stable carbon isotope patterns of marine biomarker lipids in the arctic ocean during eocene thermal maximum 2 the middle paleocene through early eocene long term gradual warming was superimposed by several transient warming events such as the paleocene eocene thermal maximum petm and eocene thermal maximum 2 etm2 both events show evidence for extreme global warming associated with a major injection of carbon into the ocean atmosphere system but the mechanisms of carbon injection and many aspects of the environmental response are still poorly understood in this study we analyzed the concentration and stable carbon isotopic delta c 13 composition of several sulfur bound biomarkers derived from marine photoautotrophs deposited in the arctic ocean at similar to 85 degrees n during etm2 the presence of sulfur bound biomarkers across this event points toward high primary productivity and anoxic bottom water conditions the previously reported presence of isorenieratene derivatives indicates euxinic conditions in the photic zone likely caused by a combination of enhanced primary productivity and salinity stratification the negative carbon isotope excursion measured at the onset of etm2 for several biomarkers ranges between 3 and 4 5 much larger than the similar to 1 4 recorded in marine carbonates elsewhere suggesting substantial enhanced isotopic fractionation by the primary producers likely due to a significant rise in pco 2 in the absence of biogenic carbonates in the etm2 section of our core we use coeval planktonic delta c 13 from elsewhere to estimate surface water delta c 13 in the arctic ocean and then apply the relation between isotopic fractionation and pco 2 originally calibrated for haptophyte alkenones to three selected organic biomarkers i e s bound phytane c 35 hopane and a c 25 highly branched isoprenoid this yields pco 2 values potentially in the range of four times preindustrial levels however these estimates are uncertain because of a lack of knowledge on the importance of pco 2 on photosynthetic isotopic fractionation

examining possible effects of seawater ph decline on foraminiferal stable isotopes during the paleocene eocene thermal maximum 1 a large body of paleoceanographic data for the paleocene eocene thermal maximum petm is based on foraminiferal stable carbon and oxygen isotope composition 13c and 18o however the proxy records could be biased due to a ph effect on stable isotopes during times when the ocean became more acidic as has been demonstrated for modern planktonic foraminifera in this paper we calculate the possible ranges of the ph effect on 13c and 18o during the petm based on the relative ph decline ph from the preperturbation steady state simulated by a carbon cycle model and the empirical relationships obtained from culture experiments with planktonic foraminifera the model is configured with eocene paleogeography and simulates ph for surface intermediate and deep water in the major ocean basins in response to various carbon input scenarios 2000 to 5000 pg c for an array of scenarios the modeled ph of the surface ocean ranges from 0 1 to 0 28 units this suggests that 13c of planktonic foraminifera may be increased by up to 2 1 and 18o may be increased by up to 0 7 corresponding to over 3 c error in paleotemperature estimate under conditions in which the model best simulates the global caco3 dissolution pattern we find marked differences in the deep sea ph between the atlantic 0 4 and pacific oceans 0 1 this would imply that the magnitude of the negative 13c and 18o excursions of benthic foraminifera in the atlantic ocean was dampened by up to 2 8 and 0 9 at maximum respectively relative to a constant ph scenario

marked decline in atmospheric carbon dioxide concentrations during the paleogene the relation between the partial pressure of atmospheric carbon dioxide pco2 and paleogene climate is poorly resolved we used stable carbon isotopic values of di unsaturated alkenones extracted from deep sea cores to reconstruct pco2 from the middle eocene to the late oligocene approximately 45 to 25 million years ago our results demonstrate that pco2 ranged between 1000 to 1500 parts per million by volume in the middle to late eocene then decreased in several steps during the oligocene and reached modern levels by the latest oligocene the fall in pco2 likely allowed for a critical expansion of ice sheets on antarctica and promoted conditions that forced the onset of terrestrial c4 photosynthesis

microstructures in diamictites of the lower gowganda formation huronian near elliot lake ontario evidence for deforming bed conditions at the grounding line abstract diamictites examined in the lower gowganda formation 2 5 2 2 ga to the north of elliot lake reveal a large number of macrostructures and microstructures from micromorphological analyses the microstructures show a group of structures indicative of both ductile and brittle deformation likely developed during glacial sedimentation the diamictites possibly were deposited in a proximal subglacial or subaqueous environment as a product of soft deforming bed sediments being extruded beneath an active ice sheet at its grounding line margin as it entered a marine basin this is the first known example of glacial deforming bed conditions being shown to have possibly developed beneath precambrian ice sheets

biogeochemical assessment of sources of organic matter and paleoproductivity during the early aptian oceanic anoxic event at shatsky rise odp leg 198 this study investigates organic rich sedimentary sequences deposited during the early aptian oceanic anoxic event oae1a at sites 1207 and 1213 on shatsky rise odp leg 198 in the west central pacific biomarker analyses provide evidence of the algal and bacterial origin of organic matter om in these sediments where the abundance of steroidal components particularly sterenes and sterones suggests that the om includes major contributions from eukaryotic sources in an environment characterized by high phytoplankton productivity the presence of alkenones at site 1213b is diagnostic of om derived from representatives of haptophyte algae among the calcareous nannoplankton and their 13c values average 31 6 are consistent with those expected during elevated pco2 the occurrence and prominence of 2 methylhopanes and 2 methylhopanones indicates significant contributions to the om from cyanobacteria which are also likely contributors of hopanoids based on their 13c compositions these biomarker data suggest that oceanic conditions perhaps nitrate or iron limited were conducive to cyanobacteria production during oae1a which appears to distinguish this event from other cretaceous oae

variations in the sterane carbon number distributions of marine source rock derived crude oils through geological time abstract the analysis of the sterane data of a large set of crude oils 414 derivedfrom marine carbonate 27 and siliciclastic source rocks 14 where influences of terrestrial or lacustrine derived organic matter can reasonably be excluded shows that there are increases in the relative content of c28 steranes and decreases in the relative content of c29 steranes through geological time there are no consistent variations in the relative content of c27 steranes through time with one major exception a proterozoic oil from oman palaeozolic and older crude oils are thus generally characterised by strong predominances of c29 steranes and low relative concentrations of c28 steranes significantly higher proportions of c28 steranes and lower proportions of c29 steranes occur in oils derived from jurassic and upper cretaceous source rocks these changes through time do not appear to reflect the chemical evolution of the sterols of one particular variety of marine organism the increase in c28 steranes may be related to the increased diversification of phytoplantonic assemblages in the jurassic and cretaceous possible sources of the c28 sterols necessary for the observed changes in crude oil steranes includes diatoms coccolithophores and dinoflagellates although the technique does not give an accurate means of determining the age of the source rock of a crude oil it is possible to distinguish younger crudes derived from the upper cretaceous and tertiary from palaeozoic and older crudes

instability in tropical pacific sea surface temperatures during the early aptian the cretaceous has long been recognized as a time when greenhouse conditions were fueled by elevated atmospheric co2 and accompanied by perturbations of the global carbon cycle described as oceanic anoxic events oaes yet the magnitude and frequency of temperature change during this interval of warm and equable climate are poorly constrained here we present a ighresolution record of sea surface temperatures ssts reconstructed using the tex86 paleothermometer for a sequence of early aptian organic rich sediments deposited during the first cretaceous oae oae1a at shatsky rise in the tropical pacific ssts range from 30 to 36 0c and include two prominent cooling episodes of 4 0c the cooler temperatures reflect significant temperature instability in the tropics likely triggered by changes in carbon cycling induced by enhanced burial of organic matter sst instability recorded during the early aptian in the pacific is comparable to that reported for the late albian early cenomanian in the atlantic suggesting that such climate perturbations may have recurred during the cretaceous with concomitant consequences for biota and the marine environment

high sea surface temperatures during the early aptian oceanic anoxic event 1a in the boreal realm the early aptian was characterized by the widespread occurrence of anoxia in the oceans known as oceanic anoxic event oae 1a intense degassing from submarine volcanic plateaus presumably resulted in high atmospheric co2 concentrations culminating in greenhouse conditions oae 1a can therefore be considered as a past natural experiment important to understand the future evolution of our climate paleotemperature estimates for oae 1a are however predominantly based on bulk oxygen isotopes which are susceptible to diagenetic overprinting while tex86 paleotemperature estimates are limited in number or derived from stratigraphically poorly constrained sections here we reconstructed for the first time sea surface water temperatures ssts based on the tex86 paleothermometer from an oae 1a section from the middle northern latitudes 39 n paleolatitude we find a sst rise starting prior to oae 1a and reaching a maximum during the event with ssts of 31 34 c 4 9 c higher than those of older hauterivian lower aptian sediments from the same sedimentary basin the end of oae 1a is marked by relatively lower ssts of 30 c these observations are supported by belemnite based oxygen isotope d18obel data and calcareous nannofossils our integrated data set clearly indicates that super greenhouse conditions prevailed during oae 1a at northern latitudes ssts are similar to those estimated for coeval low latitudinal sites suggesting that an equable warm climate with reduced latitudinal gradients characterized the early aptian

high sea surface temperatures during the early cretaceous epoch the early cretaceous epoch about 145 100 million years ago is generally thought of as a greenhouse period with high atmospheric co2 concentrations1 and high global mean temperatures2 but evidence for episodes of cooler conditions and even transient glaciations has been proposed3 4 5 6 7 8 9 here we present sea surface temperature records spanning the period from 142 to 128 million years ago berriasian barremian ages from low and mid latitudes reconstructed using the tex86 palaeotemperature proxy during this period we find sea surface temperatures exceeding 32 c at 15 20 n and averaging 26 c at 53 s these temperatures substantially exceed modern temperatures at equivalent latitudes and are incompatible with the notion of consistently cooler conditions in the earliest cretaceous moreover we find little variability in the sea surface temperature records even during the valanginian carbon isotope excursion 138 135 million years ago which was thought to be associated with marked temperature fluctuations5 we conclude that the earliest cretaceous was characterized by a warm stable climate with a lower meridional temperature gradient than today

a novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids we propose a novel tracer for terrestrial organic carbon in sediments based on the analysis of tetraether lipids using high performance liquid chromatography mass spectrometry hplc ms analysis of terrestrial soil and peats shows that branched tetraether lipids are predominant in terrestrial environments in contrast to crenarchaeol the characteristic membrane lipid of non thermophilic crenarchaeota which is especially abundant in the marine and lacustrine environment based on these findings an index was developed the so called branched and isoprenoid tetraether bit index based on the relative abundance of terrestrially derived tetraether lipids versus crenarchaeol this bit index was applied to surface sediments from the angola basin where it was shown to trace the outflow of the congo river furthermore analyses of particulate organic matter from the north sea showed relatively higher bit indices in water column particulate organic matter near large river inputs a survey of globally distributed marine and lacustrine surface sediments shows that the bit index in these environments correlates with the relative fluvial input of terrestrial organic material making this index generally applicable the new proxy allows the rapid assessment of the fluvial input of terrestrial organic material in immature sediments up to 100 ma old

alkenone and boron based pliocene pco2 records abstract the pliocene period is the most recent time when the earth was globally significantly 3 c warmer than today however the existing pco2 data for the pliocene are sparse and there is little agreement between the various techniques used to reconstruct palaeo pco2 this disagreement coupled with the general low temporal resolution of the published records does not allow a robust assessment of the role of declining pco2 in the intensification of the northern hemisphere glaciation inhg and a direct comparison to other proxy records are lacking for the first time we use a combination of foraminiferal 11b and organic biomarker alkenone derived carbon isotopes proxies to determine the concentration of atmospheric co2 over the past 5 ma both proxy records show that during the warm pliocene pco2 was between 330 and 400 ppm i e similar to today the decrease to values similar to pre industrial times 275 285 ppm occurred between 3 2 ma and 2 8 ma coincident with the inhg and affirming the link between global climate the cryosphere and pco2

the carbon isotopic response of algae cyano bacteria archaea and higher plants to the late cenomanian perturbation of the global carbon cycle insights from biomarkers in black shales from the cape verde basin dsdp site 367 abstract the stable carbon isotopic compositions of free and sulfur s bound biomarkers derived from algae cyano bacteria archaea and higher plants and total organic carbon toc during the first phase of the late cenomanian turonian oceanic anoxic event oae were measured in black shales deposited in the southern proto atlantic ocean in the cape verde basin dsdp site 367 to determine the response of these organisms to this major perturbation of the global carbon cycle resulting from widespread burial of marine organic matter the average positive isotope excursions of toc and biomarkers varied from 5 1 to 8 3 the 13c values were cross correlated to infer potential common sources of biomarkers this revealed common sources for c31 and c32 hopanes but no 1 1 relationship for pristane and phytane the correlation of 13ctoc with the 13c value of sulfur s bound phytane is the strongest this is because s bound phytane is derived from phytol that originates from all marine primary producers algae and cyanobacteria and thus represents a weighted average of their carbon isotopic compositions the 13c values of s bound phytane and c35 hopane were also used to estimate pco2 levels before the oae burial event pco2 levels are estimated to be ca 1300 ppmv using both biomarkers and the independent maximum rubisco fractionation factors at times of maximum organic carbon burial rates during the oae reconstructed pco2 levels are estimated to be ca 700 ppmv however compared to other c t oae sections the positive isotope excursion of s bound phytane is also affected by an increased production during the oae when we compensate for this we arrive at pco2 levels around 1000 ppmv a reduction of ca 25 this indicates that burial of organic matter can have a large effect on atmospheric co2 levels

biogenic silica in surface sediments of the south china sea controlling factors and paleoenvironmental implications abstract we mapped the spatial distribution of biogenic silica bsi based on a total of 355 surface sediment samples from the south china sea to provide a basin wide bsi data set for paleoenvironmental reconstruction in the region the results show that bsi relative abundance calcium carbonate percentage siliceous test total abundance grain size and sediment magnetic susceptibility all show distinct spatial distribution patterns that are affected by environmental drivers the gradual increase in bsi from the continental shelf to the abyssal plain suggests that decreased dilution of terrigenous sediments plays a greater role in bsi preservation than does increasing dilution by caco3 decreasing productivity or siliceous dissolution the bsi correlation is weak for diatom abundance but relatively good for radiolarians confirming that radiolarians are the primary contributor to bsi fluxes in the low latitude south china sea in contrast increased dissolution results in a decrease in caco3 with increasing water depth reflecting the different preservation patterns of these two biogenic components correlation analysis also reveals a positive correlation between bsi and fine grain size perhaps reflecting the ability of clay minerals to protect bsi from dissolution volcanic ash and glass also can retard dissolution by increasing the pore water saturation of sio2 in abyssal basin sediments

gradual and sustained carbon dioxide release during aptian oceanic anoxic event 1a a period of ocean anoxia about 120 million years ago coincided with high temperatures a reconstruction of co2 concentrations shows that volcanic outgassing from the ontong java plateau caused co2 levels to double during the anoxic event

toward an orbital chronology for the early aptian oceanic anoxic event oae1a 120 ma abstract the early aptian oceanic anoxic event oae1a 120 ma represents a geologically brief time interval in the mid cretaceous greenhouse world that is characterized by increased organic carbon accumulation in marine sediments sudden biotic changes and abrupt carbon isotope excursions indicative of significant perturbations to global carbon cycling the brevity of these drastic environmental changes

microfacies biostratigraphy and geochemistry of the hemipelagic barremian aptian in north central tunisia influence of the oae 1a on the southern tethys margin upper barremian lower upper aptian hemipelagic deposits of the hamada formation in the djebel serdj area north central tunisia were studied in detail with regard to microfacies biostratigraphy 13 c stratigraphy and geochemistry our data provide insights into the palaeoenvironmental evolution and sea level fluctuations of the tunisian shelf the unusually expanded deposits consist of mud wacke and packstones which reflect mid and outer ramp depositional environments planktonic foraminifer and 13 c stratigraphy allowed us to establish a detailed time frame and the recognition of the lower aptian oceanic anoxic event 1a oae 1a as well as time equivalent deposits of shallowmarine carbonate platform drowning based on our microfacies studies we subdivide the studied sections into four genetic intervals a pre oae 1a interval an oae 1a and platform drowning equivalent interval and a post platform drowning interval we present a 3rd order sea level curve for the tunisian shelf deriving from the results of our microfacies studies deposits of the oae 1a in the sections investigated are characterised by bioclastic wacke and packstones with high abundances of poorly preserved radiolarians and moderately to well preserved planktonic foraminifers suggesting a transgression and an eutrophication of the upper water column scarceness of benthic macrofossils low abundances of small benthic foraminifers and ostracods possibly suggest dysoxic conditions at the seafloor mudstones of the platform drowning time equivalent deposits directly overlying the oae 1a are partly showing a pronounced drop in carbonate content and are scarce of macrofossils 2008 elsevier b v all rights reserved

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

organic geochemistry stable isotopes and facies analysis of the early aptian oae new records from spain western tethys abstract the early aptian oceanic anoxic event oae1a is a time interval characterized by increased organic carbon accumulation in marine sediments notable sedimentary and biotic changes and abrupt carbon isotope excursions indicative of significant major palaeoenvironmental changes linked to a perturbation in the global carbon cycle here we present the study of four sections recording the oae1a early aptian in spain which are located in two broad basins respectively located in the south and the north of iberia the southern iberian palaeomargin carbonero la frontera and cau sections and the basque cantabrian basin puentenansa section which represent depositional settings ranging from shallow marine distal ramp cau and drowned platform puentenansa to pelagic environments carbonero la frontera biomarker compositions c isotope profiles biostratigraphic data and facies analysis from the four sections are correlated and integrated the c isotope curves all present a clear negative excursion followed by a positive shift the integration of the c isotope curves with the biostratigraphic data has been used to correlate the studied sections and to tentatively identify the eight segments formerly proposed from the alpine domain and subsequently identified in sections worldwide four main groups of compounds are present in all sections n alkanes isoprenoids hopanes and steranes n alkanes and acyclic isoprenoids pristane and phytane are dominant in most samples the hopanes are represented by a range of c 27 to c 35 components with the specific isomers varying amongst the sections due to differences in thermal maturity steranes occur as a range of c 27 c 28 and c 29 isomers whereas diasteranes only occur in the most thermally mature section carbonero other compounds of interest include gammacerane and dinosterane differences in thermal maturity appear to be the first order control on different biomarker assemblages amongst the studied sections the carbonero section is thermally mature whereas the nearby la frontera and cau sections are immature puentenansa has intermediate values organic matter is derived from a range of terrestrial marine and bacterial sources the dominance of the c 29 sterane isomers in all sections suggests a strong contribution from higher plants the presence of gammacerane indicates water column stratification and high c 29 c 30 hopane ratios suggest anoxia at the water sediment interface respectively sedimentologic analysis also suggests anoxic conditions during sedimentation but evidence for strong and persistent water column anoxia is equivocal the correlation of the sections reveals that sedimentation of organic rich facies started earlier in pelagic and later in the shallow marine settings which can be related to an expansion of the favorable conditions for organic matter accumulation and preservation from deep marine waters to shallower platform environments during the development of oae1a

sterane biomarkers as indicators of palaeozoic algal evolution and extinction events abstract algae are among the oldest organisms known to inhabit the earth s biosphere with a record dating back some 2 7 ga only few marine algae produce hard parts that can be preserved over geologic time and consequently their fossil record is incomplete molecular fossils or biomarkers add complementary information to the fossil palynomorph record steroids are important constituents of eukaryotic cell membranes and are preserved in sediments as steranes c28 and c29 steranes are indicators for the presence of green and c27 steranes for the presence of red algae respectively the relative abundance of steranes allows the investigation of the fossil record for palaeozoic algal diversification and evolution in this study 500 palaeozoic rock samples representing a broad facies variety from the upper ordovician to the p t boundary were investigated for sterane compositions in addition three profiles covering the hirnantian the f f and the hangenberg event were analyzed for possible shifts in the sterane distribution associated with extinction events a sharp increase of the c28 c29 sterane ratio from 0 70 at the devonian carboniferous boundary implies a fundamental change in the green algae assemblage from more primitive mainly c29 sterane producing algae to modern c28 sterane producing algae for all investigated extinction events a pronounced but short lived rise in the c28 sterane content occurs that is attributed to an episodic increase in prasinophytes the gradual radiation of algae may have been triggered by frequent mass extinctions in the upper devonian culminating with the massive decline of acritarchs at the d c boundary the coeval rise in the c28 c29 sterane ratio indicates the presence of an non encysting algal group and coincides with the global augmentation of numerous filamentous codiacea siphonales and the rise of euspondyle and metaspondyle dasycladales

calcareous nannoplankton response to surface water acidification around oceanic anoxic event 1a ocean acidification induced by atmospheric co2 may be a major threat to marine ecosystems particularly to calcareous nannoplankton we show that during the aptian 120 million years ago oceanic anoxic event 1a which resulted from a massive addition of volcanic co2 the morphological features of calcareous nannofossils traced the biological response to acidified surface waters we observe the demise of heavily calcified nannoconids and reduced calcite paleofluxes at the beginning of a pre anoxia calcification crisis ephemeral coccolith dwarfism and malformation represent species specific adjustments to survive lower ph whereas later abundance peaks indicate intermittent alkalinity recovery deepwater acidification occurred with a delay of 25 000 to 30 000 years after the dissolution climax nannoplankton and carbonate recovery developed over 160 000 years under persisting global dysoxia anoxia

interpreting carbon isotope excursions carbonates and organic matter abstract variations in the carbon isotopic compositions of marine carbonate and organic carbon provide a record of changes in the fraction of organic carbon buried through time and may provide clues to changes in rates of weathering and sources of organic carbon paired carbonate and organic carbon isotope determinations provide a possibility of interpreting not only changes in the global carbon cycle through time but changes in atmospheric pco2 as well interpretations of these types of data are typically rather qualitative a quantitative basis is required to develop a better understanding of changes in the carbon cycle for this purpose we employ a simple model of the global carbon cycle which is subjected to a number of different perturbations each lasting 500 ky i e much longer than the residence times of carbon and phosphorus in the ocean atmosphere system in addition to standard considerations of carbon mass and isotopic fluxes to the ocean atmosphere system from weathering and volcanism and fluxes of organic carbon and carbonate carbon to sediments the model incorporates sensitivity of the photosynthetic carbon isotope effect to changes in pco2 the inclusion of this parameter leads to unexpected carbon isotope responses to forcing that causes increased rates of organic carbon burial a series of simple to more complex simulations illustrates the significant effects of varying differences between the carbon isotopic composition of sedimented carbonate and organic carbon b with constant b a 50 increase in organic carbon burial produces a parallel increase in carbonate and organic carbon isotopic compositions however the same simulation with b responsive to pco2 changes produces an initial parallel 13 c increase but this is followed by an even greater 13 c enrichment in organic carbon because pco2 falls in response to increased organic carbon burial the counterintuitive overall result of the enhanced organic carbon burial event is that the carbonate carbon isotopic composition actually decreases because of the more substantial increase in 13 c org in addition we illustrate the effects on carbon isotopic compositions of the oceanic inorganic carbon reservoir and buried organic matter of a 50 increase in volcanic co2 outgassing a 50 increase in weathering rate with coupled phosphate and riverine carbon flux responses a 50 decrease in shale associated organic carbon weathering a 50 decrease in silicate weathering rate and the possible effects of the rise in abundance of c4 plants in the late miocene to recent we compare the model simulated carbon isotopic responses for some of these experiments to paired carbonate and organic carbon records to illustrate how these records might be interpreted in light of the model response

absence of major vegetation and palaeoatmospheric pco2 changes associated with oceanic anoxic event 1a early aptian se france the deposition of organic rich sediments during the late early aptian oceanic anoxic event oae 1a has been interpreted to result in a major decrease of palaeoatmospheric co2 concentrations accompanied by significant changes in the terrestrial flora in order to test this hypothesis the oae 1a interval in the vocontian basin se france has been studied with a combined approach including stable carbon isotopes organic geochemistry and palynology to estimate changes in palaeoatmospheric co2 levels across the oae 1a the 13c composition of presumed algal biomarkers low molecular weight n alkanes steranes and of bulk carbonate carbon are used our results yield estimated early aptian carbon dioxide partial pressure pco2 values three to four times the preindustrial level and only a moderate drop across the black shale event this moderate drop in pco2 is supported by palynological results the frequency patterns of climate sensitive sporomorphs incl pteridophyte spores bisaccate pollen and classopollis spp display only minor fluctuations throughout the studied section and indicate relatively stable patterns of terrestrial vegetation during and after formation of the oae 1a black shale the occurrence of a characteristic early aptian carbon isotope pattern across the oae 1a interval permits accurate chemostratigraphic correlation with the well studied livello selli interval of the cismon record n italy the contemporaneous formation of individual black shale layers at both sites indicates that transient episodes of dysoxic anoxic bottom waters prevailed over large areas in the w tethys ocean independent of depositional setting comparison of the palynological data from the two locations displays significant differences in the frequency patterns of bisaccate pollen the contrasting pollen spectra are interpreted to reflect prominent changes in the palaeoceanographic current patterns and or selective sorting due to sea level rise rather than latitudinal shifts of the major floral belts

black shale deposition atmospheric co2 drawdown and cooling during the cenomanian turonian oceanic anoxic event 1 oceanic anoxic event 2 oae2 spanning the cenomanian turonian boundary ctb represents one of the largest perturbations in the global carbon cycle in the last 100 myr the 13ccarb 13corg and 18o chemostratigraphy of a black shale bearing ctb succession in the vocontian basin of france is described and correlated at high resolution to the european ctb reference section at eastbourne england and to successions in germany the equatorial and midlatitude proto north atlantic and the u s western interior seaway wis 13c offset between 13ccarb and 13corg is shown to be a good pco2 proxy that is consistent with pco2 records obtained using biomarker 13c data from atlantic black shales and leaf stomata data from wis sections boreal chalk 18o records show sea surface temperature sst changes that closely follow the 13c pco2 proxy and confirm tex86 results from deep ocean sites rising pco2 and sst during the late cenomanian is attributed to volcanic degassing pco2 and sst maxima occurred at the onset of black shale deposition followed by falling pco2 and cooling due to carbon sequestration by marine organic productivity and preservation and increased silicate weathering a marked pco2 minimum 25 fall occurred with a sst minimum plenus cold event showing 4 c of cooling in 40 kyr renewed increases in pco2 sst and 13c during latest cenomanian black shale deposition suggest that a continuing volcanogenic co2 flux overrode further drawdown effects maximum pco2 and sst followed the end of oae2 associated with a falling nutrient supply during the early turonian eustatic highstand

limited range of interspecific vital effects in coccolith stable isotopic records during the paleocene eocene thermal maximum 1 small but significant differences exist among stable carbon and oxygen isotopic excursions measured in coccolith dominated bulk carbonate and planktic foraminifera during the paleocene eocene thermal maximum petm one hypothesis suggests that the bulk carbonate isotopic record is compromised by changing nannofossil assemblages since modern nannofossils show a large 5 permil range of interspecific vital effects new techniques are employed here to separate different size fractions of coccoliths from petm sediments at odp site 690 for isotopic analysis removing a major portion of the variation in nannofossil assemblages isotopic compositions of coarse and fine coccolith fractions dominated by coccoliths of genus chiasmolithus and toweius respectively differ by less than 0 5 permil for both oxygen and carbon the near monogeneric toweius record closely parallels the main trends in the bulk carbonate isotope records including multiple steps in the negative carbon isotopic excursion suggesting that the trends in the bulk carbonate record are not artifacts of changing species assemblages because both coccolithophorids and symbiont bearing foraminifera like acarinina must inhabit the photic zone it is unlikely that the 103 year lags in isotope event onset between coccoliths and acarinina reflect true time transgressive invasion of isotopically depleted co2 into the water column the small range of vital effects among paleocene coccoliths is unlikely to result from diagenetic homogenization and instead may reflect more similar carbon acquisition strategies of paleocene coccolithophorid algae due to larger and or more similar cell sizes and higher atmospheric carbon dioxide the small range of vital effects suggests that bulk carbonate records are likely reliable for other early and pre cenozoic sediments where foraminifera are often scarce

extremely high sea surface temperatures at low latitudes during the middle cretaceous as revealed by archaeal membrane lipids the middle cretaceous 125 88 ma greenhouse world was characterized by high atmospheric co 2 levels the general absence of polar ice caps and much higher global temperatures than at present both 1 8 o based and model based temperature reconstructions indicate extremely high sea surface temperatures ssts at high latitudes however there are a number of uncertainties with sst reconstructions based on 1 8 o isotope data of foraminifera due to diagenetic overprinting effects and tenuous assumptions with respect to the 1 8 o value of cretaceous seawater the paleoecology of middle cretaceous marine organisms and seawater ph here we applied a novel sst proxy i e text tetraether index of 86 carbon atoms based on the membrane lipids of marine crenarchaeota derived from middle cretaceous sedimentary rocks deposited at low latitudes the text proxy indicates that tropical ssts in the proto north atlantic were at 32 36 c during the early albian and late cenomanian early turonian this finding agrees with sst estimates based on 1 8 o paleothermometry of well preserved foraminifera as well as global circulation model calculations the text proxy indicates cooler ssts 27 32 c for the equatorial pacific during the early aptian which is in agreement with sst estimates based on 1 8 o paleothermometry

timing and magnitude of early aptian extreme warming unraveling primary δ18o variation in indurated pelagic carbonates at deep sea drilling project site 463 central pacific ocean abstract in order to elucidate early aptian marine paleotemperature evolution across the period of enhanced organic carbon corg burial oceanic anoxic event oae 1a stable isotope analyses were performed on pelagic limestones at deep sea drilling project site 463 central pacific ocean the 18o data exhibit a distinct anomaly by 2 spanning the oae 1a interval i e a 6 m thick phytoplanktonic corg rich unit constrained by magneto bio and 13c stratigraphy elucidation of paleotemperature significance of the 18o shift is made by taking account of recent sr ca evidence at the same section which revealed that geochemical signals in carbonate poor lithologies are relatively unaltered against burial diagenesis by discriminating 18o values from carbonate poor samples caco3 contents 5 30 wt it appears that an abrupt rise in sea surface temperatures ssts by 8 c 1 7 shift in 18o occurred immediately before oae 1a whereas a cooling mode likely prevailed during the peak corg burial in terms of its stratigraphic relationship as to the corg rich interval and to a pronounced negative 13c excursion as well as its timescale the observed sst rise resembles those associated with the paleocene eocene thermal maximum and more strikingly jurassic toarcian oae this observation is consistent with the hypothesis that these paleoenvironmental events were driven by a common causal mechanism which was likely initiated by the greenhouse effect via massive release of ch4 or co2 from the isotopically light carbon reservoir and terminated by a negative productivity feedback

orbital tuning as an inverse problem chronology of the early aptian oceanic anoxic event 1a selli level in the cismon apticore 1 orbital tuning the process of fitting sedimentary cycles to orbital periodicities can estimate with high resolution the timing and duration of key events in the geological record we formulate here orbital tuning as the inverse problem of finding the variation in sedimentation rate that matches sediment cycles with orbital periodicities instead of obtaining a single best estimate we apply a bayesian formulation and define a probability distribution of sedimentation rate variations that result in powerful orbital periodicities by sampling this distribution with a monte carlo method we quantify the uncertainty in the inferred sedimentation rates due to uncertainties in the tuning periods and to components of the sedimentary signal that are unrelated to orbital cycles the method is applied to the chronology of a 30 m interval in the cismon apticore borehole southern alps italy that includes the early aptian oceanic anoxic event 1a selli level estimated to last 1 11 0 11 ma 95 interval the 13c record shows a sudden negative shift of about 1 at the base of the selli level 22 47 ka followed by a recovery to preshift values in 240 ka consistent with a scenario where light carbon is quickly added and then flushed out of the ocean atmosphere system