profiles of trace elements and stable isotopes derived from giant long lived tridacna gigas bivalves potential applications in paleoclimate studies this study investigates the environmental and biological controls on trace element partitioning and stable isotope composition of modern giant long lived bivalves tridacna gigas with the aim to use these archives for paleoclimatic reconstructions firstly the intra shell variability is studied by measuring time equivalent profiles in the different shell layers characterised by different growth rates secondly the inter site variability is studied by comparing profiles derived from three modern specimens collected in sites across the indo pacific region characterised by different ranges of temperature and productivity these results show that 18o profiles are highly reproducible across the shell regardless of significantly different growth rates shell 18o is primarily controlled by water 18o and temperature comparison of intra shell mg ca profiles shows a clear and systematic partitioning where inner layer mg ca values are a least 2 3 times higher than outer layer and hinge areas inner layer mg ca shows seasonal oscillations but superimposed on an ontogenetic trend with increasing values and increasing amplitude mg ca oscillations with age the sr ca profiles do not show clear reproducible seasonal trends in the different shell zones it is concluded that mg ca and sr ca profiles appear to reflect a combination of biological and environmental controls that will need to be disentangled before using these proxies in paleoclimatic studies finally intra shell ba ca profiles are reproducible in great detail for all modern specimens studied inter site comparison shows that the amplitude and the timing of the ba ca peaks appear to reflect the timing and the amplitude of the chlorophyll peaks associated with phytoplankton blooms at each locality making this tracer a potential paleoproductivity indicator

growth and high resolution paleoenvironmental signals of rhodoliths coralline red algae a new biogenic archive we investigated rhodoliths coralline red algae from a subtropical locality in the gulf of california lithothamnium crassiusculum and a subarctic locality in newfoundland lithothamnium glaciale for their potential as paleoenvironmental archives using microanalytical geochemical techniques to measure variations in 18o mg and ca rhodoliths are potentially well suited as recorders of shallow water paleoenvironmental signals because they 1 have worldwide distribution from the tropics to polar regions 2 are long lived from decades to centuries and 3 display well developed growth bands our results indicate that rhodolith growth bands preserve ultrahigh resolution records of paleoceanographic paleoclimatic change and likely constitute an important new archive for reconstructing the paleoenvironmental history of littoral neritic areas in which these algae are found the 18o content of individually sampled rhodolith growth bands ranges from 2 4 to 4 6 in l crassiusculum and from 3 2 to 0 3 in l glaciale in both cases the range of 18o values suggests a slightly lower amplitude of variation in sea surface temperature than that actually measured in the ocean at the two study sites both l crassiusculum and l glaciale show a negative offset from isotopic equilibrium electron microprobe analysis of magnesium and calcium in growth bands reveals cyclic variations with values ranging between 7 7 18 5 mol mgco3 in l glaciale and 13 2 22 5 mol mgco3 in l crassiusculum in addition electron microprobe element maps highlight individual growth bands provide a powerful approach to study rhodolith formation and indicate that the specimens we analyzed have vertical growth rates of 250 450 m yr

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

reconstructing past seawater mg ca and sr ca from mid ocean ridge flank calcium carbonate veins proxies for past seawater chemistry such as mg ca and sr ca ratios provide a record of the dynamic exchanges of elements between the solid earth the atmosphere and the hydrosphere and the evolving influence of life we estimated past oceanic mg ca and sr ca ratios from suites of 1 6 to 170 million year old calcium carbonate veins that had precipitated from seawater derived fluids in ocean ridge flank basalts our data indicate that before the neogene oceanic mg ca and sr ca ratios were lower than in the modern ocean decreased ocean spreading since the cretaceous and the resulting slow reduction in ocean crustal hydrothermal exchange throughout the early tertiary may explain the recent rise in these ratios

diagenetic stabilization of aragonite and low mg calcite i trace elements in rudists abstract cretaceous rudists with thick multilayered bimineralic aragonite and low mg calcite shells have been studied for the effects of meteoric diagenesis on their textural and chemical attributes the original fine compact prismatic or cellular prismatic microstructures of low mg calcitic layers have been preserved frequently despite the vagaries of their subsequent diagenetic histories these layers usually suffered only partial recrystallization which caused fusion of crystal units rounding of prism comers and partial cementation confined to intercrystalline and intraparticle pore spaces in contrast the originally aragonitic parts of the shell usually suffered either complete dissolution or at best retained some vestiges of their crossed lamellar or complex crossed lamella microstructures synsedimentary submarine diagenetic events such as borings by endolithic fauna internal micritic and or peloidal sedimentation and submarine aragonite and or high mg calcite cements within the primary inter and intraparticle pore spaces were coeval with rudist accretion the subsequent meteoric cementation has been characterized by the formation of bladed and equant ferroan calcites which occluded the residual primary and secondary porosities diagenetic stabilization of aragonite to diagnetic low mg calcite and low mg calcite to diagenetic low mg calcite is believed to have been a two stage process initially sr and na have been partially depleted during an early meteoric diagenetic phase calcitization of metastable phases with expulsion of sr at a slower rate than that of na this stage is followed by incorporation of more mn fe and mg due to precipitation of late ferroan calcite stabilization of aragonite causes more pronounced trace element repartitioning than the stabilization of low mg calcite however the degree of repartitioning depends not only on mineralogy but also on the structural buildup of a given shell layer suggesting that factors such as water rock ratio surface kinetics are of considerable sig ificance for the process of diagenetic stabilization rudist skeletal components with preserved original mineralogy and texture have trace element chemical signatures analogous to holocene marine bivalves this similarity argues for comparable chemical composition of the cretaceous and holocene seawater as well as for similar modes of incorporation of trace elements into mollusc shells

oceanographic control on shell growth of arctica islandica bivalvia in surface waters of northeast iceland implications for paleoclimate reconstructions absolutely dated annually resolved sea surface temperature records from middle to higher latitudes covering long time intervals are crucial to better understand the climate system such data can potentially be obtained from variations in shell growth of long lived bivalves such as arctica islandica this study presents the first statistically robust 178 yr long composite chronology covering 1835 2012 based on sixteen live collected and subfossil specimens of a islandica from unpolluted shallow waters of northeast iceland between 1875 and 1996 up to 43 of the variation in annual shell growth was explained by sst during february to september faster growth occurred when temperatures were warmer and food supply was elevated however the correlation was subject to strong temporal variations likewise the inter series correlation synchrony among time series was intermittently stronger and weaker if more uniform environmental conditions prevailed over a longer time interval and the habitat was solely influenced by one of the major currents in this region the warm nutrient rich irminger current or the cold nutrient poor east iceland current the agreement between growth records of contemporaneous specimens broke down and the correlation between shell growth and sst was at minimum however when the habitat was under the alternating influence of both currents the inter annual variability of shell growth and synchrony in growth among the specimens were at maximum and the correlation between sst and shell growth strengthened as demonstrated here the relationship between shell growth of a islandica and environmental variables is highly complex and depends on oceanographic parameters these findings should be taken into account in subsequent studies in order to reliably reconstruct sst and other environmental variables from shells of this species

sclerosponges as a new potential recorder of environmental changes lead in ceratoporella nicholsoni lead concentrations have been analyzed on a 223 yr profile through the aragonitic skeleton of the reef building caribbean sclerosponge ceratoporella nicholsoni by using laser ablation inductively coupled plasma mass spectrometry a parallel study of the 13 c distribution in the skeleton validates the previously established mean annual growth rate of 230 m yr at least for long term important environmental changes the pb trend in the specimen displays a general increase from 0 30 ppm ca a d 1760 to 2 15 ppm ca a d 1984 a major threefold increase occurred after 1930 this pb profile is analogous to results acquired from ice or coral cores and clearly highlights the potential of sclerosponges as a new proxy of environmental changes for time series extending over several centuries

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

chemical and isotopic architecture of the belemnite rostrum abstract macrofossil calcite is of great importance for quantitative reconstructions of palaeoenvironment and palaeoseasonality the calcite rostra of belemnites jurassic to cretaceous marine invertebrates are especially suited for such investigations because they are comparatively large and are structured by growth bands despite their use in chemostratigraphic and palaeoenvironmental studies much of the internal variability of geochemical signatures in rostra is poorly understood here multiple profiles through a belemnite rostrum of passaloteuthis bisulcata 183 myr old were analyzed for 13c and 18o values as well as mg ca sr ca and mn ca ratios geochemical signatures of the central 1 2 mm of the profiles indicate diagenetic cementation along the apical zone for which original porosity of up to 40 can be inferred the overall 13c and 18o values of the other well preserved parts of the belemnite fluctuate by 1 per mil but are nearly uniform within single growth bands in contrast sr ca and mg ca in the well preserved parts show growth rate and crystal shape related variability close to the central apical zone strongly bent calcite crystals are enriched in mg up to 70 and sr up to 50 through the remainder of the rostrum higher calcite precipitation rate can account for mg depletion of 15 and sr enrichment of 15 with respect to co genetic calcite precipitated at a slower rate no indication for temperature control on mg ca or sr ca is detected in the investigated specimen overall the new findings indicate that 13c and 18o analyses of belemnite rostra produce consistent results regardless of the sampling area within the rostrum and that growth rate effects on element incorporation are minor with respect to the control exerted by secular changes in seawater composition through time additionally the central part of the rostrum where strong calcite crystal bending is observed should be avoided for sampling when studying elemental composition of the calcite for palaeoenvironmental reconstructions

late cretaceous and early paleogene nutrient and paleoproductivity records from blake nose western north atlantic ocean 1 we evaluate phosphorus p and biogenic barium bio ba as nutrient burial and export productivity indicators for the late cretaceous and early paleogene combining these with calcium carbonate caco3 organic carbon c and bulk caco3 c isotopes 13c sample ages span 36 71 ma 1 sample 0 5 m y for a depth transect of sites in the western north atlantic blake nose ocean drilling program leg 171b sites 1052 1051 and 1050 we use a multitracer approach including redox conditions to investigate export productivity surrounding the global paleocene 13c maximum 57 ma reducing conditions render most of the bio ba record not useful for export productivity interpretations p and organic c records indicate that regional nutrient and organic c burial were high at 61 and 69 ma and low during the paleocene 13c maximum a time of proposed global high relative organic c burial observed organic c burial changes at blake nose cannot explain this c isotope excursion

micro x ray fluorescence μxrf line scanning on cretaceous rudist bivalves a new method for reproducible trace element profiles in bivalve calcite the reconstruction of palaeoclimate on a sub annual scale requires the measurement of chemical proxies in fossil material at a high spatial resolution while various methods for trace element analysis on the micrometre scale are available they are usually destructive to the sample or not widely accessible this study evaluates the performance of a table top micro x ray fluorescence scanner in obtaining reproducible trace element profiles on bivalve calcite standard calibration and repeatability tests demonstrate the robustness of results obtained with this new generation micro x ray fluorescence device that uses a comparatively high excitation energy of 30 w results show that elemental abundances measured using this fast readily accessible and non destructive analytical setup are reproducible on the g g level and therefore suitable for the analysis of the abundance of commonly studied elements in bivalve calcite for example sr mn and fe spectra obtained in this study show considerable improvement in terms of signal to noise ratio compared to earlier table top xrf studies reliability of the measurements is tested using a conservative detection and quantification limit count rates of ca are used to check for point measurements disturbed by irregularities on the sample surface furthermore the method allows semi quantitative two dimensional element mapping which is a convenient tool for the detection of diagenetic alteration in fossil samples the method reveals records of sr ca fe ca and mn ca ratios in a late campanian vaccinites vesiculosus shell with sr ca ratios showing a trend opposite to mn ca and fe ca resulting trace element records are discussed in terms of seasonal cyclicity in the late cretaceous and diagenetic alteration of the fossil shell this article is protected by copyright all rights reserved

seasonal variation of hydrographic and nutrient fields during the us jgofs arabian sea process study abstract between september 1994 and december 1995 the us jgofs arabian sea process experiment collected extensive high quality hydrographic data temperature salinity dissolved oxygen and nutrients during all seasons in the northern arabian sea an analysis of this unique data suite suggests the presence of many features that are described in the canonical literature but these new data provided the following insights 1 although the seasonal evolution of mixed layer depths was in general agreement with previous descriptions the deepest mixed layer depths in our data occurred during the late ne monsoon instead of the sw monsoon 2 the region exhibits considerable mesoscale variability resulting in extremely variable temperature salinity ts distributions in the upper 1000 db this mesoscale variability is readily observed in satellite imaging in the high resolution data taken by a companion onr funded project and in underway adcp data 3 the densest water reaching the sea surface during coastal upwelling appeared to have maximum offshore depths of 150 m and s close to the core value 25 for the saline arabian sea water asw but salinities in these upwelling waters were relatively low the densest water found at the sea surface during late ne monsoon conditions has s 24 8 and relatively high salinities suggesting that they are a source for the asw salinity maximum 4 persian gulf water pgw with a core of 26 6 forms a widespread salinity maximum despite the considerable extent of this feature persian gulf outflow water with a salinity 4 of 39 at its source can only be a minor contributor within the standard us jgofs sampling grid maximum salinities on this surface are 36 8 at stations near the gulf falling to values as low as 35 3 at the stations farthest removed from its influence even at our standard stations closest to the gulf n 1 and n 2 the high salinity low nutrient persian gulf water has only a modest direct effect on nutrient concentrations this pgw salinity maximum is associated with the suboxic portions of the arabian sea s oxygen minimum zone 5 the salinity maximum associated with red sea water rsw core 27 2 in the jgofs study region is clearly evident at the southermost sampling site at 10 n s 15 elsewhere this signal is weak or absent and salinity on the 27 2 surface tends to increase towards the persian gulf suggesting that the disappearance of this salinity maximum is due at least in part to the influence of the persian gulf outflow 6 inorganic nitrogen to phosphate ratios were lower frequently much lower than the standard redfield ratio of 15 1 16 1 by atoms at all times and all depths suggesting that inorganic nitrogen was more important than phosphate as a limiting nutrient for phytoplankton growth and that the effects of denitrification dominated the effects of nitrogen fixation 7 the water upwelling off the omani coast during the sw monsoon has inorganic nitrogen to silicate ratios that were higher 2 1 than the 1 1 ratio often assumed as the ratio of uptake during diatom growth 8 the temporal evolution of inorganic nitrogen to silicate ratios suggests major alteration by diatom uptake only during the late sw monsoon cruise tn050 in august september 1995 9 widespread moderate surface layer nutrient concentrations occurred during the late ne monsoon 10 a zone of high offshore nutrient concentrations was encountered during the sw monsoon but instead of being associated with offshore upwelling it may represent offshore advection from the coastal upwelling zone the influence of an eddy or both 11 although our data do not contradict previous suggestions that the volume of subtoxic water may be reduced the sw monsoon they suggest a weaker re oxygenation than indicated by some previous work similarly they do not confirm results suggesting that secondary nitrite maxima may be common in waters with oxygen concentrations 5 m

ligamental increments of the mid holocene pacific oyster crassostrea gigas are reliable independent proxies for seasonality in the western bohai sea china abstract modern living and mid holocene shells of crassostrea gigas from the western bohai sea in china were subjected to sclerochronological analysis with the aim of determining whether their concave bottoms and growth breaks on resilifer surfaces as well as corresponding translucent growth bands visible in cross section have seasonal significance an additional aim was to obtain ontogenetic information from mid holocene fossil shells we compared 18 o and 13 c profiles compiled with high and low sampling resolution for the same shell in order to test the consistency of the results and identify a suitable sampling strategy for future sclerochronological studies the results show that concave bottoms on the resilifer surface and corresponding translucent growth bands in cross section formed during the cold season these features are appropriate indicators of annual growth increments in fossil c gigas shells moreover growth breaks located near convex tops indicate annual growth increments for that part of the shell which grew when the organism was sexually mature therefore spawning related growth breaks and alternating winter freeze shocks concave bottoms are excellent morphological features in determining annual growth increments consequently the life span growth rate and timing of spawning and death can be determined from the increments of ligament growth of these fossil oyster shells for future sclerochronological studies an adaptive micro sampling strategy could be used for different increments of ligament growth that represent different seasons such a strategy would be more efficient in providing reliable insights into growth history of shells with variable growth rates of annual increments

estimating reservoir sedimentation rates at large spatial and temporal scales a case study of california 1 previous reservoir sedimentation models have ignored two key factors for large spatial and temporal modeling of multiple reservoirs trapping by upstream dams and decreasing sediment trapping as reservoirs fill we developed a spreadsheet based model that incorporates both factors using california as a case study we used measured sedimentation rates to estimate sediment yields for distinct geomorphic regions and applied those rates to unmeasured reservoirs by region statewide reservoirs have likely filled with 2 1 billion m3 of sediment to date decreasing total reservoir capacity by 4 5 about 200 reservoirs have likely lost more than half their initial capacity to sedimentation

chemical labelling of oyster shells used for time calibrated high resolution mg ca ratios a tool for estimation of past seasonal temperature variations abstract the geochemical compositions of biogenic carbonates are increasingly used for palaeoenvironmental reconstructions the skeletal 18o temperature relationship is dependent on water salinity so many recent studies have focused on the mg ca and sr ca ratios because those ratios in water do not change significantly on short time scales thus those elemental ratios are considered to be good palaeotemperature proxies in many biominerals although their use remains ambiguous in bivalve shells here we present the high resolution mg ca ratios of two modern species of juvenile and adult oyster shells crassostrea gigas and ostrea edulis these specimens were grown in controlled conditions for over one year in two different locations in situ monthly mn marking of the shells has been used for day calibration the daily mg ca ratios in the shell have been measured with an electron microprobe the high frequency mg ca variation of all specimens displays good synchronism with lunar cycles suggesting that tides strongly influence the incorporation of mg ca into the shells highly significant correlation coefficients 0 70

late cretaceous upwelling system along the southern tethys margin israel interrelationship between productivity bottom water environments and organic matter preservation organic rich upper cretaceous sequences in israel were deposited in an extensive highly productive upwelling linked system which prevailed along the southern tethys margin and lasted for 19 m y santonian to late maastrichtian an understanding of the spatial and temporal characteristics of this system was gained through detailed paleontological and geochemical analyses of subsurface sequences in two basins in israel representing an outer shefela and an inner zin facies belt the nature of the upwelling system and its effect on the sedimentary record is related to two basic environmental parameters namely paleoproductivity intensity and oxygen levels at the bottom the assessment of these parameters and their interrelationship has been performed through the development of paleontological foraminiferal criteria which are independent of the organic matter content following the establishment of these criteria it is concluded that the productivity reached its maximum intensity during the late campanian which was also the time of most notable differentiation between the center of the upwelling system in the inner belt and the less intense conditions in the outer basin this distribution is expressed in varied lithology organic rich carbonates phosphorites and siliceous rocks at the core of upwelling and a uniform lithology organic rich carbonates at the margin of this system the uniform lithology of the maastrichtian in both basins composed of organic rich carbonates is ascribed to a gradual weakening of productivity the bottom conditions in the inner belt during the late campanian the time of maximum surface productivity were near anoxic changing to more aerated dysaerobic conditions during the early maastrichtian in the outer belt a more aerated bottom dysaerobic prevailed throughout the late campanian to late maastrichtian the elevated organic matter content in both basins reflects the overall environment of high productivity its actual variations however seem to be unrelated to changes in surface productivity and bottom oxygen levels

new oxygen isotope evidence for long term cretaceous climatic change in the southern hemisphere a new composite 18 o record generated from calcareous fine fraction and bulk sediments from the exmouth plateau details long term cretaceous climatic change at mid latitudes in the southern hemisphere assessment of new and previously published 18 o data indicates that a mid cretaceous global climatic optimum was achieved sometime between the time of the cenomanian turonian boundary and the middle turonian when surface ocean paleotemperatures were the highest of the past 115 m y periods of cooling and warming that reversed the general patterns were superimposed on long term aptian turonian warming and turonian maastrichtian cooling trends respectively extrapolation of southern hemisphere paleotemperature trends to maastrichtian paleotemperature data from a low latitude pacific guyot implies that maximum mid cretaceous low latitude paleotemperatures could have been in excess of 33 c

a critical assessment of mollusk 18 o 16 o mg ca and 44 ca 40 ca ratios as proxies for cretaceous seawater temperature seasonality seasonal temperature fluctuations of tethyan coastal water are recorded in a pristine 80 my old rudist shell from turkey in order to critically assess factors other than seawater temperature that might have influenced the shell geochemical record three different paleo temperature proxies 18o mg ca and 44ca were applied in a qualitative manner all three proxies reflect the same cyclical trends and thus yield robust evidence for seasonal fluctuations in late cretaceous surficial seawater temperature this suggests the successful application of the new 44ca temperature proxy to fossil mollusk calcite the direct comparison of the three data sets however demonstrates that all proxies are fraught with problems similar to other studies 18o 16o ratios point to warmer summer temperature maxima than those in comparable costal settings today nevertheless the 18o 16o proxy is subject to environmental factors that might lead to an overestimation of peak temperatures moreover mg ca molar ratios are less sensitive to environmental factors but were strongly affected by the ion regulating capability of the rudist bivalve that responded to the low mg ca ratio of cretaceous seawater similarly uncertainties of the 44ca composition of cretaceous seawater and the complex bio calcification of mollusks presently limit the interpretation of 44ca values in terms of absolute seawater temperature the multiproxy approach applied here however documents that these limitations do not obscure the dominant patterns of seasonal sea surface temperature variations recorded in the biogeochemical rudist archive

mg ca and sr ca ratios in planktonic foraminifera proxies for upper water column temperature reconstruction reliable temperature estimates from both surface and subsurface ocean waters are needed to reconstructpast upper water column temperature gradients and past oceanic heat content this work examines therelationships between trace element ratios in fossil shells and seawater temperature for surface dwellingforaminifera species globigerinoides ruber white and globigerina bulloides and deep dwelling species globorotalia inflata globorotalia truncatulinoides dextral and sinistral and pulleniatina obliquiloculata mg ca and sr ca ratios in shells picked in 29 modern core tops from the north atlantic ocean are calibratedusing calculated isotopic temperatures mg ca ratios on g ruber and g bulloides agree with published dataand relationships for deep dwelling species mg ca calibration follows the equation mg ca 0 78 0 04 exp 0 051 0 003 t with a significant correlation coefficient of r

calcium carbonate veins in ocean crust record a threefold increase of seawater mg ca in the past 30 million years chemical sr mg and isotopic 18o 87sr 86sr compositions of calcium carbonate veins ccv in the oceanic basement were determined to reconstruct changes in sr ca and mg ca of seawater in the cenozoic we examined ccv from 10 basement drill sites in the atlantic and pacific ranging in age between 165 and 2 3 ma six of these sites are from cold ridge flanks in basement 46 ma which provide direct information about seawater composition ccv of these young sites were dated using the sr isotopic evolution of seawater for the other sites temperature corrections were applied to correct for seawater basement exchange processes the combined data show that a period of constant low sr ca 4 46 6 22 mmol mol and mg ca 1 12 2 03 mol mol between 165 and 30 ma was followed by a steady increase in mg ca ratios by a factor of three to modern ocean composition mg ca sr ca relations suggest that variations in hydrothermal fluxes and riverine input are likely causes driving the seawater compositional changes however additional forcing may be involved in explaining the timing and magnitude of changes a plausible scenario is intensified carbonate production due to increased alkalinity input to the oceans from silicate weathering which in turn is a result of subduction zone recycling of co2 from pelagic carbonate formed after the cretaceous slow down in ocean crust production rate

87sr 86sr and sr ca investigation of jurassic mollusks from scotland implications for paleosalinities and the sr ca ratio of seawater measurements of 87 sr 86 sr sr ca 18 o and 13 c were performed on molluskan fos sils from the great estuarine group scot land to deduce paleosalinity patterns and hydrodynamic environments in this classic jurassic marginal marine succession fos sils are found as winnowed accumulations in shell beds that bear low diversity assem blages consistent with deposition in a la goonal paleoenvironment previous studies have concluded that estuarine mixing of seawater and freshwater took place based on correlated trends in 18 o and 13 c most notably in the mussel praemytilus strathair densis from the kildonnan member this interpretation is shown to be incorrect based on 87 sr o 13 c and the sr ca ratio this is consistent with a lagoonal hydrology controlled more by seasonal changes in evaporation precipitation and flooding than by direct inputs of seawater or river ine water transported over large distances lagoons containing the oyster praeexogyra in the duntulm formation have similar in ferred o and c isotope characteristics but based on their 87 sr 86 sr ratios they have a higher proportion of seawater than the praemytilus lagoons of the kildonnan member the data thus far suggest that many of the lagoonal environments in the great es tuarine group were nearly hydrologically closed at least over the interval represent ing the molluskan invasion of these habi tats rendering o and c isotopes unreliable proxies of paleosalinity because strontium isotopes are not directly affected by evap oration of the lagoons knowledge of marine and freshwater 87 sr 86 sr ratios along with estimates of sr concentration are used to calculate the proportion of seawater in the brackish water mixture unio is nearly al ways the most radiogenic taxon compared to other genera in closely adjacent sedimen tary strata confirming its freshwater affin ity the purported marine brackish bivalve tancredia yields a low paleosalinity of 4 only slightly more saline than unio and praemytilus at 1 3 the oyster praeexo gyra hebridica yields paleosalinities between 2 and 26 attesting to the wide salinity tolerance of this species thus far only neomiodon from the dun tulm and staffin bay formations show co variant relationships between 87 sr 86 sr and ca sr ratio that can be reconciled with a dynamic response to seawater freshwater mixing the slopes of these trends converge at 0 7068 which is close to the early cal lovian seawater composition of 0 7069 us ing values of dsr from modern aragonite se creting mollusks the sr ca ratio of middle jurassic seawater is constrained from the best correlated mixing line to be 5 4 0 6 millimoles mole in contrast sr ca ratios in the great estuarine group lagoons and continental watershed range from 5 4 to 19 0 these are much higher than the av erage value of 2 3 for modern rivers but typical of sr ca ratios in rivers draining arid climate regions the semirestricted hy drodynamic regime inferred from the high seawater like 18 o values and high but uni form sr ca ratios in many of the great es tuarine group mollusks is consistent with a seasonally dry mediterranean style climate for the middle jurassic of britain

origin of the extreme polymetallic enrichment cd cr mo ni u v zn of the late cretaceous early tertiary belqa group central jordan abstract the sedimentary formations of the late cretaceous to early tertiary belqa group correspond to pure to slightly clayey limestones and minor black shales characterized by a remarkable enrichment in phosphorous and various redox sensitive elements cd cr mo ni u v zn phosphorous enrichment is related to the great phosphorite deposition event that has occurred at the southern margin of the tethys ocean during this period the very low organic matter contents in the limestones despite their strong enrichment in redox sensitive elements is attributed to a deposition in anoxic water but under shallow water conditions permitting the bacterial degradation of a large part of the organic matter most of the elements constituting the belqa group sediments have been deposited from the sea water either directly by chemical precipitation most ca and redox sensitive elements or indirectly through biogenic activity p part of ca and u except for the minor detritial contribution presents in some limestones and more significantly in the shales such an origin is also supported by the ree patterns of the limestones which are similar to that of the present sea water the anomalously high concentrations of some redox sensitive trace metals cr ni and probably cd compared to worldwide black shales is explained by an exogenic metal flux corresponding to the leaching of the huge amounts of ophiolites obducted during the collision between the african arabian and eurasian plates at the same time as the deposition of the belqa group sediments uranium is substituted for calcium in biogenic apatite in the limestones but was also directly precipitated from sea water in the black shales in relation with the suboxic environment with the periodic anoxia developed during their deposition in restricted deeper basins the pyrometamorphism resulting from the burning of organic rich levels in clayey limestones has created a further enrichment of redox sensitive elements in the resulting marbles by a volume loss resulting from decarbonatation reactions and the combustion of the organic matter

silicon and zinc biogeochemical cycles coupled through the southern ocean zinc is vital for the physiology of oceanic phytoplankton the striking similarity of the depth profiles of zinc to those of silicate suggests that the uptake of both elements into the opaline frustules of diatoms and their regeneration from these frustules should be coupled however the zinc content of diatom opal is negligible and zinc is taken up into and regenerated from the organic parts of diatom cells thus since opaline frustules dissolve deep in the water column while organic material is regenerated in the shallow subsurface ocean there is little reason to expect the observed close similarity between zinc and silicate and the dissimilarity between zinc and phosphate here we combine observations with simulations using a three dimensional model of ocean circulation and biogeochemistry to show that the coupled distribution of zinc and silicate as well as the decoupling of zinc and phosphate can arise in the absence of mechanistic links between the uptake of zinc and silicate and despite contrasting regeneration length scales our simulations indicate that the oceanic zinc distribution is in fact a natural result of the interaction between ocean biogeochemistry and the physical circulation through the southern ocean hub our analysis demonstrates the importance of uptake stoichiometry in controlling ocean biogeochemistry and the utility of global scale elemental covariation in the ocean in understanding these controls zinc and silicon distributions co vary in much of the global oceans observations and numerical modelling suggest that this co variation can arise in the absence of mechanistic links between the uptake of zinc and silicate

diagenetic stabilization of aragonite and low mg calcite ii stable isotopes in rudists abstract cretaceous rudists having thick multilayered bimineralic aragonite and low mg calcite shells have been studied for the effects of phreatic vadose meteoric diagenesis on their microstructural and isotopic attributes rudist skeletal components with preserved original mineralogy of aragonite and low mg calcite and with preserved microstructures have isotopic signatures analogous to holocene marine bivalves this similarity argues for a comparable isotopic composition of the cretaceous and holocene seawater as well as for a similar mode of incorporation of stable isotopes into their shells diagenetic stabilization of rudist shells appears to have been a two stage process with low mg calcite diagenetic calcite lmc dlmc and particularly aragonite diagenetic calcite a dlmc transformation as the first step and cementation as a later development the direct a dlmc mineralogical transformation calcitization results in initial depletion in 18o of 2 and the subsequent diagenetic precipitation of ferroan calcite spar causes depletion in 13c as well as an additional decrease in 18o the former due to introduction of organically derived co2 into the diagenetic aquifer in contrast 13o and 13c isotopic depletions in the originally lmc skeletal components are both related to the precipitation of the late diagenetic ferroan sparry calcite cement the earlier calcitization stage being of subordinate importance only

sea surface temperature record of a late cretaceous tropical southern tethys upwelling system abstract late cretaceous sea surface temperatures ssts were reconstructed based on tex 86 data from the unique high productivity upwelling system in the southern tethys margin israel ssts were determined from two oil shale sequences of the santonian early maastrichtian 85 to 68 ma in southern efe syncline and central shefela basin israel paleo latitude 8 15 n these two sampling sites represent the inner and outer belts of the upwelling system our tex 86 data indicate a significant long term sst cooling trend from 36 0 to 29 3 c during the late santonian and the early campanian in the southern tethys margin consistent with the opening of the equatorial atlantic gateway eag based on our data from the equatorial region and literature data from the polar region we reassessed the equator to pole sst gradient to 22 c this value is closer to the modern ocean equator to pole sst gradient 30 c than suggested from previous studies furthermore the sst data suggests the presence of cooler surface water in the inner belt 27 7 c caused by the upwelling system and warmer surface water 29 2 c further seaward in the outer belt

and ratios in skeletal calcite of mytilus trossulus covariation with metabolic rate salinity and carbon isotopic composition of seawater minor element and isotopic compositions of marine bivalve calcite are frequently used as proxy records of seawater temperature and salinity although molluscan calcite is secreted at or near oxygen isotope equilibrium the influence of metabolic activity i e vital effects on skeletal srca ratios and 13c values is not well known we present measurements of skeletal chemistry from a consecutive samples milled in chronological order from the organism s final year of growth and b adjacent samples within three separate growth bands of the marine mussel mytilus trossulus to investigate chemical disequilibrium effects among different parts of the shell seawater temperature and salinity were monitored for one year at squirrel cove british columbia at the end of the year a young rapidly growing mussel mussel a and an old slowly growing mussel mussel b were harvested from this site growth bands within the shells were sampled to provide a chronological record of shell carbonate chemistry results from consecutive samples show 1 a significantly higher average srca ratio in mussel a than that in mussel b and 2 13c values that correlate well with salinity in mussel a but not in mussel b results from time equivalent adjacent samples show 1 higher srca and 13c values near the ventral margin than at time equivalent regions on lateral margins of the shell and 2 little or no variation in 18o values these observations suggest that skeletal chemistry srca and 13c is primarily controlled by rate of mantle metabolic activity and secondarily modified by variation in seawater salinity because metabolic activity in the mantle at the site of carbonate precipitation varies with shell curvature the composition of calcite secreted along lateral margins is influenced to a greater extent by metabolic activity than calcite secreted coevally at the central margin of the shell hence the chemistry of calcite secreted at the ventral margin is precipitated in near equilibrium with seawater and allows accurate estimation of seawater srca ratios and carbon isotopic composition in contrast shell precipitation along lateral margins is dominantly controlled by metabolic activity and calcite chemistry is not in equilibrium with ambient seawater in this context we present a biomineralization model where variations in skeletal srca and 13c values are explained in the context of mantle metabolic activity and seawater salinity

calcareous nannofossils as paleoproductivity indicators in upper cretaceous organic rich sequences in israel abundant and diverse calcareous nannofossil assemblages were found in organic rich carbonate sequences which accumulated in a campanian maastrichtian upwelling belt along the southeastern tethys the sequences studied represent the inner shallower and the outer deeper parts of the upwelling belt the paleoenvironmental significance of selected nannofossil taxa and their utility in productivity reconstruction was established by comparing their distribution to foraminifera and dinocyst based productivity profiles based on the calcareous nannofossil assemblages a high productivity group and a low productivity group of species were determined the distribution of these groups agrees well with the dinocyst and foraminifera based productivity curves and hence can be used to record paleoproductivity changes the ratio between the high productivity and low productivity nannofossil groups the nannofossil index of productivity nip is proposed here as a productivity proxy that can be utilized in reconstructing basinal productivity development a quantitative analysis of the nannofossil assemblages indicates that their abundance and diversity increase towards the open sea in the outer and less productive part of the upwelling belt in the inner and more productive part of the upwelling belt the nannofossils assemblages become less abundant and less diverse relative to those of the open marine environment micula decussata and watznaueria barnesae are common to abundant in most samples m decussata becomes more abundant in poorly preserved samples on the other hand the distribution of w barnesae matches better with intermediate productivity levels

middle late cretaceous climate of the southern high latitudes stable isotopic evidence for minimal equator to pole thermal gradients a detailed 18 o and 13 c stratigraphy has been generated from analysis of well preserved albian early maastrichtian foraminifera from deep sea drilling project dsdp sites 511 and 327 falkland plateau 58 s 62 s paleolatitude in the southern south atlantic and cenomanian and coniacian santonian foraminifera from dsdp site 258 naturaliste plateau 58 s paleolatitude in the southern indian ocean these results when combined with previously published maastrichtian stable isotope data from ocean drilling program odp site 690 weddell sea 65 s paleolatitude provide new insight into the climatic and oceanographic history of the southern high latitudes during middle late cretaceous time the planktonic foraminifer 18 o curves reveal a gradual warming of surface waters from the albian through the cenomanian followed by extremely warm surface waters from the turonian through the early campanian long term cooling of surface waters began in the late early campanian and continued through the end of the maastrichtian the benthic foraminifer 18 o record generally parallels changes in the oxygen isotopic curves defined by shallow dwelling planktonic foraminifera the vertical oxygen and carbon isotopic gradients were relatively low during the albian cenomanian high from the turonian early campanian and then low during the late campanian and maastrichtian foraminiferal oxygen isotopic data from published sources and this study are averaged for each site corrected for latitudinal changes in salinity based on modern day surface water values and plotted versus paleolatitude for the late albian coniacian santonian and late maastrichtian differences between lowand high latitude surface water paleotemperatures are estimated at 14 c during the late albian and late maastrichtian but the coniacian santonian reconstruction reveals only a 0 4 c latitudinal temperature gradient uncertainty regarding cretaceous salinity gradients and possible diagenetic alteration of 18 o values introduce error into our estimates of paleolatitudinal thermal gradients however apparent low equator to pole temperature differences could indicate much higher poleward heat transport than at present

mg ca sr ca and stable isotope δ18o and δ13c ratio profiles from the fan mussel pinna nobilis seasonal records and temperature relationships 1 we present new annually resolved 18o 13c mg ca and sr ca ratio records for two shells of the fast growing mediterranean fan mussel pinna nobilis collected from proximal spanish coast sea grass meadows the relationship between the potential geochemical proxies and ontogenetic and environmental controlling factors is investigated specifically the use of shell mg ca and sr ca ratios as potential calcification temperature proxies the latter calculated from measured shell 18o values has been assessed the 18o cycles along the growth axis indicate that our p nobilis specimens are 10 5 and 4 5 years old shell sr ca ratios do not exhibit any consistent interannual cyclicity and are not correlated to temperature a subtle ontogenetic effect on shell mg ca ratios was observed during the first 4 5 years of recorded growth but was highly evident during the organism s later growth years in p nobilis shells different mechanisms influence ontogenetic variation in shell mg ca and 18o records shell mg ca ratios from the first 4 5 years of growth correlate significantly to temperature in a best fit relationship described by the equation mg ca 17 16 1 95 exp 0 022 0 004 t p nobilis shell mg ca records therefore are a valid temperature proxy only during an early growth phase for the same range of temperatures shell mg ca ratios in p nobilis are approximately 1 3 lower than those reported for inorganic calcite but 3 to 4 times higher than in another bivalve species mytilus trossulus and 4 to 16 times higher than in foraminifera we suggest these offsets are due to a higher degree of similarity between seawater and calcification fluid composition in p nobilis than in other bivalves and foraminifera the observed shell mg ca ratio change per c of 2 2 also is lower than that observed for inorganic and other biogenic calcites our findings strongly support taxon and species specific mg ca temperature relationships for bivalves and other calcifying organisms an appreciation of the physiology and calcification mechanisms of any biogenic carbonate archive therefore is paramount prior to the application of stable isotope and element ca ratio proxies for paleotemperature reconstructions

ba ca ratios in shells of arctica islandica potential environmental proxy and crossdating tool abstract ba ca shell time series of marine bivalves typically show flat background levels which are interrupted by erratic sharp peaks evidence from the literature indicates that background ba ca shell ratios broadly reflect salinity conditions however the causes for the ba ca shell peaks are still controversial and widely debated although many researchers link these changes to primary productivity freshwater input or spawning events the most striking feature is that the ba ca shell peaks are highly synchronous in contemporaneous specimens from the same population for the first time we studied ba ca shell in mature and ontogenetically old up to 251 year old specimens of the long lived arctica islandica also we analyzed specimens from surface water and deeper water the typical pattern of low background and erratic peaks persisted throughout ontogeny however due to decreasing sampling resolution and greater time averaging in older slower growing shell portions the background ba ca shell values appeared to gradually increase with ontogenetic age whereas the peaks became attenuated and broader despite that ba ca shell maxima were still highly synchronous among contemporaneous specimens from the same locality and habitat confirming previous reports from short lived species computing of annual ba ca shell averages largely eliminated any bias introduced by time averaging and sampling resolution strongly elevated annual ba ca shell peaks in specimens from surface waters iceland faroe islands isle of man during the 1980s appear to coincide with an extreme primary productivity pulse recorded by remote sensing however due to the lack of in vivo experiments we cannot ultimately test a causal link between annual ba ca shell excursions and primary productivity we propose that ba ca shell time series specifically the highly synchronous ba ca shell peaks and annual ba ca shell values in contemporaneous specimens from the same locality can serve as a tool to verify crossdating and facilitate the construction of statistically robust growth increment width master chronologies long term environmental reconstructions based on bivalve shell growth chronologies can likely greatly benefit from this new technique

short term environmental change in a jurassic lagoon deduced from geochemical trends in aragonite bivalve shells the bathonian age inverbrora member of the brora coal formation northern scotland was deposited in a predominantly fresh water coastal lagoon setting however two prominent shell beds within the mostly argillaceous succession have been interpreted as resulting from temporary inundation of marine water and establishment of brackish conditions the ensuing lagoon hydrology and paleoenvironment were investigated by measuring stable isotopic 18o and 13c and trace element mg sr mn ba variations within five exceptionally well preserved aragonite shells of the bivalve isognomon murchisoni transects were sampled across the visible growth banding with a resolution of 0 25 0 15 mm for stable isotopes and 0 05 mm for trace elements oxygen and carbon isotope data define a broadly covariant trend 18o between 0 4 and 4 8 peedee belemnite pdb 13c between 2 2 and 0 7 pdb that supports a variably brackish water setting with slight seasonal evaporation absolute trace element values vary from shell to shell but show consistent patterns of covariation profiles of mg ca across shell layers display multiple sharp episodic minima that are coincident with peaks in sr ca and ba ca this is interpreted as documenting inundation of the restricted brackish water lagoon by relatively cooler seawater leading to a temporary increase in metabolic activity of the bivalves less frequent minima in mg ca sr ca 18o and 13c record fresh water influx and dramatic salinity reduction in the lagoon bivalve metabolic efficiency was decreased and in some cases breaks in shell growth occurred this study shows that in hydrodynamically complex settings trace element variation in bivalve shells can provide a detailed record of short term environmental change

stable isotope fractionation in live benthic foraminifera from the southern california borderland live specimens of benthic foraminifera have been analyzed from surface sediment samples collected from 108 to 1134 m depth in the southern california borderland the temperature and isotopic composition of the ambient water and dissolved inorganic carbon have also been measured to permit comparison of foraminiferal compositions to expected equilibrium values the species analyzed break down into four groups which reflect the influence of mineralogy aragonite vs calcite biological fractionation vital effect and microhabitat effects on isotopic composition the aragonitic hoeglundina elegans show an enrichment in 18o relative to equilibrium calcite of 0 41 0 in shallower water increasing to at least 1 06 0 in deeper water the 13c enrichment of h elegans relative to the dissolved inorganic carbon dic is also depth dependent increasing from 1 27 0 at 108 m to 2 13 0 at 940 m this depth dependence results from the change in composition of the dic the 13c composition of h elegans remains constant with depth for some unknown reason one possible explanation is that the change in composition of the dic is balanced by an increase in hoeglundina hco 3 fractionation with decreased temperature the 13c values of the cassidulina species are almost identical to those of the ambient dissolved inorganic carbon dic and reflect the decrease in the 13c of the dic with depth the 13c values of species not in 18o equilibrium vary independently of the changing composition of the dic there is a correlation between 13c and 18o among coeval species consistent with the model which explains vital effect as the result of incorporation of isotopically light metabolic co2 into the shell the magnitude of disequilibrium is relatively constant for 18o but not for 13c suggesting that in isotopic stratigraphy studies it may be difficult to calibrate the 13c of different species as has been done with 18o there appears to be a relationship between taxonomic group and vital effect the foraminifera in approximate 18o equilibrium with the water including species of cassidulina bolivina uvigerina and globobulimina are members of the family cassidulinidae or superfamily buliminacea those not in 18o equilibrium including species of pyrgo quinqueloculina triloculina and lenticulina belong to the families miliolidae and vaginulinidae no disequilibrium species have been found as yet in the low oxygen environments of the borderland this observation and published findings on the ultrastructure of benthic foraminifera suggest that isotopic behavior may be related to a foraminifer s ability to exchange gases rapidly with its ambient water

late turonian climate variability in the bohemian cretaceous basin a sclerochronological study of inoceramus hercules shells from the upohlavy quarry czech republic abstract the 18o record of well preserved shells of the inoceramid inoceramus hercules from the upohlavy working quarry czech republic provides an insight into the climate variability in the late turonian benthic environment of the bohemian cretaceous basin similar to modern bivalves this inoceramid species built its shell near equilibrium with the oxygen isotope value of the ambient water due to the nearly year round shell growth sequentially sampled 18o values allowed to estimate the narrowest sub annual temperatures fluctuations that prevailed during lifetime of the organisms in accordance with previous studies reconstructed temperatures suggest colder water conditions 19 0 0 9 c during the earliest late turonian coinciding with the hyphantoceras event also known as hitch wood event than during the later part of the substage 20 9 1 1 c climate warming however did not affect the sub annual temperature fluctuations evenly but predominantly affected the warmest part of the year at least 4 0 c on the contrary the coldest recorded temperatures remained more or less invariant varying not much more than 1 0 c across the studied time interval the observed changes in the benthic temperature estimates likely reflect shifts in seasonal sea surface temperature amplitudes in response to climate forcing given the widespread distribution of i hercules in the upper turonian lower coniacian hemipelagic strata of europe the present study sets the basis for future continent wide sub annually resolved climate reconstructions

isotopic and chemical intra shell variations in low mg calcite of rudist bivalves mollusca hippuritacea disequilibrium fractionations and late cretaceous seasonality isotopic 13c 18o and elemental mg sr mn fe compositions were analysed in sclerochronological profiles of several shells of late cretaceous rudist bivalves from greece turkey somalia and the arabian peninsula the preservation of original compositions of low mg calcite of outer shell layers is indicated by constant and high sr generally low fe and mn and the preservation of fibrous prismatic ultrastructures cyclic variations in 18o and mg are interpreted to reflect seasonal temperature salinity cycles and thus annual growth increments in shells of torreites amplitudes of correlated 13c and 18o cycles cannot be related to reasonable palaeotemperatures or salinity this isotopic pattern reflects vital fractionations of an extent which is unknown from modern bivalves in contrast almost identical ranges and amplitudes of 18o cycles are observed in 13 shells of five species from santonian campanian localities in central greece and northern turkey suggesting that seasonal variations in environmental conditions were recorded without significant vital fractionations the effect of seasonal salinity changes on 18o of the shells is evaluated and mean palaeotemperatures are constrained within the range of 30 32 5 c the annual range of temperature was estimated to be 7 c assuming a constant salinity this agrees with other isotopic proxies of late cretaceous palaeotemperatures and with global circulation models which predict higher low latitude sea surface temperatures than the present ones

variability in late cretaceous climate and deep waters evidence from stable isotopes abstract strong climatic and temperature fluctuations mark the late campanian and maastrichtian as indicated by stable isotope records from the equatorial pacific site 463 and middle and high latitude south atlantic sites 525 689 and 690 the first major global cooling decreased intermediate water temperatures iwt by 5 6 c between 73 70 ma at the same time sea surface temperature sst decreased by 4 5 c in middle and high latitudes intermediate waters iw temporarily warmed by 2 c in low and middle latitudes between 70 68 5 ma global cooling resumed between 68 5 65 5 ma when iwt decreased by 3 4 c and sst by 5 c in middle latitudes about 450 ka before the cretaceous tertiary boundary rapid global warming increased iwt and sst by 3 4 c though sst in the tropics changed little during the last 200 ka of the maastrichtian climate cooled rapidly with iwt and sst decreasing by 2 3 c during the global cooling at 71 70 ma and possibly at 67 65 5 ma the sources of cold intermediate waters in the equatorial pacific indo pacific and south atlantic were derived from the high latitude north pacific in contrast during the global climate warming between 65 2 65 4 ma the middle latitude south atlantic was closest to the source of iw production and implies that the low latitude tethys played a major role in global climate change climate changes sea level fluctuations and associated restricted seaways appear to be the most likely mechanisms for the alternating sources of iw production

high temperatures in the late cretaceous arctic ocean to understand the climate dynamics of the warm equable greenhouse world of the late cretaceous period it is important to determine polar palaeotemperatures the early palaeoceanographic history of the arctic ocean has however remained largely unknown because the sea floor and underlying deposits are usually inaccessible beneath a cover of floating ice a shallow piston core taken from a drifting ice island in 1970 fortuitously retrieved unconsolidated upper cretaceous organic rich sediment from alpha ridge a submarine elevated feature of probable oceanic origin a lack of carbonate in the sediments from this core has prevented the use of traditional oxygen isotope palaeothermometry here we determine arctic palaeotemperatures from these upper cretaceous deposits using tex86 a new palaeothermometer that is based on the composition of membrane lipids derived from a ubiquitous component of marine plankton crenarchaeota from these analyses we infer an average sea surface temperature of approximately 15 degrees c for the arctic ocean about 70 million years ago this calibration point implies an equator to pole gradient in sea surface temperatures of approximately 15 degrees c during this interval and by extrapolation we suggest that polar waters were generally warmer than 20 degrees c during the middle cretaceous approximately 90 million years ago

mechanism and controls of silicification of fossils in limestones silicification of calcitic fossils occurs along thin solution films at which calcite dissolves and silica precipitates the mechanism is replacement controlled by force of crystallization whereby the growth of the silica phase exerts pressure across the silica carbonate contact increasing the gibbs free energy and hence solubility of shell calcite physical evidence for force of crystallization controlled replacement includes restriction of carbonate dissolution to the silica carbonate contact and euhedral quartz terminations at some quartz calcite contacts correlations among some replacement quartz types and fossil taxa indicate that shell microstructure and bulk pore water silica concentration control replacement quartz type

the giant pacific oyster crassostrea gigas as a modern analog for fossil ostreoids isotopic ca o c and elemental mg ca sr ca mn ca proxies 1 modern analogs are an essential part of palaeoclimate studies because they provide the basis for the understanding of geochemical signatures of fossils ostreoids are common in many sedimentary sequences and because of their fast growth high temporal resolution sampling of past seasonal variability is possible here two shell structures of modern giant pacific oysters crassostrea gigas the chalky substance and foliate layers have been sampled for trace element distributions mg sr mn and stable isotope variability c o ca oxygen isotopes exhibit a clear seasonal signature mean carbon isotope values of different oysters agree within 0 1 but ontogenic variability is complicated by shell growth patterns and potential small vital effects the calcium isotope ratios are found to be constant throughout ontogeny within analytical precision at a value of 44 40ca 0 68 0 16 2 sd srm 915a which is consistent with other bivalve species calcium isotope ratios in oyster shell material might thus be a possible proxy for palaeo seawater calcium isotope ratios element ca ratios are significantly higher in the chalky substance than in the foliate layers and especially high sr ca and mn ca ratios are observed for the first growth season of the oysters mg ca ratios in the chalky substance show a negative correlation with 18o values compatible with a temperature dependence whereas this correlation is absent in the foliate layers seasonal changes of sr ca are controlled by metabolic processes whereas for mn ca an additional environmental control is evident

the maastrichtian transgression onto the northwestern flank of the proto oman mountains sequences of rudist bearing beach to open shelf facies

stable isotope sclerochronology of rudist bivalves growth rates and late cretaceous seasonality the almost complete translation of shell accretion to vertical growth was a successful morphogenetic adaptation of rudist bivalves which replaced coral algal hydrozoan communities in most tethyan shallow marine environments during the cretaceous growth rates of rudist shells are therefore important in reconstructions of cretaceous shallow marine benthic communities carbon and oxygen isotopic compositions were analyzed in sclerochronological profiles through the shells of two late cretaceous rudist bivalves from greece and turkey values of 13 c vary between 0 8 and 2 2 in the hippuritid vaccinites ultimus and between 0 8 and 2 6 in the radiolitid gorjanovicia cf costata ranges in 18 o are 5 3 to 2 9 and 4 6 to 2 1 respectively a distinct cyclicity of 13 c and 18 o in both shells reflects late cretaceous seasonality and indicates annual vertical growth increments of 45 mm in v ultimus and 54 mm in gorjanovicia the concentrations of minor elements are similar to those of extant bivalves with low mg calcite shells

concentration of carbon dioxide in the late cretaceous atmosphere stable carbon isotope data from late cretaceous maastrichtian palaeosols in india are used to estimate the concentration of carbon dioxide in the late cretaceous atmosphere we show that the maastrichtian atmosphere is unlikely to have contained more than about 1300 ppm by volume of co 2 this value agrees with an independently modeled value of co 2 in the late cretaceous atmosphere a low concentration of the greenhouse gas carbon dioxide in the maastrichtian atmosphere relative to concentrations in the earlier cretaceous is consistent with palaeotemperature information from terrestrial plant and marine fossils which suggest that the global climate cooled toward the end of the cretaceous period

coupling between sulfur recycling and syndepositional carbonate dissolution evidence from oxygen and sulfur isotope composition of pore water sulfate south florida platform u s a sulfur cycling in fe poor organic rich shelf carbonates known to have rapid rates of so4 2 reduction remains poorly studied despite the volumetric significance of shelf deposits in modern and ancient carbon budgets we investigated sulfur cycling in modern carbonates of the florida platform from end member depositional environments muddy sands from the atlantic reef tract and finer grained mudbank and island flank deposits from florida bay relations between pore water chemistry so4 2 co2 ca 2 cl and oxygen and sulfur stable isotope compositions of so4 2 require direct coupling between sulfur redox cycling and syndepositional carbonate dissolution oxygen isotope compositions of pore water sulfate were remarkably shifted away from the established value for marine so4 2 9 5 despite near normal so4 2 cl ratios chemical evolution was least in reef tract pore waters and greatest in florida bay relative to overlying seawater mudbank sediments exhibited sulfate depletion with 18oso4 and 34sso4 values both increasing by about 7 more bioturbated island flank sediments colonized by thalassia grass had a 5 increase in 18oso4 variable 34sso4 values 17 7 to 23 3 and exceptionally high ca 2 cl ratios the large excess of ca 2 up to 1 7 mm requires a much larger acid source than the amounts derived from utilization of dissolved o2 0 3 mm and small degrees of net so4 2 reduction 0 5 mm reduced a conceptual model was constructed using chemical and isotopic data on natural pore waters and on sulfate isotope fractionation factors obtained from sediment incubation experiments the model outputs show that pore water compositions can be explained by a redox cycle where microbial so4 2 reduction is followed by very efficient h2s oxidation thus maintaining virtually invariant so4 2 cl ratios the enhanced o2 transport may be driven by associated marine grass rhizome systems and microbial communities established in bioturbated sediments the net result of the cycle is that the rate of sulfide oxidation which is largely balanced by the rate of microbial sulfate reduction is stoichiometrically related to the rate of carbonate dissolution this is consistent with previously reported rates of carbonate dissolution 400 mol cm2 yr and average rates of sulfate reduction 200 mol cm2 yr from the florida platform and a 2 1 stoichiometry

seeing red in cyclic stratigraphy spectral noise estimation for astrochronology 1 fundamental to the development of astronomical time scales is the recognition of oscillatory variability within stratigraphic data and its evaluation relative to a null noise hypothesis in this study monte carlo simulations are used to investigate the suitability of two commonly used noise hypotheses the conventional and robust ar1 approaches and the results highlight important limitations in both for cyclostratigraphic application perhaps most problematic the robust ar1 method can result in inflated confidence level estimates and excessive clumping of false positives within the low frequency portion of the spectrum especially when the underlying noise process has a high lag 1 autocorrelation given typical cyclostratigraphic records this technique will often impose significant eccentricity band variability even in the case of pure ar1 noise an alternative spectral noise estimation method is proposed to overcome these problems which simultaneously allows for departures from the ar1 assumption and obtains high statistical power that is the ability to accurately identify astronomical signals when they are present in the data we apply the method to un tuned 18o data from miocene sediments of the ceara rise indicating statistically significant spectral power at frequencies that are consistent with the published orbital interpretation of weedon et al 1997 furthermore evaluation of the frequency arrangement of the significant spatial bedding periods using the average spectral misfit method for astrochronologic testing reveals that the null hypothesis of no orbital influence can be rejected with a high degree of confidence the 99 8 confidence level

oxygen isotopes in meteoric calcite cements as indicators of continental paleoclimate because meteoric water 18 o values decrease with decreasing ambient temperature and increasing latitude 18 o values of meteoric calcite cement should exhibit a similar relation with paleolatitude and be an indicator of continental paleotemperatures to test this we compiled isotopic and paleolatitude data for 20 meteoric cements and nine speleothems ranging in age from devonian to modern and in paleolatitude from 3 5 to 83 mean 18 o values for meteoric cements and speleothems both show the same negative correlation with paleolatitude the 18 o vs latitude trend for these carbonates is almost identical to that predicted for modern inland environments but differs from the trend for coastal environments this suggests that the ground water controlling the ultimate composition of meteoric cement is derived predominantly from inland recharge if it is assumed that the modern meteoric water 18 o vs temperature relation is valid for the past and that insignificant evaporation occurred prior to carbonate precipitation then coastal and inland paleotemperatures can be calculated from the 18 o values of meteoric calcite 18 o mcl and seawater 18 o sw by using the equations t coastal 13 3 32 6 0 231 0 0613 18 o mcl 18 o sw and t inland 17 8 16 2 0 572 0 1233 18 o mcl 18 o sw where t is temperature in c calcite precipitated from coastal meteoric water at temperatures between 0 and 25 c will exhibit a narrow range in 18 o 6 to 4 where 18 o sw 0 the 18 o of calcite precipitated from inland meteoric water will be sensitive to paleotemperature ranging from 14 to 5 where 18 o sw 0 for temperatures of 0 to 25 c

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

climatic fluctuations and seasonality during the late jurassic oxfordian early kimmeridgian inferred from δ18o of paris basin oyster shells abstract oxygen isotope data from biostratigraphically well dated oyster shells from the late jurassic of the eastern paris basin are used to reconstruct the thermal evolution of western tethyan surface waters during the early oxfordian early kimmeridgian interval seventy eight oyster shells were carefully screened for potential diagenetic alteration using cathodoluminescence microscopy isotope analyses were performed on non luminescent parts of shells n 264 intra shell 18 o variability was estimated by microsampling along a transect perpendicular to the growth lines of the largest oyster shell the sinusoidal distribution of the 18 o values along this transect and the dependence of the amplitude of variations with bathymetry suggest that intra shell variability reflects seasonal variations of temperature and or salinity average amplitudes of about 5 c in shallow water environments and of about 2 3 c in deeper offshore environments are calculated these amplitudes reflect minimum seasonal temperature variation our new data allow to constrain existing paleotemperature trends established from fish tooth and belemnite 18 o data and are in better agreement with paleontological data more specifically a warming trend of about 3 c is reconstructed for oceanic surface waters during the early to middle oxfordian transition with maximum temperatures reaching 24 c in the transversarium zone late middle oxfordian from the transversarium zone to the bimmamatum zone a cooling of about 7 c is indicated whereas from the bimmamatum zone temperatures increased again by about 7 c to reach 24 c in average during the cymodoce zone early kimmeridgian

chemical variation in pennsylvanian brachiopod shells diagenetic taxonomic microstructural and seasonal effects abstract to improve our ability to use minor and trace element mte variation in biotic carbonates as diagenetic and paleoenvironmental indicators we performed electron probe microanalysis on more than 100 late pennsylvanian brachiopod shells from texas kansas missouri and new mexico texturally preserved specimens of the genera crurithyris composita and neospirifer from all three regions were analyzed as were eridmatus specimens from texas twenty measurements were made in two transects across each shell shell microstructure and cathodoluminescence were described for each spot analyzed three modern shells were analyzed for comparison diagenesis as indicated by cathodoluminescence and or absence of microstructure tends to enrich shells in fe and mn x ca 0 7 mmol mol and deplete shells in na and s mg content shows no consistent trend with diagenesis in fabric retentive nonluminescent shell areas mg na and s contents vary twofold to sevenfold depending on taxonomy microstructure and season overall taxonomy is the dominant factor controlling mte composition na and s concentrations are consistently highest in crurithyris and eridmatus intermediate in neospirifer and lowest in composita in taxa with mixed microstructure composita neospirifer secondary fibrous layer calcite contains 1 5 to 2 times more na than does interlayer prismatic calcite thus whole shell na contents of these taxa depend on the proportion of fibrous and prismatic shell seasonal cycles are revealed in mte transects across growth lines mg na and s contents commonly vary by more than a factor of two between maxima presumably summer and minima winter within the same shell retention of taxonomic microstructural and seasonal effects in shell chemistry argues for preservation of original chemistry in fabric retentive nonluminescent paleozoic brachiopod shells

silica replaced fossils through the phanerozoic a systematic survey of 1863 papers on macrobenthic assemblages reveals that an average of 21 of published paleozoic papers concern silicified fossils but that average drops to just 4 for post paleozoic papers during the paleozoic silicified fossil occurrences do not significantly correlate with the amount of shelf chert outcrop area time duration of geologic intervals or carbonate rock volume this substantial drop in numbers of silicified fossils coincides temporally with increased importance of aragonite faunas following the end permian extinctions however qualitative measurements of secular changes in abundance and diversity of siliceous sponges are consistent not only with the post paleozoic decline in fossil silicification but also with fluctuations in the amount of silicified fossils throughout the paleozoic the facies distribution of silicified fossils in the permian of west texas also suggests that the distribution of silicified fossils may reflect the occurrence of siliceous sponges the decline in silicified fossils after the permian may be related to a concomitant rise in offshore bedded chert deposition and movement of the locus of biogenic silica formation from nearshore to offshore regions beginning in the triassic rather than with the expansion of diatoms in the cretaceous

oxygen isotope fluctuations in a modern north sea oyster crassostrea gigas compared with annual variations in seawater temperature implications for palaeoclimate studies abstract a total of 181 oxygen isotope values from sequential samples of the left shell of a modern pacific oyster crassostrea gigas that lived on a sub tidal oyster bank in the list basin north sea germany shows periodically varying values between 1 3 and 2 5 in order to test whether these 18 o fluctuations reflect seawater temperature changes the isotope values of the shell were compared to actual seawater temperature variations from the region c gigas serves as an excellent proxy for temperature of palaeoseawater and the results show that the examined oyster precipitated its shell in 18 o equilibrium with the ambient seawater a cessation of the oyster shell calcification starts at water temperatures below 6 c at lower temperatures than previously thought for crassostrea for palaeoclimate investigations the termination of shell production is important because the lowest temperatures might not be represented in the shell higher water temperatures are therefore potentially over represented in time spans when the shell grows faster and mean oxygen isotope values may potentially bias the mean seawater temperatures of annual variations towards higher temperatures

autopsy of a reservoir facies architecture in a multidam system elwha river washington usa the 2011 2014 removal of two large dams on the elwha river washington state the largest dam removal yet completed globally created extensive cutbank exposures of reservoir sediments allowing the first characterization of the facies architecture of sediments through direct observation in reservoirs worldwide and providing an unparalleled opportunity to assess the relationship between environmental influences such as changes in sediment supply and their expression in the stratigraphic record using a combination of facies description from observation of 49 measured sections and 100 exposures and analysis of digital elevation models and historic aerial photographs we delineated the characteristic depositional zones of each reservoir and mapped the evolution of the subaerial delta over the life span of the reservoir former lake mills the younger upstream reservoir was characterized by a tripartite subaerial gilbert style delta that prograded 1 km into the main reservoir from 1927 to 2011 sediments were composed of coarse grained topset beds steeply dipping foreset beds and a fine grained gently dipping prodelta while individual event horizons were discernible in fine grained sediments of former lake mills their number and spacing did not correspond to known drawdown or flood events former lake aldwell impounded from 1913 to 2011 was initially defined by the rapid progradation of a gilbert style subaerial delta prior to the upstream completion of glines canyon dam however the 1927 closure of glines canyon dam upstream caused the delta to evolve to a fine grained mouth bar type delta indicative of low finer grained sediment this evolution combined with a previously unrecognized landslide deposit into the upper delta plain suggests that understanding the exogenic influences on reservoir sedimentation is critical to interpretation and prediction of the sedimentation within individual systems

tropical seasonality in the late campanian late cretaceous comparison between multiproxy records from three bivalve taxa from oman abstract geochemical proxy records from calcite shells of bivalves constitute an important archive for the reconstruction of palaeoenvironmental conditions on sub annual timescales however the incorporation of these trace element and stable isotope proxies into the shell is influenced by a multitude of physiological and environmental factors that need to be disentangled to enable reliable reconstruction of palaeoclimate and palaeoenvironment in this study records of multiple proxies in three bivalve taxa from the same late campanian locality in oman are used to study the expression of various geochemical proxies in relation to each other and to the palaeoenvironment micro x ray fluorescence mapping allows the localization discussion and evasion of diagenetically altered parts of the fossil shells x ray fluorescence line scanning calibrated with laser ablation inductively coupled plasma mass spectrometry is used to measure trace element profiles through well preserved calcitic parts of the shells records of stable carbon and oxygen isotope ratios of shell calcite are combined with these high resolution trace element concentration profiles to study sub annual variations in shell chemistry and reconstruct changes in the palaeoenvironment of the bivalves on a seasonal scale spectral analysis routines are used to detect cyclicity in stable isotope 18o and 13c and trace element mg ca sr ca s ca and zn ca records differences in seasonal expression between these chemical proxies and between individual shells are discussed in terms of the relative influence of palaeoenvironment and potential species specific physiological effects stable oxygen isotope ratios between shells suggest a local palaeotemperature seasonality of 8 c around an annual mean of 28 c with the shell of the rudistid torreites sanchezi milovanovici yielding slightly higher average temperatures the discussion of the application of various mg ca palaeotemperature calibrations on mg ca records in these bivalve species emphasizes the complexity of using trace element proxies in extinct bivalve species it shows that long term changes in mg ca ratios in ocean water need to be taken into account and that mg ca ratios in bivalves might be influenced by vital effects sr ca and s ca ratios in these fossil taxa are likely controlled by growth and metabolic rates of the shell although an influence of local salinity on strontium to calcium ratios cannot be excluded sub annual variations in zinc concentrations in shell calcite may reflect seasonal variations in palaeoproductivity and redox conditions in the water column

geochemistry of brachiopods oxygen and carbon isotopic records of paleozoic oceans abstract combined trace element and isotope studies of 319 brachiopods covering the ordovician to permian time span show that 13c and 18o in well preserved specimens varied during the paleozoic the overall 13c secular trend is in accord with the previously published observations but its details are obscured by vital isotopic fractionation effects at generic level nonetheless the results suggest that the negative correlation between marine 13ccarbonate and 34ssulphate deteriorates at time scales of 106 years due to the long residence time and thus slow response of so42 in the ocean for oxygen isotopes all devonian and older specimens have 18o of 4 while the well preserved permian samples have near present day 18o of about 1 pdb this isotopic dichotomy is probably not due to post depositional phenomena salinity or biogenic fractionation effects this leaves open the perennial arguments for a change in 18 o 16 o of sea water versus warmer ancient oceans the present data are difficult to explain solely by the temperature alternative the coincidence of the proposed shift in 18o with the large late paleozoic changes in marine 87 sr 86 sr 13 c 12 c 34 s 32 s and sea level stands argues for a tectonic cause and for a change in 18 o 16 o of sea water although such explanation is difficult to reconcile with global balance considerations and with isotopic patterns observed in alteration products of ancient basalts and ophiolites whatever the precise cause or combination of causes the implications for tectonism and or paleoclimatology are of first order significance

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

evolution of middle to late cretaceous oceans a 55 m y record of earth s temperature and carbon cycle a new 55 m y global compilation of benthic foraminifera 13 c and 18 o for the middle to late cretaceous shows that there was widespread formation of bottom waters with temperatures 20 c during the cretaceous greenhouse world these bottom waters filled the silled north atlantic and probably originated as thermocline or intermediate waters in the tropical oceans carbon burial during the cretaceous oceanic anoxic events produced a positive 13 c shift in global carbon reservoirs but this is not particularly large especially by comparison with the remarkable late paleocene carbon maximum the interbasin 13 c gradient was unusually large during the cretaceous hot greenhouse probably because the north atlantic sills prevented the free exchange of waters in the deep basin the hot greenhouse ended when the equatorial atlantic gateway opened sufficiently to flood the deep north atlantic with relatively cool polar waters formed in the southern ocean

benchtop μxrf as a tool for speleothem trace elemental analysis validation limitations and application on an eemian to early weichselian 125 97 ka stalagmite from belgium abstract variations of trace element e g mg sr ba fe zn etc concentrations along a speleothem s growth axis constitute important paleoclimate proxies the use of laboratory micro x ray fluorescence spectrometry as a fast and cheap alternative for conventional mass spectrometry techniques for trace element analysis on speleothems has been explored in the past and yielded satisfactory results however within the speleothem community there is need for an in depth investigation of the full potential of this analytical technique compared to other types of paleoclimate archives benchtop xrf analysis on speleothems is analytically more challenging because of the high crystalline speleothem matrix and the low abundance of the elements of interest in this study several speleothem samples with differences in mineralogy calcite versus aragonite and composition are investigated various instrumental parameters are tested and recommendations are made for future studies applying xrf analysis to speleothems quantification based on a multiple standard calibration and an assessment of the error is carried out through validation with mass spectrometry techniques it is confirmed that benchtop xrf devises are able to generate speleothem trace element records successful results were obtained for sr mg and fe while zn and ba were quantified in samples characterized by high concentrations nevertheless caution has to be taken when interpreting the results due to the presence of diffraction caused by the crystallinity of the samples the elements which provide reliable results are sample specific and depend on the type of matrix and elemental abundance these findings are applied on an eemian to early weichselian stalagmite from the han sur lesse cave belgium time series were constructed for mg and sr creating a multiproxy dataset together with previously obtained stable isotope 13c and 18o ratios growth rate and stalagmite morphology it appears that mg and sr are not primarily controlled by prior calcite precipitation but rather by changes in vegetation activity above the cave

secular oscillations in the carbonate mineralogy of reef building and sediment producing organisms driven by tectonically forced shifts in seawater chemistry the primary mineralogy of oolites and early marine carbonate cements led sandberg nature 305 1983 19 22 to divide the phanerozoic eon into three intervals of aragonite seas and two intervals of calcite seas hardie geology 24 1996 279 283 has shown that these oscillations together with synchronous oscillations in the mineralogy of marine potash evaporites can be explained by secular shifts in the mg ca ratio of seawater driven by changes in spreading rates along mid ocean ridges the hardie model also predicts that high mg calcite should precipitate along with aragonite as it does in today s aragonite sea we have uncovered oscillations in the carbonate mineralogy of hypercalcifying organisms ones that have produced massive skeletons large reefs or voluminous bodies of sediment that correspond to sandberg s aragonite seas and calcite seas and that are predicted by the hardie model particular groups of corals sponges and algae appear to have been dominant reef builders only when favored by an appropriate mg ca ratio in seawater in early and middle paleozoic calcite seas calcite i reefs were dominated by calcitic tabulate heliolitid and rugose corals and calcitic stromatoporoids in contrast during the period of late paleozoic early mesozoic aragonite seas aragonite ii aragonitic groups of sponges scleractinian corals and phylloid algae as well as high mg calcitic red algae were principal reef builders during late cretaceous time at the acme of calcite ii massive rudists displaced aragonitic hermatypic corals in today s aragonite sea aragonite iii scleractinian corals are again dominant reef builders along with high mg calcitic coralline algae major sediment producing algae exhibit temporal patterns similar to those of reef builders calcitic receptaculitids flourished during calcite i whereas aragonitic dasycladaceans did not become dominant rock formers until aragonite ii during calcite ii calcitic nannoplankton formed massive coccolith chalks in warm shallow seas of the late cretaceous after the mg ca ratio of seawater had reached a very low value and calcium concentration a very high value as the mg ca ratio of seawater rose and calcium concentration fell during the cenozoic era individual coccoliths on average became less massive and encrusted cells less thickly by pliocene time during aragonite iii the prominent genus discoaster secreted only narrow rayed coccoliths that covered less than 25 of the cell surface also during aragonite iii the aragonitic green alga halimeda emerged as the dominant skeletal sediment producer in reef tracts the influence of seawater chemistry on skeletal secretion appears to have been especially strong for morphologically simple taxa that exert relatively weak control over their own calcification such groups include algae sponges corals and bryozoans morphological simplicity also permits these groups to adopt vegetative or colonial modes of growth that confer success in competition for space on reefs this linkage in addition to the basic chemical demands of hypercalcification has given the mg ca ratio of seawater strong control over the success of individual reef building taxa more generally this ratio appears to have strongly influenced evolutionary changes in the skeletal mineralogy of sponges and cheilostome bryozoans throughout their history we conclude that throughout phanerozoic time a chain of causation has extended from mid ocean ridge processes via seawater chemistry to the mineralogical and biological composition of reef communities and bioclastic carbonate deposits

deep sea paleotemperature record of extreme warmth during the cretaceous oxygen isotope analyses of well preserved foraminifera from blake nose 30 n paleolatitude north atlantic and globally distributed deep sea sites provide a long term paleotemperature record for the late albian maastrichtian interval that is difficult to reconcile with the existence of significant cretaceous ice sheets given reasonable assumptions about the isotopic composition of cretaceous seawater our results suggest that middle bathyal water temperatures at blake nose increased from 12 c in the late albian through middle cenomanian to a maximum of 20 c during the latest cenomanian and earliest turonian bottom waters were again 12 c during the middle campanian and cooled to a minimum of 9 c during the maastrichtian correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from blake nose comparison of global bottom water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late albian through late cenomanian to a hot greenhouse phase during the latest cenomanian through early campanian then to cool greenhouse conditions during the mid campanian through maastrichtian

high resolution analysis of trace elements in crustose coralline algae from the north atlantic and north pacific by laser ablation icp ms we have investigated the trace elemental composition in the skeleta of two specimens of attached living coralline algae of the species clathromorphum compactum from the north atlantic newfoundland and clathromorphum nereostratum from the north pacific bering sea region amchitka island aleutians samples were analyzed using laser ablation inductively coupled plasma mass spectrometry la icp ms yielding for the first time continuous individual trace elemental records of up to 69 years in length the resulting algal mg ca sr ca u ca and ba ca ratios are reproducible within individual sample specimens algal mg ca ratios were additionally validated by electron microprobe analyses amchitka sample algal sr ca u ca and ba ca ratios were compared to algal mg ca ratios which previously have been shown to reliably record sea surface temperature sst ratios of sr ca from both clathromorphum species show a strong positive correlation to temperature dependent mg ca ratios implying that seawater temperature plays an important role in the incorporation of sr into algal calcite linear sr ca sst regressions have provided positive but weaker relationships as compared to mg ca sst relationships both algal mg ca and sr ca display clear seasonal cycles inverse correlations were found between algal mg ca and u ca ba ca and correlations to sst are weaker than between mg ca sr ca and sst this suggests that the incorporation of u and ba is influenced by other factors aside from temperature

the temperature relationship in coralline aragonite influence of variability in and skeletal growth parameters this paper provides an evaluation of two of the most likely pitfalls of sr ca thermometry i e the effect of biogenic cycling of sr vs ca in the surface ocean and the effect of variable extension rate on sr incorporation in coralline aragonite the authors also report calibration of the sr ca temperature relationship for three coral species porites lobata pocillopora eydouxi and pavona clavus collected for the hawaiian and galapagos islands analyses of seawater samples show significant spatial and depth variability in the sr ca ratio the uncertainty introduced by this effect is estimated to be 0 2 degrees c for corals located in tropical oligotrophic waters and potentially larger for corals located in upwelling areas sr ca along two different growth axes of a galapagos pavona clavus with annual extension rates of approximately 6 and 12 mm y respectively indicate an offset of 1 2 degrees c with higher sr ca values associated with slower extension rates the offset observed between the two growth axes may be the result of variations in extension and or calcification rate these results are important in determining past sea surface temperatures for reconstruction of paleoclimates

multi proxy reconstructions of northeastern pacific sea surface temperature data from trees and pacific geoduck abstract we demonstrate the potential for developing sea surface temperature sst reconstructions in the northeast pacific from combinations of tree ring and growth increment chronologies of the long lived marine bivalve the pacific geoduck six pacific geoduck chronologies developed from site along the washington british columbia coast are compared and combined with tree ring chronologies from california to alaska all chronologies are annually resolved and strongly relate to local to regional scale sst though differences in the response season as well as the spectral properties of the two proxies are observed both proxy types closely track sst and when used in combination yield a more robust sst reconstruction than tree ring or geoduck chronologies could provide alone in total variance explained in sst is 63 9 at the regional scale and 68 2 at a local scale providing sst estimates for more than 60 years prior to the start of continuous instrumental records in this region this study represents one of the few climate reconstructions where both proxies are annually resolved and is the first to integrate regional networks of geoduck chronologies and tree ring chronologies

mg ca sr ca and stable isotopes in modern and holocene protothaca staminea shells from a northern california coastal upwelling region this study explores the potential of intertidal protothaca staminea shells as high resolution geochemical archives of environmental change in a coastal upwelling region mg ca and sr ca ratios were analyzed by excimer laser ablation inductively coupled plasma mass spectrometry la icp ms at sub weekly temporal resolution in shells growing 1 mm per month growth patterns of a modern p staminea shell from humboldt bay california collected in december 1999 made it possible to infer a lifespan from 1993 to 1998 growth hiatuses in the shell may have excluded records of extreme events mg ca ratios appeared to be partly controlled by water temperature the correlation coefficient between temperature and mg ca was r 0 71 in one of four growth increments significant year to year differences in the sensitivity of mg ca to temperature in p staminea could not be explained however sr ca ratios appeared to be more closely related to shell growth rate oxygen isotopes measured at 2 week temporal resolution in the same shell did not show a clear relation to local temperature in summer possibly because temperatures were higher and less variable at the king salmon mudflat where the shell was collected than in the main channel of humboldt bay where water properties were monitored negative shell 13c values 0 5 marked spring and summer coastal upwelling events the mg contents of p staminea midden shells dated to 3 ka and 9 ka were significantly lower than in the modern shell this may have resulted from degradation of a mg rich shell organic matrix and precluded quantitative interpretation of the older high resolution records elevated 13c values in the 3 ka shell suggested that the individual grew in highly productive or stratified environment such as a shallow coastal embayment or lagoon

oxygen isotope and mg ca composition of late visean mississippian brachiopod shells from sw iberia palaeoclimatic and palaeogeographic implications in northern gondwana abstract latest visean brachiopod shells gigantoproductus sp from the pedroches basin of sw spain were sampled in order to obtain chemical and isotopic evidence that may help first to assess if primary geochemical and isotopical signals are preserved in these shells and second to reconstruct temporal variations in palaeoceanographic and palaeoclimatic conditions in northern gondwana during this time span microtexture cathodoluminescence cl and ultrastructure under sem of the brachiopods were examined to avoid sampling of shell portions altered after deposition shell portions classified as non luminescent nl and non luminescent to slightly luminescent nl sl present geochemical signatures within the ranges considered normal for recent brachiopods that have not undergone significant diagenetic modification these include low to undetectable fe and mn contents high sr values and 18o values similar to those of carbonates in equilibrium with seawater on the other hand valve areas that are luminescent l or moderately luminescent with luminescent portions ml l present higher fe and mn contents lower sr concentrations and lower 18o values than those corresponding to nl and nl sl shells this suggests a greater diagenetic alteration of these portions and that they acted as microzones of reaction with the diagenetic fluids temporal trends through the studied interval show a spread in 13c values much lower than that observed for contemporaneous samples up to 1 6 thus obscuring the 13c global signal at the time scale resolution of this study in contrast the 18o record of brachiopod calcite 18oc shows an overall increase of 1 relative to v pdb from the oldest to the youngest samples this is accompanied by a 30 decrease in mg ca ratios of the brachiopod calcites confirming that at least part of this shift in 18oc was related to cooling combination of mg ca and 18oc proxies established in this paper although not full proof for brachiopods yet allowed for the calculation of a temperature drop of 3 3 c and a change in seawater 18ow that becomes 0 4 more positive during this interval the data are consistent with regional seawater cooling that accompanied an increase in continental ice volume over a relatively short time period of

geochemistry of dissolved trace metals cadmium copper zinc in the scheldt estuary southwestern netherlands impact of seasonal variability the distribution of dissolved cd cu and zn in the scheldt estuary has been studied during eight axial surveys carried out between february 1987 and february 1988 the observed metal salinity profiles depend on the season during spring and summer when the river water is anoxic containing traces of dissolved sulfide the dissolved metal concentrations in the riverine endmember are extremely low this observation is ascribed to formation of sparingly soluble metal sulfides in the water column during winter when the river water is not totally devoid of oxygen 10 40 saturation the dissolved cu and zn concentrations in the riverine endmember are an order of magnitude higher but rapid removal is apparent in the very low salinity zone flocculation of organometal complexes or coagulation of colloid associated metals sediment resuspension and formation of particulate fe and mn oxyhydroxides are likely to be involved in the removal process at higher salinities maxima of dissolved zn at 6 9 10 3 cu at 9 18 10 3 and cd at 12 21 10 3 are consistently found over the year these maxima are ascribed to dissolution and desorption of particulate metal forms with increasing salinity reoxidation of trace metal sulfides during transport from the anoxic or suboxic upper estuary to the fully oxygenated lower estuary is suggested as the first step in the mobilization process during phytoplankton blooms desorption of cd and zn but not cu is suppressed which is attributed to the ph increase related to primary production and to biological uptake the impact of mobilization processes in the scheldt estuary is reflected by effective dissolved cd and cu concentrations which are much higher than the observed metal concentrations in the river water based on these findings it is expected that restoration of the dissolved oxygen concentration which is a major goal of the present day management of the scheldt estuary will lead to an increase in the dissolved metal transport to the north sea

gastropod carbonate δ18o and δ13c values record strong seasonal productivity and stratification shifts during the late eocene in england high resolution 18o and 13c measurements obtained from the gastropod clavilithes macrospira provide the most detailed record of seasonal change in temperature range 14 c seawater chemistry and bottom water ventilation yet obtained from late eocene strata type bartonian ca 40 ma the 18o oscillations suggest a linear rate of long term growth and rapid growth in spring early summer coherence analysis shows that 13c patterns vary from being closely in phase with respect to annual 18o oscillations to being antiphase with a phase shift toward a spring or more rarely an autumnal 13c peak these patterns are attributed to unstable seasonal productivity and or the development of a seston rich bottom layer in which the 13c gradients arising from seasonal eutrophication were perturbed by spring storms such episodes may have led to the decline and extinction of oligotrophic marine biota with photosymbionts including nummulites in the late eocene

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

intra annual variation in the stable oxygen and carbon and trace element composition of sclerosponges 1 this paper presents data to support the presence of 1 intra annual signals in the chemical composition 18o and sr ca of the skeletons of sclerosponges from the bahamas and 2 variable rates of skeletal accretion these conclusions are based on data obtained by using a microsampling method for the stable oxygen and carbon isotopes in which material was extracted at a resolution of one sample every 34 m and a laser microprobe which obtained trace element data every 20 m sr mg and pb an age model was established using a combination of changes in the concentration of pb the change in the 13c of the skeleton of the sclerosponges and u th isotopic measurements these methods yield a mean growth rate of 220 m yr but suggest that the growth rate in this particular sclerosponge was not constant the calculated growth rate is within error identical to that determined by u th methods the variable growth rate was confirmed through spectral analysis of the 18o and sr ca data that showed peaks corresponding to the annual cycle in these parameters as well as peaks corresponding to growth rates of approximately 128 212 270 and 400 m yr the presence of these additional frequencies suggests a growth rate between approximately 100 and 300 m yr these conclusions were supported by modeling of oxygen isotopic data measured on a scleractinian coral as well as model isotope data generated on synthetic time series these findings have important implications for the use of sclerosponges as proxies of paleoclimate because they emphasize the need for a precise yearly chronology in order that proxy data can be compared with climatic variables

evaluating the impact of acetic acid chemical pre treatment on old and cremated bone with the perio spot technique and perios endos profiles abstract the impacts of diagenesis on archaeological and palaeontological bone complicate investigations of in vivo chemical and isotopic characteristics such bone is often pre treated in an attempt to remove diagenetic alteration prior to trace element or isotopic analyses although very few standardized approaches exist for evaluating pre treatment effectiveness in this pilot study we characterize the diagenetic alteration and assess the impact of acetic acid chemical pre treatment on the trace element and structural characteristics of four bones from belgium including an early medieval cremated bone from broechem and three representative old bones of different ages ca 40 130 ka from the late pleistocene sedimentary sequence of scladina cave each bone was analyzed before and after acetic acid pre treatment using the perio spot technique and perios endos profiles we measured trace element concentrations with laser ablation inductively coupled plasma mass spectrometry la icp ms and micro x ray fluorescence spectroscopy xrf structural characteristics were investigated with raman spectroscopy and fourier transform infrared spectroscopy ftir our results indicate that chemical pre treatment had little to no significant impact on the trace element content of the early medieval cremated bone had the most impact on the youngest bone from scladina cave and had less impact on the trace element content of two older bones from scladina cave this suggests that the effectiveness of acetic acid chemical pre treatment is greater for bones undergoing early diagenetic processes has minimal impact on highly crystalline cremated bone and may preferentially leach in vivo signatures from bones undergoing later diagenesis the weights of leachates removed from each bone also correspond well with their hypothetical diagenetic states indicating that researchers could potentially assess the diagenetic state of bones by weighing the leachates produced during acetic acid pre treatment therefore our new approach may provide a valuable step toward effectively and consistently differentiating among in and ex vivo trace element signatures and by proxy those of their isotopes in archaeological and palaeontological bone

differences in the delta 18 o and delta 13 c signatures of seasonal laminae comprising travertine stromatolites abstract alternation of sparry and micritic laminae in modern nonmarine travertine stromatolites from creeks in the arbuckle mountains of oklahoma and from eocene hot water deposits in the palm park formation of new mexico represent seasonal accumulations the sparry laminae with upright biogenic structures represent spring summer accumulations whereas the micritic laminae with flat lying microbial remains represent fall winter accumulations the 18o values of the modern creek waters average 5 04 spring summer and 5 25 fall winter smow and calcite precipitated in equilibrium with these waters should have 18o values of approximately 6 4 and 5 2 pdb for spring summer and fall winter precipitates respectively 18o values for calcite which precipitated during three month periods on test objects in the creek waters average 6 5 for spring summer and 4 9 for fall winter the sparry and micritic laminae comprising the naturally occurring modern stromatolites from these creeks average 6 4 for sparry spring summer and 5 2 for micritic fall winter laminae thus the agreement between 18o values for precipitates which formed in isotopic equilibrium with the creek water composition precipitates on test objects and the sparry and micritic laminae comprising naturally occurring modern stromatolites confirm the seasonal origin of the laminae the 13c values for the creek waters the test objects and the naturally occurring laminae of the stromatolites are higher in the sparry spring summer than the micritic fall winter deposits the 18o values obtained as a result of lamina by lamina analyses of the eocene hot water travertine stromatolites of new mexico do not display a seasonal trend but the 13c values are consistently higher in the sparry laminae than in the micritic laminae in addition increased concentrations of trace elements occur in the sparry relative to the micritic laminae of the hot water stromatolites the lamina by lamina stable isotopic and trace elemental analyses provide confirmation of the seasonal origin of the sparry spring summer and micritic fall winter laminae comprising the ancient stromatolites

stratigraphy and palaeogeography of the capo milazzo area ne sicili italy clues to the evolution of the southern margin of the tyrrhenian basin during the neogene abstract the neogene sedimentary sequence of capo milazzo ne sicily italy with particular reference to the niocene interval is described in detail and a paleoenvironmental evolution for the late miocene pliocene time is proposed the sequence represents a portion of the northern side of the calabrian arc and documents the response of the coastal environment to the complex events salinity crisis opening of the tyrrhenian basin which affected the mediterranean basin during the neogene the beginning of rifting and increased subsidence of the northern sectors along ne sw faults are recorded in the late tortonian together with a southbound marine transgression documented by clastic littoral facies the transgressive trend continued during the early messinian though the moderate subsidence maintained a neritic environment in which a small reef complex adjacent to a lagoon developed emersion and karstic erosion of the early messinian limestones is recorded in the late messinian time equivalent of the lower evaporite reactivation of ne sw faults at this time favoured the formation of large breccias collapsed from the peripheral portions of the reef complex subsequent lowering of the nw sector allowed the area to ne reached by a limited marine episode during the intra messinian transgression high energy stream deposits coeval with the deposition of the lago mare facies in the mediterranean end the messinian sequence the pliocene sequence fossilizes a complex palaeotopography with submerged highs and narrow depressions a rapid marine transgression is recorded at the miocene pliocene boundary with the development of circalittoral epibathyal environments tensional movements during the latest messinian earliest pliocene and late pliocene are recorded by a system of fractures and respective fillings that affect the upper portion of the early messinian limestones the erosion and reworking of most early pliocene sediments into late pliocene bathyal deposits together with the local presence of clastic foreset deposits and large blocks of messinian limestones collapsed into the lower part of late pliocene deep water sediments document a mid pliocene event likely referable to the middle pliocene tectonic phase

late cretaceous campanian carbon isotope events sea level change and correlation of the tethyan and boreal realms abstract carbon stable isotope stratigraphy provides unique insights into environmental change during the campanian the longest 83 5 71 3 ma but least well understood stage of the late cretaceous a new carbon isotope 13c profile for a 500 m thick campanian basal maastrichtian tethyan pelagic hemipelagic section near el kef northern tunisia is calibrated using data from a biostratigraphically well constrained succession at kalaat senan the general shapes of the tunisian 13c reference curve and published tethyan 13c profiles from elles tunisia and bidart sw france and a boreal curve for the trunch borehole eastern england are remarkably similar in all three areas a positive carbon isotope event of 0 2 13c in the mid campanian dated at 78 7 ma and a negative excursion of 0 4 in the upper campanian at 74 8 ma can be correlated between tunisia and england a positive excursion of 0 3 at 83 7 ma spans the santonian campanian boundary these isotope events enable precise inter regional correlations that are consistent with published nannofossil data review of campanian sea level data from north africa the middle east and northern europe indicates that major shifts in 13c profiles coincide with changes in eustatic sea level relatively stable 13c values in the lower campanian and their long term fall through the upper campanian reflect high and then falling eustatic sea levels and increased carbonate production short term 600 kyr positive excursions record greater organic productivity and or organic matter preservation and decreased carbonate fluxes during periods of rapid sea level rise and the drowning of carbonate platforms excursions were terminated by falling nutrient supply and increased carbonate deposition associated with epicontinental sea expansion and renewed carbonate platform growth during the late transgression and highstand negative excursions are linked principally to reworking of marine and terrestrial organic matter during rapid sea level fall carbon isotope stratigraphy is a powerful tool for correlation which can be used to test the validity of campanian global biostratigraphic frameworks and improve our understanding of the nature and timing of late cretaceous sea level change

improving the detection of shell alteration implications for sclerochronology abstract sclerochronology makes use of fossil shell archives to establish records allowing for investigation of high resolution environmental dynamics nevertheless this potential can often not be fully exploited due to the interplay between paleoenvironmental variability vital effects and the potential diagenetic modification of skeletal materials which often results in highly complex records a novel dynamic approach aiming to separate pristine from altered shell material for paleoclimate and paleoenvironmental reconstructions is proposed seventeen fossil bivalve shells requieniid rudists pectinids and chondrodonts from two neighbouring lower cretaceous albian shallow water sections lusitanian basin western portugal were analysed for their major and trace elemental compositions using high resolution quantitative xrf line scans their complex records were subject to a novel statistical analysis protocol which tested mono and multi species datasets as well as comparing shells from both locations characteristic elemental associations reveal the differential impact of early and late diagenetic alteration processes the incorporation of elements associated with detrital contribution fe si al is attributed to syn depositional bioerosion shell boring in clear contrast shell portions showing a strong correlation between fe and mn are indicative of later diagenetic alteration the influence of each process is different at each site revealing local differential alteration pathways mono specific comparisons provides identical geochemical responses suggesting that intra specific differences do not control the observed elemental patterns in contrast inter species tests rendered a clear separation in the way elements are incorporated in the shells of pectinids and requieniids e g as evidenced by differences in mg or sr content such differences can be linked to differential biomineralization pathways easily detected by the applied method we present a new dynamic method for distinguishing pristine from altered shell material not relying on arbitrary diagenetic thresholds for trace element content by clearly identifying shell alteration pathways syn to post depositional processes are recognized a progressive cleaning of the elemental dataset allows paleoenvironmental studies to be based on the most pristine data contributing to unravelling the complex interplay between climate environmental dynamics and their impact on biomineralization processes and sclerochronological archives

neogene ice volume and ocean temperatures insights from infaunal foraminiferal mg ca paleothermometry antarctic continental scale glaciation is generally assumed to have initiated at the eocene oligocene transition yet its subsequent evolution is poorly constrained we reconstruct changes in bottom water temperature and global ice volume from 0 to 17 ma using 18o in conjunction with mg ca records of the infaunal benthic foraminifer o umbonatus from ocean drilling program odp site 806 equatorial pacific 2500 m considering uncertainties in core top calibrations and sensitivity to seawater mg ca mg ca sw we produce a range of mg ca temperature mg casw calibrations our favored exponential temperature calibration is mg ca 0 66 0 08 mg casw0 27 0 06 e 0 114 0 02 bwt and our favored linear temperature calibration is mg ca 1 21 0 04 0 12 0 004 bwt bottom water temperature mg casw 0 003 0 02 stated errors are 2 s e the equations are obtained by comparing o umbonatus mg ca for a paleocene eocene section from ocean drilling program odp site 690 weddell sea to 18o temperatures calculated assuming ice free conditions during this peak warmth period of the cenozoic this procedure suggests negligible effect of mg casw on the mg distribution coefficient dmg application of the new equations to the site 806 record leads to the suggestion that global ice volume was greater than today after the middle miocene climate transition 14 ma odp site 806 bottom waters cooled and freshened as the pacific zonal sea surface temperature gradient increased and climate cooled through the pliocene prior to the plio pleistocene glaciation of the northern hemisphere the records indicate a decoupling of deep water temperatures and global ice volume demonstrating the importance of thresholds in the evolution of the antarctic ice sheet

species richness and abundance patterns of tethyan cretaceous rudist bivalves mollusca hippuritacea in the central eastern mediterranean and middle east analysed from a palaeontological database abstract data about the stratigraphical and regional distribution of cretaceous rudist bivalves in the central eastern mediterranean and middle east from the barremian to the maastrichtian have been compiled in a taxonomic databank system the investigated region comprises northern central and southern regions of the cretaceous tethys the regionally different quality of taxonomic data is critically discussed both species richness and abundance number of species records peak in the early aptian late cenomanian and early campanian temporal patterns in species richness are examined in relation to evolutionary innovations of the group crises in species richness and abundance during the early and mid cretaceous were coeval with oceanic anoxia associated with platform drowning also regional emergence affected large parts of the apulian plate and other central tethyan carbonate platforms during the mid cretaceous period of globally high sea level so that these crises can be attributed to regional environmental perturbations induced by either oceanic anoxia or tectonic movements the cenomanian turonian transition marks an important faunal turnover as indicated by the demise of taxonomic groups which are characterised by recumbent ecological morphotypes and predominantly aragonitic shells during the turonian they were replaced by associations dominated by largely calcitic radiolitidae and hippuritidae among which elevator morphotypes dominated the stratigraphy of many post turonian deposits in the studied region is too imprecise for a detailed analysis of late cretaceous distributional patterns and the demise of rudists during the maastrichtian in particular the regional pattern of species richness and abundance is similar throughout most of the investigated region a notable exception is the broad north eastern african shelf from libya to lebanon where rudists were almost completely absent after the coniacian this coincided with shallow water phosphorite and black shale formation on the extended shelf of this region indicating the upwelling of nutrient rich waters and stagnant conditions during this time campanian maastrichtian species rich associations thrived along the north eastern afro arabian margin now exposed in south eastern turkey iran the united arab emirates uae and oman this region forms the single distinct faunal province during the cretaceous in the studied region as indicated by an endemism of 40 at the genus level the low species richness and abundance of hippuritidae on turonian maastrichtian central tethyan carbonate platforms when compared with regions having mixed calcareous siliciclastic sedimentation is interpreted to argue against a widespread photosymbiosis in the group several aspects of this study highlight the importance of regional tectonic and oceanographic controls of distributional and perhaps also evolutionary patterns of rudist bivalves their delineation still suffers from the regionally different quality of stratigraphical and taxonomic data

gulf of maine shells reveal changes in seawater temperature seasonality during the medieval climate anomaly and the little ice age article i nfo in this study we use subannually resolved oxygen isotope values of fossil dead collected and modern live caught bivalve shells arctica islandica l from the northwestern atlantic gulf of maine usa to reconstruct past seasonal changes in seawater temperature our results indicate decreased seasonal temperature amplitude of about 1 6 c or 21 during medieval times ca ad 1033 1062 compared to shells from the early little ice age ca ad 1321 1391 and during the late 19th century ad 1864 1886 additionally seasonal oxygen isotope data suggest that summers were cooler and winters were warmer in the gulf of maine during the 11th century compared to summers and winters in the 14th century and the late 19th century the inferred decreased seasonality during medieval times likely resulted from increased stratification of the coastal waters due to warmer seawater temperatures as seawater cooled during the little ice age we suggest that increased vertical mixing of the coastal surface waters was a major driving factor for the observed increase in the amplitude of the seasonal seawater temperature cycle