decadal increases of anthropogenic co2 in the subtropical south atlantic ocean along 30 s 1 using high quality data for dissolved inorganic carbon and related properties obtained about 10 years apart 1992 1993 2003 we examined decadal increases of anthropogenic co2 nctcal along 30 s whp a10 section in the subtropical south atlantic significant nctcal was detectable down to an isopycnal surface of 27 3 1000 m water depth averaged nctcal in sub antarctic mode water samw 26 6 27 0 350 700 m was 6 8 1 6 mol kg 1 and that in antarctic intermediate water aaiw 27 1 27 4 700 1200 m was 3 6 1 4 mol kg 1 in samw nctcal was higher by 7 mol kg 1 west of 15 w than east of it while nctcal in aaiw did not show such a distinct east west difference for deep waters significant nctcal was detected in antarctic bottom water at depths greater than 4500 m in the cape basin longitude 2 e 10 e no significant nctcal could be detected for north atlantic deep water nadw we attributed nctcal being higher west of 15 w in samw to differences of water mass distributions and flows from a water column inventory we estimated the uptake rate of anthropogenic co2 over the decade from 1992 1993 to 2003 to be 0 6 0 1 mol m 2 a 1 which is half the rate in the south pacific 1 0 0 4 mol m 2 a 1

stable isotope stratigraphy of brachiopods from pennsylvanian shales in texas stable isotope stratigraphies have been generated for brachiopods from five late pennsylvanian sections upper winchell cycle finis shale colony creek shale necessity cycle and wayland shale in north central texas to examine the relationship between isotopic composition paleoenvironment and sea level change nonluminscent calcite from more than 300 specimens of 4 species of brachiopod composita subtilita crurithyris planoconvexa eridmatus texana neospirifer cameratus was analyzed sedimentological and paleontological data are used as evidence for paleoenvironmental change higher 18 o values of brachiopod shells occur in intervals of greatest paleodepth as indicated by fossil content and lithology these higher 18 o values reflect a decrease in bottom temperature with increased water depth normalized for paleodepth the 18 o values of the brachiopods are similar in all of the units except the wayland shale for which they are 0 5 higher this suggests either cooler temperatures or greater continental ice volume during the time of wayland deposition brachiopod 13 c values do not correlate with paleodepth the 13 c values of composita are consistently higher than those of crurithyris and eridmatus composita 13 c values are similar in the upper winchell cycle necessity cycle and wayland shale averaging 4 8 to 4 9 in contrast crurithyris 13 c values range from 2 5 in the necessity cycle to 4 4 in the wayland shale eridmatus values are also lowest in the necessity cycle 3 4 and greatest in the wayland shale 3 9 these differences between species do not correlate with susceptibility to diagenesis and appear to reflect a pore water influence on semi infaunal crurithyris forms the 13 c values of composita shells suggest that the late pennsylvanian ocean off eastern laurussia was enriched in 13 c by about 1 relative to the ocean off western laurussia

distribution of anthropogenic co2 in the pacific ocean 1 this work presents an estimate of anthropogenic co2 in the pacific ocean based on measurements from the woce jgofs oaces global co2 survey these estimates used a modified version of the c technique modifications include a revised preformed alkalinity term a correction for denitrification and an evaluation of the disequilibrium terms using an optimum multiparameter analysis the total anthropogenic co2 inventory over an area from 120 e to 70 w and 70 s to 65 n excluding the south china sea the yellow sea the japan east sea and the sea of okhotsk was 44 5 5 pg c in 1994 approximately 28 pg c was located in the southern hemisphere and 16 5 pg c was located north of the equator the deepest penetration of anthropogenic co2 is found at about 50 s the shallowest penetration is found just north of the equator very shallow anthropogenic co2 penetration is also generally observed in the high latitude southern ocean one exception to this is found in the far southwestern pacific where there is evidence of anthropogenic co2 in the northward moving bottom waters in the north pacific a strong zonal gradient is observed in the anthropogenic co2 penetration depth with the deepest penetration in the western pacific the pacific has the largest total inventory in all of the southern latitudes despite the fact that it generally has the lowest average inventory when normalized to a unit area the lack of deep and bottom water formation in the north pacific means that the north pacific inventories are smaller than the north atlantic

influence of changing deep ocean circulation on the phanerozoic oxygen isotopic record isotopic segregation in seawater caused by changing ocean circulation may in part explain the enigmatic oxygen isotopic record of phanerozoic marine carbonates paleoceanographic evidence suggests that circulation of warm saline deep waters has occurred during at least two periods of warm global climate those saline deep waters should have preferentially stored 18o in the deep oceans corresponding depletion of 18o in surface waters would have resulted in lower 18o of marine carbonates deposited on continental shelves modeling of paleoceanographic isotopic data suggests that this storage effect is similar in magnitude but opposite in sign to that of modern enrichment of 18o in the oceans by glacial storage modeling of carbonate compositions through time that takes into account such storage effects as predicted by changing global climate suggests that large changes in the mean oceanic isotopic composition but neither extreme temperatures nor sudden changes in mean ocean compositions are needed to explain the isotopic record

pushing the boundaries glacial interglacial variability of intermediate and deep waters in the southwest pacific over the last 350 000 years glacial interglacial changes in southern ocean s air sea gas exchange have been considered as important mechanisms contributing to the glacial interglacial variability in atmospheric co2 hence understanding past variability in southern ocean intermediate to deep water chemistry and circulation is fundamental to constrain the role of these processes on modulating glacial interglacial changes in the global carbon cycle our study focused on the glacial interglacial variability in the vertical extent of southwest pacific antarctic intermediate water aaiw we compared carbon and oxygen isotope records from epibenthic foraminifera of sediment cores bathed in modern aaiw and upper circumpolar deep water ucdw 943 2066 m water depth to monitor changes in water mass circulation spanning the past 350 000 years we propose that pronounced freshwater input by melting sea ice into the glacial aaiw significantly hampered the downward expansion of southwest pacific aaiw consistent with climate model results for the last glacial maximum this process led to a pronounced upward displacement of the aaiw ucdw interface during colder climate conditions and therefore to an expansion of the glacial carbon pool

an oceanic model for lithological and faunal changes tested on the silurian record a model for oceanic cycles is presented the cycles are expressed as changes between more humid low latitude and cooler high latitude climates p episodes and dryer low latitude and warmer high latitude climates s episodes the cyclicity may be self regulating through changes in the co 2 storage capacity of the deep ocean due to temperature changes and through changes in the oceanic input and output of dissolved carbonate the model permits over 30 predictions regarding observable changes in both deep water and shelf lithologies and variations in the abundance diversity and extinction rate of planktic and benthic faunas sedimentary changes involve fluctuations in the rate of clay deposition and carbonate production the advance and retreat of carbonate deposition on the shelf edge the timing of oolite reef and black shale formation and changes between oxic and anoxic deep water faunal effects include both iterative evolution and intermittently widespread taxa lazarus taxa these predictions agree well with changes observed in well known sequence of wenlock and ludlow age as well as changes seen in selected older and younger sequences

textural elemental and isotopic variations among constituents in middle devonian limestones north america abstract biogenic components brachiopods crinoids and corals in middle devonian limestones were manually separated from their enclosing matrix and analyzed by textural elemental and isotopic methods in order to assess the preservational state of these components in general brachiopods in these rocks are better preserved texturally than other constituents as determined by sem and cathodoluminescence observations elemental variations among the major components are compatible with a differential response to diagenesis governed by the relative stability of the original mineralogy of the component however among the most stable low mg calcite brachiopods the relationship between textural preservation and trace element content is complex this apparent complexity may be due at least par ially to our method of textural characterization of whole brachipod samples the nonluminescent portions of a set of well preserved brachipods have textural characteristics and elemental contents which are virtually indistinguishable from modern representatives consequently their 18o values 3 7 0 2 are assumed to represent primary biogenic calcite these 18o values are in the heavy end of the range of values from texturally well preserved whole brachiopods 6 6 to 2 5 texturally altered whole brachiopods 6 7 to 3 7 and texturally altered crinoids and cora s 6 7 to 2 7 this comparison suggests that marine derived pore waters were a predominant component during the principal phase of diagenesis the relatively low l8o values of well preserved brachiopods compared with modern representatives implies that middle devonian seawater was either warmer by about 10 c or depleted in 18o by about 2 3 relative to modern seawater

increase of total alkalinity due to shoaling of aragonite saturation horizon in the pacific and indian oceans influence of anthropogenic carbon inputs 1 aragonite saturation horizon ash shallowed significantly by 25 to 155 m and 16 to 124 m in the pacific and indian ocean respectively in two decades apparent oxygen utilization aou increased by 3 to 34 and 0 5 to 31 5 mol kg 1 in the pacific and indian ocean respectively at the depth of ash during this period dic increased by 12 5 to 36 8 and 5 5 to 32 mol kg 1 in the vicinity of ash in the pacific and indian ocean respectively due to combined effect of increased anthropogenic co2 and change in aou ta increased significantly by 5 to 10 and 4 to 9 2 mol kg 1 in the pacific and indian oceans respectively at the ash most likely as a result of aragonite dissolution the upward migration of ash solely due to anthropogenic co2 amounted to 6 to 58 m in the pacific and 4 to 44 m in the indian ocean

missing molluscs as evidence of large scale early skeletal aragonite dissolution in a silurian sea in the silurian carbonate platform succession of gotland sweden interreef limestone and marl sequences have shallow marine shelly assemblages dominated by brachiopods typical of many paleozoic benthic faunas locally from similar facies where early skeletal silicification occurred associated with bentonites there are rich and diverse assemblages of originally aragonitic molluscs quantitative faunal analysis suggests that massive depletion of skeletal aragonite chiefly molluscs took place and the entire molluscan fauna may generally be underrepresented by at least 100 fold previous workers on the gotland succession have already shown that abundant diagenetic limestones were sourced by early aragonitic remobilization our findings indicate molluscs as the probable source of this diagenetic calcite not aragonite mud as was previously thought the taphonomic window represented by the silicified faunas illustrates the importance of aragonitic shells among the original silurian shelf benthos and raises the possibility that the paucity of such shells among many fossil faunas may be largely an early taphonomic effect

cathodoluminescene at low fe and mn concentrations a sims study of zones in natural calcites abstract point analyses of natural calcite cements by sims confirm the earlier suggestions that 20 ppm mn is required to activate luminescence whereas fe concentrations in excess of 1400 ppm quench it partly independently of the mn content below this fe threshold luminescence is bright at mn concentrations in excess of 225 ppm in the range 20 225 mn all types of luminescence dull luminescent and nonluminescent can occur this undifferentiated domain is evident also from a compilation of literature data the type of luminescence is not a simple function of fe and mn concentrations other parameters influence cl sinc most diagenetic calcite cements have fe and mn concentrations that place them within the field of mixed cathodoluminescence these results force reassessment of models that equate the type of luminescence with the redox state of the diagenetic environment

carbon isotope excursion near the wenlock ludlow silurian boundary in the anglo welsh area oxygen and carbon isotope analyses have been performed at close sampling intervals on rocks from several exposures that show the boundary between the wenlock and ludlow series in the classic silurian areas of wales the welsh borderland and the west midlands of england our data indicate a monotonic decline in 13 c from positive to negative values across the boundary between the much wenlock limestone formation wenlock series and the lower elton formation ludlow series and correlatives in all sites investigated a slightly earlier negative excursion is also present in the upper wenlock strata of two of these localities both negative 13 c excursions appear to be contemporaneous with episodes of increased ocean ventilation and eustatic sea level lowstand postulated by kemp at least one and possibly both of the late wenlock carbon isotope depletions can also be related to the decline in pelagic graptolite diversity the distribution of the carbon isotope depletion in both carbonate platform and off shelf facies implies that this trend is unlikely to have been caused by local diagenetic alteration isotope chemostratigraphy may also provide an extra correlation tool that can be integrated with traditional biostratigraphic methods for silurian strata

sequence and isotope stratigraphy of late triassic distal periplatform limestones from the northern calcareous alps kalberstein quarry berchtesgaden hallstatt zone the kalberstein quarry at berchtesgaden exposes carnian norian deeper water hallstatt limestones conodont biostratigraphy microfacies and stable isotopes of bulk carbonate matrix were investigated the biostratigraphic results demonstrate a complete succession from the latest carnian tuvalian 3 i to the late norian sevatian 2 as expected from the periplatform setting of the hallstatt zone calculated mass accumulation rates conform partly to prograding sequences observed on the contemporary dachstein platform however discrepancies exist mainly for the middle norian pointing to an incomplete knowledge of the platform sequences the sequence stratigraphic framework based on platform data should be complemented with data from the periplatform hallstatt zone diagenetic alteration of the limestones from kalberstein quarry is low with a conodont alteration index cai 1 0 throughout the section oxygen isotope values ranging from 1 2 to 0 1 vpdb point to stabilization and cementation at very shallow burial depths in contact with seawater in a deeper water environment carbon isotope values display a clear stratigraphic trend with a rapid increase from 3 6 to 4 1 vpdb during the basal norian lacian 1 high values up to 4 2 during the lacian 2 and a slow decline starting in lacian 3 to 2 6 at the end of the norian sevatian 1 2 these trends are best explained by variations in the global organic carbon carbonate burial ratio with maximum organic carbon burial during the middle lacian

deep ocean changes near the western boundary of the south pacific ocean repeated occupations of two hydrographic sections in the southwest pacific basin from the 1990s to 2000s track property changes of antarctic bottom water aabw the largest property changes warming freshening increase in total carbon and decrease in oxygen are found near the basin s deep western boundary between 508 and 208s the magnitude of the property changes decreases with increasing distance from the western boundary at the deep western boundary analysis of the relative importance of aabw g n 28 1kgm 23 freshening heating orisopycnalheavesuggeststhatthedeepoceanstratificationchangeisthe result of both warming and freshening processes the consistent deep ocean changes near the western boundary of the southwest pacific basin dispel the notion that the deep ocean is quiescent high latitude climate variability is being directly transmitted into the deep southwest pacific basin and the global deep ocean through dynamic deep western boundary currents

oxygen isotope variations in phosphate of biogenic apatites ii phosphorite rocks abstract phosphorites from sedimentary sequences ranging in age from archaean to recent were analysed for 18 o in both the po 4 18 o p and co 3 18 o c in the apatite lattice the oxygen isotope record is considerably better preserved in phosphates than in either carbonates or cherts the use of the longinelli and nuti 8 temperature equation yields temperatures for recent phosphorites that are in good agreement with those measured in the field the 18 o p values of ancient phosphorites decrease with increasing age these changes with time are not likely to be due to post depositional exchange changes in 18 o values of seawater and variations of temperature with time can account for the 18 o p time trend but the latter explanation is preferred in ancient phosphorites 18 o c in structurally bound carbonate in apatite is not a reliable geochemical indicator

decadal changes in the caco3 saturation state along 179 e in the pacific ocean 1 to assess degrees of ocean acidification we mainly investigated decadal changes in the saturation state of seawater with respect to aragonite arg which is a more vulnerable mineral form of caco3 along the 179 e meridian woce p14n in the pacific ocean we found a maximum decrease of arg of 0 48 0 034 a 1 at 200 300 dbar isopycnal surfaces of 24 0 25 8 kg m 3 at 20 n between 1993 and 2007 the saturation horizon rose by 17 dbar 1 2 dbar a 1 at latitudes 10 n 50 n although arg mostly reflected changes in normalized dissolved inorganic carbon nct it was larger than could be explained by anthropogenic co2 storage alone decomposition of nct revealed that argwas enhanced by approximately 50 by a non anthropogenic co2 contribution represented by changes in apparent oxygen utilization our results suggest that ocean acidification can be temporarily accelerated by temporal changes in oceanic conditions

anoxic events in the late frasnian causes of the frasnian famennian faunal crisis carbon isotope data collected from five frasnian famennian boundary sections in central europe show two positive 13 c excursions in the late frasnian 367 ma both anomalies coincided with the deposition of the bituminous lower and upper kellwasser horizons the carbon isotope patterns indicate two phases of enhanced burial and subsequent recycling of organic carbon a maximum formation of warm saline waters on the subtropical to tropical epicontinental shelves during late frasnian transgressive episodes may have induced oceanic oxygen deficits variations in the c org burial rates may have resulted in changes in the co 2 concentrations in the oceans and in the atmosphere culminating in global climatic changes we propose that the repeated co occurrences of sea level fluctuations anoxic conditions and global climatic changes during the late frasnian would affect especially the subtropical to tropical shallow water communities and reef ecosystems which were severely affected during the frasnian famennian faunal crisis

a brachiopod calcite record of the oceanic carbon and oxygen isotope shifts at the permian triassic transition the permian triassic p t mass extinction was the most dramatic of all such events but its cause has thus far remained elusive1 3 carbon and oxygen isotope analyses may offer clues to this puzzle because their results identify major changes in the earth s exosystem4 5 several studies have already dealt with carbon and oxygen isotope records at the p t transition2 6 11 but we present here empirical data derived from the brachiopod shell calcite whose isotope composition generally corresponds to that of the sea water in which the animals lived originally12 15 these data allow us to assess quantitatively the magnitude of changes in the earth s exosystem during that critical time interval

δ18o and δ13c values of modern brachiopod shells abstract researchers have not rigorously tested the hypothesis that calcite from modern brachiopod shells is precipitated in oxygen isotope equilibrium with ambient seawater isotopic variability at the intraspecimen and intertaxon levels has not been examined without such data for modern brachiopods similar data from ancient brachiopods cannot be accurately interpreted in this study a survey is made of 18 o and 13 c values of terebratulid rhynchonellid thecideidine and craniacean brachiopods from antarctica the bay of fundy curacao japan new zealand norway puget sound palau sicily and south africa this suite of samples provides a wide range of taxonomic levels temperatures salinities and depositional environments for evaluating the degree of isotopic equilibrium attained during precipitation of brachiopod calcite new data indicate that modem brachiopod calcite is not always precipitated in oxygen and carbon isotope equilibrium with ambient seawater calcite from the primary layer and specialized shell structures hinge brachidium foramen interarea muscle scars are depleted in both 18 o and 13 c a characteristic of biological fractionation or vital effects often found in other calcerous marine organisms our findings suggest that these portions of the brachiopod shell should be avoided during sampling of ancient brachiopods secondary layer calcite the material most often analyzed in ancient brachiopods has higher 18 o and 13 c values which approach and sometimes correspond with predicted equilibrium values therefore secondary layer calcite is the most suitable portion of the brachiopod shell for use as an ancient seawater proxy although near equilibrium precipitation in secondary layer calcite is encouraging to those studying the isotopic composition of ancient oceans these data come with caveats large intraspecimen variability in the 18 o values of secondary layer calcite 1 in some samples limits the use of brachiopods as precise indicators of the 18 o value or temperature of ancient seawater the 18 o and 13 c values of secondary layer calcite deviate from predicted equilibrium values toward the lower values of the primary layer and specialized shell structures indicating a measurable vital effect in most cases measured 18 o values are lower than the calculated equilibrium values dictated by seasonal variations in the 18 o value and temperature of seawater ontogenetic variations in the 13 c values of secondary layer calcite have also been measured and must be assessed when interpreting ancient data modern brachiopods occur in a wide range of seawater salinities and temperatures therefore the relation between salinity and the 18 o value of seawater must be known to correctly calculate the temperature of calcite precipitation from secondary layer 18 o values errors of up to 15 c are found if ambient seawater is assumed to have a constant 18 o value e g 0 smow and the 18 o values of secondary layer calcite are used to calculate temperature coupled with vital effects and intraspecimen variability these errors can obscure the resolution of secular variations in the rock record

assessing the biomineralization processes in the shell layers of modern brachiopods from oxygen isotopic composition and elemental ratios implications for their use as paleoenvironmental proxies abstract fossil brachiopod shells are often used as valuable archives to reconstruct paleoenvironmental conditions in deep time however biomineralization processes can impact their fidelity as geochemical proxies brachiopod shells comprise an outer primary layer a secondary fibrous layer and sometimes a tertiary columnar layer therefore it is essential to assess the potential effects of the biomineralization processes in each of the different shell microstructures of modern brachiopods this study analyses the oxygen isotopic composition together with li ca na ca mg ca and sr ca data at high spatial 20 50 m resolution in seven modern brachiopod species focusing on differences between the primary secondary and tertiary layers in all studied species 18o values of the outer primary layer are consistently out of equilibrium with seawater also this shell layer is enriched in li na mg and sr contrary to the primary layer the innermost secondary layer is near or at oxygen isotopic and elemental equilibrium with ambient seawater the columnar tertiary shell layer if present has the least variable and the heaviest oxygen isotopic composition within the range of equilibrium values with seawater this tertiary layer however is depleted in minor and trace elements relative to the other shell layers thus the tertiary layer is more suitable for oxygen isotopic studies whereas the innermost secondary layer of the most mature parts of the shell is the best target in two layered shells while we do not observe any clear interspecific relationships between mg ca and sr ca ratios on one hand and environmental parameters such as temperature salinity and ph on the other hand there is a positive interspecific relationship between na ca and salinity and a negative interspecific relationship between li ca and temperature suggesting their potential use as proxies of physicochemical parameters of seawater

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

bathymetric and isotopic evidence for a short lived late ordovician glaciation in a greenhouse period the end ordovician glaciation is distinct among phanerozoic glaciations in that co 2 levels were generally high yet major continental ice sheets accumulated on the gondwana supercontinent new oxygen isotopic data indicate substantial changes in sea water temperatures and ice volume coinciding with glacio eustatic changes in sea level reflecting the growth and decay of the gondwana ice cap major glaciation was apparently confined to the hirnantian and was 0 5 1 m y long rather than the 35 m y of earlier estimates carbon isotope values indicate significant changes in carbon cycling as the oceans changed from a state with warm saline bottom waters to a state with cold deep water circulation and then back again we believe that the changes in the carbon cycle effected a reduction in p co 2 levels in the oceans and atmosphere and thus promoted glaciation but were unable to sustain icehouse conditions in a greenhouse world

oxygen and carbon isotopic composition of ordovician brachiopods implications for coeval seawater one hundred and two articulate brachiopods and twenty one marine cements from ordovician strata were analyzed for oxygen and carbon isotopes these together with 200 previously published analyses of ordovician brachiopods mostly of upper ordovician age define a general trend of increasing 18o values with decreasing age from a minimum of 10 5 in the earliest ordovician to a maximum of 1 5 at the ordovician silurian boundary the 13c values show a general positive correlation with 18o and increase from 2 5 in the earliest ordovician to as high as 7 at the ordovician silurian boundary the magnitudes of ordovician excursions for both 18o and 13c are similar to those reported previously for the entire phanerozoic different genera of brachiopods from the same stratigraphie level did not yield any large differences in their isotopic compositions suggesting that vital effects did not influence decisively the isotope values of the studied skeletal parts petrographic examination and trace element analyses indicate that brachiopod shells from llandeilo to ashgill strata are well preserved and thus may have retained their primary isotopic signatures the same criteria for the tremadoc arenig and some llanvirn brachiopods suggest partial diagenetic alteration of 18o values in these samples but this does not preclude their utility as a recorder of a primary 13c signal the observed 18o trend for the well preserved portion of the record may reflect progressive cooling during ordovician perhaps complemented by a changing 18o values of seawater the latter could have been a consequence of a net increase in the rate of high temperature water rock interaction relative to its low temperature counterpart as indicated also by the large coeval decrease of marine 87sr86sr superimposed on the above long term 18o trend is a positive excursion of about 2 at the end of the ordovician probably reflecting a large expansion of polar ice caps the magnitude of this excursion indicates a degree of glaciation comparable to that at the height of the quaternary glacial episodes the secular 13c trend may reflect a progressive increase in marine organic productivity and or enhanced organic deposition in the ordovician oceans particularly noticeable at the time of the terminal ordovician glaciation

palaeokarst tidal erosion surfaces and stromatolites in the silurian eke formation of gotland sweden irregular scalloped erosion surfaces in the shelf carbonate sequences of the lower eke formation ludlow series upper silurian in the east of gotland sweden comprise series of shallow hollows separated by sharp crested ridges and cavities with sculptured undercut walls cut into lithified sediment these represent analogues of the solution basins formed in modern coastal and subaerial karst terrains discrete erosional cavities merge on enlargement by breaching of the intervening walls to leave remnant tapering ridges sets of the ridges and basins seen in surface view show an average width of basins of 1 2 m with relief of 40 50 cm and pronounced n s axes for the ridges this alignment may reflect the local drainage direction the lowermost erosion surface passes laterally into a planar mineralized horizon at the top of the underlying hemse group that was resistant to and forms the base level of erosion because of restricted exposure of higher eke formation sediments the upper limit of erosion remains unknown there is no evidence of caliche or subaerial diagenetic textures but solution vugs are common in the eroded limestones marine hard bottom biota attached to some surfaces and transition from scalloped to planar surfaces indicate erosion in tidal zones but subaerial karstic erosion is also inferred the resubmerged karst eroded topography is overlain by shallow marine carbonates including small organic buildups finely layered stromatolitic mats developed over the initial infill in subtidal environments and grew to form domed mounds within the erosional cavities they abut sharply against bounding side walls and overhangs some emergence is evident from desiccation features in the upper parts of mounds biostratigraphical evidence dating the events from initial uplift and karstic erosion to covering of the drowned relief topography places the whole sequence within upper ludlow times

geochemical and climatic effects of increased marine organic carbon burial at the cenomanian turonian boundary perhaps the most significant event in the cretaceous record of the carbon isotope composition of carbonate1 2 other than the 1 2 5 negative shift in the carbon isotope composition of calcareous plankton at the cretaceous tertiary boundary3 is the rapid global positive excursion of 2 13c enrichment which took place between 91 5 myr and 90 3 myr late cenomanian to earliest turonian c t boundary event 1 4 5 this excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon tdc reservoir resulting from an increase in rate of burial of 13c depleted organic carbon which coincided with a major global rise in sea level5 during the so called c t oceanic anoxic event oae 6 here we present new data from nine localities which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the c t boundary7 8 is nearly synchronous with that for carbonate and is widespread throughout the tethys and atlantic basins fig 1 as well as in more high latitude epicontinental seas the postulated increase in the rate of burial of organic carbon may have had a significant effect on co2 and o2 concentrations in the oceans and atmosphere and consequent effects on global climate and sedimentary facies

palaeontological and isotope evidence for warm saline deep waters in ordovician oceans today s oceans are characterized by cold bottom waters produced at high latitudes here we present morphological and oxygen isotope data for brachiopods from the caradocian upper ordovician trenton group in new york which indicate that both temperature and salinity increased with depth in ordovician oceans production of warm saline deep waters in low to mid latitude evaporative seas and reduced production of cold deep water may have been favoured by high sea level warm global climate and fortuitous positioning of continents1 5 the resulting ocean circulation system was markedly different from that of today lower oxygen contents of warm saline deep waters may have contributed to the deposition of organic rich sediments which are abundant in caradocian strata6 7but rare in modern ocean sediments

detecting the progression of ocean acidification from the saturation state of caco3 in the subtropical south pacific progression of ocean acidification in the subtropical south pacific was investigated by using high quality data from trans pacific zonal section at 17 s world ocean circulation experiment section p21 collected in 1994 and 2009 during this 15 year period the caco3 saturation state of seawater with respect to calcite cal and aragonite arg in the upper water column 400 dbar decreased at rates of 0 037 a 1 and 0 025 a 1 respectively east of 145 w longitude these rates are among the fastest in the world s oceans in contrast at longitudes 170 e 145 w cal and arg decreased relatively slowly at 0 008 a 1 and 0 005 a 1 respectively the arg saturation horizon occurred at a depth of about 1200 dbar at the westernmost end of the section and shoaled eastward to about 20 dbar from 1994 to 2009 it migrated upward at a rate of 5 2 dbar a 1 west of 145 w decomposition of the temporal changes of showed that the accumulation of anthropogenic co2 in the ocean accounted for more than half of the more rapid rate of decline of in the eastern section was attributable to a relatively large contribution of organic matter remineralization whereas the slower rate in the central section was attributed to a decrease of anthropogenic co2 uptake caused by rising water temperatures an important finding of this study was that acidification of the upper water column was enhanced by processes related to the oxygen minimum zone in the eastern subtropical south pacific ocean

the control of cathodoluminescence in dolomite by iron and manganese variations in the cathodoluminescent properties of carbonates are usually attributed to differing proportions of manganese mn2 as the most important activator and iron fe2 as the main inhibitor of luminescence interactions between manganese and iron concentrations and the luminescent properties of dolomite are demonstrated by petrographic and chemical analyses of 86 samples of dolomite representing a range of depositional environments and ages cambrian to cretaceous and a wide geographical distribution north america and europe iron and manganese are positively correlated in the dolomites with the former showing a greater range of variation very small amounts of manganese are sufficient to activate the luminescence and as little as 100 ppm mn2 is present in highly luminescing samples the intensity of luminescence is not proportional to the manganese concentration iron begins to quench luminescence as its concentration reaches 10 000 ppm above that level luminescence is rapidly lost and total extinction occurs among samples containing more than 15 000 ppm fe2 regardless of the manganese concentration

high resolution correlations between gotland and estonia near the base of the wenlock the strata of the ireviken event can be correlated between gotland sweden and the viki core on saaremaa estonia with a high degree of precision most of the ten datum planes are found with a precision of better than 0 1 m in the lower and upper visby beds on gotland and high in the mustjala member of the jaani formation on saaremaa five of the latest llandovery early wenlock units defined by these datum planes are between c 0 12 and 1 77 m thick on gotland and 0 12 and 0 67 m in estonia the duration of each was between a few thousand and c 31 000 years the stratigraphic resolution achieved in the interval of the ireviken event is 10 000 years ultimate range ends are lacking within a preceding slightly longer interval but the pattern of intermittent presence of some taxa agrees well with an unchanged relative rate of sedimentation their coeval presence in different places indicates ecological regional or more widespread changes

inorganic carbon in the indian ocean distribution and dissolution processes 1 this study uses nearly 25 000 carbon measurements from the woce jgofs global co2 survey to examine the distribution of dissolved inorganic carbon dic and total alkalinity ta in the indian ocean shallow and intermediate distributions of inorganic carbon do not strictly follow temperature and salinity because of differing surface gradients and vertical biological processes that work to modify the circulation derived features anthropogenic co2 has increased the shallow dic by as much as 3 decreasing the vertical dic gradient deep ocean dic and ta increase toward the north because of the decomposition and dissolution of organic and inorganic particles calcite saturation depths range from 2900 3900 m with the deepest saturation depth in the central indian ocean variations of aragonite saturation depth 200 1400 m are similar to calcite but the deepest saturations are in the southwestern indian ocean the shallowest aragonite saturation depths are found in the bay of bengal in the northern arabian sea and bay of bengal the current aragonite saturations are 100 and 200 m shallower respectively than in preindustrial times estimates of carbonate dissolution rates on isopycnal surfaces range from 0 017 to 0 083 mol kg 1 yr 1 in deep waters upper water column dissolution rates range from 0 to 0 73 mol kg 1 yr 1 with a local maximum occurring in intermediate waters just below the aragonite saturation horizon dissolution is also generally higher north of the chemical front at 10 20 s there is some evidence for significant sedimentary sources in the northern indian ocean

late pennsylvanian seasonality reflected in the 18o and elemental composition of a brachiopod shell to evaluate the potential for the study of late pennsylvanian seasonality detailed isotopic and elemental analyses were performed on a single specimen of the brachiopod neospirifer dunbari shell preservation was evaluated by petrographic and cathodoluminescence microscopy carbonate powders from 112 spots were collected from the sectioned shell for isotopic analyses and 369 spots on the complementary thin section were analyzed by electron microprobe for chemical composition in the nonluminescent part of the shell mg ca ratios were between 0 001 and 0 012 and na ca and s ca ratios ranged from 0 003 to 0 012 and 0 003 to 0 021 respectively values of 18 o vary between 2 3 and 1 1 contours of 18 o mg na and s concentrations parallel growth bands and reveal a record of 1 to 2 cycles mg s and na contents varied nversely with 18 o this trend is opposite to the expected diagenetic trend and is consistent with the temperature dependences of mg content and 18 o thus implying preservation of shell chemistry the 1 2 range in 18 o values suggests a seasonal temperature variation of 5 to 6 c assuming no change in the 18 o of the water this high seasonality for the tropical epicontinental sea of kansas supports climate model predictions of enhanced continentality in pangean climate detailed stable isotope and element concentration profiles across growth bands of brachiopod shells can provide quantitative records of paleozoic seasonality

deciphering kinetic metabolic and environmental controls on stable isotope fractionations between seawater and the shell of terebratalia transversa brachiopoda this study presents carbon and oxygen stable isotope data obtained from high resolution sampling 500 m of the brachiopod terebratalia transversa from the san juan islands washington state usa the aim of this study is to unravel the respective effects of physiological and environmental controls on the stable isotopic composition of brachiopod shell calcite based on an sem study of the shell a three dimensional sampling was performed in order to investigate carbon and oxygen isotope variations along isochrons and ontogenetic transects the primary as well as the outer part of the secondary shell layer display large and variable isotopic offsets as high as 7 for 13c and 6 for 18o relative to expected equilibrium values the significant positive correlations between 18o and 13c values indicate that the isotopic compositions of these shell domains are mainly controlled by kinetic isotope fractionation effects the ontogenetic 13c and 18o variations can be used to establish a growth curve of the studied specimen whose age is estimated close to 8 years the extent of apparent o 18 disequilibrium observed in this study is about as large as any yet measured in any organism which makes this brachiopod an interesting and important case the carbon and oxygen isotope compositions increase from the outer towards the inner part of the secondary layer where they reach values of 0 0 8 and 0 8 to 0 2 respectively corresponding calculated temperatures are between 12 and 13 8 c and fall in the range of seawater temperatures recorded off the san juan islands 7 13 c these results suggest that the calcite fibres were secreted more and more slowly during the thickening of the shell throughout the animal s life finally approximating isotopic equilibrium this study illustrates that the stable isotopic composition of the modern brachiopod t transversa is predominantly influenced by kinetic fractionation and to a minor degree by metabolic effects except for the innermost part of the shell the measured isotope ratios do not reflect environmental conditions during shell precipitation it remains to be tested by comparable studies whether other modern brachiopod species or even fossil brachiopods reflect comparable fractionation effects these results point out the need for re examination of paleozoic oceanographic conditions

changes in dissolved oxygen in the southern ocean with climate change 1 climate models predict that increasing greenhouse gases in the atmosphere will change our climate however the range of observations available to assess these model predictions is limited we have utilized an ocean biogeochemical model to project the impact of climate change on the oxygen cycle in the ocean and the air sea exchange of oxygen with climate change our model predicts an outgassing of oxygen from the ocean in the model the southern ocean is the region that displays the largest change in the air sea exchange of oxygen with climate change the reduced oxygen uptake in the southern ocean is dominated by a reduction in convective mixing and in the subduction rate of bottom water which decreases the amount of dissolved oxygen in the southern ocean our model results suggest that dissolved oxygen is sensitive to changes in southern ocean circulation revealing the potential to use dissolved oxygen to test model predictions of climate change from southern ocean observations collected 28 years a part we observed a decrease in dissolved oxygen that was consistent with model climate change simulation this provides credibility to the climate model predictions additional analysis and observations of dissolved oxygen are needed to substantiate our climate model simulations

middle palaeozoic extinction events faunal and isotopic data abstract at least 9 and possibly as many as 12 extinction events of global or near global impact can be discriminated in the mid palaeozoic earliest silurian to early carboniferous on the basis of brachiopod coral conodont and ammonoid data and the history of carbonate build ups isotopic data from whole rock samples are presented for three of these events based on australian carbonate sequences constrained by conodont data these data represent the initial phase of a more extensive investigation using c o s sr and nd isotopic signatures derived from conodonts articulate and inarticulate brachiopod shell and fish remains from numerous australian and european sequences the aim of the project is to identify isotopic responses to extinction events and address causes for these changes in limestone sections analysed so far variations in carbon isotope compositions on a whole rock scale are most marked at horizons that can be correlated with times of significant reduction in biomass and diversity this is despite the fact that the whole rocks are in fact multicomponent systems with respect to carbon in part arising from diagenetic rearrangements of carbon distribution within the scale of the whole rock thus the carbon isotope data do provide evidence on a whole rock scale for fundamental changes in the global carbon cycle that are correlative with extinction events it is however unlikely that the magnitude of the isotopic shift will be precisely documented from such whole rock analyses the oxygen isotope results are less obviously related to the times of carbon isotope excursion this contrast in apparent resilience to post depositional modification of pristine isotope compositions exemplifies the extreme caution needed in evaluating isotopic data from carbonates

diagenetic history of pipe creek jr reef silurian north central indiana u s a abstract calcite cements in the silurian ludlovian pipe creek jr reef north central indiana are compositionally zoned with characteristic minor element concentrations and stable isotope signatures and were precipitated in different diagenetic environments superposition and crosscutting relationships allow us to group cement zones and to relate them to the sequence stratigraphic evolution of the reef pipe creek jr reef grew in normal marine waters with the reef top high greater than 50 m above the platform floor flank facies are volumetrically important and are preserved largely as limestone in contrast to most dolomitized silurian reefs in the midcontinent syndepositional marine cements fill primary porosity and synsedimentary fractures and are interlayered with marine internal sediment now low magnesium calcite their isotopic compositions are similar to those of depositional grains and cements estimated to have precipitated from ludlovian sea waters depositional porosity was reduced by 75 by the precipitation of these syndepositional cements which stabilized the steeply dipping flank slope postdepositional clear calcite cements are interpreted as shallow phreatic and burial cements on the basis of their relationship to periods of karstification and fracturing shallow phreatic cements with concentric cathodoluminescent cl zonation precipitated in primary pores and are postdated by fractures and caves filled with middle devonian sandstone cl zonal boundaries are sharp and some near a major stratigraphic unconformity show evidence of dissolution the volumetric abundance of the individual cl zones varies in the reef indicating a complex superposition of waters of varying chemistry and rock water interaction that are probably related to relative sea level changes this important aspect of the reef stratigraphy is recorded only by the diagenetic succession because evidence of earlier sea level changes is removed by a major later regional unconformity burial cements are the youngest diagenetic feature recognized and they rest conformably or unconformably over older cements they exhibit both concentric cl zonation and sectoral zoning they are ferroan to nonferroan and they contain thin sulfide zones along growth band boundaries their isotopic compositions do not overlap with shallow phreatic or marine cement values degraded oil postdates burial cements and is composed of the same sterane class as the devonian age antrim shale the probable source rock this source contrasts with that of reef reservoirs in the michigan basin where silurian strata are commonly the hydrocarbon source

stable isotope variations in modern articulate brachiopods abstract carbon and oxygen isotopic analyses were performed on several species of holocene articulate brachiopods from various locations in the caribbean sea and in the atlantic and pacific oceans from salinities ranging between 30 and 38 pmil and over a temperature range from 4 to 28 c 39 to 82 f the dgr18o of articulate brachiopods are systematically related to the dgr18o and temperatures of the ambient waters lowenstam in 1961 concluded that articulate brachiopods secrete calcium carbonate low magnesium calcite in isotopic equilibrium with the surrounding waters the data compiled in this study along with that of lowenstam closely approximate the equilibrium calcite water end page 500 line deviation from apparent equilibrium was most evident for samples from a few cold water sites intraspecific isotopic variations in several warmer water assemblages were up to 2 pmil and isotopic variation within individual specimens as high as 1 5 pmil were noted articulate brachiopods were not separable at any taxonomic level on the basis of ranges in isotopic values the two extant orders of brachiopods the terebratulida and the rhynchonellida as well as the suborder thecideidina had essentially equivalent isotopic ranges at any given locality thus there is no evidence for significant taxonomic control of oxygen isotope fractionation among articulate brachiopods no correlation appears to exist between dgr18o and dgr13c values our results suggest strongly that isotopic data from small populations or communities of well preserved articulate brachiopods can be used in paleogeographic and paleo oceanographic reconstructions end of article last page 501

carbon isotope stratigraphy in the latest ordovician of estonia on the basis of bulk carbonate carbon isotope data from six drill cores and the type section of the porkuni stage of estonia 13c curves were compiled which altogether cover nearly the whole succession of the latest ordovician hirnantian well known as a time of short lived glaciation and mass extinction in pre porkuni and silurian rocks 13c values were low from 0 2 to 1 7 for the porkuni stage three intervals of the curve were established 1 lower a positive shift up to 6 7 2 middle part with variable values from 3 3 to 5 4 and 3 upper phase with slightly decreased values from 3 2 to 3 6 the correlation with the dob s linn scotland kerogen 13c curve shows that the first two intervals coincide with the normalograptus extraordinarius graptolite biozone the third one with the n persculptus biozone

isotope paleontology growth and composition of extant calcareous species abstract isotope paleontology uses the isotopic composition of fossil remains of organisms to make inferences about the physical surroundings of growth of the organisms especially temperature and to obtain clues about life history and modes of growth in calcareous fossils oxygen isotopes are mainly used in the former and carbon isotopes in the latter however since physical surroundings and organism response are intimately associated both types of information are contained in each of the isotopic signals to explore the potential of isotope paleontology and to provide a basis for reconstruction a broad range of extant organisms has been studied taking the pioneering work of epstein and associates as a starting point results are summarized for a representative sampling of these studies with emphasis on work at the laboratories of the authors from the mid seventies to the present the organisms considered are nannoplankton benthic algae planktonic and benthic deep sea foraminifera larger foraminifera sponges corals bryozoans polychaetes arthropods bivalves gastropods cephalopods and vertebrates fish otoliths the survey broadly suggests that regarding oxygen isotopes materials tend to be precipitated close to equilibrium with the surrounding seawater as postulated by urey and that for carbon isotopes disequilibrium is the rule life spans growth rates differential seasonal growth and age of reproductive activity can be extracted under favorable circumstances from individual shells and skeletal parts in detail the interpretation of isotope records of individual shells is quite complicated and simple models will fail to give satisfactory results in many or most cases

petrophysical record of the late silurian shallow water carbonate facies across the lau event prague synform czech republic and dynamic time warping alignment of the magnetic susceptibility logs

isotope shifts in the late permian of the delaware basin texas precisely timed by varved sediments closely spaced samples 285 in number of varved sediments from the upper permian in delaware basin texas have been analyzed for 13ccarb 13corg 18ocarb corg ccarb and calcite dolomite 13c records a dramatic rise from 2 8 to 5 7 in only 4400 years detected in three sections across the basin extrapolating smoothly through a 600 year interruption by a local west side of the basin fresh water inflow evidenced by low 18o this continuity and low corg within the basin both indicate that the excess net deposition of corg necessary to generate the rise in 13c took place in the ocean external to the delaware basin correlation with similar records from the zechstein basin suggest that the event was world wide although this poses obvious difficulties for the carbon cycle the rate of rise of 13c and its sustained high level must imply conversions of oxidized carbon to reduced carbon that are very large depending on which reservoirs were involved

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

early devonian marine isotopic signatures brachiopods from the upper gaspe limestones gaspe peninsula quebec canada abstract brachiopods from the upper gaspe limestones gaspe peninsula eastern canada document the isotopic geochemistry 18o 13c and 87sr 86sr of marine calcites for the siegenian and emsian stages early devonian nonluminescent brachiopods nlb from five species of a deep water benthic community show a narrow range of 13c values 1 3 to 1 7 average 1 5 and a much wider range of 18o values 2 7 to 4 6 average 3 7 that partially overlaps the field of luminescent brachiopods this is probably related to retention of fabric during diagenesis despite oxygen isotope exchange the heaviest 18o values for nonluminescent brachiopods 3 3 siegenian 2 7 emsian are interpreted as the signature of marine low mg calcite the 18o values for the gas e brachiopods suggest a negative 18o shift at the end of the early devonian the heaviest 18o values documented by previous workers for late early devonian emsian brachiopods cluster around 4 5 a figure that differs by 1 8 from the heaviest value for gaspe brachiopods this difference is most likely related to the growth of the gaspe brachiopods in deeper and cooler seawater as suggested by independent sedimentologic and biologic evidence rather than a 7 c warming of ocean surface temperatures or a rapid 7 ma shift in the 18o of seawater in a period of nonglaciation the 87sr 86 data for early devonian brachiopods fill the early devonian gap in the burke et al 1982 curve for devonian seawater the siegenian value is slightly more radiogenic than the younger emsian ones and support a continuous decrease in 87sr 86sr values from latest silurian to middle devonian time

early silurian glaciations in brazil abstract the opening of the brazilian paleozoic basins during the late ordovician was followed by a tectonic stabilization in the silurian at the time of the early silurian glaciations deposition of continental sandstones prevailed in the basins offshore environments were present in the amazonas basin and to a smaller extent in the parana basin the ice sheets advanced over fluviatile and littoral sediments except for the south margin of the amazonas basin where the glacial diamictites immediately overlie marine facies the ice produced much meltwater even when advancing and this was probably climatically controlled the ice movements were from the northwest at the northern margin of the amazonas basin and towards the northeast at the southern margin in the parnaiba basin and its outliers the jatoba basin and cariri valley the ice came from southeast and probably also from east further to the south in the parana basin it came from the north and northeast four glaciations have been dated to the early silurian the oldest is dated as latest ashgill and or earliest llandovery in the parana basin as evidenced from tillites in the upper rio ivai and lower vila maria formations including the former iapo formation it is contemporaneous with a glaciation in the cape basin south africa the next glaciation is dated as early middle llandovery gregarius graptolite zone and is present in the amazonas basin and the andean belt and probably also in the parnaiba basin and its outliers the two youngest tillites were widespread in the northern brazilian basins amazonas parnaiba and jatoba basins and cariri valley as well as in the andean belt and are dated as early late llandovery possibly starting already in the late middle llandovery and latest llandovery to earliest wenlock the latter tillite is the most widespread one assuming these glaciations are related to polar positions the apparent migration of the south pole ice cap must have been quite rapid from central north africa in late ashgill towards central brazil in the middle late llandovery the glaciation in the parana basin took place up to 45 from the late ashgillian south pole the cool climate continued during the silurian but no new glaciations are known before latest devonian

decadal increases of anthropogenic co2 in the south pacific subtropical ocean along 32 s 1 to estimate decadal increases of anthropogenic co2 in the ocean distributions of dissolved inorganic carbon ct corrected by apparent oxygen utilization and salinity nctant were investigated along the world ocean circulation experiment woce hydrographic programme whp p6 section based on data obtained 10 years apart significant increases of nctcal were detected down to 1500 m 27 5 water depth above which the sub antarctic mode water samw and the antarctic intermediate water aaiw are found the decadal increases of nctcal on the isopycnal surfaces 26 6 26 9 of samw were higher 5 8 mol kg 1 to the east of 160 w than to the west of it while the increases in aaiw were almost constant on the isopycnal surfaces 27 0 27 5 the averaged increases of nctcal in samw and aaiw were 10 3 1 and 4 1 2 0 mol kg 1 respectively small but significant increases of nctcal and salinity normalized ct nct were also found approximately 3 0 and 5 0 mol kg 1 respectively in abyssal waters occupying depths greater than 3500 m at longitude 180 160 w which correspond to circumpolar deep water spatial differences of anthropogenic co2 accumulation are discussed in terms of water mass distributions the water column inventory of increases of anthropogenic co2 in the south pacific subtropical ocean was estimated to be 1 0 0 4 mol m 2 yr 1 which is almost the same as that previously reported

constraints on asteroid magnetic field evolution and the radii of meteorite parent bodies from thermal modelling abstract paleomagnetic measurements of ancient terrestrial and extraterrestrial samples indicate that numerous planetary bodies generated magnetic fields through core dynamo activity during the early solar system the existence timing intensity and stability of these fields are governed by the internal transfer of heat throughout their parent bodies thus paleomagnetic records preserved in natural samples can contain key information regarding the accretion and thermochemical history of the rocky bodies in our solar system however models capable of predicting these field properties across the entire active lifetime of a planetary core that could relate the processes occurring within these bodies to features in these records and provide such information are limited here we perform asteroid thermal evolution models across suites of radii accretion times and thermal diffusivities with the aim of predicting when fully and partially differentiated asteroids generated magnetic fields we find that dynamo activity in both types of asteroid is delayed until 4 5 5 5 myr after calcium aluminium rich inclusion formation due to the partitioning of 26al into the silicate portion of the body during differentiation and large early surface heat fluxes followed by a brief period

brachiopods as indicators of original isotopic compositions in some paleozoic limestones the original stable isotopic composition of paleozoic marine carbonate rocks is important to establish a baseline for evaluating diagenetic alteration and providing a reliable data base for modeling exogenic geochemical cycles of the elements we have compared the 18 o and 13 c values in the nonluminescent portions of brachiopods with similar published data of whole brachiopods other whole fossils and estimates of original isotopic composition of marine cements the oxygen and carbon isotopic records for each of these paleozoic components show generally good internal consistency significant discrepancies however were noted between results on the different components isotopic and trace element data presented in this study suggest that permo carboniferous whole brachiopods are little altered chemically nonetheless a more reliable but not fool proof approach for obtaining pristine isotopic values is microsampling of least altered regions based on cathodoluminescence in conjunction with staining techniques and elemental analyses the carbon and oxygen isotopic compositions of all components decrease in 18 o and 13 c in geologically older material neither temporal trend is monotonic however oxygen isotopic results suggest an important positive shift in 18 o of about 2 during the early carboniferous whereas the carbon isotope trend shows a major positive shift 2 3 during the mid carboniferous

water column denitrification rates in the oxygen minimum layer of the pacific ocean along 32 s 1 to date estimates of water column denitrification rates in global and basin scale nitrogen budgets do not include any values obtained in the open ocean outside the oxygen minimum zones omzs the high quality 32 s pacific repeat hydrographic surveys conducted in 1992 2003 and 2010 offer an opportunity to estimate denitrification rates on basin scales in the open ocean away from the eastern tropical pacific etp oxygen minimum zones here extended optimum multiparameter analysis and n are used to estimate water column denitrification ndeni in the oxygen minimum layer oml 1100 2000 dbar water column denitrification rates for 2003 and 2010 are estimated from the regression analysis using ndeni and transit time distribution ages based on cfc12 estimated mean denitrification rates in the oml at 32 s range from 3 1 to 7 5 mol n m 3 yr 1 2 6 6 8 mmol n m 2 yr 1 with a thickness of 900 m the oml denitrification rates are 2 3 orders of magnitudes lower than those estimated in the omzs of etp however their significance to pacific nitrogen budget needs to be investigated in the future although uncertainties remain our results may ultimately contribute to an improved understanding of marine nitrogen cycles

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

the δ18o record of phanerozoic abiotic marine calcite cements monomineralic abiotic marine cements formed in low latitude phanerozoic reefs provide the direction and amplitude of secular variation of delta sup 13 c and delta sup 18 o in marine calcite and defines two end member compositions 580 to 360 my minus 7 to minus 5 per thousand delta sup 18 o sub pdb and 360 to present minus 3 to 0 per thousand delta sup 18 o sub pdb sampling of the devono carboniferous transition 375 320 my at several global sites reveals a rapid change in carbonate isotopic compositions bracketed within fammenian to early visean aged strata a 7 to 15 my time interval this shift corresponds to a 2 offset in mean delta sup 13 c and 3 4 offset in delta sup 18 o the abruptness of such change and its overall correlation with variations in sup 87 sr sup 86 sr delta sup 34 s delta sup 13 c and li al ratios in marine sediments suggests a primary offset in marine water composition

paleoenvironmental changes in the silurian indicated by stable isotopes in brachiopod shells from gotland sweden ratios of stable carbon and oxygen isotopes in brachiopod shells more than 370 specimens esp atrypa reticularis from the silurian of gotland sweden have been analysed preservation of biological skeletal ultrastructures observed in sem micrographs and cathodoluminescence analyses indicate that usually no diagenetical alteration occurs the silurian of gotland consists of 440 m carbonate deposits spanning the late llandovery to late ludlow epochs 431 411 m y repeatedly uniform sequences of micritic limestones and marks are interrupted by complex structured reefs and adjacent platform sediments previously the alteration of facies is interpreted as the result of sea level fluctuations caused by a gradual regression with superimposed minor transgressive pulses the silurian sequence of gotland exhibits principally parallel carbon and oxygen isotope records corresponding closely to the topostratigraphic units lower values occur in periods dominated by deposition of marly sequences higher values are observed in periods dominated by reefs and extended carbonate platforms the isotope ratios are influenced by local as well as global factors the oxygen isotope ratios are interpreted to reflect paleosalinity changes due to varying freshwater input rather than changes in paleotemperature consequently the facies distribution of gotland is interpreted as resulting from changes in terrigenous input caused by different rates of continental weathering and freshwater runoff rather than by sea level fluctuations periods of arid climate and therefore anti estuarine downwelling of oxygenated surface water appear as short episodes of reef growing 1 5 m y in an epoche characterized by a tropic humid climate which causes an estuarine circulation and the upwelling of co2 rich deep water carbon isotope ratios are obviously connected to these changes in circulation by the advection of 13c rich surface water arid episodes or upwelling of 13c depleted deep water humid episodes of a silurian ocean which itself reveals generally euxinic deep water conditions due to the burial of organic carbon in black shales

climatic and oceanographic isotopic signals from the carbonate rock record and their preservation stable isotopic data from marine limestones and their constituent fossils and marine cements can provide quantitative evidence for changes in global climate and ocean circulation oxygen isotopic data can indicate changes in temperature and ocean composition whereas stratigraphic variation in carbon isotope ratios may reflect changes in the carbon cycle that can be linked to changes in oceanic productivity and atmospheric greenhouse gases terrestrial carbonates meteoric cements calcretes and speleothems similarly offer significant potential for understanding the evolution of terrestrial climates by providing evidence for the composition of rainwater and the nature of vegetative cover primary environmental isotopic signals may be obscured by the effects of post depositional diagenetic alteration cementation and replacement reactions can take place in a wide range of diagenetic environments the diagenetic history of an individual limestone is determined by a combination of its mineralogical diagenetic potential and depositional setting together with subsequent changes in relative sea level and burial history carbon isotopic values are less prone to alteration during diagenesis than oxygen values but shifts can be significant where organogenic carbon is incorporated linear covariation of carbon and oxygen values is not a reliable indicator of diagenetic alteration water rock interaction and fluid mixing may produce non linear distributions attempts to determine long term changes in climatic and oceanographie conditions through isotope stratigraphy of shallow water limestones must include an assessment of the diagenetic history of the materials analysed petrographic examination using conventional microscopy backed up where appropriate by cathodoluminescence and scanning electron microscopy together with elemental and strontium isotopic analysis can help to identify the effects of diagenetic alteration where material with a range of different degrees of alteration is preserved in the same sediment it may be possible to compare patterns of isotopic and elemental variation and to attempt to unravel the effects of diagenesis in order to determine primary environmental isotopic signals recent research has shown that these techniques can be successfully employed in both phanerozoic and precambrian sediments

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

comment on oxygen and carbon isotopic composition of ordovician brachiopods implications for coeval seawater by h qing and j veizer

the implication of the oxygen isotope records in coexisting cherts and phosphates 18 o values have been determined for 53 coexisting chert phosphate pairs from the phanerozoic and precambrian in addition 18 o values were also determined for 18 biogenic phosphates from the phanerozoic the oxygen isotope data for the chert phosphate pairs permit the calculation of the temperatures of formation of the chert phosphate pairs as well as the 18 o of the waters in which they equilibrated in turn the calculated 18 o of the waters permit the calculation of temperatures from the isotopic data of the biogenic phosphates the temperatures for the tertiary and mesozoic samples are compatible with the literature values determined from oxygen isotope data for well preserved calcareous marine skeletal remains the temperatures calculated from the chert phosphate pairs of the paleozoic are usually higher and vary in cycles of about a 150 million year period the early precambrian temperatures are as high as 80 c and decrease with time the use of chert phosphate pairs for temperature determinations are sufficiently promising to warrant further investigations of this type on well preserved chert phosphate or carbonate phosphate pairs

carbon and oxygen isotopic composition of silurian brachiopods gotland sweden palaeoceanographic implications abstract one hundred and seventy two non luminescent brachiopod shells from the silurian sequence of gotland were investigated for their carbon and oxygen isotopic composition diagenetic alteration of the shell calcite was excluded by means of petrographic trace element and cathodoluminescence analysis oxygen and carbon isotopic signals vary considerably within the uppermost llandovery to the ludlow average 18o and 13c values of well defined stratigraphic units range from 2 4 to 5 9 and 1 to 8 respectively we observed parallel trends in the carbon and oxygen isotope curves with the most prominent shifts occurring in the lower wenlock upper wenlock and middle ludlow average 18o values 2 4 to 2 9 recorded in the middle ludlow are among the highest 18o values reported for the early palaeozoic the recorded 18o variations cannot solely be explained by changes in sea surface temperature and salinity the variations in the isotopic signals correlate negatively with changes in sea level heavy carbon and oxygen signals coincide with sea level lowstands whereas light signals are recorded during sea level highstands sea level highstands were probably characterized by the formation of warm saline waters on subtropical epicontinental shelves inducing oxygen deficiency in the basins alumshale facies the low 18o values are attributed to 18o depletion in surface waters owing to the storage of 18o enriched saline waters in the basins low 13c values are explained by a low surface water productivity since nutrients were not supplied to the photic zone but rather stored in the deeper ocean during sea level lowstands colder waters that formed in higher latitudes may have represented the main intermediate water source a better ventilation of the basins is documented by the deposition of well aerated sediments whereas the high 18o values are explained by the change in oceanic circulation the high 13c values are attributed to an enhanced primary productivity and possibly to an enhanced burial of corg the model discussed here may provide an attractive scenario for accounting for the recorded short term variations in the isotopic signals without the necessity of introducing an isotopic correction factor for silurian sea water

temporal and spatial variations in bomb produced radiocarbon along beagle2003 lines revisits of whp p06 a10 and i03 i04 in the southern hemisphere oceans abstract radiocarbon 14 c in dissolved inorganic carbon was measured during revisit cruises along world ocean circulation experiment hydrographic programme whp lines a10 in the south atlantic i03 i04 in the indian and p06 in the south pacific oceans from august 2003 to january 2004 during the blue earth global expedition 2003 beagle2003 zonal means of the water column inventory of bomb produced 14 c in 2003 2004 in the south atlantic indian and south pacific oceans were about 180 128 and 159 10 12 atoms m 2 respectively the smallest zonal inventory along the i03 line among the three lines was primarily due to a sampling bias because the i03 line in the indian ocean was along 20 s which is more equatorward than the other two lines along approximately 30 s in the south atlantic and south pacific oceans the i03 line in the indian ocean had the smallest zonal inventory of bomb produced 14 c and the largest of bomb produced 137 cs suggesting that the distribution of bomb 14 c in the indian ocean is determined primarily by the thermocline ventilation within the indian ocean the history of bomb 14 c over time suggests that the bomb 14 c inventory in the southern subtropical regions increased steadily up to the early 1990s the rate of increase then slowed between the early 1990s and 2003 2004 because of a decrease in the bomb 14 c influx from the atmosphere to the surface ocean the highest bomb 14 c inventory among the southern subtropical regions was in the subtropical indian ocean however the contribution of the indonesian throughflow from the north pacific and indian oceans to this large inventory in the indian ocean is not clear the 14 c data along the beagle2003 lines in 2003 2004 were compared with those obtained during whp in the 1990s and during the south atlantic ventilation experiment in the late 1980s the zonal averages of the decadal changes in 14 c revealed that bomb 14 c continued to increase between the late 1980s 1990s and 2003 2004 in the southern subtropical regions of the south atlantic and south pacific oceans in the indian ocean an increase in the natural 14 c as a result of circulation changes also contributed to the apparent decadal increase of the bomb 14 c all of our results suggest that the distribution of bomb 14 c in the southern hemisphere is governed primarily by thermocline ventilation processes within the southern hemisphere

fabric retentive non luminescent brachiopods as indicators of original delta 13 c and delta 18 o composition a test abstract fabric retentive non luminescent helderbergian brachiopods from open marine deposits analogous to brachiopods used in other studies to determine paleo oceanic stable isotopic composition exhibit depleted 13c values immediately below the erosional contact and more enriched values of 13c at greater stratigraphic distances below this surface in addition 13c values of these brachiopods display a marked shift across the erosional surface and values above it are essentially the same as those 30 m or more beneath the surface complementing these trends whole rock analyses metastable high agnesian calcite constituents echinoderms as well as early equant calcite cement also exhibit an increased depletion trend in 13c values as the helderberg oriskany contact is approached from below fabric retentive luminescent as well as obviously recrystallized brachiopods display stable isotopic values similar to those of fabric retentive non luminescent brachiopods thus best preserved fabric retentive non luminescent brachiopods exhibit values similar to obviously recrystallized brachiopods diagenetically altered metastable constituents echinoderms stable early meteoric cements and whole rock samples helderberg strata of new york state were affected by early meteoric diagenesis during a siegenian exposure event prior to deposition of the overlying marine oriskany sandstone meteoric diagenesis during this exposure gave rise to a characteristic carbon isotopic depletion trend approaching the helderberg oriskany contact all of the skeletal constituents underwent isotopic exchange during early diagenetic exposure to meteoric waters consequently the practice of using fabric retentive non luminescent brachiopods as indicators of their original chemistry and by extension paleo oceanic chemistry is questioned

isotope signatures associated with early meteoric diagenesis the environments in which carbonate diagenesis proceeds have been documented in previous studies of holocene and late pleistocene sediments and limestones on barbados west indies variations in the carbon and oxygen isotopic composition of limestones produced during early freshwater diagenesis have been observed in this study to occur in specific patterns six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework 1 the subaerial exposure surface is characterized by strongly 12c enriched limestones 13c compositions of underlying limestones grow progressively heavier with increasing depth 2 the subaerial exposure surface may also be marked by slight 18o enrichment 3 an abrupt shift in 18o values may differentiate sediments above the exposure surface from those below 4 sediments altered in the marine meteoric mixing zone may be characterized by positive covariance between their 18o and 13c compositions 5 the vadose phreatic boundary may be marked by a sharp increase in 13c values in the seaward portions of a fresh groundwater system and 6 samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of 18o and a wide range of 13c compositions analysis of samples from five palaeozoic and mesozoic formations which contained petrographic evidence of early freshwater diagenesis showed that isotope patterns similar to those observed in barbados limestones have been preserved in rocks as old as mississippian these isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks they might be used to identify limestones diagenetically altered in meteoric environments to identify mixing zone cements and dolomites and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations

anthropogenic co2 in the southern ocean distribution and inventory at the indian atlantic boundary world ocean circulation experiment line i6 1 the southern ocean where various water masses are formed mode intermediate deep and bottom waters has a high potential to absorb anthropogenic co2 cant however most data based and model estimates indicate low cant inventories south of 50 s in order to investigate this paradox the distribution of cant is estimated between south africa and antarctica world ocean circulation experiment woce line i6 based on a back calculation technique previously used in the north atlantic kortzinger et al 1998 and adapted here for application in the southern ocean at midlatitudes 30 50 s formation and spreading of mode and intermediate waters results in a deep penetration of cant down to 2000 m south of 50 s significant concentrations of cant were estimated in circumpolar deep water 10 mol kg and antarctic bottom water aabw 20 25 mol kg higher concentrations are detected along the continental slope in aabw presumably formed in prydz bay compared to aabw of weddell sea origin the distribution of cant obtained north of 50 s compares well with previous data based and model estimates but large disagreements are found in the south however although transient tracers are not used in the back calculation technique employed here the distribution of cant is remarkably well correlated with cfcs we reevaluated the column inventories of cant for the southern ocean and found higher values at high latitudes 70 90 mol m2 compared to the subtropical subantarctic region 40 80 mol m2 these results support the idea that deep and bottom water formation in the southern ocean is a key process in the natural sequestration of anthropogenic co2

oxygen isotope variations in phosphate of biogenic apatites iii conodonts abstract the method for measurement of the isotopic composition of oxygen in phosphates has been improved and adapted for analysis of small quantities of apatite down to 10 mg this extension enables one to analyze hand picked conodont samples with an analytical reproducibility better than 0 5 1 46 samples of conodonts ranging from the ordovician to the pennsylvanian of north america were analysed some insoluble phosphatic residues ichthyoliths and inarticulate brachiopods of the same time range were also measured the range of the 18o values of the analysed conodonts is between 15 and 19 it shows a general trend of decreasing d18o with increasing age from an average value of about 19 in the pennsylvanian to 17 in the ordovician this trend parallels that previously detected in marine phosphorites for the time range between the devonian and pennsylvanian our data are in agreement with independent paleoclimatic information specifically we detect maximum18o enrichment at the end of the pennsylvanian and minimum enrichment at the end of the devonian the difference between these two extremes is equivalent to about 10 c from about 40 to 30 c assuming constant isotopic composition of ocean water the success of oxygen isotopic analysis of conodonts raises the possibility of their use in paleozoic paleo oceanography in a similar way to foraminifera in the mesozoic cenozoic

early paleozoic paleogeography of the northern gondwana margin new evidence for ordovician silurian glaciation during the early paleozoic transgressions and the distribution of sedimentary facies on the northern gondwana margin were controlled by a regional nnw sse to almost north south striking structural relief in early silurian times a eustatic highstand enabled the sea to reach its maximum southward extent

a search for shocked quartz grains and impact ejecta in early silurian sediments on gotland sweden all bentonite and bentonite resembling layers thicker than a few millimetres from a 120m thick early silurian sequence on gotland sweden were searched for shocked quartz grains of comet or asteroid impact origin although more than 200000 quartz grains from 86 bentonite samples were studied not one single grain with multiple planar shock features was found the studied sequence represents sedimentation during a period of about 2 million years impact frequencies estimated from the cratering record and astronomical observations indicate that during a 2 myr period on average 20 comet or asteroid bodies larger than 0 5 km in diameter strike the earth the number of smaller impacting bodies is many times higher in the light of this high frequency of impacts the absence of any shocked quartz bearing fallout layer in our sequence indicates that lateral spreading of such ejecta is relatively restricted during small and medium scale impact events the results also show that shocked quartz in general is absent or extremely rare in volcanic ash this strengthens the case for an impact related origin of shocked quartz grains in the cretaceous tertiary boundary days

black shales and carbon isotopes in pelagic sediments from the tethyan lower jurassic detailed sampling and analysis of jurassic pelagic limestones and marls from italy hungary and switzerland have enabled construction of an isotope stratigraphy across the pliensbachian toarcian boundary with resolution to the zonal level the oxygen isotope record is unremarkable the carbon isotopes however show two positive excursions one relatively minor during the pliensbachian margaritatus zone subnodosus subzone the other more major during the toarcian early falciferum zone where a maximum 13c value of 4 52 pdb is attained these intervals are known to be favoured periods of organic rich sedimentation in diverse parts of the globe and the isotopic excursions are interpreted as a response to abnormally high rates of storage of organic carbon in the sedimentary record a comparable phenomenon has been documented from the cenomanian turonian boundary in the cretaceous where it has been referred to the influence of an oceanic anoxic event some italian sections spanning this lower jurassic interval contain organic rich shales in the falciferum zone the isotopic signatures from their included locally manganiferous carbonate betray a considerable diagenetic overprint and they cannot therefore be incorporated in a composite isotopic curve carbon isotopes from the organic carbon itself are extremely negative falling to 33 pdb and in one section examined in detail correlate with the calcium carbonate content of the shales they may reflect a partial change to a non calcified planktonic biota during deposition of this lime poor interval possibly responding to upwelling and increased fertility of near surface waters the onset of upwelling may have been as early as spinatum tenuicostatum zone time that is at the pliensbachian toarcian boundary

18o16o and 13c12c in lower paleozoic articulate brachiopods implications for the isotopic composition of seawater three hundred and eleven articulate brachiopods with extensive geographic coverage spanning the cambrian to silurian stratigraphic interval were analyzed for oxygen and carbon isotopic composition cambrian samples have 18o 7 ordovician samples 2 4 and silurian samples 1 9 confirming the previously established trend towards lighter isotopic compositions with increasing age throughout the lower paleozoic forty nine best preserved ordovician and silurian samples were identified based on scanning electron microscopy and trace element analysis they were found to bracket the isotopic compositions of over 85 of specimens from these stratigraphic intervals supporting widespread preservation of the isotopic signal some latest ordovician and lower ludlovian samples associated with shale sequences are apparently enriched in 18o these are interpreted as an environmental phenomenon perhaps related to water temperature and glaciation a number of silurian samples of varying genera and stratigraphic levels are highly enriched in 13c up to 6 some are shale related but some are associated with carbonate bearing basins these are also thought to represent near original compositions but a single environmental cause is unknown the present data show that luminescence is not a decisive criterion for evaluating the degree of brachiopod preservation whole shell values were isotopically similar to their nonluminescent portions for both oxygen and carbon

the valanginian carbon isotope event a first episode of greenhouse climate conditions during the cretaceous lower cretaceous pelagic carbonates outcropping along the southern alps of northern italy provide a record of tethyan palaeoceanography as well as of low frequency fluctuations in the global carbon cycle the carbonate c isotope stratigraphy established at five selected localities in the southern alps allows an accurate picture to be drawn of the duration and amplitude of the valanginian c isotope event 13c values near 1 25 1 50 determined in berriasian and lower valanginian sediments are replaced by more pdsitive 13c values near 3 in the late valanginian the carbonate c isotope excursion ends in the early hauterivian with values fluctuating between 1 5 and 2 the carbonate c isotope excursion is accompanied by a positive excursion in the total organic carbon c isotope curve the valanginian c isotope excursion identified in tethyan sediments correlates with a c isotope excursion recorded in the western north atlantic in the gulf of mexico and in the central pacific dsdp sites 534 391 535 and 167 by analogy with the aptian stage also marked by a significant positive c isotope excursion the time of positive 13c values is regarded as a time of accelerated carbon cycling coupled with increased burial rates of organic carbon and detrital material in oceanic sediments a warm and humid climate possiblycoupled with a high atmospheric co2 content and a high global sea level may have triggered the acceleration of the global carbon cycling in this case the valanginian c isotope event would reflect a first episode of greenhouse earth conditions during the cretaceous

silurian conodont based correlations between gotland sweden and saaremaa estonia correlations between the silurian successions of gotland and the east baltic are based on the narrowest stratigraphic units that can be distinguished in both areas in order further to increase precision true ends of ranges in measured sections have been used instead of pooled formational faunas where outcrops and collections permit some previous correlations are confirmed in other cases there are considerable changes both in levels of correlation and in precision the major differences are found mostly when one or more of the major gaps have remained unrecognized and stratigraphic units therefore have been extended and translated upwards or downwards at least some of these gaps decrease in magnitude southwards in estonia gaps at these levels are also noted on gotland although they are small and probably do not extend across the island the patterns through time of deposition during secundo episodes and gaps during primo episodes agree very well with what can be predicted from a model of oceanic and climatic cyclicity

carbonate particulate sedimentation and facies within the lower silurian hogklint patch reefs of gotland sweden abstract lower wenlockian bioherms within the hogklint formation of the silurian gotland show a myriad of carbonate particulate sedimentation which can be divided into three broad facies inter reef sediments intra reef sediments and inter skeletal sediments mass wasting and normal wave action enhanced during storms together with tidal currents are believed to be the major mechanisms of sediment transport inter reef sediments can be divided into proximal and distal deposits with grain size and grain support decreasing from the reef mass into the inter reef areas intra reef sediments represent sedimentation in hollows channels and depressions on the reef surface grain support of inter skeletal sediments increase towards the top of the reefs reflecting the high water energies that were operating outside the reefs graded fills fine scale cross and planar stratification and grain size related to pore size are features which reflect the pumping action by waves and or tidal currents of sediment into cavities within the hogklint patch reefs the bioclastic sediments that are associated with the hogklint patch reefs are derived by mechanical destruction of reef knobs built by the large frame builders encrusting organisms and also the reef dwellers bioerosion is considered to have been a minor process in providing bioclastic sediment

environmental and physiological influences on isotopic and elemental compositions of brachiopod shell calcite implications for the isotopic evolution of paleozoic oceans abstract brachiopods from the demissa bed middle devonian hamilton group biologically regulated the incorporation of mg sr and na into their shell calcite significant taxonomic differences in the elemental contents of three species athyris spiriferoides mediospirifer audacula and mucrospirifer mucronatus may be related to differences in calcification processes in contrast no significant difference or vital effects were observed between the isotopic values of mediospirifer audacula and athyris spiriferoides from erie 18o 0 03 p 0 949 13c 0 76 p 0 083 and genessee counties 18o 0 39 p 0 471 13c 0 06 p 0 854 this suggests that these brachiopods did not exert a biological control over their isotopic compositions and that their shell calcites reflect ambient physicochemical conditions isotopic compositions in unaltered shell calcites of brachiopods from genessee county which was close to the basin depocentre are heavy for carbon 13c x 5 01 pdb and oxygen 18o x 2 85 pdb compared to the species sampled at the basin s edge erie county 13c x 2 79 pdb 18o x 3 83 pdb there is a significant separation in isotopic values between the deeper and shallower water brachiopods of the basin 18o 0 98 p 0 0005 13c 2 22 p 0 0005 the 18o variation suggests a temperature salinity change with water depth whereas the change in 13c composition probably records an enrichment depletion of organic matter with water depth this observation has significant implications for paleozoic ocean isotopic evolution studies because many global changes in marine 18o and 13c are based on isotopic shifts of similar magnitude