oxygen isotope signatures from land snail helix melanostoma shells and body fluid proxies for reconstructing mediterranean and north african rainfall abstract in this paper we show that oxygen isotope ratios from the shell carbonate of the land snail helix melanostoma reflect local rainfall parameters stable oxygen isotopes were measured in the body fluid 18 o body and shells 18 o shell of live collected h melanostoma along a north south transect across the gebel akhdar in northeast libya 18 o body ranged between 8 1 and 13 0 whilst 18 o shell ranged between 1 0 and 2 8 to investigate the relationship between snail oxygen isotope composition and climate these measurements were correlated with ambient air temperature relative humidity rainfall amount and the 18 o composition of rainwater 18 o rain strong and significant correlations were found between 18 o shell and 18 o rain and between 18 o shell and rainfall amount r 2 0 79 and 0 85 respectively suggesting that h melanostoma shells can be used as a proxy for past rainfall conditions when combined in multiple linear regressions 18 o rain and rainfall amount explained 90 of the variance in 18 o shell r 2 0 90 simple and multiple linear regressions were used to develop predictive models for these climate parameters as h melanostoma shells are commonly found in mediterranean and north african archaeological and geological deposits the predictive equations developed in this study hold great potential for reconstructing pleistocene to holocene rainfall and aridity patterns in the gebel akhdar and for assessing the relationship between environmental changes and human behavioural changes

the eurogeul first report of the palaeontological palynological and archaeological investigations of this part of the north sea abstract the eurogeul is the shipping lane gully in front of rotterdam harbour due to the combination of suction dredging and fishing activities diverse faunae are found on its bottom this paper briefly describes the fauna consisting of 13 terrestrial mammals and six marine mammal species radiocarbon dating gave two time periods from which the bones originate ca 37 500 48 500 bp and ca 7 8000 bp pollen sampling gave similar results respectively an interstadial before the last glacial maximum and the early holocene boreal period human artefacts dating from the boreal period add to our understanding of the quaternary history of the southern north sea area

calibration of shell δ18o from the common whelk buccinum undatum highlights potential for palaeoenvironmental reconstruction abstract the common whelk buccinum undatum is a commercially important gastropod found throughout the north atlantic one method of age and life history analysis for gastropod species is the use of oxygen isotope ratio 18o measurements from their shells which is a well established technique for the reconstruction of historical seawater temperatures at the time of shell biomineralization palaeotemperature calibrations have been developed for different types of calcium carbonate as well as species specific equations to produce the most accurate seawater temperature reconstructions here we investigate the four layer internal structure of b undatum shells and confirm an aragonite composition using micro raman spectroscopy mrs we then calibrate a species specific palaeotemperature equation for this gastropod species this was achieved through the isotopic analysis of shells from laboratory reared specimens of known provenance reared at specific seawater temperatures to produce the following t c 14 96 0 15 4 94 0 22 x 18oshell 18owater the calibrated equation differs significantly from previously published data derived from both aragonite and calcite an offset of 1 04 0 41 was discovered between observed 18oshell values and those expected under equilibrium suggesting a species specific vital effect the calibrated equation was used to reconstruct accurate high resolution historical seawater temperatures from three sites across the u k shetland the menai strait and jersey with this new accurate calibration both modern and fossil b undatum shells now have the potential to be employed as high resolution archives of recent and historical seawater temperature

comparative sclerochronology of modern and mid pliocene c 3 5 ma aequipecten opercularis mollusca bivalvia an insight into past and future climate change in the north east atlantic region records of environment contained within the accretionarily deposited tissues of fossil organisms afford a means of detailed reconstruction of past climates and hence of rigorous testing of numerical climate models we identify the environmental factors controlling oxygen and carbon stable isotopic composition and microgrowth increment size in the shell of modern examples of the queen scallop aequipecten opercularis this understanding is then applied in interpretation of data from mid pliocene a opercularis from eastern england on the basis of oxygen isotope evidence we conclude that winter minimum seafloor temperature was similar to present values typically 6 7 c in the adjacent southern north sea and that summer maximum seafloor temperature was a few degrees lower than present values typically 16 17 c this contrasts with evidence from other proxies that winter and summer temperatures were higher than present the pattern of seasonal variation in microgrowth increment size suggests the existence of intense thermal stratification in summer we therefore conclude that summer surface temperatures were much higher maxima well over 20 c than those recorded isotopically on the seafloor and that the annual range of surface temperature probably over 14 c was greater than now at the times in the mid pliocene when the investigated a opercularis were alive taken in conjunction with other proxy evidence of warmer winters as well as summers the data point to substantial fluctuation up to 10 c in winter minimum temperatures during the mid pliocene in the north east atlantic region this fluctuation may be attributable to variation in the strength of the gulf stream north atlantic drift since the pliocene has been widely used as a test bed for numerical models of a greenhouse earth the results have implications for prediction of future climate in the north east atlantic region under the influence of anthropogenic global warming

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

oxygen isotopes from phorcus osilinus turbinatus shells as a proxy for sea surface temperature in the central mediterranean a case study from malta abstract the marine topshell phorcus osilinus turbinatus is a common component of many archaeological sites in the mediterranean this species has been successfully used as a palaeoclimate proxy in italy to test whether 18 o from p turbinatus shells can serve as a reliable palaeoclimate archive for other regions of the mediterranean we collected live p turbinatus from the northeast coast of malta each month for a year the 18 o shell values of the outermost growth increments of these live collected shells ranged between 0 4 and 2 4 these values correspond to growing temperatures calculated from shell edge 18 o of between 15 c and 27 c calculated shell edge sea surface temperatures are highly correlated with instrumental records of sea surface temperature recorded over the period of collection the individuals analysed for this study are smaller than p turbinatus from populations studied elsewhere in the mediterranean nonetheless 18 o shell provides a robust record of sea surface temperatures suggesting that smaller younger shells in archaeological deposits can still provide reliable palaeothermometry records this study extends the upper growth limit p turbinatus by 2 c compared with the previous studies of p turbinatus in the mediterranean and suggests that contrary to the previous studies growth shutdown does not occur in all p turbinatus when sea surface temperatures exceed 25 c this may reflect the higher sample resolution that can be obtained from smaller faster growing shells or it may reflect actual higher growth tolerances of p turbinatus populations in malta by showing that p turbinatus precipitate their shells in 18 o equilibrium with surrounding sea water this study reinforces the potential for the stable isotope chemistry of p turbinatus shells preserved in mediterranean archaeological sites to provide a window into the climate and seasonality regimes of the past

oxygen isotope fractionation in marine aragonite of coralline sponges oxygen isotope values of the extant caribbean coralline sponge ceratoporella nicholsoni are compared with published temperatures and 18o of water calculated from salinities the measured values from aragonitic sponge skeletons have a mean offset of 1 0 0 1 from calculated calcite equilibrium values aragonite calcite 1 0010 this is in good agreement with published values from synthetic aragonite they further agree with published near equilibrium oxygen isotope values of temperate and cold water molluscs and foraminifera extrapolated to the temperature range of the coralline sponges these results and the mode of skeleton formation of ceratoporella nicholsoni suggest that these sponges precipitate aragonite close to isotopic equilibrium the temperature dependence of oxygen isotopic fractionation between the aragonite of ceratoporella nicholsoni and water is only roughly constrained by the available data due to the narrow temperature range of the caribbean reef sites however as the data suggest oxygen isotopic equilibrium we can calculate a well constrained temperature equation combining temperate and cold water equilibrium values from molluscs and foraminifera with our sponge data full size image 1 k and full size image 1 k

mitigation of groundwater level deterioration of the nubian sandstone aquifer in farafra oasis western desert egypt el farafra oasis is included in the new valley project which started in the 1960s this project is based exclusively on groundwater of the well known nubian sandstone aquifer nsa the hydraulic head drawdown problem in farafra oasis constitutes a big problem because it threatens the availability of the only water source in the oasis hydrogeologically farafra oasis belongs to the huge artesian unrenewable fossil water nubian from sandstone aquifer the problem began to appear at the end of the 1990s instantaneously with increased drilling of deep water wells huge quantities of water 267 million m3 are derived from the aquifer every year hydraulic head depression cones are formed around the main reclamation areas where the groundwater surface lowered by 35 m below the ground surface numerical modeling was used to investigate the hydrodynamic impacts of the present and planned groundwater extraction on the groundwater levels besides the possible means of mitigating the continuous decrease of the groundwater levels the aquifer simulation indicated that there is a significant head decline of the groundwater particularly in the first productive zone four scenarios were applied to signify the present and future development plans for the next 20 years i e year 2033 applying the present conditions reveal that heads are more declined than now another 30 and 17 8 m in the first and second productive zones respectively are expected to be added to the present groundwater drawdowns groundwater is expected to decline significantly if the pumping rates are to be increased by 50 in response to natural development of the agricultural society and continuous need to more cultivation lands groundwater heads are expected to be lower by about 40 m in the first productive zone and 24 m in the second productive zone the third plan examines the impact of reducing the pumping rate by about 25 on groundwater levels by applying recent irrigation techniques as drop and sprinkler irrigation methods instead of the presently used flood irrigation in this case simulated drawdowns are expected to decline and the maximum drawdowns recorded are 19 and 10 m through the next 20 years in the first and second productive zones respectively to mitigate the groundwater level deterioration the study suggests the reduction of pumping rates by about 20 by applying the recent irrigation techniques besides reclamation of about 11 000 feddan 4620 hectare to accommodate the increasing population and need of cultivation lands in the oasis in the next 20 years according to plan the simulated groundwater levels are expected to decrease by about 20 3 and 12 m at the end of the simulation period year 2033 this means that the rate of head decline is lowered to about 1 m year for the first productive zone and 0 6 m year for the second productive zone with the increase in the cultivation area by about 16 therefore the study recommends the fourth plan to manage the groundwater resource in farafra oasis

using species specific paleotemperature equations with foraminifera a case study in the southern california bight abstract species specific paleotemperature equations were used to reconstruct a record of temperature from foraminiferal 18 o values over the last 25 kyr in the southern california bight the equations yield similar temperatures for the 18 o values of globigerina bulloides and neogloboquadrina pachyderma in contrast applying a single paleotemperature equation to g bulloides and n pachyderma 18 o yields different temperatures which has been used to suggest that these species record the surface to thermocline temperature gradient in santa barbara basin an isotopically distinct morphotype of g bulloides dominates during glacial intervals and yields temperatures that appear too cold when using a paleotemperature equation calibrated for the morphotype common today when a more appropriate paleotemperature equation is used for glacial g bulloides we obtain more realistic glacial temperatures glacial interglacial temperature differences g i t calculated in the present study indicate significant cooling 8 10 c throughout the southern california bight during the last glacial maximum lgm the magnitude of glacial cooling varies from 8 c near the middle of the southern california bight tanner basin and san nicolas basin to 9 c in the north santa barbara basin and 9 5 10 c in the south velero basin and no name basin our temperature calculations agree well with previous estimates based on the modern analog technique in contrast studies using n pachyderma coiling ratios u k 37 indices and transfer functions estimate considerably warmer lgm temperatures and smaller g i t

an overview of biomineralization processes and the problem of the vital effect biomineralization links soft organic tissues which are compositionally akin to the atmosphere and oceans with the hard materials of the solid earth it provides organisms with skeletons and shells while they are alive and when they die these are deposited as sediment in environments from river plains to the deep ocean floor it is also these hard resistant products of life which are mainly responsible for the earth s fossil record consequently biomineralization involves biologists chemists and geologists in interdisciplinary studies at one of the interfaces between earth and life leadbeater and riding 1986 biomineralization refers to the processes by which organisms form minerals the control exerted by many organisms over mineral formation distinguishes these processes from abiotic mineralization the latter was the primary focus of earth scientists over the last century but the emergence of biogeochemistry and the urgency of understanding the past and future evolution of the earth are moving biological mineralization to the forefront of various fields of science including the earth sciences the growth in biogeochemistry has led to a number of new exciting research areas where the distinctions between the biological chemical and earth sciences disciplines melt away of the wonderful topics that are receiving renewed attention the study of biomineral formation is perhaps the most fascinating truly at the interface of earth and life biomineralization is a discipline that is certain to see major advancements as a new generation of scientists brings cross disciplinary training and new experimental and computational methods to the most daunting problems it is however by no means a new field the first book on biomineralization was published in 1924 in german by w j schmidt schmidt 1924 and the subject has continued to intrigue a dedicated community of scientists for many years until the early 1980s the field was known as

comparison of species specific oxygen isotope paleotemperature equations sensitivity analysis using planktonic foraminifera from the cariaco basin venezuela abstract the oxygen isotope compositions of seven species of planktonic foraminifera globigerinoides ruber pink globigerina bulloides globorotalia menardii globigerinoides sacculifer orbulina universa globorotalia crassaformis and neogloboquadrina dutertrei were measured from biweekly sediment trap samples collected in cariaco basin venezuela between 2003 and 2008 sixteen published paleotemperature equations were used to estimate calcification temperatures from this 18 o data as part of the cariaco time series routine in situ water column chemistry measurements and hydrographic monitoring has occurred since 1995 the calcification temperature estimates were compared with these monthly water column temperature measurements to ascertain species depth habitats and to determine which equations yielded the most realistic temperature estimates no single equation provided accurate temperature estimates for all species rather the equations yielded temperature estimates that varied by 2 4 c for each species overall species specific paleotemperature equations based on plankton tow samples yield the coldest temperature estimates while generic equations produce the warmest temperatures our results indicate that when using planktonic foraminiferal 18 o to make paleotemperature estimates equations must be carefully selected on a species by species basis here we provide general guidelines for selecting paleotemperature equations we also evaluated how well the 18 o difference between the surface dwelling g ruber and the deeper dwelling n dutertrei estimates the surface to thermocline temperature gradient the 18 o is small 0 61 during winter due to upwelling and increases 1 37 during summer as upwelling ceases and surface waters become thermally stratified

preliminary evaluation of potential stable isotope and trace element productivity proxies in the oyster crassostrea gigas abstract as most bivalve mollusks are filter feeders or deposit feeders predatory septibranchs poromyacea being the notable exception they are closely linked with the activity of primary producers perhaps this is nowhere more evident than in shallow water habitats influenced by seasonal phytoplankton blooms in these systems photoautotrophs are capable of changing the physical and chemical properties of the water column in turn clams ingest large quantities of phytoplankton and precipitate their shells in these chemically altered waters thus clam shells likely archive valuable information about phytoplankton dynamics in shallow water habitats to better understand this relationship we investigated geochemical records from two potential productivity proxy systems archived in shells of the oyster crassostrea gigas that live in the san francisco bay estuary california usa here we present multi year records of shell carbon isotope 13ccarb and barium calcium ba cacarb variation these archives are compared with records of environmental variation using oxygen isotopes 18ocarb as a temporal marker we also present high resolution 13ccarb 18ocarb and ba ca profiles associated with the 2003 spring phytoplankton bloom our results suggest that the prominent positive 13ccarb excursion present in shell material deposited in the spring of 2003 most likely reflects photosynthetic enrichment of the dissolved inorganic carbon pool calibration of stable isotopes with calculated chlorophyll a concentrations measured during the bloom suggests that our 13ccarb sample variation reflects phytoplankton abundance with 3 to 4 day resolution these findings highlight the potential utility of stable isotope records as tools for reconstructing patterns of primary productivity elevated ba ca values are recorded each year in the spring thus like stable isotope profiles ba ca profiles from these specimens demarcate individual years of shell growth and establish ontogenetic age low and high resolution ba ca profiles do not however correlate with the 2003 spring phytoplankton bloom casting doubt on the relationship between ba ca ratios and phytoplankton blooms although the ba ca peak timing loosely correlates with freshwater discharge events peak amplitude does not leaving the environmental cause trigger of these peaks unknown nevertheless the san francisco bay estuary seems like an ideal environment in which to further investigate the relationship between skeletal geochemical variation and patterns of primary productivity

inter site variability in the season of shellfish collection on the central coast of british columbia high resolution stable oxygen isotope analysis of the bivalve saxidomus gigantea from shell midden sites was applied to identify seasonal patterns of resource procurement on the central coast of british columbia canada a total of 90 archaeological shells were examined from eight distinct sites spanning a 4500 year period combining micro growth pattern analysis with high resolution stable oxygen isotope sampling allows for a precise season of collection to be determined in estuarine bivalves recovered from archaeological sites the results of the stable oxygen isotope analysis provide insights into seasonally structured harvest of s gigantea butter clam which is associated with different types of sites the results show a variety of patterns including multi seasonal collection intensive seasonal harvesting and casual supplemental use of butter clams at different locations

sclerochronology and geochemical variation in limpet shells patella vulgata a new archive to reconstruct coastal sea surface temperature 1 climate archives contained in shells of the european limpet patella vulgata accumulated in archaeological deposits can potentially provide much needed information about holocene environmental change in midlatitude coastal areas before reconstructing climate information preserved in these zooarchaeological records we studied the controls on oxygen and carbon isotope ratios 18o and 13c respectively in modern specimens we tested the hypothesis that p vulgata precipitates its shell in isotopic equilibrium with the ambient water by comparing 18oshell with predicted values predicted 18oshell was constructed using observed sea surface temperature sst records and the equilibrium fractionation equation for calcite and water we assumed a constant 18owater value of 0 10 vsmow based on published regional measurements comparison of 18oshell with predicted values revealed that 18oshell values were higher than expected by 1 01 0 21 consequently estimated sst calculated from 18oshell was 4 2 2 3 c lower than observed sst however because of the relatively uniform offset between observed and expected 18o an adjustment can be made to account for this predictable vital effect thus past climate can be reliably reconstructed using this temperature proxy once the offset is taken into account 13c values have a similar cyclicity to the 18o variation and therefore vary seasonally however 13c is slightly out of phase relative to 18o an overall negative shift in 13cshell over the lifetime of the individual indicates a vital effect associated with ontogeny further study of environmental and ecological factors that influence shell 13c is required to evaluate fully the potential of carbon isotope ratios as a useful environmental proxy

stable isotope vital effects in coccolith calcite uncertainties about the origin of the many disequilibrium or vital effects in a variety of calcifying organisms and whether these effects are constant or variable have hampered paleoceanographic application of carbon and oxygen isotopic ratios unraveling the source of these effects will improve paleoceanographic applications and may provide new information on changes in cell physiology and ecology culture of eight species of coccolithophorids a dominant marine phytoplankton group reveals a 5 array of disequilibrium or vital effects in both the carbon and oxygen isotopic composition of coccolith calcite in moderate light and nutrient replete cultures oxygen isotopic fractionation and carbon isotopic fractionation correlates directly with cell division rates and correlates inversely with cell size across a range of species however when growth rates of a single species are increased or decreased by higher or lower light levels 18o is relatively invariant likewise growth rate variations as a function of temperature do not influence coccolith 18o the slope of the 18o vs temperature relation in cultures of both gephyrocapsa oceanica and helicosphaera carteri is the same as for abiogenic carbonates this suggests a constant species specific isotopic fractionation which does not vary with cell physiology the constancy of vital effects suggests that coccolith stable isotopes will provide reliable phase for paleoceanographic reconstruction of temperature and seawater chemistry as long as monospecific fractions are analyzed or changes in nannofossil assemblages are accounted for with species specific correction factors we suspect that the cell size and its constraints on the rate of co2 diffusion relative to c fixation may be the first order influence on coccolith stable isotope vital effects a quantitative model of this process may provide important constraints on mechanisms of carbon acquisition of coccolithophorids in both modern and extinct species

palaeoenvironmental reconstructions by stable isotopes of middle miocene gastropods of the central paratethys abstract the stable isotopes of carbon and oxygen were used to provide information of mixing of marine and freshwater and subsequently used to determine palaeosalinities in the middle to late miocene st margarethen zollhaus section upper sarmatian mactra zone pannonian a succession of three gastropod assemblages indicates changing environmental conditions from a limnic fluviatile to littoral mudflat and a sublittoral marine environment several shells of the main representatives of the three assemblages potamides hartbergensis hilber granulolabium bicinctum brocchi potamides disjunctus sowerby and additionally shells of lymnaea sp a typical freshwater gastropod and pomatias conicus a terrestrial gastropod were taken for stable isotope analyses oxygen and carbon isotope data of the freshwater endmember are distinctively lower 18 o 4 5 13 c 9 than of the marine endmembers 18 o 2 2 13 c 2 3 in contrast to the expected intermediate isotopic composition between the freshwater and marine environment the shells of supposed brackish environments have higher 18 o values than the shells of the marine environment these higher 18 o values are explained by evaporation which affected the protected areas of riverine to lacustrine environments and small pools on mudflats formerly considered to be the habitats of the brackish assemblages thus the oxygen and carbon isotope data extend the already existing palaeoenvironmental information

shell midden sclerochronology abstract sclerochronological analysis of shell midden faunal remains offers a unique opportunity to study climate and environmental change in relation to human activity middens exist near most aquatic habitats almost worldwide for much of the late pleistocene and holocene they afford good preservation of accretionary calcium carbonate remains such as mollusk shells and fish otoliths in comparatively well dated contexts as such midden samples are a source of sequential proxy records of past climate and environmental conditions and may provide detailed pictures of human environment interaction however midden samples present several challenges to the development and application of sclerochronological proxies including unique taphonomic concerns here these challenges are outlined within descriptions of the major applications of midden sclerochronology archeological concerns including season of capture reconstructing the history of anthropogenic environmental impacts and paleoclimate environment proxy reconstructions

instrumental seismicity of central idaho hypocenters of regionally recorded earthquakes that occurred in central idaho from 1944 through october 1985 have been recomputed with travel times calibrated by locally recorded aftershocks of the borah peak idaho earthquake of 1983 the effect of the relocation is to define more sharply the sizes and relative positions of seismic source zones in central idaho and to move epicenters systematically south often by more than 10 km from their previously cataloged positions the distribution of epicenters of the borah peak main shock and early aftershocks suggests that the fault segment that ruptured in the main shock was approximately a parallelogram with one pair of sides parallel to the zone of surface fault scarps associated with the earthquake and with the other pair of sides parallel to the slip vector of the earthquake such a rupture shape would be expected on geometrical grounds if the 1983 rupture zone were terminated on the north and south by intersection with adjacent segments of the lost river fault that have the same slip vector as the 1983 rupture epicenters of earthquakes occurring before 1983 define a seismic zone the white cloud peaks zone that is approximately parallel to the borah peak aftershock zone but situated from 30 to 40 km to the west the relocated epicenters may also be interpreted as defining a north northeast trending seismic zone near seafoam and a north northeast trending seismic zone that is situated north and west of challis here called the twin peaks myers cove zone the seafoam zone includes the epicenter of the largest instrumentally recorded central idaho earthquake prior to the borah peak earthquake the magnitude 6 1 shock of 12 july 1944 the region within 25 km of the epicenter of the borah peak main shock was quiescent for at least two decades before the main shock for magnitudes mb lg of 3 5 and greater

strontium to calcium ratios in the marine gastropod conus ermineus growth rate effects and temperature calibration here we investigate the potential of sr ca ratios in the marine gastropod conus ermineus for reconstructing seawater temperatures we present annually resolved records of sr ca and 18o for four shells collected alive from the flower garden banks national marine sanctuary in the gulf of mexico our results show that variations in sr ca and 18o covary with the in situ seasonal temperature cycle sr ca and temperature are positively correlated in contrast with the inverse relationship found in inorganically precipitated aragonite the seasonal sr ca variability is superimposed on a long term trend of increasing sr ca with age both the seasonal and long term ontogenetic changes in sr ca are associated with variations in growth rate defined here as the shell linear extension rate ler the seasonal variability in ler is superimposed on a long term decrease with ontogeny thus the covariance of sr ca ratios with temperature and ler suggests that sr incorporation is likely driven by temperature influence on growth rate rather than by thermodynamic effects unlike the seasonal variability the ontogenetic effect is characterized by inverse covariation between sr ca and ler suggesting that sr ca variability is not controlled by growth rate alone but probably by two different biomineralization mechanisms one related to temperature and the other related to age we use the seasonal sr ca signal of four shells to construct a temperature calibration to minimize the ontogenetic effects we separate the records into juvenile and adult growth stages and calculate the sr ca temperature t relationships juvenile sr ca mmol mol 1 0 042 0 008 t c 0 24 0 21 r2 0 66 adult sr ca mmol mol 1 0 072 0 014 t c 0 05 0 34 r2 0 68 applying the calibration to a single specimen provides mean annual temperature estimates within 1 c of the in situ temperature record but resolves the seasonal variability only within 3 5 c the large error in the seasonal estimates reflects the high variability among specimens to reduce the uncertainty on seasonal temperatures we propose combining records from multiple shells to generate an average temperature record the potential of this approach needs however to be validated in other locations

an explanation of the effect of seawater carbonate concentration on foraminiferal oxygen isotopes abstract stable oxygen isotope ratios of foraminiferal calcite are widely used in paleoceanography to provide a chronology of temperature changes during ocean history it was recently demonstrated that the stable oxygen isotope ratios in planktonic foraminifera are affected by changes of the seawater chemistry carbonate system the 18 o of the foraminiferal calcite decreases with increasing co 3 2 concentration or p h this paper provides a simple explanation for seawater chemistry dependent stable oxygen isotope variations in the planktonic foraminifera orbulina universa which is derived from oxygen isotope partitioning during inorganic precipitation the oxygen isotope fractionation between water and the dissolved carbonate species s h 2 co 3 hco 3 co 3 2 decreases with increasing p h provided that calcium carbonate is formed from a mixture of the carbonate species in proportion to their relative contribution to s the oxygen isotopic composition of caco 3 also decreases with increasing p h the slope of shell 18 o vs co 3 2 of orbulina universa observed in culture experiments is 0 0022 mol kg 1 1 spero et al 1997 whereas the slope derived from inorganic precipitation is 0 0024 mol kg 1 the theory also provides an explanation of the nonequilibrium fractionation effects in synthetic carbonates described by kim and o neil 1997 which can be understood in terms of equilibrium fractionation at different p h the results presented here emphasize that the oxygen isotope fractionation between calcium carbonate and water does not only depend on the temperature but also on the p h of the solution from which it is formed