sea level fall and coastal water cooling during the late holocene in southeastern brazil based on vermetid bioconstructions abstract the relative sea level variation curve obtained by dating and leveling vermetid shells from northern santa catarina state 26 3 s presents fall trend during all the last 4 0 cal ka bp which matches previous results based on the same kind of indicator for the brazilian coast between 3 s and 28 s chemical and isotopic analyses of 50 vermetid bioconstructions from distinct localities of south southeastern brazilian coast indicate possible changes in the coastal water temperature these changes may have been caused by oscillations in the strength of brazilian coastal current which carries la plata plume northward being therefore responsible for the penetration of cold and less saline water masses in the study area this is a reasonable explanation for the scarcity of vermetid biolithites around 3 4 2 6 cal ka bp and 0 5 0 cal ka bp

reconstructing daily temperatures from growth rates of the intertidal bivalve mollusk chione cortezi northern gulf of california mexico abstract we establish a model for the reconstruction of average daily sea surface temperatures from calcification rates of an intertidal bivalve mollusk the rate of shell production in chione cortezi carpenter 1864 ex sloat ms is mainly controlled by water temperature ontogenetic age and the effect of tidal cycles statistical methods developed by dendrochronologists can successfully extract the water temperature signal from daily growth increment chronologies after removal of noise the growth rates are expressed as scaled daily growth indices average daily water temperatures during the first half of the year are highly correlated with the scaled daily growth index values of recent and subrecent specimens using the multi valued function presented here increment width analysis can reconstruct daily average water temperatures with a mean error of less than 3 this technique provides an independent method for reconstructing temperatures in fossil specimens of species with living representatives and can supplement high resolution temperature reconstructions based on geochemical analysis

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

using stable isotopes to quantify water uptake by cyclobalanopsis glauca in typical clusters of karst peaks in china in this study stable isotopes 18o and 2h were used to determine the sources of water for cyclobalanopsis glauca in two habitats limestone outcrops and thin soils in clusters of karst peaks in southwest china where soils are scattered only in rock gaps and are underlain by rigid carbonate rocks we used a direct inference approach and the isosource mixing model to estimate the contributions of different sources to the plant xylem water the results showed that adult c glauca growing on limestone outcrops mainly used water from soils in rock gaps which comprised 65 of all water sources during the rainy season and water from rainwater sources during the rain dry season and dry season the proportion of deep water used increased during the dry season in contrast young c glauca growing on limestone outcrops relied on a mixture of rainwater and soil water during the rainy and the rain dry seasons and on rainwater in the dry season accounting for 66 3 and 64 0 of water use respectively adult c glauca on thin soils mainly used soil water in rainy seasons a mixture of soil water and rain water in the rain dry season and rainwater in the dry season water held within bedrock was essential for meeting plant transpiration requirements in karst peak cluster areas the results will provide knowledge for the effective protection of vulnerable karst environments and for the recovery of vegetation on karst rocky desertification areas

effect of mineralogy salinity and temperature on li ca and li isotope composition of calcium carbonate li ca and li isotope ratios in marine and freshwater calcium carbonates are potential tracers of past environmental variables such as weathering intensity and temperature to make use of their potential requires full understanding of the fractionation of li ca and 7 li 6 li during growth of calcium carbonate this study improves such understanding with two sets of new measurements on inorganic calcites and aragonites precipitated over a range of salinity and on the test of benthic foraminifera formed at a range of temperatures li ca in inorganic calcite increases by a factor of four as salinity increases from 10x to 50x inorganic aragonite demonstrates no significant change in li ca over the same salinity range the difference in behaviour is probably due to the incorporation mechanism of li substitution of li in the ca 2 site in aragonite makes growth solution li ca the key variable while interstitial incorporation of li in calcite means that the growth solution li concentration is more important compared to the growth solution 7 li 6 li is c3x lower in calcite and c11x lower in aragonite with no relationship to salinity for either mineral similar isotope fractionation to these inorganic experiments are observed for biogenically produced calcite foraminifera and aragonite corals this suggests little biological control during li incorporation into biogenic calcium carbonates the difference in fractionation between calcite and aragonite is consistent with an equilibrium isotope fractionation reflecting different incorporation mechanisms for li into the two minerals four samples of the benthic foraminifera uvigerina precipitated over a temperature range of 14 8c have li ca ranging from 18 5 to 13 1 amol mol the ratio is inversely related to temperature with a sensitivity of 2 5f0 8 per 8c this sensitivity is similar to that observed in a previous study of foraminiferal li ca but about half that observed during inorganic calcite growth the large variability in both li ca and temperature sensitivity exhibited between various foraminifera species suggests an additional control on calcite li ca apart from those of salinity and temperature observed in this study d 2004 elsevier b v all rights reserved

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

the relationship between water masses and benthic ostracod assemblages in the western coral sea southwest pacific abstract the bathymetric distribution of 67 ostracod genera identified in 42 sediment samples water depth range 370 3776 m from the western coral sea is documented statistical analyses of this dataset support preliminary observations that the vertical distribution of the ostracod fauna is largely controlled by the three water masses present in the studied area four ostracod assemblages are recognised assemblage i consisting mainly of ostracods present in the deep water assemblage ii consisting of ubiquitous ostracods and ostracods mostly confined to the antarctic intermediate water and assemblages iii and iv with ostracods characteristic of the western south pacific central water temperature food supply and dissolved oxygen level are believed to be the most important factors influencing the ostracods bathymetric zonation the present work establishes the potential of ostracods for use in palaeoceanographic reconstruction in the western pacific ocean

evolution of the western margin of australia during the rodinian and gondwanan supercontinent cycles abstract the proto darling fault zone and its successor the darling fault extend for 1 000 km along the western continental margin of australia and appear to have been active at several periods during the geological past deformation commenced at 2 570 ma and affected late archaean granitoids along the western margin of the yilgarn craton much of the later activity reflects events related to the accretion and breakup associated with the rodinia and gondwanaland supercontinent cycles in the north rocks of the northampton and mullingarra complexes form part of a high grade grenvillian orogenic belt lying to the west of the darling fault referred to as the pinjarra orogen they underwent granulite facies metamorphism 1080 ma ago and form part of the global collisional event that resulted in the amalgamation of rodinia these rocks extend southward beneath phanerozoic sedimentary cover the perth basin where they are constrained to the east by the darling fault and to the west by the dunsborough fault the latter marking the eastern boundary of the leeuwin complex the leeuwin complex is a fragment of pan african crust that has traditionally been considered part of the pinjarra orogen it is composed predominantly of upper amphibolite to granulite facies felsic orthogneisses derived from a type anorogenic granitoids conventional and shrimp u pb zircon geochronology has established that the granitoids evolved between 780 ma and 520 ma and were metamorphosed at 615 ma these events are equated with rifting associated with the breakup of rodinia sm nd whole rock data support the juvenile nature of the crust and provide no evidence for the involvement of pre existing archaean continental material during the phanerozoic the dunsborough and darling faults were reactivated as normal faults defining the inner arm of a major rift system within eastern gondwanaland and controlling sedimentation in the perth basin that now overlies the grenvillian terrane major normal movement on the darling fault ceased by the late jurassic and it appears that continental breakup in the early cretaceous occurred along fractures closely related to the western boundary of the leeuwin complex that defined the eastern margin of the outer arm of the rift system breakup between australia and greater india commenced at 132 ma and was followed by eruption of the bunbury basalt at 130 ma and 123 ma this possibly resulted from hot spot activity beneath eastern gondwanaland and may have been a reflection of the kerguelen plume though the evidence is equivocal it is argued from the petrographic geochemical and isotopic characteristics together with the likely contiguity of the eastern gondwanaland continents since the assembly of rodinia that the leeuwin complex evolved within an intracrustal rift and is not an exotic terrane it is distinct from adjacent portions of the pinjarra orogen and should be considered a separate terrane it is recommended that use of the term pinjarra orogen be confined to rocks recording the grenvillian events thereby excluding those rocks the leeuwin complex that evolved during the later pan african orogeny

interaction between the enso and the asian monsoon in a coral record of tropical climate the oxygen isotopic composition of a banded coral from the western equatorial indian ocean provides a 150 year long history of the relation between the el nino southern oscillation enso phenomenon and the asian monsoon interannual cycles in the coral time series were found to correlate with pacific coral and instrumental climate records suggesting a consistent linkage across ocean basins despite the changing frequency and amplitude of the enso however decadal variability that is characteristic of the monsoon system also dominates the coral record which implies important interactions between tropical and midlatitude climate variability one prominent manifestation of this interaction is the strong amplitude modulation of the quasi biennial cycle

ostracod faunas and water masses across the continental margin off southwestern africa changes in composition of modern benthic ostracod faunas across the continental margin of southwestern africa occur at boundaries between and within major water masses a mixed layer antarctic intermediate water aaiw boundary at 200 m an aaiw salinity minimum zone at 650 m an aaiw bathyal thermocline at 1000 m and the aaiw north atlantic deep water nadw boundary at 1500 m in addition two population changes occur within the nadw at 1 8 2 0 km and 2 0 3 0 km the antarctic bottom water assemblage is sparse and poorly preserved

estimating greater paleodepths with ostracodes especially in past thermospheric oceans abstract modern ostracodes show significant morphologic and taxonomic changes with increasing depth deep psychrospheric faunas are less diverse and more cosmopolitan than shallow faunas individuals are larger rarer and blind their carapaces seem better designed relative to the mass of construction material used speciation is slower taxa are older longer ranging and for the most part now confined to abyssal and bathyal environments deep thermospheric ostracodes found in pre psychrospheric oceans or isolated basins are different their deep origin seems related to the ability of shelf species to submerge past what is a formidable thermal barrier to test morphologic changes that reflect faunal submergence in thermospheric oceans such as existed in the atlantic before about 40 m y b p the basis for an adaptive structural theory is explored this leads to a search for limits expressive of rapid change both in the structure of morphology and in water mass structure examination of the ostracodes from core samples of cretaceous age from nine d s d p sites in the south atlantic suggests that the rio grande rise walvis ridge aseismic system has both been a water mass barrier and yet remained deep at least mid bathyal over the last 100 m y no evidence of either shallow ostracodes from the shelves of africa south america or those of islands were found indicating that models proposed previously that there would have been an archipelago or shallow submerged causeway across the rio grande rise walvis ridge during the late cretaceous are probably in error

mollusc and brachiopod skeletal hard parts intricate archives of their marine environment the biogenic carbonate hard parts of fossil bivalves cephalopods and brachiopods are among the most widely exploited marine archives of phanerozoic environmental and climate dynamics research the advent of novel analytical tools has led many workers to explore non traditional geochemical and petrographic proxies and work performed in neighbouring disciplines sheds light on the complex biomineralization strategies applied by these organisms these considerations form a strong motivation to review the potential and problems related to the compilation and interpretation of proxy data from bivalve cephalopod and brachiopod hard parts from the viewpoint of the sedimentologist and palaeoceanographer specific focus is on the complex biomineralization pathways of a given dissolved ion or food particle from its aquatic environment via the digestion and biomineralization apparatus in molluscs and brachiopods and its incorporation into a biomineral given that molluscs and brachiopods do not secrete their hard parts from seawater but rather from their mantle and periostracum this paper evaluates differences and similarities of seawater versus that of body fluids cephalopods bivalves and brachiopods exert a strong biological control on biomineralization that to some degree may buffer their shell geochemistry against secular changes in seawater chemistry disordered amorphous calcium carbonate precursor phases later transformed to crystalline biominerals may be significant in carbonate archive research due to expected geochemical offset relative to the direct precipitation of stable phases a reasonable level of understanding of the related mechanisms is thus crucial for those who use these skeletal hard parts as archives of the palaeo environment the impact of what is commonly referred to as biological factors on the geochemistry of mollusc and brachiopod hard parts is explored for conventional isotope systems such as carbon oxygen strontium and traditionally used element to calcium ratios in particular the often used 13ccarb or the mg ca and sr ca elemental proxies are fraught with problems an interesting new research field represents the analysis calibration and application of non traditional proxies to mollusc and brachiopod hard parts examples include the carbonate clumped isotope 47 approach and the analysis of the isotopes of ca mg n li s or element to ca ratios such as li ca or b ca and rare earth elements based on considerations discussed here a series of do s and don ts in mollusc and brachiopod archive research are proposed and suggestions for future work are presented in essence the suggestions proposed here include experimental work also field experiments making use of recent archive organisms or where possible a reasonable recent analogue in the case of extinct groups moreover the detailed understanding of the architecture of mollusc and brachiopod hard parts and their ultra structures must guide sampling strategies for geochemical analyses where feasible a detailed understanding of the diagenetic pathways and the application of multi proxy and multi archive approaches should form the foundation of fossil carbonate archive research the uncritical compilation of large data sets from various carbonate shelled organisms collected at different locations is not encouraged

assessing the reproducibility and reliability of estuarine bivalve shells saxidomus giganteus for sea surface temperature reconstruction implications for paleoclimate studies studies using oxygen isotopes y 18 o of mollusk shells to determine paleotemperature need to assume water y 18 o values which could severely influence calculated temperatures we analyzed aragonitic shells of the butter clam saxidomus giganteus deshayes 1839 to determine the reproducibility of the isotopic signal between individuals and to assess how precisely temperature could be calculated given known salinity and temperature furthermore carbon isotopes are also investigated as an environmental proxy the abundance of well preserved s giganteus shells in archeological and geological deposits in northwestern north america makes them a particularly suitable species for paleoclimate studies seasonally resolved stable oxygen isotope profiles in three s giganteus shells collected from the same site in puget sound washington usa were well correlated 0 77br 2 b0 87 although there were differences up to 0 58x in high resolution y 18 o profiles of the three shells the difference between the average y 18 o of each shell was less than half of this 0 19x and half of what has been reported for between colony coral variability y 13 c profiles on the other hand were more complex with shell y 13 c being about 2 5x lower than expected equilibrium values however this roughly conforms to the idea that about 10 of the shell carbon originates from metabolic co2 both y 18 o and y 13 c indicate that s giganteus do not grow during periods of reduced salinity despite the excellent reproducibility of y 18 o between shells and the fact that salinity effects were duly considered calculated temperature still differed from instrumental temperature applying different salinity y 18 o water relationships to average shell y 18 o and considering salinity from the shell collection site and a nearby offshore station resulted in calculated average water temperatures ranging from 1 7 to 6 4 8c warmer than measured although we could not determine if s giganteus precipitate their shells in isotopic equilibrium we believe that the difficulty in predicting temperature arose from not being able to accurately determine

reconstructing el nino southern oscillation activity and ocean temperature seasonality from short lived marine mollusk shells from peru abstract a critical need exists for quantitative reconstructions of long term el nino southern oscillation enso variability in the eastern tropical pacific presented here is a method to quantitatively estimate past changes 1 in the seasonal amplitude of sea surface temperature sst in the peruvian coastal upwelling system and 2 in the amplitude of enso related interannual variability in the eastern tropical pacific the seasonal amplitude of sst t along the length of the peruvian coast is strongly correlated with the nino1 2 index we show that the frequency distribution of t values provided by a modern sample of 13 mesodesma donacium shells faithfully reflects modern enso variability at the regional scale including the range of anomalies from la nina to moderate el nino events but excludes extreme warm anomalies because of high shell mortality we propose to use the frequency distribution of enso anomalies in paleoclimate studies for comparisons between shell records coral records and gcm simulations reconstruction uncertainties can be quantified using monte carlo simulations the method presented here opens new perspectives for quantitative paleo enso reconstructions in the eastern pacific since it may be applied with any mollusk species from peru provided at least one annual cycle of sst is faithfully recorded by shell 18 o

benthonic ostracods and deep watermasses a qualitative comparison of southwest pacific southern and atlantic oceans abstract the upper depth limits of the dominant cosmopolitan deep water benthonic ostracod taxa present in five localities in the southern ocean kerguelen plateau southeast australian continental slope and southwest pacific chatham rise tasman sea coral sea are compared to investigate the degree to which the position of intermediate and deep watermasses antarctic intermediate water aaiw deep water dw and antarctic bottom water aabw control the vertical faunal succession although none of the taxa studied is restricted to one watermass their upper depth limits appear to be closely related to the position of antarctic intermediate water aaiw taxa showing the most consistent pattern include krithe upper depth limit above aaiw poseidonamicus upper depth limit in lower aaiw but in underlying deep water on the kerguelen plateau and pterygocythere mucronalatum dw but in aabw on the kerguelen plateau bathyal above approximately 1000 m upper depth levels of taxa species diversity species turnover and changes in the proportion of the dominant deep sea taxa krithe and poseidonamicus match closely that of the atlantic ocean dingle and lord 1990 however the upper depth limits of the abyssal taxa poseidonamicus and dutoitella appear to be very different in the cape basin se atlantic and the sw pacific with respect to watermass characteristics for example in the atlantic poseidonamicus has its upper limit within lower north atlantic deep water nadw whereas in the sw pacific it occurs consistently within the aaiw these discrepancies in the upper depth level of abyssal taxa between the pacific and atlantic oceans suggest that different watermasses or other environmental variables control their upper range in different oceanic basins it follows that these differences must be taken into account if deep sea ostracods are to be used as a reliable means to trace modern or reconstruct ancient watermass pathways between ocean basins

the long lived mollusc arctica islandica a new paleoceanographic tool for the reconstruction of bottom temperatures for the continental shelves of the northern north atlantic ocean the carbonate shell of the bivalve arctica islandica has been recognized for more than a decade as a potentially important marine geochemical biorecorder owing to this species great longevity 200 years and wide geographic distribution throughout the northern north atlantic ocean a region vital to global climate and ocean circulation however until now this potential has not been realized owing to the difficulty of precisely sampling the shell of this slow growing species using newly available automated microsampling techniques combined with micromass stable isotope mass spectrometry a stable oxygen isotope record 1956 1957 and 1961 1970 has been obtained from a live captured 38 year old a islandica specimen collected near the former position of the nantucket shoals lightship 41 n 69 w the shell s 18o signal is compared with an expected signal derived from ambient bottom temperature and salinity data recorded at the lightship for the same period the results show that a islandica s 18o record 1 is in phase with its growth banding confirming the annual periodicity of this species growth bands 2 is in oxygen isotopic equilibrium with the ambient seawater 3 shows a consistent shell growth shutdown temperature of 6 c which translates into an 8 month may december shell growth period at this location and 4 records the ambient bottom temperature with a precision of 1 2 c these results add important information on the life history of this commercially important shellfish species and demonstrate that a islandica shells can be used to reconstruct inter and intra annual records of the continental shelf bottom temperature

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

biogenic and abiogenic low mg calcite blmc and almc evaluation of seawater ree composition water masses and carbonate diagenesis the ree and shale normalized paas reesn values of modern brachiopods biogenic low mg calcite blmc represented by several species from high to low latitudes from shallow to deep waters and from warm and cold water environments define three distinct average seawater trends the warm and cold water brachiopods define two indistinguishable p 0 050 groups that mimic open ocean seawater ree chemistry exhibiting the typical lree enrichment with a slightly positive to negative ce anomaly followed by an otherwise invariant series other recent brachiopods from an essentially siliciclastic seabed environment are distinct in both ree and reesn trends from the previous two populations showing a slight enrichment in the mrees and an increasing trend in the hrees other groups of modern brachiopods are characterized by elevated reesn trends relative to the normal groups as well as by complexity of the series trends the most characteristic feature is the decrease in the hrees in these brachiopods from areas of unusual productivity i e such as upwelling currents fluvial input and aerosol dust deposition preserved brachiopods from the eocene and silurian exhibit reesn trends and ce anomalies similar to that of the open ocean modern brachiopods although their enriched ree concentrations suggest precipitation of blmc influenced by extrinsic environmental conditions preservation of the blmc was tested by comparing the ree and reesn trends of preserved eocene brachiopods to those of oligocene brachiopods that were altered in an open diagenetic system in the presence of phreatic meteoric water the altered blmc is enriched by approximately one order of magnitude in both ree and reesn trends relative to that in blmc of their preserved counterparts similarly the ree and reesn of preserved silurian brachiopod blmc were compared to those of their enclosing altered lime mudstone which exhibits features of partly closed system phreatic meteoric water diagenesis despite these differences in the diagenetic alteration systems and processes the rees and reesn trends of the blmc of altered brachiopods and of originally mixed mineralogy lime mudstones now diagenetic low mg calcite are enriched by about one order of magnitude relative to those observed in the coeval and preserved blmc in contrast to the changes in ree and reesn of carbonates exposed to phreatic meteoric water diagenesis are the ree compositions of late burial calcite cements precipitated in diagenetically open systems from burial fluids the ree and reesn trends of the burial cements mimic those of their host lime mudstone with all showing slight lree enrichment and slight hree depletion exhibiting a chevron pattern of the reesn trends the overall enrichment or depletion of the cement reesn trends relative to that of their respective host rock material reflects not only the openness of the diagenetic system but also strong differences in the elemental and ree compositions of the burial fluids evaluation of the ce ce sn and la pr pr sn anomalies suggests precipitation of the burial calcite cements essentially in equilibrium with their source fluids

an evaluation of mg ca sr ca and ba ca ratios as environmental proxies in aragonite bivalve shells the influence of salinity and water chemistry on mg ca sr ca and ba ca ratios in the aragonitic shells of the manila clam was investigated clams were reared at constant temperature 20 c under different controlled conditions of salinity commonly encountered in their natural habitat clams were held in three tanks with a constant salinity of 35 for the first 35days and then two tanks were changed to lower salinities 20 and 28 for the next 29days individual shell mg ca sr ca and ba ca ratios were studied through time despite stable conditions temperature salinity and mg cawater for clams reared at salinity 35 during the experiment mg ca shell ratios increased through the time moreover the salinity decrease at t35 slowed the increase of mg ca shell ratios at salinity 28 and resulted in an mg cashell decrease at salinity 20 despite similar mg cawater ratios in the different salinity treatments microprobe analyses illustrate that mg varies along contemporaneous growth lines the variable shell mg ca ratios suggest that incorporation of magnesium into shell carbonate is strongly regulated by the organism and not by environmental conditions interestingly microprobe analyses illustrated that mg was not associated with shell sulfur as other studies have suggested sr ca shell ratios of clams reared at salinity 35 and under constant conditions were also not as constant as expected if sr ca ratios were an environmental proxy there was an inverse correlation between shell sr ca and salinity despite a slight positive correlation between salinity and sr ca ratios of the water indicating that sr ca ratios do not reflect environmental conditions a strong inverse correlation between salinity and ba ca shell ratios and a positive correlation between ba ca shell and ba ca water was observed therefore ba ca shell ratios seem to be a promising proxy of high resolution 1day salinity variations in estuarine waters via the relationship between ba ca water and salinity this study clearly illustrates that both mg ca and sr ca ratios in aragonite shells are not under environmental control and that ba ca ratios are with the later tracking high resolution water ba ca ratios and hence estuarine salinity variations

strong kinetic effects on sr ca ratios in the calcitic bivalve pecten maximus although sr ca ratios in abiogenic calcite are strongly controlled by precipitation rates such a kinetic effect has never been demonstrated in calcitic bivalve shells therefore we report sr ca ratios together with daily growth rates in the calcitic shells of four individuals of the bivalve pecten maximus age class i ratios of sr ca were found to be variable among individuals that grew at the same location illustrating that vital effects dominate over environmental controls although daily growth rate was correlated with shell sr ca ratios it explained only half of the sr ca variations however daily shell surface area increment an estimation of the total quantity of carbonate precipitated for a given time explained 74 of the sr ca variability in the shells of p maximus this proves for the first time in a calcitic bivalve that shell sr ca partitioning is mainly controlled by kinetic effects the sr ca ratio should therefore be tested as a potential proxy of calcification rate in modern or fossil calcitic biocarbonates

late quaternary deep ocean circulation a review of paleoceanographic studies dealing with late quaternary deep water circulation in the oceans is presented these studies which are based on the analysis of deep sea benthic foraminiferal faunal and geochemical data and sedimentological data are discussed in light of physical oceanographic conditions in the modern ocean we include in this review a re evaluation of benthic foraminiferal data from north atlantic and southern ocean piston cores and suggest that the dominance of uvigerina during glacial intervals reflects increased amounts of organic carbon at the sea floor compared to modern values a number of geochemical studies have suggested that the production or characteristics of north atlantic deep water nadw changed during glacial times although these changes have been thought to result from a cessation of overflow water from the norwegian greenland seas it is suggested here that seasonal sea ice cover was possible over southern portions of the norwegian sea during glacial intervals the presence of seasonally open water would have allowed norwegian sea overflow water to have been produced although perhaps at lower volumes and with different hydrographic properties than at present the record of antarctic bottom water aabw circulation does not show a simple relationship with paleoclimatic oscillations indicating that changes in oceanographic conditions in the southern ocean had little effect on aabw formation the aabw record contrasts with the glacial interglacial cycles of nadw suggesting no direct link between aabw and nadw circulation a variety of data suggests that changes in pacific deep water circulation occurred as a result of glacial production of north pacific deep water or from an increased flux of southern ocean water

the effect of submarine groundwater discharge on nutrient and salinity regimes in a coastal lagoon off perth western australia abstract submarine groundwater discharge sgd into a coastal lagoon off perth western australia contains nitrate and silicate in concentrations two orders of magnitude higher than those of the receiving waters this discharge delivers enough nitrate to replace that dissolved in the lagoon water mass about every eight days and enough silicate to replace the lagoon silicate in about 48 days the delivery rate of nitrate nitrogen by sgd is equal to about 48 of that required for observed growth rates of lagoon macrophytes surface salinity is lower close to the shore as a result of sgd during calm conditions a salinity front was observed in the lagoon with a nearshore pool of nutrient enriched water floating above the more saline ocean water

quaternary paleoceanography of the deep arctic ocean based on quantitative analysis of ostracoda abstract ostracodes were studied from deep arctic ocean cores obtained during the arctic 91 expedition of the polarstern to the nansen amundsen and makarov basins the lomonosov ridge morris jesup rise and yermak plateau in order to investigate their distribution in arctic ocean deep water aodw and apply these data to paleoceanographic reconstruction of bottom water masses during the quaternary analyses of coretop assemblages from arctic 91 boxcores indicate the following ostracodes are common at all depths between 1000 and 4500 m and species distribution is strongly influenced by water mass characteristics and bathymetry quantitative analyses comparing eurasian and canada basin assemblages indicate that distinct assemblages inhabit regions east and west of the lomonosov ridge a barrier especially important to species living in lower aodw deep eurasian basin assemblages are more similar to those living in greenland sea deep water gsdw than those in canada basin deep water two upper aodw assemblages were recognized throughout the arctic ocean one living between 1000 and 1500 m and the other having high species diversity at 1500 3000 m downcore quantitative analyses of species abundances and the squared chord distance coefficient of similarity reveals a distinct series of abundance peaks in key indicator taxa interpreted to signify the following late quaternary deep water history of the eurasian basin during the last glacial maximum lgm a gsdw aodw assemblage characteristic of cold well oxygenated deep water 3000 m today inhabited the lomonosov ridge to depths as shallow as 1000 m perhaps indicating the influence of gsdw at mid depths in the central arctic ocean during termination 1 a period of high organic productivity associated with a strong inflowing warm north atlantic layer occurred during the mid holocene several key faunal events indicate a period of warming and or enhanced flow between the canada and eurasian basins a long term record of ostracode assemblages from kastenlot core ps2200 5 1073 m water depth from the morris jesup rise indicates a quasi cyclic pattern of water mass changes during the last 300 kyr interglacial ostracode assemblages corresponding to oxygen isotope stages 1 5 and 7 indicate rapid changes in dissolved oxygen and productivity during glacial interglacial transitions

benthic ostracods and deep water masses in the atlantic ocean ostracod faunas at six locations are compared and related to distributions in an atlantic ocean wide data base five widely developed vertical faunal sequences are recognised at particular levels within deep water masses henryhowella fauna lower part of antarctic intermediate water krithe fauna upper north atlantic deep water poseidonamicus bosquetina fauna upper part of lower nadw dutoitella fauna lower part of lower nadw legitimocythere fauna antarctic bottom water these faunas are correlated with previously established deep water benthic foraminiferal assemblages and their possible palaeo oceanographic use is discussed

impact of sample pretreatment on the measured element concentrations in the bivalve arctica islandica correlating metal to calcium me ca ratios of marine biogenic carbonates such as bivalve shells to environmental parameters has led to contradictory results biogenic carbonates represent complex composites of organic and inorganic phases some elements are incorporated preferentially into organic phases and others are incorporated into inorganic phases chemical sample pretreatment to remove the organic matrix prior to trace element analysis may increase the applicability of the investigated proxy relationship though its efficiency and side effects remain questionable we treated inorganic calcium carbonate and bivalve shell powder arctica islandica with eight different chemical treatments including h2o2 naoh naocl and acetone and analyzed the effects on 1 me ca ratios sr ca mg ca ba ca and mn ca 2 organic matter n content and 3 mineralogical composition of the calcium carbonate the different treatments 1 cause element and treatment specific changes of me ca ratios 2 vary in their efficiency to remove organic matter and 3 can even alter the phase composition of the calcium carbonate e g formation of ca oh 2 during naoh treatment among all examined treatments there were none without any side effects in addition certain me ca changes we observed upon chemical treatment contradict our expectations that lattice bound elements sr and ba should not be affected whereas non lattice bound elements mg and mn should decrease upon removal of the organic matrix for instance we observe that naocl treatment did not alter sr ca ratios but caused unexpected changes of the mg ca ratios the latter demonstrates that the buildup of complex biogenic composites like the shell of arctica islandica are still poorly understood

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

recent deep sea benthic foraminiferal distributions in the south china and sulu seas thirty nine surface sediment samples collected from the south china and sulu seas were examined to determine the bathymetric distribution of benthic foraminifera in these two basins and the factors responsible for these distributions the benthic foraminiferal faunas of both basins are highly diverse but have low absolute abundances benthic number and species diversity systematically decrease with increasing water depth four faunal assemblages were identified for each basin byq mode principal component analysis theglobocassidulina subglobosa uvigerina assemblage 1500 m and theuvigerina assemblage 1400 m represent the shallowest assemblages in the south china sea and sulu sea respectively and are found within the oxygen minimum zone of each basin where the sedimentary organic carbon content is highest and the pore water oxygen penetration depth zo is shallowest thebulimina aculeata assemblage occurs at water depths between 1700 and 2000 m in the southeastern south china sea and is also associated with relatively high sedimentary organic carbon content theastrononion pusillum assemblage is found in south china sea at the depths between 1500 and 3200 m below the lysocline 3200 m in the south china sea this assemblage is replaced by the agglutinatedrhabdammina abyssorum assemblage this assemblage reflects the presence of a water mass that is highly undersaturated with respect to calcite in the sulu sea thepyrgo murrhina assemblage occupies water depths from 1400 to 2200 m below 2200 m two deep water assemblages are present that are both dominated byoridorsalis umbonatus a correlation between various environmental and benthic foraminiferal variables indicates that salinity temperature sediment grain size water depth and bottom water oxygen concentration are not key factors controlling the benthic foraminiferal distribution in either the south china sea or the sulu sea rather organic carbon content and oxygen penetration depth in sediments appear to play important roles in determining the distribution of benthic foraminifera in both basins

investigation of li ca variations in aragonitic shells of the ocean quahog arctica islandica northeast iceland interannual and intra annual variations in lithium to calcium ratio were investigated with high temporal resolution in the aragonitic outer shell layer of juvenile arctica islandica mollusca bivalvia collected alive in 2006 off northeast iceland li ca shell ranged between 7 00 and 11 12 mol mol 1 and presented well marked seasonal cycles with minimum values recorded at the annual growth lines a general pattern was a progressive increase in li ca shell from march to may followed by a plateau in june and a decrease down to minimum values in july august li ca shell was correlated with d 18 o shell derived temperature but the strength of this relationship was weak r 2 p shell in a islandica may most likely be explained 1 by calcification rate and or 2 by significant river inputs of li rich silicate particles flowing to the sea as soon as snow melts in the first case li ca shell may be a useful proxy for addressing seasonal variations of growth rate in bivalves that lack discernable microgrowth patterns abrupt decreases of li ca shell may in turn help identify growth retardations due to harsh environmental conditions alternatively if li ca shell variations are linked to particulate li inputs by rivers this could be a new proxy for the intensity of mechanical weathering of icelandic basalts with interesting perspectives for the reconstruction of frequency and intensity of past jokulhlaups subglacial outburst floods further works including experimental studies are needed to test these hypotheses