planktonic foraminiferal mg ca as a proxy for past oceanic temperatures a methodological overview and data compilation for the last glacial maximum as part of the multi proxy approach for the reconstruction of the glacial ocean margo incentive published and unpublished temperature reconstructions for the last glacial maximum lgm based on planktonic foraminiferal mg ca ratios have been synthesised and made available in an online database development and applications of mg ca thermometry are described in order to illustrate the current state of the method various attempts to calibrate foraminiferal mg ca ratios with temperature including culture trap and core top approaches have given very consistent results although differences in methodological techniques can produce offsets between laboratories which need to be assessed and accounted for where possible dissolution of foraminiferal calcite at the sea floor generally causes a lowering of mg ca ratios this effect requires further study in order to account and potentially correct for it if dissolution has occurred mg ca thermometry has advantages over other paleotemperature proxies including its use to investigate changes in the oxygen isotopic composition of seawater and the ability to reconstruct changes in the thermal structure of the water column by use of multiple species from different depth and or seasonal habitats presently available data are somewhat limited to low latitudes where they give fairly consistent values for the temperature difference between late holocene and the lgm 2 3 5 c data from higher latitudes are more sparse and suggest there may be complicating factors when comparing between multi proxy reconstructions

calibration of the planktonic foraminiferal mg ca paleothermometer sediment trap results from the guaymas basin gulf of california 1 the mg ca ratio has been measured in two surface dwelling species of planktonic foraminifera globigerinoides ruber and globigerina bulloides from biweekly sediment trap samples collected in guaymas basin gulf of california between august 1992 and november 1997 the guaymas basin experiences significant seasonal changes in sea surface temperature sst 16 33 c and thus is an ideal location for testing the temperature dependence of mg incorporation into foraminiferal calcite the planktonic foraminiferal mg ca ratios are directly compared with concurrent temperature measurements from the study site the results from the sediment trap study reveal a strong positive correlation between sst and the mg ca ratio in both g ruber r2 0 86 and g bulloides r2 0 90 the mg ca ratio increases exponentially by 7 per 1 c change in temperature for g ruber and by 6 for g bulloides these results indicate that the mg ca ratio in g ruber and g bulloides accurately records the measured seasonal surface temperature cycle and interannual variability in the guaymas basin within 1 c the greatest deviation between mg ca estimated sst and observed sst occurs in the spring and fall for both species this variability is attributed to rapidly changing hydrographic conditions and possible offset between the time of calcification and the temperature measurements in addition g ruber and g bulloides exhibit very high mg ca ratios during the strong el nino southern oscillation years of 1992 and 1997 verifying their potential to record sst up to 33 c and 28 c respectively the trace metal data are compared with foraminiferal oxygen isotope and alkenone measurements made on the same suite of sediment trap samples to assess the internal consistency of these temperature proxies strong correlations exist between the 18o and mg ca for g ruber r2 0 86 and g bulloides r2 0 79 similarly sea surface temperature estimates from mg ca ratios are in good agreement with alkenone derived temperature estimates r2 0 89 for g ruber and r2 0 81 for g bulloides

barremian danian chemostratigraphic sequences of the cauvery basin india implications on scales of stratigraphic correlation abstract chemostratigraphic concepts postulate that distinct chemozones could be recognized from rock records to help correlate geographically separated strata many studies have upheld this view but were limited to classic boundaries such as cenomanian turonian or cretaceous tertiary only a few elements and isotopic compositions were made use in such studies an attempt to recognize chemozones of barremian danian strata of the cauvery basin south india through whole rock chemistry had revealed many complex signals and depositional events as expressed by bulk geochemical profiles the signals indicate major shift in sedimentation pattern from dynamic depocenter to stable depositional conditions during santonian varying sensitivities of different elements towards prevalent depositional conditions are also inferred trends of geochemical composition indicated domination of single depositional control all through the depositional history basinal configuration that limited terrestrial sediment source and episodic influx of detrital materials presence of distinct change in whole rock geochemistry across geochronological and lithostratigraphic boundaries is deciphered through a statistical tool anova these results demonstrate that visual delineation of chemozones in a long ranging rock record would be tenuous and has to be exercised with caution

relative precipitation rates of aragonite and mg calcite from seawater temperature or carbonate ion control the temperature and degree of carbonate mineral supersaturation co3 2 ion concentration of seawater are the two most likely controlling variables on the compositions of recent marine carbonate cements the relative importance of these variables is difficult to assess in nature because they have similar trends with depth 0 1500 m and latitude in modern oceans we carried out laboratory experiments to investigate the relative growth rates of calcite mg calcite and aragonite in seawater as functions of both temperature 5 25 and 37 c and of carbonate ion concentration 2 5 to 15 times supersaturated with respect to calcite the precipitation rates of aragonite relative to those of calcite increase strongly with increasing temperature and are not affected greatly by changes in saturation state at 5 c calcite precipitation rates are nearly equivalent to those of aragonite regardless of the degree of saturation at both 25 and 37 c aragonite precipitation rates are much more rapid than those of calcite up to a factor of 4 except at very low saturation states calcite compositions vary from less than 5 mol mgco3 at 5 c to 14 mol mgco3 at 37 c our results suggest that the well documented shift toward precipitation of lower mol mg calcite and the decrease in abundance of aragonite cements with increasing oceanic depth and latitude can be attributed largely to lower temperatures

surface and subsurface seawater temperature reconstruction using mg ca microanalysis of planktonic foraminifera globigerinoides ruber globigerinoides sacculifer and pulleniatina obliquiloculata laser ablation inductively coupled plasma mass spectrometry microanalyses of mg ca across individual final chambers of three planktonic foraminifera species globigerinoides ruber g sacculifer and pulleniatina obliquiloculata reveal significant interspecies differences in test mg concentrations whereas these three species have similar mg ca values at low sea surface temperatures similar to 22 degrees c they diverge markedly at high sea surface temperatures similar to 29 degrees c explanations for these differences in species mg ca values based on detailed comparison of species intratest mg ca distributions suggest that compositional variability within tests cannot account for the observed deviation of species mg ca values in warm water equatorial regions multiple regression modeling and delta o 18 analysis of globigerinoides sacculifer tests indicate that interspecies differences in mg ca values result from different depth habitats the average mg ca values of g ruber final chambers reflect the temperature of the surface mixed layer 0 25 m whereas those of g sacculifer and pulleniatina obliquiloculata correlate best with subsurface temperatures at 50 75 m and 100 125 m water depths respectively mg ca calibration to the temperatures at these depths reveals a similar temperature control on mg test composition in all species combining our results with mg ca values from published culturing experiments we derive a generalized equation for the effect of temperature and seawater salinity on foraminiferal mg ca we also show that the mg ca composition of specific calcite layers within foraminiferal tests including the low mg ca layers of globigerinoides ruber and g sacculifer and the cortex layer of pulleniatina obliquiloculata correlates with seawater temperature and can be used as an additional proxy for seawater temperature

a model of early calcite cementation in alluvial fans evidence from the burdigalian sandstones and limestones of the valles penedes half graben ne spain abstract the valles penedes half graben developed during a neogene extensive period as part of the catalan coastal ranges in the northwestern edge of the valencia trough the neogene deposits of the valles penedes half graben consist of from base to top three lithostratigraphic complexes i a lower continental complex of aquitanian early langhian age ii a continental to marine complex with reefal carbonate platforms of langhian age and iii an upper continental complex of middle serravallian tortonian age this study focuses on the calcite cements of the lower continental complex consisting of red beds mudstones sandstones and conglomerates and lacustrine limestones deposited in alluvial fan environments the studied materials are cemented by calcite precipitated from meteoric waters that circulated through the sediments during the early diagenesis at shallow burial depths the calcite cement was studied by means of petrographic cathodoluminescence microprobe and 18o and 13c isotopic analysis the petrographic and geochemical results show that these cements vary according to the sedimentary environment i sandstones deposited in proximal alluvial fan environments cemented by calcite with low contents of mg fe mn sr and na 13c values of 7 4 pdb and 18o values from 6 5 to 6 2 pdb ii sandstones sedimented in medium to distal alluvial fan environments cemented by mn rich and mg fe sr and na poor calcite with 13c values from 7 9 to 6 9 pdb and 18o values from 10 5 to 8 6 pdb and iii lacustrine limestones of distal alluvial fan environments cemented by fe rich calcite with variable contents of mn and low contents of mg sr and na the distribution of these calcite cements allows us to propose a model of fluid circulation and early calcite cementation within an alluvial fan indicating spatial and temporal variations in chemical composition of meteoric water during migration from proximal to distal alluvial fan environments residence time of waters eh ph conditions and the degree of sediment water interactions influenced by the mineral composition of the host sediments are the most important parameters controlling variations in calcite cement composition

a refined method for calculating paleotemperatures from linear correlations in bamboo coral carbon and oxygen isotopes bamboo corals represent an emerging paleoclimate archive with the potential to record variability at intermediate depths throughout much of the global ocean realizing this potential has been complicated by biologically mediated vital effects which are evident in linear correlations of skeletal carbon 13c and oxygen 18o isotope composition previous efforts to develop a bamboo coral 18o paleothermometer by accounting for such vital effects have not been completely successful as they still rely on empirical calibrations that are offset from the temperature dependence of abiogenic experiments here we describe an approach that better corrects for bamboo coral vital effects and allows paleotemperatures to be calculated directly from the abiogenic temperature dependence the success of the method lies in calculating apparent equilibrium carbon and oxygen isotope fractionation at the temperature ph and growth rate of each coral as well as in the use of model ii regressions rigorous propagation of uncertainty suggests typical errors of 2 3 c but in select cases errors as low as 0 98 c can be achieved for densely sampled and strongly correlated data sets this lower limit approaches the value attributed to uncertainty in ph and growth rate estimates alone as predicted by a series of pseudoproxy experiments the incorporation of isotopically light metabolic co2 appears to be negligible in most pacific corals but may be significant in atlantic specimens potentially requiring an additional correction the success of the method therefore hinges on how well complex environmental systems and biomineralization strategies are constrained with the most reliable temperatures occurring when calcifying fluid ph growth rate and incorporation of metabolic carbon into skeletal calcite are constrained using multiple geochemical proxies

seasonal variations in sr mg and p in modern speleothems grotta di ernesto italy sub annual variations in trace element chemistry and luminescence have recently been demonstrated from speleothems and offer the potential of high resolution palaeoclimatic proxies however no studies have yet examined microscopic trace element variations in relation to modern cave conditions in this study the spatial variations in trace element sr mg and p concentrations in speleothems a stalagmite and a soda straw stalactite from the alpine ernesto cave temperature 6 6 0 1 c in a forested catchment in ne italy have been studied using secondary ion mass spectrometry sims and compared with environmental parameters and waters in the modern cave an annual lamination exists in the stalagmite and soda straw stalactite in the form of clear calcite with narrow visible layers which are uv fluorescent and interpreted to contain soil derived humic fulvic acids washed into the cave during autumn rains microanalyses were undertaken of seven annual laminae probably deposited during the 1960s in the stalagmite and seven laminae in the 1990s for the stalactite the analysis results show that sr consistently has a trough and p a peak centred on the inclusion rich layer mg shows mainly a negative covariation with sr in laminae formed in the 1990s but a positive covariation in the stalagmite formed in 1960s the spatial scale of the main geochemical variations is the same as that of annual laminae of inclusion poor and inclusion rich couplets mass balance arguments are used to show that the p is inorganic in form and presumably occurs as individual phosphate ions within the calcite most drip waters show limited chemical variations but a summer peak in trace elements in 1995 and a decrease in mg ca in the following winter are notable more pronounced covariations in mg ca and sr ca are shown by a site with highly variable drip rates where ratios increase at slow drip rates the strongest seasonal variations are found in pool waters where ratios increase reflecting significant ca removal from the water into the calcite during the winter in response to seasonal pco2 variations in cave air thus the cave waters compositions tend to reflect climate conditions such that mg ca and sr ca are tentatively interpreted to be higher when climate conditions are dry combining results from the speleothems and cave water along with the behaviour of each trace species mg ca variations in the speleothems are considered to reflect their variation in the cave waters whereas sr incorporation is also dependent on precipitation rate in this case mainly controlled by temporal variations in pco2 in the cave and conceivably also by inhibitors such as phosphate p adsorption a fraction of which is subsequently incorporated within calcite depends on aqueous phosphate concentration and water flux both of which should increase during the autumn therefore multiple trace element profiles in speleothems reflect multiple aspects of environment seasonality and conditions and hence a calibration against weather records is desirable to establish their palaeoclimatological meaning the strong annual variation of trace elements and particularly p can provide chronological markers for high resolution studies of other climate proxies such as stable isotopes

calcite and aragonite precipitation from seawater solutions of various salinities precipitation rates and overgrowth compositions abstract the reaction rate and composition of calcite and aragonite overgrowths precipitated from seawater solutions of various salinities i e s 5 15 25 35 44 were determined at 25 c and 10 2 5 atm co2 partial pressure using a constant disequilibrium seeded technique the rate data were fitted to an empirical rate law of the form log r n c or a 1 log k where n is the empirical reaction order and k is the rate constant calcite precipitation rates in seawater solutions do not vary appreciably as a result of salinity variations over the range investigated while those for aragonite show an increase in going from the higher i e s 35 44 to the lower i e s 5 15 25 salinity range this study also confirms previously published findings that above a given saturation state i e c 2 6 aragonite precipitates more rapidly than calcite at 25 c the incorporation of sr2 in aragonite and mg2 in calcite overgrowths are independent of the precipitation rate the partition coefficient of sr2 in aragonite is approximately equal to unity and is unaffected by salinity variations between 5 and 44 however the mg2 partition coefficient in calcite increases with decreasing salinity of the parent seawater solutions possibly as a result of variations in the sulfate content of the solutions and solids the experimental results were discussed in the context of a number of geological environments

methane derived carbonate cementation of marine sediments from the kattegat denmark geochemical and geological evidence abstract methane derived carbonate cementation of holocene marine sediment occurs at several locations in the kattegat denmark generally the carbonate cemented sandstones occur at the seafloor as individual slabs or widely distributed thinly lithified pavements in some areas the lithified sandstones take the form of large and spectacular vertical pillar and mushroom like bodies standing up from the seafloor the carbonate cement consists of aragonite high mg calcite and dolomite the high mg calcite is the most widespread carbonate solid phase found aragonite is primarily associated with shell accumulations in the sediments so far dolomite has only been recorded as cement in the large vertical lithified sandstone bodies the carbonates are remarkably depleted in 13c i e generally in the range of 55 to 45 pdb and are therefore interpreted as being the result of methane oxidation by sulphate reducing bacteria in the anaerobic diagenetic zone of the sediments however the oxygen isotopic composition and the concentrations of minor elements indicate that carbonate precipitation took place under relatively constant temperature and salinity conditions in normal marine pore fluids the habit and mineralogy of the carbonate cemented sandstone observed most likely are controlled by the effect of bacterial activity and upward gas migration on the interstitial geochemical microenvironment the lithified sediments were subsequently exposed as spectacular sandstone formations on the seafloor by submarine erosion data from onshore exploration wells reveal that methane is encountered in eemian early weichselian late quaternary marine deposits the chemical composition and the isotopic signatures of the methane suggest a gas of microbial origin and it is thought that the gas is generated within the host marine quaternary sediment the locations of submarine gas seeps along with those of the carbonate cemented sandstone formations and the onshore gas seeps show a linear distribution which largely coincides with the extension of the fennoscandian border zone thus the seeps may be controlled by the structural framework in the northeastern part of the danish subbasin

late holocene variability of upper north atlantic deep water temperature and salinity 1 magnesium calcium ratios in benthic foraminifera cibicidoides pachyderma from a sediment core on the laurentian slope 1854 m exhibit strong millennial scale fluctuations during the past 4000 years we convert these data to seawater paleotemperatures using a new monospecific linear equation results suggest that the temperature of upper north atlantic deep water dominated by labrador seawater today has varied by at least 2 c during the late holocene millennial scale coolings coincide with previously identified periods of increased drift ice and regional glacier advances including the little ice age paired oxygen isotope measurements indicate that salinity and perhaps density were reduced during the cold periods we discuss possible mechanisms for transmitting this cold fresh signal from surface waters to intermediate depths our reconstructed late holocene ranges in upper north atlantic deep water properties greatly exceed those of the instrumental record and imply that large changes may be yet to come

quasi periodicity and global symmetries in interdecadal upper ocean temperature variability recent studies find interannual i e 3 to 7 year decadal i e 9 to 13 year and interdecadal i e 18 to 23 year periodicities and a trend dominating global sea surface temperature sst and sea level pressure slp variability over the past hundred years with the interdecadal signal dominating sub el nino southern oscillation enso frequencies we isolate interdecadal frequencies in sst and slp records by band passing with a window admitting 15 to 30 year periods from 1900 to 1989 the rms of interdecadal filtered sst and slp anomalies is largest in the extratropics and eastern boundaries first mode empirical orthogonal functions eofs explain about half the interdecadal variance in both variables with the tropical warm phase peaking near 1900 1920 1940 1960 and 1980 from 1955 to 1994 eof spatial patterns of interdecadal sst slp and 400m temperature t400 anomalies reveals global reflection symmetries about the equator and global translation symmetries between ocean basins with tropical and eastern ocean ssts warmer cooler than normal covarying with stronger weaker extratropical westerly winds cooler warmer ssts in western central subarctic and subantarctic frontal zones safzs stronger weaker subtropic and subarctic gyre circulations in north pacific and north atlantic oceans and warmer cooler basin and global average ssts of 0 1 c or so evolution of interdecadal variability from the tropical warm phase to the tropical cool phase is propagative also characterized by reflection and translation symmetries during the tropical warm phase cool sst anomalies along western central safzs are advected slowly eastward to the eastern boundaries and subsequently advected poleward and equatorward by the mean gyre circulation the latter conducting extratropical sst anomalies into the tropics a delayed action oscillation model is constructed that yields the quasiperiodicity of interdecadal variability in a manner consistent with these global symmetries in both pattern and evolution

oxygen isotopes and mgco3 in brachiopod calcite and a new paleotemperature equation abstract modern brachiopods and their ambient seawater compiled from 34 localities covering shallow waters from the poles to the tropics were analyzed for their oxygen isotopic compositions and srco3 and mgco3 contents if the routine seawater 18o composition and the mgco3 effect on oxygen isotopes are considered in calculations calcification temperatures are concordant with measured ambient seawater temperatures the srco3 contents of modern brachiopods appear to be unrelated to ambient growth temperatures while their mgco3 contents exhibit some relationship with temperature and growth rate controlled in part by ambient productivity or clearance rates or local environment and by taxonomic affinity such as presence or absence of caeca linear least squares regression analysis yields a new oxygen isotope paleotemperature equation for brachiopod calcite which makes adjustment for shell mgco3 contents and covers habitats with water temperatures ranging from 2 to 32 c t c 16 192 3 468 c sw mg c n 319 r 2 0 98 the mg effect adjustment is based on the change in shell calcite 18o by 0 17 per mol mgco3 jimenez lopez et al 2004 this adjustment is critical to the determination of calcification temperatures for modern articulated brachiopods especially the ones from cold and warm water habitats and or the ones with exceptionally low or high mgco3 contents which otherwise may be offset lower or higher by as much as 7 c furthermore this adjustment may be critical for fossil brachiopods and other marine calcitic invertebrates with variable mgco3 contents and when using their 18o and 47 for determining ancient seawater 18o compositions and temperatures

further constraints on the diagenetic influences and salinity effect on globigerinoides ruber white mg ca thermometry implications in the mediterranean sea we analyzed mg ca ratios of the planktonic species globigerinoides ruber white picked from 49 box core samples covering the whole mediterranean sea and 2 core tops from the atlantic ocean over the entire data set we found no significant correlation between mg ca and 18o derived calcification temperatures this lack of correlation is chiefly due to the presence of an early diagenetic mg rich calcite coating which can constitute up to 20 of the total shell calcite in the central and eastern mediterranean basin and result in anomalously high mg ca values and a high scattering in the western mediterranean sea however g ruber mg ca scattering shows smaller amplitude and mg rich calcite remains under the xrd detection limit sem observations indicate that only a few samples are affected by trace amounts of post mortem calcite overgrowths most of this calcite being likely removed during the chemical cleaning for mg ca analyses using core top sediments from the western mediterranean sea we performed an empirical calibration exercise which confirms that g ruber mg ca is not only related to temperature but it is also significantly affected by sea surface salinity this salinity effect is not specific to high salinity environments such as the mediterranean sea since it appears to be coherent with recent results obtained on indo pacific and atlantic surface sediments which suggest that a 1 psu change in sss results in a 1 7 c mg ca temperature bias this sensitivity to salinity is significantly higher than those deduced from culture experiments

influence of mg2 on the kinetics of calcite precipitation and calcite crystal morphology abstract the kinetics of calcite growth in the presence of mg2 has been studied by both a ph free drift method and by visual observation our experiments show that the calcite growth rate is reduced by the presence of mg2 the higher the mg ca ratio in the solution the lower the growth rate in a caco3 supersaturated solution the inhibition of calcite growth by the presence of mg2 is caused by mg2 being incorporated into the original calcite seed surfaces and developing new crystal surfaces the mg2 distribution on the calcite surfaces is not uniform as there is likely to be different mg2 densities on the newly developed surfaces than on the original surfaces of the calcite seeds this causes the calcite crystal morphology to change the significance of creating error in using the initial rate data rather than the equilibrium rate data for the prediction of the calcite precipitation kinetics is discussed

sr mg ratios of modern marine calcite empirical indicators of ocean chemistry and precipitation rate holocene biotic and abiotic marine calcite have a similar range of mg contents 0 to 22 and 4 to 21 mol mgco3 respectively yet biotic calcite has sr2 concentrations that are consistently 1250 ppm higher than those of abiotic calcite as in laboratory experiments a positive linear relation is observed between dsr and calcite mg content this produces two distinct linear trends on a plot of sr2 vs mg2 concentrations principal axes of variation for both trends have similar slopes yet distinctly different sr2 concentration intercepts biotic y 0 024x 1298 r2 0 70 abiotic y 0 027x 47 r2 0 77 the similar slopes of these trends reflect the constancy of mgca and srca ratios of modern seawater equations describing the dependence of dsr on calcite mg content are derived from both trends biotic dsr 3 16 x 10t 6 ppm mg 0 169 abiotic dsr 3 52 x 10 6 ppm mg 0 0062 characterization of sr mg trends for holocene materials allows comparison with analogous trends from ancient samples to estimate relative changes in seawater mgca and srca ratios the relatively high sr contents of biotic calcite result from rapid precipitation rates associated with shell accretion in marine organisms calcites precipitated from seawater in laboratory experiments have dsr values that are similar to those of biotic marine calcite suggesting that both precipitate at approximately the same rate our estimates of surface area normalized precipitation rates in planktonic and benthonic foraminifera are comparable to those of seeded ph stat experiments we conclude that the dsr values for biotic and experimental marine calcite are kinetically controlled whereas the lower precipitation rates of abiotic marine calcite yield dsr values that approximate equilibrium conditions experimentally derived equations describing the relation between dsr and calcite precipitation rate indicate that the offset in sr content between biotic and abiotic calcite is the result of abiotic precipitation rates that are two to five orders of magnitude lower than those of biotic precipitates however observations of naturally occurring marine cements suggest that the five order of magnitude offset best represents natural system processes

δ18o values 87sr86sr and sr mg ratios of late devonian abiotic marine calcite implications for the composition of ancient seawater abstract late devonian frasnian abiotic marine calcite has been microsampled and analyzed for 87 sr 86 sr ratios 18o and 13c values and minor element concentrations portions of marine cement crystals from the alberta and canning basins have escaped diagenetic alteration and preserve original marine 18o values 4 8 0 5 pdb 13c values 2 0 to 3 0 pdb 87 sr 86 sr ratios 0 70805 3 and sr mg weight ratios 0 04 to 0 05 marine 87 sr 86 sr ratios are globally consistent and can be correlated within the alberta basin and among the alberta canning and williston basins correlation of isotopic and chemical data strengthen the conclusion that marine cements from the leduc formation preserve original marine 18o values which are 3 to 4 lower than those of modern marine cements these low 18o values are best explained by precipitation from 18o depleted seawater and not by elevated seawater temperature or diagenetic alteration for comparison with devonian data analogous data were collected from holocene mg calcite and aragonite marine cements from enewetak atoll marshall islands mg calcite and aragonite marine cements are in isotopic equilibrium with ambient seawater and mg calcite cements are homogeneous with respect to sr and mg contents empirically derived homogeneous distribution coefficients for mg and sr in modern abiotic mg calcite from enewetak atoll are 0 034 and 0 15 respectively an equation describing the dependence of dsr on mg content was based on a compilation of sr and mg data from holocene abiotic marine calcite dsr 3 52 10 6 ppm mg 6 20 10 3 unlike that derived from experimental data this sr mg relation is consistent over a range of 4 to 20 mol mgco3 and may represent precipitation phenomena which are minimally controlled by kinetic effects comparison of sr and mg contents of analogous devonian and holocene marine cements suggests that the mg ca ratio of late devonian seawater was significantly lower and that the sr ca ratio was significantly higher than that of modern seawater

field based validation of a diagenetic effect on g ruber mg ca paleothermometry core top results from the aegean sea eastern mediterranean recent work across the mediterranean sea has illustrated the salinity and overgrowth effects on planktonic foraminiferal mg ca which potentially confound the use of this as a temperature proxy for paleoceanographic reconstructions to test and verify these effects we present new aegean sea results which reveal mg ca values that were unreasonably high to be explained by temperature or salinity variations alone confirming that foraminiferal mg ca is affected by diagenesis we have specifically targeted globigerinoides ruber w sensu stricto from a series of modern core tops spanning a strong sea surface salinity gradient and a minor sea surface temperature range along a north south aegean sea transect scanning electron microscopy analyses show that g ruber specimens were covered by microscale euhedral crystallites of inorganic precipitates this secondary calcite phase seems to be responsible for the anomalously high mg ca ratios and likely formed near the sediment water interface from caco3 supersaturated interstitial seawater we also have clear evidence of diagenetic alteration in a north south direction along the aegean sea possibly depending on salinity and calcite saturation state gradients these observations illustrate the necessity of alternative techniques e g flow through time resolved analysis or laser ablation inductively coupled plasma mass spectrometry to potentially overcome these diagenetic issues and develop a more reliable and sensitive temperature proxy in similar subtropical settings characterized by high salinity excessive evaporation and restricted circulation

the diagenesis of the late dinantian derbyshire east midland carbonate shelf central england carbonate cements in late dinantian asbian and brigantian limestones of the derbyshire carbonate platform record a diagenetic history starting with early vadose meteoric cementation and finishing with burial and localized mineral and oil emplacement the sequence is documented using cement petrography cathodoluminescence trace element geochemistry and c and o isotopes the earliest cements pre zone 1 are locally developed non luminescent brown sparry calcite below intrastratal palaeokarsts and calcretes they contain negligible fe mn and sr but up to 1000 ppm mg their isotopic compositions centre around 18o 8 5 13c 5 0 calcretes contain less 13c subsequent cements are widespread as inclusion free low mg low fe crinoid overgrowths and are described as having a dead bright dull cathodoluminescence the dead cements zone 1 are mostly non luminescent but contain dissolution hiatuses overlain by finely detailed bright subzones that correlate over several kilometres across dead bright subzones there is a clear trend in mg 500 900 ppm mn 100 450 ppm and fe 80 230 ppm zone 1 cements have isotopic compositions centred around 18o 8 0 and 13c 2 5 zone 2 cement is bright thin and complexly subzoned it is geochemically similar to bright subzones of zone 1 cements dull zone 3 cement pre dates pressure dissolution and fills 70 or more of the pore space it generally contains little mn fe and sr but can have more than 1000 ppm mg increasing stratigraphically upwards the 18o compositions range from 5 5 to 15 and the 13c range is 1 to 3 20 00 zone 4 fills veins and stylolite seams in addition to pores it is synchronous with pb ba f ore mineralization and oil migration zone 4 is ferroan with around 500 ppm fe up to 2500 ppm mg and up to 1500 ppm mn isotopic compositions range widely 15o 2 7 to 9 and 13c 3 8 to 2 50 unaltered marine brachiopods suggest a dinantian seawater composition around 15o 0 smow but vital isotopic effects probably mask the original 13c pdb value pre zone 1 calcites are meteoric vadose cements with light soil derived 13c and light meteoric 18o an unusually fractionated pluvial 15o smow value of around 6 is indicated for local dinantian meteoric water calcrete 18o values are heavier through evaporation zone 1 textures and geochemistry indicate a meteoric phreatic environment fe and mn trends in the bright subzones indicate stagnation and precipitation occurred in increments from widespread cyclically developed shallow meteoric water bodies meteoric alteration of the rock body was pervasive by the end of zone 1 with a general resetting of isotopic values zone 3 is volumetrically important and external sources of water and carbonate are required emplacement was during the namurian early westphalian by meteoric water sourced at a karst landscape on the uplifted eastern edge of the derbyshire east midland shelf the light 18o values mainly reflect burial temperatures and an unusually high local heat flow but an input of highly fractionated hinterland derived meteoric water at the unconformity is also likely relatively heavy 13c values reflect the less altered state of the source carbonate and aquifer zone 4 is partly vein fed and spans burial down to 2000 m and the onset of tectonism light organic matter derived 13c and heavy 18o values suggest basin derived formation water combined with textural evidence of geopressures this relates to local high temperature ore mineralization and oil migration low water to rock ratios with host rock buffering probably affected the final isotopic compositions of zone 4 masking extremes both of temperature and organic matter derived co2

incorporation and preservation of mg in globigerinoides sacculifer implications for reconstructing the temperature and 18o 16o of seawater using bathymetric transects of surface sediments underlying similar sea surface temperatures but exposed to increasing dissolution we examined the processes which affect the relationship between foraminiferal mg ca and 18o we found that globigerinoides saccculifer calcifies over a relatively large range of water depth and that this is apparent in their mg content on the seafloor foraminiferal mg ca is substantially altered by dissolution with the degree of alteration increasing with water depth selective dissolution of the chamber calcite formed in surface waters shifts the shell s bulk mg ca and 18o toward the chemistries of the secondary crust acquired in colder thermocline waters the magnitude of this shift depends on both the range of temperatures over which the shell calcified and the degree to which it is subsequently dissolved in spite of this shift the initial relationship between mg ca and 18o determined by their temperature dependence is maintained we conclude that paired measurements of 18o and mg ca can be used for reconstructing 18owater though care must be taken to determine where in the water column the reconstruction applies

kinetic control of morphology composition and mineralogy of abiotic sedimentary carbonates abstract conventional thinking has long held that the abiotic precipitation of calcium carbonate occurs with a causal relationship between fluid my ca ratios and crystal morphology crystal composition and carbonate mineralogy resulting in the formation of meteoric equant low magnesium calcite and marine acicular high magnesium calcite and aragonite problematically calcites with varying amounts of incorporated magnesium occur either as equant or acicular crystals and aragonite may coexist with calcite in either environment commonly however a systematic relation exists between crystal morphology composition mineralogy and rates of reactant supply to growing crystal surfaces for example equant rather than acicular crystals of calcite form in modern deep and or cold marine meteoric phreatic and deep burial settings where the degree of carbonate saturation and or rates of fluid flow are low in areas of higher saturation and or fluid flow such as in warm shallow marine and meteoric vadose environments acicular calcite may predominate this relation is also seen in systems in which aragonite and calcite form in intimate association aragonite precipitation is favored when rates of reactant supply are high calcite forms when rates are low such relations suggest that crystal morphology composition and mineralogy are controlled by the kinetics of surface nucleation and the amount of reactants principally carbonate ions at growth sites precipitating phases are the ones which can best accommodate such excess reactants ambient mg ca ratios only indirectly control the nature of inorganically precipitated carbonate phases

carbonate cements in a modern red sea reef north of jeddah saudi arabia abstract subsea carbonate cements vary in their types and distribution in a modern coral reef formation north of jeddah saudi arabia the petrographic characteristics of cemented reefs were studied by scanning electron microscope and x ray diffraction methods the cements consist basically of acicular aragonite and magnesium calcite containing 17 mole mgco3 the predominant cement in the red sea reefs is aragonite which is generally restricted to the intraskeletal cavities of coral whereas the mg calcite develops as a cryptocrystalline cement filling and coating the reef components

in situ δ18o and mg ca analyses of diagenetic and planktic foraminiferal calcite preserved in a deep sea record of the paleocene eocene thermal maximum we report 18o and minor element mg ca sr ca data acquired by high resolution in situ secondary ion mass spectrometry sims from planktic foraminiferal shells and 100 500 m sized diagenetic crystallites recovered from a deep sea record odp site 865 of the paleocene eocene thermal maximum petm the 18o of crystallites 1 2 pee dee belemnite pdb is 4 8 higher than that of planktic foraminiferal calcite 3 6 pdb while crystallite mg ca and sr ca ratios are slightly higher and substantially lower than in planktic foraminiferal calcite respectively the focused stratigraphic distribution of the crystallites signals an association with petm conditions hence we attribute their formation to early diagenesis initially sourced by seafloor dissolution burndown ensued by reprecipitation at higher carbonate saturation the mg ca ratios of the crystallites are an order of magnitude lower than those predicted by inorganic precipitation experiments which may reflect a degree of inheritance from donor phases of biogenic calcite that underwent solution in the sediment column in addition sims 18o and electron microprobe mg ca analyses that were taken within a planktic foraminiferal shell yield parallel increases along traverses that coincide with muricae blades on the chamber wall the parallel 18o and mg ca increases indicate a diagenetic origin for the blades but their 18o value 0 5 pdb is lower than that of crystallites suggesting that these two phases of diagenetic carbonate formed at different times finally we posit that elevated levels of early diagenesis acted in concert with sediment mixing and carbonate dissolution to attenuate the 18o decrease signaling petm warming in whole shell records published for site 865

occurrence and significance of microbialites in the uplifted tasmaloum reef sw espiritu santo sw pacific abstract in the sw pacific ocean subduction of the d entrecasteaux ridge system has caused rapid uplift of the central new hebrides island arc the maximum uplift rate of 6 mm yr 1 occurs along the southwest coast of espiritu santo island near tasmaloum the tasmaloum uplifted reef sequence internal structure which is strongly linked to its tectonic context was investigated through a series of drill holes to depths up to 42 m although a stable tropical coast would undergo approximately 120 m of post glacial sea level rise the net relative sea level rise on such a rapidly uplifting coast is only about 20 m colonization of the tasmaloum fringing reef occurred by 24 ka upon a pre reef substrate composed of a thick bioclastic sand formation accumulated during the last glacial period during the post glacial sea level rise the vertical succession of reef assemblages reflects environmental and bathymetric variations controlled by the interplay of rapid but variable rates of sea level rise and more or less constant uplift of 5 6 mm yr 1 microbialite crusts composed of high magnesian calcite laminae occur in the tasmaloum reef from 20 to 6 ka and are particularly abundant from 16 to 10 ka the development of microbialite crusts is related to nutrient enrichment of interstitial waters through mixing with meteoric groundwater after 6 ka when sea level ceased rising in the region and continuing uplift caused rapid emergence of the reef microbialites disappear within the subtidal assemblages several explanations can be put forward for their disappearance in particular nutrient input changes are a likely cause a new hydrologic and oceanographic regime was established when sea level ceased rising this change was accompanied by warming of tropical waters

comparison of high resolution sub annual records of trace elements in a modern 1911 1992 speleothem with instrumental climate data from southwest australia high spatial resolution measurements of mg p u sr ba and na using 193 nm excimer laser ablation inductively coupled plasma mass spectrometry has revealed clearly resolvable annual cycles in a modern speleothem from southwestern australia the age of this stalagmite is established by the dates of emplacement and removal of the boardwalk where it grew 1911 1992 this chronological constraint allows for the first confident comparison between the instrumental climate record and speleothem trace element content eleven laser ablation transects across a 0 5 mm wide section of the speleothem growth axis were measured cycles that could be matched between adjacent transects were stacked into a master record to minimise variability between tracks and permit greater confidence in comparing the trace elements to the instrumental climate record p and u positively and mg inversely mimic the sudden 20 decrease in annual rainfall experienced by this region since 1965 we argue that p from seasonal vegetation decay is transported to the speleothem before it is mineralised in the soil owing to the low p retention capacity of southwest australian soils both vegetation activity and the transport of vegetation derived hpo42 are sensitive to rainfall groundwater p concentration may also influence the transport of u through the strong affinity between phosphate and uranyl ions mg appears to be sensitive to groundwater residence time as this affects drip water mg ca composition by preferential loss of ca during drier episodes when calcite precipitates before reaching the stalagmite the effects of groundwater residence time may also be important for sr on inter annual scales however the behaviour of sr on the annual cycle is opposite to mg but compatible with ba and na which are shown to depend on speleothem growth rate

echinoderm skeletal preservation calcite aragonite seas and the mg ca ratio of phanerozoic oceans abstract the alternation between abiotic calcite and aragonite precipitation in shallow seawater and the oscillation of seawater mg ca ratio throughout the phanerozoic are both popular hypotheses echinoderms with well preserved stereom provide new empirical evidence that supports both these hypotheses analyses are reported from 29 specimens cambrian to eocene age containing ossicles preserved either as mg calcite 3 3 to 8 mole mgco3 or as mixed calcite and dolomite 5 to 12 5 mole mgco3 echinoderms with high mole mgco3 occur in the early cambrian and late carboniferous to triassic low values come from the silurian and jurassic to cretaceous the average composition of echinoderms with preserved stereom does not fall below 3 5 mol mgco3 during the phanerozoic and reaches its highest mean value of 16 0 mol mgco3 today an empirical partition coefficient of 0 03182 for modern tropical echinoids is used to indicate the mg ca ratio of ancient seawater from the mg ca ratio of fossil stereom some assumptions are involved and a likely error is calculated from the mg2 variation of modern echinoids high mean seawater mg ca ratios are calculated for early cambrian 3 3 and the late carboniferous to triassic 2 3 but never reached today s value of 5 2 low mg ca ratios 1 1 are indicated from jurassic to cretaceous echinoderms the 29 echinoderm samples plot close to first order mg ca seawater oscillations derived from geochemical models and mg ca ratios determined from fluid inclusions but considerable discrepancies exist when shorter 106 myr time intervals are considered further data and improved understanding of mg partitioning is required before accurate secular variation in the mg ca of seawater can be determined from echinoderms however they are an underused resource in this context and provide an excellent seawater archive

mg sr and sr isotope geochemistry of a belgian holocene speleothem implications for paleoclimate reconstructions in this study variations in mg ca sr ca and 87sr 86sr ratios in a holocene belgian speleothem cave secondary carbonate deposit are interpreted in terms of changes in water residence time and changes in weathering processes possibly induced by changes in west european climate a stalagmite from the pere noel cave belgium was dated with the tims u th method and was deposited between 13 and 2 ka bp the 1000 mg ca ratio varies between 4 9 and 26 and displays short term changes but no significant long term trend the 1000 sr ca ratio varies between 0 09 and 0 31 and displays both short term changes and a long term decreasing trend from 12 9 to 3 5 ka in parallel the sr isotopic composition of the speleothem decreases from 0 7090 at 12 9 ka to 0 7088 at 3 5 ka the sr isotope ratio is higher than expected from the overlying limestone 87sr 86sr 0 7081 which implies an external source of radiogenic sr most probably from a silicate phase short term and long term changes in mg ca sr ca as well as long term changes of 87sr 86sr ratios can be explained by changes in the dissolution and precipitation processes of the host limestone these processes are controlled by changes in water residence times linked to changes in the water excess precipitation minus evapo transpiration c 2000 elsevier science b v all rights reserved

strontium magnesium and barium incorporation in aragonitic shells of juvenile arctica islandica insights from temperature controlled experiments abstract in order to constrain spatial and temporal temperatures and environmental conditions in the north atlantic ocean during the holocene high resolution seasonal to annual marine proxies with excellent chronological constraints are needed the long lived ocean quahog arctica islandica which has the potential to provide a precise annually dated record via crossdating techniques is a fairly well developed and tested marine proxy archive in particular oxygen isotopes derived from a islandica shell carbonate have provided a wealth of information on marine climate and ocean circulation dynamics however shell derived oxygen isotopes are influenced by both the isotopic source water signature covarying with salinity and seawater temperature if seawater isotopic signature is not known temperature reconstructions become challenging thus an independent technique to estimate past seawater temperatures is highly desired however based on previous studies on adult and juvenile clams the utility of elemental ratios in a islandica shell material as environmental proxies remains questionable to further evaluate the influence of seawater temperature on elemental and isotopic incorporation during biomineralization a islandica shells were grown at constant temperatures under two regimes during a 16 week period from march 27 to july 21 2011 at the darling marine center in walpole maine individual juvenile clams were stained with calcein and cultured at 10 30 0 30 c for six weeks after this the clams were again stained with calcein and cultured at 15 00 0 40 c for an additional 9 5 weeks average salinity values were 30 20 0 70 and 30 70 0 70 in the first and second phases of the experiment respectively continuous sampling within and across the temperature conditions from 10 30 c to 15 00 c coupled with the calcein markings provided the ability to place each sample into a precise temporal framework and to establish exact average growth rates for the shells sampled after accounting for changes in the isotopic composition of seawater oxygen isotopes from one sampled shell effectively recorded seawater temperatures during the study and also gave confidence to the temporal fit of the data elemental ratios sr ca mg ca ba ca from five aragonitic shells were determined via laser ablation inductively coupled plasma mass spectrometry sr ca and mg ca data showed little coherence with temperature during the culture experiment including the rapid 5 c increase in seawater temperature however ba ca ratios showed an inverse relationship with seawater temperatures although this relationship was noisy additionally salinity interactions were present during the 15 00 c treatment further highlighting complex incorporation of elements during biomineralization incorporation of sr mg and ba were strongly and variably impacted by growth rates combined the results from these culture experiments demonstrate that sr ca mg ca ba ca ratios in juvenile a islandica shell material are dominated by physiological processes and thus not reliable as environmental proxies

using the chemical composition of carbonate rocks on mars as a record of secondary interaction with liquid water in the search for habitable environments on mars sites that have been altered by liquid water represent an important target quickly dissolving and precipitating carbonates found in multiple locations on mars represent a key potential mineral indicator of locations with a history of aqueous alteration and therefore possible habitability recent liquid surface water on mars may differ significantly from the fluids either sedimentary hydrothermal or pedogenic that formed carbonate minerals on mars interactions of carbonate rocks with such recent surface water may therefore cause changes in chemistry and mineralogy with depth that form weathering profiles recording the conditions of alteration to test the prediction that martian carbonates may record a signature of aqueous alteration on mars we performed reactive transport modeling of putative carbonate outcrops on mars using the reactive transport code crunchflow model inputs included two parent rocks chosen based on the carbonate rich rock at gusev crater comanche one consisting of 60 magnesite 20 siderite and 20 porosity and one consisting of 50 magnesite 20 siderite 9 calcite 1 6 rhodochrosite and 20 porosity reacting solutions consisted of four scenarios acidic sulfate containing solutions perhaps resulting from an acid vapor scenario dilute solutions resulting from martian analog basalt dissolution concentrated solutions resulting from modeled evaporation of the dilute solutions and solutions based on the results of the phoenix lander modeling was performed under low oxidation and high oxidation conditions based on the modeling results a carbonate rock would become enriched in siderite upon interaction with acidic water under low oxidation conditions the same rock would become enriched in calcite after interaction with ca enriched solutions a carbonate rock reacting under more oxidizing conditions would preferentially dissolve siderite leaving a surface enriched in magnesite and ferric oxide therefore the mg rich carbonates on mars are consistent with possible interaction with liquid water under oxidizing conditions similar to those measured at the phoenix landing site future detailed chemical and mineralogical profiles through weathered rock into the unaltered interior of carbonate rocks may therefore allow the quantitative interpretation of the aqueous history and possible habitability of locations on mars

composition of carbonate overgrowths produced on iceland spar calcite crystals buried in bahamian carbonate rich sediments abstract high magnesium calcite overgrowths were precipitated on iceland spar calcite crystals buried in bahamian sediments their composition was within the range of carbonate cements in this area the precipitation rate of the overgrowths was slower and the magnesium content higher than predicted from laboratory experiments possibly due to adsorption of organic compounds

the significance of chemical isotopic and detrital components in three coeval stalagmites from the superhumid southernmost andes 53 s as high resolution palaeo climate proxies abstract stalagmites are important palaeo climatic archives since their chemical and isotopic signatures have the potential to record high resolution changes in temperature and precipitation over thousands of years we present three u th dated records of stalagmites ma1 ma3 in the superhumid southern andes chile 53 s they grew simultaneously during the last five thousand years ka bp in a cave that developed in schist and granodiorite major and trace elements as well as the c and o isotope compositions of the stalagmites were analysed at high spatial and temporal resolution as proxies for palaeo temperature and palaeo precipitation calibrations are based on data from five years of monitoring the climate and hydrology inside and outside the cave and on data from 100 years of regional weather station records water insoluble elements such as y and hree in the stalagmites indicate the amount of incorporated siliciclastic detritus monitoring shows that the quantity of detritus is controlled by the drip water rate once a threshold level has been exceeded in general drip rate variations of the stalagmites depend on the amount of rainfall however different drip water pathways above each drip location gave rise to individual drip rate levels only one of the three stalagmites ma1 had sufficiently high drip rates to record detrital proxies over its complete length carbonate compatible element contents e g u sr mg which were measured up to sub annual resolution document changes in meteoric precipitation and related drip water dilution in addition these soluble elements are controlled by leaching during weathering of the host rock and soils depending on the ph of acidic pore waters in the peaty soils of the cave s catchment area in general higher rainfall resulted in a lower concentration of these elements and vice versa the mg ca record of stalagmite ma1 was calibrated against meteoric precipitation records for the last 100 years from two regional weather stations carbonate compatible soluble elements show similar patterns in the three stalagmites with generally high values when drip rates and detrital tracers were low and vice versa 13c and 18o values are highly correlated in each stalagmite suggesting a predominantly drip rate dependent kinetic control by evaporation and or outgassing only c and o isotopes from stalagmite ma1 that received the highest drip rates show a good correlation between detrital proxy elements and carbonate compatible elements a temperature related change in rainwater isotope values modified the ma1 record during the little ice age 0 7 0 1 ka bp that was 1 5 c colder than today the isotopic composition of the stalagmites ma2 and ma3 that formed at lower drip rates shows a poor correlation with stalagmite ma1 and all other chemical proxies of ma1 hendy tests indicate that the degassing controlled isotope fractionation of ma2 and ma3 had already started at the cave roof especially when drip rates were low changing pathways and residence times of the seepage water caused a non climatically controlled isotope fractionation which may be generally important in ventilated caves during phases of low drip rates our proxies indicate that the neoglacial cold phases from 3 5 to 2 5 and from 0 7 to 0 1 ka bp were characterised by 30 lower precipitation compared with the medieval warm period from 1 2 to 0 8 ka bp which was extremely humid in this region

mid pliocene deep sea bottom water temperatures based on ostracode mg ca ratios abstract we studied magnesium calcium mg ca ratios in shells of the deep sea ostracode genus krithe from a short interval in the middle pliocene between 3 29 and 2 97 ma using deep sea drilling sites in the north and south atlantic in order to estimate bottom water temperatures bwt during a period of climatic warmth results from dsdp and odp sites 552a 610a 607 658a 659a 661a and 704 for the period ma reveal both depth and latitudinal gradients of mean mg ca values shallower sites 552a 610a and 607 have higher mean mg ca ratios 10 3 9 7 10 1 mmol mol than deeper sites 661a 6 3 mmol mol and high latitude north atlantic sites 552a 610a 607 have higher mg ca ratios than low latitude 658a 9 8 mmol mol 659a 7 7 mmol mol 661a 6 3 mmol mol and southern ocean 704 8 0 mmol mol sites converting mg ca ratios into estimated temperatures using the calibration of dwyer et al 1995 dwyer g s cronin t m baker p a raymo m e buzas j s correge t 1995 north atlantic deepwater temperature change during late pliocene and late quaternary climatic cycles science 270 1347 1351 suggests that mean middle pliocene bottom water temperatures at the study sites in the deep atlantic were about the same as modern temperatures however brief pulses of elevated bwt occurred several times between 3 29 and 2 97 ma in both the north and south atlantic ocean suggesting short term changes in deep ocean circulation

elemental systematics of the calcitic skeleton of corallium rubrum and implications for the mg ca temperature proxy abstract the high mg calcite skeleton of corallium rubrum was analyzed from living colonies collected from a wide range of depths 15 m to 607 m and environmental settings in the mediterranean sea an overarching goal was to better understand the calcification process and incorporation of elements into the slow growing skeleton of both shallow and deep water specimens and more specifically to clarify the veracity of geochemical proxies for reconstructing seawater temperatures the coral internal structure including growth bands were determined by scanning electronic microscopy sem and petrographic techniques trace elements li b mg sr and ba compositions of the coral skeleton were obtained by solution and laser ablation inductively coupled plasma mass spectrometry icp ms results show that the skeleton of the deep water specimens has an internal microstructure similar to shallow water colonies with the medullar and the annular zones clearly distinguishable in both shallow and deep water specimens in general the bands of the deep water samples are very thin and equidistant compared to the irregular banding of the shallow water specimens banding differences relate to the contrasting environmental dynamics with the shallow water specimens being exposed to large seasonal fluctuations compared to the relative stable conditions of those inhabiting bathyal depths the inner medullar and outer annular portions differ in their trace element concentrations mg ca sr ca and li ca ratios are higher in the medullar zone and seem to be influenced by growth kinetics whereas b ca and ba ca are similar in both zones and hence unaffected by growth rate the variability of elemental ratios is lower in the deep water specimens growth bands are highly correlated to mg ca sr ca and li ca suggesting common mechanism s controlling the incorporation of these elements into the coral skeleton mg ca ratios were especially depleted in the dark bands although the mean mg ca of each specimen is positively correlated to ambient seawater temperature the intra annual variations and amplitudes differ and do not correlate to the band widths these findings suggest that intra and inter annual variations of mg ca cannot be used to reconstruct a continuous time series of long term seasonal temperature records however the mean mg ca composition can serve as a valuable proxy to estimate mean palaeoseawater temperature at a given site within the mediterranean

impact of biomineralization processes on the mg content of foraminiferal shells a biological perspective the mg ca ratio in foraminiferal shells is widely used as a proxy for paleotemperatures nevertheless it seems that the basic mg content of foraminifera is determined by biological factors as can be concluded from the large inter species and intrashell variability and the frequent deviations from inorganic behavior this paper discusses three possible ways by which foraminifera can control or modify the mg content in their shell 1 involvement of organic matrix in the precipitation process that may alter the partition coefficient of mg in biogenic calcite 2 controlled conversion of transient amorphous phases to calcite and 3 modification of the mg concentration in the parent solution from which the crystals precipitate the first two mechanisms are probably responsible for the precipitation of high mg calcite phases whole shell or sublayers while the third mechanism leads to the formation of low mg calcite phases we propose a model adapted from epithelial cells that allows massive mg2 removal from the biomineralization site this model is especially relevant to the planktonic and deep benthic low mg foraminifera that are frequently used for paleotemperature reconstructions we discuss the possible biological roles of mg in the shell in terms of the calcite polymorph conservation the in vivo chemical stability of the shell the functions of mg as a stabilizer of transient phases and as a controlling agent of the precipitation process several temperature sensitive biological processes that may influence the mg ca ratio of the shell are suggested and a model that combines biogenic and inorganic considerations is presented the model uses mg heterogeneity in the shell together with temperature response biologic and inorganic of biomineralization processes to account for the deviation of planktonic foraminifera from inorganic calcite at equilibrium with seawater

partitioning of mg sr ba and u into a subaqueous calcite speleothem abstract the trace element geochemistry of speleothems is becoming increasingly used for reconstructing palaeoclimate with a particular emphasis on elements whose concentrations vary according to hydrological conditions at the cave site e g mg sr ba and u an important step in interpreting trace element abundances is understanding the underlying processes of their incorporation this includes quantifying the fractionation between the solution and speleothem carbonate via partition coefficients where the partitioning d of element x dx is the molar ratio x ca in the calcite divided by the molar ratio x ca in the parent water and evaluating the degree of spatial variability across time constant speleothem layers previous studies of how these elements are incorporated into speleothems have focused primarily on stalagmites and their source waters in natural cave settings or have used synthetic solutions under cave analogue laboratory conditions to produce similar dripstones however dripstones are not the only speleothem types capable of yielding useful palaeoclimate information in this study we investigate the incorporation of mg sr ba and u into a subaqueous calcite speleothem cd3 growing in a natural cave pool in italy pool water measurements extending back 15 years reveal a remarkably stable geochemical environment owing to the deep cave setting enabling the calculation of precise solution x ca we determine the trace element variability of modern subaqueous calcite from a drill core taken through cd3 to derive dmg dsr dba and du then compare these with published cave cave analogue and seawater analogue studies the dmg for cd3 is anomalously high 0 042 0 002 compared to previous estimates at similar temperatures 8 c the dsr 0 100 0 007 is similar to previously reported values but data from this study as well as those from tremaine and froelich 2013 and day and henderson 2013 suggest that na sr might play an important role in sr incorporation through the potential for na to outcompete sr for calcite non lattice sites dba in cd3 0 086 0 008 is similar to values derived by day and henderson 2013 under cave analogue conditions whilst du 0 013 0 002 is almost an order of magnitude lower possibly due to the unusually slow speleothem growth rates

origin of cap carbonates an experimental approach abstract an experimental study was carried out to assess the abiotic natural reactions associated with carbonate precipitation leading to the formation of neoproterozoic cap carbonate sequences for this purpose synthetic seawater solutions were prepared reflecting the presumed composition of neoproterozoic seawater these solutions were heated to 40 c undergoing degassing and or evaporation while monitoring their chemical composition sulphate concentration mg ca molar ratio and identifying the precipitated minerals the experimental results are in good agreement with previous studies allowing us to constrain the type of carbonate precipitates formed in the ocean during the snowball earth aftermath among the phases precipitated during heating of the solutions mg bearing carbonate minerals i e mg calcite magnesite and dolomite remain of minor importance compared to ca carbonates especially aragonite consequently the basal dolostone units of the cap carbonates i e cap carbonates s s were originally in the form of caco3 and evolved spontaneously toward dolomite cap carbonates s l i e cap limestones containing aragonitic cement could result from the degassing of the whole ocean and the concomitant precipitation of aragonite the calculated thicknesses of carbonates formed in this way are of the order of several metres in line with the field observations although this process of abiotic carbonate precipitation does not rule out biologically mediated carbonate formation it may represent an alternate route to produce carbonate particularly in environments which are not yet colonized by bacteria after the global ice melting

benthic carbonate factories of the phanerozoic marine carbonate precipitation occurs in three basic modes abiotic or quasi abiotic biotically induced and biotically controlled on a geologic scale these precipitation modes combine to form three carbonate production systems or factories in the benthic environment 1 tropical shallow water factory dominated by biotically controlled mainly photo autotrophic and abiotic precipitates 2 cool water factory dominated by biotically controlled mainly heterotrophic precipitates and 3 mud mound factory dominated by biotically induced mainly microbial and abiotic precipitates sediment accumulations of the factories differ in composition geometry and facies patterns and some of these differences appear prominently in seismic data thus facilitating subsurface prediction the characteristic accumulation of the tropical factory is the flat topped often reef rimmed platform in cool water systems reefs in high energy settings are scarce and hydrodynamic influence dominates producing seaward sloping shelves and deep water sediment drifts often armored by skeletal framework the typical accumulation of the mud mound factory is groups of mounds in deeper water where the mud mound factory expands into shallow water it forms rimmed platforms similar to the tropical factory the tropical factory is most productive the mud mound factory reaches 80 90 and the cool water factory 20 30 of the tropical growth rate the three factories represent end members connected by transitions in space transitions in time are linked to biotic evolution

temperature control on the incorporation of magnesium strontium fluorine and cadmium into benthic foraminiferal shells from little bahama bank prospects for thermocline paleoceanography surface sediments from little bahama bank lbb intersecting the subtropical thermocline were used to assess the influence of temperature on the incorporation of mg sr f and cd into shells of benthic foraminifera samples were obtained from twelve cores along the southern slope of lbb covering a temperature range of 18 4 5 c between 301 and 1585 m we studied the composition of ten calcitic and one aragonitic species which are often used in paleochemical reconstructions mg ca ratios decrease with increasing water depth in all benthic species both with calcitic and aragonitic mineralogy showing a strong correlation with water temperature similar decrease is seen in sr ca but with no correlation with temperature none of the benthic species studied here exhibits a depth or temperature related change in f ca similar trends are observed when using an ocean wide dataset which includes shallow and deep core tops 300 5000 m we suggest that temperature is the primary control on the mg content of benthic foraminifera based on inorganic precipitation experiments and thermodynamic considerations presented here a 30 40 decrease in the mg distribution coefficient in calcite may be expected as a result of a temperature change from 25 c to 5 c which is about half the observed change in lbb a calibration curve applied to c pachyderma data from core tops along the slope of little bahama bank suggests that water temperature may be inferred from mg ca ratios with an uncertainty of about 0 8 c therefore the mg content of benthic foraminifera may provide a new independent temperature proxy for studying shallow waters paleoceanography the linear decrease in sr ca with increasing depth is not correlated with temperature the trend is constant from the ocean surface down to 5 km suggesting that pressure related effects on the calcification process are a more likely explanation than post depositional dissolution mg ca ratios in aragonitic shells of h elegans covary with temperature in accord with recent observations from corals in contrast the sr and f chemistry of h elegans is very different than that of corals and inorganically precipitated aragonites the disparities between the elemental composition of biogenic and inorganic phases and the large intergeneric and interspecific differences observed both in planktonic and benthic foraminifera implicate temperature related physiological processes in regulating the coprecipitation of elements in foraminiferal shells our work demonstrates that cd ca ratios of shallow calcitic species reflect the vertical distribution of nutrients no significant influence of temperature on the partitioning of cd into the shells was found our data extend the previous deep water calibration boyle 1992 thereby allowing for the reconstruction of the nutrient chemistry of shallow thermocline waters

biogeochemical controls on palaeoceanographic environmental proxies a review scientific observations of our oceans and climate go back no more than a couple of hundred years most of our information about the evolution of earth s ocean climate system relies instead on proxies primarily measurements of sediment components that respond to changes in environmental parameters this paper provides an overview of some of the most important biological and geochemical proxies and outlines their contribution to our understanding of the ocean climate system we also discuss some of the challenges that need to be overcome to obtain accurate records these include better understanding of the controls on the mechanisms of biomineralization the impacts of post depositional dissolution and diagenesis on primary proxy relationships proxy validation and analytical considerations

influence of temperature on the composition of magnesian calcite overgrowths precipitated from seawater a constant disequilibrium technique was used to determine the composition of magnesian calcite overgrowths precipitated on pure calcite seeds from artificial seawater at 5 25 and 40 c the amount of magnesium incorporated in the overgrowths at a given temperature is independent of the precipitation rate over a wide range of saturation states and is believed to correspond to a composition in true equilibrium with seawater the distribution coefficient of magnesium dmg2 c in the magnesian calcite overgrowths increases almost linearly with temperature being 0 0121 0 0013 at 5 c 0 0172 0 0022 at 25 c and 0 0271 0 0013 at 40 c these values apply only to magnesian calcites precipitated from standard composition seawater since a previous study has shown dmg2 c to be a function of the mg2 ca2 ratio in the parent solution results of this study are compared with values reported previously by other workers and with the compositional distribution of naturally occurring magnesian calcite cements and ooids found in seawater it appears that variations in temperature are not sufficient to account for the compositional variability of naturally occurring inorganic marine magnesian calcite cements

error propagation for velocity and shear stress prediction using 2d models for environmental management pasternack g b gilbert a t wheaton j m buckland e m 2006 error propagation for velocity and shear stress prediction using 2d models for environmental management journal of hydrology 328 1 2 227 241 sponsorship us fish and wildlife service contracting entity for calfed bay delta ecosystem restoration program cooperative agreement dcn 113322g003