major and rare earth elements in rainwaters from japan and east china sea natural and anthropogenic sources abstract rainwater samples collected from tokyo and nearby locations in japan as well as from two locations over the east china sea have been analyzed for their rare earth elements rees and major ions the major ion compositions of these samples show the contributions of oceanic crustal and anthropogenic sources and suggest the relative importance of these sources rainwater samples collected in tokyo and chofu a town about 8 km from metropolitan tokyo have distinctly higher so42 and no3 content than in rainwater samples from the coastal area and the east china sea whereas the major ion compositions of the latter two areas are dominated by sea salt the rainwater samples also have variable ree compositions with various enrichment of light rees over heavy rees rainwater samples from chofu are significantly enriched in light rees whereas those collected in tokyo have loess or shale like ree composition rainwater from both places however has similar major ion compositions the enrichment of light rees in the chofu rainwater samples corresponds to the typical signature of an anthropogenic source the y ho ratios in these samples are all higher than average crustal values and in general increase with increasing enrichment of light rees this indicates that physical mixing of crustal and oceanic sources of the rees cannot account for the variations of the y ho ratios furthermore although the anthropogenic source of the rees is generally characterized by a high y ho ratio factors such as particle rainwater interactions ph and speciation of rees may also be responsible for the variable abundance and fractionation of rees and y ho in these rainwaters

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

cenozoic evolution of asian climate and sources of pacific seawater pb and nd derived from eolian dust of sediment core ll44 gpc3 1 the large diameter piston core ll44 gpc3 from the central north pacific ocean records continuous sedimentation of eolian dust since the late cretaceous two intervals resolved by nd and pb isotopic data relate to dust coming from america prior to 40 ma and dust coming from asia since 40 ma the intertropical convergence zone itcz separates these depositional regimes today and may have been at a paleolatitude of 23 n prior to 40 ma such a northerly location of the itcz is consistent with sluggish atmospheric circulation and warm climate for the northern hemisphere of the early to middle eocene since 40 ma correlations between nd 7 55 end t 10 81 and pb 18 625 206 4pb 18 879 15 624 207 4pb 15 666 38 611 208 4pb 38 960 0 8294 207 6pb 0 8389 2 0539 208 6pb 2 0743 isotopes reflect the progressive drying of central asia triggered by the westward retreat of the paleo tethys comparisons between the changes with time in the isotopically well defined dust flux and nd and pb isotopic compositions of pacific deep water allow one to draw two major conclusions 1 dust bound nd became a resolvable contribution to pacific seawater only after the one order of magnitude increase in dust flux starting at 3 5 ma therefore eolian nd was unimportant for pacific seawater nd prior to 3 5 ma 2 the lack of a response of pacific deep water pb to this huge flux increase suggests that dust bound pb has never been important instead mobile pb associated with island arc volcanic exhalatives probably consists of a significant contribution to pacific deep water pb and possibly to seawater elsewhere far away from landmasses

seasonal contributions of catchment weathering and eolian dust to river water chemistry northeastern tibetan plateau chemical and sr isotopic constraints relative to winter it is noticeable that both the lowest and the highest 87 sr 86 sr values of the buha river waters occurred in the monsoon season indicating a sensitive response of carbonate versus silicate weathering sources to hydrological forcing on a seasonal basis a significant decrease in na cation together with lower sr isotope ratios is consistent with a greater proportion of carbonate weathering relative to silicate weathering in the early monsoon season high temperature and increased rainfall during the peak of the monsoon facilitate an increased proportion of ions derived from silicates partly from groundwaters to river water in other seasons elemental and 87 sr 86 sr ratios vary much less indicating a constant ratio of silicate to carbonate weathering consistent with limited variation in discharge our results highlight that in a semiarid region where climatic conditions vary seasonally in addition to silicate and carbonate contributions supply from eolian dust may also play a significant role in controlling seasonal variations in chemistry of river waters

new constraints on the sources and behavior of neodymium and hafnium in seawater from pacific ocean ferromanganese crusts the behavior of dissolved hf in the marine environment is not well understood due to the lack of direct seawater measurements of hf isotopes and the limited number of hf isotope time series obtained from ferromanganese crusts in order to place better constraints on input sources and develop further applications a combined nd hf isotope time series study of five pacific ferromanganese crusts was carried out the samples cover the past 38 myr and their locations range from sites at the margin of the ocean to remote areas sites from previously unstudied north and south pacific areas and water depths corresponding to deep and bottom waters for most of the samples a broad coupling of nd and hf isotopes is observed in the equatorial pacific end and ehf both decrease with water depth similarly end and ehf both increase from the south to the north pacific these data indicate that the hf isotopic composition is in general terms a suitable tracer for ocean circulation since inflow and progressive admixture of bottom water is clearly identifiable the time series data indicate that inputs and outputs have been balanced throughout much of the late cenozoic a simple box model can constrain the relative importance of potential input sources to the north pacific assuming steady state the model implies significant contributions of radiogenic nd and hf from young circum pacific arcs and a subordinate role of dust inputs from the asian continent for the dissolved nd and hf budget of the north pacific some changes in ocean circulation that are clearly recognizable in nd isotopes do not appear to be reflected by hf isotopic compositions at two locations within the pacific ocean a decoupling of nd and hf isotopes is found indicating limited potential for hf isotopes as a stand alone oceanographic tracer and providing evidence of additional local processes that govern the hf isotopic composition of deep water masses in the case of the southwest pacific there is evidence that decoupling may have been the result of changes in weathering style related to the buildup of antarctic glaciation

has the atmospheric supply of dissolved calcite dust to seawater influenced the evolution of marine 87sr 86sr ratios over the past 2 5 million years 1 by analyzing the geochemistry of chinese loess this study examines if the flux of calcite dust from the chinese loess plateau to the north pacific influenced the evolution of marine 87sr 86sr ratios between 2 5 million years ago ma and the present calcite comprises 10 wt of chinese loess and contains 1 104 nmol of sr g with an 87sr 86sr ratio of 0 711 a compilation of literature data suggests that the calcite dust flux emanating from eastern asia has averaged either 2 1013 or 1 1014 g yr since the onset of northern hemisphere cooling 2 5 ma the factor of 5 difference between the estimates reflects discrepancies inherent to methods for determining dust fluxes to seawater at present these discrepancies remain unresolved calcite dust is completely dissolved during transport in the atmosphere and ocean thus the marine sr input from eolian calcite dissolution has averaged either 2 108 or 1 109 mol yr a mass balance model demonstrates that the lower estimate has very little influence on seawater 87sr 86sr ratios whereas the higher estimate has possibly elevated seawater 87sr 86sr ratios by 18 since 2 5 ma when combined with previously reported effects of northern hemisphere glaciation on the riverine sr flux this shift is sufficient to reproduce the entire plio pleistocene marine sr record while more research is required to constrain dust flux estimates these findings suggest that the atmospheric supply of eolian calcite to seawater may represent a previously overlooked process linking climate change to the marine sr cycle

spatial distribution of dissolved neodymium and end in the bay of bengal role of particulate matter and mixing of water masses abstract the concentration and isotope composition of dissolved nd have been measured in the water column along an 87 e transect gio1 section of international geotraces program in the bay of bengal bob to investigate the effect of water mass mixing and nd release from particulate matter in determining these properties the concentration of nd in surface waters of the bob shows a north south decreasing non linear trend 46 to 22 pmol kg with salinity whereas its depth profiles typically show a high value in surface waters a minimum 15 to 23 pmol kg in the shallow subsurface 50 200 m followed by a gradual increase with depth the nd concentration of bob waters is generally higher than that in nearby oceanic basins on the other hand the e nd values in the bob are less radiogenic compared to those reported for other regions of the global oceans except baffin bay the north atlantic subpolar gyre and the niger delta margin and show a greater variation in the upper water column surface waters of the southernmost profile 6 n show a more radiogenic e nd value 8 which decreases to 15 in the northernmost profile 20 n close to the values for dissolved and particulate phases of the ganga brahmaputra g b rivers this latitudinal trend is most likely a result of variations in mixing proportion between the more radiogenic indonesian throughflow surface waters iw and unradiogenic bob low salinity water the former s signature being more clearly discernible in surface waters of the two southernmost profiles 6 n and 8 5 n attempts to balance the nd budget in the water column based on an inversion model suggest that in addition to water masses other source s is required the strength of which is estimated to vary from 1 to 65 of the measured nd concentration the calculations also show that the e nd of this additional source s has to be in the range of 16 2 typical of g b river sediments these observations coupled with the north south distribution of dissolved nd and e nd indicate that this additional source is release from particulate phases supplied by the g b river system the calculations also bring out the presence of hot spots of nd release excess nd near the sediment water interface along the northern slope of the bay indicating supply of nd from continental margin sediments this study underscores the significant role of dissolved particulate nd from the ganga brahmaputra river system in contributing to the dissolved nd budget of the global oceans

the estuarine chemistry of rare earth elements comparison of the amazon fly sepik and the gulf of papua systems abstract a comparison of the amazon fly gulf of papua and sepik river systems has shown that there are two distinct processes operating on dissolved rare earth elements ree in estuaries large scale salt induced coagulation in the low salinity region and small to extensive release in the mid to high salinity region fractionation of the ree occurs during both removal and release the order of removal follows lree mree hree and the order of release follows hree mree lree where l m and h refer to light middle and heavy ree respectively hence estuarine reactions can modify the relative abundance of dissolved ree reaching the oceans operating in tandem the removal and release lead to the preferential removal of the lree and the preferential release of hree during estuarine mixing this combination in turn results in an effective river water flux river flux after modifications by estuarine chemistry which is evolved toward the ree composition of seawater which has a heavy ree enriched composition when normalized against the ree composition of rivers or the earth s continental crust the increase of dissolved ree in the mid to high salinity waters of the amazon and fly estuaries suggests a sediment and or suspended sediment source the lack of ree increases in the sepik river estuary strengthens this explanation as the mixing zone of this estuary is located over a deep shelf where there is little physical contact between bottom sediment and estuarine waters in marked contrast the amazon and fly estuaries are dominated by the active resuspension and deposition of bottom sediments the resupply of ree accompanied by fractionation may result from ree carbonate complexation during the reaction of seawater with suspended particles and or bottom sediment estuarine and shelf sediments may be important sources of dissolved nd to the oceans thereby helping to maintain the inter ocean differences in the nd isotopic composition of seawater by reducing the residence time of nd in the oceans

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

the pre ignimbrite phreato plinian and phreatomagmatic phases of the akdag zelve ignimbrite eruption in central anatolia turkey abstract the eruptive sequence of the 7 6 ma old akdag zelve ignimbrite azi eruption comprises five units totalling up to 50 m on akdag mountain they are in stratigraphic order a the main pumice fall deposit up to 10 m b the lower surge series up to 4 m c the upper pumice beds up to 0 8 m d the upper surge series up to 5 m and e the akdag zelve ignimbrite up to 40 m the main pumice fall deposit shows a second distal thickness maximum about 20 km from the source whereas the upper pumice beds form a simple nne extending fan the source area about 6 km north northeast of kaymakli is inferred from fallout thickness size and amount of lithic clasts depositional facies and flow directions of the surge deposits the main pumice fall deposit encloses accretionary lapilli up to 6 cm in size indicating a steady phreatomagmatic influence on the eruptive style from the very beginning the major surge sequence beneath the ignimbrite is similar to that of the 1400 yr b c minoan eruption on santorini greece and resembles the minoan b stratigraphic unit attributed to phreatomagmatic eruptions due to ingression of seawater into the conduit similarly the depositional environment of marshes and marginal flats of a lacustrine basin in cappadocia accounts for the external water supply and the generation of surges during the azi eruption estimates of eruption column height of 45 km indicate that the azi eruption ranks in the order of the 1956 bezymianny 1815 tambora and the waimihia plinian pumice eruption of new zealand volume estimates of the erupted tephra are on the order of 41 5 km 3 for the main pumice and 0 35 km 3 of the upper pumice

mineralogical variation of sr nd isotopic and elemental compositions in loess and desert sand from the central loess plateau in china as a provenance tracer of wet and dry deposition in the northwestern pacific we determined sr and nd isotopic compositions and major trace and rare earth element ree compositions of evaporite and detrital minerals in loess and desert sand from the central loess plateau clp where 80 of the loess deposits in china are found the loess exhibited a narrow range of variation in 87sr 86sr 0 715 0 001 a sequential extraction experiment on the loess however showed that water and acetic acid hoac soluble minerals mainly halite and calcite hydrochloric acid hcl soluble minerals chlorite and phosphate and hcl insoluble minerals illite kaolinite smectite vermiculite feldspar and quartz have distinct 87sr 86sr ratios approximately 0 7111 0 0004 0 7141 0 0004 and 0 7195 0 0010 respectively the water and hoac soluble ratios were regionally uniform and were close to the 87sr 86sr value of river water from the huanghe yellow river and the maximum 87sr 86sr value of spring rainwater in japan suggesting selective solution of eolian halite and calcite into the chinese river water and into the japanese rainwater the mineralogical elemental and sr nd isotopic compositions of hcl soluble and insoluble minerals in the clp loess were different from those of the northern desert sand but were indistinguishable from those of its fine grained fraction supporting the view that the loess is composed of the fine grained fraction of desert sand that was transported to the southeast in the atmosphere the 87sr 86sr end and gd yb values of hcl insoluble minerals in the clp loess were almost identical to those of airborne dust soil minerals and deep sea sediments in the northwestern pacific considered to be of eolian origin suggesting dissolution of the loess evaporite minerals during atmospheric transportation these relationships demonstrate the usefulness of sr isotopes of water and hoac soluble minerals and sr and nd isotope ratios and ree compositions of acid insoluble minerals in loess as provenance markers for wet and dry deposition respectively

rare earth element composition of precipitation precipitation particles and aerosols we report the rare earth element ree composition of aerosols and precipitation dissolved and particle phases from bermuda lewes delaware and woods hole massachusetts there is large scale fractionation of rees between the continents atmosphere and the oceans the ree compositions of atmospheric samples are highly fractionated relative to 1 each other e g aerosol precipitation pairs 2 the upper crust of the earth and 3 seawater precipitation samples exhibit markedly convex up shale normalized patterns large negative eu anomalies and large and systematic depletions in the heavy ree lu yb er dy aerosols are strongly depleted in the heavy ree which dissolutions experiments show are attributable to the presence of hree enriched refractory minerals we argue that in situ selective dissolution of mineral aerosol particles is responsible for the unusual ree composition of precipitation this has major implications for the interpretation of the biogeochemical cycles of rees in the oceans particularly the partitioning between solution and particle phases residence times and the composition of seawater

calcite dust and the atmospheric supply of nd to the japan sea abstract we report neodymium concentrations and isotope ratios e nd measured in the carbonate and silicate fractions of chinese loess the goal of the study is to investigate if the atmospheric supply of dissolved calcite dust to the oceans influences the cycling of nd in seawater we primarily focus on the japan sea because it receives large quantities of dust from eastern asia and it has a known nd isotope composition and a simple hydrologic budget a steady state atmospheric transport model is used to calculate the flux of soluble nd delivered to the japan sea surface by the wet deposition of dissolved calcite dust this information is then incorporated in a steady state two box model in order to evaluate controls on dissolved e nd values as well as to calculate the residence time of nd in seawater on average calcite in fresh chinese loess contains 150 nmol of nd g 1 with an e nd of 8 6 the atmospheric input of dissolved calcite to the japan sea surface is 7 4 10 12 g yr 1 which corresponds to a dissolved nd flux of 1 1 10 18 pmol yr 1 this flux represents the largest input of nd to the basin and it is required to produce the e nd composition of japan sea waters approximately 65 of the nd flowing from the japan sea surface into the western north pacific originates directly from the input of dissolved calcite dust downwelling surface water and the remineralization of settling particles containing nd scavenged from surface water contribute 77 of the nd in the japan sea deep which indicates that 50 of the deep nd originates from calcite dust the e nd composition of deep water is balanced by a benthic flux but the input is a factor of 10 lower than the calcite dust flux and accounts for only 23 of the deep nd surface and deep waters in the japan sea have nd residence times with respect to particle scavenging of 14 and 530 yr respectively these findings reveal that the atmospheric supply of dissolved calcite dust to the japan sea is a more important component of the marine nd cycle in this basin than previously recognized

rare earth elements in japan sea sediments and diagenetic behavior of ce ce results from odp leg 127 the relative effects of paleoceanographic and paleogeographic variations sediment lithology and diagenetic processes on the recorded rare earth element ree chemistry of japan sea sediments are evaluated by investigating ree total abundances and relative fractionations in 59 samples from ocean drilling program leg 127 ree total abundances ree in the japan sea are strongly dependent upon the paleoceanographic position of a given site with respect to terrigenous and biogenic sources ree concentrations at site 794 yamato basin overall correspond well to aluminosilicate chemical indices and are strongly diluted by sio2 within the late miocene pliocene diatomaceous sequence eueu values at site 794 reach a maximum through the diatomaceous interval as well most likely suggesting an association of eueu with the siliceous component or reflecting slight incorporation of a detrital feldspar phase ree at site 795 japan basin also is affiliated strongly with aluminosilicate phases yet is diluted only slightly by siliceous input at site 797 yamato basin ree is not as clearly associated with the aluminosilicate fraction is correlated moderately to siliceous input and may be sporadically influenced by detrital heavy minerals originating from the nearby rifted continental fragment composing the yamato rise the biogenic influence is largest at site 794 moderately developed at site 797 and of only minor importance at site 795 reflecting basinal contrasts in productivity such that the yamato basin records greater biogenic input than the japan basin while the most productive waters overlie the easternmost sequence of site 794 cece profiles at all three sites increase monotonically with depth and record progressive diagenetic lree fractionation the observed cece record does not respond to changes in oxygenation state of the overlying water and cece correlates slightly better with depth than with age the downhole increase in cece at site 794 and site 797 is a passive response to diagenetic transfer of lree except ce from sediment to interstitial water at site 795 the overall lack of correlation between cece and lanybn suggests that other processes are occurring which mask the diagenetic behavior of all lrees first order calculations of the ce budget in japan sea waters and sediment indicate that 20 of the excess ce adsorbed by settling particles is recycled within the water column and that an additional 38 is recycled at or near the seafloor data from masuzawa and koyama 1989 thus because the remaining excess ce is only 10 of the total ce there is not a large source of ce to the deeply buried sediment further suggesting that the downhole increase in cece is a passive response to diagenetic behavior of the other lrees the ree chemistry of japan sea sediment therefore predicts successive downhole addition of lrees to deeply buried interstitial waters

the contemporary physical and chemical flux of aeolian dust a synthesis of direct measurements of dust deposition abstract the deposition of aeolian or windblown dust is widely recognized as an important physical and chemical flux to ecosystems dust deposition adds exogenous mineral and organic material to terrestrial surfaces and can be important for the biogeochemical cycling of nutrients there have been many studies that characterize the physical and chemical composition of dust however few studies have synthesized these observations in order to examine patterns geochemical fluxes we have compiled observations of dust deposition rates particle size distributions psd mineralogy and bulk elemental and organic chemistry the rates of dust deposition observed across the globe vary from almost 0 to greater than 450 g m 2 yr 1 sites receiving dust deposition can be partitioned into broad categories based on there distance from dust source regions when compared to global dust models our results suggest some models may underestimate dust deposition rates at the regional and local scales the distance from the source region that dust is deposited also influences the particle size distributions mineralogy and chemical composition of dust however more consistent dust sampling and geochemical analyses are needed to better constrain these spatial patterns on average the concentrations of most major elements si al fe mg ca k in aeolian dust tend to be similar 20 to the composition of the upper continental crust ucc but there is substantial variability from sample to sample in contrast some elements tend to be depleted na or enriched ti in dust likely as a result of soil weathering processes prior to dust emissions trace elements especially heavy metals are consistently enriched in dust relative to the ucc ecologically important nutrients such as n and p are also present in dust deposition the geochemical flux attributable to dust deposition can be substantial in ecosystems located proximal to dust source regions we calculate estimates of elemental flux rates based on the average chemical composition of aeolian dust and varying rates of deposition these estimated flux rates are useful as a rough gauge of the degree to which dust deposition may influence biogeochemical cycling in terrestrial ecosystems and should be utilized to better constrain deposition estimates of global dust models

variable hfsrnd radiogenic isotopic compositions in a saharan dust storm over the atlantic implications for dust flux to oceans ice sheets and the terrestrial biosphere isotopic characterization of aerosol mineral particles atmospheric dust of varying sizes is essential in classifying source areas and for determining the source of dust deposited over oceans and icesheets however the effect of atmospheric transport on radiogenic isotopic compositions is not well constrained making provenance interpretation difficult in order to investigate the isotopic variability of 176hf 177hf 87sr 86sr and 143nd 144nd we analyzed eight airborne dust samples in two size fractions collected along a cross atlantic transect through a dust storm originating in the sahara in late 2002 past measurements of 176hf 177hf 87sr 86sr and 143nd 144nd of dust have focused primarily on coarse sized particles 30 m whereas far field deposition is primarily finer particles 2 m strontium or neodymium isotopic sorting based on distance is not evident in our dataset however the combined isotopic ratios of the dust collected suggest a saharan origin hafnium isotopic compositions show an east to west trend towards more radiogenic compositions across the atlantic suggesting grain and mineral sorting during dust transport along the 4000 km transect transport models with variable dust particle diameter and wind speed demonstrate the preferential depletion of the high density mineral zircon during transport of dust from the source area the transport model combined with a simple two component mixing model show that the hf isotopic composition changes can be explained by the loss of the mineral zircon during transport modeling of this zircon effect with distance from the dust source in the hf isotopic composition of marine terrestrial and glacial dust deposits may reveal additional information concerning dust transport and sources in the geologic past

dissolved rare earth elements and hydrography in the sulu sea because most southeast asian basins are flushed rapidly by waters from the western pacific the effects of respiration and silica dissolution within those basins are hardly discernible based on general hydrographic and geochemical observations broecker et al 1987 however a different situation is expected for the sulu sea because its deep water is isolated from other deep sea basins by shallow sills of 400 m depth hence any heterogeneity of elemental distributions within the basin must be ascribed to vertical physical and biogeochemical processes we have obtained detailed vertical profiles of dissolved rare earth elements rees together with conductivity temperature depth ctd and hydrographic measurements in the sulu sea during the 1996 97 hakuho maru cruise vertical profiles clearly indicate that the ree iii s are enriched in the deep water due to regeneration and are involved in vertical biogeochemical cycling the light ree iii s la pr and nd showed a subsurface maximum at 500 m and a minimum 1500 m in depth none of the hydrographic properties or nutrients shows such features therefore the ree iii s and their elemental ratios may be useful as tracers of water masses the relationship of ree iii s versus dissolved si suggests that the ree iii s are regenerated in a delayed fashion relative to si and it is likely that their dissolution largely occurs at the bottom interface the mean residence time of the deep water is estimated to be 300 6 150 yr consequently the calculated benthic flux of ree iii s becomes roughly comparable with the river and atmospheric fluxes because of oxidation to ce iv the ce profile shows a decrease from 6 pmol kg at the surface to a constant value at 3 9 pmol kg below 1500 m unlike the other rees the rees in the sulu sea are enriched in the middle rees and ce relative to those of the north pacific deep water and must derive from local sources around the sulu sea copyright 1999 elsevier science ltd

nd isotope records of late ordovician sea level change implications for glaciation frequency and global stratigraphic correlation abstract detailed records of ice sheet advances and retreats are reconstructed for the hirnantian and katian ages of the late ordovician using nd isotopes e nd as a sea level proxy in three study sections from the western margin of laurentia two shallow water platform sections located south and north of the paleo equator and one deep water section located in a continental slope rise setting when sea level was high and paleo shorelines had migrated eastward the e nd value of seawater in the vicinity of each of the study sections shifted toward the e nd value of the eastern panthalassa ocean 4 0 by contrast when sea level was low and paleo shorelines had migrated westward the e nd value of seawater shifted toward the e nd value of the continental weathering flux from laurentia 8 5 0 2 2 mean these stratigraphic patterns of changing e nd values are interpreted to reflect the eustatic sea level fluctuations that previous studies have documented in response to gondwanan ice sheet advances and retreats thus linking the e nd sea level proxy to late ordovician global scale climate changes the e nd profiles for the two platform sections yielded similar proxy sea level curves with five cycles of oscillation recorded during the latest katian and hirnantian three additional cycles of late katian sea level change are recognized in the e nd profile of the deep water continental slope rise section the combination of e nd 13 c and graptolite biostratigraphic data facilitates a precise interregional correlation of the hirnantian age and the paleoclimate changes that took place during this interval the new correlations support previous findings that the hirnantian ice age comprised two major glacial periods separated by a minor interglacial during the early part of the metabolograptus persculptus biozone the younger glacial confined to mid m persculptus biozone time led to more extensive sea surface cooling than did the earlier one and resulted in extensive eustatic sea level drawdown and c cycle changes it records the strata most often recognized as hice the hirnantian carbon isotope excursion in sedimentary successions worldwide such as anticosti island scotland estonia siberia and south china the results of this study support and strengthen the view that glaciation predated the hirnantian age in the late ordovician and that the records of small positive 13 c excursions in katian successions from baltica and eastern north america are themselves proxy indicators of glaciation frequency and eustatic sea level changes

geochemical characterization of the luochuan loess paleosol sequence china and paleoclimatic implications abstract chemical major and trace element and isotopic sr nd analyses of the luochuan loess paleosol sequence in china were performed in order to examine the following problems 1 potential source heterogeneity 2 element behavior during pedogenesis 3 paleoclimatic implications and 4 the use of loess data to determine the average composition of the upper continental crust new results clearly indicate that rb sr u and ce abundances are severely depleted in paleosols relative to their parental loess the behavior of these elements is strongly controlled by the breakdown of primary minerals such as carbonate sr or by alteration processes in highly oxidizing environments ce and u the pattern of element variations through the upper section of the luochuan sequence mimics the magnetic susceptibility signal both in position and in intensity thus reinforcing the pedogenesic origin of the enhanced magnetic susceptibility in paleosols all loess samples display highly uniform ree patterns except for ce characterized by the upper continental crust ucc ratios la yb n 10 and eu eu 0 66 the paleosol ree patterns are similar to those of the loess with the same lree hree fractionation but they also show distinct and variable negative ce anomalies nd and sr isotopic compositions are rather uniform in both loess and paleosols and do not vary with stratigraphic position nd 10 5 to 9 2 87 sr 86 sr 0 715 to 0 719 the isotopic homogeneity in the luochuan sequence strongly suggests a uniform source region during the entire period of deposition since 800 ka ago to the present several conclusions may be drawn from the present study 1 1 no geochemical distinction can be made between loess layers l1 to l7 the sources and the dust storm trajectories must have been essendally the same for the last 800 ka 2 2 some elements e g ca rb sr u ce are strongly fractionated by pedogenesis between loess and paleosols ce mobility in soils is clearly demonstrated but the process responsible for this leaching is still poorly understood 3 3 systematic variations of element abundances and ratios between loess and paleosols can be used as chemical indicators for pedogenesic intensity and so for paleoclimatic change these chemical indicators serve a function similar to that of oxygen isotopes in deep sea sediments pelagic foraminifera or that of magnetic susceptibility in loess sequences they are different recorders of paleoclimatic change 4 4 the striking uniformity of ree patterns and la th ratios in the luochuan loess and paleosols as well as in loess worldwide is an excellent starting point for estimating the average composition of the upper continental crust

global neodymium hafnium isotope systematics revisited global nd hf isotope systematics can be mainly described with two linear arrays the global silicate earth array the terrestrial array and the global ferromanganese crust and nodule array the seawater array the offset between these two arrays provides evidence for the sources and mechanisms by which these elements are added to ocean water however the reason for this offset is under debate with the two preferred hypotheses being i incongruent release of hf during continental weathering and ii hydrothermal contribution of hf to the seawater budget here we present new nd and hf isotope data on glacio marine core top sediments from around the perimeter of the antarctic continent the results range from ehf 30 0 to ehf 3 9 and end 21 3 to end 0 9 reflecting the large range of basement ages and lithologies around the antarctic continent in nd hf isotope space they confirm the systematic correlations found in rocks from other parts around the world and provide valuable insights into the previously underrepresented group of sediments with very old provenance in this paper we revisit the cause for the offset of the seawater array from the terrestrial array using simple mass balance considerations we use these calculations to test to what degree the seawater array could be a product of preferential weathering of non zircon portions of the upper continental crust implying retention of zircons in the solid residue of weathering lutetium hf and sm nd evolution and mixing calculations show that the global seawater array can be generated with continental sources only on the other hand a predominantly hydrothermal origin of hf in the ocean is not possible because the seawater hf isotopic composition is significantly less radiogenic than hydrothermal sources and requires a minimum fraction of 50 continental hf while hydrothermal sources may contribute some hf to seawater continental contributions are required to balance the budget

the estuarine geochemistry of rare earth elements and indium in the chao phraya river thailand abstract a new filtration method using a 0 04 m hollow fiber filter was applied to the river estuarine and coastal waters in the chao phraya estuary for geochemical investigation the filtered waters were analyzed for all the lanthanides y and in by using inductively coupled plasma mass spectrometry icpms the dissolved concentrations of rare earth elements rees are significantly lower than those reported previously for other rivers presumably because of effective removal of river colloids by the ultra filtration the variation of dissolved rees in the estuary is dependent on the season the light rees vary considerably in the low salinity s 3 show almost conservative trends being consistent with some of the previous works europium is strongly enriched in the river and estuarine waters compared to the south china sea waters thus the ree source of the chao phraya river must be fractionated and modified in entering to the south china sea dissolved in and ce in the high salinity s 20 25 zone of the estuary are lower than those of the offshore waters and therefore the dissolved flux of the chao phraya river cannot account for the higher concentrations of dissolved in and ce in the surface waters of the south china sea the negative ce anomaly is progressively developed with increasing salinity being consistent with continued oxidation of ce iii to ce iv in the estuary fractionation of the light to heavy rees seems to take place whereas the y ho fractionation is unclear in the estuarine mixing zone

provenance of dust in the pacific ocean eolian dust preserved in deep sea sediment cores provides a valuable indicator of past atmospheric circulation and continental paleoclimate in order to identify the provenance of eolian dust nd and sr isotopic compositions and rb sr and rare earth element ree concentrations have been determined for the silicate fractions of deep sea sediments from the north and central pacific ocean different regions of the pacific ocean are characterized by distinct air borne inputs producing a large range in end 10 to 1 stsr 86sr 0 705 0 721 la yb 5 15 eun eu 0 6 1 0 and sr nd 4 33 the average nd isotopic composition of pacific deep sea sediments eno 6 is more radiogenic than the average from the atlantic ena 8 in contrast the average 1475m 14and ratio for pacific sediments 0 114 is identical to that of atlantic sediments and to that of global average riverine suspended material the values of ena and 147sm 144nd are positively correlated for the pacific samples but negatively correlated for atlantic samples reflecting a fundamental difference between the dominant components in the end members with radiogenic nd island arc components in the pacific and lree enriched intraplate ocean island components in the atlantic samples from the north central pacific have distinctive unradiogenic end values of 10 87sr 86sr 0 715 high la yb 12 and low eun eu 0 6 and sr nd 3 6 these data are virtually identical to the values for loess from asia and endorse the use of these sediments as indicators of asian paleoclimate and paleowind directions island arc contributions appear to dominate in the northwest pacific resulting in higher end 1 to 1 and lower 87sr 86sr 0 705 and la yb 5 sediments from the eastern pacific tend to have intermediate sr and nd isotopic compositions but regionally variable sr nd and ree patterns they appear to be derived from the west margin of the north and south american continents rather than from asia our results confirm that dust provenance can be constrained by isotopic and geochemical analyses which will facilitate reconstructions of past atmospheric circulation and continental paleoclimate

rare earth elements in pore waters of marine sediments abstract the rare earth elements rees were measured in pore waters of the upper 25 cm of sediment from one site off peru and three sites on the california margin the pore water ree concentrations are higher than sea water and show systematic down core variations in both concentration and normalized pattern from these analyses and from comparison to other chemical species measured dissolved fe mn ba oxygen nitrate phosphate it is suggested that pore water rees can be grouped into three categories those that are from an fe source those that are from a poc source and cerium oxide rees from the fe source appear where anoxia is reached they have a distinctive middle ree mree enriched pattern the concentrations in this source are so elevated that they dominate ree trends in the fe oxide reduction zone the net result of flux from the poc source is relative enrichment of heavy rees hrees over light rees lrees reflecting remineralizing poc and complexation with doc a common linear ree pattern seen in both oxic and anoxic sediments is associated with this poc source as well as a hree enriched pattern that is seen in surficial sediments at the peru site overall the pore water results indicate that mn oxides are not an important carrier of rees in the oceans a ree biogeochemical model is presented which attempts to reconcile ree behavior in the water and sediment columns of the oceans the model proposes that poc fe oxide and ce oxide sources can explain the ree concentration profiles and relative abundance patterns in environments ranging from oxic sea water to anoxic pore water the model is also consistent with our observation that the ce anomaly of pore water does not exceed unity under any redox condition

neodymium isotopic variations in north pacific modern silicate sediment and the insignificance of detrital ree contributions to seawater the neodymium isotopic composition of the silicate fraction of holocene pelagic sediments from the north pacific define two provinces a central north pacific province characterized by unradiogenic and remarkably homogeneous end 10 2 0 5 and a narrow circum pacific marginal province characterized by more radiogenic and variable end 4 2 3 8 the silicate fraction in the central north pacific is exclusively eolian based on prevailing wind patterns meteorological data and neodymium isotopic data the only significant sediment source is chinese loess leaching experiments on chinese loess confirm that leachable nd is isotopically indistinguishable from bulk and residual silicate nd silicates in the circum north pacific marginal province comprise eolian loess volcanic ash and hemipelagic sediments derived from volcanic arcs a compilation of pacific seawater and mn nodule end data shows no clear spatial variation except for a general decrease from surface to deep waters from 3 to 4 and slightly lower end in bottom waters along the western north pacific due to the incursion of antarctic bottom water the relative homogeneity of bottom water end which contrasts sharply with the distinctive variation in sediment end plus the large difference between the average end of bottom waters and the central north pacific eolian silicates 4 vs 10 suggests that any contribution of ree to seawater from eolian materials is insignificant furthermore leaching of ree from eolian particles as they sink though the water column must be insignificant because nd in shallow waters is more radiogenic than nd in deeper waters that there is no contrast in the nd isotopic composition of bottom waters that overlie the central and marginal sediment provinces suggests that the ash and hemipelagic sediments derived from pacific rim volcanic arcs also contribute minimal ree to seawater the elimination of eolian ash and hemipelagic sediments leaves only near shore riverine particulates as a possibly significant particulate source of ree to seawater

dust and pollution a recipe for enhanced ocean fertilization 1 for fe contained in aeolian dust to act as a micronutrient for oceanic phytoplankton some fraction of it must first be transformed mobilized into a form soluble in ocean water fe solubilization in deliquesced mineral dust aerosols emanating from east asia during the springtime outflow conditions is investigated here with a lagrangian box model of the gas and aqueous phase chemistry the model simulates the scavenging of soluble and reactive gaseous species by mineral dust aerosols chemical reactions of these species and mineral dust ions in deliquesced solution and dissolution of fe iii oxides that occurs as a result of the acid mobilization the calculations indicate that mineral calcite caco3 strongly buffers deliquesced dust aerosols with a ph that remains close to 8 until the amount of acid added to the aerosol solution exceeds caco3 alkalinity so2 pollutant emissions are a potential source of acidity to advecting dust from east asia the model is used to simulate the chemical evolution of dust plumes formed from two contrasting documented gobi desert storms that advected dust to fe limited regions of the north pacific ocean npo these calculations indicate that only plumes with relatively high initial so2 to dust ratios are capable of delivering significant amounts of bioavailable fe to the npo the estimated change in phytoplankton population inferred from the model calculated inputs of bioavailable fe for these two episodes is consistent with the satellite measured chlorophyll a concentrations in the npo model simulations indicate that 1 large dust advection episodes that can export vast amounts of mineral dust to the open ocean should have insignificant dissolved iron fraction dif as the amount of so2 required to acidify such dust plumes is about an order of magnitude higher than what can typically be entrained in the plume during its advection 2 smaller dust plumes will generally have higher difs because they require lower amounts of so2 and even if such small plumes may not cause algae blooms they could still be important sources of dissolved fe to the npo the calculations suggest that future changes in so2 pollutant emissions from east asia either up or down may affect the productivity of the npo

sr isotopic and elemental characteristics of calcites in the chinese deserts implications for eolian sr transport and seawater sr evolution abstract calcite content sr concentrations and isotopes of calcites in the chinese deserts are systematically studied in this paper calcite contents which are calculated according to acid soluble ca contents in the deserts are generally higher in the sandy deserts than in the sandy lands and decrease roughly from northwest to northeast of china acid soluble sr is well correlated with calcite in the chinese deserts implying acid soluble sr comes mainly from the calcite dissolution sr concentrations in calcites calculated on the basis of calcite contents and acid soluble sr concentrations in the deserts have an inverse relation to calcite contents essentially mirroring the degree of sr substitution for ca in the calcite development desert calcites have regional variations in sr isotopic ratios calcite sr isotopic ratios depend on geological settings and chemical weathering the badain jaran and tengger deserts are probably affected by additional factors such as the remote groundwater cycle or overturning of underlying sand deposits only four deserts taklimakan qaidam badain jaran and tengger appear to be potential sources of eolian deposits in the chinese loess plateau clp isotopic signatures of calcite sr and silicate nd further indicate that the tengger desert was not an important source for eolian deposits in the clp eolian calcite was probably enriched due to wind sorting from the potential sources to the clp and suffered weathering leaching after it accumulated in the clp sr isotopic compositions and ca sr molar ratios of calcites are different between the deserts and the lingtai profile due to the integrated effect of wind sorting and weathering leaching it is essential to calculate accurately the 87sr 86sr ratio and sr concentration of eolian calcite entering the oceans according to geochemical data of the chinese deserts because of the importance of the chinese deserts in the global dust cycle the calculated sr concentration and 87sr 86sr ratio of eolian calcite entering the north pacific ocean are 11 75 mol g and 0 71032 respectively the calculated values in this study are close to the recommended values by jacobson jacobson a d 2004 has the atmospheric supply of dissolved calcite dust to seawater influenced the evolution of marine 87sr 86sr ratios over the past 2 5 million years geochem geophys geosyst 5 12 1 9 q12002 doi 10 1029 2004gc000750 using the same model as that of jacobson 2004 the effect of asia dust on the evolution of seawater sr isotopes is evaluated 87sr 86sr seawater increases by 0 3 10 5 if the lower dust flux of 2 34 108 mol sr yr is used in the model suggesting the little effect of asian dust on the seawater sr record in the quaternary the increase in 87sr 86sr seawater is 1 5 10 5 if the higher value of 1 17 109 mol sr yr is used as observed in the quaternary sr record these results further support the suggestions of jacobson 2004

geochemistry of the xining xifeng and jixian sections loess plateau of china eolian dust provenance and paleosol evolution during the last 140 ka abstract loess and paleosol samples from three distant sections xining xifeng jixian of the chinese loess plateau were analyzed for chemical and nd sr isotopic compositions in order to obtain information about the paleoclimatic variation during the last 140 ka these three sections represent three different climatic conditions from arid in the west xining to more humid in the east jixian across the loess plateau isotopic analyses show that all the three sections display a restricted range of 143 nd 144 nd ratios or e nd 10 0 5 indicating the dominance of relatively young and uniform upper crustal sources for the eolian dust the loess and paleosol samples have typical upper crustal 87 sr 86 sr ratios 0 714 0 718 and their variation can partly be attributed to different carbonate silicate ratios in the samples ree data from the three sections are indistinguishable from each other they show typical upper crust patterns characterized by la yb n 10 and eu eu 0 65 the high degree of chemical and isotopic homogeneity suggests that the dust source region must have undergone multiple recycling and thorough sedimentary mixing processes various chemical indicators have been used to monitor the pedogenetic intensity in these sections although results for the jixian section agree reasonably well with the known climatic conditions on the loess plateau the other two sections yield results not in agreement with some well accepted proxies like magnetic susceptibility or grain size distribution some chemical proxy indicators established in our previous work on the luochuan section such as the systematic u depletion and negative ce anomalies in ree patterns in soils are not clearly recorded in the present case the discrepancy between different climatic proxies could be related to the effective soil water budget temperature as well as the rate of development of each proxy

the geochemical balance of the rare earth elements and neodymium isotopes in the oceans profiles of ree concentrations and neodymium isotope measurements in the western indian ocean are consistent with published data from the other major oceans ree concentrations show a strong hydrographic control the influence of intermediate water masses is particularly significant surface water concentrations vary with salinity paniculate rees are less than 5 of dissolved concentration except for ce where up to 20 of total rees are present as 0 4 m particles in contrast to dissolved profiles concentration profiles of paniculate rees including ce all increase with depth ree concentrations correlate with silica over all but the deepest waters although in detail correlations are complex the neodymium isotopic composition of indian ocean seawater avg nd 0 8 3 is intermediate between that for the atlantic and pacific oceans comparison of ree data from the major oceans shows that the hrees behave more like si than do the lrees sm nd ratios are near constant for all oceans whereas ernd ratios vary between the atlantic indian and pacific oceans the fractionation of the rees in surface seawaters can be explained by fractionation factors relative to silica from 0 12 for la to 0 05 for er use of a seven box model shows that the interoceanic variations in neodymium isotopic compositions and nd concentrations cannot be reconciled unless particle water exchange is invoked the degree of exchange required is consistent with particle residence times of 1 10 yr

local and global perspectives on carbon and nitrogen cycling during the hirnantian glaciation abstract the impact of climate and ocean circulation changes on marine carbon and nitrogen cycling was investigated for a period covering the late ordovician hirnantian glaciation three sections were studied two from nevada one proximal and one distal and one from the yukon the opportunity to compare 13 c carb 13 c org and 13 c grap profiles between ocean and epeiric platform settings enabled a more thorough assessment of environmental and diagenetic factors influencing the preservation of seawater 13 c values at each stratigraphic section using the best preserved sedimentary components from the two nevada sections a lowstand sedimentary gradient of 4 was found between platform and ocean settings during the hirnantian glaciation gradients of similar magnitude have been reported from hirnantian platforms in the canadian arctic and baltic basins taking the outboard sections as the most representative of the ocean carbon pool a mean positive 13 c shift of just 2 7 0 4 is calculated which is significantly smaller than the 5 7 positive shifts recorded in epeiric platform settings the discrepancy is attributed to the effects of local carbon cycling in tropical and subtropical epeiric seas it is hypothesized that increased carbonate weathering caused 13 c values of local carbon weathering fluxes to increase which in turn caused seawater 13 c values to increase in basin proximal settings in addition nutrient dust fluxes may have contributed to increased levels of photosynthetic activity in proximal settings driving sedimentary 13 c values even higher much higher than sediment deposited in outboard settings where carbon exchanges with the surface ocean were less restrictive a 15 n profile reconstructed from deposits of the distal vinini creek section records a 1 5 positive shift through the hirnantian glacial interval interpreted as a major late ordovician upwelling zone high organic carbon 1 wt and high hydrogen indices 400 600 make the vinini creek section a suitable candidate for the preservation of original sedimentary 15 n records to explain the results a conceptual model of ocean nitrogen cycling under greenhouse climate conditions is presented that highlights the role of cyanobacteria as both primary producers and nitrogen fixers it is hypothesized that in greenhouse climates the fixed nitrogen inventory of the abyssal ocean was low due to efficient denitrification in the ocean s expansive oxygen minimum zones this caused algal productivity to become strongly dependent on continuous supplies of fixed nitrogen from cyanobacteria in the photic zone yielding sedimentary 15 n values between 0 and 2 by contrast the cooler icehouse climate of the hirnantian led to increased ocean ventilation greater partitioning of atmospheric oxygen into downwelling surface waters and oxygen minimum zone shrinkage as a result fixed nitrogen levels climbed in the ocean s abyssal depths due to the lower denitrification rates this in turn allowed nitrogen with high 15 n values to recycle back into the photic zone driving sedimentary 15 n values higher during the hirnantian glaciation

geochemical and isotopic studies of aeolian sediments in china the sr and nd isotopic rare earth element ree and major element compositions together with mineral and grain size proportions are reported for aeolian loess deposits and desert sands from several chinese localities the study was carried out in order to examine regional variations in the isotopic and geochemical features of these aeolian sediments and to constrain the provenance of chinese loess samples include loesses from the tarim and junggar basins and desert sands from the taklimakan desert in north west china loess from the ordos area and desert sands from the tengger and mu us deserts in north central china as well as loess and desert sands from the naiman area north east china ree distributions show minimal variation among the chinese loess deposits whereas those for the desert sands show regional variations new isotopic data document a latitudinal variation in sr and nd isotopic features for the loesses and desert sands the naiman and junggar loesses have distinctly lower 87sr 86sr ratios and higher end 0 values than the loesses from the tarim basin the ordos area and the loess plateau among the desert sands the naiman samples have higher end 0 values than the taklimakan tengger and mu us samples isotopic data suggest that loesses of the loess plateau were supplied from the tarim basin loesses and taklimakan desert sand and that the naiman loesses were supplied from the junggar basin loesses the latitudinal variation in the loesses and desert sands may be partly explained by isotopic variations reported previously for moraines from the tianshan and west kunlun mountains which are possible sources for the loesses and desert sands these inferences on the provenance of the loesses and desert sands are consistent with the dust transport pattern over east asia

evidence for early 12 7 ma eolian dust impact on river chemistry in the northeastern tibetan plateau abstract as one of the largest dust sources on the earth s surface dryland in central asia gives rise to thick eolian deposits over east asia e g the chinese loess plateau clp and significantly influences the regional hydrochemistry in the downwind drainage areas however the formation of thick eolian dust deposits requires not only climatic prerequisites for dust emission and transport but also climatic and topographic conditions favourable for deposition and accumulation the scarcity of widespread eolian deposition around the clp before 7 8 ma hinders a full understanding of the processes and mechanisms of central asian aridification the deposition of eolian dust also impacts the hydrogeochemistry of fluvial systems and the precipitation of authigenic phases in continental sedimentary systems could be an archive for studying eolian dust dynamics when pure eolian deposits are scarce here we present the ca mg sr concentrations and 87sr 86sr isotope compositions of bulk carbonates in a new fluvial sequence 12 7 4 8 ma of the xining basin the mg ca and sr ca ratios of the carbonate describe a power law relationship with a power coefficient of 0 8 lower than the coefficient characteristic of prior calcite precipitation pcp an input of eolian dust with the dissolution of mg rich carbonate is likely responsible for the deviation from a pure pcp process the bulk carbonates also show a general decrease of 87sr 86sr ratios from 12 7 to 4 8 ma with a transition around 8 6 ma revealed by lower sr mg ratios the comparison of these proxies to a previously reported fluvial section 12 2 5 1 ma in the linxia basin 200 km to the southeast shows that the 87sr 86sr ratios of the bulk carbonates and water soluble salts in the linxia basin are around 0 7098 which is 0 0018 lower than those in the xining basin before 8 6 ma but shows a significant rise between 8 6 and 7 0 ma the two basins share the same range of carbonate 87sr 86sr ratios when sediments are younger than 7 ma for the last 7 myrs the evolution of the 87sr 86sr ratios in bulk carbonates of fluvial sediments and pliocene quaternary eolian deposits found in the xining basin are similar to those in typical eolian red clays loess palaeosol sequences on the clp these results suggest a transition of the hydrochemical regime at 8 6 ma in the linxia basin from a catchment only influenced by the weathering of its bedrock to one significantly impacted by eolian dust input in the xining basin the carbonate elemental and 87sr 86sr ratios are consistent with a hydrochemistry more impacted by the presence of the eolian dust there the dust input occurred earlier at 12 7 ma though it has strengthened since 8 6 ma the eolian dust impact on fluvial systems in the xining basin was much earlier than in the linxia basin and also preceded the initial accumulation of widespread eolian red clays on the clp 7 8 ma suggesting a temporally propagating and spatially stepwise expansion of eolian dust delivery across the asian inland during the late cenozoic

nighttime ionospheric d region equatorial and nonequatorial 1 nighttime ionospheric d region parameters are found to be generally well modeled by the traditional h and as used by wait and by the u s navy in their earth ionosphere vlf radio waveguide programs new comparisons with nonequatorial mainly all sea vlf path observations reported over several decades are shown to be consistent with the previously determined height h 85 0 km and sharpness 0 63 km 1 these paths include npm hawaii to washington d c omega hawaii and nlk seattle to japan nwc n w australia to madagascar and nba panama to colorado in marked contrast transequatorial path observations even when nearly all sea are found to be often not well modeled for example for omega japan and jji japan to dunedin new zealand the observed amplitudes are markedly lower than those which would be expected from h 85 0 km and 0 63 km 1 or any other realistic values of h and other transequatorial observations compared with modeling include nwc to japan omega hawaii to dunedin and npm hawaii to dunedin it is suggested that the effects of irregularities in the equatorial electrojet may extend down into the nighttime d region and so account for the observed equatorial vlf perturbations through scattering or mode conversion

evidence for intense ree scavenging at cold seeps from the niger delta margin for many trace elements continental margins are the location of intense exchange processes between sediment and seawater which control their distribution in the water column but have yet to be fully understood in this study we have investigated the impact of fluid seepage at cold seeps on the marine cycle of neodymium we determined dissolved and total dissolvable td concentrations for ree and well established tracers of fluid seepage ch4 tdfe tdmn and nd isotopic compositions in seawater samples collected above cold seeps and a reference site i e away from any fluid venting area from the niger delta margin we also analyzed cold seep authigenic phases and various core top sediment fractions pore water detrital component easily leachable phases uncleaned foraminifera recovered near the hydrocast stations methane tdfe and tdmn concentrations clearly indicate active fluid venting at the studied seeps with plumes rising up to about 100 m above the seafloor depth profiles show pronounced ree enrichments in the non filtered samples td concentrations within plumes whereas filtered samples dissolved concentrations exhibit slight ree depletion in plumes relative to the overlying water column and display typical seawater ree patterns these results suggest that the net flux of ree emitted into seawater at cold seeps is controlled by the presence of particulate phases most probably fe mn oxyhydroxides associated to resuspended sediments at the reference site however our data reveal significant enrichment for dissolved ree in bottom waters that clearly relates to diffusive benthic fluxes from surface sediments neodymium isotopic ratios measured in the water column range from end 15 7 to 10 4 evidence that the end values for antarctic intermediate waters aaiw differed from those reported for the same water mass at open ocean settings shows that sediment water interactions take place in the gulf of guinea at each site however the bottom water end signature generally differs from that for cold seep minerals easily leachable sediment phases and detrital fractions from local sediments ruling out the possibility that seepage of methane rich fluids and sediment dissolution act as a substantial source of dissolved nd to seawater in the gulf of guinea taken together our data hence suggest that co precipitation of fe mn oxyhydroxide phases in sub surface sediments leads to quantitative scavenging of dissolved ree at cold seeps preventing their emission into bottom waters most probably it is likely that diffusion from suboxic surface sediments dominates the exchange processes affecting the marine nd cycle at the niger delta margin

the dissolution kinetics of major sedimentary carbonate minerals abstract among the most important set of chemical reactions occurring under near earth surface conditions are those involved in the dissolution of sedimentary carbonate minerals these minerals comprise about 20 of phanerozoic sedimentary rocks calcite and to a significantly lesser extent dolomite are the major carbonate minerals in sedimentary rocks in modern sediments aragonite and high magnesian calcites dominate in shallow water environments however calcite is by far the most abundant carbonate mineral in deep sea sediments an understanding of the factors that control their dissolution rates is important for modeling of geochemical cycles and the impact of fossil fuel co 2 on climate diagenesis of sediments and sedimentary rocks it also has practical application for areas such as the behavior of carbonates in petroleum and natural gas reservoirs and the preservation of buildings and monuments constructed from limestone and marble in this paper we summarize important findings from the hundreds of papers constituting the large literature on this topic that has steadily evolved over the last half century our primary focus is the chemical kinetics controlling the rates of reaction between sedimentary carbonate minerals and solutions we will not attempt to address the many applications of these results to such topics as mass transport of carbonate components in the subsurface or the accumulation of calcium carbonate in deep sea sediments such complex topics are clearly worthy of review papers on their own merits calcite has been by far the most studied mineral over a wide range of conditions and solution compositions in recent years there has been a substantial shift in emphasis from measuring changes in solution composition to determine batch reaction rates to the direct observation of processes occurring on mineral surfaces using techniques such as atomic force microscopy afm however there remain major challenges in integrating these two very different approaches a general theory of surface dissolution mechanisms currently lacking although see lasaga and luttge science 291 2001 2400 is required to satisfactorily relate observations of mineral surfaces and the concentration of dissolved components studies of aragonite high magnesian calcites magnesite and dolomite dissolution kinetics are much more limited in number and scope than those for calcite and provide at best a rather rudimentary understanding of how these minerals are likely to behave in natural systems although the influences of a limited number of reaction inhibitors have been studied probably the greatest weakness in application of experimental results to natural systems is understanding the often profound influences of foreign ions and organic matter on the near equilibrium dissolution kinetics of carbonate minerals

the ca isotopic composition of dust producing regions measurements of surface sediments in the black rock desert nevada dust is a relatively unconstrained flux in the geochemical cycle of ca the isotopic composition of dust derived ca has not been studied though it is an important part of any attempt at deciphering ca isotope based proxy records accordingly this study reports the elemental and calcium isotope geochemistry of 30 surface upper 0 5 cm sediments from an arid dust producer the black rock desert in northwestern nevada geochemical data for sequential water and 0 5 n hcl leaches meant to sample mobile ca and selected leached residues are presented along with x ray diffraction xrd determinations of major mineralogy bulk playa sediments have ca concentrations between 0 28 and 40 wt median 6 8 wt and calcite concentrations of 2 32 isotopically ca sampled by water leaches 60 of total ca though the degree of fractionation w a varies between 0 and 0 6 acid leaches which are the primary component of mobile ca in the sediments have 44casrm 915a values of 0 78 0 08 similar to the 44ca of modern nannofossil ooze and modern rivers this means that dust produced in closed continental basins likely has little isotopic leverage to change the ocean s isotopic composition and suggests that the ca isotopic composition of dust is tied to rivers weathering in addition while the ca concentration data in the water leach suggest that evaporative evolution controls the amount of ca in this reservoir the isotope data are inconsistent with this conclusion instead we hypothesize that adsorption of ca on clays controls the ca isotope systematics in the water leach this hypothesis requires that there is no significant isotopic fractionation during evaporite mineral precipitation and may suggest that sorption at rates appropriate for natural systems might fractionate differently than sorption at laboratory rates

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