion chromatography the spatial and seasonal variationsof the snow chemistry in dml covering the time period 1997 to 1865 are presented summer maxima insulphate and winter maxima in sea salt components are well archived in the area under investigation while for nitrate and methanesulphonic acid msa seasonal variations could not be unambiguouslydetected due to postdepositional changes average concentrations of sea salt components and nitrateare spatially uniform in the plateau region however sea salt shows an exponential decline with altitudefor elevations below 2800 m a s l non seasalt sulphate shows a 40 increase with lower snowaccumulation while msa shows a 50 decline with higher elevation and lower accumulation the outcomeof this study supports that the data of the new epica deep drilling site in dml 0 04 07 e 75 00 10 s will be geographical representative for this region high resolution analytical methods will allow accuratestratigraphic dating of the core at least for the holocene period

glacio chemical study spanning the past 2 kyr on three ice cores from dronning maud land antarctica 2 seasonally resolved chemical records the ammonium calcium and sodium concentrations from three intermediate depth ice cores drilled in the area of dronning maud land east antarctica have been investigated since all measurements were performed by a high resolution continuous flow analysis system for the first time seasonal signals of chemical trace species could be obtained from the interior of central antarctica over a period of approximately 2 millennia although the elevation as well as the accumulation rate differ between the drilling sites similar values were obtained by comparing mean concentrations spanning the last 900 years however a distinct lack of intersite correlation was found on decadal timescales despite a noticeable accumulation change apparent in one core no significant concentration change of all three species has occurred all the measured ions show clear seasonal signals over the whole records while the sea salt related component sodium peaks simultaneously with calcium the maximum ammonium concentration occurs in the snow with a time lag of 2 months after the sea salt peak more than 60 of the calcium concentration can be attributed to an ocean source elevated sodium concentrations were found within this millennium compared to mean values of the whole records but the spatially varying shape of the increase suggests that a possible climatic signal is biased by local deposition effects

plio quaternary sedimentation processes and neotectonics of the northern continental margin of the south china sea abstract analyses of over 6600 km of reflection seismic profiles on the northern continental margin of the south china sea permit the recognition of four quaternary high frequency type 1 sequences of the 4th order deposited during the past ca 690 kyr at the present day shelf edge only lowstand systems tracts characterised by a prograding clinoformal internal reflection pattern are preserved the prograding complexes can be considered as regressive units accumulated during relative sea level falls they exhibit internal discontinuities which might point to minor sea level fluctuations of the 5th order a preliminary regional relative sea level curve for the past 630 kyr is established using the present positions of the delta fronts mapped the neotectonics curve derived by subtracting eustatic sea level changes from the relative sea level curve shows that the depths of the delta fronts today are controlled primarily by regional tectonic movements and the global sea level our seismo stratigraphic interpretation documents that the area off hong kong and around the dongsha islands experienced two uplift episodes during the past 5 ma namely at the miocene pliocene boundary and at the end of the lower middle pleistocene respectively these uplift events which are centred on the dongsha rise led to its subaerial exposure and to the erosion of the pliocene and most of the pleistocene strata the change from thermal subsidence of the continental margin initiated at the end of the drift phase to the phase of magmato tectonic uplift was caused by a reorientation of the tectonic regime the recent depositional environment on the northern continental margin of the south china sea is dominated by sediment accumulation within the inner shelf and the zhujiang pearl river estuary the outer shelf and upper slope especially around the dongsha islands are characterised by bypass of terrigenous material the sedimentary column in the deepsea basin has a thickness of more than 2 km and comprises 14 depositional units starting with terrestrial rift deposits it overlies oceanic as well as transitional crust

a tectono genetic model for porphyry skarn stratabound cu au mo fe and magnetite apatite deposits along the middle lower yangtze river valley eastern china abstract the middle lower yangtze river valley metallogenic belt yrb situated along the northern margin of the yangtze craton is characterized by porphyry skarn stratabound cu au mo fe deposits in the areas of uplift and magnetite apatite deposits in cretaceous fault basins following detailed field investigations and a review of published data we recognize two episodes of magmatism and mineralization in the yrb 1 156 137 ma high k calc alkaline granitoids associated with 148 135 ma porphyry skarn stratabound cu au mo fe deposits and 2 135 123 ma shoshonitic series associated with 134 9 122 9 ma magnetite apatite deposits a type granitoids and associated alkaline volcanic have a small age range from 126 5 to 124 8 ma and are temporally spatially and genetically associated with the second episode the geodynamic history of the yrb did not experience the paleozoic to mesozoic lithospheric thickening that took place in the north china craton this process is inferred to be linked to partial melting of the delaminated lower crust at high pressures resulting in the development of c type adakitic rocks the petrochemical and sr nd isotopic data show that both the shoshonitic series and a type granitoids are quite different from adakites with only some of the k calc alkaline granitoids having adakitic signatures previous ore genesis models were established based on an assumed relationship with adakites and a continuous tectono thermal evolution from 150 to 100 ma all data obtained for the middle lower yangtze river region consistently show that the tan lu regional strike slip fault zone initiated at 233 6 to 225 6 ma from the collision between the north china and yangtze cratons and was reactivated at ca 160 ma the tan lu fault was caused by the oblique subduction of the izanagi plate which along the yrb the low angle subducted slab and the overlying crust was disrupted or broken due to the disharmonious movement of the two blocks the high k calc alkaline granitoids magmas were derived from melting of the subducted slab with some input of crustal material these magmas were emplaced at the intersections between ne and ew trending faults and formed porphyry skarn stratabound cu au mo fe deposits between 156 and 137 ma after 135 ma the subducted plate changed its direction of motion to northeast now running parallel to the eurasian continental margin and leading to large scale continental extension the shoshonitic series and subsequent a type granitoids magmatism and the development of magnetite apatite ores in the yrb took place in both fault basins and ne trending rifts between 135 and 124 ma

microelectrode studies of organic carbon degradation and calcite dissolution at a california continental rise site fine scale porewater profiles of resistivity o2 ph and pco2 were measured in situ with microelectrodes at a site on the california continental rise they are reported here with more traditional measurements of shipboard porewater no3 alkalinity and tco2 and sediment organic c and caco3 profiles a numerical model encompassing diffusion advection and multiple reaction terms is applied to these data to characterize organic carbon degradation and caco3 dissolution processes near the sediment water interface a benthic o2 flux of 58 mol cm 2 yr 1 over the top 1 mm sediment is estimated based on one measured sub mm depth scale o2 profile the numerical model indicates that this high o2 consumption rate is related to a very labile fraction of organic c which has a degradation rate constant of approximately 4 5 10 8 s 1 1 4 yr 1 and which is not mixed downward by biological mixing seasonality in the benthic o2 consumption rate of this site may be attributed to variations in the input rate of this highly labile organic c degradation rate constants of the bulk organic c by oxygen reduction and by nitrate reduction are estimated to be about the same 1 10 9 s 1 the organic c rain rate responsible for the bulk organic c is estimated to be 53 mol cm 2 yr 1 this estimate exceeds the average rain rate determined by sediment trap collections at this site saturation state profiles calculated from the in situ ph and pco2 data and from modelling the in situ o2 and ph data both indicate that the porewater is undersaturated with respect to calcite to a depth of at least 8 cm the dissolution rate constant of calcite in this caco3 poor station is determined to be 5 10 day 1 assuming the reaction order is 4 5 which is close to the minimum estimates for environments richer in calcite a uniform calcite dissolution rate constant therefore may be adequate for representing carbonate dissolution in global scale models of ocean chemistry

modeling south china sea circulation response to seasonal forcing regimes 1 a three dimensional ocean model has been utilized to study circulation and its seasonal variation in the south china sea scs in response to the forcing of the asian monsoon and the kuroshio intrusion the scs ocean model has a resolution of approximately 10 km horizontal spacing and 30 vertical levels with a realistic bottom topography the model is forced with time dependent wind stress and heat flux from national center for environmental prediction reanalysis data as well as with lateral fluxes from a pacific ocean model of 40 km horizontal resolution this study reports on the analysis of the mean seasonal circulation and dynamic processes in response to monsoonal wind stress the kuroshio intrusion and other intrinsic forcing processes it is found that the seasonal circulation in the scs is mainly driven by the monsoonal wind stress and greatly influenced by the inflow from the kuroshio intrusion strong currents along the continental margin of the scs form mean basin wide cyclonic and anticyclonic circulations in the winter and summer respectively multiscale eddies are embedded in the general circulation across the basin while mainstream of the kuroshio passes through the luzon strait without intruding into the scs partial intrusion occurs in the upper 200 m near the shelf margin southwest of taiwan at times when winter dynamic conditions prevail in the north scs the intrusion of the kuroshio into the scs also occurs at depths in all seasons mainly along the continental slope the coastal current separation to the east off southern vietnam and the associated eddy formations characterize the circulation in the south scs the simulated results compare well with the corresponding observed fields dynamical processes involved in the forced flow fields are investigated by examination of the momentum balances the analyses reveal that the circulation in the scs is generally dominated by the geostrophic currents north of the luzon strait positive nonlinearity in the zonal direction is locally intensified which leads to the formation of centripetal acceleration for the mainstream of the kuroshio to turn eastward the kuroshio intrusion at depths is governed by the ageostrophic flows and highly associated with the net westward pressure gradient force coastal jet separation to the east off vietnam is mainly associated with the local wind stress field and with the shelf topography in the summer and winter respectively sensitivity study reveals that the weakening of the kuroshio markedly enhances kuroshio s intrusion and forms an anticyclonic eddy west of the luzon strait

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

late mesozoic magmatism of the jiurui mineralization district in the middle lower yangtze river metallogenic belt eastern china precise u pb ages and geodynamic implications abstract the middle lower yangtze river metallogenic belt mlyrmb extending from daye in hubei province in the west to zhenjiang in jiangsu province in the east hosts a number of large polymetallic cu au mo fe zn pb and ag deposits and constitutes one of the most important metallogenic belts in china the cu au mo deposits in the jiurui district are an important component of the mlyrmb in this study we carried out precise and detailed zircon u pb dating for all types of magmatic rocks from the wushan ore deposit in the jiurui district three samples of cu au mo related porphyries from different ore belts at wushan were analyzed and yielded zircon u pb ages of 148 0 1 0 ma 145 4 0 9 ma and 147 3 0 9 ma respectively a series of dykes were emplaced immediately following the cu au mo related porphyries at wushan a dark colored basic dyke which intruded into the granodiorite porphyry at wujia gold deposit near wushan was dated at 144 5 1 2 ma two lamprophyre dykes taken from the north ore belt at wushan underground mining stops were dated at 143 6 0 9 ma and 144 3 0 9 ma respectively a late stage dyke which was also taken from the wushan north ore belt yielded an age of 142 6 1 0 ma and might represent the end of magmatism in the wushan ore deposit these new geochronological data demonstrate that the time range of magmatism in the wushan ore deposit is approximately between 148 ma and 143 ma showing that the magmatic activity at wushan was rapid and intensive the ages of cu au mo related porphyries from other areas in the jiurui district such as the dongleiwan yangjishan and chengmenba ore deposits were also measured and yielded zircon u pb ages of 141 5 1 7 ma 143 4 1 4 ma and 146 6 1 0 ma respectively combined with those previously reported zircon u pb age results from the jiurui district the present age data set demonstrates that extensive magmatism in the jiurui district was coeval and intensive marked by a magmatic activity in the age range of 148 to 138 ma and peaked between 148 ma and 142 ma according to the statistics of all those precise zircon u pb ages the cu au mo related porphyries in the edong and tongling districts in the mlyrmb show similar ages and they have a slightly younger peak age and a longer duration than that of the jiurui district the geographic shape of the mlyrmb in the cretaceous shows an arcuate structure the jiurui district is located at the transitional point of the arcuate structure and the edong and tongling districts are situated on both sides of the arcuate structure considering that the jiurui district has a slightly older peak age and a shorter duration of magmatic activity than that in the edong and tongling districts it seems that the arcuate structure of the mlyrmb played an important role in the formation of these cu au mo related porphyries consequently we suggest that the genesis of the late mesozoic magmatic rocks along the mlyrmb may have been due to a tectonic activity developed from southeast to northwest which probably has a close relationship with the subduction of the paleo pacific plate beneath the eurasian plate in mesozoic times

atmospheric decadal variability from high resolution dome c ice core records of aerosol constituents beyond the last interglacial along the epica dome c ice core we measured concentrations of different water soluble aerosol constituents and deduced total depositional flux records here we present high resolution sodium calcium ammonium and nitrate data covering the last 173 000 years the first three of these species are passive tracers and reveal source and long range transport changes whereas nitrate is deposited reversibly however it can be used to check isotope derived accumulation rate estimates a prerequisite to calculate total depositional fluxes during the last two transitions from glacial to interglacial periods changes in the total depositional flux differ strongly for different aerosol species the largest changes are observed in the terrestrial aerosol proxy non sea salt calcium only moderate changes occur in the marine sea salt indicator sodium while ammonium a proxy for marine bioproductivity remains rather constant in agreement with previous studies we find that only considerable glacial interglacial changes at both the terrestrial and the marine sea salt aerosol source can explain the observed pronounced changes the unprecedented high resolution of our data allows for the first time the examination of decadal variability back to the penultimate glacial period on the one hand we find occasional fast shifts occurring within a few years here we present such an event in the calcium record from the penultimate glacial period on the other hand we examine variation coefficients and pairwise correlation coefficients both determined in 200 year windows they generally reveal only moderate changes during glacial periods slightly lower variation coefficients are found concurrent with slightly higher correlation coefficients which points to a more uniform and stronger coupled atmospheric long range transport of the different aerosol species to the east antarctic plateau and less influence of cyclonic activities during cold periods the opposite is observed for interglacial periods with probably even reinforced importance of cyclonic influences during the last interglacial period the marine isotope stage 5 5 this period reveals no evidence for abrupt climatic changes in any of the species however the marine sea salt aerosol indicator sodium shows a distinct minimum followed by a pronounced increase this pattern is explained by significantly reduced sea ice production in the indian southern ocean sector which is believed to be the dominant source of sodium deposited in dome c during warm periods

introduction to the special issue on spatial modelling and analysis of ore forming processes in mineral exploration targeting abstract ore deposits are diverse with much of their diversity attributable to the complex interplay of ore forming processes with a variety of geological environments over a range of scales and both in space and time this diversity makes it difficult for geoscientists to accurately predict the location of undiscovered ore deposits improving our understanding of the processes that are critical to ore deposit formation would help us to hone our predictive capabilities however this task is difficult to achieve as we cannot observe these genetic processes first hand and different parameters and ingredients are important at different scales modelling offers a means of simulating and analysing ore forming processes and their mappable expressions this knowledge can then be used to build a predictive model by translating key process components into spatial proxies that can be mapped or recognized in mineral exploration data modelling and analysis of ore forming processes are therefore critical for the future success of mineral exploration currently underutilized in exploration targeting the application of statistical and mathematical concepts can help steer geoscientists towards a better understanding of the complex geological processes critical in the formation of mineral deposits and ultimately improved exploration success rates this editorial article presents a brief introduction to the main concepts that support a collection of articles published in a virtual special issue vsi of ore geology reviews entitled spatial modelling and analysis of ore forming processes in mineral exploration targeting the articles examine three critical themes 1 translating the expressions of ore forming processes and critical parameters of mineral systems into mappable spatial proxies 2 identifying mineral deposit footprints through geochemical and geophysical data analysis and 3 targeting and improving the discovery chance of mineral deposits by way of spatial data analysis

spatial variability of surface sediment porewater ph and related water column characteristics in deep waters of the northern south china sea abstract this study analyzes the ph of surface sediment porewater i e 2 3 cm below the water sediment interface and concentrations of caco3 and organic carbon oc in 1192 sediment cores from the northern south china sea in water depths ranging from 137 to 3702 m this is the first study in the literature to analyze the large scale spatial variability of deep water surface sediment ph over a large ocean basin the data showed strong spatial variations in ph the lowest ph values

stable isotope records from dronning maud land antarctica the european project for ice coring in antarctica epica includes a comprehensive pre site survey on the inland ice plateau of dronning maud land this paper focuses on the investigation of the o 18 content of shallow firn and ice cores these cores were dated by profiles derived from dielectric profiling and continuous flow analysis measurements the individual records were stacked in order to obtain composite chronologies of o 18 contents and accumulation rates with enhanced signal to noise variance ratios these chronologies document variations in the last 200 and 1000 years the o 18 contents and accumulation rates decreased in the 19th century and increased during the 20th century using the empirical relationships between stable isotopes accumulation rates and the 10 in firn temperature the variation of both parameters can be explained by the same temperature history but other causes for these variations such as the build up of the snow cover cannot be excluded a marked feature of the 1000 year chronology occurs during the period ad 1180 1530 when the o 18 contents remains below the long term mean cross correlation analyses between five cores from the weddell sea region and dronning maud land show that o 18 records can in some periods be positively correlated and in others negatively correlated indicating a complex climatic history in time and space

ground based measurements of spatial and temporal variability of snow accumulation in east antarctica the east antarctic ice sheet is the largest highest coldest driest and windiest ice sheet on earth understanding of the surface mass balance smb of antarctica is necessary to determine the present state of the ice sheet to make predictions of its potential contribution to sea level rise and to determine its past history for paleoclimatic reconstructions however smb values are poorly known because of logistic constraints in extreme polar environments and they represent one of the biggest challenges of antarctic science snow accumulation is the most important parameter for the smb of ice sheets smb varies on a number of scales from small scale features sastrugi to ice sheet scale smb patterns determined mainly by temperature elevation distance from the coast and wind driven processes in situ measurements of smb are performed at single points by stakes ultrasonic sounders snow pits and firn and ice cores and laterally by continuous measurements using ground penetrating radar smb for large regions can only be achieved practically by using remote sensing and or numerical climate modeling however these techniques rely on ground truthing to improve the resolution and accuracy the separation of spatial and temporal variations of smb in transient regimes is necessary for accurate interpretation of ice core records in this review we provide an overview of the various measurement techniques related difficulties and limitations of data interpretation describe spatial characteristics of east antarctic smb and issues related to the spatial and temporal representativity of measurements and provide recommendations on how to perform in situ measurements

a new bipolar ice core record of volcanism from wais divide and neem and implications for climate forcing of the last 2000 years volcanism is a natural climate forcing causing short term variations in temperatures histories of volcanic eruptions are needed to quantify their role in climate variability and assess human impacts we present two new seasonally resolved annually dated non sea salt sulfur records from polar ice cores wais divide wdc06a from west antarctica spanning 408 b c e to 2003 c e and neem neem 2011 s1 from greenland spanning 78 to 1997 c e both analyzed using high resolution continuous flow analysis coupled to two mass spectrometers the high dating accuracy allowed placing the large bi hemispheric deposition event ascribed to the eruption of kuwae in vanuatu previously thought to be 1452 1453 c e and used as a tie point in ice core dating into the year 1458 1459 c e this new age is consistent with an independent ice core timescale from law dome and explains an apparent delayed response in tree rings to this volcanic event a second volcanic event is detected in 1453 c e in both ice cores we show for the first time ice core signals in greenland and antarctica from the strong eruption of taupo in new zealand in 232 c e in total 133 volcanic events were extracted from wdc06a and 138 from neem 2011 s1 with 50 ice core signals predominantly from tropical source volcanoes identified simultaneously in both records we assess the effect of large bipolar events on temperature sensitive tree ring proxies these two new volcanic records synchronized with available ice core records to account for spatial variability in sulfate deposition provide a basis for improving existing time series of volcanic forcing

primary aerosol sea salt and soil dust deposited in greenland ice during the last climatic cycle comparison with east antarctic records ion chromatography data of ca mg cl and ca and coulter counter particle measurements are used to study the cycle of marine and continental primary aerosol reaching greenland in relation to climatic changes over the last 150 kyr a detailed comparison between greenland dome summit and antarctic vostok records provides new insight on a potential link between northern and southern patterns ca is a good indicator of continental input and is mainly emitted as caco3 an attempt is made to estimate the contribution of aluminosilicates using the concentration of insoluble particles greater than 0 5 m in diameter the relative abundance of non sea salt mg and ca and of aluminosilicate shows that the calcium content of continental background aerosol over greenland was much higher during the glacial age the neutralization capacity of carbonaceous aerosol is estimated the inverse relationship between 18o and continental input as well as the response of this input to the rapid climatic variations that have occurred during the second part of the glacial age are discussed in terms of source and transport modification in relation to the presence and the extent of the great laurentide ice cap the corresponding vostok profiles strongly suggest that some of the phenomena observed at high northern latitudes are of global concern the marine component of na nam is a good tracer of sea salt aerosol similarly to continental input it shows an inverse but more linear relationship with 18o the sensitivity of greenland and antarctic marine input to climate variations of small and large amplitude is compared and a corresponding estimation is made for the aeolian contribution the respective influence of atmospheric circulation and the water vapor cycle is discussed the chlorine to marine sodium weight ratio increases with temperature from values very close to the bulk seawater ratio during the last glacial maximum 18 20 kyr b p to values significantly higher during the holocene and warm eemian the corresponding excess of chloride hcl is discussed in terms of atmospheric transport taking into account the role of atmospheric acidity on sea salt fractionation processes owing to postdepositional phenomena similar vostok data must be considered cautiously nevertheless aerosol fractionation seems to have been much more important over the vostok site except during glacial extrema

prospectivity analysis of orogenic gold deposits in saqez sardasht goldfield zagros orogen iran abstract diverse deposit types or mineral systems form by diverse geological processes so translation of knowledge about the controls of mineralization acquired from the 4d geological modeling into 2d spatial predictor maps is a major challenge for prospectivity analysis in this regard mathematical functions have been used to model the conceptual or perceived spatial relationships between geological variables and targeted type or system of mineralization in this paper due to the different models of spatial relationships between predictors and mineral deposits we investigated the performance of different fuzzification functions to quantify the relationships we demonstrated that various types of relationships between exploration features and a mineralization type sought could be quantified using different fuzzification functions for prospectivity analysis we illustrated the process of the prospectivity analysis by using a data set of orogenic gold deposits in saqez sardasht goldfield iran prospectivity modeling of orogenic gold mineralization in the study area showed that the ne sw trending targets have priority for further prospecting of the deposits

impurity controlled densification a new model for stratified polar firn a new densification model which simulates the effect of impurities on the densification of polar firn is presented the classical densification models of herron and langway 1980 and pimienta and barnola barnola and others 1991 are modified by assuming that the activation energy for deformation is reduced by the impurities motivated by recent observations the impurity effect is formulated on an empirical basis using the seasonally varying ca2 ion concentration excellent agreement between simulated and measured high resolution density profiles confirms the new approach the same parameterization applies for greenland and antarctica despite the one order of magnitude difference in impurity concentration the new models allow us for the first time to simulate the density layering in firn down to the firn ice transition our results emphasize the importance of impurities and density layering for the air entrapment and for dating gas records of deep ice cores in particular for glacial climate conditions where the impurity concentrations are 10 100 fold higher than in modern firn

multivariate anomaly modeling of primary geochemical halos by u spatial statistic algorithm development a case study from the sari gunay epithermal gold deposit iran abstract an accurate separation of anomalous areas values in primary geochemical halos with heterogeneous spatial variations requires an appropriate algorithm that considers the complex patterns and multivariate relationships of the input geochemical data there are several problems in multivariate modeling of geochemical compositional data because such data present spurious values of spatial correlation between the variables to address this problem this paper proposes an improved u spatial statistic algorithm for 3d multivariate anomaly modeling of the geochemical dataset with compositional nature at the sari gunay epithermal gold deposit nw iran to perform 3d multivariate modeling isometric logarithmic ratio ilr as an effective method to transform compositional data from the simplex to real space and minimum maximum autocorrelation factor maf as a multivariate geostatistical method were used in an integrated analysis in comparison to the other separation techniques this integrated approach has an advantage to control the heterogeneous spatial variations in the input data in this approach we improved the u spatial statistic method by using the variogram tool theory by using this approach we identified the primary geochemical haloes associated with au as sb hg front halo elements cu ag pb near ore halo elements and ni co tail halo elements at the sari gunay gold depsoit the results were validated by using contrast coefficient and exploratory index tools by examining the 3d multivariate primary anomalous geochemical halos zones of possible hidden epithermal gold and porphyry copper gold mineralizations were recognized at this deposit for future exploration

the 1452 or 1453 a d kuwae eruption signal derived from multiple ice core records greatest volcanic sulfate event of the past 700 years 1 we combined 33 ice core records 13 from the northern hemisphere and 20 from the southern hemisphere to determine the timing and magnitude of the great kuwae eruption in the mid 15th century we extracted volcanic deposition signals by applying a high pass loess filter to the time series and examining peaks that exceed twice the 31 year running median absolute deviation by accounting for the dating uncertainties associated with each record these ice core records together reveal a large volcanogenic acid deposition event during 1453 1457 a d the results suggest only one major stratospheric injection from the kuwae eruption and confirm previous findings that the kuwae eruption took place in late 1452 or early 1453 which may serve as a reference to evaluate and improve the dating of ice core records the average total sulfate deposition from the kuwae eruption was 93 kg so4 km 2 in antarctica and 25 kg so4 km 2 in greenland the deposition in greenland was probably underestimated since it was the average value of only two northern greenland sites with very low accumulation rates after taking the spatial variation into consideration the average kuwae deposition in greenland was estimated to be 45 kg so4 km 2 by applying the same technique to the other major eruptions of the past 700 years our result suggests that the kuwae eruption was the largest stratospheric sulfate event of that period probably surpassing the total sulfate deposition of the tambora eruption of 1815 which produced 59 kg so4 km 2 in antarctica and 50 kg so4 km 2 in greenland