hot vents in an ice cold ocean indications for phase separation at the southernmost area of hydrothermal activity bransfield strait antarctica abstract during the expeditions ant xv 2 with r v polarstern in 1997 98 and nbp 99 04 with r v ib n b palmer in 1999 the first samples of hydrothermally influenced sediments of bransfield strait were obtained at hook ridge a volcanic edifice in the central basin of the strait the vent sites are characterized by white siliceous crusts on top of the sediment layer and temperatures measured immediately on deck are up to 48 5 c the shallow depth of these vent sites 1050 m particularly controls the chemistry of the pore fluids that are enriched in silica and sulfide and show low ph values chloride is depleted up to 20 and the calculated hydrothermal endmember concentration is in the range of 1 84 mm since other mechanisms for cl depletion can be ruled out clearly the composition of this fluid is attributed to phase separation while the cl depleted fluid is emanating at hook ridge a cl enriched fluid can be identified in the adjacent king george basin using a p x diagram the two corresponding endmember concentrations reveal that the phase separation takes place at subcritical conditions total depth 2500 m probably along the whole volcanic edifice

extreme cl br and δ 37 cl isotope fractionation in fluids of modern submarine hydrothermal systems microthermometric studies of sphalerite hosted fluid inclusions from fracture fillings in felsic igneous rocks of modern polymetallic massive sulfide mineralization from the jade field central okinawa trough japan and from mounds on the seafloor in the north fiji basin reveal evidence for sub critical two phase separation of seawater chemical analyses of the fluid inclusions indicate intense water rock interaction between the hydrothermal fluids and their host rocks the analyses indicate that sub critical phase separation has a much larger effect on the partitioning of chloride and bromide into liquid and vapor phase than previously reported for vent fluids this study also shows that for the first time chlorine isotope fractionation correlates with cl and br fractionation using combined cl br ratios and 37cl values allows us to discount br enriched organic matter or halite precipitation as responsible for the formation of br rich fluids moreover the same parameters exclude any significant magmatic component in the mineral forming fluids as previously proposed for similar modern sulfide deposits and other massive sulfide deposits in the geological record

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

axial summit trough of the east pacific rice 9 10 n geological characteristics and evolution of the axial zone on fast spreading mid ocean ridge the nature and morphological characteristics of axial summit troughs on fast 90 130 mm yr 1 full spreading rate and superfast spreading 130 mm yr 1 mid ocean ridge crests reflect the time integrated effects of long term magmatic cycles short term volcanic episodicity and the tensional stress regime imposed on young ocean crust two principal types of axial trough morphology have been identified and associated with distinct volcanic and tectonic processes occurring at fast and superfast spreading mid ocean ridge crests 1 narrow axial troughs 300 2000 m wide and 30 100 m deep on the east pacific rise crest are classified as axial summit graben the dimensions of axial summit graben as well as the morphological and structural character of their walls and floors suggest a primary tectonic origin an axial summit graben may contain a nested axial summit collapse trough implying that processes responsible for these endemic features may be linked near bottom side looking sonar and observational data collected using the towed vehicle argo i and submersible alvin have been used to characterize the axial summit trough of the fast spreading east pacific rise between 9 and 10 n a four stage model is presented for the evolution of this axial summit collapse trough as well as for other well studied portions of the east pacific rise crest from 21 n to 20 s we propose that the transition from a narrow surface collapse dominated axial trough to a broader fault bounded graben is controlled by the relative importance of diking volcanism hydrothermal cooling and tectonism along a ridge segment over time periods 104 years

consequences of phase separation on the distribution of hydrothermal fluids at ashes vent field axial volcano juan de fuca ridge recent studies of hydrothermal fluid chemistry at the axial seamount hydrothermal emissions study ashes vent field of axial volcano indicate separation of liquid and vapor phases during the migration of fluids to the seafloor the brine phase liquid emanates from discrete sulfide chimneys while fluid which has been through vapor phase separation flows diffusely from fissures in the surrounding basalt one possible mechanism to explain this spatial segregation of the fluid phases is based on the relative permeability terms in the equations of two phase flow a qualitative model for the distribution of fluids observed at ashes is postulated in which brine phase fluids are confined within flow conduits by a surrounding relative permeability barrier while vapor phase fluids flow diffusely into the surrounding host rock

detrital sediment supply in the southern okinawa trough and its relation to sea level and kuroshio dynamics during the late quaternary abstract during leg 195 of the ocean drilling program site 1202 was drilled in the subtropical northwestern pacific ocean beneath the kuroshio black current between northern taiwan and the ryukyu island arc on the northern flank of the i lan ridge at 1274 m water depth the upper 110 m of the site 1202 section composed of dark grey calcareous silty clay provide an expanded record of environmental changes during the last 28 kyr the sediments were deposited at high sedimentation rates between 3 0 and 5 0 m kyr and peak values of 9 0 m kyr between 15 1 and 11 2 ka bp variations in the modes and sources of detrital sediment input as inferred from sediment granulometry mineralogy and elemental xrf scanner data reflect changes in environmental boundary conditions related to sea level changes kuroshio variability and the climate driven modes of fluvial runoff the provenance data point to increased sediment supply from northwestern taiwan between 28 and 19 5 ka bp and from east china sources between 19 5 and 11 2 ka bp the change in provenance at 19 5 ka bp reflects increased fluvial runoff from the yangtze river and strong sediment reworking from the east china sea shelf in the course of increased humidity and postglacial sea level rise particularly after 15 1 ka bp the holocene was dominated by sediments that originated from rivers in northeastern taiwan for the pre holocene period prior to 11 2 ka bp low portions of sortable silt 63 10 m show that the kuroshio did not enter the okinawa trough because of low sea level in turn high proportions of sortable silt and sediment provenance from northeastern taiwan point to strong ocean circulation under the direct and persistent influence of the kuroshio during the holocene the reentrance of the kuroshio to the okinawa trough was heralded by two pulses in relative current strengthening at 11 2 and 9 5 ka bp as documented by stepwise increases in sortable silt in the lower holocene section from a global perspective environmental changes in the southern okinawa trough show affinities to climate change in the western pacific warm pool with little influence of climate teleconnections from the north atlantic realm otherwise seen in many other marine and terrestrial palaeoclimate records from southeastern asia

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

chloride depletions and enrichments in seafloor hydrothermal fluids constraints from experimental basalt alteration studies na k ca cl fluid was reacted with diabase at 400 and 425 c 400 bars and fluidrock mass ratio of 0 5 to assess the relative mobility of dissolved cl fluids from the present experiments reveal relatively large time and temperature dependent decreases in cl temperature increase enhances cl removal whereas reaction progress has the opposite effect these changes are not due to boiling and or phase separation at 400 and 425 c 400 bars cl removal from solution is accompanied by ca and na fixation respectively both experiments produced mixed layer chlorite smectite clinozoisite and albite olivine was not detected by x ray diffraction or petrographic analysis of run products from either experiment however we propose that the time dependent changes in dissolved cl result from olivine replacement by an fe hydroxy chloride phase followed by hydration effects quenched and washed alteration products however did not reveal anomalous cl which suggests that the cl bearing phase is characterized by retrograde solubility this is consistent with the relative magnitude of cl fixation observed for experiments at both temperatures and from results of an isobaric cooling experiment the experiments provide evidence for the non conservative behavior of cl during hydrothermal alteration of basalt the data are particularly important in light of the cl depleted nature of some ridge crest hot spring fluids and suggest temperatures of formation for these fluids of approximately 410 c assuming sub seafloor pressure of 400 bars in addition the retrograde solubility of the cl bearing phase responsible for cl fixation during high temperature basalt alteration may help to explain cl enrichment in hot spring fluids which have conductively cooled below 350 c

halide systematics in interstitial waters of ocean drilling sediment cores abstract the distribution of dissolved halides cl br i in interstitial waters of deep drill holes in the ocean is discussed for a number of environments hemi pelagic sediments hydrate containing sediments sediments affected by halide brines and also in hydrothermal environments the importance of the diagenesis of organic c in the production of i and br is discussed with reference to the observations of dissolved so 4 2 and nh 4 in the pore fluids more importantly in the zone of methano genesis below the so 4 2 reduction zone and usually associated with high organic c accumulation rates increases in i and br are of importance and usually are much higher than the increases observed in the so 4 2 reduction zone in pore fluids affected by dissolution of evaporites the br cl is often a strong indicator of the degree of evaporation of seawater demonstrated from results obtained in the mediterranean sea dissolution of halites on the other hand leads to br cl much lower than those of sea water in hydrothermal sediments there is no doubt that i and br contents of the fluids are influenced by hydrothermal alteration of the sediments and their organic c but signals are not clear the present study provides an overview of previous dsdp and odp studies of halide distributions in sedimentary pore waters in addition to other contributions on halide distributions in sedimentary pore waters in this symposium volume

nonconservative behavior of br cl ratios during alteration of volcaniclastic sediments abstract other than halite diagenesis and organic matter degradation cl and br are considered to be conservative in marine pore fluids consequently br cl ratios should remain constant during most diagenetic reactions nonetheless br cl molar ratios decrease to 1 27 10 3 18 less than seawater value in pore fluids from site 833 in the aoba basin of the new hebrides convergent margin despite the lack of halite diagenesis and little organic matter sediment at this site is largely volcanic ash which becomes hydrated with depth as it converts to clay and zeolite minerals these hydration reactions remove sufficient water to increase the concentrations of most solutes including cl and br the resulting concentration gradients drive diffusion but calculations indicate that diffusion does not decrease the br cl ratio some cl may be leached from the ash but insufficient amounts are available to cause the observed decrease in br cl ratio the limited source of cl suggests that proportionately more br than cl is lost from the fluids to the diagenetic solids similar nonconservative behavior of cl and br may occur during fluid circulation at ridge crests and flanks thereby influencing the halide distribution in the crust

210po 210pb dating of recent volcanic eruptions on the sea floor the globe encircling mid ocean ridge system accounts for most of the earth s volcanism and influences its heat budget morphology and the composition of the oceans it is therefore important to constrain the size frequency and compositional variability of ridge eruptions but this is made difficult by the remoteness of much of the sea floor and the paucity of applicable radioactive chronometers remote monitoring has provided indirect evidence for active ridge volcanism1 3 which in some cases has been strengthened by submersible observations4 5 but it has not been possible to date these eruptions directly here we present a new chronometer based on 210po 210pb radioactive disequilibrium which allows us to date glassy eruption products within a few years of their eruption our first results on lavas from 9 50 n on the east pacific rise confirm that the ridge erupted only months before sample collection and indicate that the eruptions extended over at least one year the chronometer begins with po volatilization during eruption all glasses analysed were 75 100 degassed a crystalline pillow interior was 20 degassed however implying that the flow surface may control po degassing during deep submarine eruptions although the 210po 210pb chronometer is useful for only a short time frame it should prove valuable for dating recent but unobserved submarine eruptions and determining details of eruptive sequences

lithium isotopic systematics of hydrothermal vent fluids at the main endeavour field northern juan de fuca ridge vent fluids issuing from the main endeavour field mef juan de fuca ridge were analyzed for 7li to help constrain subseafloor hydrothermal alteration and phase separation processes magmatic activity prior to sampling of the fluids in 1999 enhanced heat and mass transfer as indicated by the large scale but temporary changes in vent fluid chemistry in particular dissolved chloride concentrations indicate formation of supercritical cl poor vapors which affected alteration throughout the mef system 7li of fluids however ranges from 7 2 to 8 9 and reveals no significant correlation with dissolved chloride being consistent with results of hydrothermal experiments that show no lithium isotope fractionation during supercritical phase separation on a chloride normalized basis li concentration data indicate relatively short residence times or high fluid rock mass ratios of vent fluids most impacted by phase separation effects reaction path models involving li isotope data also show elevated fluid rock mass ratios boron data in contrast suggest direct input from degassing magma enhanced heat flow associated with magmatic injection at depth inhibits penetration of seawater derived hydrothermal fluid into fresh basalt particularly in those systems where magmatic volatile input is most active the inverse correlation between li cl and b cl in vapor rich vent fluids may be a useful indicator of recent subseafloor magmatic activity

salinity variations in submarine hydrothermal systems by layered double diffusive convection various mechanisms have been proposed to explain the salinity variations in vent fluids of seafloor geothermal systems new experiments reacting diabase and evolved seawater were carried out to reproduce earlier published observations of cl depletions attributed to formation of an ephemeral cl bearing mineral the absence of any cl depletions in the present study suggests that the formation of cl bearing minerals is not sufficiently widespread to account for the observed salinity variations in the vent fluids a re evaluation of both field and laboratory evidence has led to a new model for subseafloor circulation that accounts for salinity variations as well as other chemical and mineralogic observations in place of a simple single pass convection system we propose that the seafloor systems consist of two vertically nested convection cells in which a brine layer at depth heats and drives an overlying seawater cell such layering of salinities a process known in fluid mechanics as double diffusive conve

quartz solubility in the two phase and critical region of the nacl kcl h2o system implications for submarine hydrothermal vent systems at 9 50 n east pacific rise abstract experiments were performed to investigate quartz solubility in cl bearing aqueous solutions at temperature 365 430 c and pressure conditions 219 381 bars near and within the two phase region of the nacl kcl h2o system dissolved sio2 concentrations increased with pressure along a given isotherm although the magnitude of this decreased with increasing proximity to the two phase boundary upon intersection of the two phase boundary however significant concentrations of dissolved sio2 characterized vapor rich fluids at both subcritical and supercritical conditions for these fluids dissolved silica concentrations ranged from 2 81 to 14 6 mmolal increasing with dissolved chloride concentration the experimental data permit regression of a density based relationship taking account of non ideal activity concentration effects which can be used to better constrain temperatures and pressures from dissolved sio2 and chloride in high temperature vent fluids at mid ocean ridges accordingly pressure and temperature conditions in subseafloor hydrothermal reaction zones at 9 50 n east pacific rise epr were estimated applying data from this experimental study to interval 1991 2002 and new field data 2004 results indicate reaction zone at conditions ranging from 420 to 430 c at 600 to 1500 m below seafloor thus conditions predicted for 9 50 n east pacific rise epr vent fluids suggest that supercritical phase separation might be more common than previously thought

pixe and microthermometric analyses of fluid inclusions in hydrothermal quartz from the 2 2ga ongeluk formation south africa implications for ancient seawater salinity abstract the ongeluk formation mainly consists of submarine volcanics pillow lavas and sheet flows composed of basaltic andesites that are between underlying and overlying glaciogenic deposits i e the makganyene diamictite and a dropstone layer at the base of the hotazel formation respectively the stratigraphic position of the ongeluk formation indicates that the ongeluk volcanism occurred during a period of global glaciation the ongeluk volcanic rocks are host to subseafloor hydrothermal quartz deposits as drainage cavities and interpillow voids the hydrothermal quartz contains many primary type 1 and secondary type 2 liquid vapor fluid inclusions as well as inclusions that are randomly distributed without a trace of secondary healed cracks type 3 all these fluid inclusions types were individually analyzed with microthermometry and particle induced x ray emission pixe methods the results show that type 1 fluid inclusions are highly saline whereas type 2 fluid inclusions are relatively less saline type 3 fluid inclusions have bimodal peaks of salinity corresponding to those of type 1 and type 2 fluid inclusions and thus appear to represent mixtures between latter two inclusion types among the various fluid inclusion salinities of fluid inclusions a wide range in na ca values was identified in the high salinity fluid inclusions i e type 1 and a subset of type 3 which are thought to represent subseafloor fluids circulated by the ongeluk submarine volcanism the wide range in na ca values can be explained by a mixing process between na rich and ca rich fluids associated with albitization of the host basaltic andesites in the albitization process na is removed from the fluids and fixed by the host rocks by contrast ca is released from the host rocks into the fluids pixe analysis also showed two distinct trends i e vertical and horizontal on variation diagram of ca cl versus cu cl and positive correlations between mn cl cu cl zn cl and pb cl these data are best explained by the presence of other mixing processes between 1 a na rich ca and cu poor fluid 2 a ca rich na and cu poor fluid and 3 a na and cu rich ca poor fluid the cu mn zn and pb rich fluid likely represents a high temperature hydrothermal fluid from a deep reaction zone in the ongeluk subseafloor hydrothermal system by contrast the 1 na and k rich ca and cu poor endmember for the high salinity primary inclusions is considered to represent the composition of 2 2 ga ongeluk seawater we propose the estimation of 2 2 ga ongeluk seawater composition is 2237 mmol kg of na 200 1000 mmol kg of k

song hong red river delta evolution related to millennium scale holocene sea level changes abstract the song hong red river delta occurs on the northwest coast of the south china sea its evolution in response to holocene sea level changes was clarified on the basis of sedimentary facies and 14 radiocarbon dates from the 40 m long duy tien core from the delta plain and using previously reported geological geomorphological and archaeological data the delta prograded into the drowned valley as a result of early holocene inundation from 9 to 6 cal kyr bp as sea level rise decelerated the sea level highstand at 2 3 m from 6 to 4 cal kyr bp allowed widespread mangrove development on the delta plain and the formation of marine notches in the ha long bay and ninh binh areas during sea level lowering after 4 cal kyr bp the former delta plain emerged as a marine terrace and the delta changed into the present tide and wave influenced delta with accompanying beach ridges delta morphology depositional pattern and sedimentary facies are closely related to holocene sea level changes in particular falling sea level at 4 cal kyr bp had a major impact on the evolution of the song hong delta and is considered to be linked to climate changes

northern east pacific rise magnetic anomaly and bathymetric framework the oceanic crust in the eastern pacific between 7on and 30on and east of 127ow contains a fairly complete history of the spreading centers associated with the east pacific rise since 25 m y b p late oligocene in this paper we have summarized the seafloor spreading magnetic anomaly data and the bathymetric data that reflect the record of this tectonic history the well defined magnetic lineations north of the clarion fracture zone in the mouth of the gulf of california and on the east flank of the east pacific rise epr are carefully examined and used to provide a guide for interpreting the spreading pattern between the clarion and clipperton fracture zones southward of the rivera fracture zone over the mathematician ridge and over the entire epr east of the mathematician ridge between the rivera and siqueiros fracture zones the bathymetric data provide a trace of the fracture zone pattern in each of the above mentioned areas the fracture zone bathymetry and the seafloor spreading magnetic lineations on the epr south of the rivera fracture zone have a distinctive fanning pattern caused by close poles of rotation and plate boundary reorganizations all these data provide a good record of the plate reorganizations in the middle miocene at magnetic anomaly 5a time 12 5 to 11 m y b p in the late miocene at magnetic anomaly 3 4 time 6 5 m y b p and in the pliocene at magnetic anomaly 2 3 time 3 5 m y b p several abandoned spreading centers including the mathematician ridge were left behind as a result of these reorganizations the mathematician ridge is shown to be a set of ridges and trough whose origin is related to the tectonic activity associated with each of the above mentioned reorganizations since anomaly 5a

geochemical controls on hydrothermal fluids from the kairei and edmond vent fields 23 25 s central indian ridge prior to 2000 no mid ocean ridge hydrothermal systems were identified and sampled in the indian ocean the kairei field central indian ridge was discovered and sampled in 2000 gamo et al 2001 hashimoto et al 2001 this paper reports the chemical composition of hydrothermal fluids collected in 2001 from both the kairei and newly discovered edmond hydrothermal systems data are used to infer subsurface processes and conditions at the two sites as well as to place them within the global context of known hydrothermal sites on the mid ocean ridge system while both sites are located on the intermediate spreading central indian ridge their hydrologic systems have affinities with those observed on slow spreading ridges although the compositions of fluids from the four individual vents sampled at edmond and the three individual vents sampled at kairei vary respectively our interpretation is that a single source fluid at each site is subsequently modified by processes including phase separation subsurface mixing with seawater and deposition and or remobilization of metal sulfide deposits to generate the observed range of compositions both fields are located 6 km from the neovolcanic zone on steps on the east wall of the axial valley with the edmond field 160 km north of kairei and almost 1000 m deeper 3300 versus 2450 m the edmond fluids are extremely hot with maximum measured temperatures of 382 c compared to 365 c for kairei all of the fluids sampled have chlorinities greater than local ambient seawater due to phase separation of seawater at supercritical conditions visual observations suggest both sites have been active for a substantial period of time again similar to observations of slow spreading ridges our chemical data suggest that the substrate underlying kairei is highly altered while that at edmond is not significant albitization appears to be occurring below the edmond field but not at kairei the edmond fluids are by far the hottest brines yet observed venting from a mid ocean ridge hydrothermal site resulting in unusually high concentrations of several transition metals

chlorine isotope and cl br fractionation in fluids of poas volcano costa rica insight into an active volcanic hydrothermal system abstract halogen rich volcanic fluids issued at the surface carry information on properties and processes operating in shallow hydrothermal systems this paper reports a long term record of cl br concentrations and 37cl signatures of lake water and fumaroles from the active crater of poas volcano costa rica where surface expressions of magmatic hydrothermal activity have shown substantial periodic changes over the last decades both the hyperacid water of its crater lake laguna caliente and subaerial fumaroles show significant temporal variability in cl br concentrations br cl ratios and 37cl reflecting variations in the mode and magnitude of volatile transfer the 37cl signatures of the lake covering the period 1985 2012 show fluctuations between 0 02 0 06 and 1 15 0 09 condensate samples from adjacent fumaroles on the southern shore collected during the interval 2010 2012 with strong changes in gas temperature 107 763 c display a much larger range from 0 43 0 09 to 14 09 0 08 most of the variations in cl isotope br cl and concentration signals can be attributed to interaction between magma derived gas and liquid water in the volcanic hydrothermal system below the crater the 37cl were lowest and closest to magmatic values in 1 fumarolic gas that experienced little or no interaction with subsurface water and followed a relatively dry pathway and 2 water that captured the bulk of magmatic halogen output so that no phase separation could induce fractionation in contrast elevated 37cl can be explained by partial scavenging and fractionation during subsurface gas liquid interaction hence strong cl isotope fractionation leading to very high 37cl in poas fumaroles indicates that they followed a wet pathway highest 37cl values in the lake water were found mostly in periods when it received a significant input from subaqueous fumaroles or when high temperatures and low ph caused hcl evaporation it is concluded that combined monitoring of 37cl and br cl in laguna caliente and adjacent fumaroles provides valuable information on activity in the subsurface hydrothermal system with significant relevance for volcanic surveillance of poas

systematics of and postulated controls on submarine hydrothermal solution chemistry the chemical compositions of seafloor hydrothermal solutions from the galapagos spreading center 21 n and 13 n on the east pacific rise the southern juan de fuca ridge and the guaymas basin gulf of california are examined for systematic variations several elemental ratios elemental products and empirical geothermometers show much consistency among the various areas in spite of large absolute differences in elemental concentrations the results suggest that most of the major cations in these solutions are solubility controlled with respect to a similar phase assemblage at all of the sites examination of the solution chemistry in conjunction with experimental results and seafloor rock alteration data permits identification of phases which may be important in controlling the solution chemistry as potassium appears to be solubility controlled its use to calculate water rock ratios is inappropriate lithium appears to be a better element to use in these calculations a model to explain the observed solution chemistries as a result of three component mixing is discussed all of the solutions are postulated to be either the result of mixing between a seawater hydrothermal solution which has not undergone a phase separation and is hence gas containing a gas rich vapor phase and a gas poor brine phase or any one of these individual components alone the vapor and brine phases are the result of phase separation which may have occurred at some time in the past essentially all of the reported data fall within the field defined by these three components the solutions apparently have had sufficient time after the mixing event s to reequilibrate with the rock this is true for quartz as well as other chemical components the best test of this model is chloride together with gas and isotropic data as the model predicts that solutions with elevated chlorinities will be depleted in gases and enriched in 18 o and low chlorinity solutions will have elevated gas contents and lower 18 o

calibration of br cl fractionation during subcritical phase separation of seawater possible halite at 9 to 10 n east pacific rise abstract experiments were conducted to assess br cl fractionatiodn during phase separation of seawater at 400 c and 250 to 275 bars these conditions are applicable to the 9 10 n epr system where low cl concentrations and low br cl rations in vent fluids have been attributed to phase separation of seawater at conditions below the critical point of seawater 408 c 300 bars the level of br cl fractionation observed in experiments is well below that needed to account for br cl systematics at epr 9 10 n based on our experimental results we propose an alternative model involving dissolution and precipitation of halite to account for the anomalous br cl data at 9 10 n halite can be predicted to form at pressure and temperature conditions prevailing during eruption of magma at mid ocean ridges subsequent changes in physical conditions however would induce halite to dissolve and thus decrease br cl ratios of vent fluids

fe isotope fractionation during phase separation in the nacl h2o system an experimental study with implications for seafloor hydrothermal vents abstract phase separation has been proposed as a possible mechanism contributing to the fe isotope composition of hydrothermal fluids at mid ocean ridges the uncertainty results largely from the emphasis on field data that can involve competing processes that obscure cause and effect of any one process to better understand the potential significance of phase separation in the nacl fe h 2 o system on fe isotope fractionation temperature and pressure of a fe bearing nacl fluid in a titanium flow reactor were carefully adjusted to produce vapor liquid halite while the fe isotope composition between coexisting phases was monitored two different p t regions were emphasized 1 424 420 c 35 2 31 5 mpa and 2 464 466 c 29 8 24 7 mpa both regions were chosen to simulate the range of physical conditions that are experienced by hydrothermal fluids at mid ocean ridges mors decompression induced phase separation in both p t regions results in the vapor phase becoming enriched in the heavier isotopes of fe as the fe cl ratio decreases the coexisting nacl rich liquid phase remains essentially constant with respect to fe cl ratio and fe isotope composition coinciding with the lowest vapor chlorinity in the vapor liquid stability field the fe cl ratio of the vapor abruptly increases while the fe isotope fractionation between the vapor and liquid 10 3 ln v l 56 54 reached a maximum value of 0 145 0 048 subsequently fe isotope fractionation decreased upon transition into the vapor halite stability field p t region 2 we infer that the observed fe isotope fractionation between vapor liquid halite is caused by differences in fe speciation among coexisting chloride bearing phases the experimental study confirms for the first time that measurable fe isotope variability can result from phase separation in high temperature hydrothermal systems the species dependent fe isotope fractionation reported here is small relative to predicted mineral mineral and mineral fluid fractionations especially if redox effects are involved as might occur during vent fluid seawater mixing reactions and or magmatic activity associated with seafloor eruptive episodes

trace element partitioning between vapor brine and halite under extreme phase separation conditions abstract experiments were conducted to investigate the partitioning of li br rb cs and b between vapor brine and halite during subcritical and supercritical phase separation in the nacl h2o system 388 550 c 250 350 bars results indicate that li and br partition preferentially into the low salinity vapor fluids while rb and cs become more enriched in the coexisting brines under more extreme conditions of pressure and temperature in the two phase region especially near the vapor brine halite boundary strong salting out effects imposed on neutral aqueous species enhance significantly partitioning of all trace elements into the low salinity fluid dissolved boron is strongly affected by this and a particularly strong enrichment into vapors is observed a trend that can be effectively correlated with changes in reduced density exclusion of li br rb cs and b from halite when precipitated further increases the solubility of these species in the coexisting cl poor fluid in general the lack of distortion in the partitioning behavior of trace elements between vapor brine and or halite with the transition from subcritical to supercritical conditions in the nacl h2o system precludes the need for special reference to the critical point of seawater when interpreting phase relations in submarine hydrothermal systems the combination of experimentally determined trace element partitioning data with constraints imposed by mineral solubility provides a means to better understand the origin and evolution of hot spring vent fluids for example in brandon hydrothermal system 21 s epr supercritical phase separation and subseafloor mixing appear to be the main heat and mass transport mechanisms fueled by a shallow magmatic intrusion with boron systematics ruling out major contributions from magmatic degassing processes accompanying the near seafloor volcanism

chemistry of hydrothermal solutions from the southern juan de fuca ridge fluids from three vent fields on the southern juan de fuca ridge were sampled in september 1984 using the dsrv alvin the fluids are uniquely high in both chloride which ranges up to twice the seawater value and in metal content simple vapor liquid phase separation could not have produced both the high chlorinity and gas concentrations observed in these fluids the cause of the elevated chlorinity can not be uniquely identified but may be the result of either or a combination of two processes 1 subsurface formation of a degassed brine and subsequent mixing of a small amount of this brine with a hydrothermal seawater which has not undergone a phase separation and 2 dissolution of a chloride rich phase combined with a possible small loss of gas during sampling procedures although measured temperatures were all less than 300 sup 0 c quartz geothermometry suggests that the fluids have equilibrated at greater than 340 sup 0 c quartz geobarometry is also in agreement with geophysical estimates of depth to the local magma chamber copyright american geophysical union 1987

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

kuroshio in the luzon strait 1 three acoustic doppler current profilers adcps were deployed in the central luzon strait to monitor current velocity the profilers were deployed from 1997 to 1999 with the duration of deployment varying by location the observed current velocities indicated that the kuroshio flowed consistently into the south china sea further information provided by composite shipboard adcp data showed that the kuroshio intruded into the luzon strait through the deepest channels 20 5 n most of the intruded component made a loop and flowed out of the northern luzon strait but a branch of the kuroshio intruded into the south china sea while the current velocity obtained from mooring data did not show seasonal variation significant intraseasonal variation ranging from several to 100 days was found the seasonal reversal of monsoonal winds i e northeasterly in winter and southwesterly in summer did not cause noticeable variation in current velocity the miami isopycnic coordinate ocean model together with monthly wind data provided by the european centre for medium range weather forecasts was used to interpret the observed current velocity validation of the model results by the adcp data showed that the model can explain the seasonal and interannual variations in the observed velocity fields for example the model reproduced the branch of the kuroshio that consistently intruded into the south china sea the modeled velocity showed slight seasonal variation in the central luzon strait although the large interannual signal could have hindered the seasonal timescale fluctuation the interaction between the kuroshio and south china sea cyclonic flow caused variation in current velocities in both the luzon strait and the northern sector of the south china sea the model results also indicated that the kuroshio axis bent clockwise within the luzon strait and flowed into and out of the south china sea through the central and northern luzon strait respectively this pattern is similar with that shown by composite shipboard adcp data in summer the kuroshio looped west of the luzon strait with a small intruding branch confined to the northwestern south china sea in winter the intruding branch of the kuroshio extended west and into the interior of the south china sea the net zonal transport of inflow and outflow across the luzon strait calculated from the model results was primarily westward with the maximum varying from 4 8 to 6 5 sv eastward transport was found occasionally in summer in some years with a maximum from 0 3 to 2 2 sv while the kuroshio intruded consistently into the south china sea transport out of the south china sea was also observed in summer the current on the northern south china sea shelf break contributed to the outflow variation in zonal transport was caused by variation in the sea surface height ssh west of northern luzon caused by wind stress curl ekman transport driven by monsoonal winds and the strength of the kuroshio off the luzon strait had little impact on the intrusion which varied with fluctuation of the ssh west of northern luzon

seasonal variations of modern planktonic foraminifera in the south china sea although foraminiferal census and isotope analyses from sediment cores have been widely applied to paleoceanographic reconstructions in the south china sea scs their modern counterparts i e foraminiferal shells from sediment traps and plankton tows have been the subjects of few studies in this region in this investigation relative abundances of the most popular species used to reconstruct late quaternary tropical sea surface conditions have been studied in plankton tows from the scs in order to offer better constraints on the interpretation of downcore records in addition to the seasonal differences the spatial variations in the faunal assemblage are evident from south to north in the scs basin based on contemporary tows for example the species globigerinella aequilateralis is found to be relatively dominant in the southern lower latitude basin but its relative abundance is significantly higher in planktonic tows than in sediments indicating its proneness to burial dissolution pulleniatina obliquiloculata an index taxon for the kuroshio current is only abundant in the northern part of the scs basin the measured oxygen isotope compositions 18o of globigerinoides ruber globigerinoides sacculifer neogloboquadrina dutertrei and p obliquiloculata all show a good relationship with temperature in the mixed layer tmix the carbon isotope compositions 13c also display a positive distribution pattern relative to tmix but with a less significant correlation in winter months than 18o differences of 18o between shallower g sacculifer and g ruber and deep dwellers n dutertrei and p obliquiloculata accurately record the temperature gradient between the surface mixed layer and 100 m water depth supporting application of this proxy to the reconstruction of upper water column stratification

high resolution elemental records from the south china sea and their paleoproductivity implications 1 the biogenic related elements ca sr ba p cd scavenged al and ti were analyzed by inductively coupled plasma mass spectrometry icp ms and inductively coupled plasma atomic emission spectrometry icp aes for core ns93 5 from the west slope of the south china sea terrestrial input as estimated from the accumulation of ti was higher during glacials than during interglacials carbonate accumulation rates are inversely related to those of terrestrial input suggesting higher production of calcareous phytoplankton during interglacials the accumulation patterns of authigenic sr ba p and cd match that of carbonate further indicating higher calcareous phytoplankton production during interglacials scavenged al and excess sio2 which is related to biogenic opal exhibit higher accumulation rates during glacials and correspond with changes in terrestrial input this indicates that terrestrial input driven is important to siliceous phytoplankton production but not for calcareous phytoplankton production as calcareous phytoplankton is the dominant component of the biogenic sediments in the south china sea particularly during interglacials previous inference of higher productivity in the south china sea during glacials based on only the biogenic opal proxy needs to be reconsidered

influence of the kuroshio current intrusion on depositional environment in the northern south china sea evidence from surface sediment records the influence of the kuroshio current kc intrusion on the depositional environment of the northern south china sea scs is discussed based on multi proxies of surface sediments including planktonic foraminifera clay minerals and geochemical elements the results reveal that four typical planktonic foraminifera globigerinoides ruber g sacculifer neogloboquadrina dutertrei and pulleniatina obliquiloculata can be used to trace the kc flow route in the northern scs globigerinoides ruber is mainly distributed in shallower water than the south china sea branch of the kuroshio scsbk flow route while p obliquiloculata is mostly distributed in deeper water than the scsbk flow route there are high percentages of g sacculifer and n dutertrei at the scsbk flow route along the 1000 m isobath where bottom sediments consist of clayey silt and silty clay the scsbk also affects sediment distribution of various sources taiwan sourced sediments characterized by high illite and chlorite contents are transported southwestward into the deep sea environment by the scsbk and or deep water current the pearl river sediments characterized by high kaolinite and titanium ti contents are mostly transported southwestward to be distributed in the sea environment between the pearl river mouth and southeast of hainan island but hardly entered the abyssal basin the luzon island sediments characterized by high smectite content are generally deposited at the northwest of luzon island under the effect of an eddy west of luzon island these sediments were hardly transported northwestward onto the northern shelf of the scs throughout the scsbk flow route the sedimentary environment at the northwest of luzon island is relatively oxidized and higher in salinity than the northern scs which is probably connected with the kc intrusion through the luzon strait

the critical point and two phase boundary of seawater 200 500 c abstract the two phase boundary of seawater was determined by isothermal decompression of fully condensed seawater in the range of 200 500 c the pressure at which phase separation occurred for each isotherm was determined by a comparison of the refractive index of fluid removed from the top and bottom of the reaction vessel the critical point was determined to be in the range of 403 406 c 285 302 bar and was located by the inflection in the two phase boundary and by the relative volume of fluid and vapor as a function of temperature the two phase boundary of 3 2 nacl solution was found to coincide exactly with that of seawater over the range tested in the present study the boundary for both is described by a single seventh order polynomial equation the two phase boundary defines the maximum temperature of seawater circulating at depth in the oceanic crust thus the boundary puts a limit of about 390 c for seawater circulating near the seafloor at active ocean ridges 2 5 km water depth and about 465 c at the top of a magma chamber occurring at 2 km below the seafloor

phase relations and adiabats in boiling seafloor geothermal systems abstract observations of large salinity variations and vent temperatures in the range of 380 400 c suggest that boiling or two phase separation may be occurring in some seafloor geothermal systems consideration of flow rates and the relatively small differences in density between vapors and liquids at the supercritical pressures at depth in these systems suggests that boiling is occurring under closed system conditions salinity and temperature of boiling vents can be used to estimate the pressure temperature point in the subsurface at which liquid seawater first reached the two phase boundary data are reviewed to construct phase diagrams of coexisting brines and vapors in the two phase region at pressures corresponding to those of the seafloor geothermal systems a method is developed for calculating the enthalpy and entropy of the coexisting mixtures and results are used to construct adiabats from the seafloor to the p t two phase boundary results for seafloor vents discharging at 2300 m below sea level indicate that a 385 c vent is composed of a brine 7 nacl equivalent in equilibrium with a vapor 0 1 nacl brine constitutes 45 by weight of the mixture and the fluid first boiled at approximately 1 km below the seafloor at 415 c 330 bar a 400 c vent is primarily vapor 88 wt 0 044 nacl with a small amount of brine 26 nacl and first boiled at 2 9 km below the seafloor at 500 c 520 bar these results show that adiabatic decompression in the two phase region results in dramatic cooling of the fluid mixture when there is a large fraction of vapor

br cl ratios and o h c and b isotopic constraints on the origin of saline waters from eastern canada saline groundwaters were recovered from undisturbed restigouche deposit and active brunswick 12 mine zn pb volcanogenic massive sulfide deposits in the bathurst mining camp bmc northern new brunswick canada these groundwaters along with fresh to brackish meteoric ground and surface waters from the bmc have been analyzed to determine their major trace element and stable isotopic o h c and b compositions saline groundwaters total dissolved solids 22 45 g l are characterized by relatively high na ca ratios compared to brines from the canadian shield and low na clmolar and d 11 b isotopic compositions 2 5 to 11 1 compared to seawater although saline waters from the canadian shield commonly have oxygen and hydrogen isotopic compositions that plot to the left of the global meteoric water line those from the bmc fall close to the water line fracture and vein carbonate minerals at the restigouche deposit have restricted carbon isotopic compositions of around 5 to 6 the carbon isotopic compositions of the saline waters at the restigouche deposit 12 d 13 cdic are the result of fractionation of dissolved inorganic carbon by methanogenesis we suggest that unlike previous models for shield brines the composition of saline waters in the bmc is best explained by prolonged water rock reaction with no requirement of precursor seawater we suggest that elevated br cl ratios of saline waters compared to seawater may be explained by differential uptake of br and cl during groundwater evolution through water rock reaction 2007 elsevier ltd all rights reserved

geochemistry of the surface sediments of the sulu and south china seas abstract the chemical and mineralogical composition of the surface sediments of the sulu sea a deep hydrographically restricted basin in the indonesian archipelago and the neighbouring area of the south china sea have been examined the aim of the study was to characterize the geochemistry of the sediments of the isolated oxygen deficient basin and to compare them with sediments at equivalent water depths outside the basin as a prelude to a further study of the response of the composition of the sediments to oceanographic changes including possible anoxia during the last glacial maximum the concentrations of most of the chemical constituents in the surface sediments along four transects change markedly with water depth in the sulu sea ss and the south china sea scs thus caco 3 decreases from around 60 by weight in the shallowest samples 800 1000 m to around a few percent in the deepest sample at 4203 m in the scs where the ccd lies at around 4000 m in the ss however the ccd lies much deeper so that the caco 3 contents are still approximately 40 at 4500 m depth organic c also decreases with depth in both basins from values of around 1 2 in the shallowest samples to less than 1 in the deepest samples the ratios of si mg na k co cr cu ni pb rb y zr and zn to al all decrease with increasing water depth because of the change in mineralogy and sediment texture with water depth the p al is higher in shallower water in both areas because of the higher abundance of detrital phosphorite or phosphatized limestone in these sediments the sr al ratio is also higher in shallower water reflecting the supply of aragonitic shell debris from the shallow banks and shelves around the basin the ba al ratio has a maximum at 2000 m depth in the scs due to higher primary production in overlying surface waters whereas it is uniformly low in the ss manganese is also enriched at intermediate water depths in both the ss and the scs because of the presence of oxyhydroxides and this also produces a slight enrichment in mo in the same samples because of their association in this authigenic phase the concentration of i and the i c organic ratio decreases with water depth in both areas due to the higher abundance of fresh marine organic matter at the shallow water sites which scavenges proportionally more i from sea water finally the 13 c organic values tend to decrease irregularly with increasing water depth probably reflecting a higher contribution of terrestrial organic matter in deeper water a discriminant analysis of the full data set reveals that compared with the scs samples the oxygen deficient ss sediments have higher caco 3 contents lower n and s contents and lower i c organic ba al fe al k al pb al rb al ti al v al y al and zn al ratios these contrasts are brought about by the different depths of the ccd differences in the nature of the organic matter and different types of aluminosilicate detritus in the two areas although the i c organic ratios are slightly but significantly lower in the ss which may be due to the low dissolved oxygen contents of the waters of this basin the mn and mo contents and other minor elements that respond significantly to ambient bottom water oxygen levels are not significantly different in the ss and the scs moreover the organic c contents are also indistinguishable in the two areas hence the low bottom water oxygen levels in the ss do not lead to higher organic carbon contents in the surface sediments the composition of sediments in contact with waters having even lower oxygen concentrations should be evaluated in order to conduct a more definitive test of the effect of low oxygen conditions on carbon preservation comparison of glacial interglacial sediment sections from this area must take particular care to separate the effects of source variations on those potentially caused by low oxygen levels

the geochemical controls on vent fluids from the lucky strike vent field mid atlantic ridge abstract hydrothermal vent fluids were collected from the lucky strike site at 37 17 n on the mid atlantic ridge in both 1993 and 1996 seven vents were sampled with the dsv alvin in 1993 and six vents were sampled in 1996 using the rov jason during the lustre 96 cruise as three of the vents were sampled in both 1993 and in 1996 a time series of vent fluid chemistry is also reported measured temperatures ranged from 202 to 333 c at the 1618 1726 m depth of the vent field which is located on lucky strike seamount these fluids are either equal to or less than the local bottom seawater in chlorinity while the range in fluid compositions at lucky strike is generally within that observed elsewhere the unusual aspects of the fluid chemistries are the relatively high ph and low fe mn li and zn we attribute this as well as an usually low sr ca ratio to reaction with a highly altered substrate the high si and cu contents suggest a deep as well as hot source for these fluids the fluid compositions therefore suggest formation by super critical phase separation at a depth not less than 1300 m below the seafloor and reaction with a relatively oxic and previously altered substrate there is temporal variability in some of the vent fluid compositions as li k ca and fe concentrations have increased in some of the vents as has the fe mn molar ratio although the chlorinities have remained essentially constant from 1993 to 1996 while there is not a simple relationship between vent fluid compositions or temperatures and distance from the lava lake at the summit of the seamount the vent fluids from many of the vents can be shown to be related to others often at distances 200 m the most southeasterly vents eiffel tower and the marker mounds vents are distinct in chlorinity and other chemical parameters from the rest of the vents although closely related to each other within the southeastern area similarly all of the vents not in this one area appear closely related to each other this suggests one or two source fluids for many of the vents as is also inferred to be the case at tag but which is in contrast to observations on faster spreading ridges this may suggest inherently different plumbing for hydrothermal systems at slower versus faster spreading ridges

the holocene pulleniatina minimum event revisited geochemical and faunal evidence from the okinawa trough and upper reaches of the kuroshio current abstract the holocene pulleniatina minimum event pme is characterized by a very low abundance of the planktonic foraminifer pulleniatina obliquiloculata between 4 5 and 3 ka the pme occurs widely in the okinawa trough and the south china sea and can be correlated throughout this area it has been related to variability in the kuroshio current to further explore the nature of the pme we studied cores obtained from the southern okinawa trough and the upper reaches of the kuroshio current faunal census data indicate that all cores record the pme between 4 5 and 3 ka the relative abundance of neogloboquadrina dutertrei is negatively correlated to that of p obliquiloculata in the southern okinawa trough but not in the sites at the upper reaches mg ca and 18 o measurements on globigerinoides ruber shells from the southern okinawa trough indicate that there was no change in sea surface temperature or sea surface salinity during the pme the vertical structure of the water column as reconstructed by multispecies 18 o and 13 c profiles shows no consistent anomalies in the southern okinawa trough and western philippine sea during the pme these observations suggest that 1 the pme was not restricted to marginal seas but widespread in the western north pacific 2 the high abundance of n dutertrei during the pme in the okinawa trough may be a result of higher food availability in the absence of p obliquiloculata 3 no distinctive consistent anomalies in the paleoceanographic proxies are associated with the pme implying there were no changes in hydrography and productivity the absence of a linkage between faunal variation and paleoceanographic proxies indicates that we do not yet understand what causes changes in planktonic foraminiferal assemblages this lack of understanding implies that we cannot always trust fauna based paleothermometry at millennial timescales

late quaternary course changes of the kuroshio current in the ryukyu arc region northwestern pacific ocean the existence of a land bridge connecting the central southern ryukyu arc to taiwan during the last glacial stage oxygen isotope stages 2 to 4 and its postglacial disappearance are demonstrated by variations in the planktic 18o values and the frequency of pulleniatina in 11 piston cores from the okinawa trough region the upward increase in the pulleniatina group in the cores signals the progressive inflow of the kuroshio current into the okinawa trough area because this group is characteristic of the kuroshio current as revealed here by planktic foraminiferal distribution using 56 surface sediment samples collected from the whole area of this region the ryukyu taiwan land bridge caused eastward deflection of the kuroshio current at the southern end of the ryukyu arc a pulleniatina minimum event in the period from 4500 to 3000 yr b p is recognized in 10 cores from the okinawa trough and one from the northern ryukyu trench slope in contrast to the lgm the decline of pulleniatina in this event was not ascribed to cyclic climate changes such as worldwide cooling but to the formation of a barrier between taiwan and the southern okinawa arc however this regional event influences largely on the holocene climate of japan and its adjacent seas

isotope major minor and trace element geochemistry of late magmatic fluids in the peralkaline ilimaussaq intrusion south greenland abstract the persodic 1 16 ga old ilimaussaq intrusion consists of alkali granites syenites and agpaitic nepheline syenites these rocks are cut by late magmatic veins and lenses consisting of albite aegirine ussingite na2alsi3o8 oh fluorite and occasionally quartz oxygen isotope compositions of quartz indicates both orthomagmatic 18oqtz 8 5 and country rock influenced 18oqtz 10 origin while albite and aegirine do not contain fluid inclusions suitable for investigations ussingite contains secondary hydrocarbon fluid inclusions fluorite contains brine inclusions of primary and secondary origin with up to 26 3 wt naclequiv and quartz contains predominantly secondary brine inclusions with up to 29 7 wt naclequiv or ch4 h2o nacl mixtures these fluids are interpreted to reflect fluids in equilibrium with late stage melts at ilimaussaq at 450 c the carbon and hydrogen isotope composition of ch4 in ussingite 13c 6 to 3 d 121 is indicative of a magmatic abiogenic origin however the isotopic composition of ch4 in fluid inclusions in quartz veins resembles the signature of thermogenic ch4 13c 43 to 23 d 176 to 121 but the higher hydrocarbons are mostly 13c depleted in relation to ch4 up to 7 3 which is typical of abiogenically derived hydrocarbons ion chromatography of fluid inclusion leachates from the late stage veins reveals cl br ratios of 100 as such values seem to be typical of peralkaline magmatic rocks at least in the gardar province of south greenland it is suggested that this ratio is typical of gardar magmatic fluids and may be characteristic of the cl br ratio of the lithospheric mantle from which these alkaline melts are derived

effect of boiling on the acidity of hydrothermal solutions natural seawater and h2o nacl solutions were equilibrated along the two phase liquid vapor curves between 150 and 390 c to re examine the effect of liquid vapor phase separation on element fractionations between saline brines and vapor phases the experimental setup allows vapor and brine to be sampled separately at in situ p t conditions experimental vapor pressure is constrained by temperature and the electrolyte concentration of the brines with increasing temperature dissolved electrolytes react with increasing temperature to hydroxides and hcl in both seawater and h2o nacl solutions the extent of hydrolysis is more pronounced in seawater than in h2o nacl solutions because seawater contains in addition to nacl a range of other electrolytes capable of hydrolysis associated hcl has a great affinity to fractionate to the vapor phase when phase separation occurs at 365 c halite saturated vapor phases have a ph25 ph after condensation to 25 c of 1 8 seawater and 2 8 h2o nacl brines our data suggest that boiling of hydrothermal solutions followed by mixing of vapor condensates with seawater can impose ph25 values as acidic as the most acidic natural hydrothermal solutions vented on the ocean floor

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

volcanic eruption of the mid ocean ridge along the east pacific rise crest at 9 45 52 n direct submersible observations of seafloor phenomena associated with an eruption event in april 1991 in april 1991 we witnessed from the submersible alvin a suite of previously undocumented seafloor phenomena accompanying an in progress eruption of the mid ocean ridge on the east pacific rise crest at 9 45 n 52 n the volume of the eruption could not be precisely determined although comparison of pre and post eruption seabeam bathymetry indicate that any changes in ridge crest morphology resulting from the eruption were 10 m high effects of the eruption included 1 increased abundance and redistribution of hydrothermal vents disappearance of numerous vent communities and changes in characteristics of vent fauna and mineral deposits within the eruption area since december 1989 2 murkiness of bottom waters up to tens of meters above the seafloor due to high densities of suspended mineral and biogenic particulates 3 destruction of a vent community by lava flows mass wasting and possible hydrovolcanic explosion at a site known as tubeworm barbecue in the axial summit caldera asc at 9 50 6 n 4 near critical temperatures of hydrothermal vent fluids ranging up to 403 c 5 temporal variations over a 2 week interval in both temperatures and chemical isotopic compositions of hydrothermal fluids 6 unusual compositions of end member vent fluids with ph values ranging to a record low of 2 5 salinities ranging as low as 0 3 wt nacl one twelfth that of seawater and dissolved gases reaching high concentrations 65 mmol l for both co2 and h2s 7 venting at temperatures above 380 c of visually detectable white vapor that transformed to plumes of gray smoke a few centimeters above vent orifices 8 disorganized venting of both high temperature fluids black and gray smoke and large volumes of cooler diffuse hydrothermal fluids directly from the basaltic seafloor rather than from hydrothermal mineral constructions 9 rapid and extensive growth of flocculent white bacterial mats species unknown on and under the seafloor in areas experiencing widespread venting of diffuse hydrothermal fluid and 10 subseafloor downslope migration of magma normal to the ridge axis in a network of small scale 1 5 m diameter lava tubes and channels to distances at least 100 200 m outside the asc we suggest that in april 1991 intrusion of dikes in the eruption area to 200 m beneath the asc floor resulted in phase separation of fluids near the tops of the dikes and a large flux of vapor rich hydrothermal fluids through the overlying rubbly cavernous lavas low salinities and gas rich compositions of hydrothermal fluids sampled in the eruption area are appropriate for a vapor phase in a seawater system undergoing subcritical liquid vapor phase separation boiling and phase segregation hydrothermal fluids streamed directly from fissures and pits that may have been loci of lava drainback and or hydrovolcanic explosions these fissures and pits were lined with white mats of a unique fast growing bacteria that was the only life associated with the brand new vents the prolific bacteria which covered thousands of square meters on the ridge crest and were also abundant in subseafloor voids may thrive on high levels of gases in the vapor rich hydrothermal fluids initially escaping the hydrothermal system white bacterial particulates swept from the seafloor by hydrothermal vents swirled in an unprecedented biogenic blizzard up to 50 m above the bottom the bacterial proliferation of april 1991 is likely to be a transient bloom that will be checked quickly either by decline of dissolved gas concentrations in the fluids as rapid heat loss brings about cessation of boiling and or by grazing as other organisms are re established in the biologically devastated area

geochemistry of hydrothermal fluids from axial seamount hydrothermal emissions study vent field juan de fuca ridge subseafloor boiling and subsequent fluid rock interaction hydrothermal fluids collected from the ashes vent field in 1986 1987 and 1988 exhibit a very wide range of chemical composition over a small area 60 m in diameter compositions range from a 300 c gas enriched 285 mmol kg co2 low chlorinity 33 of seawater fluid to a 328 c relatively gas depleted 50 mmol kg co2 high chlorinity 116 of seawater fluid the entire range of measured compositions at ashes is best explained by a single hydrothermal fluid undergoing phase separation while rising through the ocean crust followed by partial segregation of the vapor and brine phases other mechanisms proposed to produce chlorinity variations in hydrothermal fluids precipitation dissolution of a chloride bearing mineral or crustal hydration cannot produce the covariation of chlorinity and gas content observed at ashes there is good agreement of the measured fluid compositions with compositions generated by a simple model of phase separation in which gases are partitioned according to henry s law and all salt remains in the liquid phase significant enrichments in silica lithium and boron in the low chlorinity fluids over levels predicted by the model are attributed to fluid rock interaction in the upflow zone depletions in iron and calcium suggest that these elements have been removed by iron sulfide and anhydrite precipitation at some time in the history of the low chlorinity fluids the distribution of low and high chlorinity venting is consistent with mechanisms of phase segregation based on differential buoyancy or relative permeability the relatively shallow depth of the seafloor 1540 m and the observed chemistry of ashes fluids are consistent with phase separation in the sub critical or near critical region

paleoenvironmental change in the middle okinawa trough since the last deglaciation evidence from the sedimentation rate and planktonic foraminiferal record well dated high resolution records of planktonic foraminifera and oxygen isotopes from two sediment cores a7 and e017 in the middle okinawa trough reveal strong and rapid millennial scale climate changes since similar to 18 to 17 thousand years before present kyr b p sedimentation rate shows a sudden drop at similar to 11 2 cal kyr b p due to a rapid rise of sea level after the younger dryas yd and consequently submergence of the large continental shelf on the east china sea ecs and the retreat of the estuary providing sediment to the basin during the last deglaciation the relative abundance of warm and cold species of planktonic foraminifera fluctuates strongly consistent with the timing of sea surface temperature sst variations determined from mg ca measurements of planktonic foraminifera from one of the two cores these fluctuations are coeval with climate variation recorded in the greenland ice cores and north atlantic sediments namely heinrich event 1 h1 bolling allerod b a and yd events at about 9 4 kyr b p a sudden change in the relative abundance of shallow to deep planktonic species probably indicates a sudden strengthening of the kuroshio current in the okinawa trough which was synchronous with a rapid sea level rise at 9 5 9 2 kyr b p in the ecs yellow sea ys and south china sea scs the abundance of planktonic foraminiferal species together with mg ca based sst exhibits millennial scale oscillations during the holocene with 7 cold events at about 1 7 2 3 4 6 6 2 7 3 8 2 9 6 10 6 cal kyr bp superimposed on a holocene warming trend this holocene trend together with centennial scale sst variations superimposed on the last deglacial trend suggests that both high and low latitude influences affected the climatology of the okinawa trough c 2006 elsevier b v all rights reserved

using fire regimes to delineate zones in a high resolution lake sediment record from the western united states article i nfo article history received 20 february 2012 available online 10 november 2012 paleoenvironmental reconstructions are important for understanding the influence of long term climate variabil ity on ecosystems and landscape disturbance dynamics in this paper we explore the linkages among past climate vegetation and fire regimes using a high resolution pollen and charcoal reconstruction from morris pond located on the markagunt plateau in southwestern utah usa a regime shift detection algorithm was applied to back ground charcoal accumulation to define where statistically significant shifts in fire regimes occurred the early holocene was characterized by greater amounts of summer precipitation and less winter precipitation than mod ern ampleforest fuel and warm summer temperatures allowed for large firestooccur themiddleholocenewasa transitional period between vegetation conditions and fire disturbance the late holocene climate is characterized as cool and wet reflecting an increase in snow cover which reduced opportunities for fire despite increased avail ability of fuels similarities between modern forest fuel availability and those of the early holocene suggest that warmer summers projected for the 21st century may yield substantial increases in the recurrence and ecological impacts of fire when compared to the fire regime of the last millennium

el nino like pattern in ice age tropical pacific sea surface temperature sea surface temperatures ssts in the cold tongue of the eastern equatorial pacific exert powerful controls on global atmospheric circulation patterns we examined climate variability in this region from the last glacial maximum lgm to the present using a sst record reconstructed from magnesium calcium ratios in foraminifera from sea floor sediments near the galapagos islands cold tongue sst varied coherently with precession induced changes in seasonality during the past 30 000 years observed lgm cooling of just 1 2 c implies a relaxation of tropical temperature gradients weakened hadley and walker circulation southward shift of the intertropical convergence zone and a persistent el nino like pattern in the tropical pacific this is contrasted with mid holocene cooling suggestive of a la nina like pattern with enhanced sst gradients and strengthened trade winds our results support a potent role for altered tropical pacific sst gradients in global climate variations

influence of the kuroshio current intrusion on holocene environmental transformation in the south china sea numerous studies have been conducted on the evolutionary history of the kuroshio current kc and other extensions however the history of the kc intrusion into the south china sea scs through the luzon strait has been little studied here we trace the holocene developmental history of the kc intrusion and its impact on environmental transformation in the northern scs this study involved a comprehensive analysis of planktonic foraminifera clay minerals and geochemical elements of core 05e306 sediments from the northeastern scs ams c 14 dates indicated that the sedimentation rate at the core site was most rapid 1000 cm ka before similar to 6 0 ka relatively rapid similar to 65 cm ka between 6 0 and 4 6 ka and slow similar to 24 cm ka since 4 6 ka the pulleniatina minimum event pme occurred between 4 6 and 2 7 ka together with high percentages of neogloboquadrina dutertrei and globorotalia menardii planktonic foraminifera indicated that the kc intrusion experienced three significant changes at 6 0 4 6 and 2 7 ka in turn depositional environments including input of terrigenous materials and development of biogenic materials similarly underwent three important transformations at 6 0 4 1 and 3 0 ka respectively abrupt changes in sedimentary records at the study core are contemporary with records from the tropical pacific during the holocene this indicates that development of the kc intrusion and its impact on depositional environments in the scs can be correlated with tropical factors from the low latitude oceans

degassing of metals and metalloids from erupting seamount and mid ocean ridge volcanoes observations and predictions recently it has been reported that the element polonium degasses from mid ocean ridge and seamount volcanoes during eruptions published and new observations on other volatile metal and metalloid elements can also be interpreted as indicating significant degassing of magmatic vapors during submarine eruptions this process potentially plays an important role in the net transfer of chemical elements from erupting volcanoes to seawater in addition to that arising from sea floor hydrothermal systems in this paper a framework is constructed for predicting and assessing semiquantitatively the potential magnitude and chemical fingerprints in the water column of metal and metalloid degassing using 1 predictions from a summary of element volatilities during mafic subaerial volcanism worldwide and 2 limited data from submarine volcanic effusives the latter include analyses of polonium and trace metals in near volcano water masses sampled following a submarine eruption at loihi seamount hawaii 1000 m bsl in 1996 the element volatility predictions and observations show good agreement considering the limited dataset some of the highest volatility main group and transition element enrichments in seawater over loihi are predicted by the degassing mass transfer model i present when expanded to cover all submarine volcanic activity it is predicted that exit fluxes of these elements are up to 102 103 greater by degassing than by normal mor hydrothermalism in contrast mor exit fluxes of low volatility alkali and alkaline earth elements are likely 102 106 greater from hydrothermal inputs degassing inputs to the ocean are probably highly episodic occurring almost entirely during eruptions these are times of enhanced and abnormal hydrothermalism as well although major hydrothermal and degassing events may not be chemically recognizable in real water masses as wholly distinct entities it is nevertheless possible to predict to what extent each process flavors the effluents of the other degassing at mid ocean ridges may explain a variety of observations previously ascribed to complexities occurring during hydrothermal venting and or fluid ascent in the buoyant hydrothermal plumes above ridges