isotopic evidence for early to mid cretaceous ocean temperature variability abstract stable isotopic measurements have been made on planktonic and benthic foraminifera of early to mid cretaceous early albian cenomanian age from dsdp site 463 located in the pacific ocean the degree of alteration of the foraminifera has been assessed through the application of scanning electron microscopy the oxygen isotope data support the view that during the cenomanian globigerine foraminifera such as the genus hedbergella inhabited near surface waters whilst the flattened keeled morphotypes lived deeper within the water column the carbon isotope data reveal a more complex pattern as the 13 c values from planktonic species essentially show a large overlap which is interpreted in terms of a weak 13 c gradient existing in the upper part of the ocean in contrast the oxygen isotope data from planktonic foraminifera from the late albian display no discernible depth stratification pattern and the 13 c data also show a large overlap of values indicative of a complete disruption of the upper part of the thermocline a relatively low surface to bottom water temperature gradient within the early middle albian part of the succession may reflect a well mixed ocean inferred cool ocean temperatures and or high salinities for the early albian may reflect increased oceanic poleward heat transport an increase in temperature and or decrease in salinity in the cenomanian suggests a reduction of the poleward heat flux promoting the build up of limited polar ice during this period of tropical warmth

antarctic marine temperatures late campanian through early paleocene an oxygen isotope paleotemperature study of benthic foraminifera from the upper campanian through lower paleocene section at seymour island near the coast of antarctica was done in conjunction with careful scanning electron microscope observations to monitor the state of foraminiferal preservation the isotopic compositions of those samples which were deemed to be well preserved were the basis of the conclusion that campanian through paleocene high latitude shelf waters near antarctica had temperatures between approximately 4 5 and 10 5 c temperatures during early and middle maastrichtian time were slightly higher than those of either the late campanian or late maastrichtian the inference of temperate climatic conditions in antarctica is in agreement with paleoclimatic conclusions drawn on the species composition of the planktonic foraminiferal assemblages and the character of the planktonic foraminifera as well as with published conclusions based upon paleobotanical evidence the maastrichtian and campanian water temperatures at seymour island are similar to those inferred from published isotope ratios of pacific late cretaceous benthic foraminifera from low latitudes indicating that campanian through early paleocene deep ocean waters at least in the pacific and perhaps elsewhere as well could have formed by sinking of surface waters in polar regions

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

stable isotope fractionation in benthic foraminifera from the peruvian continental margin abstract stable isotope ratios of the carbonate tests of benthic foraminifera are now widely used to reconstruct past changes in ocean circulation and chemistry such studies depend on the accuracy with which changing environmental conditions are recorded and preserved in the tests of foraminifera found in deep sea deposits assessment of this aspect of the method is best accomplished through rigorous study of modern core tops collected from a wide range of depths and bottom water temperatures stable isotope analyses of eighteen taxa of benthic foraminifera from surface sediments of the peru continental margin indicate that most foraminifera are slightly depleted in 18o relative to the benthic foram uvigerina peregrina for at least five taxa we observed subparallel 18 o temperature relationships with slopes nearly equal to that predicted by shackleton 1974 for uvigerina for seven taxa isotopic analysis of six size fractions in the range 210 590 mm reveals that with the exception of u peregrina variation between different size classes for each species is small for 18 o and for 13 c a slight inverse correlation between foraminiferal 18o and 13c content implies a complex interplay of biological and environmental factors which control isotopic composition

caco3 dissolution in sediments of the ceara rise western equatorial atlantic we have used porewater sampling by in situ techniques including whole core squeezing as well as by shipboard sectioning and whole core squeezing to estimate the rates of sedimentary organic matter oxidation and caco3 dissolution at seven sites on the ceara rise in the western equatorial atlantic ocean porewater no3 profiles at all sites show a pattern indicative of active organic matter oxidation in the upper 15 20 cm of the sediments and in a buried organic rich layer the organic c oxidation rate generally decreases with increasing water depth from a value of 22 mol cm2 y at the shallowest site 3279 m to 14 mol cm2 y at the deepest site 4675 m over this depth range the bottomwaters vary from moderately supersaturated with respect to calcite to strongly undersaturated high resolution alkalinity profiles measured in porewaters collected by in situ whole core squeezing yield estimated ca2 fluxes of 11 mol cm2 y at a site located at the depth of the calcite saturation horizon and 7 6 zmol cm2 y at a moderately undersaturated site ca2 fluxes calculated from profiles in porewaters collected by relatively coarse resolution in situ sampling methods clearly indicate that there is caco3 dissolution above the calcite saturation horizon the dissolution of aragonite may contribute to the dissolution flux at the shallowest site these ca2 fluxes as well as fluxes estimated from a model of sedimentary organic matter oxidation and calcite dissolution indicate that 36 66 of the caco3 rain to the seafloor dissolves at sites at and above the calcite saturation horizon while 52 75 of the rain dissolves at sites below this depth when these results are incorporated into the oceanic caco3 budget of milliman 1993 they indicate that 35 of caco3 production is preserved in the deep sea they suggest a caco3 accumulation rate that is 27 lower than that estimated by milliman 1993 our corg oxidation caco3 dissolution model indicates that a large fraction of the caco3 dissolution that is occurring on the ceara rise is attributable to the neutralization of metabolic acids produced during organic matter oxidation the efficiency with which organic matter oxidation dissolves caco3 that is the ratio caco3 dissolution attributable to organic matter oxidation organic matter oxidation rate generally increases as degree of undersaturation of bottomwaters increases however there are deviations from the general trend that can be attributed to site to site variations in the kinetics of organic matter oxidation and calcite dissolution this result indicates that the dissolution of caco3 as a result of organic matter oxidation in the deep sea may mask the effects of variations in surface water caco3 productivity and bottomwater chemistry on the accumulation rate of caco3 in deep sea sediments

early maastrichtian stable isotopes changing deep water sources in the north atlantic we propose that the observed short term stable isotope fluctuations reflect changes in high and low latitude intermediate to deep water sources based on a high resolution stable isotope record of planktic and benthic foraminifera from the early maastrichtian 71 3 to 69 6 ma of blake nose dsdp site 390a north atlantic sources of these waters may have been the low latitude eastern tethys and high latitude north atlantic changes in intermediate to deep water sources were probably steered by eccentricity controlled insolation fluctuations lower insolation favored the formation of high latitude deep waters due to positive feedback mechanisms resulting in high latitude cooling this led to a displacement of low latitude deep waters at blake nose higher insolation reduced intermediate to deep water formation in high latitudes yielding a more northern flow of low latitude deep waters

δ13c values of miocene pacific benthic foraminifera correlations with sea level and biological productivity 13 c 12 c ratios of miocene benthic foraminifera from 22 pacific ocean sites vary with time but are similar at almost all sites in any restricted interval 13 c values are correlated with sea levels inferred from onlap offlap curves reflecting the deposition of greater amounts of organic matter on the continental shelves during transgressions differences in 13 c between sites are correlated with local differences in biological productivity in the overlying surface waters 13 c 12 c values of benthic foraminifera show promise as indicators of marine paleoproductivity

the influence of microhabitats on the carbon isotopic composition of deep sea benthic foraminifera we report 13c and 18o values for rose bengal stained benthic foraminifera from a set of box cores from continental margin environments in the atlantic and pacific oceans these isotopic results are compared with foraminiferal distribution data and pore water 13c profiles to evaluate the importance of environmental microhabitat effects on the carbon isotopic composition of benthic foraminifera the 13c values of infaunal taxa are consistently lower than those of epifaunal taxa suggesting that microhabitat effects on test composition do exist the 13c differences between foraminiferal carbonate and bottom water dissolved inorganic carbon are not correlated with the 18o differences between benthic foraminifera tests and equilibrium calcite but they do correlate with variations in the chemistry of sediment pore waters however interspecific 18o differences as well as 13c differences between species with similar vertical distributions in the sediments indicate that taxon specific vital effects also influence test composition

environmental and biological effects on the stable isotope composition of recent deep sea benthic foraminifera from the western mediterranean sea abstract the influence of microhabitat organic matter flux and metabolism on the stable oxygen and carbon isotope composition of live rose bengal stained and dead empty tests deep sea benthic foraminifera from the gulf of lions western mediterranean sea have been studied the total range of observed foraminiferal isotope values exceeds 1 0 for 18o and 2 2 for 13c demonstrating a wide range of coexisting disequilibria relative to 18o of equilibrium calcite 18oeq and 13c of bottom water dissolved inorganic carbon 13cdic the mean 18o values reveal strongest disequilibria for the studied epifaunal to shallow infaunal species cibicidoides pachydermus uvigerina mediterranea uvigerina peregrina while values approach equilibrium in deep infaunal species globobulimina affinis globobulimina pseudospinescens the mean 13c values decrease with increasing average living depths of the different species thus reflecting a dominant microhabitat pore water signal at the axis of the lacaze duthier canyon a minimum 13cdic pore water gradient of approximately 2 1 is assessed for the upper 6 cm of the surface sediment although live individuals of u mediterranea were found in different depth intervals their mean 13c values are consistent with calcification at an average living depth around 1 cm the deep infaunal occurrence of u mediterranea specimens suggests association with macrofaunal burrows creating a microenvironment with geochemical characteristics similar to the topmost centimeter this also explains the excellent agreement between stable isotope signals of live and dead individuals the ontogenetic enrichment in both 18o and 13c values of u mediterranea suggests a slow down of metabolic rates during test growth similar to that previously observed in planktic foraminifera enhanced organic carbon fluxes and higher proportion of resuspended terrestrial organic material at the canyon axis are reflected by 13c values of u mediterranea on average 0 58 lower than those from the open slope these results demonstrate the general applicability of the 13c signal of this species for the reconstruction of past organic matter fluxes in the mediterranean sea further studies on live specimens are needed for a more quantitative paleoceanographic approach

formation of the late aptian niveau fallot black shales in the vocontian basin se france evidence from foraminifera palynomorphs and stable isotopes abstract we present paleoceanographic models for the formation of the marlstone facies and the most prominent black shale intervals of the late aptian niveau fallot black shale succession from the vocontian basin se france in the lower part of the succession the composition of benthic foraminiferal assemblages of the niveau fallot 2 and 2 black shales suggests an enhanced burial of organic matter due to more eutrophic conditions and resulting low oxygen conditions at the seafloor in the upper part of the succession including niveau fallot 3 and 4 a third order sea level fall indicated by a decrease in the stable carbon isotope values may have resulted in a reduced water mass exchange between the vocontian basin and the western tethyan ocean this may have led to dysoxic conditions at the seafloor of the vocontian basin and may have favored the formation of organic rich sediments as shown by benthic foraminiferal assemblages decreased evaporation however is proposed as the most important mechanism causing a restriction of deep water formation within the basin which finally led to the formation of the niveau fallot 3 and 4 black shales based on our investigations the formation of the niveau fallot black shales was caused by different factors the most prominent ones include sea level fluctuations increasing productivity and changes in precipitation and evaporation rates furthermore niveau fallot 3 can probably be correlated with the thalmann black shale event in california and a dark horizon at the mazagan plateau dsdp site 545

ultrahigh resolution paleomagnetic record from odp leg 169s saanich inlet british columbia initial results abstract the holocene section in saanich inlet vancouver island british columbia is 50 70 m thick cores from saanich inlet obtained during leg 169s of the ocean drilling program afford an excellent opportunity to obtain an ultrahigh resolution paleomagnetic and environmental magnetic record for the holocene and late pleistocene of western canada we have used an automated long core cryogenic magnetometer to study over 380 m of continuous u channel samples from odp sites 1033 and 1034 the two sites that constitute leg 169s holocene records of paleomagnetic inclination and intensity show excellent intra site correlation and can be used to fine tune the lithologic correlation among cores from each site the late pleistocene magnetic records provide a means of intra site correlation of the otherwise featureless marine clay near the holocene late pleistocene boundary both sites contain a magnetic intensity feature that is interpreted as a missoula type flood event on the fraser river the composite holocene inclination records from the two sites are quite similar and provide a means of comparing current age models that are based on radiocarbon dating of material from each site this comparison shows only minor differences in the available age models it also provides strong evidence that the sediments of saanich inlet represent a reliable record of geomagnetic field behavior

carbon isotope composition of tropical surface water during the past 22 000 years carbon isotope values of many species of planktonic foraminifera are size dependant values of 13c of individual size fractions are therefore an integration of low 13c values of calcite precipitated in the juvenile growth stage and high values precipitated in later stages in general the selection of a particular size fraction for downcore studies has been subjective analysis of different size fractions of planktonic foraminifera however yields different time series in downcore studies by measuring the 13c of many size fractions the 13c precipitated throughout the growth of the foraminifera can be calculated time series of the 13c of calcite precipitated in the late growth stages of planktonic foraminifera from two nearby cores from the caribbean sea result in a better correlation than time series of constant size fractions these 13c records indicate similar 13c values during the last glaciation and the late holocene and a broad deglacial minimum approximately synchronous with a minimum in the 13c records of benthic foraminifera from intermediate depth atlantic cores the deglacial minimum may be a reflection of the isotopic composition of the underlying intermediate water which may be affected by circulation changes or changes in preformed 13c values and or of the flux of water upwelled into the surface layer the small 0 2 to 0 0 glacial interglacial 13c difference in tropical surface water is also believed to be affected by the chemistry of the underlying source water

carbon and oxygen isotopic disequilibria of recent deep sea benthic foraminifera abstract the carbon and oxygen isotopic compositions of 149 samples of benthic foraminifera from deep sea core tops indicate that none of the nine species studied secrete calcium carbonate in isotopic equilibrium with ambient bottom water uvigerina pyrgo murrhina and oridorsalis tener are the closest to 18o equilibrium with average deviations about 0 4 while planulina wuellerstorfi and p murrhina are the closest to 13c equilibrium with average deviations about 1 p wuellerstorfi shows the most systematic relationship between 13c and bottom water apparent oxygen utilization the intraspecific variabilities in 18o and 13c suggest that estimates of bottom water paleotemperatures can be made to a precision of 0 7 c while estimates of past apparent oxygen utilization aou can be made to 35 mol kg based on intraspecific comparisons of the recent samples with fossils no temporal changes in the degree of either 18o or 13c disequilibrium have been detected for planulina wuellerstorfi uvigerina oridorsalis tener and globocassidulina subglobosa

deep water in the late maastrichtian ocean 1 stable isotopic data from benthic foraminifera indicate the occurrence of at least three deepwater masses in the late maastrichtian ocean given mean oceanic 18ow of 1 0 the temperature of the coolest intermediate depth waters was 5 7 c that of the deepest waters was 10 c and that of the warmest intermediate waters was 13 15 c the cool intermediate depth water mass probably originated in the high latitude southern ocean the deepest waters originated at least partly in the northern atlantic the source region for the warmest intermediate depth water mass is unknown although much of the late maastrichtian deep water was probably preconditioned for winter sinking by low or middle latitude evaporation no more than 11 of late maastrichtian deep water could have been directly actuated by low latitude sea surface evaporation at least in the southern atlantic and indian oceans heat transport by upwelling of deep water was not the primary cause of mild sea surface and coastal temperatures

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

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

micropalaeontological and geochemical evidence of mid cretaceous dysoxic anoxic palaeoenvironments in the sergipe basin northeastern brazil

trophic control of benthic foraminiferal abundance and microhabitat in the bathyal gulf of lions western mediterranean sea surface sediment was sampled at two bathyal sites in the southwestern gulf of lions in the western mediterranean sea in february and august 1997 to study the distribution and microhabitat of living rose bengal stained deep sea benthic foraminifera both standing stock and diversity of the faunas and the microhabitat of distinct species mirror the trophic situation and the depth of the oxidised layer at the different sites our results suggest that the faunas do not comprise highly opportunistic species and are adapted to rather stable environments in the axial channel of the lacaze duthiers canyon organic matter fluxes are enhanced due to advective transport of organic matter resulting in elevated oxygen consumption rates in the surface sediment and a rather thin oxidised layer the corresponding benthic foraminiferal fauna is characterised by rather high standing stock and diversity and a well developed deep infauna in addition to freshly deposited phytodetritus more degraded organic matter seems to be an important food source in contrast at the open slope organic matter fluxes and oxygen consumption rates in the surface sediment are lower and the oxidised layer is much thicker than inside the canyon the corresponding benthic foraminiferal fauna comprises mainly epifaunal and shallow infaunal species with much lower standing stocks and clear differences between february and august in august standing stocks are higher and the average living depths of most species shift towards the sediment surface these differences can be attributed to patchiness or represent a seasonal trophic signal

stable isotope composition of late cretaceous benthic foraminifera from the southern south atlantic biological and environmental effects abstract the stable carbon and oxygen isotope composition of different benthic foraminiferal species of the latest campanian and earliest maastrichtian from ocean drilling project hole 690c weddell sea southern south atlantic 1800 m paleowater depth have been investigated the total range of measured isotope values of all samples exceeds 4 for 13c and 1 1 for 18o carbon isotope values of proposed deep infaunal species are generally similar or only slightly lower when compared to proposed epifaunal to shallow infaunal species interspecific differences vary between samples probably reflecting temporal changes in organic carbon fluxes to the sea floor constantly lower 13c values for pullenia marssoni and pullenia reussi suggest the deepest habitat for these species the strong depletion of 13c values by up to 3 within lenticulinids may be attributed to a deep infaunal microhabitat strong vital effects or different feeding strategy when compared to other species or modern lenticulinids the mean 18o values reveal a strong separation of epifaunal to shallow infaunal and deep infaunal species epifaunal to shallow infaunal species are characterized by low 18o values deep infaunal species by higher values this result possibly reflects lower metabolic rates and longer life cycles of deep infaunal species or the operating of a pore water co32 effect on the benthic foraminiferal stable isotopes pyramidina szajnochae shows an enrichment of oxygen isotopes with test size comprising a total of 0 6 between 250 and 1250 m shell size although 13c lacks a corresponding trend these data likely represent the presence of changes in metabolic rates during ontogenesis these results demonstrate the general applicability of multi species stable isotope measurements of pristine cretaceous benthic foraminifera to reconstruct past microhabitats and to evaluate biological and environmental effects on the stable isotope composition

rapid strain accumulation on the ashkabad fault turkmenistan from atmosphere corrected insar 1 we have measured interseismic deformation across the ashkabad strike slip fault using 13 envisat interferograms covering a total effective timespan of 30 years atmospheric contributions to phase delay are significant and variable due to the close proximity of the caspian sea in order to retrieve the pattern of strain accumulation we show it is necessary to use data from envisat s medium resolution imaging spectrometer meris instrument as well as numerical weather model outputs from the european centre for medium range weather forecasts ecmwf to correct interferograms for differences in water vapor and atmospheric pressure respectively this has enabled us to robustly estimate the slip rate and locking depth for the ashkabad fault using a simple elastic dislocation model our data are consistent with a slip rate of 5 12 mm yr below a locking depth of 5 5 17 km for the ashkabad fault and synthetic tests support the magnitude of the uncertainties on these estimates our estimate of slip rate is 1 25 6 times higher than some previous geodetic estimates with implications for both seismic hazard and regional tectonics in particular supporting fast relative motion between the south caspian block and eurasia this result reinforces the importance of correcting for atmospheric contributions to interferometric phase for small strain measurements we also attempt to validate a recent method for atmospheric correction based on ecmwf era interim model outputs alone and find that this technique does not work satisfactorily for this region when compared to the independent meris estimates

interspecies variation in stable isotopic signals of maastrichtian planktonic foraminifera we measured stable isotopic signals of the largest specimens of all abundant species of planktonic foraminifera in late maastrichtian samples from three atlantic mid latitude and high latitude sites each sample is marked by a relatively small interspecies range of 18o values 1 2 to 0 8 each also exhibits an interspecies range of 13c values that resembles those of modern assemblages at similar latitudes 2 8 to 0 9 with greater ranges at lower latitudes these results indicate that late cretaceous planktonic foraminifera inhabited water masses characterized by a relatively narrow range of temperatures but may have occupied an array of niches as ecologically diverse as that of modern taxa maastrichtian taxa exhibit more complex relationships between skeletal morphology and vertical and seasonal paleohabitat affinities than previous paleoecologic models have assumed for example keeled taxa were not limited to cold or deep habitats and serial taxa appear to have occupied both warm near surface niches and the coolest or most saline habitats the isotopic differences between species indicate that apparent variation in maastrichtian stable isotopic signals strongly depends on the taxa analyzed narrowly constrained size fractions of rugoglobigerina species may provide a good estimate of relative variation in isotopic equilibria of near surface summer paleoconditions at low and middle latitudes gublerina species laeviheterohelix species and planoglobulina multicamerata appear the likeliest candidates for consistently tracking relative variation in isotopic equilibria of the coldest or most saline paleohabitats of maastrichtian planktonic foraminifera these isotopic results suggest that upper water column thermal gradients may have been only 3 to 5 c in mid latitude and high latitude regions they also suggest that the western and central atlantic mid latitude summer seasurface may have been much cooler or saltier in the maastrichtian than it is today finally they corroborate previous estimates of 10 c surface water at southern high latitudes

global cretaceous paleogeography international geologic correlation program project 191 abstract five global cretaceous paleogeographic maps within a plate tectonic framework are illustrated based on the ten contributions in this special volume

water mass characteristics in the cenomanian us western interior seaway as indicated by stable isotopes of calcareous organisms abstract stable oxygen isotopes taken from taxon specific planktic foraminifera are potential sources of water mass density proxy data and paleoclimate information material suitable for stable isotope analysis is uncommon in the middle to late cenomanian strata of the western interior of the usa however well preserved material from 17 correlative horizons at five localities across se montana and ne wyoming has provided an opportunity to obtain reliable 18 o data from foraminiferal samples fine fraction carbonate e g calcareous nannofossils and inoceramid prisms with the exception of inoceramids which for a benthic organism have stable isotopic compositions resembling surface dwelling calcareous organisms these data indicate that the water column was vertically stratified and water masses were anomalously depleted in 18 o within samples planktic and benthic foraminifera display strong vertical gradients in 18 o and 13 c of several per mil the vertical gradient of 18 o ranges from more negative nearer the sea surface to less negative at the sea floor with a gradient of about 4 this implies less saline warmer waters near the surface with increasingly more saline colder waters with depth this isotopic distribution indicates a stably stratified water column at least seasonally in addition a persistent vertical carbon isotope gradient of 2 3 suggests a strong nutrient gradient that if mixed would result in high surface water fertility preservation of high amounts of organic carbon in the sediments corroborates this inference although the water column was stratified overall the nutrients necessary to promote high productivity were clearly renewed at least seasonally nutrient renewal could have been achieved by 1 winter cooling of the upper layer allowing deeper seasonal mixing with nutrient rich deep waters 2 seasonal shallowing of the pycnocline into the photic zone 3 entrainment and decomposition of organic matter at the previously proposed frontal convergence 4 upwelling of nutrient rich deep waters along the previously proposed oceanic front or 5 mixing of shelf waters with more oceanic waters across an oceanic front

changes in northeast atlantic temperature and carbon flux during the cenomanian turonian paleoceanographic event the goban spur stable isotope record stable isotopes of bulk sediment and well preserved tests of planktonic and benthic foraminifera from midlatitude ne atlantic dsdp site 551 goban spur provide the first estimates of carbon isotope gradients within the water column at a lower bathyal site during the cenomanian turonian boundary interval ctbi the ctbi carbon isotope excursion is prominent up to 2parts per thousand shift in delta 13 c in the bulk coccolith signal but less pronounced approximately 0 5 parts per thousand shift in delta 13 c in planktonic and benthic foraminifera this difference indicates a very steep 13 c gradient in the upper water column and a very efficient biological pump during the ctbi carbon isotope excursion we suggest significantly increased seasonal primary production in the uppermost water column with an enhanced shallow water chlorophyll maximum as a cause for this steep carbon isotope gradient deep water and surface water temperature changes during the ctbi are estimated using benthic and planktonic foraminiferal oxygen isotopes warm deep water masses 13 16degreesc and a low temperature gradient within the water column prevailed in the late cenomanian additional warming approximately 2degreesc for both surface and deep water occurred in the latest cenomanian prior to ctbi black shale deposition this pattern of ctbi black shale deposition during a temperature maximum is also evident at two low latitude locations odp site 1050 blake nose and tarfaya southern morocco c 2003 published by elsevier b v

a time series study of the carbon isotopic composition of deep sea benthic foraminifera 1 variation of the 13c of living rose bengal stained deep sea benthic foraminifera is documented from two deep water sites 2430 and 3010 m from a northwest atlantic ocean study area 275 km south of nantucket island the carbon isotopic data of hoeglundina elegans and uvigerina peregrina from five sets of multicorer and soutar box core samples taken over a 10 month interval march may july and october 1996 and january 1997 are compared with an 11 5 month time series of organic carbon flux to assess the effect of organic carbon flux on the carbon isotopic composition of dominant taxa carbon isotopic data of hoeglundina elegans at 3010 m show 0 3 lower mean values following an organic carbon flux maximum resulting from a spring phytoplankton bloom this 13c change following the spring bloom is suggested to be due to the presence of a phytodetritus layer on the seafloor and the subsequent depletion of 13c in the pore waters within the phytodetritus and overlying the sediment surface carbon isotopic data of h elegans from the 2430 m site show an opposite pattern to that found at 3010 m with a 13c enrichment following the spring bloom this different pattern may be due to spatial variation in phytodetritus deposition and resuspension or to a limited number of specimens recovered from the march 1996 cruise the 13c of uvigerina peregrina at 2430 m shows variation over the 10 month interval but an analysis of variance shows that the variability is more consistent with core and subcore variability than with seasonal changes the isotopic analyses are grouped into 100 m size classes on the basis of length measurements of individual specimens to evaluate 13c ontogenetic changes of each species the data show no consistent patterns between size classes in the 13c of either h elegans or u peregrina these results suggest that variation in organic carbon flux does not preferentially affect particular size classes nor do 13c ontogenetic changes exist within the 250 to 750 m size range for these species at this locality on the basis of the lack of ontogenetic changes a range of sizes of specimens from a sample can be used to reconstruct 13c in paleoceanographic studies the prediction standard deviation which is composed of cruise core subcore and residual replicate variability provides an estimate of the magnitude of variability in fossil 13c data it is 0 27 for h elegans at 3010 m and 0 4 for u peregrina at the 2430 m site since these standard deviations are based on living specimens they should be regarded as minimum estimates of variability for fossil data based on single specimen analyses most paleoceanographic reconstructions are based on the analysis of multiple specimens and as a result the standard error would be expected to be reduced for any particular sample the reduced standard error resulting from the analysis of multiple specimens would result in the seasonal and spatial variability observed in this study having little impact on carbon isotopic records

stable carbon isotopes in marine porewaters abstract we present centimeter scale porewater 13 c profiles from four sites in the central equatorial pacific ocean which reveal steep porewater 13 c gradients up to 1 0 cm 1 at the deep sea sediment water interface we describe the processes controlling porewater carbon isotopic composition and incorporate them into a model of the deep sea benthic carbon cycle our measured 13 c profiles are then used to estimate carbon rain rates at two of these sites manop sites c and s the 13 c data yield organic carbon rain rates of 10 mol c cm 2 yr 1 at site c and 3 mol c cm 2 yr 1 at site s these carbon rain rates agree with recent carbon rain estimates based on sediment trap data and porewater nitrate profiles but are a factor of 2 lower than estimates based on millimeter scale porewater oxygen profiles our model results indicate that changes of the same magnitude in organic carbon rain rate and bottom water composition o 2 co 2 and 13 c have comparable effects on the carbon isotopic composition of surficial porewaters this suggests the need to consider the effects of benthic carbon cycling on the stable carbon isotope record preserved in deep sea benthic foraminifera tests

changes in east atlantic deepwater circulation over the last 30 000 years eight time slice reconstructions using 95 epibenthic 13c records eight time slices were reconstructed to trace the distribution of east atlantic deepwater and intermediate water masses over the last 30 000 years our results show that there have been three distinct modes of deepwater circulation near the stage 3 2 boundary the origin of north atlantic deep water nadw was similar to today mode 1 however after late stage 3 the source region of the nadw end member shifted from the norwegian greenland sea to areas south of iceland mode 2 a reduced nadw flow persisted during the last glacial maximum with constant preformed 13c values the nutrient content of nadw increased markedly near the azores fracture zone from north to south probably because of the mixing of upwelled antarctic bottom water aabw from below which then advected with much higher flux rates into the northeast atlantic later the spread of glacial meltwater over the north atlantic led to a marked short term ventilation minimum below 1800 m about 13 500 14c years ago mode 3 the formation of nadw recommenced abruptly north of iceland 12 800 12 500 years ago and reached a volume approaching that of the holocene in the younger dryas 10 800 10 350 years b p another short term shutdown of deepwater formation followed between 10 200 and 9 600 years b p linked to a further major meltwater pulse into the atlantic each renewal of deepwater formation led to a marked release of fossil co2 from the ocean the likely cause of the contemporaneous 14c plateaus over the last 9000 years deepwater circulation varied little from today apart from a slight increase in aabw about 7000 14c years ago it is also shown that the oxygenated mediterranean outflow varied largely independent of the variations in deepwater circulation over the last 30 000 years

late cretaceous chronology of large rapid sea level changes glacioeustasy during the greenhouse world we provide a record of global sea level eustatic variations of the late cretaceous 99 65 ma greenhouse world ocean drilling program leg 174ax provided a record of 11 14 upper cretaceous sequences in the new jersey coastal plain that were dated by in tegrating sr isotopic stratigraphy and biostratigraphy backstripping yielded a late cre taceous eustatic estimate for these sequences taking into account sediment loading com paction paleowater depth and basin subsidence we show that late cretaceous sea level changes were large 25 m and rapid k1 m y suggesting a glacioeustatic control three large d 18 o increases are linked to sequence boundaries others lack sufficient d 18 o data consistent with a glacioeustatic cause and with the development of small 10 6 km 3 ephemeral ice sheets in antarctica our sequence boundaries correlate with sea level falls recorded by exxon production research and sections from northwest europe and russia indicating a global cause although the exxon record differs from backstripped estimates in amplitude and shape

end cenomanian benthic foraminiferal extinctions and oceanic dysoxic events in the northwestern pacific ocean abstract the second largest cretaceous extinction event coincided with an oceanic anoxic event at the cenomanian turonian c t boundary this high resolution analysis of upper bathyal benthic foraminifera in central hokkaido japan indicates that the extinction event occurred in the latest cenomanian over a period of 0 2 m y 93 6 93 4 ma analysis of the dissolved oxygen index based on calcareous benthic foraminiferal wall thickness size and morphology shows that low oxygen 0 1 1 5 ml l conditions developed during a period of 0 15 m y before the c t boundary and 1 5 m y after the minimum oxygen condition 0 1 1 ml l prevailed twice during this interval similarly benthic foraminiferal extinctions occurred twice in concert with initiation of the two minimum oxygen levels coincidence of the two extinction horizons with developemt of low oxygen conditions suggests that the main cause of the extinctions was formation of dysoxic intermediate water this report suggests that the global c t boundary extinction event occurred in a stepwise fashion during the latest cenomanian 0 2 0 5 m y due to development of widespread oceanic anoxic dysoxic conditions within intermediate water masses

microhabitat preferences and stable carbon isotopes of endobenthic foraminifera clue to quantitative reconstruction of oceanic new production seventeen surface sediment samples from the north atlantic ocean off ne greenland between 76 and 81 n and nine samples from the south atlantic ocean close to bouvet island between 48 and 55 s were taken with the aid of a multiple corer and investigated for their live rose bengal stained benthic foraminiferal content within the upper 15 cm of sediment preferentially endobenthic melonis barleeanum m zaandami and bulimina aculeata as well as preferentially epibenthic lobatula lobatula were counted from 1 cm thick sediment slices each and analyzed for stable carbon and oxygen isotopic compositions of their calcareous tests live and dead specimens were counted and measured separately the carbon isotopic composition of the foraminifera was compared to that of the dissolved inorganic carbon dic of simultaneously sampled bottom water during a period of one month one station off ne greenland was replicately sampled once every week and samples were processed as above live specimens of lobatula lobatula are confined to the uppermost two centimeters of sediment live specimens of melonis spp are found down to eight centimeters within the sediment but with a distinct sub surface maximum between two and five centimeters the down core distribution of live bulimina aculeata shows a distinct surface maximum in the top centimeter and constant but low numbers down to 11 cm subbottom depth the average stable carbon isotopic composition d13c per mil vpdb of live l lobatula off ne greenland is by 0 4 0 1 per mil higher than the d13cdic of the ambient bottom water at the time of sampling there is evidence that this species calcify before the ice free season when bottom water d13cdic is supposed to be higher this would reconfirm the one to one relationship between d13c of ambient water dic and cibicids widely used by paleoceanographers live m barleeanum show a negative offset from bottom water dic of 1 7 0 6 per mil in the uppermost sediment and of 2 2 0 5 per mil in three to four centimeters subbottom depth all d13c values of live melonis spp decrease within the upper four centimeters regardless of the time of sampling and site investigated the offset of live b aculeata from bottom water d13cdic values of eight stations rather constantly amounts 0 6 0 1 per mil no matter what subbottom depth the specimens are from at one station however where is strong indication of elevated organic carbon flux the negative offset averaged over all sub bottom depths increases to 1 5 0 2 per mil buliminids actively move within the sediment and by this either record an average isotope signal of the pore water or the signal of one specific calcification depth the recorded signal however depends on the organic carbon flux and reflects general but site specific pore water d13cdic values if compared with epibenthic d13c values from the same site not influenced by pore water and related phytodetritus layer effects bulimina d13c values bear some potential as a paleoproductivity proxy specimens of melonis spp seem to prefer a more static way of life and calcify at different but individually fix depths within the sediment although live specimens thus record a stratified pore water d13c signal there is no means yet to correct for bioturbational and early diagenetic effects in fossil faunas