incorporation of ca isotopes in carapaxes of marine ostracods abstract we studied mg ca sr ca and ca isotope ratios of ostracod carapaxes from surface sediments retrieved during research cruises to the southern and equatorial eastern atlantic collected specimens originate from water depth between 30 and about 5000 mbsl and cover bottom water temperatures between 0 and 23 c analysed taxa include buntonia sp cytherella sp henryhowella sp krithe sp poseidonamicus sp and ruggieria sp calcium isotope ratios of the studied specimens are in the overall range of other marine calcifiers and show a variability of about 0 75 over a temperature range of 20 c there is no overall linear relation between temperature and ca isotope fractionation but some species show a maximum 44 40ca at intermediate temperatures mg ca and sr ca agree well with values of previously published carapaxes demonstrating large inter and intra species variability and different responses to bottom water temperatures magnesium is highly variably distributed within the carapax with mg enrichment in the inner part of the shell of most taxa this enrichment is independent from the incorporation of sr which shows less variability within the carapax the ca isotope vs sr ca systematic in the ostracods deviates from inorganic calcite and foraminifers the ostracod array is most likely controlled by either mixing of material originating from a precursor phase and newly grown calcite or rayleigh type fractionation during precipitation from a restricted fluid reservoir indicating varying degrees of ca and sr consumption during calcite precipitation the different slope of the ca isotope vs sr ca relation shown by the ostracods compared to those of inorganic calcite and foraminifers opens a new approach for the determination of ca isotope and sr ca ratios of past ocean water

clathrites archives of near seafloor pore fluid evolution δ44 40ca δ13c δ18o in gas hydrate environments aragonitic clathrites are methane derived precipitates that are found at sites of massive near seafloor gas hydrate clathrate accumulations at the summit of southern hydrate ridge cascadia margin these platy carbonate precipitates form inside or in proximity to gas hydrate which in our study site currently coexists with a fluid that is highly enriched in dissolved ions as salts are excluded during gas hydrate formation the clathrites record the preferential incorporation of 18o into the hydrate structure and hence the enrichment of 16o in the surrounding brine we measured 18o values as high as 2 27 relative to peedee belemnite that correspond to a fluid composition of 1 18 relative to standard mean ocean water the same trend can be observed in ca isotopes ongoing clathrite precipitation causes enrichment of the 44ca in the fluid and hence in the carbonates carbon isotopes confirm a methane source for the carbonates our triple stable isotope approach that uses the three main components of carbonates ca c o provides insight into multiple parameters influencing the isotopic composition of the pore water and hence the isotopic composition of the clathrites this approach provides a tool to monitor the geochemical processes during clathrate and clathrite formation thus recording the evolution of the geochemical environment of gas hydrate systems

calcium carbonate as ikaite crystals in antarctic sea ice 1 we report on the discovery of the mineral ikaite caco3 6h2o in sea ice from the southern ocean the precipitation of caco3 during the freezing of seawater has previously been predicted from thermodynamic modelling indirect measurements and has been documented in artificial sea ice during laboratory experiments but has not been reported for natural sea ice it is assumed that caco3 formation in sea ice may be important for a sea ice driven carbon pump in ice covered oceanic waters without direct evidence of caco3 precipitation in sea ice its role in this and other processes has remained speculative the discovery of caco3 6h2o crystals in natural sea ice provides the necessary evidence for the evaluation of previous assumptions and lays the foundation for further studies to help elucidate the role of ikaite in the carbon cycle of the seasonally sea ice covered regions

a laboratory model for melting erosion of a magma chamber roof and the generation of a rhythmic layering 1 a hot magma chamber can ascend by melting the roof rock a process which in turn affects the magma composition the disaggregated mineral particles which consisted the roof rock will descend in the magma chamber to form a sedimentary cumulate however the fluid dynamics leading to the formation of the sediment and how we can decipher them is unknown here we conducted a series of experiments modeling melting erosion of the roof with particle size consisting the roof rock as the parameter we find that there is a critical particle size below which the melting erosion occurs rhythmically melting erosion stops because the disaggregated particles are suspended in the magma chamber and suppress the vertical heat transfer the suspension then separates into an upper clear layer and a lower suspension layer eventually the heated stratified layers become unstable an overturn occurs and melting erosion resumes when the particles consist of two sizes such that at least one of them is smaller than the critical size a rhythmic erosion occurs particles are sorted during each erosion period and a size graded rhythmic layering is spontaneously generated we estimate that rhythmic layering can be generated from melting erosion in a basaltic magma chamber when the grain size of the roof rock is 0 6 mm assuming a vertical temperature difference of 10 c we suggest that rhythmic roof melting coupled with particle settling is one possible mechanism for generating the rhythmic layering which is commonly observed in solidified magma chambers

a rapid mechanism to remobilize and homogenize highly crystalline magma bodies the largest products of magmatic activity on earth the great bodies of granite and their corresponding large eruptions have a dual nature homogeneity at the large scale and spatial and temporal heterogeneity at the small scale this duality calls for a mechanism that selectively removes the large scale heterogeneities associated with the incremental assembly of these magmatic systems and yet occurs rapidly despite crystal rich viscous conditions seemingly resistant to mixing here we show that a simple dynamic template can unify a wide range of apparently contradictory observations from both large plutonic bodies and volcanic systems by a mechanism of rapid remobilization unzipping of highly viscous crystal rich mushes we demonstrate that this remobilization can lead to rapid overturn and produce the observed juxtaposition of magmatic materials with very disparate ages and complex chemical zoning what distinguishes our model is the recognition that the process has two stages initially a stiff mushy magma is reheated from below producing a reduction in crystallinity that leads to the growth of a subjacent buoyant mobile layer when the thickening mobile layer becomes sufficiently buoyant it penetrates the overlying viscous mushy magma this second stage rapidly exports homogenized material from the lower mobile layer to the top of the system and leads to partial overturn within the viscous mush itself as an additional mechanism of mixing model outputs illustrate that unzipping can rapidly produce large amounts of mobile magma available for eruption the agreement between calculated and observed unzipping rates for historical eruptions at pinatubo and at montserrat demonstrates the general applicability of the model this mechanism furthers our understanding of both the formation of periodically homogenized plutons crust building and of ignimbrites by large eruptions

factors determining desert dune type while most observers recognize four elemental types of desert dunes longitudinal transverse barchan and star1 3 there is little agreement about which factors determine these types the angular relationships between the resultant of sand shifting winds and both the crest and principal slipfaces of the elemental types have been discussed qualitatively for many decades these relationships have been quantified but the wide range of dune types that combine the elemental forms and the juxtaposition of different dune types show that wind regime is not the only determinant for example sand availability has been considered important we have now quantified the importance of both wind regime and sand availability as determinants of dune type we show here that the four elemental types occur in areas uniquely defined by both the equivalent sand thickness of sediments held in the dunes and a measure of directional variability of sand moving winds wind strength does not appear to be important vegetation has an ambiguous role and the particle size of dune sediments is unimportant

lateglacial and holocene climatic changes in south eastern patagonia inferred from carbonate isotope records of laguna potrok aike argentina abstract first results of strontium calcium carbon and oxygen isotope analyses of bulk carbonates from a 106 m long sediment record of laguna potrok aike located in southern patagonia are presented morphological and isotopic investigations of m sized carbonate crystals in the sediment reveal an endogenic origin for the entire holocene during this time period the calcium carbonate record of laguna potrok aike turned out to be most likely ikaite derived as ikaite precipitation in nature has only been observed in a narrow temperature window between 0 and 7 c the respective carbonate oxygen isotope ratios serve as a proxy of hydrological variations rather than of palaeotemperatures we suggest that oxygen isotope ratios are sensitive to changes of the lake water balance induced by intensity variations of the southern hemisphere westerlies and discuss the role of this wind belt as a driver for climate change in southern south america in combination with other proxy records the evolution of westerly wind intensities is reconstructed our data suggest that weak shw prevailed during the lateglacial and the early holocene interrupted by an interval with strengthened westerlies between 13 4 and 11 3 ka cal bp wind strength increased at 9 2 ka cal bp and significantly intensified until 7 0 ka cal bp subsequently the wind intensity diminished and stabilised to conditions similar to present day after a period of reduced evaporation during the little ice age strontium isotopes 87 sr 86 sr ratio were identified as a potential lake level indicator and point to a lowering from overflow conditions during the glacial 17 ka cal bp to lowest lake levels around 8 ka cal bp thereafter the strontium isotope curve resembles the lake level curve which is stepwise rising until the little ice age the variability of the ca isotope composition of the sediment reflects changes in the ca budget of the lake indicating higher degrees of ca utilisation during the period with lowest lake level

mg ca sr ca and ca isotope ratios in benthonic foraminifers related to test structure mineralogy and environmental controls we analysed mg ca sr ca and ca isotope ratios of benthonic foraminifers from sediment core tops retrieved during several research cruises in the atlantic ocean in order to improve the understanding of isotope fractionation and element partitioning resulting from biomineralisation processes and changes in ambient conditions species include foraminifers secreting tests composed of hyaline low magnesium calcite porcelaneous high magnesium calcite as well as aragonite our results demonstrate systematic isotope fractionation and element partitioning patterns specific for these foraminiferal groups calcium isotope fractionation is similar in porcelaneous and hyaline calcite tests and both groups demonstrate the previously described anomaly with enrichment of heavy isotopes around 3 4 degrees c gussone and filipsson 2010 calcium isotope ratios of the aragonitic species hoeglundina elegans on the other hand are about 0 4 parts per thousand lighter compared to the calcitic species which is in general agreement with stronger fractionation in inorganic aragonite compared to calcite however the low and strongly variable sr content suggests additional processes during test formation and we propose that transmembrane ion transport or a precursor phase to aragonite may be involved porcelaneous tests composed of high mg calcite incorporate higher amounts of sr compared to hyaline low mg calcite in agreement with inorganic calcite systematics but also porcelaneous tests with reduced mg ca show high sr ca while calcium isotopes sr ca and mg ca in benthonic foraminifers primarily appear to fractionate and partition with a dominant inorganic control delta ca 44 40 temperature and growth rate dependencies of benthonic foraminifer tests favour a dominant contribution of light ca by transmembrane transport relative to unfractionated seawater ca to the calcifying fluid thus controlling the formation of foraminiferal delta ca 44 40 and sr ca proxy signals c 2015 elsevier ltd all rights reserved less

petrology of the 1991 1995 eruption at unzen effusion pulsation and groundmass crystallization abstract effusive eruption of dacite magma 2 1 108 m3 during 1991 1995 formed a lava dome at the summit of unzen volcano japan the effusion rate was highest at the beginning 4 0 105 m3 day 4 6 m3 s and decreased roughly with time to almost zero before this pattern was repeated with a second pulse of magma supply the whole rock chemistry of lavas shows significant variation attributable to variations in phenocryst abundance the more mafic the more abundant the phenocrysts the pattern of chemical variation with time shows some difference from that of the effusion rate all phenocrysts in dacite plagioclase hornblende biotite quartz and magnetite show evidence of disequilibrium with melt although a glomerophyric aggregation of phenocrysts suggests coexistence with each other phenocrysts are isotopically heterogeneous from species to species the calculated initial melt composition was rhyodacite and was nearly constant throughout the activity in contrast the bulk phenocryst population is andesite a model explaining the textures and the isotopic heterogeneity is the capture of diorite fragments or xenocrysts by parental rhyodacite magma it is suggested that when effusion rate was high less viscous crystal poor magma exited from the reservoir groundmass glass and plagioclase microlite rims show temporal chemical variations correlating with the effusion rate the higher the effusion rate the more evolved the compositions groundmass crystallinity increased with decreasing effusion rate from 33 to 50 textures in dome lavas suggest that groundmass crystallization had been mostly completed when magma reached the conduit top the fe ti oxide temperature 880 780 c was low when the crystallinity was high micropumice erupted before dome growth provided a sample recording magmatic foam in the conduit porosity of dome lavas was lower at lower effusion rates collapse of foam magma and simultaneous escape of volatiles through the conduit top were probably responsible for the accompanying low frequency earthquakes phenocrysts were broken and the breakdown rims on hornblende phenocrysts were torn off during collapse and successive compaction when effusion waned degassing and the resultant crystallization proceeded more completely so that the magma became too viscous to flow in the conduit top and behaved as a plug resulting in a temporary halt of effusion in turn groundmass crystallization in magma below the plug increased excess pressure in the upper parts of conduit due to slow cooling the plug was scavenged when rising excess pressure overcame its effective strength then the second pulse of magma supply began strong endogenous growth and extrusion of a lava spine in the later stage probably occurred for the same reason

origin of crystal poor differentiated magmas insights from thermal gradient experiments crystal poor differentiated magmas are commonly erupted from shallow thermally zoned magma chambers in order to constrain the origin of these magmas we have experimentally investigated crystallization differentiation and crystal melt separation in presence of a thermal gradient experiments have been designed taking advantage of the innate temperature gradient of the piston cylinder apparatus and carried out on a phonolitic system at 0 3 gpa and temperature ranging from 1 050 to 800 c crystallization degree and melt composition in experimental products vary as a function of the temperature gradient in particular melt composition differentiates from tephri phonolite starting material to phonolite moving from the hotter glassy zone t 1 050 c towards the cooler heterogeneously crystallized zone t 900 c of the charge the heterogeneously crystallized zone is made up of 1 a crystal rich mushy region crystallinity 30 vol 2 a rigid crystal framework crystallinity 80 vol and 3 glassy belts of phonolitic glass at the top thermal gradient experiments picture crystallization differentiation and crystal melt separation processes occurring in a thermally zoned environment and reveal that relatively large volumes of crystal poor melt glassy belts can originate as a consequence of the instability and collapse of the rigid crystal framework analogously in thermally zoned magma chambers the development and collapse of a solidification front may represent the controlling mechanism originating large volumes of crystal poor differentiated magmas

calcium isotope δ44 40ca variations of neogene planktonic foraminifera measurements of the calcium isotopic composition 44 40ca of planktonic foraminifera from the western equatorial pacific and the indian sector of the southern ocean show variations of about 0 6 over the past 24 myr the stacked 44 40ca record of globigerinoides trilobus and globigerina bulloides indicates a minimum in 44 40casw seawater calcium at 15 to 16 ma and a subsequent general increase toward the present interrupted by a second minimum at 3 to 5 ma applying a coupled calcium carbon cycle model we find two scenarios that can explain a large portion of the observed 44 40casw variations in both cases variations in the ca input flux to the ocean without proportional changes in the carbonate flux are invoked the first scenario increases the riverine calcium input to the ocean without a proportional increase of the carbonate flux the second scenario generates an additional calcium flux from the exchange of ca by mg during dolomitization in both cases the calcium flux variations lead to drastic changes in the seawater ca concentrations on million year timescales our 44 40casw record therefore indicates that the global calcium cycle may be much more dynamic than previously assumed

controlling factors of ca isotope fractionation in scleractinian corals evaluated by temperature ph and light controlled culture experiments abstract in this study the 44ca 40ca ratios of porites australiensis grown under three different culture experiments composed of temperature ph and light controlled culture experiments are measured the temperature dependent isotope fractionation of 0 02 c deduced from this study is similar to inorganic aragonite but the degree of isotope fractionation is about 0 4 offset in corals these observations agree with earlier results on different coral species suggesting ca isotope fractionation during ca transmembrane transport in corals while in cultured corals a significant temperature dependence of 44ca is observed the relationships between calcium isotope fractionation and ph as well as light intensity are negligible therefore variation of 44ca in porites corals is mainly controlled by temperature a combination of 44ca and sr ca of corals in temperature controlled experiments cannot be explained by rayleigh type fractionation directly from a fluid which is seawater like in terms of 44ca and sr ca through coral specific biomineralization processes overall mean 44ca of scleractinian corals including previous studies are different from biogenic aragonites secreted by sclerosponges and pteropods but are comparable with those of bivalves as well as calcitic coccolithophores and foraminifers these findings are important for better understanding biomineralization in corals and in order to constrain the ca isotopic composition of oceanic ca sinks in response to climate changes and associated with shifts of calcite and aragonite seas

genesis of phosphorite crusts off peru abstract authigenic phosphorite crusts from the shelf off peru 9 40 s to 13 30 s consist of a facies with phosphatic coated grains covered by younger phosphatic laminite the crusts are composed of carbonate fluorapatite which probably formed via an amorphous precursor close to the sediment water interface as indicated by low f p2o5 ratios sr and ca isotopes as well as rare earth element patterns agreeing with seawater dominated fluids small negative ce anomalies and u enrichment in the laminite suggest suboxic conditions close to the sediment water interface during its formation increased contents of chalcophilic elements and abundant sulfide minerals in the facies with phosphatic coated grains as well as in the laminite denote sulfate reduction and consequently point to episodical development of anoxic conditions during phosphogenesis the peruvian phosphorites formed episodically over an extended period of time lasting from middle miocene to pleistocene individual phosphatic coated grains show a succession of phosphatic layers with varying contents of organic matter and sulfide rich phosphatic layers coated grains supposedly formed as a result of episodic suspension caused by high turbulence and shifting redox conditions episodic anoxia in the pore water induced pyritization in the outermost carbonate fluorapatite layer phosphatic coated grains were later transported to the place of crust formation where subsequent laminite formation was favored under lower energy conditions a similar succession of phosphatic layers with varying contents of organic matter and sulfide rich layers in the laminite suggests a formation mechanism analogous to that of individual coated grains

calcium isotope fractionation in ikaite and vaterite abstract we investigated the isotopic composition of calcium in the metastable calcium carbonate polymorphs vaterite and ikaite the synthetic vaterite precipitates show a smaller degree of ca isotope fractionation than calcite or aragonite at comparable temperatures and revealed no significant temperature sensitivity between 10 and 50 c ikaite the water bearing ca carbonate modification caco 3 6h 2 o was precipitated at 2 c in controlled laboratory experiments and in addition recovered from marine sediments and sea ice synthetic and natural ikaites show similar values of ca isotope fractionation in general ikaite is less depleted in heavy isotopes compared to calcite or aragonite at low temperatures the observed offset of vaterite and ikaite to calcite or aragonite precipitated at similar temperatures is presumably mainly related to differences in precipitation rates and regimes which seem however to be typical for the growth of these carbonate minerals small differences in ca isotope ratios of naturally formed ikaites from different locations seem to be related to different geochemical conditions in the respective sediment settings

glendonites in neoproterozoic low latitude interglacial sedimentary rocks northwest canada insights into the cryogenian ocean and precambrian cold water carbonates stellate crystals of ferroan dolomite in neritic siliciclastic and carbonate sedimentary rocks between sturtian and marinoan glaciations in the mackenzie mountains are interpreted as replaced glendonites these pseudomorphs after ikaite indicate that shallow seawater at that time was near freezing stromatolites verify that paleoenvironments were in the photic zone and physical sedimentary structures such as hummocky cross bedding confirm that the seafloor was repeatedly disturbed by storms glendonites within these low latitude continental shelf to coastal sedimentary deposits imply that global ocean water during much of cryogenian time was likely very cold such an ocean would easily have cooled to yield widespread sea ice and through positive feedback growth of low latitude continental glaciers in this situation gas hydrates could have formed in shallow water cold shelf sediment but would have been particularly sensitive to destabilization as a result of sea level change co occurrence of pisolites and glendonites in these rocks additionally implies that some ooids and pisoids might have been unlike phanerozoic equivalents characteristic of cold water sediments

origin of strontium and calcium in pedogenic needle fibre calcite nfc abstract strontium sr and calcium ca isotopic compositions and sr ca ratios have been analysed in different fractions of pedogenic needle fibre calcite nfc from the swiss jura mountains villiers neuch tel switzerland in order to determine their ca sources and to investigate the potential role of fungi in the origin of nfc 87sr 86sr ratios have been measured to trace the ca trapped within different pedogenic carbonate this ratio was compared for previously identified microscopic morphological groups of nfc the bulk soil fine earth

geochemistry of ikaite formation at mono lake california implications for the origin of tufa mounds the mineral ikaite caco 3 6h 2 o not previously observed in lake environments precipitates seasonally along the shore of mono lake california where ca hco 3 spring water mixes with cold na co 3 lake water during the winter cold water temperatures and high concentrations of po 4 3 and organic carbon inhibit calcite precipitation allowing the metastable ikaite to form during the spring warming however ikaite decomposes to form calcium carbonate and water occasionally leaving pseudomorphs of the primary precipitate the identification of modern ikaite suggests that both pleistocene and holocene tufas in the mono basin originally precipitated as ikaite this mineral may also form in other lake environments but rapid recrystallization after warming destroys the physical chemical and isotopic evidence of formation and alters the geochemical record

remobilization of andesite magma by intrusion of mafic magma at the soufriere hills volcano montserrat west indies the 1995 1999 eruption of the soufriere hills volcano montintroduction serrat has produced a crystal rich andesite containing quenchthe soufriere hills volcano montserrat located in the textured mafic inclusions which show evidence of having been molten lesser antilles island arc in the west indies began to when incorporated into the host magma individual crystals in the erupt on 18 july 1995 after about 350 years of dormancy andesite record diverse histories amphibole phenocrysts vary from young et al 1998b the eruption was preceded by a pristine and unaltered to strongly oxidized and pseudomorphed by period of seismic swarms which began in january 1992 anhydrous reaction products plagioclase phenocrysts are commonly previous earthquake crises have occurred on montserrat reverse zoned often with dusty sieve textures reverse zoned rims are in 1896 1897 1932 1935 and 1966 1967 powell 1938 also common on orthopyroxene phenocrysts pyroxene geothermometry shepherd et al 1971 initial phreatic and phregives an average temperature of 858 20 c for orthopyroxene atomagmatic activity was followed by extrusion of an phenocryst cores whereas reverse zoned rims record temperatures andesitic lava dome in november 1995 pyroclastic flows from about 880 to 1050 c the heterogeneity in mineral rim generated by gravitational collapse of the unstable dome compositions zoning patterns and textures is interpreted as reflecting have been the dominant form of activity throughout the non uniform reheating and remobilization of the resident magma eruption but periods of explosive activity producing body by intrusion of hotter mafic magma convective remobilization pumice flows and falls have also occurred robertson et results in mixing together of phenocrysts that have experienced al 1998 young et al 1998b dome growth ceased different thermal histories depending on proximity to the intruding suddenly in march 1998 and further activity up to may mafic magma the low temperature and high crystallinity are 1999 has mainly involved gravitational collapses of the interpreted as reflecting the presence of a cool highly crystalline dome and periods of ash venting with some small scale magma body beneath the soufriere hills volcano the petrological vulcanian explosive events observations in combination with data on seismicity extrusion rate the soufriere hills volcano is the only active centre and so2 fluxes indicate that the current eruption was triggered by on montserrat the volcano is a composite of at least recent influx of hot mafic magma five andesitic lava domes flanked by pyroclastic deposits rea 1974 identified four other volcanic centres all

elucidating modern geochemical cycles at local regional and global scales using calcium isotopes abstract in earth s surface environment calcium ca is an important mobile metal that is actively and passively transported in solution and within organic and mineral phases being cycled and recycled during various biogeochemical processes with the development of modern mass spectrometric techniques small variations in the stable and radiogenic isotopic compositions of ca can be measured revealing insight in these complex biogeochemical cycles and tracing and quantifying components across a range of spatial and temporal scales similar to other more routine isotope systems more than three decades of work reveal systematic variations in the partitioning of ca isotopes due to both abiotic and biological processes an overview of processes that fractionate ca isotopes at local regional and global scales is outlined here we present detailed examples of instances in which ca isotopes have provided unique insight into the functioning of earth surface processes and the cycling of ca at multiple scales future studies should target questions for which ca isotopic analysis provide unique insight and when combined with other isotope and trace element multi proxy studies better constrain the system of interest at the same time we challenge the scientific community to explore new frontiers including polar regions and other extreme environments

compaction in a mantle mush with high melt concentrations and the generation of magma chambers abstract most compaction models in the partially molten mantle have addressed the case of low intergranular melt concentrations up to a few percent here we develop a mathematical and numerical formalism adapted to the two dimensional modeling of compaction in mushes with higher melt concentrations up to a few tens of percents experimental data on mantle like mushes olivine crystals basaltic melts suggest that the mush viscosity depends in a complex way on the melt concentration three rheological thresholds occur at melt concentrations of about 5 20 and 40 respectively the first threshold corresponds to the establishment of full interconnectivity of the intergranular melt the second to the formation of a very dense suspension of crystals and the last to the development of crystal clusters in the suspension the present models take into account the stiff and drastic viscosity drops associated with these rheological thresholds intergranular melt migration associated with an initial melt pulse generates a horizon of high melt crystal ratio if the melt concentration in the initial pulse presents a local excess the horizon becomes slightly tilted as a consequence melt percolates upslope inside the tilted horizon pools at its summit and generates a pocket like zone due to the higher melt concentration the upward darcy velocity in the pocket markedly exceeds that in the horizon the result is that the pocket like impregnation is rapidly disconnected from the horizon and a new pocket develops at the summit of the partially fragmented horizon eventually the intergranular melt contained in the horizon is completely redistributed into pockets increasing the background melt concentration in the mush from 5 20 and 40 leads to an increase of the maximum melt concentration of 10 40 and 100 in the transient horizons and of 25 60 and 100 in the pockets these models suggest that magma chambers with a kilometer extent naturally result from the compaction of a mantle mush with an initial melt concentration exceeding 5

control of sulfate pore water profiles by sedimentary events and the significance of anaerobic oxidation of methane for the burial of sulfur in marine sediments abstract gravity driven mass flow deposits proven by sedimentary and digital echosounder data are indicative for prevailing dynamic sedimentary conditions along the continental margin of the western argentine basin in this study we present geochemical data from a total of 23 gravity cores pore water so 4 is generally depleted within a few meters below the sediment surface by anaerobic oxidation of methane aom the different shapes of so 4 profiles concave kink and s type can be consistently explained by sedimentary slides possibly in combination with changes in the ch 4 flux from below thus mostly representing transient pore water conditions since slides may keep their original sedimentary signature a combined analysis and numerical modeling of geochemical physical properties and hydro acoustic data could be applied in order to reconstruct the sedimentary history we present first order estimates of the dating of sedimentary events for an area where conventional stratigraphic methods failed to this day the results of the investigated sites suggest that present day conditions are the result of events that occurred decades to thousands of years ago and promote a persisting mass transport from the shelf into the deep sea depositing high amounts of reactive compounds the high abundance of reactive iron phases in this region maintains low hydrogen sulfide levels in the sediments by a nearly quantitative precipitation of all reduced sulfate by aom for the total region we estimate a so 4 or ch 4 flux of 6 6 10 10 moles per year into the zone of aom projected to the global continental slope and rise area this may sum up to about 2 6 10 12 moles per year provided that the sulfur is completely fixed in the sediments it is about twice the global value of the recent global sulfur burial in marine sediments of 1 2 10 12 moles per year as previously estimated thus aom obviously contributes very significantly to the regulation of global sulfur reservoirs which is hitherto not sufficiently recognized this finding may have implications for global geochemical models as sulfur burial is an important control factor in the development of atmospheric oxygen levels over time

continuous mixing of crystal mush and replenished magma in the ongoing unzen eruption zoning profiles of magnetite phenocrysts in the successively effused dacite of the ongoing unzen eruption from 1991 wereanalyzed to estimate the time scale of magma mixing the dacite was formed by mixing of relatively high and low temperature t end member magmas the magnetite phenocrysts derived from the low t magma are reversely zoned by the mixing with high t magma a diffusion calculation for reequilibration of the reverse zonings gives the time interval from magma mixing to quenching for the mixed dacite erupted from may 1991 to may 1993 the typical diffusion time was estimated to be a few months regardless of the effused sequence for 2 yr this indicates that the mixing was continuous during the effusion the invariability of the other mixing signatures such as the thickness of reaction rims around biotite phenocrysts also supports the continuous mixing model low t end member magma is estimated by mass balance calculation to be a crystal rich mush of dacitic composition these observations lead to a model wherein the highly crystallized remnant magma of the preceding activity has been mixed with the newly injected hot magma of similar bulk composition just prior to the effusion the proposed mechanism implies that this type of magma mixing is an inevitable process in periodically erupting polygenetic volcanoes

calcium isotope ratios in calcitic tests of benthic foraminifers abstract we analysed ca isotope ratios of the infaunal foraminiferal species cassidulina laevigata elphidium spp gyroidinoides spp and uvigerina peregrina as well as the epifaunal cibicidoides wuellerstorfi over a depth temperature gradient the calcium isotope ratios of the benthic foraminifers tests show a distinct anomaly around 4 c this anomaly is observed in both epi and infaunal species but there are also characteristic differences between both the 44 40 ca characteristics of benthic foraminifers may be explained by the interference of temperature and carbonate chemistry of the fluid on ca isotope fractionation we suggest that ca isotope composition of benthic foraminifer tests is dominantly controlled by temperature at temperatures higher than 5 c while in the temperature range below 5 c calcite saturation cc becomes an increasingly important controlling factor due to the non linear shape of the cc 44 40 ca relation of actively transported calcium the potential applicability of ca isotope ratios in benthic foraminifers for reconstruction of either temperatures or 44 40 ca sw is limited by the complex fractionation pattern below 5 c however due to the minor temperature dependence in the temperature range above 5 c benthic foraminifers might provide a possible alternative archive for 44 ca sw avoiding some uncertainties associated with planktic records relocation habitat calcification depth short time climate variability as long as a defined bottom water temperature above 5 c can be secured

calcium isotope fractionation upon experimental apatite formation abstract carbonated hydroxy apatite ca10 b nh4 k na 2b po4 6 y co3 2x 3 2 y oh 2 2x chap was synthesized in batch type experiments by mixing of calcium ca and phosphate bearing aqueous solutions and the transformation of calcite powder in aqueous solution between 11 and 65 c compositional changes of the mother solution and solid phase products were followed by powder xrd scanning electron microscopy sem edx raman spectroscopy and elemental analysis it was found that the transformation at ph values between 7 5 and 7 9 occurs via the dissolution of calcite followed by the precipitation of chap in the mixing approach crystallization of chap took place via precipitation of metastable brushite cah po4 2h2o as precursor phase that was further transformed into apatite calcium isotope fractionation led to an enrichment of the light isotope by about 0 5 to 1 1 in the solid chap compared to the aqueous solution consistently in all experimental approaches essentially independent of temperature in some experiments metastable brushite formed prior to transformation to chap and showed a reduced fractionation compared to the chap the observed ca isotope fractionation into the chap lattice resembles that of natural phosphorites and lies within the range of recently published experiments

tropical atlantic sst history inferred from ca isotope thermometry over the last 140ka exploring the potentials of new methods in palaeothermometry is essential to improve our understanding of past climate change here we present a refinement of the published 44 40ca temperature calibration investigating modern specimens of planktonic foraminifera globigerinoides sacculifer and apply this to sea surface temperature sst reconstructions over the last two glacial interglacial cycles reproduced measurements of modern g sacculifer collected from surface waters describe a linear relationship for the investigated temperature range 19 0 28 5 c 44 40ca 0 22 0 05 sst c 4 88 thus a change of 44 40ca of 0 22 0 05 corresponds to a relative change of 1 c the refined 44 40camodern calibration allows the determination of both relative temperature changes and absolute temperatures in the past this 44 40camodern calibration for g sacculifer has been applied to the tropical east atlantic sediment core geob1112 for which other sst proxy data are available comparison of the different data sets gives no indication for significant secondary overprinting of the 44 40ca signal long term trends in reconstructed sst correlate strongly with temperature records derived from oxygen isotopes and mg ca ratios supporting the methods validity the observed change of sst of approximately 3 c at the holocene last glacial maximum transition reveals additional evidence for the important role of the tropical atlantic in triggering global climate change based on a new independent palaeothermometer

rayleigh taylor instability of a particle packed viscous fluid implications for a solidifying magma 1 we performed laboratory experiments of rayleigh taylor instability of superposed viscous fluids where the upper layer contains denser spherical solid particles a series of experiments are made by varying the viscosity and the particle diameter and we measure the growth rate and the wave length of the instability the instability consists of fine scaled plumes which coalesce as they descend plumes are observed to form intermittently and the particle layer thins with time which finally descend as blobs we find that the growth rate can be explained by using the linear stability analysis for rayleigh taylor instability of viscous fluids by taking the effective viscosity of particle bed to be 20 times that of the fluid and scale the thickness of the upper layer by twice the particle diameter using this scaling we find that a partially solidified layer beneath the surface of a lava lake may become unstable by this mechanism

temperature dependence of δ 7 li δ 44 ca and li ca during growth of calcium carbonate abstract lithium and calcium isotope ratios together with the li ca element ratio have been measured in calcites precipitated inorganically at temperatures ranging from 5 to 30 c and on seasonal growth bands from a coral these measurements indicate the potential uses of these three environmental proxies carbonate li isotopes are lighter than the solution from which they grow probably due to equilibrium fractionation this fractionation is not significantly influenced by temperature and because li is not involved in any known biological process this suggests that carbonates will provide a recorder for the past li isotope composition of natural waters and hence for past weathering conditions as has been observed previously for inorganic aragonite the ca isotopes in inorganic calcite are lighter than the growth solution and are only weakly dependent on temperature this confirms that the temperature dependence observed in some species of foraminifera geochem geophys geosyst 1 2001 reflects additional isotope fractionation due to biological processes during mineralization ca isotopes may therefore provide a powerful tool with which to investigate the processes of biomineralization finally li ca ratios in inorganic and biogenic carbonates increase as temperatures decrease with a sensitivity of 4 per c this temperature dependence of li ca may prove useful to assess past temperatures in cold environments such as the deep ocean

preeruptive magma viscosity an important measure of magma eruptibility 1 using a compilation of melt compositions meltwater contents temperatures and phenocryst contents the preeruptive viscosities under magma reservoir conditions are calculated for 83 erupted magmas the basaltic to rhyolitic magmas have preeruptive viscosities over the range 101 to 108 pa s although bulk sio2 content has often been used as a qualitative measure of preeruptive magma viscosity the bulk sio2 content shows a weak correlation with magma viscosity correlation coefficient r 0 5 because of a wide range of phenocryst contents from 0 to 50 vol andesitic magmas have viscosities ranging from 102 to 107 pa s which are lower or higher than those of phenocryst poor rhyolitic magmas with 105 to 106 pa s focusing on andesitic to rhyolitic magmas the r between bulk sio2 contents and magma viscosities changes to 0 1 in contrast the melt only sio2 content from a basaltic to rhyolitic melt shows a good linear correlation with melt only viscosity r 0 9 although most of the calculated viscosities of erupted magmas fall below 106 pa s as consistent with the previous compilation study this paper describes 20 examples of highly viscous magmas with 106 pa s in most cases composed of mixtures of high silica rhyolitic melt 75 79 wt sio2 and abundant phenocrysts 30 55 vol in these highly viscous magmas 9 examples have erupted following the precursory eruption of less viscous magma suggesting that precursory dike propagation and conduit formation by the less viscous magma with 106 pa s induced the following eruption of less eruptible highly viscous magmas

calcium isotopic fractionation in microbially mediated gypsum precipitates abstract gypsum caso4 2h2o precipitation experiments were carried out at low ph in the presence of the sulfur oxidizing bacterium acidithiobacillus thiooxidans the observed ca isotopic fractionation expressed as 44 40cas f 44 40casolid 44 40cafluid at the end of each experimental time period 50 to 60 days was 1 41 to 1 09 in the biotic experiments 1 09 in the killed control and 1 01 to 0 88 in the abiotic controls as there were no strong differences in the solution chemistry and the rate at which gypsum precipitated in the biotic and abiotic controls we deduce a biological ca isotope effect on the order of 0 3 the isotope effect correlates with a difference in crystal aspect ratios between the biotic experiments 8 05 3 99 and abiotic controls 31 9 8 40 we hypothesize that soluble and or insoluble organic compounds selectively inhibit crystal growth at specific crystal faces and that the growth inhibition affects the fractionation factor associated with gypsum precipitation the experimental results help explain ca isotopic variability in gypsum sampled from a sulfidic cave system in which gypsum crystals exhibiting a diversity of morphologies microcrystalline to cm scale needles have a broad range of 44 40ca values 1 2 0 4 relative to the limestone wall 44 40ca 1 3 in light of the laboratory experiments the variation in ca isotope values in the caves can be interpreted as a consequence of gypsum precipitation in the presence of microbial organic matter and subsequent isotopic re equilibration with the ca source

ca isotope constraints on chemical weathering processes evidence from headwater in the changjiang river china abstract this study aims to clarify the relationship between chemical weathering of rocks and the carbon budget of rivers and better understand the weathering mechanisms of plateau watersheds we chose to study the jinsha river which originates from the tibetan plateau and also is in the upper reaches of the changjiang river analysis of hydrochemistry radiogenic strontium isotope and stable calcium isotopes were conducted of the jinsha river water samples which were collected along its mainstream and main tributaries in the summer the results show that the water chemistry of the mainstream waters is dominated by evaporite weathering which have low 87sr 86sr values 0 7098 0 7108 and wide range of sr contents 2 70 9 35 mol l in contrast tributaries of the jinsha river have higher 87sr 86sr 0 7090 0 7157 and lower sr contents 1 mol l moreover the ca isotopic compositions in the mainstream 0 87 1 11 are heavier than the tributaries 0 68 0 88 and could not be fully explained by the conventional mixing of different sources we suggest that secondary carbonate precipitation fractionates ca isotopes in the jinsha river and fractionation factors are between 0 99935 and 0 99963 at least 66 of ca was removed in the mainstream of the jinsha river through secondary mineral precipitation and the average value is 35 in the tributaries the results highlight that evaporite weathering results in more carbonate precipitation influencing ca transportation and cycling in the riverine system constrained by stable ca isotopic compositions and water chemistry

melt extraction in mush zones the case of crystal rich enclaves at the sabatini volcanic district central italy abstract a peculiar feature of the sabatini volcanic district svd central italy is the occurrence of crystal poor pumices and crystal rich enclaves within the same eruptive host deposit the stratigraphic sequence of pumices and enclaves indicates the tapping of a stratified magma chamber where a crystal poor phonolitic magma lay on top of a more primitive crystal rich magma the crystal rich enclaves are genetically related to the pumices and record the evolution of a solidification front in which a more differentiated melt was produced extracted and eventually erupted we collected and analyzed crystal rich enclaves from one of the largest phonolitic eruptions at the svd and used their petrological and geochemical features to reconstruct magma differentiation and crystal melt separation in the solidification front on this basis three groups of enclaves have been identified porphyritic enclaves holocrystalline enclaves and sanidinites the mineralogical variability faithfully reproduces the spatial and temporal evolution expected of a solidification front from early to intermediate crystallization conditions porphyritic and holocrystalline type to the late stage of solidification sanidinites in which the percolation of a more differentiated melt through the crystal mush triggered the instability of the solidification front results from numerical models indicate that gravitational instability is the most efficient mechanism to explain melt extraction in mush zones of medium sized 10 km 3 short lived 10 4 years magma chambers

controls on calcium isotope fractionation in sedimentary porewaters abstract the calcium isotopic composition of porewaters and authigenic carbonates in the anoxic sediments of a convergent continental margin drilled during ocean drilling program odp provides first insight into the different processes that control ca geochemistry in clastic marine organic rich sedimentary environments in 4 sites drilled during leg 204 at hydrate ridge cascadia margin offshore oregon usa sulfate is consumed during anaerobic oxidation of methane and of organic matter via sulfate reduction within the upper meters of the sedimentary section these reactions promote the precipitation of authigenic carbonates through the generation of bicarbonate which is reflected in a pronounced decrease in calcium concentration although ca isotope fractionation is observed during carbonate precipitation ca concentration in the pore fluids from odp leg 204 is decoupled from ca isotopy which seems to be mainly controlled by the release of light ca isotopes that completely overprint the carbonate formation effect different processes such as the release of organically bound ca ion exchange and ion pair formation may be responsible for the released light ca deeper within the sedimentary section additional processes such as ash alteration influence the ca isotopic composition of the porewater two sites drilled into the deeper core of the accretionary prism reveal the nature of fluids which have reacted with the oceanic basement these deep fluids are characterized by relatively high ca concentrations and low 44 40ca ratios

rheology of crystal bearing silicate melts an experimental study at high viscosities the viscosity of partially crystallized mg3al2si3o12 melts has been measured under uniaxial compression in the interval 1010 1013 poise as a function of the volume fraction of crystals these inclusions are well rounded spherulites of aluminous enstatite having the same composition as the melt and whose growth rate is negligible at the temperature of the measurements the viscosity increases by less than 1 order of magnitude for crystal fractions of 40 vol and remains newtonian up to the maximum stress exerted namely 1 kbar the einstein roscoe equation 0 1 m n provides very good fits to the measurements only if either the m or n parameter is allowed to depend on temperature for modeling of magmatic processes however the widely recommended constant values m 0 6 and n 2 5 should be adequate the rheology changes abruptly when the clustered spherulites begin to oppose shear deformation at a crystal fraction of about 40 vol the viscosity becomes non newtonian with yield strengths of a few tens of bars at temperatures at which the viscosity of the melt is higher than 1010 poise as long as the crystal fraction remains lower than 70 vol the deformation proceeds in an irregular manner with a nonuniform distribution of crystals and melt the deformation becomes again regular at low stresses with lower melt fractions but samples undergo extensive fracturation along the direction of uniaxial stress similar rheology changes have been observed during the isothermal crystallization of li2si2o5 melts which produces small ellipsoidal inclusions these results suggest that the influence of solid suspensions on the rheology of magmas is primarily determined by the crystal fraction even though additional measurements would be useful to determine the possible influence of other factors such as the size distribution or the shape of the inclusions

analog experiments on melting and contamination at the roof and walls of magma chambers abstract a series of analogue laboratory experiments were carried out to model melting and mixing processes occurring at the roof and sides of a magma chamber when hot dense mantle derived magmas are emplaced in the deep crust the experiments investigated the influence of a viscosity contrast between crustal melts and input magma the presence of crystals in the input magma and roof geometry the crust was modelled by aqueous ice or a cold low melting point wax arranged as a flat roof or in an upside down u the input magma was modelled by a hot dense aqueous solution of nano3 or feso4 which was injected into the cavity between the walls the experiments revealed the potentially important role that side wall processes may have in crustal melting and mantle magma contamination in this environment the walls melted back much faster than the roof and the melts from the opposite walls ponded next to each other under the roof and mixed with each other only in the central region when the input solution was able to crystallise it did so preferentially in the active side wall boundary layers the tiny dense crystals which were dragged up in the melt boundary layer and then dropped into the interior fluid enhanced hybridisation of the melt and contamination of the input fluid and through their influence on the boundary layer structure reduced the melting rate

mixing of stratified liquids by the motion of gas bubbles application to magma mixing mafic magma underlying more silicic magma in a reservoir can exsolve volatiles as it crystallizes forming bubbles that segregate upwards to the interface with the overlying silicic magma we describe laboratory experiments designed to investigate how gas bubbles migrate into the more viscous upper layer in one regime bubbles move individually across the interface entraining a small quantity of lower layer fluid and the two layers become progressively stirred into a homogeneous mixture in a second regime bubbles form a thin foam layer at the interface which becomes gravitationally unstable giving rise to two phase plumes which rise and produce a coarse mixture of the liquids for a given viscosity ratio the transition between these regimes occurs when the gas flux is greater than a critical value which we found to decrease with increasing viscosity ratio we estimate the critical gas flux for magmatic conditions and how vesiculation may vary with pressure degree of crystallization and the composition of volatile components mafic inclusions which are often found in silicic to intermediate lavas can form in the plume regime analysis of the instability of the foam predicts wavelengths of between 1 cm and 1 m which is consistent with the observed sizes of inclusions volatiles from the mafic magma may be efficiently transported by this mechanism into the viscous silicic magma as bubble plumes despite low stokes velocities for individual vesicles at small viscosity ratios or low gas fluxes the bubbling regime can produce hybrid magmas

calcium carbonate hexahydrate from organic rich sediments of the antarctic shelf precursors of glendonites large euhedral crystals of calcium carbonate hexahydrate were recovered from a shelf basin of the bransfield strait antarctic peninsula at a water depth of 1950 meters and sub zero bottom water temperatures the chemistry mineralogy and stable isotope composition of this hydrated calcium carbonate phase its environment of formation and its mode of precipitation confirm the properties variously attributed to hypothetical precursors of the glendonites and thereby greatly expand their use in paleoceanographic interpretation

importance of submarine landslides for non steady state conditions in pore water systems lower zaire congo deep sea fan abstract most concentration profiles of sulfate in continental margin sediments show constant or continuously increasing gradients from the benthic boundary layer down to the deep sulfate reduction zone however a very marked change in this gradient has been observed several meters below the surface at many locations which has been attributed to anoxic sulfide oxidation or to non local transport mechanisms of pore waters the subject of this study is to investigate whether this feature could be better explained by non steady state conditions in the pore water system to this end data are presented from two gravity cores recovered from the zaire deep sea fan the sediments at this location can be subdivided into two sections the upper layer about 10 m thick consists of stratified pelagic deposits representing a period of continuous sedimentation over the last 190 kyr it is underlain by a turbidite sequence measuring several meters in thickness which contains large crystals of authigenic calcium carbonate ikaite caco3 6h2o ikaite 13c values are indicative of a methane carbon contribution to the co2 pool radiocarbon ages of these minerals as well as of the adjacent bulk sediments provide strong evidence that the pelagic sediments have overthrust the lower section as a coherent block therefore the emplacement of a relatively undisturbed sediment package is postulated pore water profiles show the depth of the sulfate methane transition zone within the turbiditic sediments by the adaptation of a simple transport reaction model it is shown that the change in the geochemical environmental conditions resulting from this slide emplacement and the development towards a new steady state are fully sufficient to explain all features related to the pore water profiles particularly so42 and dissolved inorganic carbon dic the model shows that the downslope transport took place about 300 yr ago

calcium isotope fractionation during coccolith formation in emiliania huxleyi independence of growth and calcification rate 1 recently calcium isotope fractionation in the coccolithophore emiliania huxleyi was shown to exhibit a significant temperature dependency an important subsequent question in this context is whether the observed fractionation patterns are caused by temperature itself or related growth rate changes in order to separate growth and calcification rate effects from direct temperature effects batch culture experiments with the coccolithophore e huxleyi were conducted under varying light intensities despite large changes in cellular growth and calcification rates calcium isotope fractionation remained constant independence of calcium isotope fractionation on growth and calcification was also obtained in two additional sets of experiments in which growth rates changed in response to varying calcium concentration and seawater salinity these experiments also showed no direct effects of calcium concentration and salinity on calcium isotope fractionation values for calcium isotope fractionation of e huxleyi coccoliths fell within a range of 1 0 to 1 6 1000 ln confirming earlier results this range is similar to that observed in several foraminiferal species and coccolith oozes suggesting a rather homogeneous calcium isotopic composition in marine biogenic calcite our data further show that the calcium isotope fractionation does not change with changing isotopic composition of seawater this is a basic requirement for reconstructing the calcium isotopic composition of the ocean over time

seasonal formation of ikaite caco3 6h2o in saline spring discharge at expedition fiord canadian high arctic assessing conditional constraints for natural crystal growth abstract spring discharge at expedition fiord pollard et al 1999 on axel heiberg island in the canadian high arctic produces a variety of travertine forms in addition to a diverse collection of mineral precipitates this paper focuses on clusters of thermally unstable crystals believed to be the mineral ikaite caco3 6h2o growing seasonally along two spring outflows at colour peak this form of calcium carbonate mineral occurs along small sections of discharge outflow as white euhedral crystals up to 0 5 cm in length difficulty in sampling storage and transport of the samples for analysis has hampered attempts to confirm the presence of ikaite by x ray diffraction however various field observations and the remarkable instability of these crystals at normal ambient temperatures strengthens our argument this paper provides a description of these particular caco3 6h2o crystals and their environmental surroundings and attempts to determine the validity of ikaite precipitation at this site by theoretical geochemical modeling these results are compared with other reported observations of ikaite to both understand their occurrence and help delineate their geochemical characteristics it is believed that the restrictive combination of spring water chemistry and long periods of low temperatures characteristic of arctic climates are necessary for ikaite growth at this site the fact that ikaite is not forming at a second group of saline springs 11 km away allows us to more specifically outline conditions controlling its presence

calcium isotope fractionation in coccoliths of cultured calcidiscus leptoporus helicosphaera carteri syracosphaera pulchra and umbilicosphaera foliosa four species of marine calcifying algae the coccolithophores calcidiscus leptoporus helicosphaera carteri syracosphaera pulchra and umbilicosphaera foliosa were grown in laboratory cultures under temperatures varying between 14 and 23 c and one species c leptoporus under varying co32 ranging from 105 to 219 mol kg calcium isotope compositions of the coccoliths resemble in both absolute fractionation and temperature sensitivity previous calibrations of marine calcifying species e g emiliania huxleyi coccolithophores and orbulina universa planktonic foraminifera as well as inorganically precipitated caco3 but also reveal small species specific differences in contrast to inorganically precipitated calcite but similar to e huxleyi and o universa the carbonate ion concentration of the medium has no statistically significant influence on the ca isotope fractionation of c leptoporus coccoliths however combined data of e huxleyi and c leptoporus indicate that the observed trends might be related to changes of the calcite saturation state of the medium since coccoliths constitute a significant portion of the global oceanic caco3 export production the ca isotope fractionation in these biogenic structures is important for defining the isotopic composition of the ca sink of the ocean one of the key parameters for modelling changes to the marine ca budget over time for the present ocean our results are in general agreement with the previously postulated and applied mean value of the oceanic ca sink sed of about 1 3 but the observed inter and intra species differences point to possible changes in sed through earth history due to changing physico chemical conditions of the ocean and shifts in floral and faunal assemblages

mineral disequilibrium in lavas explained by convective self mixing in open magma chambers characteristic features of many porphyritic andesite and dacite lavas are that they are rich in crystals and display a range of disequilibrium features including reversely zoned crystals resorption surfaces wide ranges of mineral compositions and minerals which are not in equilibrium with the surrounding rock matrix these features are often interpreted as evidence of the mixing of magmas of contrasting composition temperature and origin1 2 here however we propose that such features can also be caused by convection within a magma body with a single composition that is heated from below and cooled from above we describe petrological observations of andesite lava erupted at the soufriere hills volcano montserrat which indicate a heating event and the intermingling of crystals that have very different thermal histories we present experimental data on a representative groundmass composition of this lava which indicate that it is difficult to explain the calcic compositions of plagioclase overgrowth rims and microphenocrysts unless parts of the magma were at temperatures much higher than the inferred average temperature the concept of convective self mixing allows us to explain the occurrence of compositions of minerals that apparently cannot coexist under equilibrium conditions

simultaneous crystallization and melting at both the roof and floor of crustal magma chambers experimental study using nh4cl h2o binary eutectic system abstract thermal and compositional evolution of magmas after emplacement of basalt into continental crust has been investigated by means of fluid dynamic experiments using a cold solid mixture with eutectic composition and a hot liquid with higher salinity in the nh 4 cl h 2 o binary eutectic system the experiments were designed to simulate cases where crystallization of a basalt magma is accompanied by melting at both the roof and floor of a crustal magma chamber the results show that thermal and compositional convection occur simultaneously in the solution the thermal convection is driven by cooling at the roof and the compositional convection is driven by melting and crystallization at the floor the roof was rapidly melted by the convective heat flux which resulted in formation of a separate eutectic melt layer the upper liquid layer with negligible mixing of the underlying liquid the lower liquid layer on the other hand a mushy layer formed at the floor the compositional convection at the floor carried a low heat flux so that the heat transfer at the floor was basically explained by simple heat conduction the thermal boundary layer in the lower liquid layer at the interface with the upper liquid layer became thicker with time and subsequently temperature decreased upward throughout the lower liquid layer compositional gradient with nh 4 cl content decreasing upward formed by compositional convection in the lower liquid layer the formation of these gradients resulted in formation of double diffusive convecting layers in the lower liquid layer the upward heat transfer was suppressed when compared with the case where the liquid region is homogenized by vigorous convection these experimental results imply that when a basalt magma is emplaced in continental crust floor melting does not always enhance the cooling of the magma but it may even reduce the total heat loss from the magma to the crusts due to suppression of convection by formation of a stabilizing compositional gradient

11 11 dune morphology and dynamics this chapter discusses the key types of sand dunes and how they can be classified and assesses the major controls on their development the processes of dune dynamics are reviewed leading to a discussion of the concept of equilibrium in solitary dune form recent advances in modeling are reviewed that show how interactions between dunes may result in equilibrium at the dune field scale rather than at the single dune scale

the contribution of experimental volcanology to the study of the physics of eruptive processes and related scaling issues a review abstract the experimental approach has become a major tool increasingly used by volcanologists in recent decades to investigate the physics of eruptive processes in complement to field and theoretical works researchers have developed various methodologies to study volcanic phenomena at reduced length scale the works involve natural or analogue materials and their types range from first order tests to identify fundamental processes and make qualitative comparison with field observations to more sophisticated experiments in which precise data obtained in a controlled environment can be used to validate outputs of theoretical models scaling is a central issue to ensure dynamic similarity between the small scale experiments and the large scale volcanic phenomena when natural conditions cannot be simulated due to inherent length scale difference and or technical limitations in this respect dimensionless numbers are used to map physical regimes and to define scaling laws which allow experimental results to be extrapolated to natural scale this review presents the variety of experimental studies conducted to investigate subterraneous and aerial volcanic phenomena involving in particular fluid particle mixtures we focus on the major scaling issues and the physical regimes investigated and we also highlight in a historical perspective some of the major advances achieved through experimental studies finally we conclude on some perspectives for future works

diagenetic alteration of magnetic signals by anaerobic oxidation of methane related to a change in sedimentation rate geochemical and rock magnetic investigations of sediments from three sites on the continental margin off argentina and uruguay were carried out to study diagenetic alteration of iron minerals driven by anaerobic oxidation of methane aom the western argentine basin represents a suitable sedimentary environment to study nonsteady state processes because it is characterized by highly dynamic depositional conditions mineralogic and bulk solid phase data document that the sediment mainly consists of terrigenous material with high contents of iron minerals as a typical feature of these deposits distinct minima in magnetic susceptibility are observed pore water data reveal that these minima in susceptibility coincide with the current depth of the sulfate methane transition smt where hs is generated by the process of aom the released hs reacts with the abundant iron oxyhydr oxides resulting in the precipitation of iron sulfides accompanied by a nearly complete loss of magnetic susceptibility modeling of geochemical data suggest that the magnetic record in this area is highly influenced by a drastic change in mean sedimentation rate sr which occurred during the pleistocene holocene transition we assume that the strong decrease in mean sr encountered during this glacial interglacial transition induced a fixation of the smt at a specific depth the stagnation has obviously enhanced diagenetic dissolution of iron oxyhydr oxides within a distinct sediment interval this assumption was further substantiated by numerical modeling in which the mean sr was decreased from 100 cm kyr 1 during glacial times to 5 cm kyr 1 in the holocene and the methane flux from below was fixed to a constant value to obtain the observed geochemical and magnetic patterns the smt must remain at a fixed position for 9000 yrs this calculated value closely correlates to the timing of the pleistocene holocene transition the results of the model show additionally that a constant high mean sr would cause a concave up profile of pore water sulfate under steady state conditions copyright 2005 elsevier ltd

calcium isotopes in deep time potential and limitations abstract calcium is an essential element in the biogeochemical cycles that regulate the long term climate state of earth the removal of co2 from the ocean atmosphere system is controlled by the burial of carbonate sediments caco3 ultimately linking the global calcium and carbon cycles this fundamental link has driven the development of the stable calcium isotope proxy with application to both ancient skeletal and non skeletal bulk carbonate sediments calcium isotope ratios 44 40ca have been used to track long term changes in seawater chemistry e g aragonite vs calcite seas and to elucidate short term climatic perturbations associated with mass extinction events however developments in the calcium isotope proxy have shown that 44 40ca values in carbonate minerals also are sensitive to changes in precipitation rates mineralogy and diagenesis thereby complicating the application of the proxy to the reconstruction of global cycles first inorganic carbonate precipitation experiments have demonstrated that carbonate 44 40ca values are sensitive to precipitation rates with higher rates generally leading to larger fractionation second 44 40ca values are sensitive to carbonate mineralogy with inorganic aragonite and calcite being on average 1 5 and 0 9 depleted relative to contemporaneous seawater respectively the effects of both changes in carbonate mineralogy and precipitation rates affect primary and secondary minerals but are particularly pronounced during carbonate diagenesis where relatively slow rates of recrystallization and neomorphism can lead to significant changes in bulk sediment 44 40ca values third changes in faunal composition expressed in skeletal fossil archives can lead to large changes in carbonate 44 40ca values that are decoupled from changes in global cycles nevertheless when these factors are appropriately considered the application of calcium isotopes in ancient carbonate sediments becomes a powerful tool for understanding biogeochemical processes that operate over many scales from diagenetic changes within the sediment pore space to regional changes across ancient carbonate platforms and to global changes in seawater chemistry through time importantly the processes that contribute to variability in carbonate 44 40ca values are likely to impact other carbonate bound proxies highlighting the potential for calcium isotopes as a tool to better understand the variability of other isotope systems

cellular calcium pathways and isotope fractionation in emiliania huxleyi the marine calcifying algae emiliania huxleyi coccolithophores was grown in laboratory cultures under varying conditions with respect to the environmental parameters of temperature and carbonate ion concentration co32 concentration the ca isotope composition of e huxleyi s coccoliths reveals new insights into fractionation processes during biomineralization the temperature dependent ca isotope fractionation resembles previous calibrations of inorganic and biogenic calcite and aragonite unlike inorganically precipitated calcite the co32 concentration of the medium has no significant effect on the ca isotope composition of the coccoliths these results indicate a decoupling of the chemical properties of the bulk medium and the calcifying vesicle cellular ca pathways of e huxleyi indicate that fractionation cannot occur at the crystal surface as occurs during inorganic precipitation the dominant processes leading to the observed ca isotope fractionation pattern in e huxleyi are most likely the dehydration of the ca aquocomplex at the plasma membrane and the attachment of dissolved ca to proteins of ca channels the independence of ca isotope fractionation from co32 and the small temperature dependence of e huxleyi are also important for defining the isotopic signature of the oceanic ca sink since coccolithophores contribute to about half the global caco3 production a relatively uniform isotopic composition of the oceanic ca sink is further supported

experiments on upward migration of a liquid rich layer in a granular medium implications for a crystalline magma chamber 1 we perform a series of experiments to investigate the situation in which a melt rich layer formed by a magma intrusion ascends through a crystalline magma chamber the initial condition is such that a heavier granular layer overlies a liquid layer the particles consisting the upper granular layer are in a jammed state and only the particles near the interface can move to form a dilated boundary layer the dilated layer detaches from the upper granular layer and forms downwelling plumes which drive a cellular convection within the liquid rich layer the convection erodes the upper granular layer and the liquid rich layer migrates upwards with time this upward migration of the liquid rich layer differs from the previously known mechanisms of liquid transport permeable flow in which the liquid migrates at the darcy velocity the stokes settling in which the individual particle settles and diapirs formed by the rayleigh taylor instability we find that the velocity of the upward migration of the liquid rich layer can be scaled by the volumetric flux of the liquid ascending through the narrow channel between the particles the upward migration of the liquid rich layer is faster than the darcy velocity in a mushy magma chamber whose crystals are in a jammed state neither the stokes settling nor the rayleigh taylor instability can occur we propose that the upward migration of the melt rich layer observed in our experiments can become an efficient mechanism of melt transport in a crystalline magma chamber

the rapid resetting of the ca isotopic signatures of calcite at ambient temperature during its congruent dissolution precipitation and at equilibrium abstract this study provides direct experimental evidence of the resetting of the calcium ca isotope signatures of calcite in the presence of an aqueous fluid during its congruent dissolution precipitation and at equilibrium at ambient temperatures over week long timescales batch reactor experiments were performed at 25 c in aqueous nacl solutions air or co2 gas mixtures were bubbled through this fluid to fix ph during congruent calcite dissolution the fluid became enriched in isotopically heavy ca and the ca isotope composition continued to become heavier after the fluid attained bulk chemical equilibrium with the mineral the 44 42ca composition of the fluid was up to 0 8 higher than the dissolving calcite at the end of the dissolution experiments calcite precipitation was provoked by increasing the reactor fluid ph after chemical equilibrium had been attained via dissolution rayleigh isotope fractionation effects were observed immediately after the ph was increased and rapid calcite precipitation occurred however isotopic exchange continued after the system chemically equilibrated eradicating this rayleigh signal taken together these observations 1 confirm dynamic mineral fluid equilibrium i e dissolution and precipitation occur at equal non zero rates at equilibrium and 2 indicate that isotopic compositions of calcite can readily equilibrate even when this mineral is in bulk chemical equilibrium with its coexisting fluid this latter observation suggests the preservation of paleo environmental isotopic signatures in calcite may require a combination of the isolation of the fluid mineral system from external chemical input and or the existence of a yet to be defined calcite dissolution precipitation inhibition mechanism

sulfate dependent anaerobic oxidation of methane at a highly dynamic bubbling site in the eastern sea of marmara cinarcik basin abstract during the marsitecruise expedition in november 2014 on board the rv pourquoi pas multidisciplinary sampling was carried out with the rov victor 6000 in order to investigate biogeochemical processes taking place at cold seep environments in the sea of marmara pore water bottom water sediment and authigenic carbonate samples were collected from two short push cores mrs dv5 pc04 8 cm mrs dv5 pc01 12 5 cm at an active methane bubbling site in the southeastern part of the cinarcik basin sulfate sulfur and oxygen isotope data as well as sulfide isotope data indicate that sulfate dependent anaerobic oxidation of methane is the dominant process in the sediments this is confirmed by archaeal lipids diagnostic for anaerobic methane oxidizers detected with strong 13c depletions the available data even allows to distinguish the dominant aom assemblages specific lipid patterns are consistent with a dominance of anme 2 archaea within the microbial community abundant authigenic carbonates mostly aragonite found at all depths show a narrow range in 13c values between 27 69 and 33 40 the carbon isotopic composition of the dissolved inorganic carbon as well as strontium and calcium isotopes confirm that the current reaction zone sulfate methane transition zone starts at the bottom of the core all shallower carbonates are witnesses of paleo seepage activity u th dating of four pure aragonite samples show the short time span that is preserved in core mrs dv5 pc01 235 60 yr b p two major earthquakes of 1766 ce and 1754 ce in the cinarcik basin might potentially have triggered the increased seepage of methane at this location

ca isotopes in carbonate sediment and pore fluid from odp site 807a the ca2 aq calcite equilibrium fractionation factor and calcite recrystallization rates in pleistocene sediments abstract the calcium isotopic compositions 44ca of 30 high purity nannofossil ooze and chalk and 7 pore fluid samples from odp site 807a ontong java plateau are used in conjunction with numerical models to determine the equilibrium calcium isotope fractionation factor s f between calcite and dissolved ca2 and the rates of post depositional recrystallization in deep sea carbonate ooze the value of s f at equilibrium in the marine sedimentary section is 1 0000 0 0001 which is significantly different from the value 0 9987 0 0002 found in laboratory experiments of calcite precipitation and in the formation of biogenic calcite in the surface ocean we hypothesize that this fractionation factor is relevant to calcite precipitation in any system at equilibrium and that this equilibrium fractionation factor has implications for the mechanisms responsible for ca isotope fractionation during calcite precipitation we describe a steady state model that offers a unified framework for explaining ca isotope fractionation across the observed precipitation rate range of 14 orders of magnitude the model attributes ca isotope fractionation to the relative balance between the attachment and detachment fluxes at the calcite crystal surface this model represents our hypothesis for the mechanism responsible for isotope fractionation during calcite precipitation the ca isotope data provide evidence that the bulk rate of calcite recrystallization in freshly deposited carbonate ooze is 30 40 myr and decreases with age to about 2 myr in 2 3 million year old sediment the recrystallization rates determined from ca isotopes for pleistocene sediments are higher than those previously inferred from pore fluid sr concentration and are consistent with rates derived for late pleistocene siliciclastic sediments using uranium isotopes combining our results for the equilibrium fractionation factor and recrystallization rates we evaluate the effect of diagenesis on the ca isotopic composition of marine carbonates at site 807a since calcite precipitation rates in the sedimentary column are many orders of magnitude slower than laboratory experiments and the pore fluids are only slightly oversaturated with respect to calcite the isotopic composition of diagenetic calcite is likely to reflect equilibrium precipitation accordingly diagenesis produces a maximum shift in 44ca of 0 15 for site 807a sediments but will have a larger impact where sedimentation rates are low seawater circulates through the sediment pile or there are prolonged depositional hiatuses

the dynamics of star dunes an example from the gran desierto mexico observations of patterns of erosion and deposition and surface wind velocity and direction on a 40 m high star dune in the gran desierto sand sea indicate that interactions between dune form and airflow as winds change direction seasonally play a major role in the formation of this dune type such interactions lead to deposition of sand in the central parts of the dune giving rise to its pyramidal shape as well as to some extension of the linear arms the major arms of the dune studied are oriented ne sw or transverse to summer sse and winter nnw winds an avalanche face up to 10 m high develops during the course of each season flow separation at the main crestline gives rise to a wide zone of lee side secondary flow which moves sand along the base of the avalanche face towards the central part of the dune where it is deposited as wind ripples migrate into zones of locally reduced flow velocity reattachment of the separated flow occurs on the lower part of the n or s arms parallel to the flow spring westerly winds move sand obliquely up the s and n arms of the dune and outwards on the e arm large scale flow separation and diversion are replaced by the development of strong helical eddies in the immediate lee of the main crestline which move sand along avalanche faces and into zones of lower flow velocity at the end of dune arms formation of star dunes in the gran desierto follows a sequence in which crescentic dunes migrating into areas of opposed winds first develop a reversing crestal ridge convergent leeside secondary flows are developed which result in the formation of linear elements parallel to each major wind direction and the concentration of sand in the central part of the dune examples of star dunes at different stages of their development can be documented

the permeability controlled accumulation of primary magma the initial accumulation of primary magma occurs just after the mantle has become permeable the accumulation is caused by the compaction of the residuum which either may be controlled by the rate of creep or by the rate of flow of the interstitial melt experimental results suggest that the rate of compaction is controlled by the permeability and a model for the accumulation process is worked out on this basis the compaction causes the formation of a lower compaction boundary and an upper layer of melt the ascending mantle of plumes and convection currents will form layers of melt situated 20 100 m apart the type of partial melting for this accumulation is critical melting

non newtonian behavior of plagioclase bearing basaltic magma subliquidus viscosity measurement of the 1707 basalt of fuji volcano japan abstract laboratory measurements of viscosity were done for basalt erupted in 1707 ad from fuji volcano japan using a concentric cylinder rotational viscometer at temperatures of 1297 1157 c 1 atm pressure and fo 2 near the ni nio buffer on cooling elongated plagioclase crystals with a mean length width ratio of ca 8 5 appeared at 1237 c followed by olivine at 1157 c at progressively lower temperatures the total crystal volume fraction increased monotonously to ca 0 25 viscosity increased from 38 9 to 765 pa s at a shear strain rate of 1 s 1 this basalt magma behaves as a newtonian fluid at temperatures greater than 1217 c but shear thinning behavior occurs at temperatures less than 1197 c because of the suspended plagioclase crystals this behavior is well approximated as a power law fluid at the onset of shear thinning the crystal volume fraction was between 0 06 and 0 13 which is attributed to the pronounced lath shape of plagioclase crystals the relative viscosity increases monotonously with increase of crystal volume fraction at a constant shear strain rate and with decrease of shear strain rate at a constant crystal volume fraction a modified form of the krieger dougherty equation is introduced herein it enables us to describe the dependencies of relative viscosity on both the crystal volume fraction and shear strain rate and consequently the onset of shear thinning behavior

potential of ikaite to record the evolution of oceanic δ18o a challenge in the quest to understand the sensitivity of the climate system is the separation of the competing effects of ice volume or sea level salinity and temperature on foraminiferal 18o we present precipitation experiments on the mineral ikaite a hydrated form of calcium carbonate found in organic carbon rich deep marine sediments that show that the hydration waters within the ikaite crystal capture the 18o of seawater 18 osw with a fractionation factor of 1 0029 0 0002 the 18osw measures the volume of continental ice with an overprint of local salinity isolation of 18osw by analysis of the hydration waters of sedimentary ikaite preserved at temperatures 4 c could be exploited to create a record of sea level during the pleistocene preliminary data of 18osw from hydration waters of ikaite at the last glacial maximum agree with estimates from modeling of pore waters that antarctic bottom water was 1 4 0 2 heavier 2006 geological society of america

viscosity of high crystal content melts dependence on solid fraction 1 the rheological properties of suspensions containing high solid fractions are investigated attention is focused on viscosity of silicate and magmatic melt systems a general empirical equation which describes the relative viscosity of suspensions as a function of suspended solid fraction is proposed in the limit of very dilute solid concentrations it reduces to the einstein equation the proposed relationship is satisfactorily applied to reproduce available experimental data relative to silicate melts moreover the extrapolation of the model to very high concentrations is compared with experimental observations on partially melted granite

the δ44ca temperature calibration on fossil and cultured globigerinoides sacculifer new tool for reconstruction of past sea surface temperatures we report direct 44ca temperature calibration on cultured and fossil calcite foraminifera showing that ca isotopes are potentially a new proxy for past sea surface temperatures sst samples have been analyzed using a 43ca 48ca double spike and thermal ionization mass spectrometry tims in order to avoid species dependent isotope fractionation we focused our investigations on a single foraminifera species globigerinoides sacculifer which is known to inhabit shallow euphotic waters in tropical and subtropical oceans ca isotope measurements were performed on cultured g sacculifer that grew in seawater kept at temperatures of 19 5 26 5 and 29 5 c a 44ca change of 0 24 0 02 per 1 c is defined by the weighted linear regression through reproduced 44ca data of the three temperatures 95 confidence level application of this new method to fossil g sacculifer of an equatorial east atlantic sediment core geob1112 5 46 7 s 10 45 0 w 3125 m indicates that the 44ca difference between marine isotope stage 1 mis 1 and mis 2 is 0 71 0 24 according to the current 44ca temperature calibration this value corresponds to a temperature difference between mis 1 and mis 2 of 3 0 1 0 c

modelling of melt segregation processes by high temperature centrifuging of partially molten granites ii rayleigh taylor instability and sedimentation summary the present experimental study deals with the laboratory modelling of two different mechanisms of gravitational percolation in partially melted rocks 1 diapiric percolation of heavy material and 2 the sedimentation of heavy particles these two mechanisms of mass transport in partially melted rocks result in different scales of the segregation process in the melt crystal matrix a centrifuge furnace was used to simulate the percolation of the heavy particle layer through the partially molten granite at temperatures of up to 1000 c samples of beauvoir granite massif central france grain size 0 16 0 5 mm with an initial degree of partial melting 45 per cent were used as a matrix a layer of pt powder suspended in a melt of the same composition as the partially melted matrix was placed on the top of the granite sample after centrifuging for various times up to 2 x lo4 s x ray images of samples were obtained and the evolution of the percolation process of heavy suspension in the partially molten granite was monitored from the pt particle distribution the diapiric or finger regime of percolation starts when the growth rate of a raleigh taylor instability of the heavy layer is faster than the stokes sedimentation velocity of individual particles in the upper layer this relationship is a complex function of the size and initial concentration of heavy particles as well as the ratio of particle to crystal size the permeability of the matrix and the heterogeneity scale in the partially melted matrix at small concentrations several per cent and at large concentrations where close packing of heavy particles results in an anomalous viscosity increase in the upper heavy layer stokes sedimentation is dominant in the vertical percolation of the heavy material the sinking velocity of the diapir decreases when the size of heavy particles in it becomes comparable with the size of crystals in the partially melted granite in this situation the vertical sinking of the diapir is not stable and the horizontal instability of the vertical mass transport starts to become important mass transport via diapiric percolation results in more efficient crystal melt segregation of partially melted rocks the percolation of individual particles provides only local melt crystal flow on a scale comparable with the heavy particle size the diapiric percolation provides a much larger scale of partial melt segregation with a length scale comparable with the diapir size

ca isotope fractionation in a high alkalinity lake system mono lake california abstract precipitation of calcium carbonate minerals from aqueous solutions causes surface controlled kinetic stable ca isotope fractionation the magnitude of fractionation depends on the relative rates of ion attachment to and detachment from the mineral surface which in turn is predicted to depend on both the saturation state and the solution stoichiometry or the ca 2 co 3 2 activity ratio experimental studies have not directly investigated the effects of varying solution stoichiometry on calcium isotope partitioning during calcite or aragonite growth but natural alkaline lake systems such as mono lake california provide a test bed for the hypothesized stoichiometry dependence mono lake has a ca 2 co 3 2 activity ratio of about 0 0001 seven orders of magnitude lower than ocean water and typical terrestrial freshwater we present chemical and isotopic measurements of streams springs lake water and precipitated carbonates from the mono basin that yield evidence of stoichiometry dependent ca isotope fractionation during calcite aragonite and mg calcite precipitation from the alkaline lake water to estimate the ca isotope fractionation factors it is necessary to characterize the lake ca balance and constrain the variability of lake water chemistry both spatially and temporally streams and springs supply ca to the lake and a substantial fraction of this supply is precipitated along the lake shore to form tufa towers lake water is significantly supersaturated with respect to carbonate minerals so caco3 also precipitates directly from the water column to form carbonate rich bottom sediments growth rate inhibition by orthophosphate likely preserves the high degree of supersaturation in the lake strontium isotope ratios are used to estimate the proportions of fresh and alkaline lake water from which each solid carbonate sample precipitated carbonate minerals that precipitate directly from lake water low ca 2 co 3 2 experience relatively large ca isotope fractionation during growth tufa and shoreline carbonates that precipitate from lake water with a significant fraction of spring water higher ca 2 co 3 2 are considerably less fractionated as predicted from theory the behavior of the mono lake ca isotope system is similar in some ways to that of the global oceans in that the average 44 40ca of lake water is positive estimated average of 1 and both riverine inputs and precipitated carbonates are isotopically light 44 40ca between 0 5 and 0 we present a calcium isotope budget of the lake to constrain the long term average lake water ca isotope composition archived water samples indicate that the lake 44 40ca varied by over 2 between 1995 and 2010 the most extreme excursions are toward higher 44 40ca and are probably caused by carbonate precipitation events induced by breakdown of chemostratification this variability indicates that the lake is out of steady state with respect to calcium isotopes and that unlike the ocean calcium isotopes in mono basin carbonate sediments likely do not record the balance between weathering and carbonate mineralization fluxes to and from the lake

isotope fractionation during ca exchange on clay minerals in a marine environment abstract in order to interpret marine porewater profiles it is mandatory to understand the behavior of calcium ca and its isotopes during cation exchange in marine sediments it has been proposed that the exchange of adsorbed ca 2 for ammonium which is a product of organic matter decomposition results in the releases of light ca from clay minerals into the porewater teichert et al 2009 in order to investigate the effect of ammonium on ca isotope fractionation experiments with clay mineral separates illites montmorillonite kaolinite and natural marine sediments from the north atlantic integrated ocean drilling project site u1306a in artificial seawater were carried out at different temperatures 4 14 21 c and ammonium concentrations 100 140 180 mm the results of the adsorption experiments carried out in artificial seawater show that during adsorption of ca 2 the light ca isotopes are favored over the heavier ca isotopes this effect is most prominent for the illite samples 1000ln 0 82 to 1 15 and kaolinite sample 1000ln 1 23 to 2 76 whereas montmorillonite and the natural marine sediments show smaller degrees of fractionation from the fluid in the range of 0 46 to 0 06 determination of the desorbed ca 2 is based on the adsorbed ca 2 left on the exchanger and reveals that the desorbed ca 2 has a significantly different isotopic signature from the surrounding fluid in general the degree of ca isotope fractionation is dependent on the ammonium concentration and does not show significant influence of temperature modeling the ca 2 desorption induced by ammonium adsorption demonstrates that according to the prevailing mineralogy and porewater sediment ratio desorbed ca 2 has the potential to shift the porewater isotopy by up to 2 5 and needs to be considered when interpreting ca isotope porewater profiles

cretaceous calcareous dinoflagellate cysts as recorder of δ44 40caseawater and paleo temperature using sr ca thermometry abstract we evaluate the potential of calcareous dinoflagellates as archives for sr ca based paleo temperature reconstructions and 44 40caseawater fluctuations on sediments from ocean drilling program expedition 113 hole 690c weddell sea southern ocean between 73 and 68 ma sr ca ratios of two cretaceous dinoflagellate species pirumella krasheninnikovii and orthopithonella globosa show a pronounced decrease consistent with a significant drop in sea surface temperature as reflected by the 18o of planktic foraminifers the apparent temperature sensitivity of the dinoflagellate cysts sr ca is 0 06 and 0 08 mmol mol c 1 using 18o derived paleo sea surface temperatures which is significant and large enough to resolve paleoenvironmental temperature changes at current analytical precision as the chemical composition of the cyst calcite appears to have a good preservation the sr ca of calcareous dinoflagellates has a potential to serve as paleo temperature proxy although the chemical composition of the cretaceous seawater and potential impacts on the cyst geochemistry is pending further inspection the ca isotope composition of the two dinoflagellate species shows identical trends of increasing 44 40ca between 73 and 67 ma the planktic foraminifer archaeoglobigerina australis and the benthic foraminifer nuttallides truempyi reveal the same increase of about 0 4 but are offset relative to the dinoflagellates by about 0 5 presumably due to species specific ca isotope fractionation bulk carbonate sediment shows significant scatter likely caused by changes in faunal composition and does not reproduce the trend revealed by the dinoflagellate and foraminifer records these observations demonstrate the importance of taxon specific records and careful determination of fractionation factors of selected archives and highlight complications arising from utilizing less suitable archives such as bulk sediments for 44 40caseawater reconstructions our records indicate strong changes in the marine ca cycle associated with the global temperature decrease towards the end of the cretaceous

biological control of calcium isotopic abundances in the global calcium cycle measurements of 44ca 40ca expressed as 44ca were made on igneous rocks and on shell and bone material from modern organisms to investigate the magnitude and origins of calcium isotopic fractionation in nature the results document a span of 4 in 44ca measured with the double spike technique to a precision of 0 15 volcanic rocks including basalt and rhyolite show little variability and cluster near 44ca 0 0 2 systematic analysis of biological samples indicates that biological processing of calcium discriminates against heavy isotopes and that biological fractionation is the primary generator of calcium isotopic fractionation in nature preliminary data suggest that calcium becomes isotopically lighter as it moves through food chains calcium carbonate shells of marine microorganisms and deep sea carbonate ooze have 44ca about 1 0 lower than seawater this fractionation causes seawater to be enriched in heavy calcium 44ca 0 9 relative to igneous rocks marine organisms consequently are isotopically heavier than their terrestrial counterparts at similar trophic level the calcium isotopic composition of living and fossil organisms may record information on diet and environment

repeated occurrences of methanogenic zones diagenetic dolomite formation and linked silicate alteration in southern bering sea sediments bowers ridge iodp exp 323 site u1341 abstract diagenetic precipitates such as dolomite and the chemistry of residual deeply buried porewater often represent the only traces of past biogeochemical activity in marine sediments a 600 m thick sedimentary section recently drilled at integrated ocean drilling program iodp site u1341 on bowers ridge southern bering sea provides insight into such a 4 3 ma old paleo diagenetic archive hard lithified calcite dolomite layers and laminae of disseminated carbonate were recovered in diatom rich sediments over a depth range of 400 m carbon isotope values of the diagenetic carbonates between 16 6 and 14 4 vpdb and strontium isotope ratios of dolomites close to past seawater values suggest carbonate precipitation induced by the production of dissolved inorganic carbon dic during elevated rates of organic carbon mineralization primarily via sulfate reduction at shallow sediment depth below the paleo seafloor diagenetic carbonates at 280 440 m below seafloor were likely also produced by the intermittent onset of sulfate reduction coupled to the anaerobic oxidation of methane aom at sulfate methane transition zones smtz these microbially mediated processes do not occur in the sediment at this site at present but were likely connected to the presence of a methanogenic zone at 2 58 2 51 ma a minimum in sulfate concentrations in modern porewaters and low sedimentary ba al ratios resulting from former sulfate depletion are reminiscent of the presence of this large methanogenic zone the minimum in sulfate concentrations is reflected in a minimum in magnesium concentrations less radiogenic strontium and isotopically light calcium in the porewater it is proposed that magnesium was removed from the porewater during carbonate precipitation and volcanic ash alteration which occurred in the former methanogenic zone and also released strontium with a less radiogenic isotope ratio and isotopically light calcium into the porewater the isotopic composition of porewater calcium was also influenced by ammonium calcium exchange on clay minerals and carbonate recrystallization our study elucidates the response of porewater element concentrations and isotopic profiles interlinked with the formation of diagenetic carbonates to changes in the deposition of organic carbon in sediments of deeper water sites 2000 m water depth over prolonged timescales it shows that variations in biogeochemical processes in response to changes in oceanographic conditions and a dynamic subseafloor biogeochemical zonation have to also be taken into account at these deep water sites for a global assessment of organic carbon burial fluxes and remineralization

ca and mg isotope fractionation during the stoichiometric dissolution of dolomite at temperatures from 51 to 126 c and 5 bars co2 pressure natural polycrystalline hydrothermal sainte colombe dolomite was dissolved in stirred titanium closed system reactors in aqueous 0 1 mol kg nacl solutions at 51 75 121 and 126 c and a pressure of 5 bars co2 in total 52 27 16 and 12 respectively of the dolomite placed in the reactors dissolved into the fluid phase during these experiments each experiment lasted from 12 to 47 days and the fluid phase in each evolved towards but did not exceed ordered dolomite equilibrium at a ph of 5 9 0 3 all aqueous reactive fluids were undersaturated with respect to all potential secondary phases including calcite and magnesite the reactive fluid compositions at the end of the experiments had a molar ca mg ratio equal to that of the dissolving dolomite and the dolomite recovered after the experiments contained only pure dolomite as verified by scanning electron microscopy the ca and mg isotopic ratios of the reactive fluids remained within uncertainty equal to that of the dissolving dolomite in the experiments performed at 51 and 75 c in contrast the ca isotopic composition of the reactive fluid in the experiment performed at 121 and 126 c was significantly greater such that 44 42casolid fluid 0 6 0 1 whereas that of mg was within uncertainty equal to that of the dissolving mineral the equilibrium fractionation factors for both divalent cations favor the incorporation of isotopically light metals into the dolomite structure our results at 121 and 126 c therefore are consistent with the one way transfer of mg from dolomite to the fluid but the two way transfer of ca from and to dolomite as equilibrium is approached during its stoichiometric dissolution the lack of mg returning to the dolomite structure at these conditions is attributed to the slow dehydration kinetics of aqueous mg as more than 12 of the dolomite dissolved during the 121 and 126 c closed system experiments our observations indicate a significant change in the ca isotopic signature of the dolomite during its stoichiometric dissolution moreover as there is no visual evidence for dolomite recrystallization during this experiment it seems likely that the resetting of ca isotopic signatures of carbonate minerals can be readily overlooked in the interpretation of natural systems

calcium isotopic fractionation during travertine deposition under different hydrodynamic conditions examples from baishuitai yunnan sw china abstract revealing the potential of ca isotopes in the research of travertine formation processes is the principal goal of this study to achieve this the hydrochemistry travertine precipitation rates and variations in ca isotopic compositions 44 40 ca of present day endogenic thermogenic travertine in two different hydrodynamic systems canal and pool are studied at baishuitai yunnan sw china in the canal where the travertine precipitation is faster 44 40 ca values of both solution and travertine show a downstream increase with ca isotopic fractionation 44 40 ca caco3 aq equal to 1 6 compared to the canal ca isotopic fractionation between travertine and aqueous ca 2 is smaller 44 40 ca caco3 aq 1 2 in the pools where travertine precipitation rates are lower the spatial variations in 44 40 ca values of solution and travertine are related to the amount of ca removed from the solution when 44 40 ca values of spring water remain stable in addition the results confirm the control of precipitation rates on ca isotopic fractionation between calcite and parent aqueous ca 2 using natural samples the observed negative correlation between 44 40 ca caco3 aq and travertine precipitation rates can be explained by the steady state kinetic surface reaction model proposed by depaolo 2011 with equilibrium and kinetic fractionation factors of eq 1 0000 0 0001 and f 0 9983 0 0002 respectively an important consequence of this study is that ca isotopes in travertine systems are good tools to have access to variations of 44 40 ca aq which are directly linked to the amount of precipitated ca this could then be useful for reconstructing past hydrodynamic conditions when applied to travertine core data

the solubility and stabilization of ikaite caco3 6h2o from 0 to 25 c environmental and paleoclimatic implications for thinolite tufa we determined the solubility of ikaite from 0 to 25 c to model its saturation state in natural waters and test the hypothesis that it is the precursor of the calcite pseudomorphs in thinolite tufa of quaternary lake lahontan reversible solubility at buffered p co 2 yields the following expression for the dissolution constant of ikaite log k ikaite 0 15981 2011 1 t where t circ k and 0 circ c leq t leq 25 circ c derived standard state properties are delta g ikaite circ 2541 9 kjmol 1 pm 0 66 delta h ikaite circ 2973 4 kjmol 1 pm 1 02 s ikaite circ 306 6 jt 1 mol 1 pm 1 2 modeling shows that ikaite is undersaturated at all temperatures in seawater and in alkaline lakes but that it rapidly approaches saturation near 0 c its precipitation in near freezing marine sediments requires large additions of hco 3 to pore fluids from the diagenetic decomposition of organic matter its crystallization in tufas of alkaline lakes howeve

submarine columns of ikaite tufa in the small ikka fjord in southwestern greenland we have studied remarkable submarine tufa columns forming over alkaline springs by abiotic precipitationof the metastable cold water mineral ikaite caco3 6h2o 1 3 the columns which support a rich marine life are up to 20 m high with annual growth of more than 50 cm we wish to nominate the locality which seems to be unique for classification as a geological world heritage site

calcium isotope fractionation in calcite and aragonite abstract calcium isotope fractionation was measured on skeletal aragonite and calcite from different marine biota and on inorganic calcite precipitation temperatures ranged from 0 to 28 c calcium isotope fractionation shows a temperature dependence in accordance with previous observations 1000 ln cc 1 4 0 021 t c for calcite and 1000 ln ar 1 9 0 017 t c for aragonite within uncertainty the temperature slopes are identical for the two polymorphs however at all temperatures calcium isotopes are more fractionated in aragonite than in calcite the offset in 44 40 ca is about 0 6 the underlying mechanism for this offset may be related to the different coordination numbers and bond strengths of the calcium ions in calcite and aragonite crystals or to different ca reaction behavior at the solid liquid interface recently the observed temperature dependence of the ca isotope fractionation was explained quantitatively by the temperature control on precipitation rates of calcium carbonates in an experimental setting lemarchand et al 2004 we show that this mechanism can in principle also be applied to caco 3 precipitation in natural environments in normal marine settings following this model ca isotope fractionation in marine ca carbonates is primarily controlled by precipitation rates on the other hand the larger ca isotope fractionation of aragonite compared to calcite can not be explained by different precipitation rates the rate control model of ca isotope fractionation predicts a strong dependence of the ca isotopic composition of carbonates on ambient co 3 2 concentration while this model is in general accordance with our observations in marine carbonates cultured specimens of the planktic foraminifer orbulina universa show no dependence of ca isotope fractionation on the ambient co 3 2 concentration the latter observation implies that the carbonate chemistry in the calcifying vesicles of the foraminifer is independent from the ambient carbonate ion concentration of the surrounding water

origin of rodingite forming fluids constrained by calcium and strontium isotope ratios in the leka ophiolite complex abstract alteration of oceanic lithosphere plays an important role in the global element cycling due to its dominant abundance on the earth s surface the formation of rodingites a ca rich lithology that occurs intimately associated with ca depleted serpentinite complexes is a widespread process during strong alteration of ocean floor lithologies and may represent a key process that influences the global ca cycle stable ca and radiogenic sr isotope compositions of rodingites and associated lithologies from the leka ophiolite complex norway preserve mantle signatures and thus provide evidence that the ca and sr sources for rodingitisation are dominantly mantle derived with no detectable seawater input the difference of 0 7 in 44 40ca of different phases found in the rocks is overall consistent with inter mineral fractionation at high temperatures related to the cao bonding environment but there are also indications for isotopic disequilibria between non cogenetic mineral phases while the water required for rodingite formation may originate from seawater the dissolved ca and sr involved in the mineral reactions during rodingitisation plg ca gros clz al can be balanced at a local scale being derived from the serpentinisation of mantle peridotites cpx1 h2o al srp chlorite ca cpx2 consequently rodingites do not act as a sink for oceanic ca instead they are a sink for ca released during serpentinisation of the oceanic lithospheric mantle

reconstruction of caribbean sea surface temperature and salinity fluctuations in response to the pliocene closure of the central american gateway and radiative forcing using δ44 40ca δ18o and mg ca ratios the 18o values of planktonic foraminifera increased in the caribbean by about 0 5 relative to the equatorial east pacific values between 4 6 and 4 2 ma as a consequence of the closure of the central american gateway cag this increase in 18o can be interpreted either as an increase in caribbean sea surface mixed layer salinity sss or as a decrease in sea surface temperatures sst this problem represents an ideal situation to apply the recently developed paleotemperature proxy 44 40ca together with mg ca and 18o on the planktic foraminifer globigerinoides sacculifer from odp site 999 although differences in absolute temperature calibration of 44 40ca and mg ca exist the general pattern is similar indicating a sst decrease of about 2 3 c between 4 4 and 4 3 ma followed by an increase in the same order of magnitude between 4 3 and 4 0 ma correcting the 18o record for this temperature change and assuming that changes in global ice volume are negligible the salinity induced planktonic 18o signal decreased by about 0 4 between 4 4 and 4 3 ma and increased by about 0 9 between 4 3 and 4 0 ma in the caribbean the observed temperature and salinity trends are interpreted to reflect the restricted exchange of surface water between the caribbean and the pacific in response to the shoaling of the panamanian seaway possibly accompanied by a southward shift of the intertropical convergence zone itcz between 4 4 and 4 3 ma differences in mg ca and 44 40ca derived temperatures can be reconciled by corrections for secular variations of the marine mg casw and 44 40ca a salinity effect on the mg ca ratio and a constant temperature offset of 2 5 c between both sst proxy calibrations

factors influencing methane derived authigenic carbonate formation at cold seep from southwestern dongsha area in the northern south china sea this paper carried out mineral and geochemical studies on a profile through a diagenetic methane derived authigenic carbonate sample that was collected from southwestern dongsha area of the northern south china sea five samples locating in the cross sectional middle mainly consist of dolomite and quartz and two samples close to the surface have a small amount of mg calcite the delta c 13 values of the samples vary between 30 59 and 0 30 vpdb with delta o 18 values ranging from 3 07 to 3 59 vpdb delta ca 44 40 values ranging from 1 35 to 1 47 srm915a indicating a contribution of methane to the carbon pool where the precipitation of authigenic carbonates occurred based on the isotope values alone it can not be distinguished if the carbon source is thermogenic gas or a mixture of biogenic methane and marine dissolved inorganic carbon the delta o 18 values are in general consistent with dolomite precipitation from a fluid similar to present seawater the observed small variation might be related to the oxygen isotope composition of seep fluid the relative small range in calcium isotope values suggests that relatively constant growth conditions and precipitation from seawater the central part of the carbonate nodule formed under the strong influence of methane seepage and the external part is less influenced by methane either due to reduced methane flux to the surface or caused by erosional exhumation of the carbonate nodule from greater depth to the sediment surface

experiments on metal silicate plumes and core formation short lived isotope systematics mantle siderophile abundances and the power requirements of the geodynamo favour an early and high temperature core formation process in which metals concentrate and partially equilibrate with silicates in a deep magma ocean before descending to the core we report results of laboratory experiments on liquid metal dynamics in a two layer stratified viscous fluid using sucrose solutions to represent the magma ocean and the crystalline more primitive mantle and liquid gallium to represent the core forming metals single gallium drop experiments and experiments on rayleigh taylor instabilities with gallium layers and gallium mixtures produce metal diapirs that entrain the less viscous upper layer fluid and produce trailing plume conduits in the high viscosity lower layer calculations indicate that viscous dissipation in metal silicate plumes in the early earth would result in a large initial core superheat our experiments suggest that metal silicate mantle plumes facilitate high pressure metal silicate interaction and may later evolve into buoyant thermal plumes connecting core formation to ancient hotspot activity on the earth and possibly on other terrestrial planets

convection and particle entrainment driven by differential sedimentation when a suspension of small particles is overlain by a clear fluid whose density is greater than that of the interstitial fluid but less than that of the bulk suspension the settling of the dense suspended particles can lead to vigorous convection in the overlying fluid this novel situation is investigated experimentally and theoretically a sharp interface is observed between the convecting upper region and a stagnant lower region in which there is unimpeded sedimentation at low reynolds number there is no transport of fluid from the upper region into the lower though there is mixing of both buoyant fluid and entrained particles from the lower region into the upper the interface between the two regions is found to descend at a constant velocity systematic laboratory measurements have determined how this velocity depends on the densities of the layers and the distributions of settling velocities of the particles a theoretical description is developed which calculates the evolution of the density of the lower region due to differential sedimentation of polydisperse particles buoyancy arguments based on the calculated density profile are used to placc upper and lower bounds on the amount of particle entrainment into the upper layer and on the rate of fall of the interface between the convecting and sedimenting regions the theoretical predictions are in good agreement with the experimental observations the analysis of the interaction between convection and sedimentation in the system considered here may be particularly relevant to the description of evolving crystal rich layers in magma chambers and of silt laden outflow from rivers and has a wide range of other industrial environmental and geological applications

calcium isotopes in the global biogeochemical ca cycle implications for development of a ca isotope proxy abstract at the earth s surface calcium ca is a critical element at a variety of scales it is soluble in natural waters a biological nutrient and a major constituent of the dominant mineral sink for carbon in the ocean caco3 there is a 4 variation in the ca isotopic composition 44ca 40ca expressed as 44ca of various ca reservoirs on earth suggesting ca isotopes as a promising tracer of ca cycling in both the present and the past fifteen years of high precision ca isotope measurements has revealed much about the behavior of ca isotopes in the earth surface environment but there remain fundamental questions concerning how ca isotopes are used to elucidate the marine and terrestrial ca cycles the current work presents a data compilation of over 70 published ca isotope studies totaling over 2600 measurements presented on a common delta scale that includes data on rivers and groundwater dust soils and soil pore fluids vegetation rainwater silicate minerals rocks and authigenic marine minerals carbonates sulfates and phosphates both modern and ancient the data compilation suggests that 1 there is a significant difference between carbonate 0 60 and silicate 44ca 0 94 2 riverine 44ca 0 88 does not simply reflect the compiled carbonate 44ca and 3 terrestrial vegetation exhibits the largest range of ca isotopic compositions 3 5 in the terrestrial setting we discuss these observations in the context of the global ca cycle exploring the extent to which seawater 44ca variability is feasible and how we can achieve accurate reconstructions of seawater 44ca over geologic time scales the current study presents simple mass balance models that quantify the leverage of inputs to change the ca isotopic composition of the ocean as this directly impacts the manner in which ca isotopes are interpreted although ca fractionates isotopically in the modern system during continental cycling the 44ca range of riverine inputs to the ocean is considerably smaller than the variability observed in putative seawater proxies such as nannofossil ooze and marine barite in the terrestrial realm plants exhibit a wide 44ca range and there is evidence that ca fluxes via biomass degradation are significant at the catchment scale we therefore assess the ability of the continental biosphere to influence riverine and consequently seawater 44ca a steady state biosphere has little leverage to alter riverine 44ca except in cases where the 44ca of the recycling flux is isotopically distinct from the 44ca of the uptake flux a non steady state biosphere can substantially impact both soil and riverine 44ca driving exchangeable ca either heavier or lighter depending on the magnitude of the recycling flux relative to the uptake flux based on estimates of the size of the global biosphere 1 5 1015 mol ca we suggest a decaying biosphere has the potential to impact riverine 44ca by tenths of a permil over time scales in the marine realm we evaluate the effect of a variable fractionation factor accompanying global removal of ca from the ocean on seawater 44ca and suggest methods by which such a mechanism can be recognized in the rock record experimental data suggest that there is considerable leverage