water chemistry of the southern tibetan plateau an assessment of the yarlung tsangpo river basin the yarlung tsangpo is the largest river draining the southern tibetan plateau along the himalayan ranges in this paper the ions and elements in the water of the yarlung tsangpo were studied in general the water of the yarlung tsangpo had a fairly high buffering capacity ph 8 8 and oxidation environment orp 190 mv total dissolved solids averaged approximately 157 mg l 1 which is higher than that of the global mean level under the dominant rock weathering due to the abundant carbonates around the river basin the ionic chemistry of the yarlung tsangpo was mainly composed of ca2 and hco3 in addition with a large amount water discharged into the river groundwater e g numerous chloride rich hot springs is another potentially important source of ions that affect the water chemistry in the yarlung tsangpo basin although watercourses on the tibetan plateau can generally be considered pristine concentrations of some toxic elements i e cd and pb were found to be higher than the who guideline for drinking water due to increasing influence from anthropogenic activities e g tourism mining operations and municipal wastewater discharge which constitute a risk to human livelihoods in both local and surrounding regions

how partial melts of mafic lower crust affect ascending magmas at oceanic ridges we present experiments showing that the lower oceanic crust should melt efficiently and quickly when heated by hot ascending magmas average plagioclase olivine and plagioclase augite pairs from the lower crust at the southwest indian ridge have melt mineral saturation boundaries at 1 190 and 1 154 c respectively and melt rapidly 0 01 mm h at 50 c or more above these temperatures melting experiments performed on olivine plagioclase and augite plagioclase mineral pairs from actual oceanic lower crustal rock samples and under conditions applicable to a mor setting 1 220 1 330 c 1 atm quartz fayalite magnetite oxygen buffer 0 25 24 h indicate that the resulting disequilibrium melts are linear mixes of the mineral compositions the rates of melting are slower than the rate of heat diffusion into a sample and are approximated as 2 43 10 26 e0 004109 t degc m s1 2 for augite melted with plagioclase 3 47 10 15 e0 002041 t degc for plagioclase melted with augite and 1 79 10 21 e0 0032 t degc for plagioclase melted with olivine our results indicate that great care must be taken in backward models using basalt chemistry alone to explore mantle melting processes assuming only crystallization and fractionation during ascent as partial melts may mix with intruded hot magma

low melt fraction connectivity of granitic and tonalitic melts in a mafic crustal rock at 800 c and 1 gpa in the absence of an externally applied stress the segregation of small amounts of granitic or tonalitic melts from their residual mafic crystals is possible only if the melt forms an interconnected network phase accordingly this research focuses on melt connectivity at low melt fraction 4 wt or 5 vol connectivity of granitic and tonalitic melts in amphibole rich rock was assessed by performing two types of piston cylinder experiments at 1 gpa and 800 c the first involved annealing samples that consisted of either alternating layers or homogeneous mixtures of calcic amphibole and metaluminous obsidian powder the second type of experiment involved creating diffusion couples here an upper cylinder of amphibole saturated granitic or tonalitic melt was placed against a lower cylinder consisting of an amphibole rich rock containing zero or a small melt granitic or tonalitic fraction the upper part of the diffusion couple was doped with emitter 151sm or 14c and functioned as an infinite melt reservoir the lower part of the diffusion couple was considered to be the host rock the experiments approached textural equilibrium which allowed us to characterize the wetting behaviour of the calcic amphibole by the hydrous silicic melt granitic or tonalitic these particular experiments also provided information concerning diffusive transport because the emitter could diffuse through the connected melt liquid in the amphibole rich rock the dihedral angle measurements show that melt connectivity was achieved this conclusion is based on the fact that the dihedral angles consistently yielded median apparent values of 53 58 for an amphibole rich rock granitic melt system and 46 48 for an amphibole rich rock tonalitic melt system however the frequency distribution of angles is found to be relatively broad the results of the diffusion couple experiments assessed using the radiographic technique complement the dihedral wetting angle measurements by showing that melt connectivity is achieved at a melt fraction less than 4wt 5 vol

can the aluminum and titanium contents of ocean sediments be used to determine the paleoproductivity of the oceans in the central equatorial pacific settling particles collected with sediment traps have al ti values greater than those of a typical crustal source the al ti values of the sediment trap material are not well correlated with either the flux of organic carbon or with total particle mass suggesting that this ratio cannot be used as a simple index of paleoproductivity however the al ti values of some trap samples are more than 3 times the ratio for typical crustal materials indicating a noncrustal source of excess al numerical analysis using linear programming indicates that the excess al is associated with opal and that this biological component carries as much as 1200 ppm of al because of the low particulate fluxes of lithogenic material in the equatorial pacific and the relatively high opal content of equatorial sediment trap material opal appears to be the predominant conveyor of al to the equatorial sediments our sediment trap al ti values are similar to ratios previously measured in equatorial sediments suggesting that measurements of this element pair in ocean sediments may be an indicator of opal rain to the seafloor the particle reactive nature of al and ti means their ratios in sediments may be relatively insensitive to opal preservation or other diagenetic processes however the al ti values of raining particles are highly sensitive to the relative proportion of opal and lithogenic material where opal lithogenic ratios are less than 20 the al ti values are indistinguishable from a crustal source ratio in addition the amount of excess al associated with opal in settling particles may be a function of the concentration of al in the water column and of the processes that fractionate dissolved al and ti these issues must be evaluated before the al ti values of ocean sediments can be used as a reliable proxy of opal flux to the seafloor

major element chemistry of the huai river basin china the chemistry of major ions ca mg na k hco3 so4 cl and si in the water of the huai river basin was studied based on samples from 52 sites from nine different water bodies in july 2008 ions and total dissolved solids tds displayed clear spatial patterns with lower concentrations in the south and higher in the north of the basin the same conditions were also found in the east line of south north water transfer project snwtp in this region the huai river main channel and hongze lake have moderate ion concentrations relative to the whole basin tds concentrations versus the weight ratios of na na ca and ternary ions demonstrate that the southern rivers shi r and pi r are mainly controlled by the weathering of carbonates whereas the northern water systems guo r shaying r nansi lake and its tributaries are dominated by the weathering of evaporites the huai river main channel hongze lake and the east line of snwtp are synergistically influenced by weathering of evaporites and carbonates yet hongze lake and the east line of snwtp are mainly controlled by evaporation and crystallization processes this study also confirmed that the huai river is the geographic division between southern and northern china most rivers of this basin have very high ionic composition relative to the global median and other world rivers the spatial patterns and ionic composition also suggest that intensive anthropogenic activities in northern areas of this basin are well characterized a comparison with who and chinese standards for drinking water indicates that the northern water systems of this basin are not suitable for use as drinking water sources and pollution control should be improved and enhanced in northern areas of the basin crown copyright c 2010 published by elsevier ltd all rights reserved

thorium 230 profiling in deep sea sediments high resolution records of flux and dissolution of carbonate in the equatorial atlantic during the last 24 000 years variations in carbonate flux and dissolution which occurred in the equatorial atlantic during the last 24 000 years have been estimated by a new approach that allows the point by point determination of paleofluxes to the seafloor an unprecedented time resolution can thus be obtained which allows sequencing of the relatively rapid events occurring during deglaciation the method is based on observations that the flux of unsupported 230th into deep sea sediments is nearly independent of the total mass flux and is close to the production rate thus excess 230th activity in sediments can be used as a reference against which fluxes of other sedimentary components can be estimated the study was conducted at two sites ceara rise western equatorial atlantic and sierra leone rise eastern equatorial atlantic in cores raised from three different depths at each site from measurements of 230th and caco3 changes in carbonate flux with time and depth were obtained a rapid increase in carbonate production starting at the onset of deglaciation was found in both areas this event may have important implications for the postglacial increase in atmospheric co2 by increasing the global carbonate carbon to organic carbon rain ratio and decreasing the alkalinity of surface waters and possibly the north atlantic deep water increased carbonate dissolution occurred in the two regions during deglaciation followed by a minimum during mid holocene and renewed intensification of dissolution in late holocene during the last 16 000 years carbonate dissolution was consistently more pronounced in the western than in the eastern basin reflecting the influence of antarctic bottom water in the west this trend was reversed during stage 2 possibly due to the accumulation of metabolic co2 below the level of the romanche fracture zone in the eastern basin

the major ion composition of silurian seawater one hundred fluid inclusions in silurian marine halite were analyzed in order to determine the major ion composition of silurian seawater the samples analyzed were from three formations in the late silurian michigan basin the a 1 a 2 and b evaporites of the salina group and one formation in the early silurian canning basin australia the mallowa salt of the carribuddy group the results indicate that the major ion composition of silurian seawater was not the same as present day seawater the silurian ocean had lower concentrations of mg2 na and so42 and much higher concentrations of ca2 relative to the ocean s present day composition furthermore silurian seawater had ca2 in excess of so42 evaporation of silurian seawater of the composition determined in this study produces kcl type potash minerals that lack the mgso4 type late stage salts formed during the evaporation of present day seawater the relatively low na concentrations in silurian seawater support the hypothesis that oscillations in the major ion composition of the oceans are primarily controlled by changes in the flux of mid ocean ridge brine and riverine inputs and not global or basin scale seawater driven dolomitization the mg2 ca2 ratio of silurian seawater was 1 4 and the k ca2 ratio was 0 3 both of which differ from the present day counterparts of 5 and 1 respectively seawaters with mg2 ca2 2 e g modern seawater facilitate the precipitation of aragonite and high magnesian calcite therefore the early paleozoic calcite seas were likely due to the low mg2 ca2 ratio of seawater not the pco2 of the silurian atmosphere

dissolution of corundum and andalusite in h2o saturated haplogranitic melts at 800 c and 200 mpa constraints on diffusivities and the generation of peraluminous melts of h2o in the aluminum alkali eigenvector could not be obtained the mechanisms and kinetics of equilibration between peraluminous from our results we propose that some h2o may provide charge minerals and granitic melt were investigated experimentally by balance for excess aluminum multicomponent diffusion models the dissolution of corundum and andalusite into h2o saturated yield eigenvalues for the corresponding aluminum alkali eigenvector metaluminous haplogranitic melt at 800 c and 200 mpa mineral of 0 3 10 to 1 9 10 cm s calculated effective and haplogranitic glass rods were juxtaposed inside platinum binary diffusion coefficients for al2o3 are higher 1 0 10 to capsules and then subjected to experimental conditions for times 3 6 10 cm s these diffusion coefficients are used to ranging from 12 to 2900 h upon melting the mineral melt calculate equilibration times between peraluminous minerals and interface retreats with the square root of time the composition of granitic melts in a model system in which two grains of corundum the melt at the interface changes with time but its asi aluminum or andalusite 1 cm apart are connected via a narrow melt column saturation index molar al2o3 cao na2o k2o at the conditions of the experiments diffusive equilibrium through remains constant at 1 20 after 480 h this value is close to initially metaluminous h2o saturated melt would be attained within the asi of an h2o saturated haplogranitic melt in equilibrium with 10 10 years at h2o activity well below saturation of the corundum or andalusite which may indicate that the composition of melt lower diffusivity of all components may increase the time to the melt at the interface follows the liquidus of these minerals in equilibration to 10 10 years approaching possible time frames the system sodium and potassium diffuse rapidly uphill across the for the generation and extraction of crustal melts entire length of the charge towards the interface resulting in a rapid and uniform increase in asi throughout the entire melt column this uphill diffusion of alkalis is due to coupling with excess aluminum entering the melt at the interface and involves long range

late cenozoic sedimentation and metal deposition in the north pacific similar major chemical variations in cores from three sites across a wide area of the north pacific are modeled by coupling the vertical and horizontal motions of the pacific plate with a constant authigenic flux of elements into the sediments superimposed over this flux is an input of detrital material of relatively constant chemical composition the major features of sediment chemistry of cores from the north pacific apparently vary in a fairly uniform and systematic manner and these variations are consistent with cenozoic plate movement elements with a significant authigenic component e g mn co cu ni display high concentrations at depth in cores that correspond to the period when the seafloor while under the low productivity subtropical gyre of the n pacific accumulated sediment at an extremely slow rate 1 mm kyr these concentrations were diluted when the sites experienced an increase in the eolian mass accumulation rate first brought about by migration into the influence of the westerlies and then dominantly by the huge input of wind blown detritus which corresponded to the onset of northern hemisphere glaciation a comparison of 10be profiles to the profiles of metal concentrations is used to reveal the occurrence of haituses in the sediment column over the past 8 m y

drainage basin weathering and major element transport of two large chinese rivers huanghe and changjiang long term records show high concentrations of dissolved major elements in the changjiang yangtze river and the huanghe yellow river the huanghe drainage basin is characterized by intense weathering and erosion of carbonates and evaporites while weathering and erosion of carbonates and silicates over the drainage basin is the main source of major elements in the changjiang the rock soil composition and tectonics of the drainage basin are more important than atmospheric precipitation in affecting major element composition of these two rivers compared with other large rivers of the world the high suspended sediment and major element loads of the changjiang and huanghe reveal intense physical and chemical erosion over the chinese continent

a review and analysis of silicate mineral dissolution experiments in natural silicate melts abstract we present a database and a graphical analysis of published experimental results for dissolution rates of olivine quartz plagioclase clinopyroxene orthopyroxene spinel and garnet in basaltic and andesitic melts covering a range of experimental temperatures 1100 1500 c and pressures 10 5 pa 3 0 gpa the published datasets of donaldson 1985 1990 and brearly and scarfe 1986 are the most complete experimental dissolution rates from all datasets are recalculated and normalized to a constant oxygen basis to allow for direct comparison of dissolution rates between different minerals dissolution rates range from 5 10 10 oxygen equivalent moles o e m cm 2 s 1 for olivine in a basaltic melt to 1 3 10 5 o e m cm 2 s 1 for garnet in a basaltic melt values of ln are arthenian for the experiments examined and activation energies range from 118 to 1800 kj o e m for quartz and clinopyroxene respectively the relationship between calculated a rt for the dissolution reactions where a is the thermodynamic potential affinity and values of is linear for olivine plagioclase and quartz we interpret this as strong evidence in support of using calculated a as a predictor of for at least superliquidus melt conditions

excess sediment 230th transport along the sea floor or enhanced water column scavenging 1 the sedimentary inventory of 230th is often employed to distinguish between areas which receive excess sediment as the result of along bottom transport from those which lose sediment as a result of winnowing this process is referred to as focusing a case is made here that at least in the western equatorial pacific the excess 230th in on equator sediment is more likely scavenged from the overlying water column by the rain of organic matter than retransported along the bottom if so lateral variations in biological productivity may well contribute to the excess 230th inventories elsewhere as well

western equatorial pacific deep water carbonate chemistry during the last glacial maximum and deglaciation using planktic foraminiferal mg ca to reconstruct sea surface temperature and seafloor dissolution 1 we present a reconstruction of deep water carbonate saturation state co32 in the western equatorial pacific for the last glacial maximum lgm and deglaciation based on changes in the mg ca ratio of planktic foraminifers with increased water depth our data suggest there have been changes in bottom water co32 over the past 25 000 years at water depths as shallow as 1 6 km the co32 reconstruction for the lgm suggests co32 was similar or slightly higher than modern values between 1 6 and 2 0 km shifting sharply to lower values an average 30 mol kg lower below 2 5 km the shift in chemistry between 2 0 and 2 5 km supports a hypothesis that pacific overturning circulation occurred deeper during the lgm with a slightly more ventilated water mass above 2 0 km the data are not consistent with enhanced preservation in this region of the deep pacific at depths greater than 2 5 km suggesting that the long held view of better preservation throughout the glacial deep pacific must be reevaluated for the deglaciation we have evidence of a co32 maximum that suggests enhanced deglacial preservation between 1 6 and 4 0 km in comparison to the holocene and the lgm the deglacial co32 was as much as 28 mol kg higher than modern between 1 6 and 4 0 km results suggest carbonate burial rates were 1 5 times greater during the deglacial than the over the past 5 kyr

seismic interpretation of pelagic sedimentation regimes in the 18 53 ma eastern equatorial pacific basin scale sedimentation and infilling of abyssal valleys understanding how pelagic sediment has been eroded transported and deposited is critical to evaluating pelagic sediment records for paleoceanography we use digital seismic reflection data from an integrated ocean drilling program site survey amat03 to investigate pelagic sedimentation across the eastern central equatorial pacific which represents the first comprehensive record published covering the 18 53 ma eastern equatorial pacific our goals are to quantify 1 basin hill scale primary deposition regimes and 2 the extent to which seafloor topography has been subdued by abyssal valley filling sediments the eastern pacific seafloor consists of a series of abyssal hills and basins with minor late stage faulting in the basement ocean crust rarely outcrops at the seafloor away from the rise crest both hills and basins are sediment covered the carbonate compensation depth is identified at 4440 m by the appearance of acoustically transparent clay intervals in the seismic data overall we recognized three different sedimentation regimes depositional high sedimentation rate transitional and minimal sedimentation low sedimentation rate regimes in all areas the sedimented seafloor mimics the underlying basement topography although the degree to which topography becomes subdued varies depositional regimes result in symmetric sedimentation within basins and subdued topography whereas minimal sedimentation regimes have more asymmetric distribution of sediments within topographic lows and higher seafloor relief regardless of sedimentation regime enhanced sediment deposition occurs within basins however we observe that basin infill is rarely more than twice as thick as sediment cover over abyssal hills if this variation is due to sediment focusing the focusing factor in the basins as measured by 230th is no more than a factor of 1 3 of the total vertical particulate rain

magmatic subsidence of the east pacific rise epr at 18 14 s revealed through fault restoration of ridge crest bathymetry 1 the fault restoration technique of de chabalier and avouac 1994 is applied to an ultra high resolution bathymetry data set from the east pacific rise epr at 18 14 s fault offsets are calculated and subtracted from the original seafloor bathymetry to examine the morphology of the unfaulted seafloor surface within an area encompassing the ridge axis 400 1600 m in dimension the restored topography reveals a gently sloping seafloor 200 m wide which slopes 5 inward toward the spreading axis we attribute this inward sloping seafloor to subsidence within the axial trough due to subsurface magmatic deflation the vertical deformation field extracted from the bathymetry is used to characterize the ridge axis fault population present in the area median fault throws 9 m for inward facing and 8 m for outward facing faults are comparable to values measured for nearby mature abyssal hill fault populations suggesting a genetic link however median fault spacings 70 and 46 m are an order of magnitude smaller and estimated total extensional strain is 3 4 greater than values measured for ridge flank faults these differences indicate the axial fault population at 18 14 s cannot be rafted onto the ridge flanks to form abyssal hill faults without significant modification presumably via volcanic burial we attribute the dense faulting observed in this area to slip on axial fissures during subsidence of the crestal region the surface subsidence of a volcanic edifice can be modeled in terms of volume change in the magma source reservoir and volume of magma withdrawn from the reservoir using the relationship derived for a sill like magma body we estimate that the axial depression at 18 14 s could represent magma withdrawal associated with a small number 4 22 of the frequent dike injection and eruption events required to build the upper crust during the evolution of the trough the subsidence volumes represented by the axial topography at 18 14 s are a small percentage of the underlying upper crustal sections 3 4 suggesting that only a minor mismatch between magma recharge and withdrawal from the axial melt lens during ongoing plate separation could account for this pronounced axial depression

major ion chemistry of the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal the ganga brahmaputra one of the world s largest river systems is first in terms of sediment transport and fourth in terms of water discharge a detailed and systematic study of the major ion chemistry of these rivers and their tributaries as well as the clay mineral composition of the bed sediments has been conducted the chemistry of the highland rivers upper reaches of the ganga the yamuna the brahmaputra the gandak and the ghaghra are all dominated by carbonate weathering ca mg and hco3 account for about 80 of the cations and anions in the lowland rivers the chambal the betwa and the ken hco3 excess over ca mg and a relatively high contribution of na k to the total cations indicate that silicate weathering and or contributions from alkaline saline soils and groundwaters could be important sources of major ions to these waters the chemistry of the ganga and the yamuna in the lower reaches is by and large dictated by the chemistry of their tributaries and their mixing proportions illite is the dominant clay mineral about 80 in the bedload sediments of the highland rivers kaolinite and chlorite together constitute the remaining 20 of the clays in the chambal betwa and ken smectite accounts for about 80 of the clays this difference in the clay mineral composition of the bed sediments is a reflection of the differences in the geology of their drainage basins the highland rivers weather acidic rocks whereas the others flow initially through basic effusives the ganga brahmaputra river system transports about 130 million tons of dissolved salts to the bay of bengal which is nearly 3 of the global river flux to the oceans the chemical denudation rates for the ganga and the brahmaputra basins are about 72 and 105 tons km yr 1 respectively which are factors of 2 to 3 higher than the global average the high denudation rate particularly in the brahmaputra is attributable to high relief and heavy rainfall

spatial and temporal analysis of water chemistry records 1958 2000 in the huanghe yellow river basin 1 the chemistry of major dissolved ions ca2 mg2 na k hco3 so42 cl and dissolved silica sio2 in the river water of the huanghe yellow river china was studied from historical records at 100 stations in the drainage basin for the period 1958 2000 not all the parameters were continuously monitored during the entire period this river system 750 000 km2 presents an exceptional temporal and spatial water chemistry variability compared to other major rivers the total dissolved solid tds concentration of the huanghe varied over 2 to 3 orders of magnitude throughout the basin with a median tds concentration of 452 mg l which is about 4 times the world spatial median value wsm in particular the concentrations of na k so42 and cl were 10 20 times higher than in other major world rivers similar to the changjiang yangtze river and many other himalayan rivers the tds at a given station is seasonally variable and inversely related to river runoff with a variation factor less than 2 0 despite a water dilution of fourfold to fivefold in the summer flood season in addition to chemical weathering of sedimentary rocks evaporation and fractional crystallization were found to be the major natural process controlling the major element chemistry of the huanghe owing to the abundance of loess and clastic rocks under arid and semiarid climates a persistent increasing trend from year to year has been observed in the concentrations of tds and all the salts except for hco3 at all main channel stations except for the uppermost lanzhou the rate of increase in the tds concentration was the highest in the middle reaches 10 52 mg l yr 1 at toudaoguai and remained to be unusually high in the lower reaches 5 5 mg l yr 1 at stations luokou and lijin the increasing trend coincided with a significant decrease in water discharge at most of the main channel stations in the past 40 years and is attributed to increasing regulations of reservoirs and intensive water withdrawal for irrigation and diversions as well as many other anthropogenic processes despite the increasing trend in tds concentrations the seaward tds flux to the sea by the huanghe has decreased dramatically from more than 20 109 kg yr in the 1960s to less than 10 109 kg yr at present due to the sharp decrease in water discharge sometimes completely dried up in the lower reaches of the river the significant decreases in sea ward fluxes of water and dissolved salts are expected to have profound physical ecological and socio economic impacts on the lower reaches of the river the coastal areas and the bohai sea

olivine dissolution in molten silicates an experimental study with application to chondrule formation mg rich olivine is a ubiquitous phase in type i porphyritic chondrules in various classes of chondritic meteorites the anhedral shape of olivine grains their size distribution as well as their poikilitic textures within low ca pyroxene suggest that olivines suffer dissolution during chondrule formation owing to a set of high temperature experiments 1450 1540 c we determined the kinetics of resorption of forsterite in molten silicates using for the first time x ray microtomography results indicate that forsterite dissolution in chondrule like melts is a very fast process with rates that range from 5 m min 1 to 22 m min 1 forsterite dissolution strongly depends on the melt composition with rates decreasing with increasing the magnesium and or the silica content of the melt an empirical model based on forsterite saturation and viscosity of the starting melt composition successfully reproduces the forsteritic olivine dissolution rates as a function of temperature and composition for both our experiments and those of the literature application of our results to chondrules could explain the textures of zoned type i chondrules during their formation by gas melt interaction we show that the olivine liquid ratio on one hand and the silica entrance from the gas phase siog into the chondrule melt on the other hand have counteracting effects on the mg rich olivine dissolution behavior silica entrance would favor dissolution by maintaining disequilibrium between olivine and melt hence this would explain the preferential dissolution of olivine as well as the preferential abundances of pyroxene at the margins of chondrules incipient dissolution would also occur in the silica poorer melt of chondrule core but should be followed by crystallization of new olivine overgrowth and or newly grown crystals while explaining textures and grain size distributions of olivines as well as the centripetal distribution of low ca pyroxene in porphyritic chondrules this scenario could also be consistent with the diverse chemical isotopic and thermal conditions recorded by olivines in a given chondrule

an appraisal of groundwater quality in seymour and blaine aquifers in a major agro ecological region in texas usa aquifer based groundwater quality assessment offers critical insight into the major hydrochemical processes and aids in making groundwater resources management decisions the texas rolling plains trp spanning over 22 counties is a major agro ecological region in texas from where highest groundwater nitrate no3 levels in the state have been reported in this study we present a comparative assessment of major hydrochemical facies pertaining to no3 contamination and a host of species such as sulfate so42 chloride cl and total dissolved solids tds in different water use classes in the seymour and blaine aquifers underlying the trp aquifer stratified groundwater quality information from 1990 to 2010 was obtained from the texas water development board and aggregated over decadal scale high groundwater salinization was found in the municipal water use class in the blaine aquifer with about 100 87 and 50 of observations exceeding the secondary maximum contaminant level for tds so42 and cl respectively in the 2000s 2000 2010 the no3 contamination was more alarming in the seymour aquifer with 82 and 61 of observations respectively exceeding the maximum contaminant level mcl in the irrigation and municipal water use classes in the 2000s salinization was more influenced by so42 and cl in the blaine aquifer and by no3 in the seymour aquifer high no3 mcl observations in the seymour aquifer occurred in the ca hco3 and ca mg hco3 facies the domains of fresh water recharge and anthropogenic influences e g agricultural activities waste disposal high so42 cl and tds observations in the blaine aquifer dominated the ca cl na cl and mixed ca mg so4 cl facies indicating evaporite dissolution mixing and solute exchange and lack of fresh recharge

effects of melt viscosity and silica activity on the rate and mechanism of quartz dissolution in melts of the cmas and cas systems the dissolution rate of quartz in melts of the cmas and cas systems at 1 600 c and 1 5 gpa is a function of both the silica activity of the melt and its viscosity in melts with low silica activity quartz dissolves more quickly than in higher asio2 melts regardless of viscosity for melts with equal asio2 dissolution is faster in the low viscosity melt quartz dissolution is controlled by interface kinetics in three of the four melts used in this study for times much greater than predicted by the model of zhang et al in contrib mineral petrol 102 492 513 1989 one melt which was previously shown to adhere to the predicted behaviour at lower temperature shows a significant activation time at higher temperature all the dissolution data indicate that there are likely to be three distinct domains of dissolution behaviour although the details of why a particular melt falls in any one domain require further study although the current database is small the relationship between quartz solubility and the dissolution constant indicate that solubility may be a useful parameter for predicting dissolution rates particularly if silica activity and melt viscosity are also known

extraterrestrial 3 he as a tracer of marine sediment transport and accumulation the deposition rate of deep sea sediments and their focused redeposition by deep sea currents can be evaluated from analyses of sedimentary 230th with a temporal resolution limited only by bioturbation6 7 10 11 230th is produced uniformly throughout the ocean by radioactive decay of dissolved 234u and is removed sufficiently fast by sorption onto sinking particles to act as a constant flux tracer of sedimentation rates but the half life of 230th 75 kyr limits its use for this purpose to the past 200 250 kyr here we explore the use of extraterrestrial 3he from interplanetary dust particles1 4 idps as a constant flux proxy that is free from this limitation a comparison of 3he with 230th in two cores from the equatorial pacific ocean indicates that the variability in the mean flux of idps over the past 200 kyr is less than 75 but in contrast to this relatively constant rate of supply of 3he to the deep sea the local burial rates of 3he and 230th have varied by a factor of five over the past 450 and 200 kyr respect ively we interpret this variability as reflecting sediment focusing with a temporal pattern that suggests regular cycles of climate driven reorganization of near bottom currents in the deep pacific ocean

biogenic flux of al to sediment in the central equatorial pacific ocean evidence for increased productivity during glacial periods we examined the flux of al to sediment accumulating beneath the zone of elevated productivity in the central equatorial pacific ocean along a surface sediment transect at 135 w as well as downcore for a 650 kyr record at 1 3 n 133 6 w across the surface transect a pronounced broadly equatorially symmetric increase in al accumulation is observed relative to ti with al ti ratios reaching values 3 4 times that of potential detrital sources the profile parallels biogenic accumulation and the modeled flux of particulate 234th suggesting rapid and preferential adsorptive removal of al from seawater by settling biogenic particles normative calculations confirm that most al is unsupported by the terrigenous fraction the observed distributions are consistent with previous observations of the relative and absolute behavior of al and ti in seawater and we can construct a reasonable mass balance between the amount of seawater sourced al retained in the sediment and the amount of seawater al available in the overlying column the close tie between al ti and biogenic accumulation as opposed to concentration emphasizes that biogenic sedimentary al ti responds to removal transport phenomena and not bulk sediment composition thus in these sediments dominated by the biogenic component the bulk al ti ratio reflects biogenic particle flux and by extension productivity of the overlying seawater the downcore profile of al ti at 1 3 n displays marked increases during glacial episodes similar to that observed across the surface transect from a background value near al ti of average upper crust the excursions in al ti are stratigraphically coincident with maxima in both bulk and caco3 accumulation and the excess al appears to not be preferentially affiliated with opaline or organic phases consistent with the similar behavioral removal of al and 234th the latter of which responds to the total particle flux the al flux reflects carbonate accumulation only because carbonate comprises the dominant flux in these particular deposits these results collectively indicate that 1 al in biogenic sediment and settling biogenic particles is strongly affected by a component adsorbed from seawater therefore the common tenet that al is dominantly associated with terrestrial particulate matter and the subsequent use of al distributions to calculate the abundance and flux of terrestrial material in settling particles and sediment needs to be reevaluated 2 the al ti ratio in biogenic sediment can be used to trace the productivity of the overlying water providing a powerful new paleochemical tool to investigate oceanic response to climatic variation 3 the close correlation between the al ti productivity signal and carbonate maxima downcore at 1 3 n suggests that the sedimentary carbonate maxima in the central equatorial pacific ocean record increased productivity during glacial episodes

do geochemical estimates of sediment focusing pass the sediment test in the equatorial pacific 1 the paleoceanographic recording fidelity of pelagic sediments is limited by chemical diagenesis and physical mixing bioturbation and horizontal sediment transport diagenesis and bioturbation are relatively well studied but the effects of physical sedimentation have been largely ignored modeling u series isotopes e g 230th can potentially quantify horizontal sediment movement but model horizontal sediment focusing often equals or exceeds the vertical particle rain we find no evidence of this level of sediment focusing in the equatorial pacific from geophysical data or sediment core comparisons the overestimate of sediment focusing by 230th is probably caused by poor model assumptions that sediment does not fractionate does not sort according to size during transport and that 230th cannot leak from slowly accumulating sediments both assumptions are weak u series methods do hold promise to quantify sediment focusing if properly calibrated with calibration the trade offs between seeking high sedimentation rates for better time resolution and the blurring by horizontal sediment focusing can be better assessed

the temporal evolution of three magmatic systems in the west eifel volcanic field germany abstract the quaternary west eifel volcanic field is the surface expression of a mantle plume that is thought to contain 1 melt the volcanoes range in age from 0 7 ma to 10 000 yr bp and the average recurrence rate of volcanism is around 3 5 10 4 eruptions per year giving a mean time between eruptions of 2875 years assuming that the field is monogenetic the presence of mafic and ultramafic xenoliths is taken as evidence for rapid single stage emplacement of magmas at velocities around 0 5 km h however the presence of clinopyroxene that preserves evidence of polybaric crystallisation belies this simple model this study uses variations in the fo content of olivine in mantle derived xenoliths and in olivine xenocrysts enclosed in cumulate xenoliths to calculate the time scale of evolution of three volcanic centres in the eifel field core rim variations in olivine are interpreted to result from fe mg interdiffusion between it and a surrounding melt using experimental determinations of the interdiffusion coefficient and approximations of magma temperature contact times have been calculated using planar and radial diffusion models the three volcanic centres studied were meerfelder maar gemundener maar and baarley the cumulate xenoliths at meerfelder maar formed at a depth of 13 km and record a magma emplacement event at between 1 and 3 years prior to eruption two suites of mantle derived olivine clinopyroxenites record a further two events at 1 8 days and 3 h prior to eruption the final event is interpreted to record the eruption of this volcano and the 3 h contact time records the time required for transport of peridotite xenoliths from the mantle to surface giving an average emplacement velocity of around 15 km h the cumulate xenoliths at gemundener maar crystallised at depths of between 4 and 22 km there are four distinct events recorded by the zoned olivine grains in the clinopyroxene rich cumulates from this locality the maximum residence time is similar to that at meerfelder maar however in this case the final magma resided in the chamber for between 23 days and 2 7 months prior to eruption allowing enough time for any entrained peridotite xenoliths to be filtered out the cumulate xenoliths from the baarley locality record a much longer history than those at the other localities in this case initially peridotitic olivine has been completely re equilibrated over 175 years prior to eruption in common with the other two localities there is evidence of multiple intrusive events at depths up to 7 km prior to final eruption the duration of the final eruption event and the interpreted depth to source of the xenoliths indicate an emplacement velocity of around 3 km h the data derived from modelling of diffusion profiles in olivine from cumulate xenoliths indicate that the magmatic systems feeding these three volcanoes were dynamic and very short lived in addition these data can be used to place constraints on the rate of cumulate formation in subvolcanic magma chambers on the basis of the data presented here it would seem that an appreciable thickness of cumulates can form over relatively short time spans days to a few years

major element chemistry of the changjiang yangtze river the chemistry of major elements ca mg na k hco3 so4 cl and si in the river water of the changjiang yangtze river was studied based on continuously monitored data at 191 stations in the drainage basin for the period 1958 1990 the results show that the total dissolved solid tds concentration of the changjiang varies over an order of magnitude throughout the basin 49 7 518 1 mg l with a medium tds concentration of 205 9 mg l about three times the global average in contrast the tds at a given main channel station varies only slightly in different seasons with a variation factor less than 2 0 despite a substantial water dilution in the summer flood season the major element chemistry of the changjiang is mainly controlled by rock weathering with the anion hco3 and the cation ca dominating the major ion composition due to the abundance of carbonate rocks in the basin a persistently increasing trend has been observed in the concentrations of so4 and to a lesser extent cl in the changjiang a signature of considerable anthropogenic impacts e g acid deposition flux calculations at datong the most downstream main channel station without tidal influence indicate that the changjiang transports ca 154 106 tons year of tds to the sea second only to the amazon in the world

chemical diffusion of major components in granitic liquids implications for the rates of homogenization of crustal melts abstract crustal anatexis coupled with melt extraction and ascent is the main mechanism by which the continental crust differentiates during diffusion controlled melting and in the absence of melt flow and mechanical mixing diffusion is the main process by which the melt phase ultimately homogenizes and mineral residuum and melt equilibrate knowing the diffusive properties of the elements within a granitoid melts is therefore essential for understanding the kinetics and mechanisms of melting as well as the compositions and nature of chemical heterogeneities in granites in this contribution we review a series of experimental studies aimed at an improved understanding of the nature and rates of chemical diffusion of major components of h 2 o saturated granite melts at anatectic conditions in the continental crust the hydrous granite system under investigation makes up 95 99 of natural restite free granitic magmas these experimental results have applications for predicting the composition of granitic liquids during processes such as anatexis magma mixing assimilation or crystallization regarding the diffusive properties the major elements of the liquid can be classified into two categories those whose diffusion is uncoupled with other elements e g si and others whose diffusion is highly coupled with the movement and gradients of other ions e g na and k with h na k ca and h with al one implication of coupled diffusion is that chemical gradients in fast diffusing ions such as na and k may persist for long times in the melt due to their chemical coupling with slow diffusing components such as al the diffusion of components through granitic melts entails two mechanisms local diffusion corresponds to the classical view of chemical diffusion and refers to the relative and random motion of an ion e g si al under apparently local gradients in chemical potential field diffusion corresponds to the long range and coordinated migration of an ionic species e g na driven by a long range chemical potential gradient created by other melt components with which it associates due to coupled diffusion this mechanism serves to erase compositional gradients at rates that are orders of magnitude greater than those by local diffusion this is because the coordinated movement requires individual ions to move only a small fraction of the entire distance over which the chemical potential gradient is established in order to achieve diffusion over distances that may span the entire liquid system the significance and implications of major element diffusivities and the occurrence of coupled diffusion and field diffusion in granitic liquids are highlighted by calculations of the rates of melt homogenization during anatexis of crustal protoliths

sediment focusing creates 100 ka cycles in interplanetary dust accumulation on the ontong java plateau the accumulation of extraterrestrial 3 he a tracer for interplanetary dust particles idps in sediments from the ontong java plateau ojp western equatorial pacific ocean has been shown previously to exhibit a regular cyclicity during the late pleistocene with a period of v100 ka those results have been interpreted to reflect periodic variability in the global accretion of idps that in turn has been linked to changes in the inclination of earth s orbit with respect to the invariable plane of the solar system here we show that the accumulation in ojp sediments of authigenic 230 th produced by radioactive decay of 234 u in seawater exhibits a 100 ka cyclicity similar in phase and amplitude to that evident in the 3 he record we interpret the similar patterns of 230 th and 3 he accumulation to reflect a common origin within the ocean climate system comparing spatial and temporal patterns of sediment accumulation against regional patterns of biological productivity and against the well established pattern of caco3 dissolution in the deep pacific ocean leads to the further conclusion that a common 100 ka cycle in accumulation of biogenic authigenic and extraterrestrial constituents in ojp sediments reflects the influence of climate related changes in sediment focusing rather than changes in the rate of production or supply of sedimentary constituents 7 2002 elsevier science b v all rights reserved

implications of equilibrium and disequilibrium among crystal phases in the bishop tuff eruption of the bishop tuff magma preserved equilibrium of exchange components and element concentrations among magnetite ilmenite biotite apatite zircon and liquid orthopyroxene and clinopyroxene were not in exchange equilibrium with the other mgfe bearing phases but they appear to have been in equilibrium among themselves internally consistent temperatures recorded by the feti oxide ti in quartz and 18 o quartz magnetite thermometers coupled with evidence for magmatic corrosion of quartz and sanidine indicate that an initially low t 700 c near h 2 o saturated high sio 2 rhyolite magma was heated up to 800 c and its crystal cargo partially melted by recharge of hotter melt from below oxygen fugacity and compositions of biotite ilmenite magnetite and silicate liquid initially adjusted by internal rearrangement of components and conservation of oxygen partial melting of feldspars liberated sr and ba back into the melt mixing during recharge eventually re introduced compatible elements e g mg ba sr as well as foreign crystals of euhedral ortho and clinopyroxene which evidently never totally re equilibrated with the rhyolite liquid introduction of co 2 and accompanying reduction in the a h 2 o during recharge raised crystallization temperatures of quartz and sanidine in the rhyolite sufficient to allow marginal regrowth of these phases with enhanced contents ti ba and sr

major ion chemistry of groundwater from perched water bodies of the azores portugal volcanic archipelago a dataset of major ion composition of 246 samples from cold water springs discharging from perched water bodies at volcanic islands azores archipelago portugal reveal waters with low mineralization which evolve due to two main geochemical processes 1 seawater spraying and 2 dissolution of primary minerals of volcanic rocks as a result water facies range from na cl to na hco3 type waters the relationship between alkali alkali earth metals and hco3 shows differences between waters discharging from perched water bodies in basaltic rocks comparing to more evolved rocks of trachytic nature the use of principal component analysis shows that water rock interaction is limited which is compatible with the geochemical observations and with the hydrogeological environment

assimilation and crystal accumulation in a mid crustal magma chamber the sausfjellet pluton north central norway the sausfjellet pluton is made up of two intrusive units emplaced into high grade metamorphic rocks of the helgeland nappe complex of the uppermost allochthon in the norwegian caledonides the eastern part of the pluton intruded marble and less voluminous calc silicate and pelitic rocks the western half is hosted predominantly by semi pelitic migmatite with intercalated marble remelting of the migmatite during pluton emplacement occurred in a thermal aureole as much as 1000 m wide the early gabbroic unit forms the southeastern part of the body it consists of hornblende bearing to hornblende rich gabbro and diorite which is thought to have crystallized from an h2o rich andesitic parental magma the younger dioritic unit underlies the central and western parts of the pluton as well as a zone as much as 200 m wide that separates the rest of the pluton from its host rocks herein the annular zone the interior or central zone of the dioritic unit is pyroxene diorite that is locally interlayered with anorthosite the western and annular zones are by comparison mineralogically heterogeneous they range from diorite to quartz monzonite and from biotite bearing two and threepyroxene assemblages to biotite hornblende assemblages neither rock type nor mafic assemblage is correlated with position in the pluton or proximity to a contact stoped blocks of a distinctive coarse grained diorite as well as pyroxenerich calc silicates are present in the gabbroic unit and the central zone of the dioritic unit the few stoped blocks observed in the western zone of the dioritic unit are predominantly quartz rich gneiss chemical variation in the central zone of the dioritic unit is interpreted to result from accumulation of pyroxenes plagioclase from an h2o poor andesitic parent these rocks have approximately constant d 18 o of 6 6f0 2x and lack evidence of in situ assimilation heterogeneities in the western and annular zones of the dioritic unit are reflected in variable anomalously enriched incompatible element contents and in d 18 o which ranges from 6 7x to 8 6x petrologic models indicate that the magma parental to the central zone could also be parental to the western and annular zones if so evolution of the western and annular zone magma was by crystal accumulation and assimilation of metapelitic host rocks as much as 20 of the mass of the western and annular zones can be ascribed to assimilated material which apparently entered the magma by stoping therefore the asymmetrical

kinetics of anorthite dissolution in basaltic melt abstract we report convection free anorthite dissolution experiments in a basaltic melt at 1280 1500 c and 0 5 gpa on two different crystallographic surfaces 1 2 1 and 3 0 2 to investigate dissolution kinetics the anisotropy of the anorthite dissolution rate along these two surfaces is negligible time series experiments at 1280 c show that anorthite dissolution is mainly controlled by diffusion in the melt within experimental uncertainty analytical solutions were used to model the dissolution and diffusion processes and to obtain the diffusivities and the saturation concentrations of the equilibrium determining component al2o3 for anorthite dissolution into the basaltic melt for the first time we are able to show the physical and chemical characteristics of quench growth effect on the near interface melt using high spatial resolution 0 3 m eds analyses for anorthite an 90 saturation in a melt with 39 53 wt sio2 and 0 4 wt h2o the concentration of al2o3 in wt depends on temperature as follows ln c s al 2 o 3 8 032 0 192 7882 287 t where t is temperature in k and errors are given at 1 level al2o3 diffusivity in basaltic melt during plagioclase dissolution can be expressed as ln d al 2 o 3 ebd plag diss 13 69 1 57 19 313 2485 t where d is in m2 s and the activation energy is 161 21 kj mol these results are applied to model the convective dissolution of anorthite in basaltic melts the model indicates that though anorthite crystals can survive for a longer time compared to olivine crystals of the same size in the same melt the former would rise for a much smaller distance compared to the olivine sinking distance due to the smaller density contrast between anorthite and melt

glacial and holocene stable isotope distributions in the southeastern indian ocean we have reconstructed glacial interglacial variations in cibicidoides wuellerstorfi 13c and 18o in the southeastern indian ocean using depth transects of cores from off western and southern australia we compare these new results with published stable isotope records to constrain glacial interglacial changes in indian ocean chemistry and circulation the strong last glacial maximum lgm deep water 13c depletions previously observed for the northeastern indian ocean did not extend throughout the low latitude glacial indian ocean we observe only a small lgm 13c decrease off southern australia in marked contrast to the strong lgm 13c depletions observed in many cores from the atlantic and western indian sectors of the southern ocean it is not yet clear whether the very low lgm 13c values in the deep northern and southwestern indian ocean are an artifact of surface ocean productivity or whether they reflect real gradients in deep water chemistry

convective crystal dissolution the effect of free and forced convection on crystal dissolution is examined both theoretically and experimentally well established relationships for heat and mass transfer are applied to obtain approximate expressions for the dissolution velocity and the associated thickness of the compositional boundary layer these expressions are found to be in good agreement with experimental observations of the dissolution of quartz crystals in basalt and nacl crystal in water when applied to light felsic crystals in basaltic magmas the expressions predict that forced convection will produce a boundary layer thickness of about 100 m and a dissolution velocity of order 10 6 cm s 1 these velocities are too slow for xenocrysts to be dissolved significantly during magma ascent in dykes but are sufficient for cm size crystals to dissolve in the interior of a convecting magma chamber larger crystals are likely to accumulate at the chamber s roof where free convection is predicted to dissolve them at velocities of order 10 7 cm s 1 in an appendix the dissolution of the chamber s walls is also considered and a velocity of order 10 8cm s 1 is predicted

lithological and hydrological controls on water composition evaporite dissolution and glacial weathering in the south central andes of argentina 33 34 s lithological and hydrological influence on fluvial physical and chemical erosion was studied in a glacierized sedimentary basin with high evaporite presence suspended particulate matter spm total dissolved solids tds and major ion concentrations were analysed for 2 years of different hydrologic condition i 2009 2010 q 100 average and ii 2010 2011 q 60 average annual hydrograph was simple regime type with one peak in summer related to snow melting the intra annual spm and tds variations were directly and inversely associated to q respectively snow chemistry showed continental influence na ca2 0 17 and atmospheric input of tds was 1 of the total exported flux river water was highly concentrated in ca2 and so42 4 mmol l 1 and in na and cl 3 mmol l 1 ca2 so42 and na cl molar ratios were 1 and related to q directly and inversely respectively major ion relationships suggest that river chemistry is controlled by evaporite gypsum and halite dissolution having a summer input from sulfide oxidation and carbonate dissolution and a winter input from subsurface flow loaded with silicate weathering products this variation pattern resulted in nearly chemostatic behaviour for ca mg2 and so42 whereas na cl and sio2 concentrations showed to be controlled by dilution concentration processes during the 2009 2010 hydrological year the fluxes of water spm and tds registered in the snow melting high q season were respectively 71 92 and 67 of the annual total whereas for equal period in 2010 2011 56 of water 86 of spm and 54 of tds annual fluxes were registered the spm fluxes for 2009 2010 and 2010 2011 were 1 19 106 and 0 79 106 t year 1 whereas tds fluxes were 0 68 106 and 0 55 106 t year 1 respectively export rates for 2009 2010 were 484 t km2 year 1 for spm and 275 t km2 year 1 for tds these rates are higher than those observed in glacierized granite basins and in non glacierized evaporite basins suggesting a synergistic effect of lithology and glaciers on physical and chemical erosion copyright 2014 john wiley sons ltd

reply to comment by r francois et al on do geochemical estimates of sediment focusing pass the sediment test in the equatorial pacific further explorations of 230th normalization

dissolution of quartz albite and orthoclase in h2o saturated haplogranitic melt at 800 c and 200 mpa diffusive transport properties of granitic melts at crustal anatectic conditions we have conducted experiments on dissolution of quartz albite orthoclase and corundum into h2o saturated haplogranite melt at 800 c and 200mpa over a duration of 120 1488h with the aim of ascertaining the diffusive transport properties of granitic melts at crustal anatectic temperatures cylinders of anhydrous starting glass and a single mineral phase quartz or feldspar were juxtaposed along flat and polished surfaces inside gold or platinum capsules with 10 wt added h2o concentration profiles in glass quenched melt perpendicular to the mineral glass interfaces and comparison with relevant phase diagrams suggest that melts at the interface are saturated in the dissolving phases after 384h and with longer durations the concentration profiles are controlled only by diffusion of components in the melt the evolution of the concentration profiles with time indicates that uncoupled diffusion in the melt takes place along the following four linearly independent directions in oxide composition space sio2 n a2o and k2o axes si na and k eigenvectors respectively and a direction between the al2o3 na2o and k2o axes al eigenvector such that the al na molar ratio is equal to that of the bulk melt and the al na k molar ratio is equal to the equilibrium asi mol al2o3 na2o k2o of the melt experiments in which a glass cylinder was sandwiched between two mineral cylinders quartz and albite quartz and k feldspar or albite and corundum tested the validity of the inferred directions of uncoupled diffusion and explored longrange chemical communication in the melt via chemical potential gradients the application of available solutions to the diffusion equations for the experimental quartz and feldspar dissolution data provides diffusivities along the directions of the si eigenvector and al eigenvector of 2 0 2 8 10 15 m 2 s and 0 6 2 4 10 14 m 2 s respectively minimum diffusivities of alkalis 3 9 10 11 m 2 s are orders of magnitude greater than the tetrahedral components of the melt the information provided here determines the rate at which crustal anatexis can occur when sufficient heat is supplied and diffusion is the only mass transport mixing process in the melt the calculated diffusivities imply that a quartzo feldspathic source rock with initial grain size of 2 3mm undergoing hydrostatic h2o saturated melting at 800 c infinite heat supply could produce 20 30 vol of homogeneous melt in less than 1 10 years slower diffusion in h2o undersaturated melts will increase this time frame

patchy deposits of cenozoic pelagic sediments in the central pacific export of pelagic carbonate tests from surface waters and their deposition at the seafloor plays a significant role in the co 2 cycle and ability of the oceans to absorb atmospheric co 2 sediment 2 3 0 th and 3 he measurements have been interpreted as evidence that significant lateral advection of pelagic material occurs in the water column leading to marked spatial variations in deposition rates and in particular to significant focusing of deposits on the pacific equator we report spatially continuous stratigraphy from two 1000 km seismic lines that show evidence of depositional anomalies near the equator accumulation rates were apparently enhanced locally by a factor of two similar to the proposed modern sediment focusing factors but the anomalies are surprisingly patchy over the 20 m y period analyzed they are not confined to an equatorial region and they are not necessarily found on adjacent seismic profiles these intermediate scale anomalies are 100 km across and represent areas of seafloor that received more deposits for one period less in following periods and vice versa variogram analysis was used to determine how the spatial scales of deposition changed over the neogene the period when the spatial scale of depositional variability was largest correlates with hiatuses in drill cores a correlation that we interpret as caused by enhanced and spatially heterogeneous carbonate dissolution at that time the study suggests that seismic stratigraphy has the potential to reveal spatial patterns related to unsteady bottom water flow and chemistry

thorium 230 normalized particle flux and sediment focusing in the panama basin region during the last 30 000 years 1 application of the 230 th normalization method to estimate sediment burial fluxes in six cores from the eastern equatorial pacific eep reveals that bulk sediment and organic carbon fluxes display a coherent regional pattern during the holocene that is consistent with modern oceanographic conditions in contrast with estimates of bulk mass accumulation rates mars derived from core chronologies two nearby sites less than 10 km apart which have different mars show nearly identical 230 th normalized bulk fluxes focusing factors derived from the 230 th data at the foot of the carnegie ridge in the panama basin are 2 in the holocene implying that lateral sediment addition is significant in this part of the basin new geochemical data and existing literature provide evidence for a hydrothermal source of sediment in the southern part of the panama basin and for downslope transport from the top of the carnegie ridge the compilation of core records suggests that sediment focusing is spatially and temporally variable in the eep during oxygen isotope stage 2 ois 2 from 13 27 ka bp focusing appears even higher compared to the holocene at most sites similar to earlier findings in the eastern and central equatorial pacific the magnitude of the glacial increase in focusing factors however is strongly dependent on the accuracy of age models we offer two possible explanations for the increase in glacial focusing compared to the holocene the first one is that the apparent increase in lateral sediment redistribution is partly or even largely an artifact of insufficient age control in the eep while the second explanation which assumes that the observed increase is real involves enhanced deep sea tidal current flow during periods of low sea level stand

particle dynamics as controlled by the flow field of the eastern equatorial pacific abstract profiles made during the jgofs egpac october 1992 time series cruise to the equator with a large aggregate profiling system laps recorded the concentration and size distribution of particles in the marine snow size range 0 5 mm diameter profiles were made routinely at local midnight during the twenty day occupation of the time series station on the equator the laps data set when combined with the ctd transmissometer data set from the egpac program s intensive profiling operation reveals a complex dynamic of particle production and aggregation driven by the equatorial flow field during the cruise the influence of the passage of a tropical instability wave tiw was observed in the transmissometer aggregate and temperature salinity data sets a peak in particle production rate occurred in conjunction with the maximum shoaling of the thermocline and a minimum in the aggregate volume concentration subsequently the particle load in the surface water increased followed by an increase in the aggregate abundance quasi oligotrophic conditions on the equator subsurface particle and aggregate maxima and decreased particle production rates toward the end of the time series corresponded to the appearance of stratified low salinity water characteristic of more northerly conditions the variations in temperature and salinity fields are ascribed to the passage of a tiw in sequence the trailing edge the northwestward flowing cool cusp water and the convergent front current meters at the equator recorded a rotational flow at 80 m with a shift from southeastward to northeastward flow during this sequence a simple conceptual model of meridional flow field is presented in which poleward transport of the upwelled water from the equator returns at shallow depths to mix with the euc the signature of this return flow is reflected in the decrease in the vertical gradients of nutrients and oxygen at the equator with respect to the poleward gradients and a subsurface particle maximum below the euc the flow field s effect on the distribution of particles is reflected in the meridional pattern of the sediment accumulation rate murray and leinen 1996 the return flow of particles to the equator is reflected in the maximum in accumulation rate near the equator the longterm influence of tiw s is reflected in the asymmetry of the accumulation rates across the equator as described by murray and leinen 1996 with the maximum accumulation rate found south of the equator a local minimum in accumulation rate at approximately 2 n and a local maximum near 4 n

time scales of magmatic processes new insights from dynamic models for magmatic assimilation we present a computational model that predicts the consequences of time dependent isenthalpic assimilation fractional crystallization afc our model combines an existing paradigm for fractional crystallization based on equilibrium thermodynamics with a kinetic model for predicting rates of mineral dissolution the isenthalpic constraint directly links the sensible heat of the magma and the latent heat of crystallization to the energy necessary for assimilation thus we predict liquid lines of descent rates of crystallization rates of cooling and ratios of assimilation to crystallization r as a function of time model simulations predict the time scale of afc processes weeks to years and show the extent to which temperature and composition of the assimilant control these time scales

enhanced sedimentation along the equator in the western pacific measurements on cores from the ontong java plateau demonstrate that on equator sediment accumulates more 230th than is produced in the overlying water column in contrast cores from 3 8 n accumulate an amount of excess 230th more nearly equal to that produced in the overlying water column taken together with the observation that both the caco3 and non caco3 components of the sediment accumulate at approximately twice the rate in on equator than in off equator cores broecker et al 1999 this requires either that the rain of the larger amount of organic matter generated above the equatorial upwelling plume entrains excess clay and 230th during its fall to the sea floor or that physical transport processes either in the upper ocean or near the sea bed redistribute sediments in such a way that they preferentially accumulate in a narrow 1 latitude equatorial centered belt

geochemistry of the amazon 1 precipitation chemistry and the marine contribution to the dissolved load at the time of peak discharge analyses of precipitation and surface water are used to estimate the fluxes of marine cyclic salts through that part of the amazon river system draining past obidos 80 of the basin at the time of peak discharge in june amazon precipitation chemistry can be devided into two principal components marine and terrestrial the marine component determined from analyses of marine rain consists of na k mg ca and cl in approximately sea salt proportions with s doubly enriched the excess sulfur is probably derived from gas phase inputs the terrestrial component makes an important contribution of k ca s and n much of which can be related to biological emissions the emission of reduced sulfur in the marine and terrestrial environment and nitrogen in the terrestrial environment is responsible for a natural acid rain in the amazon region with a ph from 4 7 to 5 7 this is about one tenth the acidity of polluted urban rain the chloride content of lowland rivers which drain regions lacking significant geologic sources of chloride shows a systematic decrease in chloride with increasing distance from the ocean this trend is used to define the cyclic salt background for amazonian surface waters cyclic salts in general make only a minor contribution relative to terrestrial inputs to the chemistry of amazon basin rivers even those draining intensely weathered terrains an estimated 17 6 cl 6 9 na 1 3 mg 3 6 s 0 4 k and 0 1 ca of the dissolved load at obidos during peak discharge is cyclic

radiocarbon age offsets of foraminifera resulting from differential dissolution and fragmentation within the sedimentary bioturbated zone 1 shells of coexisting species of planktonic foraminifera from the ontong java plateau reveal radiocarbon age offsets of up to 2200 years similar offsets are found between fragments and whole shells of single species steady state modelling of dissolution and bioturbation within the sedimentary mixed layer predicts age differences of up to several kiloyears due to the interplay between differential dissolution and fragmentation of foraminifer shells and bioturbation the observation that fragile foraminiferal shells are systematically older than those of more robust species is more difficult to explain mechanisms of chemical erosion interface dissolution and sediment redistribution are all apparently unable to explain this phenomenon a possible solution is presented in which a particular species may be represented by two distinct classes of shells which are more or less robust in this case differential dissolution and fragmentation causes an increase in the mean age as the fragile class contributes less to the remaining intact shells this study highlights the vulnerability of low sedimentation rate cores to the effects of dissolution and bioturbation

modeling of gas driven magmatic overturn tracking of phenocryst dispersal and gathering during magma mixing 1 we present a combined multiphase numerical and crystal tracking approach that provides a framework to investigate the transport and zoning of crystals associated with a gas driven mixing event mixing in compositionally intermediate to silicic magmatic systems is often initiated by gas exsolution in the recharging magma causing a density inversion and subsequent overturn the overturn is simulated for a range of bubble volume fractions bubbles and therefore indirectly for a range of reynolds numbers re all simulations show chaotic flow dynamics with fast overturn timescales of minutes to hours the large scale mixing is inefficient during a single overturn resulting in a continuously stratified system with respect to bubble volume fraction the crystal tracking algorithm provides us with information on the small scales i e 10 cm on this length scale we observe gathering of different crystals during the overturn that typically ranges on the order of tens of meters thus a complex crystal population may arise within a single overturn this gathering and dispersal of crystals is strongest and most uniform for high re for low re crystal populations are characterized by less gathering of crystals that originated from distal portions of the magma body during the overturn the crystals pass through environments of changing chemical potential we apply the damkohler number da which compares the crystallization or dissolution to the advection timescale results show an asymmetry between crystallization and dissolution crystallization times are too slow during gas driven overturn to record transient changes in chemical potential crystals most likely only record their initial as well as their final chemical environment in contrast dissolution and advection rates are of similar order suggesting potential dissolution during the overturn on the basis of the results for gas driven overturn we expect that slower physical mixing processes may be continuously recorded in the zonation pattern of the crystal phases as long as the changes in chemical potential produce crystal growth

assessment of the hydrogeochemical characteristics of groundwater in two aquifer systems in cumra plain central anatolia located in a semi arid climate cumra konya plain is one of the most important agricultural regions in turkey groundwater is the major source for agricultural domestic and other water related activities due to the insufficiency of surface water as groundwater is the only major source of water in this area it is important to know the effects of geological formations and anthropogenic activities on groundwater chemistry this study was carried out with the objective of identifying the hydrogeochemical characteristics and processes controlling the groundwater chemistry in cumra plain central anatolia turkey the study area is comprised of two main aquifers which are the semi confined aquifer of the neogene age and the unconfined aquifer of the quaternary age to identify the hydrogeochemical characteristics of groundwater in two aquifer systems and to understand the major factors and mechanisms controlling the groundwater chemistry graphical plots mineral saturations and multivariate statistical analysis of chemical constituents in the groundwater were used study results show that groundwater is generally neutral to slightly alkaline in nature with a ph ranging from 6 67 to 8 10 and the dominance of ions is in the order of ca2 mg2 na k for the neogene aquifer and hco3 so4 2 cl no3 mg2 ca2 na k and so4 2 hco3 cl no3 for the quaternary aquifer while the chemical composition of groundwater in the neogene aquifer is mainly controlled by water rock interaction including dissolution of carbonates and gypsum calcite precipitation and de dolomitization the main geochemical processes in the quaternary aquifer are reverse ion exchange evaporation dissolution of carbonates gypsum and soil salts calcite precipitation and silicate weathering the mechanism controlling groundwater chemistry in the neogene aquifer is actually regulated by the geogenic processes water rock interaction rather than by anthropogenic activities however the mechanism controlling groundwater chemistry in the quaternary aquifer is regulated by both geogenic processes and anthropogenic activities in addition anthropogenic nitrogen pollution in the study area is currently not serious but evaporation and leaching of soil salts due to anthropogenic activities increase the concentrations of ions in the quaternary aquifer

buseckite fe zn mn s a new mineral from the zaklodzie meteorite buseckite ima 2011 070 fe zn mn s is the fe dominant analog of wurtzite a new member of the wurtzite group discovered in zaklodzie and an ungrouped enstatite rich achondrite the type material occurs as single crystal grains 4 20 m in size in contact with two or more of enstatite plagioclase troilite tridymite quartz and sinoite low ni iron martensitic iron schreibersite keilite cristobalite and graphite which are also present in the type sample are not observed to be in contact with buseckite buseckite is black under diffuse illumination and nearly opaque grayish brown in transmitted light the mean chemical composition of buseckite as determined by electron microprobe analysis of the type material is wt s 35 84 fe 28 68 zn 23 54 mn 10 04 mg 1 18 sum 99 28 leading to an empirical formula calculated on the basis of 2 atoms of fe 0 46 zn 0 32 mn 0 16 mg 0 04 0 99 s 1 01 electron backscatter diffraction patterns of buseckite are a good match to that of synthetic zn 0 558 fe 0 442 s with the p6 3mc structure showing a 3 8357 c 6 3002 a v 80 27 a3 and z 2 buseckite is likely derived from the breakdown of high temperature pyrrhotite to form troilite and buseckite following the solidification of sulfide rich liquids produced during impact melting of an enstatite rich rock

sediment focusing in the panama basin eastern equatorial pacific ocean abstract age model derived sediment mass accumulation rates mars are consistently higher than 230th normalized mars in the equatorial pacific ocean during the past 25 ka the offset being highest in the panama basin suggests a significant role for deep sea sediment redistribution i e sediment focusing in this region here we test the hypothesis that downslope transport of sediments from topographically high regions that surround the panama basin is the cause of higher than expected xs230th inventories over the past 25 ka in the deeper parts of the basin we find little difference in xs230th inventories between the highest and lowest reaches of the basin furthermore there is no correlation between xs230th derived sediment focusing factors and water depth which suggests that the topographic highs do not serve as a source of xs230th a spatial analysis suggests that there may be an enhanced scavenging effect on xs230th concentrations in sediment closest to the equator where productivity is the highest although further data is necessary to corroborate this at the equator xs230th derived focusing factors are high and range from about 1 to 5 during the holocene and about 1 to 11 during the last glacial in contrast non equatorial cores show a smaller range in variability from about 0 7 to 2 8 during the holocene and from 0 7 to 3 6 during the last glacial based on 232th flux measurements we hypothesize that the location at which eolian detrital fluxes surpass the riverine detrital fluxes is approximately 300 km from the margin while riverine fluxes from coastal margins were higher during the holocene eolian fluxes were higher during the last glacial

impact of nitrogen fertilizers on the natural weathering erosion processes and fluvial transport in the garonne basin knowledge of the impact of n fertilizers on the weathering erosion processes of soils in intensively cultivated regions is of prime importance nitrification of nh4 fertilizers produces hno3 in the basin of the garonne river enhancing soil degradation their influence on the weathering rates was determined by calculating the consumption rate of atmospheric soil co2 by soil weathering and erosion and its contribution to the total dissolved riverine hco3 this contribution was found to be less than 50 which corresponds normally to a complete carbonate dissolution by carbonic acid suggesting that part of the alkalinity in the river waters is due to carbonate dissolution by an acid other than carbonic acid probably hno3

climatically driven changes in oceanic processes throughout the equatorial pacific 1 the mass accumulation rates of sedimentary components carbonate organic carbon opal barite reactive phosphate iron terrigenous minerals etc are used in many paleoceanographic reconstructions to learn about temporal and spatial changes in surficial earth processes including wind stress and direction oceanic circulation weathering rates marine productivity and ecosystem structure climate change and more in most studies it is assumed desired that the sediment accumulation represents the production and deposition of particles from the overlying water column since substantial horizontal transport imply homogenization of paleoceanographic proxies and little confidence in any paleoceanographic time series in this note we highlight some discrepancies between the different approaches used to reconstruct sediment mass accumulation rates and specifically discuss the consequences of these discrepancies to the reconstruction of paleoproductivity in the equatorial pacific we pose research questions and suggest possible approaches research strategies for the community to solve them

core top 14c ages as a function of latitude and water depth on the ontong java plateau radiocarbon measurements on core tops from the ontong java plateau confirm a previous finding by berger and killingley 1982 that at any given water depth cores taken on the equator have higher accumulation rates and younger core top ages than their off equator counterparts further these new results fortify the conclusion by broecker et al 1991 that the increase in core top radiocarbon age with water depth rules out homogeneous dissolution within the pore waters as the dominant mechanism either most of the dissolution must occur prior to burial or it must occur during the first pass through the respiration co2 rich upper pore waters after which the calcite grains become armored against further dissolution a puzzling aspect of this new data set is that despite the sizable difference in accumulation rate the extent of dissolution as measured by either the caco3 content or the ratio of caco3 in the 150 m size fraction to that in the 63 m fraction is no different off than on the equator in order to reconcile the results of this study with those obtained by hales and emerson 1996 using in situ electrodes it is necessary to call upon calcite armoring

box cores from the equatorial pacific 14c sedimentation rates and benthic mixing abstract carbon 14 determinations on box cores of calcareous ooze from the western and eastern equatorial pacific suggest that patterns of mixed layer ages sedimentation rates and mixed layer thicknesses are controlled by gradients of carbonate dissolution and fertility and by small scale redeposition processes mixed layer ages range from 3000 to 7000 years with a mode between 4000 and 5000 years sedimentation rates range from 0 8 to 2 4 cm 1000 years mixed layer depths calculated according to the box model of mixing range from 7 cm to 16 cm observed thicknesses are about one fourth smaller than calculated ones

boundary scavenging and deep sea sediment dating constraints from excess 230th and 231pa apparent sedimentation rates derived from excess 230th and 231pa in deep sea sediments accumulated during the last 25 000 years in the pacific ocean are mostly lower than the average rates determined by other independent such as 14c and 18o dating methods which may be a consequence of generally higher accumulation rates of aluminosilicate and carbonate during the last glacial that diluted the excess 230th and 231pa activities in glacial sediments the pattern of enhanced scavenging of nuclides in ocean margin areas i e boundary scavenging also changed from the glacial to the holocene fluxes of 230th and 231pa throughout the ocean varied over time responding to changes in the nature and intensity of boundary scavenging which in turn were influenced by changes in particle flux and particle composition the lower intensity of boundary scavenging of 231pa during the last glacial may also have contributed to the lower apparent sediment accumulation rates based on excess 231pa for cores in ocean margin areas