chemistry of hydrothermal fluids from the 17 s active site on the north fiji basin ridge sw pacific abstract in june 1989 a diving cruise of the french submersible nautile was made along the north fiji basin spreading ridge the objective was the geological and geochemical study of the active spreading axis and of the hydrothermal processes discovered during the kaiyo cruise in 1988 active anhydrite chimneys associated with underlaying sulfide deposits were studied in the central spreading ridge the transparent venting fluid showed significant salinity depletion the extrapolated concentrations of all the chemical species in the pure end member showed a signature similar to that of the cl depleted hydrothermal fluid from the ashes vent site in the juan de fuca ridge these features suggest that the present hydrothermal end member resulted from subcritical phase separation which generated a low salinity vapor phase followed by condensation and mixing with normal seawater in the last part of the plumbing system of the vents

terrestrial shallow water hydrothermal outflow characterized from out of space abstract we investigate the potential of satellite imagery to map and monitor the activity of shallow water hydrothermal systems which are often found around volcanic islands for this study we used publicly available data and proprietary worldview 2 satellites images with spectral bands that can penetrate up to water depths of 30 m shallow water hydrothermal sites are visible on satellite imagery primarily with publicly available data demonstrating the potential of satellite imagery to study and monitor shallow water hydrothermal activity we focus our work on volcanic islands showing intense near shore shallow water hydrothermal activity and distinct styles of hydrothermal venting satellite imagery constrains regional outflow geometry and the temporal variability or stability of these systems milos island shows hydrothermal outflow associated with reflective mineral precipitates and or bacterial mats which are stable over time 2010 2014 these outflows locally define polygonal patterns likely associated with hydrothermal convection in porous media in kueishantao island individual hydrothermal plumes charged with particles are visible at the sea surface and display great variability in intensity and distribution of plume sources 2002 2019 worldwide we have identified 15 shallow water hydrothermal sites with satellite imagery that are similar to either the milos system e g vulcano and panarea italy or the kueishantao system numerous sites in pacific volcanic islands this study demonstrates that satellite imagery can be used to map and monitor different types of shallow water hydrothermal systems at regional scale and monitor their evolution satellite data provide not only regional and temporal information on these systems unavailable to date but also the regional context for follow up in situ field data and observations e g instrumental monitoring sampling observations and mapping with divers or auvs to understand both the nature and dynamics of these systems and ultimately the associated fluxes

hydrogeochemistry and stable isotopes of thermal springs earthquake related chemical changes along belice fault western sicily abstract three geothermal systems montevago castellammare alcamo and sciacca are located along the main seismogenetic structures in western sicily concentrations of dissolved species including the gases co 2 n 2 he and the results of stable isotope measurements 18 o d and 13 c tdic in water samples collected from six thermal springs and 28 cold discharges were used to characterise their feeder aquifers and to reveal the relationships between water chemistry and regional seismicity the sciacca thermal springs differ chemically and isotopically from those of montevago and the castellammare alcamo areas the inferred deep end members of the thermal waters of montevago and castellammare alcamo are almost similar suggesting that both systems are fed by carbonate waters and selenite waters a slight contribution 1 3 of seawater during groundwater ascent it is also present the sciacca thermal springs are fed by a deep reservoir comprising a mixture of 50 carbonate water and 50 seawater during ascent towards the surface these waters interact with nacl rich evaporite layers by combination of published and present data significant temporal variations of temperature and some chemical parameters in the thermal waters of western sicily have been recorded these variations were mostly between 1966 and 1969 although the data are discontinuous it is still possible to reveal a direct link between physico chemical changes in the acqua pia and terme selinuntine springs and the 1968 belice valley earthquake within the studied springs two kinds of geochemical behaviour have been recognised the chemistry of the montevago thermal springs was permanently changed in response to changes in the groundwater system water temperature and dissolved so 4 cl na and tds showed minimum values before the earthquake and maximum values after the event almost constant values substantially higher than before were recorded after the seismic event conversely the temporal variations observed in the waters of the terme selinuntine spring from 1965 to 1991 exhibit a transient increase most probably caused by a temporary contribution of deep co 2 rich fluids caused by the strain release during the 1968 earthquake

mobility of mo u as and sb within modern turbidites modern turbidites uranium molybdenum arsenic antimony we present and discuss porewaters and sediment data of mn fe mo u as and sb within four recent turbidites from the capbreton canyon sw france the deposition of turbidites on continental margins exerts strong influence on the fate of trace metals causing trace metal migration and or immobilization the down core distribution of the elements here depends entirely of ongoing diagenetic processes rather than the diffusion of o2 the persistence of fe mn oxides under anoxic conditions led to anoxic reoxidation of numerous species as nh4 reduced s compounds and trace metals metal oxides thus control the immobilization of mo and as in the solid phase and the remobilization of u and sb to the porewaters although the low sulphide production prevents anoxic authigenesis of mo and as reducing conditions below each horizon rich in mn fe oxides resulted in u and sb accumulation the exact mechanisms of sb immobilization are not known but it is most certainly different from that of as the profile shapes of mn and u were used to estimate the age of the turbidite deposits which cannot be determined by conventional radionuclide methods our interpretations however depend on calculations of diffusion coefficient particularly for u a simple diffusive model applied to mn suggested that the age of the latest deposit noted t1 was 22 months this date is close to the time elapsed between the core sampling and the last known turbiditic event in the capbreton canyon i e martin storm 18 months using the u data set and depending on diffusion coefficients used the estimated ages of the deeper layers were 4 7 yr for t2 and 7 5 14 yr for t3 the reliability and precision of this new approach to date sediments at short timescales is limited by the ignorance of a precise value for u diffusion coefficient reducing uncertainty on u diffusion coefficient will greatly support application of the proposed approach

volcanology and petrology of volcanic products from the island of milos and neighbouring islets abstract new geochronological and volcanological data from volcanics of the island group of milos south aegean active volcanic arc allow four main cycles of volcanic activity to be distinguished ranging in age between 3 5 and 0 1 m y b p the oldest volcanic activity consists almost totally of pyroclastics and submarine products followed by subaerial ones the eruptive centers migrated in time and concentrated during the most recent volcanic phase in the central part of milos and on the island of antimilos the oldest products are dominated by andesites and dacites while the most recent ones mainly consist of rhyolites the volcanic evolution and the geochemical characters of the erupted products suggest that the feeding system of the oldest volcanism was located in the deep continental crust where contamination and fractional crystallization jointly occurred the younger cycle of volcanic activity was fed from small and relatively shallow magma chambers where contamination processes played a minor role these magma bodies are considered to responsible for the shallow thermal anomaly giving rise to the high enthalpy field on milos

on the structure of the regional scale circulation over central africa seasonal evolution variability and mechanisms abstractatmospheric circulation over central africa is dominated by the tropical easterly jet the african easterly jet and the low level westerly jet in the lower troposphere a zonal overturnin

bromide chloride fractionation in seafloor hydrothermal fluids from 9 10 n east pacific rise hydrothermal fluids collected from 9 10 n epr during 5 cruises between 1991 and 1994 were analyzed for br and cl the chlorinity of these fluids ranges between 32 6 and 860 mmol kg in comparison to local seawater values of 540 mmol kg these very low chlorinity fluids some with temperatures high enough to be within the vapor stability field were collected following a volcanic eruption in 1991 1 although fluids with chlorinities less than 250 mmol kg had been sampled once previously at axial volcano 2 the vent fluid chlorinities at 9 10 n epr were much lower than at axial volcano fluids with cl 250 mmol kg hadbr cl ratios identical to seawater in agreement with previous studies in contrast fluids with cl 250 mmol kg collected from this area hadbr cl ratios as much as 40 less than the seawater value bromide depletions observed in the low chlorinity fluids from 9 10 n epr were probably the result of fractionation of br from cl during subcritical phase separation this fractionation process appeared to be limited to fluids with cl 250 mmol kg and to require open system phase separation to produce vapors with cl 250 mmol kg at pressure and temperature conditions appropriate for 9 10 n epr requires conditions that are close to the critical point where the properties of the vapor and liquid phases are quite similar resulting in lack of fractionation in thebr cl ratio between the two phases

the use of mixing models and chemical geothermometers for estimating underground temperatures in geothermal systems abstract application of various chemical geothermometers and mixing models indicate underground temperatures of 260 c 280 c and 265 c in the geysir hveravellir and landmannalaugar geothermal fields in iceland respectively mixing of the hot water with cold water occurs in the upflow zones of all these geothermal systems linear relations between chloride boron and 18o constitute the main evidence for mixing which is further substantiated by chloride silica and sulphate relations in the geysir and hveravellir fields a new carbonate silica mixing model is proposed which is useful in distinguishing boiled and non boiled geothermal waters this model can also be used to estimate underground temperatures using data from warm springs this model as well as the chloride enthalpy model and the na li and co2 gas geothermometers invariably yield similar results as the quartz geothermometer sometimes also does by contrast the na k and the na k ca geothermometers yield low values in the case of boiling hot springs largely due to loss of potassium from solution in the upflow the results of these geothermometers are unreliable for mixed waters due to leaching subsequent to mixing

evidence for basin restriction during syn collisional basin formation in the silurian arisaig group nova scotia the arisaig basin in nova scotia canada provides a regional sedimentary record of an early silurian basin subsidence on the microcontinent of avalon the lower members of the arisaig group beechill cove and lower ross brook formations are likely to be deposited in a basin formed during syn to post collisional rifting subsidence driven by the collision of avalon and baltica the evolution of this constricted basin can be tracked by examining the geochemistry of the sedimentary rocks deposited within the basin here we report on the chemostratigraphy of the arisaig group a series of siliciclastics with a focus on understanding the redox chemistry during sedimentation the trace and major element geochemistry of this group provides insight into the oceanographic and geological processes that were influencing its depositional environment in particular concentrations of u v mo ni cd and pb indicate regional shifts in ocean redox state which serve as a proxy for changes in ocean circulation and regional tectonic activity we find evidence for anoxic conditions near the base of ross brook formation and attribute this anomaly in redox status to a significant change in physical mixing in the region trace element concentrations indicate that this anoxic event was associated with poor circulation rather than elevated productivity and organic matter burial based on these data we confirm that these sediments are deposited in a tectonically formed basin during a period of limited ocean circulation

some comparative marine chemistries of rhenium gold silver and molybdenum abstract four metals re au ag and mo whose dissolved forms in seawater can potentially be reduced to insoluble states have been measured in a variety of solids depositing under anoxic conditions hydrothermal sulfides coastal sediments and phosphorites for comparative purposes these elements have also been determined in ferromanganese minerals and pelagic sediments which have accumulated under oxidizing conditions rhenium appears to be a unique sentinel for identifying reducing depositional environments where enrichments of greater than three orders of magnitude above crustal concentrations are found molybdenum follows re in these sediments but mo is enriched also in those that accumulate under oxidizing conditions the reported mo crustal concentrations appear low in comparison to our measured sedimentary values gold and ag are concentrated in hydrothermal deposits and sulfides appear to be involved in the precipitation of these elements coastal sediments adjacent to a domestic outfall of los angeles california contain extraordinary high accumulations of anthropogenic au ag and pt the study seeks an understanding of the mobilities and sinks of these metals in the marine environment during the major weathering cycle further anthropogenic contributions to their sedimentary concentrations are identified

the geochemistry of fluids from an active shallow submarine hydrothermal system milos island hellenic volcanic arc abstract geothermal activity in the aegean island of milos greece associated with island arc volcanism is abundant both on and off shore hydrothermal fluids venting from several sites mainly shallow submarine up to 10 m but also just above seawater level in one locality were sampled over four summer field seasons some of the discharging fluids are associated with the formation of hydrothermal edifices overall the main characteristics of the hydrothermal fluids are low ph and variable chlorinity the lowest recorded ph was 1 7 and chlorinity ranged from 0 1 to 2 5 times that of seawater the highest fluid temperatures recorded on site were 115 c two main types of fluids were identified low chlorinity fluids containing low concentrations of alkalis potassium lithium sodium and calcium and high concentrations of silica and sulphate and high chlorinity fluids containing high concentrations of alkalis and calcium and lower concentrations of silica and sulphate the type locality of the high chlorinity fluids is shallow submarine in palaeochori near the east end of the south coast of the island whereas the type locality of the low chlorinity fluids is a cave to the west of palaeochori the two fluid types are therefore often referred to as submarine and cave fluids respectively both fluid types had low magnesium and high metal concentrations but were otherwise consistently different from each other the low chlorinity fluids had the highest cobalt nickel aluminium iron and chromium up to 1 6 m 3 6 m 1586 m 936 m and 3 0 m respectively and the high chlorinity fluids had the highest zinc cadmium manganese and lead up to 4 1 m 1 0 m 230 m and 32 m respectively geochemical modelling suggests that metals in the former are likely to have been transported as sulphate species or free ions and in the latter as chloride species or free ions isotopic values for both water types range between d 12 to 33 and 18 o 1 2 to 4 6 the range of fluid compositions and isotopic contents indicates a complex history of evolution for the system both types of fluids appear to be derived from seawater and thus are likely to represent end members of a single fluid phase that underwent phase separation at depth

depletion of a brine layer at the base of ridge crest hydrothermal systems the variable salinity of fluid venting from mid ocean ridges is indicative of mixing between hydrothermal seawater and fluids that have undergone supercritical phase separation in order to study the stability of a brine saturated layer that may form in the lowermost part of the hydrothermal system we have performed numerical simulations of a system that has returned into the subcritical regime for typical geological parameters it is shown that the interface between the brine layer and the overlying fluids is not very stable but vanishes by one of two dynamical mechanisms convective breakdown or vertical migration this contradicts the conventional picture of a steady layered convective system in which the brine is depleted only by dispersion and diffusion across the interface the depletion mechanism depends on the fluid dynamical stability of the brine layer convection within the brine layer results either in the convective breakdown for low excess salinity of the brine as compared to seawater or the upward migration of the interface for higher excess salinities consequently the depletion times are much shorter than for models with pure dispersion diffusion across the interface if the brine layer is static high chlorinity liquid is entrained slowly by the convecting overlying fluids leading to downward migration of the interface this gradual depletion of the brine layer results in almost constant vent salinities in agreement with measured salinities of chronic high chlorinity vents fl 2000 elsevier science b v all rights reserved

chemical characteristics of newly discovered black smoker fluids and associated hydrothermal plumes at the rodriguez triple junction central indian ridge abstract the chemical characteristics of hydrothermal fluids in the indian ocean have been revealed for the first time a hydrothermal field called the kairei field including active black smoker chimneys was discovered by rov kaiko dives at 25 19 17 s 70 02 40 e 2450 m depth on the southwestern flank of an off axis knoll located 15 miles north of the rodriguez triple junction central indian ridge after detailed tow yo surveys of the hydrothermal plume distribution the temperature of the fluid expelled from the most active chimney was almost stable 359 360 c throughout three successive days of fluid sampling the endmember fluid has a chemical composition similar to the hydrothermal fluids sampled from sediment starved mid ocean ridges in the pacific and the atlantic oceans suggesting typical interactions between hot fluid and mid ocean ridge basalts in the subseafloor reaction zone

processes controlling the heavy metal distribution in pacific ferromanganese nodules and crusts the ferromanganese precipitates existing in deep sea waters of the pacific consist of two types of deposits 1 nodules mainly are distributed in pelagic basins beneath the ccd calcite compensation depth where the rate of sedimentation is low 2 polymetallic encrustations are formed on exposed seamount rocks where currents prevent normal sediment accumulation nodules being formed in areas bordering the equatorial zone of high biological productivity grow by two different processes a early diagenetic growth by supply of metals and metal compounds from pore water and b hydrogenetic growth by supply of colloidal particles from near bottom seawater these processes lead to different kinds of oxide and different metal contents

drilling shallow water massive sulfides at the palinuro volcanic complex aeolian island arc italy a subseafloor replacement style barite and sulfide occurrence was drilled in shallow waters at the palinuro volcanic complex the northernmost aeolian arc volcano in the tyrrhenian sea italy using a lander type drilling device 11 successful drill holes yielded a total of 13 5 m of core from a sediment filled depression located at a water depth of 630 to 650 m the longest continuous drill core recovered consists of 4 84 m of massive to semimassive barite and sulfides with abundant late native sulfur overprint seafloor observations suggest that the hydrothermal system associated with the formation of the subseafloor barite and sulfide ore zone is still active although black smoker activity does not occur on the seafloor the recovered drill core shows that the subseafloor deposit is zoned with depth the top of the mineralized zone is comprised of a variably silicified vuggy barite sulfide facies that shows notable polymetallic metal enrichment while the deeper portion of the mineralized zone is dominated by massive pyrite having distinctly lower base and precious metal grades metal zonation of the barite and sulfide deposit is related to the evolution of the hydrothermal fluids in space and time the barite cap and the massive pyrite present in the deeper portion of the mineralized zone appear to have formed early in the paragenesis during the main stage of the mineralization the barite cap was brecciated and cemented by a polymetallic assemblage of barite and pyrite with minor chalcopyrite and tetrahedrite trace famatinite and rare cinnabar lower temperature precipitates formed during the main stage of mineralization include sphalerite galena pyrite opal a and barite which are associated with traces of pb sb as sulfosalts such as bournonite seligmannite or semseyite a distinct mineral assemblage of fine grained anhedral enargite hypogene covellite chalcopyrite and galena is commonly associated with colloform sphalerite galena and pyrite as a late phase of this main stage colloform pyrite and marcasite are the last sulfides formed in the paragenetic sequence the deposit is interpreted to have formed from fluids having an intermediate sulfidation state although excursions to high and very high sulfidation states are indicated by the presence of abundant enargite and hypogene covellite laser ablation and conventional sulfur isotope analyses show that pyrite formed close to the seafloor within the zone of polymetallic metal enrichment has a variable sulfur isotope composition 34s 39 to 3 whereas a more narrow range is observed in the massive pyrite at depth 34s 10 to 0 similar variations were also documented for the late native sulfur overprint overall the negative sulfur isotope ratios at depth the intermediate to very high sulfidation conditions during mineralization and the abundance of native sulfur suggest contributions of magmatic volatiles to the mineralizing fluids from a degassing magma chamber at depth biological processes are interpreted to have played a major role during late stages of ore formation the combination of a subseafloor replacement deposit with a massive to semimassive barite cap rock overlying massive pyrite the intermediate to high sulfidation characteristics and the strong biological influence on the late stages of mineralization are distinct from other modern seafloor massive sulfide deposits and represents a style of submarine mineralization not previously recognized in a modern volcanic arc environment the barite and sulfide occurrence at palinuro shares many characteristics with porphyry related base metal veins and intermediate sulfidation epithermal deposits suggesting that metallogenic processes associated with arc related magmatic hydrothermal systems are not restricted to the subaerial environment

removal of230th and231pa from the open ocean concentrations of230th and231pa were measured in particulate matter collected by sediment traps deployed in the sargasso sea site s2 the north equatorial atlantic site e and the north equatorial pacific site p as well as in particles collected by in situ filtration at site e concentrations of dissolved th and pa were determined by extraction onto manganese dioxide adsorbers at site p and at a second site in the sargasso sea site d dissolved230th 231pa activity ratios were 3 6 at sites p and d in contrast for all sediment trap samples from greater than 2000 m unsupported230th 231pa ratios were 22 35 average 29 7 ratios were lower in particulate matter sampled at shallower depths particles filtered at 3600 m and 5000 m at site e had ratios of 50 and 40 results show that suspended particulate matter in the open ocean preferentially scavenges th relative to pa most of the230th produced by decay of234u in the open ocean is removed by adsorption to settling particulate matter in contrast less than 50 of the231pa produced by decay of235u is removed from the water column by this mechanism mixing processes transport the remainder to other sinks

iridium in mississippi river suspended matter and gulf of mexico sediment the suggestion1 that a meteorite impact at the end of cretaceous time the cretaceous tertiary boundary caused the extinction of many groups of organisms and left an anomalous iridium concentration in sediments has stimulated interest in both the extinctions and in the geochemistry of ir refs 2 6 the geochemical behaviour of ir is not well understood partly because of the scarcity of concentration data for common rocks soils and waters here we report ir abundances in mississippi river suspended matter mrsm and gulf of mexico gom sediments and suggest that these values may be representative of much of the upper continental crust that accessible to rock weathering these data imply that the processes leading to the well known enrichment of iridium in deep sea sediments7 are similar to those which enrich elements such as ni and co

cobalt and platinum rich ferromanganese crusts and associated substrate rocks from the marshall islands abstract ferromanganese crusts cover most hard substrates on seafloor edifices in the central pacific basin crust samples and their associated substrates from seven volcanic edifices of cretaceous age along the ratak chain of the marshall islands are discussed the two most abundant substrate lithologies recovered were limestone dominantly fore reef slope deposits and volcanic breccia composed primarily of differentiated alkalic basalt and hawaiite clasts in a phosphatized carbonate matrix the degree of mass wasting on the slopes of these seamounts is inversely correlated with the thickness of crusts crusts are generally thin on limestone substrate away from areas of active mass wasting processes and large atolls crusts may be as thick as 10 cm maximum the dominant crystalline phase in the marshall islands crusts is mno 2 vernadite high concentrations of cobalt platinum and rhodium strongly suggest that the marshall islands crusts are a viable source for these important metals many metals and the rare earth elements vary significantly on a fine scale through most crusts thus reflecting the abundances of different host mineral phases in the crusts and changes in seawater composition with time high concentrations of cobalt nickel titanium zinc lead cerium and platinum result from a combination of their substitution in the iron and manganese phases and their oxidation potential

hydrothermal gases offshore milos island greece hydrothermal fluids emerge from the seafloor of paleohori bay on milos the gases in these fluids contain mostly co2 but ch4 concentrations up to 2 are present the stable carbon isotopic composition of the co2 near 0 indicates an inorganic carbon source dissociation of underlying marine carbonates the carbon and hydrogen isotopes of most ch4 samples are enriched in the heavy species delta 13c 9 4 to 17 8 per mille sign delta d 102 to 189 per mille sign which is believed to be characteristic for an abiogenic production of ch4 by co2 reduction fischer tropsch reactions depletions in the deuterium content of three ch4 samples to 377 are probably caused by unknown subsurface rock alteration processes secondary hydrogen isotope exchange processes between methane hydrogen and water are most likely responsible for calculated unrealistic methane formation temperatures we show that excess helium slightly enriched in 3he is present in the hydrothermal fluids emerging the seafloor of paleohori bay when the isotopic ratio of the excess component is calculated a 3he 4heexcess of 3 6 10 6 is obtained this indicates that the excess component consists of about one third of mantle helium and two thirds of radiogenic helium we infer that the mantle derived component has been strongly diluted by radiogenic helium during the ascent of the fluids to the surface

dissolved aluminium in the tamar estuary southwest england abstract distributions of dissolved al in the tamar estuary have been recorded through spring neap tidal cycles in winter and summer dissolved al is a highly reactive constituent in this estuary undergoing net removal in the very low salinity region and net input to the mid estuary the extent of both the depletion and the augmentation varied systematically with tidal energy input indicating that tidal sediment disturbance was the principal controlling agency these field data supported by the results of laboratory simulations show that the removal is regulated by sorption onto resuspended sediment particles which dominates kinetically over authigenic aluminosilicate formation removal of dissolved al by flocculation of riverborne colloids is not significant the mid estuarine input is consistent with dissolution of authigenic aluminosilicate following net remobilization of estuarine sediment the internal cycling of al in the estuary generated by these processes alters both the time course and the soluble particulate balance of the riverine discharge of al to the adjacent coastal water

gradients in the composition of hydrothermal fluids from the endeavour segment vent field phase separation and brine loss hydrothermal fluid samples collected in 1984 1987 and 1988 from a large vent field near 47 57 n on the endeavour segment of the juan de fuca ridge jfr have been analyzed for major and minor elements and gases there are of the order of 100 individual smoker vents on 10 large sulfide structures which are localized along faults and fault intersections across the vent field each sulfide structure has a characteristic fluid composition which varies very little from one vent orifice to the next or from year to year on a given structure however there are large gradients in fluid composition across the vent field with endmember chlorinity increasing from 255 mmol kg in the sw to 505 mmol kg in the ne end member concentrations of major elements are well correlated with chlorinity and endmember volatile concentrations in the lowest chlorinity fluids are approximately twice as high as in the highest chlorinity fluids the gradients in composition across the vent field and measured vent fluid temperatures 400 c are consistent with supercritical phase separation and loss of brine phase below the seafloor the factor of 2 variation in co2 and h2s is larger than expected for loss of a very high chlorinity brine concentrations of iron and manganese are not positively correlated with chlorinity suggesting that temperature and ph are more important in controlling metal solubility elevated ammonia and bromide chloride ratios indicate that there has been subseafloor interaction between the hydrothermal fluids and organic matter and high boron concentrations point to a sedimentary source

rare earth elements in the water column of lake vanda mcmurdo dry valleys antarctica abstract we present data on the composition of water from lake vanda antarctica vanda and other lakes in the mcmurdo dry valleys of antarctica are characterized by closed basins permanent ice covers and deep saline waters the meromictic lakes provide model systems for the study of trace metal cycling owing to their pristine nature and the relative simplicity of their biogeochemical systems lake vanda in the wright valley is supplied by a single input the onyx river and has no output water input to the lake is balanced by sublimation of the nearly permanent ice cap that is broken only near the shoreline during the austral summer the water column is characterized by an inverse thermal stratification of anoxic warm hypersaline water underlying cold oxic freshwater water collected under trace element clean conditions was analyzed for its dissolved and total rare earth element ree concentrations by inductively coupled plasma mass spectrometry depth profiles are characterized by low dissolved ree concentrations la ce

acidic and sulfate rich hydrothermal fluids from the manus back arc basin papua new guinea hot 88 120 c and acidic ph 2 1 hydrothermal fluids rich in sulfate were discovered venting in the desmos caldera depth 1926 m eastern manus back arc basin bismarck sea surrounded by papua new guinea the abundant sulfate 32 8 m m higher than the seawater value of 28 m m with elemental sulfur deposition around the vents and remarkably low d h 2 o and 34 s h 2 s values 8 1 and 5 6 respectively are suggestive of the incorporation of a magmatic fluid and the disproportionation of the exsolved so 2 from a magma body the desmos fluid may be similar in origin to the acidic sulfate chloride hot springs associated with subaerial volcanic activity in contrast to the typical hydrothermal end member mg concentration of 0 the desmos fluids are rich in mg 46 52 m m probably because of mg dissolution by acid attack upon magnesium silicate minerals

metal forms in sediments from arctic coastal environments in kandalaksha bay white sea under separation processes abstract this study focuses on sediments from small restricted exchange environments along the karelian shore of kandalaksha bay white sea russian arctic which are known as separating basins and are characterised by contrasting oxidising conditions within the water column and the occurrence of anoxia in the basins that were studied no significant contamination by trace heavy metals pb cu zn and cr in particular was detected the comparative study of the two most bioavailable metal forms namely labile acid soluble and organically bound alkali soluble forms indicated that acetic acid and sodium pyrophosphate released 3 11 and 2 12 respectively of the total metal content from sediments the most bioavailable parts of metals are weakly bound to organic matter and to a greater extent associated with easily soluble amorphous fe oxides among the studied elements most of the bioavailable zn and cu was most likely bound to organic substances whereas bioavailable cr and mn were controlled to a greater extent by the formation of fe oxyhydroxide the elements studied could be arranged in the following decreasing order of average potential bioavailability cu zn mn fe cr pb in the separating basins the relative proportion of labile bioavailable metals is enhanced in relation to the neighbouring open coastal sea

new boron isotopic evidence for sedimentary and magmatic fluid influence in the shallow hydrothermal vent system of milos island aegean sea greece abstract magmatic sources may contribute a significant amount of volatiles in geothermal springs however their role is poorly understood in submarine hydrothermal systems worldwide in this study new results of b and 11 b in 41 hydrothermal vent waters collected from the shallow hydrothermal system of milos island in the aegean sea were combined with previously published data from other tectonic settings and laboratory experiments to quantify the effects of phase separation fluid sediment interaction and magmatic contribution two cl extreme solutions were identified high cl waters cl as high as 2000 mm and low cl waters cl 3 mol mol and extremely low 11 b 1 4 6 3 except for the waters with mg content of near the seawater value and 11 b 10 3 17 4 these high cl waters with high b cl and low 11 b plot close to the vent waters in sediment hosted hydrothermal system i e okinawa trough or fumarole condensates from on land volcanoes implying b addition from sediment or magmatic fluids plays an important role this is in agreement with fluid sediment interactions resulting in the observed b and 11 b as well as previously reported br i cl ratios supporting a scenario of slab derived fluid addition with elevated b 11 b rich and low br cl and i cl which is derived from the dehydration of subducted sediments the slab fluid becomes subsequently mixed with the parent magma of milos the deep brine reservoir is partially affected by injections of magmatic fluid gases during degassing the results presented here are crucial for deciphering the evolution of the brine reservoirs involved in phase separation fluid sediment interaction and magmatic contribution in the deep reaction zone of the milos hydrothermal system they also have implications in the understanding of the formation of metallic vein mineralization

hydrothermal metallogenic processes off the islands of nisiros and kos in the hellenic volcanic arc abstract two submarine hydrothermal fields off nisiros and kos islands in the eastern sector of the hellenic volcanic arc have been investigated using analyses of submarine hydrothermal waters and sediments both the waters and the sediments were found to be enriched in fe mn and zn together with as mo and v in the sediments only resulting from seawater rock interaction processes similar to those described from mid ocean ridge systems differences found between the products of these processes in the two hydrothermal fields studied reflect differences between the rock types being leached the physiographic and geological conditions present including the thickness and composition of the sediment column above the volcanic rocks and the rates of mixing of hydrothermal solutions with normal seawater the geochemical features described support possible sub seafloor formation of metal sulphides at both of the hydrothermal fields studied

hydrochemistry of the cesme geothermal area in western turkey abstract hydrochemical characterization of thermal waters discharged from springs and wells in the cesme geothermal area show that there are two groups one is of thermal waters from a lower aquifer composed of triassic karst limestones which are the main potential reservoir of the area they are of na cl type and between 37 and 62 c and have total dissolved solids tds with around 35 000 mg l the other group are thermal waters derived from an upper aquifer formed by neogene terrestrial sediments these have lower discharge temperatures 37 40 c and lower tds values due to their having mixed with local groundwater before emerging the isotopic and chemical data shows that the initial aqueous solution is a mixture of modern seawater and meteoric water in various proportions enrichment in 18o and d values and tritium contents 8 1 tu of thermal waters reflect a rapid circulation and the contribution of modern seawater the thermal waters are undersaturated with respect to gypsum but oversaturated or around equilibrium with respect to dolomite and calcite several chemical geothermometry techniques applied to cesme geothermal waters gave estimated reservoir temperatures of around 85 100 c

the elemental composition and decay series radionuclide content of plankton from the east pacific mixed plankton samples collected from both the east pacific and nearshore areas off southern california were analyzed for the elements na mg cl k ca sc v cr mn fe co zn se br sr ag sb i ba la ce sm eu th and u and the decay series nuclides 238u 234u 232th 230th 228th and 226ra the concentration populations for most elements 22 out of 26 were found to be normally distributed cross correlation coefficients calculated for all possible pairs of elements showed the following associations to be highly significant na 1bcl fe 1bco ra 1bcr ca 1bsb 1bzn sr 1bree 1bth 1bk 1bv while br and se were inversely correlated with ash content principal components analysis identified members of sea salt detrital silicate and authigenic element groups enrichment factors vs pelagic clay sea salt corrected also identified those elements that are biophilic concentration factors were calculated for each element relative to seawater indicating the following relative reactivity in the photic layer th ce fe sc la sm eu mn cr zn ba ag co se sb ra v i u sr ca br k mg na cl an inverse relationship was found to exist between the log of this concentration factor and the log of the oceanic mean residence time for each element calculated from river input data suggesting biologic transport as an important mechanism for cycling these elements between their introduction into the ocean and their ultimate incorporation into the sediments in addition a biologic mechanism appears likely as an explanation for the ce depletion in seawater relative to the other ree based on its higher concentration factor in marine plankton

mineralogy of the groote eylandt manganese oxides a review abstract the mineralogy and genesis of the tetravalent manganese oxides present in the groote eylandt ore are discussed on the basis of recent mineralogical concepts their mechanisms of formation on groote eylandt are described in terms of primary sedimentation formation of vernadite romanechite pyrolusite todorokite diagenesis formation of pyrolusite supergene processes formation of cryptomelane and lithiophorite and pedogenic processes formation of chalcophanite and birnessite these geochemical processes have resulted in the formation of deposits of metallurgical ore of a cryptomelane pyrolusite mineralogy and a battery active ore of vernadite todorokite pyrolusite mineralogy

rare earth element geochemistry of central pacific ferromanganese encrustations analyses have been made of the ree contents of a suite of hydrogenous mno2 rich ferromanganese encrustations obtained from a variety of depths 1000 4700 m on the line islands archipelago the crusts form a coherent sample group the ree contents of which are distinctly higher than those of diagenetic nodules crusts from 1 to 2 km depth exhibit higher mn fe ratios and are approximately 50 ree depleted with respect to crusts below 2 km furthermore the shale normalised patterns of the ree fall into the same depth related categories crusts from depths greater than 2000 2500 m exhibit slight heavy ree depletion relative to intermediate ree whilst crusts from above that level exhibit more fractionated heavy ree enriched patterns to explain these depth related processes it is proposed that mn and fe oxides exhibit distinct behaviour with respect to ree scavenging between 1 and 2 km higher mn fe ratios in the crusts are considered to be caused by an enhanced supply of mn2 by diffusion and advection from nearshore sediments which is adsorbed by and occludes existing oxide flocs at these depths oxides therefore tend to exhibit predominantly mn oxide adsorptive properties consideration of the ree patterns shows that fe oxides must be enriched overall in ree relative to mn oxides and exhibit a flat shale normalised ree pattern whilst mn oxide exhibits a heavy ree enriched pattern comparison of dissolved ree depth profiles with the crust data enables a qualitative appraisal of the application of scavenging models to the oxide ree system the data are not simply described by either equilibrium or irreversible adsorption models alone it is concluded that whilst oxides may play a general role in creating the lree depleted seawater pattern they have little effect on individual vertical profiles except close to points where fresh oxides precipitate

mechanisms to explain the platinum concentration in ferromanganese seamount crusts abstract ferromanganese seamount crusts cover large areas of hard substrates of sea floor edifices in the central pacific they can be distinctly enriched in pt and show pt pd ratios which are several orders of magnitude greater than those orders of magnitude greater than those of seawater thirty four selected samples of the younger and the older crust generation were analyzed for mn fe ni co and pt the bulk pt concentration varies between 0 14 and 1 02 ppm and averages to 0 51 0 24 ppm the older generation is generally somewhat richer in pt 0 63 0 25 ppm than the younger one 0 39 0 15 ppm compared to the earth s upper continental crust the ferromanganese material contains about 100 times more pt in the studied depth range between 1100 and 3800 m the pt concentration is controlled by the water depth in addition to the bulk data the distribution of pt and pd is recorded through a complete ferromanganese crust profile the average pd value amounts to 16 2 8 ppb for the younger and 16 4 8 ppb for the older generation two immediate sources may be responsible for the pt concentration in the ferromanganese crusts seawater and cosmic spherules the presented thermodynamic approaches are based on the presumption that the pt tetrachlorocomplex is the prevailing species under seawater conditions precipitation of pt in seawater may take place if this complex is decomposed by reduction of pt 2 to the elemental state on the other hand the mno 2 precipitation is caused by oxidation of dissolved mn 2 ions which are supplied from the oxygen minimum zone a model reaction by combining the two half reactions is formulated assuming a coprecipitation of pt with mno 2 an alternative mechanism to explain pt enrichment in ferromanganese crusts might be surface adsorption of anionic pt tetrachloro complexes onto positively charged amorphous iron hydroxide particles cosmic spherules were discovered in samples of the older ferromanaganese crust generation the spherules are mostly concentrated in the upper part of this crust layer iron meteorites often have pt concentrations up to 20 ppm the relative quantity recovered in the grain size class 0 1 0 4 mm only amounts to 2 10 4 which is significantly too low to explain the pt content of the crust samples however smaller cosmic particles may exist and also contribute to the pt enrichment suggesting that rough crust surfaces are excellent collectors of denser detrital material the maximum pt values observed in the youngest part of the older crust generation may be explained by physical incorporation of cosmic particles

distribution patterns of the elements in the ocean a synthesis the observed partition patterns of elements between a marine solid phase e g pelagic clays deep sea manganese nodules seamount manganese crusts and plankton and seawater can be to the first approximation explained by the james and healy adsorption model except for ce co mn pb and tl which are concentrated in the solid phase through oxidative uptake processes in other words the composition of seawater is mainly controlled by the compositions of source materials i e the crustal igneous rocks and primary magmatic volatiles and the physicochemical principles regulating the adsorption processes of various chemical species in seawater onto oceanic pelagic clays

abundance distribution and bioavailability of major and trace elements in surface sediments from the cai river estuary and nha trang bay south china sea vietnam abstract major si al fe ti mg ca na k s p minor mn and trace li v cr co ni cu zn as sr zr mo cd ag sn sb cs ba hg pb bi and u elements their chemical forms and the mineral composition organic matter toc and carbonates tic in surface sediments from the cai river estuary and nha trang bay were first determined along the salinity gradient the abundance and ratio of major and trace elements in surface sediments are discussed in relation to the mineralogy grain size depositional conditions reference background and sqg values most trace element contents are at natural levels and are derived from the composition of rocks and soils in the watershed a severe enrichment of ag is most likely derived from metal rich detrital heavy minerals such as ag sulfosalts along the salinity gradient several zones of metal enrichment occur in surface sediments because of the geochemical fractionation of the riverine material the parts of actually and potentially bioavailable forms isolated by four single chemical reagent extractions are most elevated for mn and pb up to 36 and 32 of total content respectively the possible anthropogenic input of pb in the region requires further study overall the most bioavailable parts of trace elements are associated with easily soluble amorphous fe and mn oxyhydroxides the sediments are primarily enriched with bioavailable metal forms in the riverine part of the estuary natural such as turbidities and human generated such as urban and industrial activities pressures are shown to influence the abundance and speciation of potential contaminants and therefore change their bioavailability in this estuarine system

processes influencing extreme as enrichment in shallow sea hydrothermal fluids of milos island greece abstract arsenic as is naturally enriched in most terrestrial and marine hydrothermal systems its discharge from shallow sea hydrothermal vents into coastal marine environments can dramatically affect the surrounding ecosystems shallow sea hydrothermal venting of acidic ph 5 hot 40 116 c and highly sulfidic up to 3 1 mm h2s fluids occurs at palaeochori and spathi bays off the southeast coast of milos island greece two distinct types of fluids both extremely as enriched were collected from the submarine vents often within a few meters of each other 1 a high cl fluid enriched in cl by up to 47 relative to seawater depleted in mg and so4 and enriched in major na ca k b sr and br and minor trace elements si li rb ce as fe mn and ba and 2 a low cl fluid depleted in cl by up to 66 relative to seawater also depleted in na mg so4 and br the maximum concentration of as reached 39 m in the high cl fluids and up to 78 m in the low cl fluids this is approximately 3000 times the concentration of as in seawater and far exceeds the concentrations typically found in mid ocean ridge mor and back arc basin bab fluids which are typically we used a combination of elemental analyses and stable and radiogenic isotope data oxygen deuterium and strontium to understand the primary controls on as enrichment those parameters all indicated that the fluids were a mixture of seawater and a hydrothermal fluid originally derived from seawater but altered by water rock interaction subcritical phase separation boiling and vapor brine segregation since as was extremely enriched in both the high cl and the low cl thermal fluids we conclude that this element readily partitions into the vapor phase in the milos hydrothermal system the original source of as is most likely the leaching of the greenschist facies metamorphic basement rocks transpierced by an abundance of secondary quartz and calcite veins rich in pyrite it is possible that these veins were deposited from as rich magmatic fluids similar to some epithermal au deposits a poorly crystalline orpiment precipitates as hydrothermal fluids mix with overlying seawater and removes much of the dissolved as prior to discharge

gas geochemistry and co2 output estimation at the island of milos greece abstract twenty gas samples have been collected from the natural gas manifestations of milos island the majority of which is found underwater along its coast furthermore three anomalous degassing fumarolic areas kalamos paleochori and adamas have been recognized on land almost all the gases are co2 dominated with co2 ranging from 88 to 99 vol for the samples taken underwater while the on land manifestations show a wider range 15 98 due to air contamination methane reaches up to 1 0 vol h2 up to 3 2 vol and h2s up to 3 5 vol indicating a hydrothermal origin of the gases the isotope composition of he points out to mantle contributions up to 45 while the c isotope composition of co2 from 1 9 to 1 3 vs v pdb with most of the values around 0 5 suggests a prevailing limestone origin isotope composition of ch4 ranging from 18 4 to 5 0 vs v pdb for c and from 295 to 7 vs v smow for h points to a geothermal origin with sometimes evident secondary oxidation processes additionally co2 flux measurements showed high values in the three fumarolic areas up to 1100 1500 and 8000 g m2 d at kalamos paleochori and adamas respectively with the highest co2 flux values up to about 23 000 g m2 d being measured in the sea at kanavas with a floating chamber the south western part of the island was covered with a lower density prospection revealing only few anomalous co2 flux values up to 650 g m2 d the total output of the island 30 5 t d is typical of quiescent closed conduit volcanoes and comparable to the other volcanic geothermal systems of the south aegean active volcanic arc nisyros kos nea kameni methana and sousaki

shallow submarine epithermal pb zn cu au ag te mineralization on western milos island aegean volcanic arc greece mineralogical geological and geochemical constraints abstract milos island contains several epithermal deposits e g profitis ilias chondro vouno pb zn ag au te cu triades galana agathia kondaros pb zn ag bi w mo cu au and katsimoutis kondaros vani pb zn ag mn of late pliocene to early pleistocene age these deposits are hosted in calc alkaline volcanic rocks emplaced as a result of three successive magma pulses in an emergent volcanic edifice submarine rhyolitic to rhyodacitic cryptodomes at ca 2 7 ma profitis ilias chondro vouno submarine to subaerial andesite to dacite domes at ca 2 2 to 1 5 ma triades galana kondaros katsimouti vani hydrothermal alteration of the volcanic rocks includes advanced argillic both hypogene and steam heated argillic phyllic adularia sericite and propylitic types in the northern sector triades galana agathia kondaros initial magma degassing derived from andesitic dacitic intrusives along ne sw to e w trending faults resulted in the development of pre ore hypogene advanced argillic alteration dickite alunite diaspore pyrophyllite halite and pyrite in a submarine environment mineralogical data indicate common features among the profitis ilias chondro vouno kondaros katsimoutis vani and triades galana mineralized centers all of which are characterized by the presence of galena fe poor sphalerite and chalcopyrite as well as abundant barite adularia sericite and to a lesser extent calcite which are typical of intermediate sulfidation epithermal type deposits locally at triades galana and kondaros agathia high sulfidation conditions prevailed as suggested by the presence of coexisting enargite and covellite the high silver and gold content of the western milos deposits is derived from ag bearing sulfosalts polybasite pearceite pyrargyrite freibergite and tellurides gold at profitis ilias both as native gold and silver gold tellurides is present in base metal precipitates within multicomponent blebs which recrystallized to form hessite petzite altaite coloradoite and native gold mineralogical evidence e g microchimney structures copper sulfides widespread occurrence of barite aragonite suggests that precious metal mineralization in western milos mineralization formed in a submarine setting we present information on the surface distribution of au ag cu pb zn as sb hg mo bi w and cd at western milos gold is enriched at profitis ilias chondro vouno deposits and to a lesser extent at triades galana arsenic is absent from the southern sector but shows elevated concentrations together with molybdenum bismuth and tungsten at the northern sector triades galana vani deposits the differences in precious and base metal abundances may be related to the depths at which the deposits are exposed and or different sources of magma the metal signatures of the triades galana and agathia kondaros katsimouti vani mo bi w as hg ag au occurrences compared to profitis ilias te au ag reflect different sources of magma dacite rhyodacite for profitis ilias andesite dacite for triades galana and dacite for kondaros katsimoutis the enrichment of te mo w and bi in the deposits is a strong indication of a direct magmatic contribution of these metals at western milos precious and base metal vein mineralization was deposited during episodic injection of magmatic volatiles and dilution of the hydrothermal fluids by seawater the mineralization represents seafloor sub seafloor precipitation of sulfides that formed in stockwork zones base and precious metal mineralization formed from intermediate to high sulfidation state fluids and mostly under boiling conditions as indicated by the widespread occurrence of adularia associated with metallic mineralization we speculate that the widespread occurrence of boiling and the shallow depth of the precious and base metal emplacement prevented the formation of seafloor massive sulfides

the boron isotope geochemistry of smectites from sodium magnesium and calcium bentonite deposits abstract the mineralogical chemical and isotopic analyses of smectites with variable interlayer cation occupancies from bentonite deposits in various depositional environments reveal new insights into the boron sources and the fluids involved in bentonitization in marine and non marine environments smectites from bentonites have non exchangeable structural boron concentrations of 0 2 to 196 g g b smectites from sodium bentonites have higher boron concentrations 30 g g than those from magnesium or calcium bentonites most smectites have a small interstratified illitic component that has a major influence on boron concentrations requiring the use of modified fluid mineral boron partitioning coefficients which indicate that bentonites formed from fluids of highly variable boron concentrations of 100 mg l b and a chlorine content of 76 4 mg l to 59 076 mg l the sodium bentonites formed from boron rich saline fluids or brines whereas the fluids involved in calcium and magnesium bentonite formation have a more variable boron composition and salinity the 11b values of the structural boron in tetrahedral sites of smectites range from 30 1 to 12 2 the smectites from terrestrial depositional settings have 11b values of 30 1 to about 0 whereas smectites from marine depositional settings have negative as well as positive 11b values the boron isotope values indicate that all examined bentonites from terrestrial depositional settings as well as many bentonites from marine depositional settings formed from basinal fluids or brines the boron isotope geochemistry of smectites is demonstrated to be a tool for elucidating the fluids involved in the formation of clay mineral deposits it also has great potential for tracing fluids in other settings involving authigenic clay minerals such as sedimentary basins and surficial crystalline rocks as well as man made applications such as in disposal sites for highly active nuclear waste

the relationship of rainfall variability in western equatorial africa to the tropical oceans and atmospheric circulation part ii the boreal autumn abstractthis paper examines the mechanisms controlling the year to year variability of rainfall over western equatorial africa during the rainy season of october december five regions with distinct behavior are analyzed separately only two show strong associations with the ocean and atmospheric features in the global tropics these two regions in the east the eastern zaire basin and west angolan coast of the study area respectively demonstrate strikingly opposite relationships with the anomalies of sea surface temperatures ssts sea level pressure slp and east west atmospheric circulation the wet dry conditions in the eastern zaire basin are associated with el nino la nina like phases the inverse pattern is apparent for the angolan coast the other three regions lying between these two poles of variability represent a transition zone with a weak linear relationship to the circulation features the vital impact of the east west circulation cells on rainfall variability results in a stro

unusual geochemistry of hydrothermal vents on submarine arc volcanoes kasuga seamounts northern mariana arc abstract dsrv alvin dives in the northern mariana island arc recovered warm hydrothermal fluids from the summit areas of seamounts kasuga 2 and kasuga 3 as well as hydrothermal deposits of elemental sulfur fe and mn oxides and nontronite the composition of a gas rich 39 c vent fluid sampled from kasuga 2 seamount is unusual compared to other submarine hydrothermal fluids in that it is enriched by 27 in mg 2 and 17 in so 4 2 and depleted by 64 in ca 2 relative to ambient seawater the elevated concentrations of dissolved co 2 calculated from ph and a t hco 3 and so 4 2 and near absence of h 2 s suggest that the unusual composition of this sample may result from the sub seafloor addition of volcanic co 2 and so 2 to a seawater derived hydrothermal fluid resulting in 1 chemical weathering reactions whereby igneous minerals or alteration phases are attacked by co 2 adding mg 2 and other cations si and hco 3 into solution and 2 hydrolysis of so 2 to so 4 2 and s 0 adding excess so 4 2 with a light 34 s signature to the fluid and causing deposition of elemental sulfur at the seafloor vents saturation state calculations suggest that the concentrations of si and ca 2 in the fluid may be controlled at saturation with amorphous silica and dolomite respectively the origin of the 9 3 c fluid collected from kasuga 3 is difficult to determine because it is compositionally close to ambient seawater and shows possible evidence of both high and low temperature seawater rock reaction banded and interlayered deposits of nontronite and fe and mn oxides were recovered from the kasuga 3 summit with oxygen isotope geothermometry suggesting a formation temperature of 22 c for the nontronite

constraints on water depth of massive sulfide formation evidence from modern seafloor hydrothermal systems in arc related settings the results of three decades of seafloor research provide the most reliable information on the importance of water depth in massive sulfide formation available data from over 130 occurrences show that water depths of seafloor vent sites vary with plate tectonic setting and the regional magmatic and volcanic environment the shallowest hydrothermal systems in subduction related settings are hosted by arc volcanoes these shallow vent sites have a number of features in common with subaerial epithermal systems massive sulfide occurrences in arc related rifts the most likely setting for many ancient analogs are generally restricted to water depths from 700 to 2 000 m with rifts developing within old arc crust at the deeper end of this range back arc spreading centers proximal to arcs host massive sulfide deposits at depths of 1 500 to 2 000 m the deepest hydrothermal systems occur along mature back arc spreading centers distal to volcanic arcs where water depths range from 2 000 to 3 700 m these deeper vent sites probably represent the best modern analogues of ophiolite hosted massive sulfide deposits boiling of the hydrothermal fluids is common at volcanic arcs and in arc related rifts in these environments elevated magmatic gas contents of the hydrothermal fluids can contribute to the widespread occurrence of phase separation and associated gas loss by contrast the high ambient pressures in deep marine hydrothermal systems along mature back arc spreading centers prevent fluids from boiling during their ascent to the seafloor boiling controls the maximum temperature at which hydrothermal fluids discharge at the seafloor and therefore influences the metal content of seafloor sulfide deposits copper rich massive sulfides typically occur at water depths exceeding 1 000 m whereas zn and pb rich occurrences may form at any water depth boiling can be an important control on ag and au grades but is not the only factor controlling precious metal enrichment in massive sulfides shallow marine hot spring deposits can be highly enriched in trace metals such as as hg and sb submarine volcanic arc and back arc settings are geologically complex and significant variations in water depth can occur over short distances paleoenvironmental reconstruction of these environments in ancient volcanic terranes is hampered by the lack of unequivocal volcanological or sedimentological criteria that indicate water depth the relationships established here using modern seafloor observations provide important constraints on the paleoenvironmental setting of ancient volcanic hosted massive sulfide deposits

chemical controls on the composition of vent fluids at 13 11 n and 21 n east pacific rise six vent fields sampled at 13 11 n east pacific rise epr in may 1984 exhibit large interfield variations and a much wider range of chemical compositions than previously observed at 21 n measured ph at 25 c are acidic ranging from 3 1 to 3 7 sodium and chloride vary from 40 lower to 30 higher than seawater iron concentrations range from 2 to 10 mmol kg compared with 0 7 2 5 mmol kg at 21 n other sulfide forming metals cu zn cd and pb are generally lower at 11 13 n than at 21 n reliable temperature measurements were obtained at only two of the six vents and both were 350 5 c the vent fields at 21 n epr were resampled in august 1985 thus extending to almost 6 years the time period over which they have been monitored previous expeditions were made in november 1979 and november 1981 campbell et al this issue have shown that the chemistry of the hydrothermal fluids from these fields has been very stable over the period of repeated observation equilibrium calculations for the fluids from the fields at 13 n and 21 n using a greatly improved thermodynamic data base are described in this report they indicate that the chemistry is rock buffered and that the stability of these systems over time is a result of equilibrium control with respect to a greenschist type mineral assemblage at depth calculated high temperature ph of the fluids range from 4 1 to 4 7 with those from 13 11 n at the more acidic end of the range calculated affinities show that the fluids are close to or at saturation with respect to quartz albite muscovite smectite chlorite epidote and pyrrhotite the computations imply that lower temperature vents such as national geographic smoker ngs 273 c may have their silica concentrations controlled by equilibrium with respect to a phase other than quartz a comparison of fluid chemistry between ngs and vent 5 at 11 n suggests that the latter vent may also have a temperature 300 c while the fluid chemistry of a given field is compositionally stable the compositions themselves are unique for a particular field and cover a wide range between fields the processes controlling this variability probably include the depth of reaction i e pressure which is difficult to treat thermodynamically at present in addition increasing depth in the crust may be accompanied by decreasing permeability and hence a probable decrease in the water rock ratio it may be difficult to separate these two effects if the age differences between the fields at present unknown are of the order of decades then their temporal histories may have an important influence on their particular chemistries

african easterly jet south control maintenance mechanisms and link with southern subtropical waves the african easterly jet south aej s is an important feature of the central african mid tropospheric circulation and has been identified as a key contributor to convection over the region this study uses 21 year 1983 2003 reanalysis data sets of era interim ncep2 and merra2 to establish mechanisms related to aej s dynamics results demonstrate that aej s is dominated by rotational circulation and is maintained by a mid level high that forms over the kalahari region during september to november because of the role played by this high pressure system in the aej s dynamics an effort is made to understand how this anticyclone develops we show that this mid tropospheric high over the kalahari region is established in response to lower tropospheric dry convection over the region from september to november at the core of this high anticyclonic circulation is induced and maintains aej s located at the northern flank of the high a link between aej s dynamics and southern subtropical westerly waves is also revealed it is shown that when waves amplify over the southern subtropics they modify lower tropospheric heating depending on the phase of the wave this modifies the cross latitude temperature gradient throughout equatorial regions therefore modulating the intensity of the jet by clarifying the mechanisms that govern the aej s this research work contributes to insight into central africa climate mechanisms and also suggests a link between central africa and southern africa climate systems this research work also improves the foundation of new mechanisms that help to identify suitable metrics for the evaluation of global models over the central africa region

seawater dominated tectonically controlled and volcanic related geothermal systems the case of the geothermal area in the northwest of the island of euboea evia greece the northwest of the island of euboea is located in a back arc geological position at the western extremity of the north anatolian fault in that area several hot springs occur in three locations ilia gialtra aedipsos including newly found offshore springs with temperatures up to 84 c depositing ore grade thermogenic travertine the geothermal system is seawater dominated and under pressure using the local fault systems and is related to the plio pleistocene lichades volcanic centre the whole area could be characterized as the lateral tips of a major fault segment with the presence of complex networks of additional fault systems leading to fault intersections that conclusion is also supported by the travitonic data the geothermal fluids are near neutral ph sodium chloride and their chemistry is controlled by i high seawater participation ii a deep magmatic source and iii chemical composition of the bedrocks based on all the available data including drilling and temperature logging data the bedrock hosting the upflow circulation of the geothermal fluid is not in hydraulic connection with cold aquifers or permeable geological formations of the area the local metamorphic rock formations are impermeable and work as a geothermal cap also aedipsos vast deposit of thermogenic travertine probably acts as a second geothermal cap formation however at the same time it presents serious thermal anomalies since major geothermal fluid circulation has been identified inside its fractures according to chemical geothermometers the temperature of the geothermal reservoir is 140 164 c the typical geothermal gradients in the area are from 7 8 c 100 m to 18 7 c 100 m in one case an anomalous high geothermal gradient 53 9 c 100 m was found most probably due to spatial shape diversity of the geothermal reservoir a suggestion also supported by the estimated circulation depth of the geothermal fluid which varies from area to area 300 1800 m and the fluid residence time by 226ra 222rn method which is around 80 100 years

plutonium oxidation state distributions in the pacific ocean during 1980 1981 abstract the concentration of plutonium and its oxidation state distribution have been measured as a function of depth at three locations in the north pacific ocean concentration profiles were similar to those observed in the same area during 1974 with primary maxima at depths of a few hundred meters below the surface and secondary maxima near the bottom oxidation state distribution profiles were similar at the three locations with plutonium about equally divided between the reduced and oxidized forms except near the bottom there the oxidized form was more abundant and comprised 90 of the total plutonium no major change in oxidation state occurred at the depths of the shallow concentration maxima suggesting that their formation and persistence were not dependent upon a redox change the concentration maxima near the bottom coincided with the enhanced abundance of the poorly sorbed oxidized form suggesting that they resulted from the loss of oxidized plutonium from the sediments

boiling and dilution in the shallow portion of the waiotapu geothermal system new zealand abstract the waiotapu geothermal system is the largest in terms of surface extent and heat flow 17 km2 and 600 mw respectively of the 20 major geothermal systems in the taupo volcanic zone new zealand two extinct dacite cones and a rhyolite dome rise about 500 m above the waiotapu valley the majority of thermal features occurs in the valley over a relief of only 100 m and lies within coincident apparent resistivity and 30 m depth thermal anomalies thermal features comprise near neutral ph chloride springs often boiling acid sulfate springs and mud pools and mixed waters the latter including both bicarbonate chloride and acid sulfate chloride springs the majority of the sulfate discharges to the surface in the northern higher altitude area while most chloride that reaches the surface does so in the southern portion of the system comparison of measured and calculated surface chloride flux the latter from measured heat flow and reservoir chloride concentrations indicates that at least half of the deep chloride does not discharge at the surface but flows laterally to the south at shallow depths mixing with groundwater the composition of well discharges indicates a shallow 400 m reservoir of chloride fluid about 1350 mg cl kg at 230 c is diluted by a co2 rich steam heated water nil chloride at about 160 c the latter located on the margins of the system this same dilution trend is apparent from the compositional variation and k na and k mg geothermometry of hot spring waters however there is chemical and stable isotope evidence from hot springs that cold groundwater also acts as a diluent at shallow levels and very near the surface steam heated acid sulfate waters mix with the upflow boiling of the deep chloride fluids prior to dilution results in the stabilization of k feldspar in contrast dilution at shallower depths by the steam heated waters both co2 rich and acid sulfate leads to the water compositions initially shifting to k mica and interstratified clay stability and to kaolinite stability with further dilution and temperature decrease the composition and distribution of these fluids are consistent with alteration mineralogy and zonation observed in drill core although boiling occurs at deeper levels and up to the surface in the upflow zone at waiotapu mixing is also common and is the dominant process on the margin and in the near surface portion of the system boiling of deep chloride fluid is very common in the upper 1 2 km of the upflow zone of most geothermal systems though it may be quenched by mixing with marginal waters either cold groundwater in high relief terrane or steam heated waters in areas of lower relief co2 rich steam heated waters are common on the margins of systems and will generally underlie the near surface acid sulfate steam heated waters interaction with co2 rich waters will form k mica and interstratified clays while acid sulfate waters cause kaolinite and even alunite to form the former assemblage is commonly associated with typical low sulfidation epithermal gold mineralization as wallrock alteration where gold bearing veins comprise adularia and illite in contrast kaolinite is rare and alunite absent from a direct spatial and genetic association with gold mineralization in this environment this implies that mixing of the deep neutral ph chloride fluid with surficial acid sulfate waters does not commonly lead to ore grade gold deposition mixing with and cooling by co2 rich steam heated waters leads to clay stability accounting for the large halos of clay alteration and low grade metal anomalies which often surround veins of high gold grade in contrast mixing with surficial acid sulfate waters is unlikely to cause precious metal mineralization because the chloride fluids have already lost the majority of their gold through deeper boiling and dilution

description and interpretation of the composition of fluid and alteration mineralogy in the geothermal system at svartsengi iceland abstract the bulk composition and mineralogy of hydrothermally altered tholeiite along with the composition and speciation of fluid have been determined for a well defined alteration zone at 240 c and 110 bars at svartsengi iceland mass balances between the geothermal fluid and altered tholeiite relative to a seawater fresh water mixture and unaltered tholeiite indicate the overall reaction per 1000 cm 3 is 1325 gm plagioclase 1228 gm pyroxene 215 gm oxide minerals break down to form 685 gm chlorite 636 gm albite 441 gm quartz 249 gm epidote 266 gm calcite 201 gm oxide minerals 15 gm pyrite requiring an influx of 123 gm co 2 10 gm h 2 s and 4 gm na 2 o and a release of 57 gm sio 2 35 gm feo 21 gm cao 8 gm mgo and 4 gm k 2 o principal reactions deduced from textural evidence include na ca exchange in plagioclase precipitation of quartz calcite and anhydrite and formation of chlorite and epidote by reactions between groundmass minerals and fluid thermodynamic analyses of authigenic minerals and downhole fluid indicate that the fluid maintains a state close to equilibrium with the secondary mineral phases chlorite epidote albite quartz calcite prehnite anhydrite pyrite and magnetite whereas remnant primary labradorite and augite are out of equilibrium with the fluid water rock ratios for the system are determined under a variety of assumptions however the open nature of the system makes comparisons with experimental and theoretical closed system studies ambiguous

gold in seawater abstract a suite of seawater samples has been analyzed for au by inductively coupled plasma quadrupole mass spectroscopy icpms the recently developed method involves preconcentration by anion exchange followed by flow injection sample introduction into a vg plasmaquad icpms profiles in the atlantic gulf stream northeast pacific and mediterranean are presented in addition the first measurements of au in hydrothermal fluids are reported the measured concentrations of au in the atlantic and northeast pacific 50 150 fmol l are within a factor of 2 3 of recently reported values for pacific waters 1 and nearly three orders of magnitude less than reported in the literature prior to 1988 indicating contamination problems with the earlier data in general au concentrations for atlantic and pacific samples reported here are the same 50 fmol l however differences of up to a factor of 2 between the oceans cannot be ruled out due to large uncertainties associated with the pacific data mediterranean deep waters contain higher concentrations of au 100 150 fmol l this is attributed to proximal aeolian dust and or riverine sources gold is enriched in hydrothermal fluids 10 100 s of pmol l with respect to ambient seawater although the fluxes remain poorly constrained preliminary budget considerations indicate that rivers and hydrothermal venting are the most significant sources of au to the oceans

congo basin precipitation assessing seasonality regional interactions and sources of moisture precipitation in the congo basin was examined using a version of the national center for atmospheric research community earth system model cesm with water tagging capability using regionally defined water tracers or tags the moisture contribution from different source regions to congo basin precipitation was investigated we found that the indian ocean and evaporation from the congo basin were the dominant moisture sources and that the atlantic ocean was a comparatively small source of moisture in both rainy seasons the southwestern indian ocean contributed about 21 of the moisture while the recycling ratio for moisture from the congo basin was about 25 near the surface a great deal of moisture is transported from the atlantic into the congo basin but much of this moisture is recirculated back over the atlantic in the lower troposphere although the southwestern indian ocean is a major source of indian ocean moisture it is not associated with the bulk of the variability in precipitation over the congo basin in wet years more of the precipitation in the congo basin is derived from indian ocean moisture but the spatial distribution of the dominant sources is shifted reflecting changes in the mid tropospheric circulation over the indian ocean during wet years there is increased transport of moisture from the equatorial and eastern indian ocean our results suggests that reliably capturing the linkages between the large scale circulation patterns over the indian ocean and the local circulation over the congo basin is critical for future projections of congo basin precipitation

interelement relationship in abyssal pacific ferromanganese nodules and associated pelagic sediments abstract by r mode factor analysis and enrichment factor calculations most of the elements in abyssal ferromanganese nodules and associated pelagic sediments excluding common authigenic minerals like apatite barite opal and carbonates are found to be preferentially concentrated in one of the following three major phases aluminosilicates e g al si sc ga cr be na k rb and cs fe oxides e g fe p s v se te as b sn u hg pb ti ge y zr nb pd in rare earths hf th pa pu am ru and bi and mn oxides e g mn tl ag cd mg ca ba ra co ni cu zn mo sb and probably w the specific association of elements with these three phases can be explained by the difference in chemical forms of elements in seawater and by fundamental differences in physicochemical properties e g the ph of zero point of charge and dieletric constant of these three phases

the seasonal evolution of the atmospheric circulation over west africa and equatorial africa abstract this paper examines the mean annual cycle of rainfall and general circulation features over west africa and central africa for 1958 97 rainfall is examined using a 1400 station archive compiled by the first author other circulation features are examined using the ncep ncar reanalysis dataset important features of the reanalysis zonal wind field are shown to compare well with the seasonal evolution described by the radiosonde observations in addition to the well known african easterly jet aej of the northern hemisphere the seasonal evolution of its southern hemisphere counterpart is also described thermal wind calculations show that although the southern jet is weaker its existence is also due to a local reversal of the surface temperature gradient in the upper troposphere a strong semiannual cycle is shown in the 200 mb easterlies and a feature like the tropical easterly jet tej is evident south of the equator in january and february the paper describes the movement of the rainbelt

oceanic 232th a reconnaissance and implications of global distribution from manganese nodules abstract 232 th concentrations in seawater reported in the literature since 1961 are compiled and evaluated and new data are presented in general recent data are lower than old ones by 1 to 2 orders of magnitude with nearly all post 1980 data lower than 0 1 dpm 10 3 1 and pre 1980 values higher than 0 1 dpm 10 3 1 we believe this is caused by improvements in sampling and analytical techniques reliable profiles of 232 th in coastal and open ocean waters have been measured in recent years some by the newly developed neutron activation analysis and mass spectrometry techniques the data indicate external sources of 232 th to the surface and its scavenging throughout the water column we suggest that aeolian input dominates in the open ocean but fluvial input may be more important in coastal regions if mechanisms exist for recycling th from estuarine sediments some information on the global distribution pattern and marine geochemistry of 232 th in seawater can be inferred from initial 230 th 232 th activity ratios observed on surfaces of manganese nodules and crusts the rather distinct interocean variation of the 230 th 230 th activity ratio in the central gyre region averaging 160 in the south pacific 60 in the north pacific and 17 in the atlantic may reflect higher aeolian input of materials including 232 th to the atlantic and to the northern hemisphere superimposed on the large scale global trend are some small scale variations which are indicative of the following effects 1 abrupt change of water depth and hence 230 th concentration at regions of irregular seafloor topography 2 higher 232 th input at ocean boundaries and 3 enhanced supply of 232 th from hydrothermal vents it is still unclear whether seafloor sediments act as a net source or sink of dissolved 232 th and 230 th in bottom waters pore water study should be undertaken to address this important issue this task can be accomplished by the mass spectrometric technique

weathering and erosion in central vietnam over the holocene and younger dryas clay mineralogy and elemental geochemistry from the vietnam shelf western south china sea abstract clay mineralogy and elemental geochemistry of core so18401 on the vietnam shelf are used to reconstruct the history of weathering and erosion in central vietnam over the past 13 2 ka the variability of the clay species across the 13 2 ka bp together with the age model allows a subdivision into four temporal stages provenance analysis based on clay mineralogy indicates that small mountainous rivers in southern central vietnam are the major sources of terrigenous sediments on the central vietnam shelf smectite and kaolinite originated from the chemical weathering of mesozoic and neogene quaternary basaltic rocks and paleo mesozoic felsic intrusive rocks respectively under warm and humid climate conditions whereas illite and chlorite were mainly derived from physical weathering of paleo mesozoic felsic intrusive rocks and precambrian metamorphic rocks in central vietnam accordingly smectite illite chlorite ratio together with elemental ratios of al2o3 k2o tio2 al2o3 and sio2 al2o3 can be utilized to reflect the relative importance between chemical weathering and physical weathering erosion of the parent rocks in southern central vietnam higher smectite illite chlorite and al2o3 k2o ratios indicate a more important role of chemical weathering and higher tio2 al2o3 and sio2 al2o3 ratios suggest enhanced contribution of physical weathering and erosion a combination of these mineralogical and elemental proxies allows the distinction of four stages of weathering and erosion evolution in southern central vietnam over the holocene and younger dryas periods enhanced physical weathering and erosion took place during the periods 13 2 11 0 ka bp stage i and 3 9 2 0 ka bp stage iii associated with relatively arid conditions by contrast strengthened chemical weathering occurred during the periods 11 0 3 9 ka bp stage ii and 2 0 ka bp to present stage iv corresponding to more warm and humid climatic conditions our study suggests that the weathering and erosion history of southern central vietnam over the holocene is mainly controlled by the east asian monsoon climate

direct observation of the evolution of a seafloor black smoker from vapor to brine a single hydrothermal vent f vent occurring on very young crust at 9 16 8 n east pacific rise was sampled in 1991 and 1994 in 1991 at the measured temperature of 388 c and seafloor pressure of 258 bar the fluids from this vent were on the two phase curve for seawater these fluids were very low in chlorinity and other dissolved species and high in gases compared to seawater and most sampled seafloor hydrothermal vent fluids in 1994 when this vent was next sampled it had cooled to 351 c and was venting fluids 1 5 times seawater chlorinity this is the first reported example of a single seafloor hydrothermal vent evolving from vapor to brine the 1991 and 1994 fluids sampled from this vent are compositionally conjugate pairs to one another these results support the hypothesis that vapor phase fluids vent in the early period following a volcanic eruption and that the liquid phase brines are stored within the oceanic crust and vent at a later time in this case 3 years these results demonstrate that the venting of brines can occur in the same location in fact from the same sulfide edifice where the vapor phase fluids vented previously

identification of processes driving low level westerlies in west equatorial africa abstractthis paper investigates and characterizes the control mechanisms of the low level circulation over west equatorial africa wea using four reanalysis datasets emphasis is placed on the contribution of the divergent and rotational circulation to the total flow additional focus is made on analyzing the zonal wind component in order to gain insight into the processes that control the variability of the low level westerlies llw in the region the results suggest that the control mechanisms differ north and south of 6 n in the north the llw are primarily a rotational flow forming part of the cyclonic circulation driven primarily by the heat low of the west african monsoon system this northern branch of the llw is well developed from june to august and disappears in december february south of 6 n the seasonal variability of the llw is controlled by the heating contrast between cooling associated with subsidence over the ocean and heating over land regions largely south of the equator where as

arsenic antimony and bismuth in sediments and waters from the santorini hydrothermal field greece abstract chemical analyses for as and sb in santorini sediments and as in waters from the vicinity of active hydrothermal vents indicated hydrothermal enrichments of these elements in the santorini sediments relative to normal marine sediments and of as in the waters relative to normal seawater bi in the sediments falls within the range of its concentrations in normal clastic sediments as fe ratios in the sediments increase with increasing distance from the hydrothermal vents which coupled with a strong association between as and fe demonstrated by partition analysis suggests that hydrothermal as is scavenged into the sediments by freshly precipitating fe oxides and that the conditions for this become increasingly favourable away from the vents

rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments abstract analyses have been made of ree contents of a well characterized suite of deep sea 4000 m principally todorokite bearing ferromanganese nodules and associated sediments from the pacific ocean ree in nodules and their sediments are closely related nodules with the largest positive ce anomalies are found on sediments with the smallest negative ce anomalies in contrast nodules with the highest contents of other rare earths 3 ree are found on sediments with the lowest 3 ree contents and vice versa 143 nd 144 nd ratios in the nodules 0 51244 point to an original seawater source but an identical ratio for sediments in combination with the ree patterns suggests that diagenetic reactions may transfer elements into the nodules analysis of biogenic phases shows that the direct contribution of plankton and carbonate and siliceous skeletal materials to ree contents of nodules and sediments is negligible inter element relationships and leaching tests suggest that ree contents are controlled by a p rich phase with a ree pattern similar to that for biogenous apatite and an fe rich phase with a pattern the mirror image of that for sea water it is proposed that 3 ree concentrations are controlled by the surface chemistry of these phases during diagenetic reactions which vary with sediment accumulation rate processes which favour the enrichment of transition metals in equatorial pacific nodules favour the depletion of 3 ree in nodules and enrichment of 3 ree in associated sediments in contrast ce appears to be added both to nodules and sediments directly from seawater and is not involved in diagenetic reactions

noble gases in pyrites from the guocheng liaoshang gold belt in the jiaodong province evidence for a mantle source of gold abstract the recent mineral exploration programme 2009 2014 in the jiaodong gold province identified the new guocheng liaoshang gold metallogenic belt which contains reserves of 92 tonnes t au in the main deposits the ore is fault hosted in massive sulfides that make up to 25 to 95 vol the he ar isotope compositions of ore forming fluids from 20 pyrite samples from the five main deposits are reported here 3 he 4 he range between 0 41 and 2 39 r a 40 ar 36 ar are 367 to 2112 and 40 ar 4 he are 0 40 3 78 the data require four gas sources a dominant mantle derived component plus sub ordinate crustal radiogenic meteoric and basin brine components the mantle end member has 3 he 4 he 3 32 4 00 r a this is lower than most estimates for sub continental lithospheric mantle sclm 6 7 r a implying that it was probably refertilized by subduction related fluid metasomatism this is consistent with he ar isotopes reported for sclm xenoliths from basalts in the shandong province within the mineralisation province the mine au reserve is positively correlated with the proportion of mantle derived he in the ore forming fluids this implies that the fluids and by inference the gold was largely derived from mantle melts during lithospheric extension given the conspicuous association of gold ore deposits with mantle derived magma in the jiaodong peninsula we envisage that our genetic model can be applied to some extent to evaluate the potential of some mineral exploration targets

the marine geochemistry of dissolved gallium a comparison with dissolved aluminum abstract dissolved ga concentrations in the pacific ocean range from 2 to 30 picomolar they are low in surface waters 2 12 pm with a subsurface maximum at 150 300 m 6 17 pm a mid depth minimum from 500 to 1000 m 4 10 pm and increasing values with depth to a maximum in the bottom waters 12 30 pm the highest concentrations are in the central gyre with lower values toward the north and east where productivity and particle scavenging increase dissolved ga concentrations in the surface waters of the northwest atlantic are nearly an order of magnitude higher than in the central north pacific with higher values in the gulf stream than in the continental slope boundary region dissolved al concentrations in the high latitude north pacific are also lower than in the central gyre and are the lowest yet reported for this element the features are similar however to other dissolved al profiles a surface maximum 0 8 nmol kg a mid depth minimum 0 06 nmol kg and increasing concentrations toward the sediment water interface 0 4 nmol kg the vertical distributions and horizontal transects indicate three sources of dissolved ga to the oceans the surface distribution reflects an eolian source with no net fluvial input to the open ocean the subsurface maximum a feature not seen for north pacific dissolved al is attributed to vertical exchange processes the source for the deep waters of the north pacific is from a sediment surface remineralization process or a pore water flux scavenging removal throughout the water column is evident in the vertical profiles for both dissolved ga and al with intensified removal in the boundary regions where productivity and particle scavenging are at a maximum residence times of dissolved ga in surface waters are nearly an order of magnitude longer than the corresponding values for al

natural and anthropogenic radionuclide distributions in the northwest atlantic ocean we have used in situ pumps which filter large volumes of sea water through a 1 m cartridge prefilter and two mno2 coated cartridges to obtain information on dissolved and particulate radionuclide distributions in the oceans two sites in the northwest atlantic show subsurface maxima of the fallout radionuclides137cs 239 240pu and241am although the processes of scavenging onto sinking particles and release at depth may contribute to the tracer distributions comparison of predicted and measured water column inventories suggests that at least 35 50 of the pu and241am are supplied to the deep water by advection the depth distributions of the naturally occurring radionuclides232th 228th and230th reflect their sources to the oceans 232th shows high dissolved concentrations in surface waters presumably as a result of atmospheric or riverine supply activities of232th decrease with depth to values 0 01 dpm 1000 l 228th shows high activities in near surface and near bottom water due to the distribution of its parent 228ra dissolved230th produced throughout the water column from234u decay increases with depth to 3000 m values in the deep water 3000 m are nearly constant 0 6 0 7 dpm 1000 l and the distribution of this tracer and perhaps other long lived particle reactive tracers as well may be affected by the advection inferred from pu and241am data the ratio of particulate to dissolved activity for both230th and228th is 0 15 0 20 this similarity precludes the calculation of sorption rate constants using a simple model of reversible sorption equilibrium moreover in mid depths228th tends to have a higher particulate dissolved ratio than230th suggesting uptake and release of230th and228th by different processes this could occur if228th produced in surface water were incorporated into biogenic particles formed there and released as those particles dissolved or decomposed during sinking 230th produced throughout the water column may more closely approach a sorption equilibrium at all depths 230th 241am and239 240pu are partitioned onto particles in the sequence th am pu with 15 of the230th on particles compared with 7 for am and 1 for pu distribution coefficients kd are 1 3 1 6 107 for th 5 6 106 for am and 7 10 105 for pu the lower reactivity for pu is consistent with analyses of pu oxidation states which show 85 oxidized v vi pu however thekd value for pu may be an upper limit because pu like228th may be incorporated into particles in surface waters and released at depth only by destruction of the carrier phase

some comparative marine chemistries of platinum and iridium abstract iridium has seawater concentrations about one hundred times less than those of platinum as a consequence of its weaker complexing abilities with halides and of a stronger tendency to hydrolyze iridium like platinum is enriched in some ferromanganese minerals compared to palladium platinum and iridium are probably oxidized during mineral formation from the divalent and trivalent states respectively to the tetravalent ones the pelagic sediment contents of irridium as well as those of platinum are related to the manganese contents for higher platinum contents of the authigenic ferromanganese minerals the pt ir ratios approach the seawater ratio suggesting little dilution by platinum and iridium in detrital minerals the marked enrichments of platinum and iridium in the ferromanganese concretions enhance their value as potential ores for heavy metals

two cells phase separation in shallow submarine hydrothermal system at milos island greece boron isotopic evidence 1 three types of hydrothermal vent fluids herein referred to as cave submarine brine and seawater like were recovered from a shallow submerged system at milos in the aegean sea greece for detailed chemical and isotopic analyses the cave fluids discharge through rock fissures near sea level and have low ph chlorinity and b concentrations relative to seawater the submarine brine fluids are characterized by high cl and contain 10 times seawater b concentrations a scenario involving a two cells circulation is proposed one occurs at 1 2 km and another at shallower depth the deeper saline reservoir has experienced subcritical phase separation partitioning 0 42 mm b in vapor and 6 8 mm in brine with no detectable isotopic fractionation the reaction temperature in the saline reservoir is 313 c calculated from the na k ca geothermometry the vapors rise directly to form the cave vents whereas the saline fluids transport in different pathways and are influenced by seawater mixing to form the variable submarine brine fluids the seawater like fluids circulate at shallower depths where calculated temperature is 248 c and show slightly diluted b 0 36 0 41 mm and seawater 11b these fluids probably resulted from heating of down flow seawater and may have experienced groundwater discharge and partial mg removal this study represents the first two cells circulation occurring at milos and emphasizes the important role of phase separation in shallow submarine hydrothermal system

ultimate removal mechanisms of elements from the ocean abstract the surface complex formation model can adequately explain the observed partitioning of most of the elements between seawater and pelagic clays and between river water and river suspended particles the adsorption of elements on the hydrous oxide surface of iron oxide manganese oxide and clay minerals is the most important ultimate removal mechanism of most of the elements from the ocean

earthquake induced variations in the composition of the water in the geothermal reservoir at vulcano island italy abstract during 1979 1989 variations were observed in the oxygen composition of the water contained in the geothermal reservoir at vulcano island italy the reservoir water that has a magmatic origin showed an oxygen composition of 1 0 0 5 18o during periods without local tectonic earthquakes and an oxygen composition of 3 4 0 5 18o after the highest energy seismic activity that occurred recently near the island a slight increase of the 18o value in the reservoir water was also observed after a low energy sequence of tectonic earthquakes that occurred at very shallow depth just beneath vulcano island these 18o variations in the reservoir water are consistent with earthquake induced increases in the contribution from high temperature 18o rich magmatic condensate to the geothermal reservoir and with subsequent decreases in the 18o value due to 18o exchanges at the temporarily increased reservoir temperature during reactions between the highly reactive magmatic condensate and the local rocks only minor changes in the deuterium composition of the reservoir water occurred with time as the d value in the magmatic condensate released from the magma after major local earthquakes quickly approached the d value of the water contained in the geothermal reservoir also the chloride concentration in the reservoir water appears to be linked to the contribution from the magmatic fluid this chloride content seems not to have undergone major changes with time as it may be buffered by temporary increases in the reservoir temperature up to values 300 c induced by major local earthquakes this mechanism may possibly occur also in other magmatic hydrothermal systems

regional atmospheric circulation and rainfall variability in south equatorial africa abstractthis study examines daily precipitation data during december march over south equatorial africa sea and proposes a new zonal asymmetric pattern zap that explains the leading mode of weather scale precipitation variability in the region the eastern and western components of the zap separated at about 30 e appear to be a consequence of an anomalous zonal atmospheric cell triggered by enhanced low level westerly winds the enhanced westerlies are generated by a diagonal interhemispheric pressure gradient between the southwestern indian and north tropical atlantic oceans in eastern sea these winds hit the east african plateau producing low level convergence and convection that further intensifies the westerlies in western sea a subsiding branch develops in response closing the circulation cell the system gradually dissipates as the pressure gradient weakens through this mechanism simultaneous changes in two hemispheres generate a regional zonally oriented circulation that relies on clima

hydrothermal activity in the lau back arc basin sulfides and water chemistry the submersible nautile completed 22 dives during the nautilau cruise r v nadir april 17 may 10 1989 for a detailed investigation of the southern lau basin near tonga the objective of the scientific team from france germany and tonga was to understand the process of sea floor ore formation associated with hydrothermal circulation along the valu fa back arc ridge behind the tonga kermadec trench the four diving areas between lat 21 25 s and 22 40 s in water 2000 m deep were selected on the basis of results from cruises of the r v jeancharcot and r v sonne the nadir cruise provided proof of hydrothermal activity in all four areas over more than 100 km as indicated by the widespread occurrence of hydrothermal deposits and by heat flow conductivity and temperature measurements near the sea bottom the most spectacular findings were high temperature white and black smokers and associated fauna and ore deposits hydrothermal water chemistry and sulfide composition data presented here indicate that this hydrothermal field is very different from the hydrothermal fields in oceanic ridges this difference is seen in the water chemistry of the hydrothermal fluid ph 2 and high metal content and the chemical composition of sulfides enrichment in ba as and pb

subaqueous hot springs in koycegiz lake dalyan channel and fethiye gocek bay sw turkey locations chemistry and origins abstract in this study horizontal temperature measurements along organized grids have been used to detect subaqueous hot springs the study area located in the southwest of turkey and comprised of koycegiz lake dalyan channel and fethiye gocek bay was scanned by measuring temperatures horizontally 2 3 m above the bottom of the lake or sea after analyzing the temperature data along the grids the locations with anomalous temperature values were detected and divers headed here for further verification accordingly among these anomalies the divers confirmed seven of them as subaqueous hot springs three of these hot springs are located in the koycegiz lake three of them are located in the dalyan channel and one hot spring is located in the fethiye gocek bay at the locations where temperature anomalies were detected the divers collected samples directly from the subaqueous hot spring using a syringe type sampler we evaluated these water samples together with samples collected from hot and cold springs on land and from local rivers lakes and the sea with an aim to generate a conceptual hydrogeochemical model of the geothermal system in the study area this model predicts that rainwater precipitating in the highlands percolates through fractures and faults into the deeper parts of the earth s crust here it is heated and ascends through the sea bottom via buried faults pervious carbonate nappes that are underlain and overlain by impervious rocks create a confined aquifer the southern boundary of the carbonate marmaris nappes is buried under alluvium and or sea lake water bodies and this phenomenon determines whether hot springs occur on land or subaqueous the chemical and isotopic properties of the hot springs point to seawater mixing at deep levels thus the mixing most probably occurs while the water is ascending through the faults and fractures the gas geochemistry results reveal that the lowest mantle he contributions occur in the samples from koycegiz lake whereas the highest ones are found in samples from the dalaman plain for the first time we made use of the micro xrf sediment core scanning itrax scanner for exploring the relation between subaqueous geothermal occurrence and chemical properties of the surrounding sediments the spatial elemental distribution of sea lake bottom sediments suggests that depending on the surrounding rock units and the temperature of the hot spring the sediments around the spring can be enriched with certain elements