the effect of low temperature hydrothermal alteration on the remanent magnetization of synthetic titanomagnetites a case for acquisition of chemical remanent magnetization the effect of hydrothermal alteration on the thermoremanent magnetization trm of synthetic titanomagnetite tm40 fe2 6ti0 4o4 has been studied to simulate the alteration that occurs in the oceanic crust pseudo single domain titanomagnetite grains similar in size to those often found in oceanic basalts were dispersed in a permeable but rigid glass matrix this resulted in a trm in the sample which was subsequently oxidized in acidic solutions while a magnetic field 0 1 mt was applied perpendicular to the trm direction the experiments were conducted in a non magnetic stainless steel pressure vessel at 150 c in solutions of acidity varying from ph 2 to ph 7 in addition to being time and temperature dependent the acquired chemical remanent magnetization crm was also found to be very ph dependent the degree of maghemitization increased drastically as the acidity of the hydrothermal solution was increased in accordance with a process controlled by the loss of iron ions in aqueous solutions long term storage experiments at carefully chosen temperatures demonstrated that no significant viscous remanent magnetization was acquired during heating it was found that during the alteration of tm40 to titanomaghemite the crm is along the ambient field direction from the onset and not partly or wholly along the trm direction as has been found in previous air oxidation experiments this has important implications for the possible cause of anomalous skewness of marine magnetic anomalies and for the anomalous directions of natural remanent magnetization found in some oceanic basalt samples

evidence of a shallow water submarine hydrothermal field off zannone island from morphological and geochemical characterization implications for tyrrhenian sea quaternary volcanism discoveries from multibeam bathymetry and geochemical surveys performed off zannone island western pontine archipelago tyrrhenian sea provide evidence of an undocumented hydrothermal field characterized by ongoing fluid emissions and morphologically complex giant depressions located in shallow water 250 m that host pockmarks mounds small cones and active fluid vents and which are interpreted as complex fluid escape features developed both through vigorous explosive events and steady seepage their spatial distribution suggests that the ne sw trending faults bounding the ponza zannone structural high and the shallow fractured basement are favorable conditions for the upward migration of hydrothermal fluids moreover we performed a detailed geochemical study to investigate the source of the hydrothermal fluids the geochemical signature of the collected fluids provides information of active co2 dominated degassing with a significant contribution of mantle volatiles with measured 3he 4he values 3 0 ra that are similar to those recorded at stromboli and panarea volcanoes the hydrothermal system produces volatiles that may originate from residual magma batches similar to the pleistocene trachytes cropping out in the se sector of ponza island that were probably intruded in the shallow crustal levels and never erupted the discovery of the zannone hydrothermal field updates the record of active hydrothermal areas of the mediterranean sea moreover the recognition of several giant hydrothermal depressions characterized by a complex morphology is peculiar for the mediterranean sea

hydrothermal germanium over the southern east pacific rise germanium enrichment in the oceanic water column above the southern axis of the east pacific rise results from hydrothermal solutions emanating from hot springs along the rise crest this plume signature provides a new oceanic tracer of reactions between seawater and sea floor basalts during hydrothermal alteration in contrast to the sharp plumes of 3he and manganese the germanium plume is broad and diffuse suggesting the existence of pervasive venting of low temperature solutions off the ridge axis

response of the indian ocean to the tibetan plateau thermal forcing in late spring abstractthe thermal effect of the tibetan plateau tp is known to exert substantial impacts on the atmospheric general circulation suggesting that it may also influence the wind driven circulatio

dolomitization a critical view of some current views the principal models in vogue today for dolomitization are the mixing zone and the sabkha models despite the wide acceptance of these models there has been little critical assessment of their validity such an assessment is the objective of the present paper a close look at the dorag mixing zone model badiozamani 1973 reveals several serious weaknesses 1 the range of freshwater seawater mixtures that meet the dorag requirement for dolomitization shrinks to a small window if the geologically more realistic disordered dolomite is used in the calculations instead of the ordered dolomite on which the model is based 2 in none of the known modern coastal mixing zones in limestone or lime sediments has replacement by dolomite been observed 3 in a number of dolomites interpreted to be of mixing zone origin dolomite has precipitated without dissolution of the calcite substrate evidence that negates the fundamental premise of the dorag model in addition to these weaknesses isotope and trace element data used to identify mixed water dolomite are inadmissible because 1 isotopic fractionation factors for dolomites remain unresolved 2 isotope values uncorrected for temperature for a host of dolomites interpreted to be of different origins overlap 3 nonisomorphous trace elements such as na in dolomite cannot on theoretical grounds be relied on to identify dolomitizing fluids similar overall objections can be brought against folk and land9s 1975 schizohaline version of mixing zone dolomitization in summary mixing zone models have such weak underpinnings that they should be questioned as viable explanations for massive dolomitization contemporaneous dolomite formation in modern sabkhas is well documented but the important question of whether the mechanism of dolomite formation is replacement or direct precipitation remains to be resolved in the well studied sabkha at abu dhabi brine chemistry changes have been used as evidence of a replacement origin for the dolomite but it is shown here that this evidence is far from unequivocal an alternative origin of direct precipitation of dolomite is offered an origin in keeping with dolomite precipitation known from other modern sabkhas and saline lakes and in line with our laboratory experience with dolomite synthesis moreover it is suggested here that in general contemporaneous dolomite will form at low temperatures only by direct precipitation a mechanism that requires special conditions of highly super saturated waters of high mg ca ratio and elevated co 3 hco 3 concentrations this may explain why modern dolomite is mainly restricted to evaporitic environments a bias not shared by ancient dolomites in contrast replacement dolomite appears to require at low temperatures long reaction times or 10 4 yr a requirement that is mainly to be met in large regional groundwater flow systems both marine and nonmarine a third dolomitization model considered here is that of baker and kastner 1981 based on the experimental finding that sulfate ions inhibit or retard dolomitization a number of modern sedimentary dolomites are not in accord with this model in that they are forming from brines with large sulfate concentrations 2 to 70 times that of seawater thus the baker kastner model should be held in abeyance until these serious contradictions are resolved the current emphasis on mixing zone and sabkha dolomitization has diverted attention from other promising avenues of approach to the dolomite problem four of these avenues each of which deemphasizes the special water approach are briefly addressed and are as follows 1 influence of temperature and time 2 mass transfer processes 3 burial diagenesis of epigenetic dolomites 4 fluid inclusion studies at elevated temperatures the dolomite problem essentially disappears ordered dolomite can be made in the laboratory in days at 100 degrees c what is more at temperatures above 60 degrees c ca rich waters become dolomitizing fluids which makes most natural subsurface waters capable of dolomitization at low temperatures time may be the key element so that seawater will become a major dolomitizing fluid only where stable circulation systems such as kohout convention can drive seawater through carbonate platforms for many thousands to millions of years this paper has tried to show that currently favored models of dolomitization carry serious uncertainties enough to warn us to look more critically at the validity of these models and also it is hoped enough to spur new efforts to find new solutions to the problems of dolomitization

ekman heat transport for slab oceans a series of schemes designed to include various representations of the ekman driven heat fluxes in slab ocean models is introduced they work by computing an ekman mass flux then deducing heat fluxes by the surface flow and an opposite deep return flow the schemes differ by the computation of the return flow temperature either diagnosed from the sst or given by an active second layer both schemes conserve energy and use as few parameters as possible simulations in an aquaplanet setting show that the schemes reproduce well the structure of the meridional heat transport by the ocean compared to a diffusive slab ocean the simulated sst is more flat in the tropics and presents a relative minimum at the equator shifting the itcz into the summer hemisphere in a realistic setting with continents the slab model simulates correctly the mean state in many regions especially in the tropics the lack of other dynamical features such as barotropic gyres means that an optimal mean state in regions such as the mid latitudes will require additional flux corrections 2011 springer verlag

the quantum event of oceanic crustal accretion impacts of diking at mid ocean ridges seafloor diking eruptive events represent the irreducible quantum events of upper oceanic crustal accretion they record events by which a large portion of the oceanic crust has formed through geological history since 1993 the u s navy s real time sound surveillance system has allowed location of ongoing acoustic signatures of dike emplacement and basalt eruptions at ridge crests in the northeast pacific these diking eruptive events trigger a sequence of related rapidly evolving physical chemical and biological processes magmatic volatiles released during these events may provide nutrients for communities of subseafloor microorganisms some of which thrive in high temperature anaerobic environments many of the organisms identified from these systems are archaea if microorganisms can thrive in the water saturated pores and cracks within deep volcanically active portions of our planet other hydrothermally active planets may harbor similar life forms

geochemistry and origin of archaean quartz cordierite gneisses from the godthabsfjord region west greenland we report new data on the major minor and trace element compositions of metasedimentary quartzcordierite gneisses qcg an important member of the archaean malene supracrustal suite found throughout the godthabsfjord region of west greenland the analyzed qcg contain assemblages of quartz cordierite biotite garnet anthophyllite gedrite staurolite sillimanite plagioclase with abundant accessory zircon and minor rutile monazite and allanite and broadly resemble cordierite orthoamphibole rocks found in a great number of other metamorphic terrains chemically the qcg are characterized by 1 high but variable sio2 59 87 wt relative enrichments in mgo feo and al2o3 mg 0 35 0 85 and depletions in na2o k2o and especially cao 2 low concentrations of sc cr co ni and sr 3 high concentrations of y nb zr hf ta th u and ree rare earth elements with prominent negative eu anomalies in each case 5 high concentrations of ga 18 55 ppm with variable ga al ratios that are significantly higher than average crustal material low cr and ni together with enriched and fractionated ree displaying negative eu anomalies distinguish the malene qcg from published accounts of most other archaean sedimentary rocks furthermore all of the above mentioned trace element characteristics distinguish the qcg from ordinary malene clastic metasediments quartzites psammites and pelites suggesting a separate origin for the qcg these data point towards chemically evolved felsic igneous rocks being the source of the qcg consequently we propose that the malene qcg represent metamorphosed felsic volcaniclastic sediments that underwent hydrothermal alteration by heated seawater prior to metamorphism which resulted in gain of mg and fe loss of alkalis and lime and possibly eu and sr the overall trace element characteristics of the qcg elevated ga zr nb ree etc are features shared by a type granites and their volcanic equivalents such igneous rocks may represent the ultimate source material for the qcg protolith

boundary layer dynamics and cross equatorial hadley circulation the behavior of the hadley circulation is analyzed in the context of an idealized axisymmetric atmosphere it is argued that the cross equatorial hadley circulation exhibits two different regimes depending on the depth of the planetary boundary layer and the sea surface temperature gradient in the equatorial regions the first regime corresponds to a classic direct circulation from the summer to winter hemisphere the second regime differs in that the return flow rises above the boundary layer in the winter hemisphere and crosses the equator within the free troposphere this equatorial jump is associated with a secondary maximum in precipitation on the winter side of the equator the transition between these two regimes can be understood through the dynamical constraints on the lowlevel flow strong virtual temperature gradients are necessary for the return flow to cross the equator within the planetary boundary layer however the mass transport driven by such a temperature gradient is highly sensitive to the thickness of the boundary layer for a weak temperature gradient or a shallow boundary layer the return flow is prevented from crossing the equator within the the boundary layer and instead must do so in the free troposphere these dynamical constraints act equally in a dry and a moist atmosphere however a comparison between dry and moist simulations shows that the equatorial jump is much deeper in a moist atmosphere this is interpreted as resulting from the feedbacks between the large scale flow and moist convection which results in establishing a very weak gross moist stability for the equatorial jump

the mechanical impact of the tibetan plateau on the seasonal evolution of the south asian monsoon the impact of the tibetan plateau on the south asian monsoon is examined using a hierarchy of atmospheric general circulation models during the premonsoon season and monsoon onset april june when westerly winds over the southern tibetan plateau are still strong the tibetan plateau triggers early monsoon rainfalldownstream particularlyoverthebay ofbengalandsouth china the downstreammoist convection is accompanied by strong monsoonal low level winds in experiments where the tibetan plateau is removed monsoon onset occurs about a month later but the monsoon circulation becomes progressively stronger and reaches comparable strength during the mature phase during the mature and decaying phase of monsoon july september when westerly winds over the southern tibetan plateau almost disappear monsoon circulation strength is not much affected by the presence of the tibetan plateau a dry dynamical core with east west oriented narrow mountains in the subtropics consistently simulates downstream convergence with background zonal westerlies over the mountain in a moist atmosphere the mechanically driven downstream convergence is expected to be associated with significant moisture convergence the authors speculate that the mechanically driven downstream convergence in the presence of the

volcanic and hydrothermal processes in submarine calderas the kulo lasi example sw pacific abstract the study area is located at the transition between the northern end of the tonga trench and the north fiji fracture zone where tectonic movements are reputed to be the fastest in the world to the southeast of futuna island a broad area of volcanism occurs within a region characterized by a change in the tectonic fabric between a ne sw oriented volcanic graben and the n s oriented alofi ridge in 2010 the active volcano kulo lasi which represents the most recent volcanic episode in the futuna area was discovered in the center of this extensive volcanic zone kulo lasi is a 20 km diameter shield volcano that rises 400 m above the seafloor it is composed of basaltic to trachy andesitic lava with no obvious geochemical affinity with the tonga subduction that occurs 500 km to the east the central caldera is 5 km in diameter and 300 m deep and is located at a water depth of 1500 m diving operations with the submersible nautile and high resolution auv mapping have revealed the presence of numerous active and inactive hydrothermal fields on the floor and the walls of the caldera four tectono volcanic stages can be distinguished at kulo lasi caldera in stage 1 the shield volcano is built annular reverse faults develop at the summit and control circulation of water rock dominated hydrothermal fluids and high temperature alteration of rocks along the nascent normal faults mixing of hydrothermal fluids with seawater is favored along normal superficial faults leading to the formation of low temperature fe mn mineralization at the summit of the volcano during stage 2 the caldera collapse gradually revealing outcrops of the altered and mineralized zones formed during stage 1 as the magma chamber cools and collapses less heat is available as a result medium to low temperature

metabasalts axial hot springs and the structure of hydrothermal systems at mid ocean ridges knowledge of the chemical transfer and mineralogical transformations that occur when sea water reacts with basalt at elevated temperatures and pressures can be used along with geological and geophysical data to deduce the typical structure and evolutionary sequence for hydrothermal systems within the oceanic crust along the axis of a mid ocean ridge studies of metabasalt and metadiabase dredged from fault scarps along the axial valley of the mid atlantic ridge reveal consistent relationships among the bulk chemistry of the altered rocks and their secondary mineralogy mineral abundances and mineral compositions especially for chlorite these relationships can be interpreted in terms of the distribution of alteration with respect to time temperature and water rock ratio in young crust assemblages of chl ab ep act chl ab ep act qtz chl ab qtz and chl qtz are produced at successively higher effective sea water to rock ratios within the temperature range of the greenschist facies 250 to 450 c toward higher ratios chlorites tend to become more mg rich pillow basalts of layer 2 are commonly altered under these conditions by sea water on the descending rather than the ascending limb of a convection system this type of alteration which reflects moderately high water rock ratios may characteristically occur above a still partially molten magma chamber as the magma chamber solidifies and is then penetrated more pervasive alteration of the deeper part of layer 2 and of layer 3 occurs at lower water rock ratios producing solutions such as those recovered from springs on the galapagos rift and the east pacific rise at 21 n localized upwelling limbs of the convection system can produce veins filled with quartz sulfides and fe rich chlorite

crustal processes at spreading centers recent discoveries and research on mid ocean ridges mor s in the last four years have greatly increased our knowledge of this fundamental type of plate boundary the last iugg review of mor research was in 1975 aumento et al 1975 and its omission as a topic in 1978 may have reflected a feeling that spreading centers were reasonably well understood since that time however there has been a surfeit of important new observations and exciting research and there is now a turmoil of innovative ideas about the processes which create and leave their imprint on two thirds of the earth s crust new seismic measurements have been made and interpreted as evidence for the existence of shallow axial magma chambers amc beneath intermediate total opening rate 5 9 cm yr and fast 9 18 cm yr spreading centers fig 1 yet there is controversy as to whether they are steady state whether they persist beneath slow ridges as well in the steady state what the dimensions and shape of the chamber are its relation to oceanic crustal stratigraphy and its relation to observations in ophiolites black smoker hydrothermal vents have been discovered in the pacific spewing forth 350 c fluids blackened by polymetallic sulfide precipitates this discovery is embroiled in debate as to how long the vents last whether they occur at slow spreading rates as well whether the enormous heat flux of the vents freeze the magma chamber even at fast spreading rates their influence on geochemical balances in the ocean and the value of the sulfide deposits commercially it has been found that our initial view of mor s as two dimensional linear structures has served us well as an initial working model but must be significantly modified to account for variations in tectonic volcanic and hydrothermal activity along strike as well as for episodicity of these processes deep sea drilling project dsdp samples have raised fundamental questions about formation of the magnetic source layer hydrothermal circulation and fault mechanisms along the mor spreading centers which penetrate existing lithosphere along strike as propagating rifts have modified our views of how plate boundaries reorient themselves and how v shaped magnetic and topographic trends are formed we have also found that transform faults may modify spreading center processes for some distance away from their intersections with mor s and that rigid plate transform faults may fail to develop at fast spreading centers under certain conditions resulting in en echelon overlapping of spreading centers this review will focus on these developments and several others only example references to these topics will be given in the text and many important topics will not be discussed directly e g petrology and geochemistry mantle convection research on lithosphere older than 1 m y however i have tried to compile and have included an extensive bibliography for u s research on a broader range of mor topics for mid 1978 to mid 1982 which is the main purpose of this report pre 1978 references are occasionally included where appropriate abstracts are not included

hydrothermalism in the mediterranean sea abstract hydrothermalism in the mediterranean sea results from the collision of the african and european plates with the subduction of the oceanic part of the african plate below europe high heat flows in the resulting volcanic arcs and back arc extensional areas have set up hydrothermal convection systems most of the known hydrothermal sites are in shallow coastal waters

regime change behavior during asian monsoon onset abstractas the itcz moves off the equator on an aquaplanet the hadley circulation transitions from an equinoctial regime with two near symmetric significantly eddy driven cells to a monsoon like regime with a strong thermally direct cross equatorial cell intense low latitude precipitation and a weak summer hemisphere cell dynamical feedbacks appear to accelerate the transition this study investigates the relevance of this behavior to monsoon onset by using primitive equation model simulations ranging from aquaplanets to more realistic configurations with earth s continents and topography a change in the relationship between itcz latitude and overturning strength is identified once the itcz moves poleward of about 7 monsoon onset is associated with off equatorial ascent in regions of non negligible planetary vorticity and this is found to generate a vortex stretching tendency that reduces upper level absolute vorticity in an aquaplanet this causes a transition to the cross equatorial therm

chemical alteration of the oceanic crust the alteration of the upper oceanic crust through sea water basement rock interaction produces different and distinct alteration zones with increasing depth the zonation generally shows a consistent worldwide pattern

an estimate of hydrothermal fluid residence times and vent chimney growth rates based on210pb pb ratios and mineralogic studies of sulfides dredged from the juan de fuca ridge abstract the210pbpb ratios across two sulfide samples dredged from the juan de fuca ridge are used to estimate the growth rate of the sulfide material and the residence time of the hydrothermal fluid within the oceanic crust from the onset of basalt alteration 210pb is added to the hydrothermal fluid by two processes 1 high temperature alteration of basalt and 2 if the residence time of the fluid is on the order of the 22 3 year half life of210pb by in situ growth from222rn krishnaswami and turekian 1982 stable lead is derived only from the alteration of basalt the210pb pb ratio across one sample was 0 5 dpm 10 6 g pb and across the other it was 0 4 dpm 10 6 g pb these values are quite close to the238up b ratios of basalts from the area suggesting that the residence time of the hydrothermal fluid from the onset of basalt alteration is appreciably less than the mean life of210pb i e the time required for ingrowth from the radon an apparent growth rate of 1 2 cm yr is derived from the slope of the210pb pb curve for one of the samples this is consistent with its mineralogy and texture which suggest an accretionary pattern of development there is no obvious sequential growth pattern and virtually no gradient in210pb pb across the second sample this is consistent with alteration of the original210pb pb distribution by extensive remobilization reactions which are inferred from the mineralogic and textural relationships of the sample

atmospheric pressure and gravity summary gravity green s functions for a column load of a model atmosphere on a spherical elastic earth are presented and they are used to evaluate the contribution of global atmospheric pressure variations to local gravity the green s functions are found to be relatively insensitive to the details of the model atmosphere but they are dependent on the temperature at the base of the column and on the relative height difference between the base of the column and the gravity station the total signal that global pressure systems contribute to gravity is about 30 gal of which about 90 per cent is produced by the atmosphere within 50 km of the gravity station a zone between 50 and 1000km from the gravity station contributes a couple of gal as does the remainder of the globe this pattern the coherence scale of pressure fluctuations the time and spatial scales appropriate to the hydrostatic approximation and the distance of the gravity station from the oceans suggest a division of the globe into local regional and global zones data requirements processing details and the reliability of the computed signal are different in each zone the local zone is within about 50 km of the gravity station within this zone pressure changes rapidly in time but is spatially coherent so that hourly observations of pressure and temperature at the gravity site alone are sufficient to compute an accurate correction except when a front is passing through the regional zone extends from the edge of the local zone to between several hundred and a thousand kilometres the signal from this zone is small and is only weakly coherent with the signal from the central zone so that a rather sparse array of hourly samples of pressure and temperature are required the gravity signal from the global zone can reach about a gal it varies on a time scale of days and is influenced by the response of the oceans to pressure variations previously reported observations that the admittance between local pressure and gravity residuals depends on epoch frequency or site are most probably due to incorrect modelling a proper local regional temperature and global correction can adequately account for the gravity signal from the atmosphere to within a few tens of ngal in the diurnal band and about 100 ngal in the days to seasonal band except during extreme weather conditions the application of the local correction lowers the power spectral density of the gravity residuals in every band from seasonal to hourly the regional global and temperature corrections lower the residual noise in the seasonal and synoptic bands but are not consistently effective at periods less than about half a day

deformation induced by polar motion variations in the geocentric position of the earth s rotation axis polar motion cause deformation within the earth we estimate the effects of this deformation on radial and horizontal positions of points on the earth s surface on baseline lengths between those points and on surface gravity the effects of the oceans and of the earth s anelasticity on this deformation are found to be negligible peak to peak variations in radial motion are typically 10 20 mm over a year horizontal displacements are less than 7 8 mm variations in baseline length can be as large as 30 40 mm variations of up to 13 gal in surface gravity are possible these numbers are all small enough that they can probably not be used to learn about the earth however they are large enough to affect noticeably present high quality geodetic observations

hydrothermal iron rich deposits from the teahitia mehitia and macdonald hot spot areas southwest pacific abstract during cruise so 47 of r v sonne iron oxyhydroxide crusts of restricted extent were recovered from teahitia and moua pihaa seamounts in the teahitia mehetia hot spot area and from macdonald seamount in the macdonald hot spot area the crusts show complex layering and incorporate volcanic ash layers they consist of goethite feldspar and pyroxene and display low contents of transition elements apart from fe it is believed that the crusts were deposited from relatively low temperature hydrothermal fluids these low temperatures preclude the formation of sulphide deposits the type of hydrothermal mineral recovered may be a function of the thermal regime of the system and the elevation which controls the pressure of the venting fluids the shallower depths of these seamounts compared to the axes of mid ocean ridges may therefore be responsible for the style of mineralization initially magmatic vapours migrating upwards through the hot spot volcano are thought to be absorbed into seawater at comparatively shallow levels to deposit sulphide minerals within the volcanic pile the fe oxyhydroxide deposits are the residual low temperature deposits formed when the spent hydrothermal fluid reached the crest of the seamount these deposits therefore differ fundamentally from those found at the crest of mid ocean ridges where sulphide mounds are deposited directly upon interaction of the boiling hydrothermal fluid with seawater the discovery of hydrothermal iron oxyhydroxide crusts in these two hot spot areas is only the second such finding after loihi seamount southeast of hawaii

an assessment of the effect of chemical scavenging within submarine hydrothermal plumes upon ocean geochemistry profiles of 210pb over the endeavour and north cleft segments of the juan de fuca ridge are used to model a time scale for the scavenging by hydrothermal plumes of reactive elements in seawater the hydrothermal plumes above these ridge segments are sites of intense scavenging removal of 210pb at endeavour the total 210pb activities within the plume are as low as 8 dpm 100 l and dissolved activities are as low as 3 dpm 100 l at the north cleft which is characterized by higher particulate fe concentrations the total 210pb activities are 4 5 dpm 100 l the dissolved activities are 1 2 dpm 100 l and the 210pb activities are deficient with respect to the activity of the 210po daughter these are perhaps the lowest 210pb activities ever measured in the deep sea the large gradient of 210pb between the plume and surrounding deep water suggests that scavenging is focused into the plumes through horizontal transport the implication therefore is that this process might impact the ocean on a scale larger than that local to the ridge crest by coupling published measurements of particle flux from endeavour with 210pb activities on particles trapped at that site the total volume of seawater stripped of 210pb per year for that site was calculated to be 7 4 1012 l y globally the extrapolated volume flux of seawater stripped of reactive constituents is 5 7 1015 l y such that the entire ocean is processed in this manner in 2 4 105 y the geochemical cycle of elements with ocean residence times much shorter than this e g pb and th will not be greatly affected by hydrothermal scavenging on the other hand this process holds significance for the geochemistry of other elements scavenged by hydrothermal plumes such as p and v whose ocean residence times are 104 y

evidence of an early alteration process driven by magmatic fluid in mururoa volcano evidence for a deuteric alteration process induced by a magmatic fluid has been found in the feeder zone of the mururoa volcano french polynesia within the dikes where basaltic glass does not show any evidence of pervasive alteration vesicles are filled with dioctahedral smectites and calcite while olivine phenocrysts are replaced by dioctahedral smectites ankerite and calcite the 13c signature of carbonates the carbon and h2o content of the whole rocks and their impoverishment in deuterium are compatible with the presence of magmatic co2 during the crystallization of intruding lavas and exclude contamination by seawater mass balance calculations on selected thin sections photographs of partly filled up vesicles and replaced olivine crystals constrain assuming a closed system interaction the chemical composition of the initial fluid and the respective amounts of the initial solid phases involved in the alteration process thermodynamic modelings using the eq3 6 software package correctly predict the mineralogic chemical and isotopic exchanges accompanying alteration thus validating the closed system assumption the model which allows prediction of the influence of co2 on the alteration products shows that above a 0 25 co2 mole fraction in the initial fluid the alteration is entirely controlled by the chemical composition of the initial solid phases the presence of co2 implies the precipitation of dioctahedral smectites and carbonates instead of the magnesian smectites commonly observed in co2 free systems the mururoa feeder zone shows alteration features typical of a closed system interaction between the basaltic rock and a magmatic fluid in which seawater did not take part

analysis of superconducting gravimeter data from table mountain colorado summary we present an analysis of more than two years of data from the superconducting gravimeter co24 at the national oceanic and atmospheric administration s table mountain geodetic observatory tmgo near boulder colorado the gravity data sampled at intervals of 5 s were cleaned for gaps disturbances and oisets and then decimated to 1 hr and an eterna analysis was done to determine the tidal gravimetric factors and phases during which the atmospheric pressure loading and the period and damping of the free core nutation were obtained we nd t 418 14 days and 1152 q 2848 a short period analysis of the ve quietest days in the seismic mode band 200 600 s shows the combined instrument site noise to be one of the lowest of all the superconducting gravimeters analysed to date for the long periods a local tide including various ocean loading models is subtracted from the data and the residual gravity shows very good correlation with iers polar motion instrument drift is well tted by a positive exponential function with a value of about 5 gal yr 1 at the end of the record analysis of the pressure using a complex frequency dependent admittance shows some improvement in noise over using a simple scalar admittance function in the slichter mode and core mode bands there are no signi cant peaks to be noted more de nitive evidence of signals from the earth s core will require stacking using the global geodynamics project network tmgo is an extremely stable site with excellent noise characteristics

the geochemistry of inorganic germanium in natural waters we present the initial results from a survey of the distribution of dissolved inorganic germanium in rivers in the oceans and in hydrothermal vents and plumes in the ocean germanium cycling mimics that of silica since siliceous organisms incorporate ge as a trace constituent in biogenic opal the vertical and horizontal distributions of ge concentrations in seawater are thus identical to those of silica ge si 0 7 10 6 and reflect uptake into and dissolution from the frustules of siliceous organisms germanium enters the ocean via dissolution of continental and seafloor silicates the naturally weathered flux from continents to oceans carries a dissolved ge si atom ratio in rivers of about 0 7 10 6 which reflects the ratio in average continental granites rivers draining industrial regions with significant coal combustion are contaminated with ge leached from fly ash particles resulting in ge si ratios up to tenfold above the naturally weathered background the flux to the oceans via high temperature alteration of seafloor basalts hot springs produces a ge anomaly in hydrothermal plumes over the east pacific rise crest 20 s combining the observed ge and 3he anomalies in plumes with 3he si observations in hot springs suggests that the ge si hydrothermal flux to the oceans is about 4 10 6 near the ratio for average oceanic basalts 2 6 10 6 vent effluents from the galapagos hot springs measured directly display ge si ratios of 16 10 6 suggesting that the ratio is variable between vent fields metalliferous sediments accumulating on the epr crest 17 s are enriched in germanium suggesting that a fraction of the hydrothermal germanium source on the rise crest is scavenged into these rapidly accumulating iron and manganese hydroxyoxide phases

meridional ekman heat fluxes for the world ocean and individual ocean basins abstract monthly climatological estimates of wind stress and sea surface temperature are used to compute meridional ekman heat fluxes in the world ocean qualitatively the annual cycles of the atlantic and pacific oceans are quite similar but quantitatively the pacific estimates are up to several times larger than the atlantic estimates the indian ocean exhibits an annual mean southward flux over nearly all of the 24 5 n 31 5 s latitude belt which qualitatively supports an annual mean net southward heat flux for this region as determined by surface heat balance requirements a large southward heat flux in the indian ocean centered at about 7 5 n during northern hemisphere summer is responsible for a global ekman heat flux distribution with an annual cycle in the tropics that qualitatively resembles the results of oort and vonder haar

impact of mountains on tropical circulation in two earth system models abstracttwo state of the art earth system models esms were used in an idealized experiment to explore the role of mountains in shaping earth s climate system similar to previous studies removing mountains from both esms results in the winds becoming more zonal and weaker indian and asian monsoon circulations however there are also broad changes to the walker circulation and el nino southern oscillation enso without orography convection moves across the entire equatorial indo pacific basin on interannual time scales enso has a stronger amplitude lower frequency and increased regularity a wider equatorial wind zone and changes to equatorial wind stress curl result in a colder cold tongue and a steeper equatorial thermocline across the pacific basin during la nina years anomalies associated with enso warm events are larger without mountains and have greater impact on the mean tropical climate than when mountains are present without mountains the centennial mean pacific walker circulation wea

monsoons as eddy mediated regime transitions of the tropical overturning circulation monsoons are generally viewed as planetary scale sea breeze circulations caused by contrasts in the thermal properties between oceans and land surfaces that lead to thermal contrasts upon radiative heating1 2 but the radiative heating evolves gradually with the seasons whereas the onset of monsoon precipitation and the associated circulation changes such as reversal of surface winds occur rapidly3 4 here we use reanalysis data to show that the onset of the asian monsoon marks a transition between two circulation regimes that are distinct in the degree to which eddy momentum fluxes control the strength of the tropical overturning circulation rapid transitions of the circulation between the two regimes can occur as a result of feedbacks between large scale extratropical eddies and the tropical circulation5 using simulations with an aquaplanet general circulation model we demonstrate that rapid eddy mediated monsoon transitions occur even in the absence of surface inhomogeneities provided the planet surface has sufficiently low thermal inertia on the basis of these results we propose a view of monsoons in which feedbacks between large scale extratropical eddies and the tropical circulation are essential for the development of monsoons whereas surface inhomogeneities such as land sea contrasts are not

two years of continuous measurements of tidal and nontidal variations of gravity in boulder colorado we report here on the results of an analysis of 2 years of data from noaa s superconducting gravimeter located at the table mountain gravity observatory in boulder colorado observed tidal parameters corrected for ocean loading effects are compared with theoretical tidal parameters predicted for a non hydrostatic inelastic earth model and demonstrate excellent agreement tidal residuals corrected for polar motion and a linear instrument drift are highly correlated with gravity changes measured by two absolute gravimeters over the same time period the admittance to local pressure is found to be 0 356 gal mbar however this admittance factor is found to be seasonally and frequency dependent correlations between rainfall events and gravity changes are observed attempts to model these gravity changes as exponential functions of time were unsuccessful

lithium isotopes in hydrothermally altered basalts from hengill sw iceland abstract the li isotope signatures of hydrothermal fluids are remarkably constant li 7 8 0 1 9 irrespective of the water rock ratio w r permeability temperature or fluid involved seawater or meteoric high temperature hydrothermal fluids represent the second most significant source of li to the ocean yet the homogeneity of the li isotopic signatures of this source remains to be explained and in this context the lack of data for the corresponding altered phases is problematic we measured li contents and li isotope signatures as well as mineralogy composition and local fluid temperature in hyaloclastites collected from a borehole in the hellisheidi geothermal system iceland which have been altered by high temperature aqueous fluids from 170 to 300 c li is more enriched in the solid phases than the other alkali metals highlighting its greater ability to be incorporated into secondary phases especially at high temperatures 250 c mass balance calculations show that the low li concentrations in hydrothermal fluids are best explained by a high water rock ratio and a high permeability of this system the li isotopic signature of the altered hyaloclastites li 7 between 1 9 and 4 0 remains close to the fresh basalt at deep levels and high temperatures 290 300 c as measured li 7 range between 3 7 and 4 0 and decreases at shallower depths and lower temperatures 150 270 c li 7 between 1 9 and 3 1 a mass balance model involving basalt dissolution secondary phase formation and successive isotope equilibrium during the migration and the cooling of the percolating fluid was developed the corresponding apparent mineral fluid li isotope fractionation factors resulting from precipitation of secondary phases li minerals fluid 7 range between 0 at 300 c and 8 5 at 170 c and highlight a key role of chlorite applying the same approach to mid ridge oceanic hydrothermal systems allows the relatively homogeneous isotope signatures of high temperature fluids of various locations to be explained

dominant control of the south asian monsoon by orographic insulation versus plateau heating heat emitted from the tibetan plateau as dry heat and water vapour has long been assumed to be the main driver of the south asian summer monsoon but new work suggests that in fact it is the neighbouring mountains that are the major influence william boos and zhiming kuang use an atmospheric model to show that flattening the tibetan plateau has little effect on the monsoon so long as the himalayas and surrounding mountain ranges remain the plateau does boost rainfall locally along its southern edge but it is the build up of hot moist air over india insulated from colder drier air by the himalayas that drives large scale monsoon circulation the elevation of the tibetan plateau is thought to cause its surface to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales here however an atmospheric model is used to show that flattening of the tibetan plateau has little effect on the monsoon provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved the tibetan plateau like any landmass emits energy into the atmosphere in the form of dry heat and water vapour but its mean surface elevation is more than 5 km above sea level this elevation is widely held to cause the plateau to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales1 2 3 4 5 observations of the present climate however do not clearly establish the tibetan plateau as the dominant thermal forcing in the region peak upper tropospheric temperatures during boreal summer are located over continental india south of the plateau here we show that although tibetan plateau heating locally enhances rainfall along its southern edge in an atmospheric model the large scale south asian summer monsoon circulation is otherwise unaffected by removal of the plateau provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved additional observational and model results suggest that these mountains produce a strong monsoon by insulating warm moist air over continental india from the cold and dry extratropics these results call for both a reinterpretation of how south asian climate may have responded to orographic uplift and a re evaluation of how this climate may respond to modified land surface and radiative forcings in coming decades

deep sea and shallow water hydrothermal vent communities two different phenomena hydrothermal vent communities from 76 areas lying at depths from 0 to 4100 m were split into two groups bdeepq and bshallow waterq based on the occurrence of vent obligate restricted to hydrothermal vents taxa of a high rank genus and family the two groups were then compared based on a large set of environmental faunistic and community parameters the degree of obligacy of fauna sharply changes at the depth of approximately 200 m in 21 shallow water areas located at depths b200 m vent obligate taxa are absent or their taxonomic rank does not exceed a species the total number of vent obligate species in shallow water is 8 and their obligacy is uncertain data from 55 areas lying at depths from 200 to 4100 m indicate there are ca 400 obligate species in 47 of these areas obligate vent taxa of the genus or the family rank are present obligate taxa of the genus rank appear at 200 m depth and of the family rank at 386 m the depth ca 200 m corresponds well with differences in community structure and composition and environmental parameters deep sea n200 m hydrothermal communities differ from shallow water ones b200 m in a much higher ratio of vent obligate taxa deep sea vent communities are also distinguished by the lack of diatom and algae bacterial mats phytoplankton lower species richness the development of large sulphide structures higher role of active vents in structuring communities in space replication of a set of dominant taxa in communities within large regions reproduced through the succession at newly formed vent fields more pronounced concentric and vertical zonality higher biomass of macrofauna the important role of symbiotrophic forms dominating the biomass the ratio of species with a bpointq species range endemic to small areas is higher in the deep sea there are no significant differences between the vent and non vent biogeography both in shallow waters and the deep ocean modern deep sea hydrothermal vent communities have a longer evolutionary history than their shallow water counterparts to explain major differences between deep and shallow water hot vent communities evolutionary processes need to be analysed over long geological periods and within global vertical zones it is suggested that the proportion of organic matter derived from chemosynthesis and photosynthesis plays a crucial role in evolution when calculated for global zones this proportion increases with depth to a certain critical level that separates deep and shallow water hot vent communities and fauna vertical zonation in the distribution of obligate taxa in hydrothermal vent communities indicates that this level is reached at approximately 200 m depth

major element variations in basalts and diabases from the north arm mountain massif bay of islands ophiolite implications for magma chamber processes at mid ocean ridges abstract the major element compositions of aphyric diabases from the north arm mountain massif range from primitive basalts to highly evolved ferrobasalts from modeling of these compositional variations it is clear that the diabases have undergone highly variable 10 to 90 increments of crystallization at low pressures the dominant minerals inferred to have crystallized from the liquids that formed these diabases are olivine plagioclase and clinopyroxene the same minerals that dominate the underlying cumulate gabbroic and ultramafic rocks the projection of these compositions onto pseudo liquidus phase diagrams suggests that the primary magma s from which this north arm suite was produced were generated by melting at 10 25 kbar or greater pressure there is no indication in the major element variations of these diabases of the operation of high pressure crystal factionation processes which is not surprising because low pressure fractionation processes will effectively mask evidence for earlier high pressure processes it is suggested that the tapping of intercumulus liquid from crystal mush areas and the tapping of discrete fractionated magmas within the roof zone of magma chambers is a method of producing a wide variety of magma compositions from a single magma chamber in which the majority of the chamber may be actively convecting and therefore remain relatively uniform in composition

the dynamics of idealized convection schemes and their effect on the zonally averaged tropical circulation in this paper the effect of a simple convection scheme on the zonally averaged tropical general circulation is examined within an idealized moist gcm to obtain broad classifications of the influence of convection on the tropics this is accomplished with a simplified convection scheme in the style of betts and miller the scheme is utilized in a moist gcm with simplified physical parameterizations gray radiation with zonally symmetric slab mixed layer ocean boundary conditions comparisons are made with simulations without a convection scheme i e with large scale condensation lsc only with the moist convective adjustment mca parameterization and with various formulations and parameter sets with a simplified betts miller sbm scheme with the control run using the sbm scheme the tropics become quieter and less dependent on horizontal resolution as compared with the lsc or mca simulations the hadley circulation mass transport is significantly reduced with the sbm scheme as is the itcz precipitation an important factor determining this behavior is the parameterization of shallow convection without shallow convection the convection scheme is largely ineffective at preventing convection from occurring at the grid scale the sensitivities to convection scheme parameters are also examined the simulations are remarkably insensitive to the convective relaxation time and only mildly sensitive to the relative humidity of the reference profile provided significant large scale condensation is not allowed to occur the changes in the zonally averaged tropical circulation that occur in all the simulations are understood based on the convective criteria of the schemes and the gross moist stability of the atmosphere

progressive dolomitization of florida limestone recorded by alkaline earth element concentrations in saline geothermal submarine springs 1 studies in the late 1970s revealed that the effluents of saline geothermal submarine springs on the west florida shelf have compositions nearly identical to seawater except for distinct ca enrichments and mg depletions probably resulting from dolomitization during annual visits between 1996 and 2003 we collected high purity effluents from four submarine springs and from warm mineral springs wms which is located on land filtered effluents were analyzed for major ions and for sr and ba these analyses confirm the seawater like composition of the effluents as well as the ca enrichment and mg depletion the alkaline earth elements sr and ba like ca and ra are significantly enriched in the effluents compared to ambient seawater by average factors of 1 6 and 3 8 respectively about 9 and 12 for wms the mg depletion and the sr and ba enrichments while invariant over the 7 year sampling period increase gradually from south to north consistent with progressive dolomitization of limestone along the purported convective flow path of the warm seawater the ca enrichment shows no obvious trend because besides dolomitization gypsum dissolution is an independent source of ca a simple mass balance indicates that the ca excess is fully accounted for by these two processes in all four submarine springs this is not the case for wms where a residual ca excess points to a third source of ca presumably limestone dissolution that occurs upon mixing of the modified seawater with fresh groundwater from the floridan aquifer system

low temperature alteration of the upper oceanic crust and the alkalinity budget of seawater abstract while the input of river alkalinity into seawater is relatively well known the complementary acidity production is poorly understood using the major element budget of seafloor alteration of the upper 500 m of 120 ma old oceanic crust at dsdp odp sites 417a 417d and 418a in the central western atlantic we estimate the acidity flux associated with the low temperature weathering of the upper oceanic crust the acidity flux is calculated based on major element fluxes and charge balance considerations the relevant chemical fluxes from seawater to the upper crust are 4 1 0 1 1 4 1 4 2 2 0 6 and 12 2 1011 mol yr 1 for k mg na and silicate ca respectively the associated acidity flux is 3 5 3 1011 eq yr 1 relative to continental weathering these fluxes are significant for k and silicate ca but are minor for na mg and acidity thus riverine fluxes of alkalinity are not significantly balanced by acidity fluxes from low temperature upper ocean crust alteration

the equatorial energy balance itcz position and double itcz bifurcations the intertropical convergence zone itcz migrates north south on seasonal and longer time scales previous studies have shown that the zonal mean itcz displacement off the equator is negatively correlated with the energy flux across the equator when the itcz lies in the northern hemisphere energy flows southward across the equator and vice versa the hemisphere that exports energy across the equator is the hemisphere with more net energy input and it is usually the warmer hemisphere but states with a double itcz straddling the equator also occur for example seasonally over the eastern pacific and frequently in climate models here it is shown how the itcz position is connected to the energy balance near the equator in a broad range of circumstances including states with single and double itczs taylor expansion of the variation of the meridional energy flux around the equator leads to the conclusion that for large positive net energy input into the equatorial atmosphere the itcz position depends linearly on the cross equatorial energy flux for small positive equatorial net energy input the dependence of the itcz position on the cross equatorial energy flux weakens to the third root when the equatorial net energy input or its curvature become negative a bifurcation to double itcz states occurs simulations with an idealized aquaplanet general circulation model gcm confirm the quantitative adequacy of these relations the results provide a framework for assessing and understanding causes of common climate model biases and for interpreting tropical precipitation changes such as those evident in records of climates of the past

supra subduction zone extensional magmatism in vermont and adjacent quebec implications for early paleozoic appalachian tectonics metadiabasic intrusions of the mount norris intrusive suite occur in faultbounded lithotectonic packages containing stowe moretown and cram hill formation lithologies in the northern vermont rowe hawley belt a proposed ordovician arc trench gap above an east dipping subduction zone rocks of the mount norris intrusive suite are characteristically massive and weakly foliated have chilled margins contain xenoliths and have sharp contacts that both crosscut and are parallel to early structural fabrics in the host metasedimentary rocks although the mineral assemblage of the mount norris intrusive suite is albite 1 actinolite 1 epidote 1 chlorite 1 calcite 1 quartz intergrowths of albite 1 actinolite are probably pseudomorphs after plagioclase 1 clinopyroxene the metadiabases are subalkaline tholeiitic hypabyssal basalts with preserved ophitic texture a backarcbasin tectonic setting for the intrusive suite is suggested by its lree light rare earth element enrichment negative nbta anomalies and ta yb vs th yb trends although no direct isotopic age data are available the intrusions are broadly ordovician because their contacts are clearly folded by the earliest acadian silurian devonian folds field evidence and geochemical data suggest compelling along strike correlations with the coburn hill volcanics of northern vermont and the bolton igneous group of southern quebec isotopic and stratigraphic age constraints for the bolton igneous group bracket these backarc magmas to the 477 458 ma interval a tectonic model that begins with east dipping subduction and progresses to outboard west dipping subduction after a syncollisional polarity reversal best explains the intrusion of deformed metamorphosed metasedimentary rocks by backarc magmas

patterns and processes of alteration in the lavas and dykes of the troodos ophiolite cyprus alteration patterns in the lavas and dykes of the troodos ophiolite cyprus record a complex history of axial hydrothermal alteration crustal aging and subsequent uplift and emplacement of the ophiolite field mapping shows that distribution of five alteration zones each with distinct mineralogical geochemical and hydrologie characteristics is influenced by igneous stratigraphy structure and the nature and thickness of the overlying sediments paragenetic sequences of secondary minerals indicate that alteration conditions changed progressively as the crust cooled and moved off axis along spreading axes low temperatures 50 c were maintained by the rapid flow of seawater in and out of the lavas and only minimal alteration took place in contrast lower water rock ratios and higher temperatures 200 c in the dykes promoted extensive seawater rock interaction although the sharp rise in temperature between the two regimes generally coincides with the lava dyke transition late stage intrusions or hydrothermal upwelling zones locally cause high temperature alteration to extend upward into the lavas as a segment of crust moved off axis temperatures remained low in the lavas and progressively decreased from 250 to 80 c in the dykes high permeability in the uppermost lavas led to the downward migration of an oxidative alteration front whose thickness and spatial distribution was dependent upon the rate and nature of sedimentation and thus the original seafloor morphology although field relations show that alteration has a consistent vertical pattern in troodos the alteration zones are not laterally continuous and the stratigraphie depth of their boundaries varies considerably

time series studies of vent fluids from the tag and mark sites 1986 1990 mid atlantic ridge a new solution chemistry model and a mechanism for cu zn zonation in massive sulphide orebodies

noise levels of superconducting gravimeters at seismic frequencies summary until recently superconducting gravimeters sgs have been used principally in tidal studies periods 6 24 hr due to their high sensitivity and low drift rates this paper considers the performance of these instruments as long period seismometers particularly in the normal mode band periods 1 54 min to judge their suitability in providing useful information to seismology it is important to determine their noise characteristics compared to other established instruments such as spring gravimeters we compare several continuously recording instruments the sgs in esashi japan wuhan china strasbourg france and cantley canada and the spring gravimeter et 19 and seismometer sts 1 at the black forest observatory bfo germany we also include non permanent instruments the sg102 at bfo as well as the et 18 in metsahovi finland the ve quietest days out of the available records are stacked to obtain the power spectral density of the noise in the frequency band 0 05 20 mhz 50 s to 6 hr our reference is the new low noise model designed for seismometers only at the bfo site were there several instruments that could be compared even so in order to obtain the best individual data for each instrument the records selected were not simultaneous the noise characteristics of the diierent instrument site combinations are compared leading to conclusions about site selection instrument modi cations and the recent potential of sgs to contribute to seismic normal mode studies we refer to our previous work on the seismic noise magnitude a summary statistic derived from the power spectral density which has been used to rank the performance of instrument site combinations

reconciling temperatures of metamorphism fluid fluxes and heat transport in the upper crust at intermediate to fast spreading mid ocean ridges 1 current models of the mineralogical and chemical modification of the crust within mid ocean ridge hydrothermal systems at intermediate to fast spreading ridges are difficult to reconcile with the temperature distribution predicted by the required fluid fluxes in particular the sharp increase in metamorphic grade passing down from the lavas into the sheeted dike complex places important constraints on the flow of fluid through the crust this distribution of metamorphic temperatures has typically been discussed in terms of a step in permeability in the downwelling limb of a single pass convection cell simple modeling of this system shows that downwelling fluid cools the crust too efficiently for high temperature metamorphism of the upper dikes to occur in the downflow zone in fact temperatures throughout most of the sheeted dike complex are too high three alternative models are considered fluid rock reaction during the cooling of each dike from magmatic temperatures is difficult to reconcile with cooling rate estimates for dikes reaction rates required to grow metamorphic minerals and the relatively constant composition of many hydrothermal vents metamorphism during reheating of the crust after fluid flow slows or stops is difficult to reconcile with the required fluid fluxes during metamorphism based on the sr isotopic composition of the sheeted dike complex and cannot produce high enough temperatures in the upper dikes and low temperatures in the lower lavas in contrast fluid rock reaction in the sheeted dike complex as hot fluids migrate upward after being heated by the underlying magma source appears to be consistent with the data in this model downwelling seawater cools the recharge zone and the fluid only becomes hot enough to significantly alter the crust once it approaches the conductive boundary layer overlying the magma chamber metamorphism of the sheeted dike complex then largely occurs in the discharge zone

hydrothermal vent waters at 13 n on the east pacific rise isotopic composition and gas concentration abstract gas concentrations and isotopic compositions of water have been measured in hydrothermal waters from 13 n on the east pacific rise in the most mg depleted samples 5 10 3 moles kg the gas concentrations are 3 4 5 10 5 cm 3 stp kg helium 0 62 1 24 cm 3 stp kg ch 4 10 80 16 71 10 3 moles kg co 2 the samples contain large quantities 95 126 cm 3 kg of h 2 and some carbon monoxide 0 26 0 36 cm 3 kg which result from reaction with the titanium sampling bottles 13 c in methane and co 2 16 6 to 19 5 and 4 1 to 5 5 respectively indicate temperatures between 475 and 550 c whereas 13 c co is compatible with formation by reduction of co 2 on ti at 350 c close to the sampling temperature 3 he 4 he are very homogeneous at 7 5 0 1 r a 3 he 4 he 1 0 10 5 and very similar to already published data as well as ch 4 3 he ratios between 1 4 and 2 1 10 6 18 o and d in water show enrichments from 0 39 to 0 69 and from 0 62 to 1 49 respectively these values correspond to w r ratios of 0 4 7 the distinct 18 o enrichments indicate that the isotopic composition of the oceans is not completely buffered by the hydrothermal circulations the 3 he enthalpy relationship is discussed in terms of both hydrothermal heat flux and 3 he mantle flux

geochemistry of silurian devonian volcanic rocks in the coastal volcanic belt machias eastport area maine evidence for a pre acadian arc the coastal volcanic belt in easternmost maine consists of silurian devonian volcanic rocks related to the convergence of avalonia with the leading edge of composite laurentia just before and during early stages of the acadian orogeny new major and trace element analyses from the machias eastport area indicate that the early to late silurian volcanic rocks in the dennys edmunds and leighton formations formed in a continental arc environment in contrast to some earlier interpretations these rocks have a continuous compositional range from basalt through andesite to rhyolite the mafic rocks in these formations are calc alkaline and show subduction related geochemical signatures on various discrimination diagrams whereas the felsic rocks have geochemical characteristics of volcanic arc granites in contrast the thick volcanic deposits of the younger late silurian eastport formation are bimodal and tholeiitic and have transitional to within plate geochemical signatures thus the transition over time as the acadian seaway closed from subduction and arc settings to continental extension can been seen in this rock sequence and it constrains the time of avalonia s docking regionally volcanic rocks in the kingston terrane of southern new brunswick are likely correlatives of the earlier arc volcanic rocks dennys edmunds and leighton formations while eastport formation analogues are found in the coastal maine magmatic province cranberry island series and probably the passamaquoddy bay volcanic series which similarly appear to have formed after the transition to an extensional environment occurred although other extensional settings cannot be entirely ruled out basalts in the post acadian perry formation indicate continental extension was also active in the late devonian

geochemistry of submarine warm springs in the limestone cavern of grotta azzurra capo palinuro italy evidence for mixing zone dolomitisation abstract subtidal springs in and around the submarine limestone cavern of grotta azzurra at capo palinuro italy discharge fluids which are warm 10 excess si alkalinity ca2 sr2 and mn relative to seawater are likely derived from the groundwater component or dissolution hydrothermal alteration of the host rocks magnesium has been removed from the seawater component in exchange for ca2 due to dolomitisation of the limestone and or hydrothermal alteration reactions saturation state calculations suggest that the vented fluids are near saturation with respect to calcite and supersaturated with respect to dolomite this and the presence of dolomite in the host rocks and cave floor sediments suggest that mixing zone dolomitisation of the limestones is occurring perhaps kinetically assisted by elevated temperature and or bacterial mediation in the reducing subseafloor zone one possible end member condition is considered for the thermal fluid zero mg which suggests an end member temperature of 50 5 c and a fluid composition derived from 38 seawater and 62 groundwater the heat source for the circulating fluids is uncertain but may involve warm underlying igneous rocks or heating via the geothermal gradient a continuous in situ record of vent fluid temperature salinity ph and o2 concentration collected within the cavern is consistent with our interpretation of the fluid origin and suggests that tidal forcing affects circulation and venting of the warm fluids

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

coupling of trade winds with ocean circulation damps itcz shifts abstractthe position of the intertropical convergence zone itcz is sensitive to the atmosphere s hemispheric energy balance lying in the hemisphere most strongly heated by radiative and turbulent surface energy fluxes this study examines how the ocean circulation through its cross equatorial energy transport and associated surface energy fluxes affects the itcz s response to an imposed interhemispheric heating contrast in a coupled atmosphere ocean general circulation model shifts of the itcz are strongly damped owing to a robust coupling between the atmosphere s hadley cells and the ocean s subtropical cells by the trade winds and their associated surface stresses an anomalous oceanic wind driven cross equatorial cell transports energy across the equator strongly offsetting the imposed heating contrast the circulation of this cell can be described by the combination of trade wind anomalies and the meridional gradient of sea surface temperature which sets the temperature contrast between its up

constructional features of troodos type oceanic crust relationships between dike density alteration magnetization and ore body distribution and their implications for in situ oceanic crust quantitative relationships are demonstrated between dike density and hydrothermal alteration magnetization location of volcanic massive sulfide vms ore bodies and a number of other properties in a 40 by 15 km segment of the extrusive series of the troodos ophiolite low temperature alteration extends from the sediment extrusive interface to close to the 25 dike density surface while the onset of greenstone type alteration is closely associated with the 50 dike density surface these associations are explained in terms of the regional scale variations in the dike density contour surfaces following the form of the top of the gabbroic layer of the ophiolite an upper magnetic zone characterized by stable high remanence terminates just below the 25 dike density surface a deeper magnetic zone characterized by high induced magnetization straddles the top of the sheeted complex volcanic massive sulfide bodies are concentrated in a narrow depth range centered about 0 1 km above the 25 dike density surface a model for the postridge crest evolution of ore bodies accounts for this optimum depth range for preservation physical property changes with dike density and the depth distribution of vms ore bodies and prospects for the ophiolite as a whole support this model similar relationships appear to be present in the samail macquarie island newfoundland and chilean ophiolites and icelandic crust as a result of relationships found in the troodos ophiolite an alternative is proposed to the current lithologic profile for ocean drilling program hole 504b

the geochemical nature of the igneous rocks of the sharbot lake domain central metasedimentary belt ontario two bimodal mafic silicic suites of igneous rocks the sharbot lake volcanic rocks and the lavant igneous complex are identified geochemically in the sharbot lake domain of the central metasedimentary belt in ontario and their genesis and thermotectonic environment are evaluated the sharbot lake volcanic rocks comprise a series of basalts characterized by light rare earth element lree depletion and relatively high concentrations of fe2o3 tio2 mno v and y together with rhyolites and silicic pyroclastic rocks they are intruded by rocks of the lavant igneous complex which comprises tholeiitic gabbros characterized by lree enrichment and low concentrations of fe2o3 tio2 mno v and y and granitoid rocks the trace element signatures of the mafic rocks of the sharbot lake volcanic sequences are most like those of back arc tholeiitic basalts and those of the lavant igneous complex are comparable to those of low k tholeiitic basalt suites the trace element signatures of the silicic rocks ass

the effect of ocean mixed layer depth on climate in slab ocean aquaplanet experiments the effect of ocean mixed layer depth on climate is explored in a suite of slab ocean aquaplanet simulations with different mixed layer depths ranging from a globally uniform value of 50 2 4 m in addition to the expected increase in the amplitude of the seasonal cycle in temperature with decreasing ocean mixed layer depth the simulated climates differ in several less intuitive ways including fundamental changes in the annual mean climate the phase of seasonal cycle in temperature differs non monotonically with increasing ocean mixed layer depth reaching a maximum in the 12 m slab depth simulation this result is a consequence of the change in the source of the seasonal heating of the atmosphere across the suite of simulations in the shallow ocean runs the seasonal heating of the atmosphere is dominated by the surface energy fluxes whereas the seasonal heating is dominated by direct shortwave absorption within the atmospheric column in the deep ocean runs the surface fluxes are increasingly lagged with respect to the insolation as the ocean deepens which accounts for the increase in phase lag from the shallow to mid depth runs the direct shortwave absorption is in phase with insolation and thus the total heating comes back in phase with the insolation as the ocean deepens more and the direct shortwave absorption dominates the seasonal heating of the atmosphere the intertropical convergence zone follows the seasonally varying insolation and maximum sea surface temperatures into the summer hemisphere in the shallow ocean runs whereas it stays fairly close to the equator in the deep ocean runs as a consequence the tropical precipitation and region of high planetary albedo is spread more broadly across the low latitudes in the shallow runs resulting in an apparent expansion of the tropics relative to the deep ocean runs as a result the global and annual mean planetary albedo is substantially 20 higher in the shallow ocean simulations which results in a colder 7c global and annual mean surface temperature the increased tropical planetary albedo in the shallow ocean simulations also results in a decreased equator to pole gradient in absorbed shortwave radiation and drives a severely reduced 50 meridional energy transport relative to the deep ocean runs as a result the atmospheric eddies are weakened and shifted poleward away from the high albedo tropics and the eddy driven jet is also reduced and shifted poleward by 15 relative to the deep ocean run

hydrogeological investigations at the membach station belgium and application to correct long periodic gravity variations 1 a comprehensive hydrogeological investigation regarding the influence of variations in local and regional water mass on superconducting gravity measurements is presented for observations taken near the geodynamic station of membach belgium applying a regional water storage model the gravity contribution due to the elastic deformation of the earth was derived in addition the newtonian gravity effect induced by the local water mass variations was calculated using soil moisture observations taken at the ground surface about 48 m above the gravimeters the computation of the gravimetric effect is based on a digital elevation model with spatially discretized rectangular prisms the obtained results are compared with the observations of a superconducting gravimeter sg we find that the seasonal variations can be reasonably well predicted with the regional water storage model and the local newtonian effects shorter period effects depend on the local changes in hydrology this result shows the sensitivity of sg observations to very local water storage changes

chemistry of waters sampled from oceanic basement boreholes 1979 1988 waters have been sampled from the basement section of four deep sea drilling project holes 395a 396b 418a and 504b since 1979 in an attempt to determine the composition of oceanic basement formation waters samples have been obtained by two methods active in which water is drawn under negative pressure from the interstices of the wall rocks and passive in which it is collected from the open borehole the most successful sampling has been done on re entering the holes months to years after they were last disturbed by drilling and or pumping of surface seawater downhole most of the samples show large changes in composition from seawater that are consistent with alteration of basalts at the in situ temperatures of 10 to 146 c the samples are typically depleted in mg2 k na sulfate and 87sr and enriched in ca2 and si however all of the samples are contaminated to some extent mainly by seawater which is either introduced during drilling or sampling flows downhole due to underpressure in the upper basement or mixes downhole due to convective overturn in the hole itself the latter process is apparently common and dilutes any formation water which may enter the hole via diffusion and horizontal convection in hole 504b the tritium content of the waters indicates that 24 to 35 of the surface seawater which originally filled the hole is still present after periods of 470 to 1233 days the more general problem of what has displaced the surface seawater and produced the large chemical changes observed in the borehole waters whether exchange with formation water or simply reaction of seawater with the wall rocks of the hole remains unsolved as a result no component of true basement formation water has been identified unambiguously in any of the holes this problem may be solved by 1 compartmentalizing a hole with a series of plugs to limit downhole mixing or 2 using a straddle packer to draw a series of samples from the interstices of the wall rocks of a hole either shortly after drilling or later following re entry in either case an array of chemical tracers will have to be measured either in situ or in the laboratory to infer the nature of the waters obtained

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

a stable isotope study of the hydrothermal alteration of the east taiwan ophiolite abstract the east taiwan ophiolite eto occurs as allochthonous fragments in the lichi melange and has been suggested to have formed at an active ridge ridge transform fault in a marginal basin the brecciated plutonic sequence has experienced a pre brecciation ocean ridge type high temperature metamorphism as well as a post brecciation off axis type low temperature metamorphism whereas the extrusive sequence has been subjected only to an off axis low temperature hydrothermal alteration stable isotopic studies of the eto show a slightly decreasing trend in oxygen isotope compositions from basalt through plagiogranite gabbro to ultramafic rocks the isotopic compositions of the eto basalts indicate low temperature interaction with seawater under variable water rock ratios the amphiboles from the eto gabbro show low 18o i e 3 1 to 3 8 and high d i e 19 to 9 values this is interpreted as having resulted from high temperature interaction with seawater derived hydrothermal fluid the plagioclase in the gabbro is mostly albitic in composition and exhibits very high 18o values i e 12 0 which may have resulted from low temperature reaction with 18o enriched fluid such 18o enriched fluid may have been derived from a high temperature seawater plutonic rock interaction system the antigorite and lizardite chrysotile serpentinites in the eto formed in oceanic environments under pre and post brecciation metamorphic conditions respectively the isotopic compositions of the antigorite are compatible with its formation in an oceanic environment although the 18o values of the lizardites chrysotiles are comparable to those of oceanic serpentines their d values ranging from 91 to 57 are too low to be accounted for by reaction with seawater derived fluid post formation hydrogen isotope exchange between the lizardite chrysotile and local meteoric waters during after on land emplacement of the serpentinites is postulated as a probable explanation calcite veins are ubiquitous in the eto three carbon sources are identified inorganic seawater carbon juvenile carbon and organic carbon in the last case it is shown that some calcite veins may contain a substantial amount of co2 derived from the ch4 oxidation process the organic carbon was most likely derived from organics in the surrounding lichi mudstone therefore the calcite veins with an organic carbon signature are suggested to have formed after the eto emplacement within the lichi melange

modulation of monsoon circulations by cross equatorial ocean heat transport abstractmotivated by observations of southward ocean heat transport oht in the northern indian ocean during summer the role of the ocean in modulating monsoon circulations is explored by couplin

alteration of the oceanic crust implications for geochemical cycles of lithium and boron abstract fresh tholeiitic basalt glass has been reacted with seawater at 150 c water rock mass ratio of 10 and fresh diabase has been reacted with a na k ca cl fluid at 375 c water rock mass ratios of 1 2 and 5 to understand better the role of temperature basalt composition and water rock mass ratio on the direction and magnitude of b and li exchange during basalt alteration at 150 c slight but nevertheless significant amounts of b and li were removed from seawater and incorporated into a dominantly smectite alteration phase at 375 c however b and li were leached from basalt b behaved as a soluble element and attained concentrations in solution limited only by the b concentration in basalt and the water rock mass ratio li however was less mobile for example at water rock mass ratios of 1 2 and 5 the percent of li leached from basalt was 58 70 and 92 respectively this suggests some mineralogic control on li mobility during hydrothermal alteration of basalt especially at low water rock mass ratios in general these results as well as those for b are consistent with the temperature dependent chemistry of altered seafloor basalt and the chemistry of ridge crest hydrothermal fluids based on the distribution and chemistry of products of seafloor weathering low 150 c and high temperature hydrothermal alteration of basalt and the chemistry of ridge crest hydrothermal fluids it was estimated that alteration of the oceanic crust is a li source for seawater this is not true for b however since the hot spring flux estimated for b is balanced by low temperature basalt alteration these data coupled with b and li flux estimates for other processes e g continental weathering clay mineral adsorption authigenic silicate formation and formation of siliceous skeletal material yield new insight into the b and li geochemical cycles calculations performed here indicate relatively good agreement between the magnitude of b and li sources and sinks the geochemical cycle of b however may be affected by serpentinization of mantle derived peridotite in oceanic fracture zones serpentinites are conspicuously enriched in b and if the b source for these rocks is seawater then an additional b sink exists which must be integrated into the b geochemical cycle however until more data are available in terms of areal extent of serpentinization serpentite chemistry and isotopic composition the importance of b in these rocks with respect to the b geochemical cycle remains speculative at best

ocean atmosphere land feedbacks in an idealized monsoon summary an intermediate complexity atmospheric model coupled with a simple land surface model and a mixedlayer ocean model is used to investigate the processes involved in an idealized monsoon occumng on a single rectangular continent idealized divergences of ocean heat transports are specified as an annual average q flux in this simple coupled configuration the mechanisms that affect land ocean contrast and in turn the seasonal movement of the continental convergence zones are examined these include soil moisture feedbacks cooling of tropical oceans by ocean transport ventilation defined as the import into continental regions of low moist static energy air from ocean regions where heat storage opposes summer warming and the interactive rodwellhoskins mechanism in which rossby wave induced subsidence to the west of monsoon heating interacts with the convection zone the fixed ocean transports have a substantial impact on the continental convection if q flux is set to zero subtropical subsidence and ventilation tend to substantially limit the poleward movement of summer monsoon rainfall when land hydrology feedbacks are active the drying of subtropical continents disfavours continental convection even in the tropics when ocean transports are included tropical oceans are slightly disfavoured as regions for producing convection which by contrast favours continental convection the monsoon circulation then produces moisture transport from the ocean regions that allows substantial progression of convection into the subtropics over the eastern portion of the continent the western portion of the continent tends to have a dry region of characteristic shape this east west asymmetry is partly due to the interactive rodwell hoskins mechanism the ventilation is of at least equal importance in producing east west asymmetry and is the single most important process in limiting the poleward extent of the continental convection zone

origin of basal dolomitic claystone in the marsili basin tyrrhenian sea abstract red brown dolomitic claystones overlay the marsili basin basaltic basement at odp site 650 sequential leaching experiments reveal that most of the elements considered to have a hydrothermal or hydrogenous origin in a marine environment such as fe cu zn pb co ni are present mainly in the aluminosilicate fraction of the dolomitic claystones their vertical distribution content and partitioning chemistry of trace elements and ree patterns suggest enhanced terrigenous input during dolomite formation but no significant hydrothermal influence from the underlying basaltic basement positive correlations in the c and o isotopes in the dolomites reflect complex conditions during the dolomitization the stable isotopes can be controlled in part by temperature variations during the dolomitization majority of the samples however form a trend that is steeper than expected for only temperature control on the c and o isotopes the latter indicates possible isotopic heterogeneity in the proto carbonate that can be related to arid climatic conditions during the formation of the basal dolomitic claystones in addition the dolostones stable isotopic characteristics can be influenced by diagenetic release of heavier 18o from clay dehydration and or alteration of siliciclastic material strontium and pb isotopic data reveal that the non carbonate fraction the dye of the dolomitic claystones is controlled by saharan dust 75 80 and by material with isotopic characteristics similar to the aeolian arc volcanoes 20 25 the non carbonate fraction of the calcareous ooze overlying the dolomitic claystones has a sr and pb isotopic composition identical to that of the dolomitic claystones indicating that no change in the input sources to the sedimentary basin occurred during and after the dolomitization event combination of climato tectonic factors most probably resulted in suitable conditions for dolomitization in the marsili and the nearby vavilov basins the basal dolomitic claystone sequence was formed at the initiation of the opening of the marsili basin 2 ma which coincided with the consecutive glacial stage the glaciation caused arid climate and enhanced evaporation that possibly contributed to the stable isotope variations in the proto carbonate the conductive cooling of the young lithosphere produced high heat flow in the region causing low temperature passive convection of pore waters in the basal calcareous sediment we suggest that this pumping process was the major dolomitization mechanism since it is capable of driving large volumes of seawater the source of mg2 through the sediment the red brown hue of the dolomitic claystones is terrigenous contribution of the glacially induced high eolian influx and was not hydrothermally derived from the underlying basaltic basement the detailed geochemical investigation of the basal dolomitic sequence indicates that the dolomitization was most probably related to complex tectono climatic conditions set by the initial opening stages of the marsili basin and glaciation

geothermal springs of the west florida continental shelf evidence for dolomitization and radionuclide enrichment abstract on the sea bed of the west florida continental shelf about 45 km ssw of ft myers florida an 85 km 2 area has been discovered in which six thermal springs discharge warm chemically altered seawater from vents and seepage zones the spring water apparently originates in the subsurface ocean around the florida platform and penetrates the highly porous strata of the platform about 500 1000 meters below sea level it percolates toward the interior of the platform and is geothermally heated to about 40 c en route then it rises along more vertical flow channels and is discharged in warm submarine springs beneath the platform several chemical processes alter the percolating seawater one process seems to be a secondary dolomitization of the limestone of the platform because in the discharging seawater magnesium is lower by 2 7 mmole kg and calcium higher by 3 6 mmole kg than in normal seawater with the same chlorinity other reactions within the sediments of the platform enrich the spring effluents 1000 fold in 226 ra 10 000 fold in 222 rn and 90 fold in 228 ra compared to the seawater surrounding the platform thus the springs may be important sources of radionuclides for the gulf of mexico the percolating seawater also loses all of its oxygen and nitrate to reduction processes loses most of its phosphate and 40 of its 238 u and roughly quadruples its silica content coastal carbonate platforms are fairly common geological features thus processes like those beneath the west florida shelf may function on a world wide basis to play an important role in the diagenesis of carbonate sediments

the response of hadley circulation extent to an idealized representation of poleward ocean heat transport in an aquaplanet gcm abstractdeeper theoretical understanding of hadley circulation hc width and the mechanisms leading to hc expansion is gained by exploring the response of a zonally symmetric slab ocean aquaplanet