natural tracers for identifying the origin of the thermal fluids emerging along the aegean volcanic arc greece evidence of arc type magmatic water atmw participation abstract the aegean volcanic arc is the result of a lithosphere subduction process during the quaternary time starting from the soussaki area from west to east the arc proceeds through the islands of egina methana milos santorini the columbus bank kos and nisyros volcano tectonic activities are still pronounced at santorini and nisyros in form of seismic activity craters of hydrothermal explosions hot fumaroles and thermal springs a significant number of cold water springs emerge in the vicinity of hot waters on these islands chemical and isotopic analyses were applied on water and fumaroles samples collected in different areas of the volcanic arc in order to attempt the assessment of these fluids stable isotopes of water and carbon have been used to evaluate the origin of cold and thermal water and co 2 chemical solute concentrations and isotopic contents of waters show that the fluids emerging in egina soussaki methana and kos areas represent geothermal systems in their waning stage while the fluids from milos santorini and nisyros proceed from active geothermal systems the 2 h 18 o cl relationships suggest that the parent hydrothermal liquids of nisyros and milos are produced through mixing of seawater and arc type magmatic water atmw with negligible to nil contribution of local ground waters and with very high participation of the magmatic component which is close to 70 in both sites a very high magmatic contribution to the deep geothermal system could occur at santorini as well perhaps with a percentage similar to nisyros and milos but it cannot be calculated because of steam condensation heavily affecting the fumarolic fluids of nea kameni before the surface discharge the parent hydrothermal liquid at methana originates through mixing of local groundwaters seawater and atmw with a magmatic participation close to 19 all in all the contribution of atmw is higher in the central eastern part of the aegean volcanic arc than in the western sector this difference which is spotted in the variable isotopic composition of the sampled fluids from west to east along the arc is probably due to several causes including the tectonic regime the depth of the deep reservoir below sea level the age of volcanic activity and in general the geomorphologic state of each island

strong biological controls on sr ca ratios in aragonitic marine bivalve shells 1 it is well known that skeletal remains of carbonate secreting organisms can provide a wealth of information about past environments sr ca ratios have been successfully used as a temperature proxy in corals and sclerosponges previous work on aragonitic bivalve shells has not been conclusive but suggests a major control of growth rate on sr ca ratios as many studies have used bivalve growth rates to determine temperature we tested if sr ca ratios could predict temperature through its relationship with growth rate shells from the two species of clams from the same family veneroidea studied here saxidomus giganteus and mercenaria mercenaria show vastly different seasonal sr ca profiles a strong relationship between average annual sr ca ratios and annual growth rate was found in s giganteus shells from both washington r2 0 87 and alaska r2 0 64 usa but not in m mercenaria shells from north carolina usa furthermore the sr ca growth rate relationship was also evident upon a more detailed inspection of subannual growth rates in s giganteus r2 0 73 although there were significant positive correlations between sr ca ratios and temperature in s giganteus shells the correlations were weak 0 09 r2 0 27 and thus sr ca ratios cannot be used as a reliable temperature proxy in these species of aragonitic bivalves it is clear from this study that sr ca ratios are not under thermodynamic control in either clam species since thermodynamics predict a negative correlation between sr ca ratios and temperature in aragonite this points toward dominance of biological processes in the regulation of sr2 this is also reflected by the largely differing sr ca partition coefficients dsr in these shells dsr 0 25 when compared to inorganic coral and sclerosponge studies dsr 1 all of which show a negative dependence of sr ca on temperature we suggest that caution be taken when using sr ca in any biogenic aragonite as a temperature proxy when the dsr greatly deviates from one as this indicates the dominance of biological controls on sr ca ratios

oxygen and carbon isotopes in modern fresh water ostracod valves assessing vital offsets and autecological effects of interest for palaeoclimate studies abstract the isotopic composition of modern benthic ostracod and mollusc carbonate the oxygen isotope composition of lake water 18ow the carbon isotope composition of dissolved inorganic carbon 13cdic and water temperatures were monitored during a year at different water depths in two lakes ammersee and starnberger see southern germany the aim was to test whether the valves are built in isotopic equilibrium and how seasonal water temperatures are recorded in the shells we find systematic offsets between 18o of valve carbonate compared to 18o expected for a theoretical calcite formed in isotopic equilibrium offsets are higher than 2 for different species of the candona group 1 5 for cytherissa lacustris and around 0 8 for limnocythere inopinata and darwinula stevensoni they seem to be constant for all instars of a species and temperature independent mean water temperatures of the calcification period are readily reflected in the valve 18o if corrected for the offsets 13c of valve carbonate is mainly controlled by 13c of the dissolved carbonate in ambient lake water but seems to be biased by micro habitat effects and vital offsets the study provides information on the seasonality of valve formation thus potentially allowing the quantification of temporal and spatial water temperature gradients from specific 18o records

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

making it and breaking it in the midwest continental assembly and rifting from modeling of earthscope magnetotelluric data abstract a three dimensional lithospheric scale resistivity model of the north american mid continent has been estimated based upon earthscope magnetotelluric data details of the resistivity model are discussed in relation to lithospheric sutures defined primarily from aeromagnetic and geochronologic data which record the southward growth of the laurentian margin in the proterozoic the resistivity signature of the 1 1 ga mid continent rift system is examined in detail in particular as relates to rift geometry extent and segmentation an unrecognized expanse of concealed proterozoic deltaic deposits in kansas is identified and speculated to result from axial drainage along the southwest rift arm akin to the rio grande delta which drains multiple rift basins a prominent conductor traces out cambrian rifting in arkansas missouri tennessee and kentucky this linear conductor has not been imaged before and suggests that the cambrian rift system may have been more extensive than previously thought the highest conductivity within the mid continent is imaged in minnesota michigan and wisconsin where it is coincident with paleoproterozoic metasedimentary rocks the high conductivity is attributed to metallic sulfides and in some cases graphite the former is a potential source of sulfur for multiple mineral deposits types occurrences of which are found throughout the region finally the imprint left within the mantle following the 1 1 ga rifting event is examined variations in lithospheric mantle conductivity are observed and are interpreted to reflect variations in water content depleted versus metasomatized mantle imprinted upon the mantle by the keweenawan mantle plume

the applicability of trace elements in freshwater shells for paleogeochemical studies experimental studies on modern aragonitic shells of the gastropods melanopsis praemorsum and m tuberculata yielded bulk distribution coefficients of 0 31 for sr and of 0 48 for ba between the shells and their ambient waters these partition coefficients are about three times lower than their inorganic equivalents h2o leaching experiments of modern shells indicate that sr and ba dissolve congruently with no effect on the original sr and ba contents of the shells conversely the na ca mg ca and k ca ratios in the shells and in the extrapallial fluids are constant independent of variations in the habitat water chemistry this vital effect dominates the shell composition regarding the latter three ion ratios moreover dissolution experiments suggest that there is leaching of a significant fraction of na mg and k which is presumably not bound to the mineral s lattice this preferential dissolution starts before any mineralogical alteration occurs the laboratory data are supported by a sharp decrease of the na ca ratio observed in aragonitic fossils during early diagenesis in contrast with its constancy in live specimens these results clearly demonstrate that sr and ba can be used for environmental studies whereas na mg and k cannot

aragonite stromatolitic buildups from santorini aegean sea greece geochemical and palaeontological constraints of the caldera palaeoenvironment prior to the minoan eruption ca 3600 yr bp this study received financial support from projects cgl2008 00594 and cgl2011 2348 plan nacional ministerio de ciencia e innovacion spain pa additional funding for analyses was provided by the mexican in103211 papiit project cc

new insights into the initiation and venting of the bronze age eruption of santorini greece from component analysis the late seventeenth century bc minoan eruption of santorini discharged 30 60 km3 of magma and caldera collapse deepened and widened the existing 22 ka caldera a study of juvenile cognate and accidental components in the eruption products provides new constraints on vent development during the five eruptive phases and on the processes that initiated the eruption the eruption began with subplinian phase 0 and plinian phase 1 phases from a vent on a ne sw fault line that bisects the volcanic field during phase 1 the magma fragmentation level dropped from the surface to the level of subvolcanic basement and magmatic intrusions the fragmentation level shallowed again and the vent migrated northwards during phase 2 into the flooded 22 ka caldera the eruption then became strongly phreatomagmatic and discharged low temperature ignimbrite containing abundant fragments of post 22 ka pre minoan intracaldera lavas phase 3 phase 4 discharged hot fluidized pyroclastic flows from subaerial vents and constructed three main ignimbrite fans northwestern eastern and southern around the volcano the first phase 4 flows were discharged from a vent or vents in the northern half of the volcanic field and laid down lithic block rich ignimbrite and lag breccias across much of the nw fan about a tenth of the lithic debris in these flows was subvolcanic basement new subaerial vents then opened up probably across much of the volcanic field and finer grained ignimbrite was discharged to form the e and s fans if major caldera collapse took place during the eruption it probably occurred during phase 4 three juvenile components were discharged during the eruption a volumetrically dominant rhyodacitic pumice and two andesitic components microphenocryst rich andesitic pumices and quenched andesitic enclaves the microphenocryst rich pumices form a textural mineralogical chemical and thermal continuum with co erupted hornblende diorite nodules and together they are interpreted as the contents of a small variably crystallized intrusion that was fragmented and discharged during the eruption mostly during phases 0 and 1 the microphenocryst rich pumices hornblende diorite andesitic enclaves and fragments of pre minoan intracaldera andesitic lava together form a chemically distinct suite of ba rich zr poor andesites that is unique in the products of santorini since 530 ka once the minoan magma reservoir was primed for eruption by recharge generated pressurization the rhyodacite moved upwards by exploiting the plane of weakness offered by the pre existing andesite diorite intrusion dragging some of the crystal rich contents of the intrusion with it

sublacustrine precipitation of hydrothermal silica in rift lakes evidence from lake baringo central kenya rift valley abstract many lakes in volcanic regions are fed by hot springs that in some basins can contribute a large percentage of the annual recharge especially during times of aridity it is important to recognize any contemporary hydrothermal contribution in paleoenvironmental reconstruction of lake basins because recharge from thermal waters can potentially confuse paleoclimatic signals preserved in the lacustrine sedimentary record hot spring deposits travertine sinter provide the most tangible evidence for thermal recharge to lakes although subaerial spring deposits have been widely studied lacustrine thermal spring deposits especially sublacustrine siliceous sinters remain poorly known detailed field petrographic and scanning electron microscope sem studies have been made of fossil sublacustrine sinter exposed at soro hot springs along the northeastern shoreline of ol kokwe a volcanic island in lake baringo kenya modern hot springs at soro which discharge na hco3 cl waters from a deep reservoir 180 c have thin 1 10 mm friable microbial silica crusts around their subaerial vents but thicker 1 cm sinter deposits are not forming the fossil sinter which is present as intergranular cements and crusts in littoral conglomerates and sandstones is composed mainly of opaline silica opal a three types of fossil sinter are recognized 1 massive structureless silica which fills intergranular pores and forms crusts up to 5 cm thick 2 pore lining silica some of which is isopachous and 3 laminated silica crusts which formed mainly on the upper surfaces of detrital particles all three types contain well preserved diatoms including lacustrine planktonic forms microbial remains mainly filamentous and coccoid bacteria including cyanobacteria and extracellular polymeric gels are locally abundant in the opaline silica together with detrital clays and thin laminae composed of authigenic chlorite most of the hydrothermal silica precipitated when the thermal springs were submerged by fresh lake water silica precipitated upon rapid cooling of thermal 90 c waters at and just below their interface with the overlying cooler 25 c lake waters microbial mats locally acted as a filter that limited mixing and rapid dilution of the thermal fluids some of the silica originally may have been soft and partly gelatinous planktonic diatoms and detrital clay rained down then became incorporated in the amorphous silica following a fall in lake level the opal a lithified and partly altered to cristobalite opal c and chalcedony the lowest fossil sinters were later encrusted by calcite stromatolites with calcite and quartz forming late pore filling cements the age of the sublacustrine sinters is unknown but some of the deposits could date back to the late pleistocene similar conglomerates cemented by hydrothermal silica are present along fault lines at neighbouring lake bogoria such rocks may provide evidence for deep hot fluid recharge to lakes when encountered in the geological record

strontium isotopes and rare earth element geochemistry of hydrothermal carbonate deposits from lake tanganyika east africa at cape banza north tanganyika lake fluids and aragonite chimneys have been collected many times since the discovery of this sublacustrine field in 1987 this sampling has been investigated here for the sr isotopic compositions and the rare earth element features of the carbonates and a few fluid samples the 87sr 86sr ratios of the chimneys indicate that they have precipitated from a mixture of lake water more than 95 and hydrothermal fluids no zoning in the chimneys was detected with our sr data for the rare earth elements the situation is more complex the external walls of the chimneys are rare earth element poor la 500 ppb yb 200 ppb la yb 2 to 3 4 their shale normalised rare earth element patterns suggest that they are in equilibrium with the inferred carbonate depositing fluids the rare earth element concentrations of the internal walls of the chimneys are significantly light rare earth elements lree enriched with la contents sometimes up to 5 ppm we suggest that they contain more vent fluid rare earth elements than the external wall samples possibly adsorbed on the surface of growing crystals or simply hosted by impurities it was not possible to constrain the nature of these phases but the variations of the compositions of the internal wall materials of the active chimneys with time as well as data obtained on an inactive chimney indicate that this rare earth element excess is mobile partition coefficients were calculated between the external wall aragonite and carbonate depositing fluid the results are strikingly similar to the values obtained by sholkovitz and shen 1995 on coral aragonite and suggest that there is no significant biologic effect on the incorporation of rare earth elements into coral aragonite and that the various carbonate complexes involved me co3 complexes are the main lree carriers in seawater cantrell and byrne 1987 instead of me co3 2 in banza fluids have the same behaviour during aragonite precipitation

hydrothermal activity associated with off axis volcanism in the peru basin abstract products of low temperature hydrothermal activity are widespread in the peru basin and are associated with late tertiary oceanic island type intraplate volcanics hydrothermal activity is still taking place as indicated by a series of sharp high and narrow temperature anomalies over one of the volcanic cones submarine hydrothermal activity associated with off axis volcanism has been frequently observed elsewhere but was usually found to be limited to seamounts in the peru basin a hydrothermal halo was found in sediments surrounding hydrothermally active seamounts in addition to hydrothermal precipitates on the tops of the seamounts todorokite birnessite fe nontronite goethite and silica were found on top of young volcanic edifices and occur as coatings on volcanic rocks and in nuclei of manganese nodules the hydrothermal precipitates in the sediments are mg fe silicates as is the case in the adjacent bauer basin the proportion of hydrothermal precipitates in the sediments increases with depth in the cores down to the appearance of the basalt that indicates the beginning of intraplate volcanism 5 million years ago sediments overlying late tertiary volcanic rocks are locally enriched in hydrothermal material by solutions percolating upwards directly into the sediment in these sediments apatite and phillipsite appear to have been precipitated directly from these ascending hydrothermal solutions

depositional facies and aqueous solid geochemistry of travertine depositing hot springs angel terrace mammoth hot springs yellowstone national park u s a petrographic and geochemical analyses of travertine de positing hot springs at angel terrace mammoth hot springs yellow stone national park have been used to define five depositional facies along the spring drainage system spring waters are expelled in the vent facies at 71 to 73 8c and precipitate mounded travertine composed of aragonite needle botryoids the apron and channel facies 43 728c is floored by hollow tubes composed of aragonite needle botryoids that encrust sulfide oxidizing aquificales bacteria the travertine of the pond facies 30 62 8c varies in composition from aragonite needle shrubs formed at higher temperatures to ridged networks of calcite and aragonite at lower temperatures calcite ice sheets calcified bubbles and aggregates of aragonite needles fuzzy dumbbells pre cipitate at the air water interface and settle to pond floors the prox imal slope facies 28 54 8c which forms the margins of terracette pools is composed of arcuate aragonite needle shrubs that create small microterracettes on the steep slope face finally the distal slope facies 28 30 8c is composed of calcite spherules and calcite feather crys tals despite the presence of abundant microbial mat communities and their observed role in providing substrates for mineralization the com positions of spring water and travertine predominantly reflect abiotic physical and chemical processes vigorous co 2 degassing causes a 12 unit increase in spring water ph as well as rayleigh type covariations between the concentration of dissolved inorganic carbon and corre sponding d 13 c travertine d 13 c and d 18 o are nearly equivalent to aragonite and calcite equilibrium values calculated from spring water in the higher temperature 50 738c depositional facies conversely

accidental gas emission from shallow pressurized aquifers at alban hills volcano rome italy geochemical evidence of magmatic degassing abstract recent studies suggested that alban hills rome is a quiescent and not an extinct volcano as it produced holocene eruptions and several lahars until roman times by water overflow from the albano crater lake alban hills are presently characterized by high p co2 in groundwaters and by several cold gas emissions usually in sites where excavations removed the superficial impervious cover gas consists mostly of co 2 with minor h 2 s and the diffuse co 2 soil flux is locally very high accidental gas blowouts occurred during shallow well drillings tens to hundreds m depth in zones with no surface gas manifestations indicate the presence of gas pressurized aquifers confined underneath impermeable layers within both the volcanic rock pile and the underlying pleistocene loose sediments degassing mostly occurs in correspondence of bordering faults of buried horsts cut in the mesozoic carbonate basement hosting the main aquifer carbon isotopic composition 13 c co2 suggests that co 2 is at least partly originated by thermal decarbonation of these limestones 3 he 4 he isotopic ratio of the gas up to 1 9 ra is the same or even slightly higher than that of olivine and clinopyroxene fluid inclusions of the alban hills volcanic products indicating a possible magmatic source for the gas low r ra values compared to morb and island arc magmas are characteristic of the potassic roman comagmatic province and reflect a deep involvement of crustal material in the magma genesis the lack of high temperature fumaroles can be explained by an efficient meteoric cold water penetration and circulation in the volcano permeable terrains

seafloor precipitated carbonate fans in the neoproterozoic rainstorm member johnnie formation death valley region usa cm sized carbonate seafloor fans occur in the neoproterozoic rainstorm member of the johnnie formation death valley usa the fans formed in a mixed carbonate clastic succession near storm wave base at the base of parasequences on a storm dominated ramp petrographic observations indicate that the fans were originally precipitated as aragonite and later inverted to calcite during diagenesis although not directly dated the rainstorm member preserves a large magnitude negative carbon isotopic anomaly down to 11 pdb tentatively correlated to the largest known carbon isotope excursion found in many stratigraphic successions around the world between 585 ma and 550 ma thus the age distribution of seafloor aragonite fans in neoproterozoic strata appears more widespread than previously thought occurring in strata significantly younger than the last widespread neoproterozoic glaciation rainstorm member carbonate fans and oolitic units representing time correlative shallower environments record similar carbon isotope ratios during the negative carbon isotopic anomaly the carbon isotopic homogeneity displayed between fans and other carbonate sediments implies that waters across the shelf were well mixed rather than stratified during the late neoproterozoic isotopic anomaly in addition the similarity of carbon isotope ratios shared among fans along a stratigraphic horizon on a m to cm scales suggests that the local source of alkalinity required for fan growth was derived from a well mixed reservoir likely seawater rather than local diagenetic fluids increased alkalinity and the presence of inhibitors to carbonate nucleation perhaps fe2 under anoxic conditions likely fostered precipitation of aragonite crystal fans on the seafloor

isotope geochemistry of recent magmatism in the aegean arc sr nd hf and o isotopic ratios in the lavas of milos and santorini geodynamic implications in this comparative study of variations in the isotopic compositions sr nd o and hf of the calc alkaline magmas of the largest two volcanoes milos and santorini of the aegean arc eastern mediterranean we demonstrate the complexity of the processes governing the evolution of the magmas on the scale both of the arc and of each volcano on santorini the crustal contamination processes have been limited effecting the magma gradually during its differentiation the most differentiated lavas rhyodacite and pumice are also the most contaminated on milos by contrast these processes are very extensive they are expressed in the143nd 144nd vs 87sr 86sr diagram as a continuous mixing curve between a mantle and a crustal end member pole defined by schists and metavolcanic rocks outcropping on these volcanoes in contrast with santorini the least differentiated lavas on milos are the most contaminated these isotopic singularities can be correlated with the geodynamic evolution of the aegean subduction zone consisting of alternating tectonic phases of distension and compression the genesis of rhyolitic magmas can be linked to the two phases of distension and the contamination of the calc alkaline mantle derived magmas with the intermediate compressive phase the isotopic characteristics of uncontaminated calc alkaline primitive magmas of milos and santorini are directly comparable to those of magmas generated in subduction zones for which a contribution of subducted sediments to partial melts from the mantle is suggested such as in the aleutian sunda and lesser antilles island arcs however in spite of the importance of the sediment pile in the eastern mediterranen oceanic crust 6 10 km the contribution of the subducted terrigenous materials remains of limited amplitude

santorini eruption radiocarbon dated to 1627 1600 b c precise and direct dating of the minoan eruption of santorini thera in greece a global bronze age time marker has been made possible by the unique find of an olive tree buried alive in life position by the tephra pumice and ashes on santorini we applied so called radiocarbon wiggle matching to a carbon 14 sequence of tree ring segments to constrain the eruption date to the range 1627 1600 b c with 95 4 probability our result is in the range of previous less precise and less direct results of several scientific dating methods but it is a century earlier than the date derived from traditional egyptian chronologies

mineralogical and geochemical constraints on the origin of ferromanganese crusts from the rivera plate western margin of mexico abstract marine hydrogenetically precipitated ferromanganese crusts are widespread in the pacific ocean they occur as pavements coating volcanic or sedimentary hard rock substrates mainly on the slopes of seamounts plateaus and hills in ocean basins and continental margins we studied three ferromanganese crusts from one dredge haul from the rivera plate western margin of mexico which are up to 15 mm thick and grow directly on a substrate of pillow basalt fragments they consist of laminated botryoidal porous aggregates mostly of fe and mn oxyhydroxides and up to 10 silicates xrd analysis showed the predominance of poorly crystallized mineral phases in the crusts that include mn feroxyhyte and vernadite and an authigenic smectite like clay detrital minerals probably derive from granodiorites of the eastern wall of the neighboring middle america trench scattered barite grains occur on the crust surface and suggest plume fall out derived from hydrothermal vents although a possible pelagic source cannot be dismissed ratios between major fe mn si and trace co ni cu elements reveal that such crusts are predominantly hydrogenetic in origin although they show a hydrothermal influence that increases in the outer layers iron contents range from 16 2 to 25 2 wt and manganese from 3 4 to 14 5 wt the fe mn ratio ranges from 1 6 to 7 0 the sio 2 al 2 o 3 ratio ranges from 4 3 to 6 6 indicating the presence of biogenic silica radiolarians the concentrations of copper up to 383 ppm and cobalt up to 534 ppm are significantly below those of the typical hydrogenetic crusts whereas ni up to 1320 ppm is about the same or slightly lower ree normalized profiles and ree values 486 to 732 ppm match those reported for hydrogenetic crusts but suggest a hydrothermal contribution for the later crust layers the inferred crust growth rates using the co chronometer 44 and 229 mm myr are higher than those reported for pure hydrogenetic crusts mostly 1 to 6 mm myr thus indicating an increasing hydrothermal influence the highest growth rate 229 mm myr corresponding to the outer crust layers suggests a regional hydrothermal input of iron and manganese to seawater the intensification of regional submarine hydrothermal activity began about 13 000 yr ago and may be related to the tectonic activity in the complex junction of the rivera cocos pacific and north america plates

the origin of iron rich muds at the kameni islands santorini greece abstract hydrothermal sediments form in several places within the santorini caldera the sediments at the most active hot submarine spring at sw nea kameni consist of 40 48 fe 2 o 3 and 8 15 sio 2 but only little al 2 o 3 0 5 1 6 p 0 1 0 3 mn 100 450 ppm sr zr ba zn and v 30 200 ppm and cu ni and y 1 30 ppm are present the sediments contain more fe and p and less si al mn and many trace elements than sediments formed at less active springs at palaea kameni the differences probably being caused by faster deposition rates of fe at nea kameni and less dilution by rock detritus which delivers al si and mn the santorini sediments differ much from other exhalative sediments at present or old spreading centers for example on the east pacific rise in the red sea or at en kafala which are rich in mn cu zn ni and ba hydrothermal rock leaching probably occurs at much lower ph values at santorini than on the east pacific rise causing a more complete breakdown of the leached rock at santorini the very low trace element to iron ratios in the rocks at santorini therefore prevent the hydrothermal solutions there from being very rich in trace elements the very acid leaching solutions at santorini are created by extensive oxidation of hydrogen sulfide to sulfuric acid a process that is readily possible due to the close proximity of the oxygen rich atmosphere to the top of the magma chamber

the formation of travertine shrubs mammoth hot springs wyoming the structure and microbiology of active travertines is described from canary and minerva springs with emphasis on shrubs growing in terracette pools these dendritic growths of aragonite consist of intricately branched sprays containing thousands of radiating needles shrub microstructure could be explained by the principle of keimauslese and the preferential elongation of sharp protuberances in a rapidly depositing environment the shrubs and other active travertines contain unicellular and filamentous bacteria estimates of total bacteria numbers ranged from 0 6 1 7 10 5 mm 3 but biomass was low and always less than 1 of the travertine by weight no evidence was found to indicate that bacteria played a role in shrub growth or morphology but crystal trapping on bacterial strings may influence travertine fabrics on cascades the shrubs are considered to have developed by inorganic processes in hot spring waters supersaturated with aragonite

low temperature hydrothermal deposits of franklin seamount woodlark basin papua new guinea abstract hydrothermal deposits of siliceous fe mn oxides from a few cm to 7 m in height are widespread at the summit and caldera floor of franklin seamount a 250 m high edifice of basaltic andesite lava tubes pillows and talus located near the western propagating tip of the woodlark spreading axis some deposits are venting clear fluid at about 30 c the hydrothermal constructions are composed predominantly of x ray amorphous protoferrihydrite mixed with variable amounts of opaline silica and greenish nontronite most deposits are covered by mm thick black crusts of vernadite and feroxyhyte which are mineralised bacterial formations genus leptothrix of hydrogenous origin microbes also influenced formation of the fe rich parts of the deposits as evidenced by filamentous protoferrihydrite pseudomorphs of gallionella blocky inorganic particles of protoferrihydrite and ferrihydrite occur as rare interior phases nontronite formed by precipitation from hydrothermal solutions commonly involving replacement of microbial protoferrihydrite and silica patchy and lenticular birnessite partly altered by biogenic processes to vernadite occurs within siliceous protoferrihydrite matrices in dark cm thick outer margins of some edifices this is considered hydrothermal in origin reflecting percolation of hydrothermal fluids through porous protoferrihydrite opal aggregates to more oxidised conditions near the exterior related to mixing with seawater the different mineralogical associations are reflected by geochemistry trace elements in the manganiferous phases were derived partly from the primary hydrothermal solution and partly from seawater with which this was extensively diluted at the depositional site and also deeper within the volcanic structure of franklin seamount most of the fe mn cu zn and pb was derived from the primary hydrothermal fluid from limited data nontronitic portions of the deposits contain more cu zn and pb than the siliceous protoferrihydrite rich portions migration of redox boundaries and redistribution of elements during flow through processes influence development of the typical zoned structure of the deposits uranium thorium decay series equilibria at both actively venting and inactive sites at franklin seamount yield ages not exceeding 43 years

rare earth element distribution in exhalites associated with broken hill type mineralisation at the pinnacles deposit new south wales australia abstract rare earth element ree concentrations in exhalites and pelites associated with strata bound base metal broken hill type mineralisation have been measured for the early proterozoic pinnacles deposit in western new south wales garnetites garnet rich rocks and sulphide rich garnet gahnite bearing rocks exhibit a wide variety of ree concentrations particularly lree and eu which cannot be related entirely to changes in mineralogy but show some correlation with stratigraphic position relative to the main orebody exhalites lying in the footwall to the mineralised rocks have negative eu anomalies and steep lree enriched patterns whereas exhalites in the hanging wall to the ores and silicate rich rocks from within the ore lenses have zero or positive eu anomalies and less lree enriched patterns hree have more consistent values throughout the deposit but in places are strongly depleted non mineralised pelites are slightly enriched in the ree relative to shale composite values and have negative eu anomalies it is argued in this paper that because the variations in data can be related to the stratigraphic location of samples relative to the orebodies that the observed ree distributions are due to fluctuations in ree concentrations in the primary exhalative fluids rather than differential mobilisation of ree during a second post depositional episode of hydrothermal alteration or mobilisation of the ree during prograde granulite facies metamorphism or retrograde amphibolite facies metamorphism which has affected the area the lack of association between metamorphic mineral assemblages and ree distribution and the absence of any homogenisation of the ree concentrations suggest that the data reflect the primary exhalative fluid composition and that the variations in ree data reflect changes in palaeoenvironmental conditions such as f o 2 and temperature a corollary to this conclusion is that there was minimal mobilisation of the ree during subsequent metamorphism

seismogenesis and state of stress in the uk abstract in this paper i present a compilation of focal mechanisms for earthquakes with magnitudes greater than 3 0 ml in the british isles that can be used to help constrain our understanding of seismicity and it s driving forces in the british isles the fault plane solutions consist of both previously published mechanisms for significant british earthquakes and new solutions calculated from regional and local data for more recent and smaller earth quakes that were previously unpublished focal mechanisms for earthquakes in the uk are dominantly strike slip with northwest southeast compression and northeast southwest tension or reverse with northwest southeast com pression in many cases there is also an oblique component to the slip p and t axes from individual solutions are relatively well constrained in azimuth though less so in dip with p axes orientation for most events clustering between north and north west indicating sub horizontal compression however some spatial variation in p and t axes orientation is also apparent with near north northeast compression and east west extension in north west scotland changing to northwest southeast compression in england and wales i estimate a best fitting stress tensor under the assumption of uniform stress using two different inversion methods for both the entire focal mechanism data set and two different subsets of the data the results from the two different datasets suggest that there is a significant difference in the stress state between northwest scotland and england and wales calculated 1 directions for england and wales are northwest southeast consistent both with existing stress data and expected stresses from first order plate motions by contrast the inversion results for northwest scotland show near east west extension with possible 1 and 2 directions lying in a north south band and that the magnitudes of 1 and 2 are similar the relative magnitude of the principal stresses r determined for england and wales suggests that the intermediate stress 2 is close to the average value of 1 and 3 the clear difference in the stress inversion results between northwest scotland and england and wales suggests that the principal stress directions expected from first order plate motions have been modified in scotland by local stress conditions due to glacio isostatic adjustment

mn ba hg mineralization at shallow submarine hydrothermal vents in bahia concepcion baja california sur mexico coastal submarine hydrothermal venting occurs on the west shore of the fault bounded bay of bahia concepcion along a stretch of about 700 m of rocky shoreline diffuse hydrothermal seepage of water and continuous gas bubbling mainly co2 and n2 take place through the sediment covered seafloor at shallow depth 5 to 15 m in addition at about 500 m se a cluster of hot springs occurs within the intertidal zone the temperature and ph of the hydrothermal fluids varies from 72 to 87 c and 5 95 to 6 02 in the submarine diffuse venting area and reaches 62 c and ph of 6 68 in the intertidal hot springs mn ba hg mineralization is presently forming as a result of the hydrothermal venting at the intertidal hot springs moss like crusts of manganese oxides and structureless detrital aggregates cemented by opal a barite and calcite occur around the main discharge conduits these aggregates are overlaid by silica carbonate fine layered stromatolitic aggregates that extend some meters from the hot springs forming crusts and coalescing rims over volcanic pebbles and boulders manganese crusts are made up of barium rich x ray amorphous todorokite like and romanechite phases and represent a rare example of a manganese deposit formed in a shallow submarine hydrothermal environment in the submarine diffuse venting area the hydrothermal precipitates are less conspicuous and consist in millimeter thick iron oxyhydroxide coatings on volcanic cobbles and boulders these coatings are composed of poorly crystallized six line ferrihydrite accompanied by minor cinnabar and fine grained colloform pyrite textures and fabrics of the mineral assemblages suggest microbial mediation for mineral deposition the vent precipitates display a significant enrichment of hg as and sb arsenic is probably adsorbed onto mn and fe oxide substrates the nasc north american shale composite normalized ree patterns of the vent precipitates show a pronounced positive eu anomaly that is probably inherited from the hydrothermal fluid

textural transition in an aragonite travertine formed under various flow conditions at pancuran pitu central java indonesia abstract a large travertine mound at pancuran pitu central java indonesia displays various types of lamination reflecting different hydrological conditions to understand the geomicrobiological processes of the laminated travertines we investigated the mound s hydrology water chemistry texture microbial composition and volume percentage of carbonate mineral vpc we identified four types of travertines dense travertine 80 vpc flow rate 200 cm s lithified microbial travertine 60 vpc flow rate 70 cm s fragile microbial travertine 30 vpc flow rate 10 cm s and poorly lithified microbial mat

genesis of ferromanganese crusts from the tag hydrothermal field the rare earth element ree geochemistry and nd isotopic composition of marine ferromanganese crusts allow insight into their environment of deposition we present ree along with major and trace element data from a suite of samples collected near an active hydrothermal site from the mid atlantic ridge and demonstrate extreme ree variability over short spatial scales both positive and negative ce anomalies are observed along with varied fractionation of the rees some of the fe mn crusts are formed directly from low temperature hydrothermal fluids channelled over 3 km from any high temperature vent site a significant hydrothermal component is observed in one fe mn crust sampled other samples collected from the same area are predominantly hydrogenous and form at a wide range of accumulation rates depending on the hydrothermal plume input the identification of extreme heterogeneity in source and depositional environment within one hydrothermal field suggests that 1 this variability can be resolved both spatially and temporally within a fossil hydrothermal deposit and 2 the integrated record provided by bulk analysis should be interpreted with caution

microbialite formation in seawater of increased alkalinity satonda crater lake indonesia abstract the crater lake of the small volcanic island satonda indonesia is unique for its red algal microbial reefs thriving in marine derived water of increased alkalinity the lake is a potential analogue for ancient oceans sustaining microbialites under open marine conditions current reef surfaces are dominated by living red algae covered by non calcified biofilms with scattered cyanobacteria and diatoms minor caco3 precipitates are restricted to the seasonally flooded reef tops which develop biofilms up to 500 m thick dominated by the cyanobacteria pleurocapsa calothrix phormidium and hyella microcrystalline aragonite patches form within the biofilm mucilage and fibrous aragonite cements grow in exopolymer poor spaces such as the inside of dead lysed green algal cells and reef framework voids cementation of lysed hadromerid sponge resting bodies results in the formation of wetheredella like structures hydrochemistry data and model calculations indicate that co2 degassing after seasonal mixis can shift the carbonate equilibrium to cause caco3 precipitation increased concentrations of dissolved inorganic carbon limit the ability of autotrophic biofilm microorganisms to shift the carbonate equilibrium therefore photosynthesis induced cyanobacterial calcification does not occur instead passive diffusion controlled eps mediated permineralization of biofilm mucus at contact with the considerably supersaturated open lake water takes place in contrast to extreme soda lakes the release of ca2 from aerobic degradation of extracellular polymeric substances does not support caco3 precipitation in satonda because the simultaneously released co2 is insufficiently buffered subfossil reef parts comprise green algal tufts encrusted by microstromatolites with layers of fibrous aragonite and an amorphous unidentified mg si phase the microstromatolites probably formed when lake satonda evolved from seawater to ca2 depleted raised alkalinity conditions because of sulfate reduction in bottom sediments and pronounced seasonality with deep mixing events and strong co2 degassing the latter effect caused rapid growth of fibrous aragonite while mg si layers replaced the initially mg calcite impregnated biofilms this could be explained by dissolution of siliceous diatoms and sponge spicules at high ph followed by mg calcite dissolution and mg silica precipitation at low ph due to heterotrophic activity within the entombed biofilms

evidence from cosmic ray exposure cre dating for the existence of a pre minoan caldera on santorini greece cosmic ray exposure cre dating was performed on the caldera cliffs of santorini with the aim of detecting cliff segments predating the minoan eruption 17th century bce the methodology involved the determination of in situ produced cosmogenic 36cl concentration in basaltic to rhyodacitic whole rocks cropping out in the cliffs after the samples were processed following the chemical protocol of 36cl preparation for silicate rocks 36cl concentrations were measured by accelerator mass spectrometry ams important challenges during the implementation procedure were related to large amounts of radiogenic 36cl complex modeling of inherited 36cl and dominance of the thermal and epithermal low energy neutron capture production pathway nevertheless quantitative assessments on the basis of the contribution of the low energy neutron capture pathway percent to the total production rate validated the calculated cre dates current cre ages demonstrate that an ancient caldera existed on pre minoan santorini occupying at least the northern half of the modern day caldera

compositional and morphological features of aragonite precipitated experimentally from seawater and biogenically by corals abstract the morphology and composition of abiogenic synthetic aragonites precipitated experimentally from seawater and the aragonite accreted by scleractinian corals were characterized at the micron and nano scale the synthetic aragonites precipitated from supersaturated seawater solutions as spherulites typically 20 100 m in diameter with aggregates of sub micron granular materials occupying their centers and elongate fibrous needles radiating out to the edge using sr isotope spikes the formation of the central granular material was shown to be associated with high fluid ph and saturation state whereas needle growth occurred at lower ph and saturation state the granular aggregates have significantly higher mg ca and ba ca ratios than the surrounding fibers two types of crystals are identified in the coral skeleton aggregates of sub micron granular material and bundles of elongate fibrous crystals that radiate out from the aggregates the granular materials are found in centers of calcification and in fine bands that transect the fiber bundles they have significantly higher mg ca and ba ca ratios than the surrounding fibers the observed relationship between seawater saturation state and crystal morphology and composition in the synthetic aragonites was used as a framework to interpret observations of the coral skeleton we propose that coral skeletal growth can be viewed as a cyclical process driven by changes in the saturation state of the coral s calcifying fluids when saturation state is high granular crystals precipitate at the tips of the existing skeletal elements forming the centers of calcification as the saturation state decreases aragonitic fibres grow in bundles that radiate out from the centers of calcification

isotopic and chemical assessment of geothermal potential of the colli albani area latium region italy abstract the chemical and isotopic compositions of low temperature mineral waters discharged over the colli albani region south of rome italy are those of highly immature waters of essentially meteoric origin formed through absorption of gases emanating from greater depth followed by cation leaching of country rock at shallow levels the composition of the gases discharged points to the presence at depth of a co2 producing high temperature system in its waning stage low h2 and unsaturated hydrocarbon contents as well as relative he ar and n2 contents indicate long residence time for the rising gas phase of the order of 1 ma on the basis of these findings temperatures higher than 120 c appear unlikely to exist at shallow depth

trigonal dendritic calcite crystals forming from hot spring waters at waikite north island new zealand amorphous silica and calcite form the deposits in the vent and on the discharge apron of waikite spring 100 ws 100 which is located in the waikite geothermal area on north island new zealand these precipitates formed from spring water that has a temperature of 90 c and a ph of 8 1 8 8 the opaline silica is restricted to areas around the vent where cooling and evaporation of the spring water triggered precipitation the calcite deposits in the spring vent and on the discharge apron are formed of large up to 15 cm long asymmetrical dendrite crystals that are characterized by multiple levels of branching branches grew preferentially from the downflow side of their parent branch all branches have a trigonal transverse cross section except in areas where competition for growth space induced merger of neighboring crystals the primary branches of the dendrite crystals are sub perpendicular to the substrate even in areas where the discharge apron slopes at a high angle up to 80 on the steeper parts of the discharge apron the plate like primary branches form the floors of the small terrace pools whereas their distal edges form the rims of the pools growth of these dendrite crystals is attributed to abiotic processes high levels of saturation with respect to calcite were caused by rapid co2 degassing of the sheets of spring water that flowed down the steep discharge apron calcite crystals with different crystal morphologies characterize other springs near this spring the variation in crystal morphologies from spring to spring is attributed to different levels of saturation that are related to the initial pco2 of the spring water upon discharge and the rate of co2 degassing at each spring

botryoidal aragonite and its diagenesis botryoidal aragonite is a spectacular growth form occurring as mamelons up to 100 mm in diameter three examples of this particular carbonate cement have been discovered in two distinct areas in new caledonia small scale mamelons have been recognized within pleistocene reefal terraces at ouvea an island of the loyalty archipelago and in the red sea large scale mamelons of botryoidal aragonite exist within pleistocene reefal terraces along the um gheig region of the egyptian coast in addition a similar botryoidal cement partly dolomitized but exhibiting aragonite relics occurs within a miocene reef in the same region mamelons of botryoidal aragonite are isolated and or coalescent but grow only on fixed substrates they occur within cavities of varied origin their fabrics are characterized by fans of elongate euhedral crystals of aragonite fibres botryoidal aragonite can be preceded or followed by other types of cements or internal sediment despite similar mineralogy petrography and ultrastructure there are differences between the fabrics of the pleistocene botryoids from the red sea and ouvea and the miocene botryoids from the red sea the former are of submarine origin as confirmed by the strontium content 8500 10 500 ppm and isotopic composition 18o between 0 10 and 0 19 pdb the latter related to a miocene karst are rich in strontium average 13 600 ppm and have an isotopic composition average 18o 10 50 pdb indicative of non marine precipitation diagenesis of these botryoidal aragonites consists of slight dissolution for pleistocene botryoids and mineralogical transformation for the miocene botryoids the latter exhibit the diagenetic sequence aragonite calcite dolomite the aragonite to calcite transformation is a dissolution reprecipitation process the void distribution and size influencing the distribution and the size of the replacement calcite crystals

geochemistry and crystal morphology of aragonite cements of mixing zone origin barbados west indies abstract isopachous aragonite ray cement arc lines large rugs 5 cm through a 4 m interval recovered in core samples from a borehole drilled along the southeast coast of barbados the vuggy cement interval is 12 16 m below core top and most of the interval is below the modern water table 13 m the top of the interval corresponds to the top of the 194 ka coral reef terrace which is unconformably overlain by the 122 ka terrace arc was precipitated after a period of meteoric diagenesis during which vuggy porosity was produced arc shows variable ultrastructures including 1 loosely packed randomly oriented rays the 100 arc has uncharacteristically low 13c values relative to predicted and reported values for marine aragonite cement likewise the 18o values are lower than both reported and most predicted o18o values for marine aragonite stable isotope compositions of this cement fall along a mixing line between aragonite equilibrium compositions calculated for meteoric and marine end member fluids strontium concentrations are greater than in most known marine aragonite this suggests precipitation from fluids with an elevated sr ca ratio such fluids are found in modern barbados mixed waters whose elevated sr ca ratios result from updip meteoric dis olution of aragonite magnesium concentrations are slightly higher and more variable than in reported pleistocene marine aragonite sodium concentrations are lower than expected marine values and covary with changes in 13c and 18o values isotope and minor element geochemistry of these cements suggests precipitation from mixed meteoric marine waters fluid mixing models for modern barbados waters suggest precipitation from mixed fluids ranging from 50 to 75 seawater precipitation of aragonite from mixed waters may be facilitated by degassing of co2 charged mixed waters within large vugs and by mg ca ratios sufficiently elevated to inhibit precipitation of calcite

vent development during the minoan eruption 1640 bc of santorini greece as suggested by ballistic blocks abstract the minoan eruption on santorini greece was a major plinian caldera forming event that occurred at ca 1640 bc the eruption is generally divided into four distinct phases 1 plinian phase 2 phreatomagmatic base surge 3 ash flow phase and 4 non welded ignimbrite many ballistic blocks mostly consisting of older lava fragments with diameters up to several meters were ejected during phases 2 and 3 as caldera collapse followed the eruption the precise vent location is unknown but its position during phase 1 has been inferred from the pumice isopachs of the plinian deposits the location of the vent during the following phases has been estimated by measuring thickness variations flow directions within the pyroclastic flows and impact directions of ballistic blocks in this study the vent location has been estimated by analysis of the size distribution of the ballistic blocks phase 2 blocks show no clear size dependant distribution pattern blocks ranging between 0 15 and 1 60 m in diameter are found throughout almost the entire deposit but are concentrated in the southeastern parts and within a circle of 14 km diameter thus suggesting a maximum range of at least 6 7 km the center of that circle is regarded as the most probable ejection region it is proposed that the subaerial vent of phase 1 developed into an fracture opening to the sw along the general tectonic trend very large blocks up to 3 m in diameter or possibly more were also ejected during phase 3 with the largest ones being found only in the northern half of the island group near the caldera rim it therefore appears that at least one other vent opened in the northern half of the caldera possibly as a new sw ne trending fracture

variation in sr uptake in the shell of the freshwater gastropod bithynia tentaculata from lake arreo northern spain and culture experiments abstract the sr uptake features in bithynia tentaculata aragonite shells from monthly collections in lake arreo northern spain over a two year period are compared with those from the same species grown in culture experiments with similar waters under controlled temperature the shell aragonite of b tentaculata from lake arreo formed in isotopic equilibrium with the lake water a comparison of the stable oxygen isotope values 18o from the shells and waters allowed the selection of suitable shells for sr uptake studies the sr ca molar ratio in b tentaculata shells sr cashell from the lake and from the culture experiments positively correlate with some chemical parameters like conductivity and solute composition some environmental factors such as ph and t have minor influence on sr incorporation into shells as reported from other aragonitic mollusks the sr cashell exhibits a good positive correlation with the sr ca of the water sr caw using linear regression however a polynomial function equation better fits the sr cashell and the sr caw r2 0 890 p 2 923e 11 above a value of 0 0025 for sr caw the ratios of sr cashell present small changes this pattern reveals a noticeable variation of the partitioning coefficient kdsr with sr caw the kdsr for b tentaculata shell aragonite obtained in this study is 0 290 0 078 n 25 and it is close to the mean values obtained for other non marine aragonitic mollusks kdsr values in b tentaculata are influenced by the variations in sr caw that mask the t effect this feature together with the influence of physiological processes on the trace element incorporation may explain the observed kdsr pattern

provenance of lithogenic surface sediments and pathways of riverine suspended matter in the eastern mediterranean sea evidence from 143nd 144nd and 87sr 86sr ratios in order to characterize the provenance of lithogenic surface sediments from the eastern mediterranean sea ems residual leached fraction of 34 surface samples have been analysed for their 143 nd 144 nd and 87 sr 86 sr isotope ratios the sample locations bracket all important entrances of riverine suspended matter into the ems as well as all sub basins of the ems the combined analyses of these two isotope ratios provide a precise characterization of the lithogenic fraction of surface sediments and record their dilution towards the central sub basins we reconstruct provenance and possible pathways of riverine dispersal and current redistribution assuming more or less homogenous isotopic signatures and flux rates of the eolian fraction over the ems lithogenic sediments entering the ionian sea from the calabrian arc and the adriatic sea are characterized by high 87 sr 86 sr isotope ratios and low end 0 values average 87 sr 86 sr 0 718005 and end 0 11 06 n 5 aegean sea terrigenous sediments show an average ratio of 87 sr 86 sr 0 713089 n 5 and values of end 0 7 89 n 5 the aegean isotopic signature is traceable up to the southwest south and southeast of crete the sediment loads entering the ems via the aegean sea are low and spread out mainly through the strait of casos east of crete surface sediments from the eastern levantine basin are marked by the highest end 0 values 3 3 n 6 and lowest 87 sr 86 sr isotope ratios average 0 709541 n 6 reflecting the predominant input of the nile sediment the influence of the nile sediment is traceable up to the ne trending eastern flank of the mediterranean ridge the characterization of the modern riverine dispersal and eolian flux based on isotope data may serve as a tool to reconstruct climate coupled variations of lithogenic sediment input into the ems d 2002 elsevier science b v all rights reserved

seawater strontium and sr ca variability in the atlantic and pacific oceans abstract seawater sr and sr ca exhibit spatial gradients of 2 3 globally with the deep ocean more enriched relative to the surface in latitudinal transects the highest surface values are found at high latitudes and associated with areas of upwelling a pronounced upper ocean vertical sr gradient is attributable to the production of celestite skeletons by surface dwelling acantharia coupled to a shallow dissolution cycle the upper ocean residence time of sr with respect to celestite cycling is much shorter than its global oceanic residence time although the magnitude of seawater sr ca variability is relatively small it is significant with respect to high precision paleoceanographic applications sr ca gradients in the contemporary ocean also complicates evaluating quaternary changes in seawater sr ca that may have resulted from other processes such as aragonite recrystallization during sea level low stands

the oxygen and carbon isotope distribution in the mediterranean water masses abstract the oxygen and carbon stable isotope compositions of the present day mediterranean waters have been measured in order to evaluate their variability which is related to the specific climatic and hydrological conditions within the basin the experimental equation between the 18 o value and the salinity of water based on 300 measurements on surface intermediate and deep waters sampled during the vicomed 2 and 3 cruises in the western central and eastern mediterranean has a slope of 0 27 a value which is significantly lower than the slope of 0 45 as defined in the northeast atlantic ocean this difference in the 18 o salinity relationship which occurs immediately in the alboran basin is basically a characteristic of the climatic regime of the mediterranean i e of an excess evaporation over fresh water input the largest variations of these two parameters 18 o of water and 13 c of co 2 are observed in the surface waters mostly in the western mediterranean this evolution mirrors the progressive eastward restriction which separates the less evaporated and more productive western basins from the more evaporated and less productive eastern basins the intermediate waters constitute a homogeneous layer however their 18 o values decrease eastward by 0 35 at maximum due to progressive dilution by mixing with overlying and underlying water masses their 13 c values decrease also eastward by 0 35 at maximum due to an increasing input of nutrients issued from the regeneration of sinking organic particles the deep waters have similar 18 o values but slightly higher 13 c values often by less than 0 1 than the overlying intermediate waters indicating generally well ventilated conditions due to active winter convection