trace element chemistry of non marine ostracods as a means of palaeolimnological reconstruction an example from the quaternary of kashmir northern india abstract recent work has demonstrated the use of sr ca and mg ca ratios in the calcite of ostracod shells for reconstructing the palaeosalinity and palaeotemperature of lakes in this study the technique was applied to a lacustrine sequence of late quaternary age the upper karewa formation in kashmir northwest himalaya ostracods are the only fossils found in abundance in the upper karewa sediments and are thus important for the reconstruction of upper karewa palaeoenvironments trace element analyses of multiple shell samples of the ostracod ilyocypris bradyi sars 1890 were performed using inductively coupled plasma atomic emission spectrometry the results show that the palaeo lake was even more dilute than the modern residual lakes in kashmir reconstructed molar sr ca ratios for the palaeo lake waters vary between 30 10 4 and 42 10 4 compared with observed values of 46 110 10 4 for the modern residual lakes changes in the molar mg ca ratios with unchanging sr ca are attributed to variations in water temperature the palaeo lake probably receded from the study site at between 116 and 80 ka and lacustrine sedimentation gave way to subaerial loess deposition the lack of any increasing trend in the reconstructed sr ca values together with structural and sedimentological evidence suggests that the lake was drained by tectonic tilting or warping of the basin floor rather than by climatically induced desiccation

biological remains geochemistry and stable isotopes for the reconstruction of environmental and hydrological changes in the holocene lakes from north sahara abstract a detailed reconstruction of the holocene palaeoenvironments and palaeohydrology is presented for wwamp and lacustrine calcareous sediments which lie in closed depressions along the northern margin of the great western erg algeria it is based on a multidisciplinary approach using numerous techniques the chronological framework is established on the basis of 23 14 c dates on inorganic calcite and mollusc shells ranging from ca 9300 to 3000 yr b p and on an isolated 14 c age of ca 10 900 yr b p the significance of various environmental markers is discussed biological remains are abundant and diversified about 150 taxa including diatoms chrysophytes charophytes ostracods molluscs and foraminifera they provide information on the water chemistry total salinity ionic ratio ph and partial pressure of carbon dioxide and on the habitats water depth development of aquatic plants ephemerality etc emphasis is given to the total salinity individual organisms and palaeobiological assemblages are ordered as a function of their salt requirements and tolerances calibration based on modern diatom samples allows a tentative estimate of the palaeosalinities which range from fresh to marine like and even hypersaline waters attention is drawn to the possible colonization of marine organisms in continental basins without any connection with the sea stable isotope analyses have been carried out on both inorganic and biogenic mollusc and ostracod shells charophyte gyronites carbonates the 18 o contents demonstrate wide changes in the hydrological balance fluctuations in 13 c contents inform on water mixing residence time and on the importance of biological effects on total dissolved inorganic carbon geochemical analyses were performed on inorganic calcite and on ostracod shells high contents in fe and mn indicate reducing environments during stages of high salinity sr ca and mg ca are used as salinity indicators zn mg ratios suggest that the major water supply was the aquifer of the great western erg today down to about 50 m rather than surface waters from the atlas mountains salinities resulted from the balance between inputs from the water table evaporation rate leaching of pre existing salt crusts and seepage through the lake bottom a reconstruction of the evolution of the palaeosystems through time and space has been attempted with special attention to the instability of the water and ionic balances for different time scales short term fluctuations occurring during a single hydrological cycle annual or seasonal are deduced from the apparent discrepancies between the various indicators found in a given sample long term 10 2 10 3 years changes confirm the existence of a climatic phase being wetter than today from at least ca 9300 and may be from ca 10 900 yr b p to 3000 yr b p for the first time the salinity deduced from diatoms and the 18 o content of the water deduced from that of the carbonate at 25 c are used simultaneously to model the hydrological history of the basins and to estimate the relative humidity of the atmosphere during the holocene major environmental trends recorded from ca 9300 to 3000 yr b p do not show a clear synchronims between the different profiles studied therefore they cannot be interpreted in terms of palaeoclimate but instead demonstrate the importance of local hydrology in the evolution of closed basins associated with groundwater a common situation in arid and semi arid zones

catastrophic debris avalanche deposit of socompa volcano northern chile between 10 000 and 500 yr ago the socompa volcano in northern chile experienced a catastrophic collapse of a 70 deg sector of the original cone causing a debris avalanche that descended nearly 3000 m vertically and traveled more than 35 km from the volcano the deposits cover some 490 sq km and have a minimum volume of 15 cu km parts of the original cone slumped in a nearly coherent form and are now preserved as large blocks more than 400 m high the primary avalanche traveled northwestward over sloping ground before coming to rest transiently forming a prominent marginal ridge and then slid away northeastward to form a secondary flow overriding much of the primary avalanche deposit abundant prismatic jointed dacite blocks within the debris avalanche deposit and a thin fine grained pumiceous deposit beneath it suggest that the collapse was triggered by magmatic activity and may have been accompanied by a violent lateral blast collapse was followed by eruption of pumiceous pyroclastic flows and extrusion of voluminous dacite domes

non linear variation with salinity of sr ca and mg ca ratios in water and aragonitic bivalve shells and implications for paleosalinity studies abstract fresh water and sea water usually differ considerably in their sr ca and mg ca ratios this suggests that these ratios in fossil shells could be used to determine paleosalinities calculation of the sr ca and mg ca ratios in mixtures of sea water and average fresh water using a mixing equation shows that the ratios first increase rapidly with salinity to about 100 but subsequently remain nearly constant the source of most of the ca sr and mg in mixtures of fresh and sea water is the sea water thus except at low salinities the trace element to ca ratio of mixtures differs little from that in sea water analysis both of waters across a spectrum of salinities and of aragonitic mollusc shells growing in water of various salinities conforms to the predicted pattern however trace element to ca ratios offer potential for paleosalinity determination in waters of salinity below about 100

sr ca mg ca ratios and sr and stable isotopes of biogenic carbonates from the late miocene velona basin central apennines italy provide evidence of unusual non marine messinian conditions abstract the sr ca and mg ca ratios of fossil ostracod and mollusc shells from a late miocene early messinian lacustrine sequence in the velona basin central apennines italy were used to calculate the sr ca and mg ca of waters in which these taxa lived sr ca of these waters were always higher than the sr ca calculated for the messinian seawater despite the broad salinity ranges fresh water oligo mesohaline inferred from the paleontological analyses the estimated mg ca water from the velona samples are below the mg ca value for coeval seawater even though they represent relatively high values when compared with many non marine waters the salinity variations of the velona lacustrine system recorded by changes in faunal assemblages are linked to variable inputs of na cl from deep groundwaters and are not reflected in significant changes in sr ca and mg ca of the waters calculated from shell chemistry the combination of 18 o signatures and sr isotopic ratios from molluscs from the velona basin suggests a non marine environment during some episodes of the lake history given the saline inputs the waters in the lake would attain a large solute concentration oligo to mesohaline although they retained the meteoric 18 o signature we compare the paleohydrochemical inferences from the studied sequence with other messinian records and we show the importance of combining paleoecological and geochemical proxies to obtain consistent paleoenvironmental reconstructions

the strontium magnesium and sodium composition of recent scleractinian coral skeletons as standards for palaeoenvironmental analysis to establish standards for the palaeoenvironmental interpretation of scleractinian coral bearing strata the geochemistry of the three major trace element constituents of living scleractinian coral skeletons is discussed in relation to possible controls on their concentrations experiments were conducted in which the sr ca and mg ca ratios of the seawater were altered and the resultant change in skeletal composition monitored the partition coefficient of strontium ksr was shown to be linear ranging from approximately half to over ten times the normal seawater sr ca ratio increases in the magnesium concentration of seawater decreased ksr growth rates were increased through the addition of calcium and strontium but decreased by magnesium the sodium and magnesium contents of the skeleton were unaffected by their seawater concentrations relative to calcium or strontium magnesium however was affected by growth while sodium by salinity

geochemistry of ostracode calcite part 2 the effects of water chemistry and seasonal temperature variation on candona rawsoni abstract reconstruction of lake paleochemistry from the isotope and trace element composition of fossil ostracodes requires an understanding of geochemical variations induced by the seasonality of shell formation monthly field collections of live candona rawsoni from two hyposaline lakes in the eastern dakotas reveal large variations in 18 o values 2 5 o and mg ca and sr ca ratios up to 35 among individual adults within the same assemblage because the measured variations in water chemistry were small the amplitude of ostracode 18 o and mg ca variations must result from seasonal temperature variation ostracode sr ca ratios which should be temperature independent shows strong positive covariance with shell mg ca these results imply that sr uptake in ostracode calcite increases with the mg content of the shell the partitioning coefficient for mg on the other hand appears to decreases at high values of mg ca in the host water the geochemical variability in the field collections indicates that c rawsoni populations are composed of multiple overlapping generations that attain maturity at different times many juveniles apparently undergo several molts in mid summer and persist as penultimate instars a 1 into the following spring geochemical analysis of late instar juvenile c rawsoni from lacustrine sedimentary records is likely to provide information on mid summer conditions large numbers of fossil ostracodes should be analyzed from each stratigraphic interval to eliminate seasonal noise from the paleochemistry records of temperate region lakes

calibration of past water temperature in the sea of japan based on mg ca of ostracode shells of two shallow marine species in the genus cytheropteron abstract compared to mg ca temperature calibrations in deep sea ostracodes and the use of these calibrations to understand past conditions there have been few studies of shallow marine ostracode taxa in the present study mg ca temperature calibrations were constructed for two shallow marine ostracode species belonging to the genus cytheropteron in the recent sediments of the sea of japan in order to reconstruct the past water temperature record in shallow sea areas the mg ca of adult cytheropteron miurense and cytheropteron sawanense shells from nine bottom sediment samples was positively correlated with the mean annual water temperature wt according to the following equation wt c mg ca of ostracode shell mmol mol 0 94 9 53 comparison of the regression curves of mg ca versus wt for six genera showed similar temperature sensitivity of mg uptake in shells of cytheropteron sarsicytheridea and the genus krithe in most cases but lower than those for genera bythocypris and loxoconcha and xestoleberis hanaii the regression equation was applied to late pliocene and the resulting past water temperatures were compared to modern oceanographic data from water depths of 50 to 150 m in the sea of japan which is the paleodepth estimated to encompass the habitat of ostracode assemblages decreasing variation in the obtained past wt with the increase in the number of fossil ostracode valves from one to four suggests that more than four ostracode valves are required to reconstruct the mean annual wt using the equation established with c miurense and c sawanense thus the mean annual wt during the late pliocene based on analysis of four specimens ranged from 8 9 to 11 6 c which is similar to or slightly lower than the wt observed today

paleohydrology of lake kinneret during the heinrich event h2 abstract during the last glacial period lake kinneret the sea of galilee fluctuated between high and low water levels reflecting the hydrological conditions of the lake watershed here we focus on the hydrology of the lake after its retreat from the last glacial mis2 27 25 ka bp highest stand of 170 m below mean sea level m bsl to the low stand of 214 m bsl at 24 21 ka bp the limnological hydrological history of this time interval is recovered from trench and borehole that were dug and drilled in the southwestern shore of the lake at ohalo ii archeological site cyprideis torosa ostracoda recovered from the trench yielded elemental 87sr 86sr and 18o isotope data that provide information on the shore environment during the low stand period the 87sr 86sr and sr ca ratios in the ostracods varying between 0 70789 and 0 70815 and 0 0017 and 0 0030 respectively indicate contributions of waters from the last glacial lake and regional runoff the increase in the 87sr 86sr ratios reflects the decreasing effect of the last glacial lake kinneret waters and enhanced contribution of local runoff that washed down dried mountain soils that were previously developed during the wet and vegetated glacial the lake retreat at 24 ka bp coincided with the heinrich event h2 at the northern atlantic h2 was expressed by severe aridity in lake kinneret dead sea watershed the limnological hydrological change at post h2 was accompanied by 2 decrease in the 18o value from 2 to 4 reflecting the change in the composition of the east mediterranean rain sources the last glacial lake 87sr 86sr ratio is similar to the tiberias spa saline waters and distinctly different from the modern lake kinneret fresh waters 87sr 86sr 0 70785 compared to 0 70760 respectively this difference is explained by enhanced contribution of ca chloride brines with high 87sr 86sr values to the last glacial lake and reduced jordan river contribution due to cold freezing conditions at its headwaters while the modern lake kinneret is more affected by low 87sr 86sr freshwater from the jordan watershed

mineralogy and sr mg geochemistry of charophyte carbonates a new tool for paleolimnological research abstract the carbonate biominerals formed in the oogonial cells and on stems of charophytes reveal intra specific and species to species variations within the genus chara calcite high magnesian calcite hmc and aragonite may be present in both oogonium and stem calcifications and for the first time evidence is presented of polymineral calcification hmc aragonite within single oogonial cells the data indicate strong specific differences in the biological mechanisms of mineralization within this group of plants among the various species of the genus chara studied there is no correlation between the charophyte carbonate mineralogy and the salinity of water where they formed calcite hmc and aragonite may all be present in charophyte calcifications formed in low salinity waters on the contrary there is an overall relationship between the mineralogy of these carbonates and the mg ca ratio of the water in which they formed sr content in charophyte calcite and high mg calcite reflect directly the sr ca ratio of the host water whereas mg content in these carbonates probably depends on the temperature and the mg ca ratio of the water partitioning coefficients for mg and sr for some widespread species are discussed our results indicate that charophyte carbonates may be used as paleohydrochemical proxies and imply that special attention must be paid to the mineralogical control of charophyte carbonates when they are to be used in isotopic studies

resolving the upper ocean warm layer improves the simulation of the madden julian oscillation here we show that coupling a high resolution one column ocean model to an atmospheric general circulation model dramatically improves simulation of the madden julian oscillation mjo to have realistic strength period and propagation speed the mechanism for the simulated mjo involves both frictional wave convective conditional instability of the second kind frictional wave cisk and air sea convective intraseasonal interaction ascii in particular better resolving the fine structure of upper ocean temperature especially the warm layer produces more vigorous atmosphere ocean interaction and strengthens intraseasonal variations in both sst and atmospheric circulation this helps organize and strengthen deep convection inducing a stronger kelvin wave like perturbation and frictional near surface convergence to the east in addition the warmer sst ahead of the mjo also acts to destabilize the boundary layer and enhance frictional convergence these lead to a more realistic eastward propagating mjo a suite of sensitivity experiments were performed to show the robustness of the mechanisms and to demonstrate 1 that mean state differences are not the main contributors to the improved simulation of our coupled model 2 the role of sst variability in enhancing frictional convergence and intraseasonal variations in precipitation and 3 that the simulation is significantly degraded when the first ocean model layer is thicker than 10 m our coupled model results are consistent with observations and demonstrate a simple but effective means to significantly improve mjo simulation and potentially also forecasts

north atlantic deepwater temperature change during late pliocene and late quaternary climatic cycles variations in the ratio of magnesium to calcium mg ca in fossil ostracodes from deep sea drilling project site 607 in the deep north atlantic show that the change in bottom water temperature during late pliocene 41 000 year obliquity cycles averaged 1 5 c between 3 2 and 2 8 million years ago ma and increased to 2 3 c between 2 8 and 2 3 ma coincidentally with the intensification of northern hemisphere glaciation during the last two 100 000 year glacial to interglacial climatic cycles of the quaternary bottom water temperatures changed by 4 5 c these results show that glacial deepwater cooling has intensified since 3 2 ma most likely as the result of progressively diminished deepwater production in the north atlantic and of the greater influence of antarctic bottom water in the north atlantic during glacial periods the ostracode mg ca data also allow the direct determination of the temperature component of the benthic foraminiferal oxygen isotope record from site 607 as well as derivation of a hypothetical sea level curve for the late pliocene and late quaternary the effects of dissolution on the mg ca ratios of ostracode shells appear to have been minimal

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

solution collapse depressions and suspensates in the limnocrenic lake of banyoles ne spain a high resolution seismic reflection survey in the banyoles limnocrenic solution lake allowed penetration of dense suspensates occupying cone like bottom depressions of different size the depressions result from the dissolution and collapse of underlying eocene calcareous and gypsiferous materials over which lacustrine sediments of varying thicknesses have accumulated the suspensates occupying the depressions present three main types of seismic signatures stratified semistratified and transparent the densities of the suspensates and the water depths of their tops which fluctuate continuously vary from one depression to another the maximum seismically recorded suspensate thickness is 44 m morphological and structural features seismic characters and variable degrees of hydraulic activity point to the existence of different stages of maturity in the lake bottom depressions this work brings new insight on the dynamics and evolution of limnocrenic solution lakes

strontium content of ostracods indicates lacustrine palaeosalinity individual non marine ostracod valves contain sr in proportion to the sr content of their host lake water two commonly coexisting large planktonic species mytilocypris praenuncia and australocypris robusta have a sr distribution coefficient kd sr ca of 0 082 which is independent of temperature in the range 10 18 c if the relationship between salinity and the sr content of a hydrologically simple lake is known palaeosalinities can be calculated from fossil ostracods we present here palaeosalinities for the past 10 000 yr for lake keilambete victoria calculated from ostracod sr ca of fossil material which are in striking agreement with independent interpretations of palaeosalinity the range of salinity spans 14 95 we also show that a reliable quantitative continuous indicator of lacustrine palaeosalinity is important for the elucidation of continental palaeoenvironments for palaeoclimatology and archaeology and ocean continent climatic correlations and interactions

magnesium content of non marine ostracod shells a new palaeosalinometer and palaeothermometer abstract ostracods are microcrustaceans with calcitic carapaces each consisting of two valves or shells that grow by moulting and regeneration of sequentially larger valves up to nine times before reaching maturity the mg content of these valves is species dependent and is a function of their growth stage and the temperature salinity mg content and mg ca ratio of their host water newly formed partly calcified valves of the non marine nektic ostracod mytilocypris henricae have high mg contents 100 000 ppm mg in caco3 at individual shell weights of 2 g this relative mg content decreases as calcification proceeds until shell weights exceed 120 g whereupon the mg content is constant and useful as an indicator of the ostracod s environment mg ca ratios in individual ostracod valves from several species of the genera mytilocypris and australocypris from culture experiments and a series of australian lakes indicate that the valve s mg content increases as a function of increasing temperature and salinity within the range 11 25 c and for waters containing 24 2325 ppm mg the molar mg ca ratio in these ostracods fully calcified valves increases by 0 0015 or 370 ppm mg in caco3 per 1 c and per change of 125 ppm mg in solution for most mainland australian lakes a change in water composition of 125 ppm mg corresponds to a change of 3 5 in salinity for a given mg content of a lake the mg ca ratio of the water may vary within the range of common lacustrine values without significantly affecting mg uptake in the ostracod valves these relationships can provide palaeosalinities and or palaeotemperatures for ostracods recovered from continental sediments for mg partitioning an increase in temperature and salinity produce increased mg content in ostracods whereas for 18o fractionation in biogenic calcite an increase in temperature produces a decrease in 18o of the ostracod and an increase in salinity leads to an increase in 18o of the ostracod thus a combination of 18o and mg measurements on non marine ostracods should enable unique resolution of palaeotemperature and palaeosalinity variations

diagenesis of fossil ostracods implications for stable isotope based palaeoenvironmental reconstruction a protocol for assessing the diagenetic alteration of ostracod carapaces for use in palaeoenvironmental reconstruction is proposed based on comparison between fossil carboniferous and recent specimens recent ostracods have a carapace ultrastructure of fine 0 5 m diameter crystals of primary low magnesium calcite the degree of recrystallisation in fossil ostracods is assessed based on the carapace ultrastructure and geochemistry six diagenetic stages are identified 1 replacement of the original finely crystalline calcite carapace with neomorphic calcite 2 framboidal and euhedral pyrite growth 3 ferroan calcite carapace replacement and cavity void filling cement 4 ferroan dolomite carapace replacement and void fills 5 siderite growth and 6 sphalerite and barite mineralisation stage 1 occurs during early shallow burial stages 2 3 soon after and stages 4 6 during much later burial possibly hydrothermal alteration ostracods and macrofossils exhibiting diagenetic stages 1 5 were analysed for oxygen and carbon isotope ratios the oxygen isotope compositions clearly reflect the diagenetic stages the most negative oxygen isotopes 18o 12 9 represent the precipitation of ferroan dolomite stage 4 and the most positive values of the neomorphic calcite 18o 0 9 represent stage 1 and are within the predicted range of carboniferous seawater 18o 4 to 0 the diagenetic protocol established here is specific to palaeozoic fossil ostracods from carbonate and clastic sediments that were subject to shallow burial diagenesis and later hydrothermal alteration nevertheless the approach could be used to assess the utility of fossil ostracods for palaeoenvironmental interpretation from a wide range of geological settings

deep sea ostracode turnovers through the paleocene eocene thermal maximum in dsdp site 401 bay of biscay north atlantic abstract previous low resolution studies suggest that ostracodes in contrast with deep sea foraminifera largely survived the massive environmental changes of the paleocene eocene thermal maximum petm in a new high resolution study from the continental slope 1800 m paleodepth ne atlantic we also find extensive survivorship of ostracode faunas but this is accompanied by a temporary drop in species diversity and ecological diversity during the petm there are 12 common ostracode species before the petm that are reduced to only two species at the same time as the benthic foraminiferal extinction event all but three species reappear in the later parts of the petm and statistical analysis suggests that most of the apparent lazarus species might be found with sufficient sampling of petm faunas we find no evidence for an excursion fauna of ostracodes as has been detected in calcareous nannofossils planktic foraminifera and benthic foraminifera however the ostracode assemblages changed from a relatively diverse ecological assemblage before and after the petm to one dominated by infaunal species typical of low oxygen conditions during the petm the absence of major extinction and the temporary nature of species disappearances are comparable to turnovers in shallow marine ostracodes and stands in sharp contrast to the 50 species level extinction in benthic foraminifers

quantifying closed basin lake temperature and hydrology by inversion of oxygen isotope and trace element paleoclimate records lake systems are important paleoclimate archives that preserve ecosystem and hydrologic responses to critical periods in earth history such as carbon cycle perturbations and glacial interglacial cycles geochemical measurements of biogenic carbonate for example 18o 13c 87sr 86sr li u sr and mg are indicators of hydrologic variability in lake systems throughout the geologic record in this study we present a new closed basin lake modeling approach hybim the hydrologic balance inverse model that employs a system of total differential equations and uses the measured 18o sr ca and mg ca of biogenic carbonate to determine changes in temperature runoff and lake evaporation using equally spaced time steps these equations are simultaneously solved to constrain the hydrologic parameters of the lake as recorded in biogenic carbonate we use a monte carlo approach to account for uncertainty in the input parameters such as 18o temperature relationships partition coefficient uncertainty and watershed solute chemistry for illustrative purposes we apply the model to two ostracod valve datasets covering different timescales 1 the cretaceous songliao basin northeast china and 2 holocene lake miragoane haiti modern water measurements of water isotopes and cation concentrations from each location are required as model inputs we compare our modeling results with author interpretations and geologic observations the modeling approach presented in this study can be applied to other closed basin lake records can be modified for other calcifying species for example gastropods or mollusks or with calibration to inorganic lacustrine carbonate in addition this approach holds promise for extension with additional proxy measurements that is d u ca or li ca and changing source area on tectonic timescales using proxies that reflect changing source lithology that is sr and pb isotopes future incorporation of age model uncertainty in the monte carlo approach will also provide utility by quantifying temporal uncertainty on the hydrologic response recorded by lake sediments

variability in ostracod partition coefficients d sr and d mg implications for lacustrine palaeoenvironmental reconstructions living and sub recent ostracods were collected from four lakes and foul springs located in belgium france and spain characterized by low water mg ca ratios from 0 08 to 0 65 valves of ostracods belonging to cyprideis torosa candona neglecta c marchica and c candida have been extensively analysed for their magnesium and strontium contents with respect to calcium comparisons of these results are made using the same elements from the waters in which the ostracod valves calcified our results offer new and somewhat different interpretations with respect to the uptake of mg and sr in the calcitic ostracod valves these findings include the following 1 the partition coefficient l sr for ostracods belonging to the same genus candona is not a constant the observed variability in d sr values could be due to the rare of biological calcification although more investigations are necessary to assess the influence of this factor it is possible that some taxa grouped under the genus candona belong to a different genus 2 even at the species level cyprideis torosa the ostracod d sr cannot be considered to be constant at low water mg ca ratio 0 65 our d sr value for c torosa is higher than those determined by others for c torosa calcified in evolved marine water 3 the mg ca ratio of the water appears as a major factor influencing d mg for ostracods for low water mg ca values similar to 2 d mg drastically increases this phenomenon is also effective for inorganic calcite implying a non biologic effect that could be linked to mg2 adsorption consequently large variations in me content of fossil ostracod valves from selected lacustrine sequences with expected low water mg ca similar to 2 can be due to small variations in water mg ca c 1998 elsevier science b v all rights reserved

coprecipitation and isotopic fractionation of boron in modern biogenic carbonates abstract the abundances and isotopic composition of boron in modern biogenic calcareous skeletons from the gulf of elat israel the great barrier reef australia and in deep sea sediments have been examined by negative thermal ionization mass spectrometry the selected species foraminifera pteropoda corals gastropoda and pelecypoda yield large variations in boron concentration that range from 1 ppm in gastropod shells to 80 ppm in corals the boron content of the biogenic skeletons is independent of mineralogical composition and is probably related to biological vital effects the 11 b values of the carbonates range from 14 2 to 32 2 relative to nbs srm 951 and overlap with the 11 b values of modern deep sea carbonate sediments 11 b 8 9 to 26 2 the variations of 11 b may be controlled by isotopic exchange of boron species in which 10 b is preferentially partitioned into the tetrahedral species and coprecipitation of different proportions of trigonal and tetrahedral species in the calcium carbonates carbonates with low 11 b values 15 may indicate preferential incorporation of tetrahedral species whereas the higher 11 b values 30 may indicate 1 1 uptake of both boron species assuming equilibrium with seawater 2 2 preferential incorporation of b oh 4 from in situ high ph internal fluids of organisms that are isolated from seawater the b content and 11 b values of deep sea sediments foraminifera tests and corals are used to estimate the global oceanic sink of elemental boron by calcium carbonate deposition as a result of enrichment of b in corals a substantially higher biogenic sink of 6 4 0 9 10 10 g yr is calculated for carbonates this is only slightly lower than the sink for desorbable b in marine sediments 10 10 10 g yr and approximately half that of altered oceanic crust 14 10 10 g yr thus carbonates are an important sink for b in the oceans being 20 of the total sinks the preferential incorporation of 10 b into calcium carbonate results in oceanic 11 b enrichment estimated as 1 2 0 3 10 12 per mil g yr the boron isotope composition of authigenic well preserved carbonate skeletons may provide a useful tool to record secular boron isotope variations in seawater at various times in the geological record the potential use of boron isotope geochemistry in skeletons as a tracer for palaeoenvironments is demonstrated in ostracoda and foraminifera from the gulf of carpentaria australia the 11 b values of glacial age buried skeletons 4 0 and 4 9 respectively are lower than that of their modern equivalents 17 6 and 13 3 respectively this may reflect a terrestrial boron isotope signature of the water in the gulf during the late quaternary when it was isolated from the ocean

the holocene paleolimnology of lake issyk kul kyrgyzstan trace element and stable isotope composition of ostracodes the stable isotope and trace element geochemistry of ostracode shells from lake issyk kul kyrgyzstan provide an important new paleoclimate record for central asia the n 18 o n 13 c sr ca mg ca and u ca composition of shells from the species candona neglecta found in two piston cores constrains the paleohydrology of the lake from 8700 to 1000 calendar yr before present these data combined with robust chronologies based on 16 ams 14 c dates suggest that the region went from a relatively moist climate in the early holocene to a more arid climate in the late holocene intense freshwater input presumably glacial runoff flowed into the lake from 8700 to 8300 cal yr bp as evident from the n 18 o and n 13 c values from 8300 to 6900 cal yr bp n 18 o and sr ca values indicate that the lake was relatively fresh and an open basin and u ca values suggest that the lake was well mixed with well oxygenated bottom waters there is a transition zone between 6900 and 4900 cal yr bp when n 18 o and sr ca values rapidly increase and mg ca and u ca values rapidly decrease during this period the lake evolved from an open freshwater well mixed lake to a closed more saline less well mixed lake for the remainder of the record n 18 o sr ca mg ca and u ca are relatively constant implying conditions similar to modern conditions although the slight increasing trend in sr ca may suggest an increase in salinity over this period the n 13 c values were approximately in equilibrium with atmospheric co2 in the early part of the record but became relatively negative in the later part of the record this indicates that the dominant mechanism controlling the isotopic composition of dissolved inorganic carbon shifted from exchange with the atmosphere to variations in biological productivity fl 2001 elsevier science b v all rights reserved

tufa as a record of perennial fresh water in a semi arid rift basin kapthurin formation kenya lithological and biological features of a fossiliferous tufa in the kapthurin formation baringo kenya reveal the presence of a lush wetland in a semiarid environment during the middle pleistocene ca 500 ka in this portion of the east african rift valley four geological sections each between 3 m and 8 m in thickness exposed over a distance of 0ae5 km reveal a 1 to 2 m thick paludal tufa which is composed of three carbonate beds two dark grey silty claystones and a reddish brown silty palaeosol high resolution stratigraphic analysis carbonate petrography stable isotope and elemental geochemistry clay mineralogy and fossil remains molluscs ostracods diatoms and charophytes reveal a ground water fed system that fluctuated in depth and periodically disappeared altogether oxygen isotope ratios d 18 o of tufa matrix range from 4ae5 to 8ae0 vienna pee dee belemnite and become more positive up section indicating the decreasing influence of fault related fluids and increasing residence time or freshness of wetland water rather than evaporative enrichment this spring was situated on a lake margin during low lake levels thrived during periods of increased ground water input and was ultimately replaced by an alkaline lake the wetland would appear to have existed during a cool interval within the generally warm marine isotope stage 13 or perhaps during the warm second half of marine isotope stage 13 the ground water source of this wetland arose through a fault system thus the position of the tufa deposit is controlled structurally but the timing and duration of the wetland system may have been influenced by both climatic and tectonic factors

meltwater events and the mediterranean reconnection at the saalian eemian transition in the black sea abstract the last glacial interglacial transition or termination i t i is well documented in the black sea whereas little is known about climate and environmental dynamics during the penultimate termination t ii here we present a multi proxy study based on a sediment core from the se black sea covering the penultimate glacial and almost the entire eemian interglacial 133 5 0 7 122 5 1 7 ka bp proxies comprise ice rafted debris ird o and sr isotopes as well as sr ca mg ca and u ca ratios of benthic ostracods organic and inorganic sediment geochemistry as well as tex 86 and u k 37 derived water temperatures the ending penultimate glacial mis 6 133 5 to 129 9 0 7 ka bp is characterised by mean annual lake surface temperatures of about 9 c as estimated from the tex 86 palaeothermometer this period is impacted by two black sea melt water pulses bswp ii 1 and 2 as indicated by very low sr ca ostracods but high sedimentary k al values anomalously high radiogenic 87 sr 86 sr ostracod values max 0 70945 during bswp ii 2 suggest a potential himalayan source communicated via the caspian sea the t ii warming started at 129 9 0 7 ka bp witnessed by abrupt disappearance of ird increasing 18 o ostracod values and a first tex 86 derived temperature rise of about 2 5 c a second abrupt warming step to ca 15 5 c as the prelude of the eemian warm period is documented at 128 3 ka bp the mediterranean black sea reconnection most likely occurred at 128 1 0 7 ka bp as demonstrated by increasing sr ca ostracods and u ca ostracods values the disappearance of ostracods and toc contents 2 document the onset of eemian sapropel formation at 127 6 ka bp during sapropel formation tex 86 temperatures dropped and stabilised at around 9 c while u k 37 temperatures remain on average 17 c this difference is possibly caused by a habitat shift of thaumarchaeota communities from surface towards nutrient rich deeper and colder waters located above the gradually establishing halo and redoxcline

ostracod shell chemistry as proxy for paleoenvironmental change abstract the application of ostracod shell chemistry as a paleoenvironmental tool has grown within the past decades most studies have investigated mg and sr in ostracod shells as proxies for temperature and salinity and the use of a wide range of trace elements as prospective paleoenvironmental indicators has yet to be developed for lacustrine systems only a few preliminary studies have used trace metals in paleolimnological studies such as cd ba and zn as paleonutrient indicators or mn fe and u as redox and oxygenation indicators this paper reviews the state of the art of geochemical analyses in microfossils such as ostracods foraminifera and corals and provides insights in new trace element proxies with the goal to promote the use of trace elements in ostracod shells as paleoenvironmental proxies in paleoceanography foraminifera and corals are most prominently used to reconstruct past climate conditions well established proxies such as 18o mg ca and sr ca provide information about changes in sea surface temperatures in addition a great number of new proxies have been developed recently such as radiogenic isotopes and redox sensitive trace elements in paleolimnology ostracod shell chemistry is widely used to assess paleohydrological changes reconstruction of temperature and salinity changes in lake environments is often achieved by oxygen isotopes as well as mg ca and sr ca ratios but depending on the hydrological and geological settings of the lake system local calibrations are needed to assess which proxy is suited to reflect which processes new proxies need to be tested by novel techniques that recently have become available compared to conventional instrumentation used in ostracod shell chemistry methods such as laser ablation icp ms and nanosims allow single shell analysis and provide high resolution data the potential of ostracods in paleolimnology is not yet fully assessed but can be developed by learning from paleoceanographic studies

paleosalinity from trace metals in fossil ostracodes compared with observational records at devils lake north dakota usa abstract the chemistry of closed basin lakes responds directly to the hydrologic budget through evaporative concentration of dissolved salts and the sediments of these basins contain several excellent fossil and geochemical proxies for past changes in water chemistry and salinity the trace metal content of ostracode shells among the most promising of these paleosalinity methods is further explored in this study of mg and sr partitioning in candona rawsoni a widespread ostracode of the north american great plains the molar distribution coefficients kd mg and kd sr for this species k d mg ca caco 3 0 004 mg 2 ca 2 h 2 o 9 68 10 5 t c k d sr sr ca caco 3 sr 2 ca 2 h 2 oz 0 406 are determined from laboratory experiments in which c rawsoni are cultured under controlled temperatures and salinities our formulation of kd mg contains a correction term for excess mg that is incorporated into the shell during early calcification the accuracy of the distribution coefficients is tested against field collections of live ostracodes from a suite of 12 dakota lakes the kd inferred values for mg2 ca2 h2o and sr2 ca2 h2o are in close accord with the same ratios measured in the lakes a comparison of ostracode reconstructed and historically measured salinities for devils lake north dakota shows good agreement within the salinity range preferred by c rawsoni 1 10 0 although salinity excursions beyond this optimum are poorly represented in the sedimentary record in most lakes salinity is more readily inferred from mg ca h2o than sr ca h2o because sr solubility is a complex function of several carbonate phases as shown for devils lake sr ca h2o may not vary systematically with the salinity of some brines

barium in planktonic foraminifera abstract reconstructions of ba distributions in ancient oceanic surface waters could provide new insight into paleoceanographic change calcite shells of planktonic foraminifera potentially provide a means of reconstructing such paleo ba distributions if lattice bound ba can be determined on shells recovered from deep sea cores planktonic foraminifera shells from a series of cores were purified of non lattice bound ba associated with organic or sedimentary phases by a combination of physical agitation oxidative reductive steps acid leaches and a novel alkaline dtpa step to dissolve barite a sequential dissolution of a large sample of cleaned shells of the planktonic foraminifer globigerinoides conglobatus indicates homogeneous distribution of ba in the shell material comparison of shells from sediments sediment traps and plankton tows indicates no significant differences in the ba content of the purified shells cleaned samples of the planktonic foraminifera globigerinoides sacculifera g ruber g conglobatus orbulina spp and globoquadrina dutertrei from the equatorial pacific north atlantic and mediterranean sea have ba ca ratios between 0 6 and 1 0 mol mol 0 8 to 1 4 ppm variation in foraminiferal ba contents between the three basins is consistent with the trend in surface seawater ba the calculated distribution coefficient for ba incorporation in these five species based on these data is 0 19 0 05 several species of the non spinose planktonic foraminifera globorotalia have ba ca ratios ranging from 2 to 13 mol mol these high ba contents might be explained by differences in the way these foraminifera precipitate their shells a temporal record of ba ca in samples of globigerinoides and orbulina from a core in the northwest atlantic suggests that the ba concentration of surface waters at this site has not changed by more than 20 over the last 14 kyr

sedimentary geochemical and hydrological history of lake kinneret during the past 28 000 years abstract the sedimentary geochemical and hydrological history of lake kinneret sea of galilee is reconstructed for the past 28 kyrs based on three sedimentary cores drilled at the lake and a trench dug at the shore of the prehistorical ohalo ii site during the past 28 kyrs either laminated or massive fine grained sediments were deposited in the lake comprising primary calcites and fine grain detritus sr ca mg ca 87sr 86sr ratios and 18o values of live and fossil ostracod shells cyprideis torosa and primary calcites together with xrd grain size and carbonate content analyses indicate contribution of the following types of waters to the lake 1 jordan river 2 regional runoff and 3 ca chloride brines currently comprises the tiberias spa brine during the last glacial period 28 24 ka the lake rose to its highest stand of 170 m below sea level bsl expanding over the kinnarot basin and converging with the southern hypersaline lake lisan at that time waters were mainly supplied to the lake by the jordan river and regional runoff with enhanced contribution of the dead sea ca chloride brine primary calcites were precipitated from the lake s solution forming sequences of laminated sediments on the lake s floor at 24 22 ka coinciding with heinrich event h2 at the north atlantic the lake retreated below the modern level of 214 m bsl depositing mainly flood related sediments at its margins the lake slightly rose during the younger dryas and subsequently declined towards the modern level with decreasing contributions of the jordan river waters brines and regional runoff reflecting a continuous aridification of the region during the holocene

faunal and geochemical evidence for changes in intermediate water temperature and salinity in the western coral sea northeast australia during the late quaternary abstract ostracod assemblages and geochemical analyses of valves of specific ostracod taxa are used to reconstruct both qualitatively and quantitatively bottom water temperatures bwt for the last 100 000 years in the western coral sea the investigated core 51gc21 is situated in the lower reaches of the antarctic intermediate water at 1630 m water depth first we ran a principal coordinate analysis pcoa of 42 surface samples from the coral sea and then compared fossil assemblages with results of the pcoa in addition we selected well preserved speciments of the two genera krithe and bythocypris for mg ca analyses the mg ca is used to infer past changes in bwt for intermediate waters of the western coral sea results indicate large temperature fluctuations over the last 100 000 years of interest is the documentation that the bwt was similar to the present day temperature during part of isotope stage 3 comparison between our temperature record and the benthic foraminifer 18o record of core 51gc21 and with the 18o variations in seawater as reconstructed by labeyrie et al 1987 allowed assessment of past changes in bwt salinity and density thus we identify for the western coral sea three distinct periods on the basis of water mass density changes i e for isotope stage 1 stages 2 3 and 4 and stage 5 our temperature record also indicates a good correlation with the 60 s summer insolation calculations for the period between 25 000 yr b p and 75 000 yr b p comparison of our results from this study with other records from the western pacific the ontong java plateau in particular reveal the role of new guinea as an oceanographic barrier a wet phase recorded on continental australia coincides with our high bottom water temperature record for isotopic stage 3

quantification of paleotemperature changes during isotopic stage 2 in the la draga continental sequence ne spain based on the mg ca ratio of freshwater ostracods past summer temperature changes are quantified from the la draga sequence banyoles ne spain during stage 2 24 10 ka bp using trace element content in lacustrine ostracod valves the high resolution results from this new method are compared to summer paleotemperature reconstructions from sequences from the north atlantic area providing a discussion about the magnitudes of some temperature changes in ne spain and offshore portugal the coldest part of stage 2 is not documented at the classical date of similar to 18 c 14 ka bp similar to 21 5 calendar ka bp but rather occurred later date of ca 17 15 ka cal bp in the north atlantic area the onset of the bolling allerod interstadials was relatively synchroneous at similar to 14 6 ka cal bp although the magnitude of the bolling allerod improvement was more important in the southern area than in the northern area the duration of the younger dryas is discussed even if different durations are reported from calendar ages it seems that the summer temperature cooling of the younger dryas was similar around the north atlantic area c 1996 elsevier science ltd

mg ca ratios in the shells of cultured specimens and natural populations of the marine ostracode xestoleberis hanaii crustacea abstract we studied mg ca ratios in the shells of the shallow water ostracode xestoleberis hanaii ishizaki 1968 ishizaki k 1968 ostracodes from uranouchi bay kochi prefecture japan tohoku university science report second series geology 40 1 1 45 in laboratory cultured and field collected samples x hanaii was cultured in our laboratory from a 7 to adult stage under controlled temperatures 15 28 c results of the culture experiments show that the mg ca ratio of x hanaii is strongly correlated with water temperature within the temperature range of 15 28 c in the field collected samples seasonally fluctuating mg ca ratios of their shells parallel the variation in the seasonal seawater temperature and the water temperature estimated from the mean value of the adult stage samples collected on any given date agreed quite well with the average water temperature for the period of 8 days prior to the collection date based on the changes in mg ca ratios and shell morphology in the course of ontogeny we suggest that mg is contained in the organic matter which is one of the shell components that form the network or the framework within which the calcite crystals are formed

karstification without carbonic acid bedrock dissolution by gypsum driven dedolomitization aggressive karstification can take place where dolomite and gypsum are in contact with the same aquifer gypsum dissolution drives the precipitation of calcite thus consuming carbonate ions released by dolomite lake banyoles in northeastern spain is a karst lake supplied by sublacustrine springs and karstic collapse is occurring in the immediate vicinity of the lake lake water is dominated by mg ca and so 4 hco 3 and is supersaturated with calcite that is actively accumulating in lake sediments water chemistry sulfur isotope composition local stratigraphy and mass balance modelling suggest that the primary karst forming process at at lake banyoles is dedolomitization of basement rocks driven by gypsum dissolution karstification takes place along the subsurface contact between the gypsiferous beuda formation and the dolomitic perafita formation this process is here recognized for the first time to cause karstification on a large scale this is significant because it proceeds without the addition of soil generated carbonic acid gypsum driven dedolomitization may be responsible for other karstic systems heretofore attributed to soil generated carbonic acid