late cenomanian to middle turonian high resolution carbon isotope stratigraphy new data from the munsterland cretaceous basin germany abstract new high resolution carbon isotope stratigraphies from two basinal pelagic carbonate successions in northern germany halle and oerlinghausen munsterland cretaceous basin resolve late cenomanian to early mid turonian carbon cycle variations at timescales of less than 100 kyr beside the major carbon isotope excursion of the late cenomanian oceanic anoxic event oae 2 11 small scale distinct features are precisely resolved in the 13c carbonate curve and related to boreal macrofossil zonations the small scale carbon isotope events correspond to secular 13c carbonate variations identified previously in the english chalk the boreal high resolution 13c carbonate curve shows a detailed coincidence with two tethyan 13c curves from italy what demonstrates the interregional significance of the 13c dates and allows their correlation within error limits of 40 kyr furthermore the new 13c curve enables the calibration of boreal and tethyan macro and microfossil zonations accordingly the tethyan calcareous nannoplankton boundary nc13 nc14 corresponds to the boreal fo of c woollgari the index taxon for the lower middle turonian boundary the cyclic appearance and the temporal spacing of the small scale carbon isotope events suggest that orbital forcing exerted control on surface water productivity and organic matter preservation at the sea floor

the impact of layer perturbation potential energy on the east asian summer monsoon abstractthis paper analyzes the relationship between the 1000 850 hpa layer perturbation potential energy lppe as the difference in local potential energy between the actual state and the reference state and the east asian summer monsoon easm using reanalysis and observational datasets the easm is closely related to the first order moment term of lppe lppe1 from the preceding march to the boreal summer over three key regions the eastern indian ocean the subtropical central pacific and midlatitude east asia the lppe1 pattern with negative values over the eastern indian ocean positive values over the subtropical central pacific and positive values over east asia corresponds to negative lppe1 anomalies over the south of the easm region but positive lppe1 anomalies over the north of the easm region which lead to an anomalous downward branch over the southern region but an upward branch over the northern region the anomalous vertical motion affects the local meridional circulation ov

tropical wide teleconnection and oscillation i teleconnection indices and type i type ii states the tropical oscillation of the enso monsoon el nino southern oscillation asian monsoons system is studied based on 34 year simulations of an atmospheric general circulation model with specified sea surface temperature sst together with some observed data for the same period in particular two indices are studied the first is the generalized index of indian monsoon rainfall imr and the other is an index by which the interaction non interaction between the enso and the indian monsoon system is assessed in order to examine the validity of the first index the indian subcontinent and the near equatorial western pacific were selected as two key locations they correspond approximately to the dominant regions in the first empirical orthogonal function of precipitation for boreal summer and winter respectively these two regions form the western rim of a horseshoe teleconnection pattern in their respective seasons the time coefficients of empirical orthogonal function mode 1 in the two seasons are taken as the key indices which are referred to as the tropical wide oscillation index toi having defined the spatial patterns in both seasons the lead lag teleconnection structure associated with the enso monsoon system is studied the result is that the toi for boreal summer is more useful than the toi for boreal winter for identifying the lead lag nature of the enso monsoon the new index is then related to traditional indices like the imr and the southern oscillation index but proves to be a more comprehensive index for lead lag correlations with key variables while the latter the toi for winter has no precursory signal for the indian monsoon for the following summer the second index is the walker circulation index wai which represents the eastward westward shift of the updraught region of the walker circulation it is proposed that the wai can usefully distinguish between years when the enso monsoon oscillation operates type i and years when it does not type ii if the sst in the key region has a climatologically close to normal condition the state of the coupled equatorial system is in type ii on the other hand if the deviation from climatology is large the tropical wide oscillation will continue to be active these years are type i elimination of the type ii years from the data significantly enhances the time lagged correlations between the toi and some key variables such as sst as a result the biennial oscillation becomes clearer

development of incisions on a periodically emergent carbonate platform natih formation late cretaceous oman abstract subaerial exposure of carbonate platforms is generally recorded by karstification and pedogenesis whereas erosion features such as incisions along emersion surfaces have seldom been observed and studied however the recognition of incisions and the characterization of their fill may facilitate definition and hierarchy of sequence boundaries especially along exposure surfaces that do not otherwise present clear petrographic evidence for emersion in the natih formation late albian early turonian oman two successive incision surfaces are present in the upper part of the first third order depositional sequence seismic interpretation of regional subsurface data has allowed the quantification of progradational geometries within the natih sequence i carbonate platform and the correlation of incision surfaces with forced regressive prograding wedges on the margins of the intrashelf basin detailed geological sections and correlations have been made from three outcrop localities allowing a precise description of geometries and facies of incision fills morphology orientation and extent of these incisions have been assessed from detailed seismic interpretation coupled with forward seismic modeling the integration of outcrop and seismic data sets at the regional and local scales allows the interpretation and discussion of the origin and factors controlling the development of these incisions and a refinement of the stratigraphic model these two incisions record rapid sea level variations 500 ky with a magnitude of approximately 20 and 30 m that occurred during the early cenomanian this is probably not a unique case since for the same time interval incisions have been observed in siliciclastic systems in western canada and india and in carbonate systems on the arabian plate

crustal structure seismic stratigraphy and rift processes of the continental margin off eastern canada ocean bottom seismic refraction results off nova scotia two crustal seismic refraction profiles were obtained on the continental margin of eastern canada these lines were located on the upper continental rise and on the outer continental shelf off nova

middle late pleistocene deep water circulation in the southwest subtropical pacific 1 the modern 13cdic distribution in southwest subtropical pacific deep waters is consistent with a regional mixing regime between water masses of open pacific ocean and tasman sea origin this mixing regime is reconstructed across the middle late pleistocene using a record of benthic foraminiferal 13c in a sediment core from the new caledonia trough the relative influence on the mixing regime from open pacific ocean deep waters is seen to be significantly reduced during glacial in comparison to interglacial stages over the past 1 1 ma the spatial 13c gradient in the southern ocean between deep waters entering the tasman sea and the open pacific ocean is shown to be consequently greater during glacial than interglacial stages but was generally reduced across the period of the middle pleistocene transition the existence of strong spatial chemical gradients in the glacial southern ocean limits its capacity to act as an enhanced sink for atmospheric carbon

oxygen level primary productivity and water turbulence during the oae2 interval of zagros basin sw iran benthic foraminiferal variations in the carbonate microfacies abstract cenomanian turonian boundary upper sarvak formation benthic foraminiferal assemblages were analyzed to reconstruct oxygen level primary productivity and water turbulence in the izeh zone zagros basin the interplay between environmental perturbations during the oceanic anoxic event 2 oae2 and regional tectonic activities in the zagros basin resulted in formation of various benthic foraminiferal assemblages in the study section the oae2 interval at the region of study starts with extinction of rotaliporids at the onset of 13c positive excursion peak a which is associated with population of infaunal benthic foraminifera especially bolivina alata the following interval at the onset of whiteinella archaeocretacea biozone is characterized by the total absence of benthic taxa and dominance of planoheterohelicids heterohelix shift in the black shale strata indicating expansion of oxygen minimum zone and unhospitable conditions for both benthic and planktic foraminifera the upper part of oae2 interval including 13c peaks b and c coincides with harbinger of neo tethys closure in the arabian plate causing a compressional tectonic regime and creation of uplifted terrains in the basin the relative sea level started to locally fall in this succession which was accompanied by a better ventilation of seafloor lower toc contents and reappearance of benthic foraminifera

carbon and oxygen isotope fractionations between aragonite and calcite of shells from modern molluscs carbon and oxygen isotope fractionations between calcite and aragonite were investigated by analyzing marine gastropods and bivalves that lived under temperate to tropical climates species that secrete both aragonite and calcite layers were studied to ensure similitude of changes in the isotopic composition of water in diet and in metabolic activity during shell growth aragonite and calcite layers from the adult parts of the shell were identified and mapped by using raman spectroscopy powder samples were obtained by micro drilling under a stereo microscope thirty six pairs of aragonite calcite samples were obtained from ten gastropod and five bivalve species biogenic aragonite is c 13 enriched by 0 95 0 81 and o 18 enriched by 0 37 0 65 relative to co existing biogenic calcite direction and magnitude of the carbon isotope fractionation are compatible with those already determined by using low temperature experimental approaches the observed oxygen isotope difference between biogenic aragonite and calcite is assigned to the difference similar to 0 4 parts per thousand in the acid fractionation factor values that must be taken into account during digestion of carbonate polymorphs at 90 degrees c it is concluded that biogenic calcium carbonate polymorphs precipitate close to but not in isotopic equilibrium with seawater therefore empirical oxygen isotope fractionation equations that were established on the basis of modern mollusc shells and ambient waters should be preferred for the calculation of aquatic paleotemperatures

comparative high resolution chemostratigraphy of the bonarelli level from the reference bottaccione section umbria marche apennines and from an equivalent section in nw sicily consistent and contrasting responses to the oae2 abstract the bonarelli level bl from the upper cenomanian portion of the reference bottaccione section central italy is characterized by the presence of black shales containing high toc concentrations up to 17 and amounts of caco 3 near to zero in the absence of carbonate and consequently of relative carbon and oxygen isotopic data the elemental geochemistry revealed to be a very useful tool to obtain information about the palaeoclimatic and palaeoceanographic evolution of the tethys ocean during the oae2 based on several geochemical proxies rb v ni cr si ba the bl is interpreted as a high productivity event driven by increasingly warm and humid climatic conditions promoting an accelerated hydrological cycle the enrichment factors of peculiar trace metals zn cd pb sb mo u provide further insight about the h 2 s activity at the seafloor during the organic rich sediment deposition and permitted us to evaluate the use of ba as palaeoproductivity tracer in conditions of high rate of sulphate reduction by comparing geochemical records from the reference bottaccione section central italy with those previously obtained for the coeval calabianca section northwestern sicily different degrees of oceanic anoxia were delineated and ascribed to different abundance and type degradable or refractory of organic matter which are limiting factors in the bacterial sulphate reduction reactions and in subsequent euxinic conditions at seafloor in the tethys realm based on a ciclostratigraphic approach consistent fluctuations at 100 ky scale in the chemostratigraphic signals from the two sections are inferred to be expression of a strong orbital climatic forcing driving changes in the oceanic environment during the bl deposition

interdecadal change of the structure of the enso mode and its impact on the enso frequency in the late 1970s the enso cycle exhibited frequency change the oscillation period increased from 2 4 yr high frequency during 1962 75 to 4 6 yr low frequency during 1980 93 observations suggest that this frequency change was accompanied by a significant change in the structure of the coupled enso mode in comparison with the high frequency regime the structure of the coupled mode in the low frequency regime shows three distinctive features during the warm phase of enso the eastward shift of the westerly anomalies the meridional expansion of the westerly anomalies and the weaker intensity of the easterly anomalies in the eastern pacific to test the robustness of the relationship between the oscillation period and the structure of the coupled mode the authors designed empirical atmospheric models based on observations and coupled them with the ocean model of zebiak and cane numerical experiments demonstrate that the enso period is sensitive to changes in the wind anomaly pattern in a way much like the observed enso frequency structure relation the increase of the enso period after 1980 is mainly due to the eastward shift of the zonal wind stress with respect to the sst anomalies physical explanations of the dependence of enso frequency on the structure of the coupled mode are provided by diagnosing the relative contributions of the thermocline feedback and zonal advection feedback on enso evolution

changes in the relationship between northeast china summer temperature and enso 1 northeast china nec summer temperature tends to be lower higher than normal in el nino la nina developing years during 1950s through mid 1970s the relationship between the nec summer temperature and el nino southern oscillation enso is weakened or even becomes opposite in 1980s and 1990s the present study documents this interdecadal change and investigates plausible reasons for this change before the late 1970s enso affects the nec summer temperature through modulating the south asian heating and consequently the midlatitude asian circulation after the late 1970s the connection between enso and the indian summer monsoon and that between the south asian heating and the midlatitude asian circulation have been weakened this leads to a weakening of enso impacts on the nec summer temperature it is found that the nec summer temperature variations are closely related to the north atlantic sea surface temperature sst and circulation changes in 1980s and 1990s in particular a tripole north atlantic sst anomaly pattern in boreal spring is a good precursory for the nec summer temperature anomalies the nec summer temperature displays a negative correlation with the summer sst surrounding the maritime continent in 1980s and 1990s in many years the tropical north pacific and the north atlantic sst anomalies can contribute in concert to the midlatitude asian circulation changes and the nec summer temperature anomalies these effects overcome those of the central and eastern equatorial pacific sst anomalies leading to a same sign relationship between the nec summer temperature and the central and eastern equatorial pacific sst anomalies

synoptic scale characteristics and atmospheric controls of summer heat waves in china summer heat waves with persistent extreme high temperatures have been occurring with increasing frequency in recent decades these extreme events have disastrous consequences for human health economies and ecosystems in this study we examine three summers with intense and protracted heat waves the summers of 2003 2006 and 2013 with high temperatures located mainly in southeastern southwestern and eastern china respectively the synoptic scale characteristics of these heat waves and associated atmospheric circulation anomalies are investigated in the early heat wave episode of 2003 a heat center was located in the southeast coastal provinces during the first 20 days of july the maximum southward displacement of the east asian jet stream eajs induced anticyclonic anomalies to the south associated with southwestward intensification of the western north pacific subtropical high wnpsh and extreme high temperatures were found only to the south of the yangtze river in the later episode a poleward displacement of the eajs and an enhanced wnpsh over the midlatitudes of eastern china resulted in a heat dome over the region and the heat wave extended northward to cover a larger area of eastern china the coupling between the westward enhanced wnpsh and poleward displaced eajs was found in the east china heat wave of 2013 as well but the area of high temperatures reached far to the north in august 2013 with below normal temperatures located in a small region of south china in the 2006 southwestern drought and heat wave extreme poleward displacement of the eajs associated with extraordinary westward extension of the wnsph resulted in further blocking of the moisture supply from the southwest monsoon large scale moisture deficiencies dry conditions and downslope winds were common features of all investigated heat wave episodes but in 2006 low level heat lows associated with a well mixed layer due to intensive daytime heating and atmospheric turbulence were emphasized

on the relationship between western maritime continent monsoon rainfall and enso during northern winter abstract several studies have reported that indonesian rainfall is poorly correlated with el nino southern oscillation enso events during the northern winter wet monsoon season this work studies the relationship between the nino 3 5 s 5 n 150 90 w sea surface temperature sst and the maritime continent monsoon rainfall during 1979 2002 the study indicates that the correlations are mostly negative except in the vicinity of sumatra and malay peninsula smp including the western sections of java and borneo where the correlations range from zero to weakly positive the monsoon rainfall during enso events is influenced by a pair of anomalous walker cells and a low level closed circulation centered near the philippines east of smp the rainfall is negatively correlated with nino 3 sst the anomalous low level wind over the indian ocean west of smp causes rainfall to also be correlated negatively with nino 3 sst but rainfall over smp is sheltered from this effect because of the high mountains along

basalt seawater interaction the plenus cold event enhanced weathering and geochemical change deconstructing oceanic anoxic event 2 cenomanian turonian late cretaceous oceanic anoxic event 2 cenomanian turonian ca 94 ma represents a major palaeoceanographic phenomenon that took place during an interval of extreme global warmth when large amounts of organic matter entered the marine burial record probably triggered by increased availability of nutrients for planktonic biota three sections eastbourne sussex uk raia del pedale campania italy and tarfaya morocco recording this event illustrate the influence on marine geochemistry of mafic volcanic rock seawater interaction anoxia to euxinia and re oxygenation and cooling during the so called plenus cold event the eastbourne section represents the organic lean epicontinental pelagic deposits of the english chalk the raia del pedale section represents a shallow water platform carbonate on the tethyan continental margin also largely devoid of organic matter and the tarfaya core represents an atlantic margin site where cyclically bedded organic rich sediments were well developed correlation between all three sections is readily achieved by biostratigraphy and carbon isotope stratigraphy 13ccarb and 13corg over the oceanic anoxic event 2 interval represented by a characteristic broad positive carbon isotope excursion the stratigraphic range of the plenus cold event defined by the presence in two discrete levels of boreal fauna and an excursion to heavier oxygen isotope values in the english chalk can be identified in raia del pedale and tarfaya by using the carbon isotope curve as a correlative tool similarly a section in southern france allows its co existing osmium isotope excursion to relatively unradiogenic values to be placed in the context of the oceanic anoxic event in all three analysed sections a fall to lower osmium isotope values clearly pre dated the onset of oceanic anoxic event 2 as defined by the initial rise in carbon isotope values allowing the putative magmatic mafic event as a trigger for the oceanic anoxic event an initial drop in sulphur isotope ratios 34scas at eastbourne correlates with the osmium isotope curve suggesting that isotopically light sulphur could have been derived from a mafic igneous source re oxygenation of sediments of all three investigated sections during the plenus cold event is variably illustrated by change in cerium calcium iodine calcium molybedenum calcium and uranium calcium ratios according to the redox behaviour of the elements in question and whether controls on seawater chemistry were local or global in nature changes in molybdenum isotope ratios from tarfaya and portions of the sulphur isotope curve from eastbourne and raia del pedale also indicate the probable presence of more oxygen rich bottom waters during the plenus cold event oxidation by such waters of previously deposited organic rich shales as well as loss of anoxic euxinic sinks is credited with temporarily enriching global seawater in a range of other redox sensitive trace metals for example v cr co ni cu zn and cd during ongoing basalt seawater interaction indicated by persistent relatively non radiogenic osmium isotope seawater values however early diagenetic enrichment of manganese in the english chalk over much of the oceanic anoxic event interval is broadly correlative in time with relatively low osmium isotope values in sections elsewhere a relationship that may be due to the lack of affinity of manganese with carbon rich shales hence allowing relatively elevated concentrations of the element in marine waters to persist during leaching of mafic rocks unlike other redox sensitive species the calcium isotope and lithium isotope ratios from eastbourne and raia del pedale indicate an increase in global weathering during the initial phase of oceanic anoxic event 2 and the shift in strontium isotopes and osmium isotopes to more unradiogenic values during the event suggests that not only construction but also destruction of one or more large igneous provinces was probably a proximal cause of this major palaeoceanographic phenomenon by elevating nutrient levels and planktonic productivity in large tracts of the world ocean globally widespread carbon burial and silicate weathering are both identified as important mechanisms for drawing down atmospheric carbon dioxide that in the absence of overwhelming volcanogenic replenishment of this greenhouse gas during the early phase of oceanic anoxic event 2 caused the plenus cold event

paleoenvironmental changes across the mid cenomanian event in the tropical atlantic ocean demerara rise odp leg 207 inferred from benthic foraminiferal assemblages abstract this study is based on cenomanian sediments of ocean drilling program odp sites 1258 and 1260 from demerara rise leg 207 western tropical atlantic off suriname 1000 and 500 m paleo water depth respectively studied sediments consist of laminated black shales with toc values between 3 and 18 and include the mid cenomanian event mce a positive carbon isotope excursion predating the well known oceanic anoxic event 2 oae 2 benthic foraminiferal assemblages of the continuously eutrophic environment at demerara rise are characterized by low diversities 9 species per sample and large fluctuations in abundances indicating oxygen depletion and varying organic matter fluxes dominant species at both sites are bolivina anambra gabonita levis gavelinella dakotensis neobulimina albertensis praebulimina prolixa and tappanina cf laciniosa benthic foraminiferal assemblages across the mce show a threefold pattern 1 stable ecological conditions below the mce interval indicated by relatively high oxygenation and fluctuating organic matter flux 2 decreasing oxygenation and or higher organic matter flux during the mce with decreasing benthic foraminiferal numbers and diversities site 1258 and a dominance of opportunistic species site 1260 and 3 anoxic to slightly dysoxic bottom water conditions above the mce as indicated by very low diversities and abundances or even the absence of benthic foraminifera slightly dysoxic conditions prevailed until oae 2 at demerara rise a comparison with other atlantic ocean and tethyan sections indicates that the mce reflects a paleoceanographic turning point towards lower bottom water oxygenation at least in the proto north atlantic ocean and in the tethyan and boreal realms this general trend towards lower oxygenation of bottom waters across the mce is accompanied by ongoing climate warming in combination with rising sea level and the development of vast shallow epicontinental seas during the middle and late cenomanian these changes are proposed to have favoured the formation of warm and saline waters that may have contributed to intermediate and deep water masses at least in the restricted proto north atlantic and tethyan ocean basins poor oxygenation of the late cenomanian sediments and the changes in benthic foraminiferal assemblages across the mce

the mid cenomanian event prelude to oae 2 a detailed synthesis of litho and biostratigraphic investigations of the cenomanian pelagic limestones of the scaglia bianca formation in the umbria marche basin shows that the bonarelli level which is the regional sedimentary expression of the oae 2 represents the climax of a 2 myr long cycle of black shale deposition that began in the mid cenomanian planktonic foraminiferal rotalipora cushmani zone this long term cycle began with a prominent short term event named mid cenomanian event mce which is associated with several changes in the biotic and abiotic records in particular a comparison of the available litho bio and chemostratigraphic data from the umbria marche basin allows recognition of the mce based on a a significant change in the sedimentary and tectonic regimes b a reorganisation of planktonic foraminiferal assemblages c a major change in benthic foraminifera d a major turnover in the radiolarian assemblages e a 0 7 positive shift in the carbon isotope values and f a positive shift of carbonate sr ca ratio moreover the mce is preceded 400 kyr by a short term 0 5 negative excursion in the oxygen isotope record the above mentioned changes in carbon and oxygen isotope values can be confidently correlated over different basins and oceans and seem to occur in correspondence with a major sea level fall these lines of evidence define the mce as an outstanding event associated with large scale changes in the oceanic structure and palaeoclimate the mce and the subsequent cyclical deposition of organic rich beds serve as a case study to better understand differences and similarities between mesozoic black shales and cenozoic sapropels and related palaeoceanographic changes controlled by orbital climate cycles

calcareous nannoplankton response to late albian oceanic anoxic event 1d in the western north atlantic well preserved nannofossil and stable isotope records from the mid cretaceous of ocean drilling project leg 171b western north atlantic indicate cyclical productivity based variations in surface water characteristics suggesting orbitally paced changes in upwelling intensity and the strength of deep mixing associated with oceanic anoxic event oae 1d paleontologic and isotopic evidence suggest that collapse of upper water column stratification associated with oae1d was preceded by approximately 1 m y of progressively decreasing water column stability and increasing surface water fertility thirteen species went extinct during a short ca 200 k y interval associated with oae1d nine of these have morphological characters suggesting adaptation to specific depths in the photic zone simultaneous extinction of these depth zoned species suggests that stratification collapse disrupted the habitat space for these specialized forms resulting in extinction a cyclostratigraphic model provides age estimates of several important nannofossil datums including the first appearances of eiffellithus turriseiffelii 100 95 ma and corollithion kennedyi 99 55 ma

the albian cenomanian transition and oceanic anoxic event 1d an example from the boreal realm the upper albian to lower cenomanian interval in the hanover area germany is characterized by a well developed lithological transition from upper albian monotonous marly claystones of several hundred metres thickness which become enriched in biosilica in the topmost albian to increasingly caco3 rich marls and limestones in the lower and middle cenomanian this study presents a new 165 m thick composite record spanning the latest albian to mid early cenomanian ca 103 0 to 97 5 ma based on two core drillings at anderten in the central lower saxony basin east of hanover which is a sub basin of the north german basin due to the lack or delayed occurrences of tethyan biostratigraphic markers for the late albian and early cenomanian in the boreal realm the definition of the albian cenomanian boundary as based on the lowest occurrence of thalmanninella globotruncanoides is not applicable in order to overcome this issue an integrated biostratigraphic chemostratigraphic approach has been employed in addition to biostratigraphy calcareous nannofossils ostracods planktonic foraminifera and inoceramids the anderten succession has been studied using sedimentary geochemistry caco3 total organic carbon toc 13c and 18o ray logging and x ray fluorescence core scanning this approach enabled successful correlation of the composite anderten record to european reference sections in england south east france and italy as well as to further low resolution records from the lower saxony basin wunstorf and konrad 101 core this work has made it possible to identify the 13ccarb expression of i the oceanic anoxic event 1d ii the albian cenomanian boundary interval and iii potentially the lower cenomanian event s chemostratigraphic age assignments are supported by biostratigraphic results calcareous nannofossils indicate an extended upper cretaceous 0 uc0 zone upper albian up to uc2 upper lower cenomanian and the occurrence of the ostracod physocythere steghausi supports an early cenomanian age for most of the upper part of the composite record notably influxes of the planktonic foraminifer thalmanninella aff reicheli have previously been described from this area and the first appearance of this taxon is usually used to define the base of the middle cenomanian substage however findings from the anderten cores and elsewhere suggest that this taxon has an apparently earlier first appearance questioning previous age assignments from the boreal realm solely based on planktonic foraminifera due to both moderately well preserved microfossils and high sedimentation rates the drilled succession of anderten is considered as a potential boreal reference section for the albian cenomanian transition this article is protected by copyright all rights reserved

high resolution stable isotope records from the upper cretaceous rocks of italy and spain glacial episodes in a greenhouse planet high resolution 13c and 18o records from upper albian to lower santonian pelagic carbonates of the contessa quarry section in italy exhibit large positive oxygen isotopic excursions of 1 in the lower cenomanian and upper turonian coniacian strata within the uncertainties of biostratigraphic correlation these positive excursions appear to correspond to times of large sea level regressions in global sequence stratigraphic sea level curves several lines of evidence suggest that the major 18o excursions in contessa reflect episodes of global cooling and not differential diagenesis numerical models of oxygen isotope exchange during diagenesis show that a high contrast in the degree of alteration would be required to produce these signals as artifacts of diagenesis and lithological data provide no evidence for such large contrasts in the degree of alteration furthermore although precise correlation with a section in the south of spain is hampered by stratigraphic complexities the general sequence of major positive 18o excursions is reproduced it is unlikely that differential diagenesis would produce similar artifacts in multiple sites one explanation for the link between episodes of global cooling and sea level falls is that global cooling events led to polar ice sheet accumulation lowering sea level although ice free conditions have been inferred from evidence for a much warmer climate in late cretaceous time our results suggest that the relationship between continental high latitude ice sheets and overall climatic warmth warrants further examination

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

mid cretaceous albian santonian sea surface temperature record of the tropical atlantic ocean paleoclimate records of geologic time periods characterized by extreme global warmth such as the mid cretaceous are important for a better understanding of the earth9s climate system operating in an exceptionally warm mode here we applied an organic geochemical proxy tex 86 on organic matter rich albian santonian sediments recovered from ocean drilling program leg 207 sites 1258 and 1259 on demerara rise to reconstruct sea surface temperatures ssts in the western equatorial atlantic preceded by a stepwise cenomanian warming trend 31 35 c the onset of the cretaceous thermal maximum coincided here with the cenomanian turonian boundary event once established this extreme warm climate regime characterized by averaged tropical ssts close to 35 c lasted up to the turonian coniacian transition two pronounced cooler intervals 2 3 c interrupt this otherwise remarkably stable record providing the first 18 o independent evidence for middle turonian cooling that previously has been attributed to glacioeustatic sea level lowering coniacian ssts decline stepwise reaching a minimum in the santonian 32 33 c where cooling is most pronounced presumably concomitant with the first progressive opening of a deep water passage through the equatorial atlantic gateway

a southern hemisphere record of global trace metal drawdown and orbital modulation of organic matter burial across the cenomanian turonian boundary ocean drilling program site 1138 kerguelen plateau despite its assumed global nature there are very few detailed stratigraphic records of the late cenomanian to the early turonian oceanic anoxic event 2 from the southern hemisphere a highly resolved record of environmental changes across the cenomanian turonian boundary interval is presented from ocean drilling program site 1138 on the central kerguelen plateau southern indian ocean the new data lead to three key observations firstly detailed biostratigraphy and chemostratigraphy indicate that the record of oceanic anoxic event 2 is not complete with a hiatus spanning the onset of the event a decrease in glauconite and highly weathered clays after the onset of oceanic anoxic event 2 marks the end of the hiatus interval which can be explained by a relative sea level rise that increased sediment accommodation space on the kerguelen plateau margin this change in depositional environment controlled the timing of the delayed peak in organic matter burial during oceanic anoxic event 2 at site 1138 compared with other oceanic anoxic event 2 locations worldwide a second key observation is the presence of cyclic fluctuations in the quantity and composition of organic matter being buried on the central kerguelen plateau throughout the latter stages of oceanic anoxic event 2 and the early turonian a close correspondence between organic matter sedimentary elemental compositions and sediments recording sea floor oxygenation suggests that the cycles were mainly productivity driven phenomena available age control points constrain the periodicity of the coupled changes in sedimentary parameters to ca 15 to 50 ka suggesting a link between carbon burial and astronomically forced climatic variations precession or obliquity in the southern hemisphere mid latitudes both during and after oceanic anoxic event 2 fluctuations that were superimposed on the impact of global scale processes finally trace metal data from the non sulphidic black shale unit at site 1138 provide the first evidence from outside of the proto north atlantic region for a global drawdown of seawater trace metal mo inventories during oceanic anoxic event 2 this article is protected by copyright all rights reserved

on the weakening relationship between the indian monsoon and enso analysis of the 140 year historical record suggests that the inverse relationship between the el nino southern oscillation enso and the indian summer monsoon weak monsoon arising from warm enso event has broken down in recent decades two possible reasons emerge from the analyses a southeastward shift in the walker circulation anomalies associated with enso events may lead to a reduced subsidence over the indian region thus favoring normal monsoon conditions additionally increased surface temperatures over eurasia in winter and spring which are a part of the midlatitude continental warming trend may favor the enhanced land ocean thermal gradient conducive to a strong monsoon these observations raise the possibility that the eurasian warming in recent decades helps to sustain the monsoon rainfall at a normal level despite strong enso events

amino acid geochronology of individual foraminifer pulleniatina obliquiloculata tests north queensland margin australia a new approach to correlating and dating quaternary tropical marine sediment cores 1 in this study we demonstrate the utility of amino acid geochronology based on single foraminiferal tests in quaternary sediment cores from the queensland margin australia the large planktonic foraminifer pulleniatina obliquiloculata is ubiquitous in shelf slope and basin sediments of north queensland as well as pantropical oceans fossil tests are resistant to dissolution and retain substantial concentrations of amino acids 2 4 nmol mg 1 of shell over hundreds of thousands of years amino acid d and l isomers of aspartic acid asp and glutamic acid glu were separated using reverse phase chromatography which is sensitive enough to analyze individual foraminifera tests in all 462 pulleniatina tests from 80 horizons in 11 cores exhibit a systematic increase in d l ratios down core d l ratios were determined in 32 samples whose ages are known from ams 14 c analyses in all cases the asp and glu d l ratios are concordant with 14 c age d l ratios of equal age samples are slightly lower for cores taken from deeper water sites reflecting the sensitivity of the rate of racemization to bottom water temperature beyond the range of 14 c dating previously identified marine oxygen isotope stage boundaries provide approximate ages of the sediments up to about 500 000 years for this longer time frame d l ratios also vary systematically with isotope correlated ages the rate of racemization for glu and asp was modeled using power functions these equations can be used to estimate ages of samples from the queensland margin extending back at least 500 000 years this analytical approach provides new opportunities for geochronological control necessary to understand fundamental sedimentary processes affecting a wide range of marine environments index terms 4267 oceanography general paleoceanography 4850 oceanography biological and chemical organic marine chemistry 3022 marine geology and geophysics marine sediments processes and transport keywords queensland margin marine sediment amino acid racemization geochronology foraminifera quaternary stratigraphy citation hearty p j m j o leary d s kaufman m c page and j bright 2004 amino acid geochronology of individual foraminifer pulleniatina obliquiloculata tests north queensland margin australia a new approach to correlating and dating quaternary tropical marine sediment cores paleoceanography 19 pa4022 doi 10 1029 2004pa001059

an investigation of interannual rainfall variability in africa abstract interannual variations in african rainfall are examined using rotated principal component analysis pca applied to anomalies from the annual mean as well as seasonal anomalies the rotated pca loading patterns suggest several preferred continental scale rainfall anomaly patterns the dominant features of year to year variations in african rainfall appear to be the high spatial coherence of rainfall anomalies over large portions of the continent in addition several dipole regions that is adjacent regions which tend to experience rainfall anomalies of opposite sign are found and discussed one dipole region the sub saharan region appears to have a relationship with a characteristic atlantic sea surface temperature anomaly pattern during boreal summer during austral summer the tendency for a large scale dipole pattern in southeast africa is apparent as is an association of this pattern with the warm and cold phases of the el nin southern oscillation enso phenomenon normalized rainfal

why the properties of el nino changed during the late 1970s following the abrupt north pacific climate shift in the mid 1970s the period amplitude spatial structure and temporal evolution of the e1 nifio notably changed theory is needed to explain why the coherent changes in several el nifio characteristics are nearly synchronized with the decadal climate shift while the decadal variation in the equatorial thermocline could potentially change el nino behavior observation indicates that from the pre shift 1961 1975 to the post shift 1981 1995 period the change of equatorial eastern pacific thermocline is insignificant our numerical experiments with a coupled atmosphere ocean model illustrate that the observed changes in enso properties may be attributed to decadal changes in the surface winds and associated ocean surface layer dynamics without changes in the mean thermocline a theoretical analysis is presented to elucidate the mechanisms by which the decadal variations in winds and upwelling modify the structure and propagation of the e1 nifio and amplify and prolong the e1 nifio la nifia cycle the dominant period of the e1 nifio increased from 2 3 years during 1960s and 1970s to 4 5 years during 1980s and 1990s during this time the amplitude of e1 nifio also increased an and wang 2000 these changes were accompanied by a notable modification in the evolution pattern and spatial structure of the coupled ocean

interannual variability of summer monsoon onset over the western north pacific and the underlying processes climatological summer monsoon onset over the south china sea scs and the western north pacific wnp defined as the region of 108 208n 1208 1608e displays three distinct stages around mid may monsoon rain commences in the scs and the philippines in early to mid june the monsoon rain extends to the southwestern philippine sea after mid july the rainy season starts in the northeastern part of the wnp the onset anomaly however displays an in phase interannual variation across the entire wnp domain the standard deviation of the onset date increases eastward from 3 pentads in the scs to 5 pentads in the northeastern part of the domain the large onset variability in the wnp is mainly attributed to large year to year changes of the seasonal cycle

cenomanian to campanian carbon isotope chemostratigraphy from the western interior basin u s a abstract late cretaceous carbon isotope curves generated for localities in europe asia and the deep sea records have provided the foundation for development of a contiguous intercontinental chemostratigraphic framework despite the development of carbon isotope records from selected stratigraphic intervals in the western interior basin however a comprehensive 13c record comparable to those developed in europe and asia and from odp sites had not yet been completed this study reports a new high resolution cenomanian to campanian carbon isotope record for the central western interior basin of north america that makes a key contribution to the intercontinental correlation the curve is correlated to the well developed molluscan biostratigraphic framework for the western interior basin as well as a revised geochronology based on integration of new radioisotopic dating and astrochronology developed in the same core records from where the 13c data were derived the new 13c record reflects not only major perturbations in the global carbon cycle such as the mid cenomanian event and the cenomanian turonian ocean anoxic event 2 but also smaller excursions that have been recognized in records from europe and asia this shows that the western interior shallow epeiric sea was not isolated for any appreciable part of cenomanian to early campanian time it consistently recorded changes in the global marine carbon cycle observed elsewhere a critical attribute of the chemostratigraphic dataset produced in this study is its linkage with a revised late cretaceous time scale assignment of revised ages to western interior carbon isotope events that are globally expressed will allow export of the improved time scale to localities within and outside the western interior where similar carbon isotope records have been generated this chronostratigraphic tool will allow a number of stratigraphic and geochemical hypotheses to be more rigorously tested

warm tropical ocean surface and global anoxia during the mid cretaceous period the middle of the cretaceous period about 120 to 80 myr ago was a time of unusually warm polar temperatures1 repeated reef drowning in the tropics2 and a series of oceanic anoxic events oaes that promoted both the widespread deposition of organic carbon rich marine sediments and high biological turnover3 4 5 6 7 8 the cause of the warm temperatures is unproven but widely attributed to high levels of atmospheric greenhouse gases such as carbon dioxide7 8 9 10 11 12 in contrast there is no consensus on the climatic causes and effects of the oaes with both high biological productivity and ocean stagnation being invoked as the cause of ocean anoxia3 4 5 6 7 8 here we show using stable isotope records from multiple species of well preserved foraminifera that the thermal structure of surface waters in the western tropical atlantic ocean underwent pronounced variability about 100 myr ago with maximum sea surface temperatures 3 5 c warmer than today this variability culminated in a collapse of upper ocean stratification during oae 1d the breistroffer event a globally significant period of organic carbon burial that we show to have fundamental stratigraphically valuable geochemical similarities to the main oaes of the mesozoic era our records are consistent with greenhouse forcing being responsible for the warm temperatures but are inconsistent both with explanations for oaes based on ocean stagnation and with the traditional view reviewed in ref 12 that past warm periods were more stable than today s climate

pacific east asian teleconnection how does enso affect east asian climate observational evidence is presented to show a teleconnection between the central pacific and east asia during the extreme phases of enso cycles this pacific east asian teleconnection is confined to the lower troposphere the key system that bridges the warm cold events in the eastern pacific and the weak strong east asian winter monsoons is an anomalous lower tropospheric anticyclone cyclone located in the western north pacific the western north pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures the anomalies persist until the following spring or early summer causing anomalously wet dry conditions along the east asian polar front stretching from southern china northeastward to the east of japan kuroshio extension using atmospheric general circulation and intermediate models the authors show that the anomalous philippine sea anticyclone results from a rossby wave response to suppressed convective heating which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central pacific warming the development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling both the anticyclone and the cooling region propagate slowly eastward the development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades the rapid establishment of the philippine sea wind and sst anomalies implies the occurrence of extratropical tropical interactions through cold surge induced exchanges of surface buoyancy flux the central pacific warming plays an essential role in the development of the western pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone sst interaction and midlatitude tropical interaction in the western north pacific

late cretaceous eocene nannofossil and magnetostratigraphic correlations near gubbio italy abstract using a modified sample preparation technique we have been able to establish a detailed lower campanian to upper eocene nannofossil stratigraphy in the bottaccione and contessa highway sections near gubbio appearance and extinction levels of virtually all the commonly used calcareous nannofossil zonal markers have been recognized and can now be closely correlated with the planktonic foraminifera zonation and the magnetic reversal stratigraphy previously established in these sections comparisons with the nannofossil calibrations of the oceanic magnetic anomaly sequence in deep sea drilling project dsdp sites suggest that magmetic subchrons c17n and c25n are missing in the bottaccione section the observed variability of the relative stratigraphic position of most plankton events is confirmed to less than one magnetic subchron absolute abundance paleobiogeographic restriction and differential preservation render some of the traditionally used biostratigraphic events less reliable than others

biscutum constans coccolith size patterns across the mid cretaceous in the western tethys paleoecological implications abstract the morphometric record of the calcareous nannofossil species biscutum constans from the western tethys indicates that this species underwent marked size changes across the latest barremian cenomanian interval 28 myrs significant size reduction occurred during the core of the early aptian oceanic anoxic event oae 1a 120 ma and soon after oae 1a followed by a 9 myr long interval characterized by small specimens larger coccoliths marked the middle to late albian and particularly the lower part of the nannofossil subzone nc10a was characterized by abundant large specimens a minor size decrease coincided with the late albian oae 1d onset 100 ma but very small size was reached again during the latest cenomanian oae 2 94 4 ma the sequence of relatively long millions of years intervals marked by different average sizes is interpreted to reflect adaptation to changing paleoecological conditions temperature and fertility were not directly influencing the size of b constans on shorter time scale abrupt changes in ocean chemistry related to large igneous provinces submarine volcanism played a central role in secretion of small b constans coccoliths to face ocean acidification during oae 1a and oae 2 contrarily during the late early aptian early albian time interval smaller b constans size was related to cooler temperature which possibly also promoted co2 sequestration in cooler surface waters forcing b constans to produce small coccoliths to survive lowered ph in addition pulses of subaerial volcanism of the southern kerguelen plateau may have further affected the ocean chemistry the termination of intense volcanism and warmer temperature in the middle albian early cenomanian coincided with restoration of bigger b constans specimens

an interdecadal change in the relationship between the western north pacific ocean and the east asian summer monsoon this study reveals that the relationship between the western north pacific ocean wnpo 0 55 n 100 165 e and the east asian summer monsoon easm experiences a well defined interdecadal change in the late 1980s and early 1990s the easm related wnpo sea surface temperature anomaly ssta pattern changes from the dipole pattern wnpo dipole wnpod that develops over the period between 1968 and 1987 p1 to a tripole pattern wnpo tripole wnpot between 1991 and 2010 p2 the positive negative phase of the wnpod is characterized by warm cold sstas in the japan sea and kuroshio oyashio extension region and cold warm sstas in the subtropical wnpo whereas the positive negative phase of the wnpot shows warming cooling in the kuroshio extension region ker and cooling warming in the south of kamchatka peninsula skp and philippine sea ps during p1 p2 the wnpod wnpot can be regarded as the first second leading mode of summer wnpo sst variability and its positive phase is associated with a weakened wnpo subtropical high and thereby the deficient summer rainfall in the yangtze river valley together with a strong easm and vice versa the change in the wnpo easm relationship may be caused by interdecadal changes in the relationship of the equatorial central pacific ecp with the wnpo and easm and an increase in summer ker sst variability during p2 because the ecp warming induced cyclonic anomalies move northwestwards and intensify summertime ecp warming is able to generate a strong easm and significant cooling over the two poles of the wnpot skp and ps these strengthened impacts of the ecp on the wnpot and easm contribute to the strengthened wnpot easm relationship during p2 in addition summer ker sst variability increases between 1991 and 2010 and this may have enhanced the impact of the ker on the easm during p2 these two factors probably cause the easm related wnpo ssta pattern to change from the wnpod in p1 to the wnpot in p2

calcareous nannoplankton proxies for palaeoenvironmental reconstruction of the albian cenomanian succession in north western israel mount carmel region abstract we present data on the calcareous nannofossil distribution in the albian cenomanian borehole ct8 obtained from the carmel area nw israel the nannofloral assemblage consists of 113 species with watznaueria spp dominating the entire succession the detailed calcareous nannofossil biostratigraphy of this section is established and seven nannofossil sub zones are recognised for the first time the age of the tavasim tuff v2 is biostratigraphically identified as late albian the quantitative analysis of the calcareous nannofossils suggests warm open marine or coastal mainly oligotrophic conditions throughout the entire succession of borehole ct8 with evident fluctuations of temperatures and fertility and a general trend towards cooling in the uppermost part of the sequence middle late cenomanian temperature and nutrient variations correspond to those in the western tethys thus suggesting at least a supra regional extent of processes detected in the carmel region the biostratigraphy shows no evidence of hiatuses in the studied section but the absence of positive carbon isotope anomalies associated with the oceanic anoxic event oae 1d and mid cenomanian event elsewhere suggests that the oae 1d is possibly missing in the studied section due to a hiatus around the isfiye fm arqan fm boundary

recent changes in enso teleconnection over the western pacific impacts the eastern china precipitation dipole abstractthe eastern china precipitation dipole ecpd features an out of phase relationship between boreal summer precipitation over the middle and lower reaches of the yangtze river and the hetao region to its northwest the precipitation dipole is strongly influenced by enso teleconnections over the western tropical pacific here it is shown that a pronounced weakening of both the rainfall variability over eastern china as well as the precipitation dipole structure occurred around the mid 1990s the changes have been analyzed by considering two epochs one during 1979 95 and the other during 1996 2009 the characteristic feature of the circulation anomaly during the first epoch is the well known east asia pacific pacific japan eap pj pattern a quasi meridional teleconnection pattern emanating from the western tropical pacific on the other hand during the latter epoch eastern china precipitation variability occurs as an integral part of the circulation anomalies over the western pacific in contrast

pacific east asian teleconnection part ii how the philippine sea anomalous anticyclone is established during el nino development the anomalous philippine sea anticyclone psac conveys impacts of el nino to east asian climate during the mature and decay of an el nino from the winter to ensuing summer it is shown that the anomalous psac forms in fall about one season prior to the peak el nino its strength increases with the el nino intensity and its sign reverses during a la nina the psac formation concurs with abnormal deepening of the east asian trough and with increasing number of northward recurvature of tropical storms in the western pacific the psac establishment is abrupt coupling with a swing from a wet to dry phase of an intraseasonal oscillation iso and often concurrent with early retreat of the east asian summer monsoon the iso becomes inactive after psac establishment the development of the psac is attributed to combined effects of the remote el nino forcing tropical extratropical interaction and monsoon ocean interaction the developing el nino induces off equatorial as cending rossby wave responses and land surface cooling in northeast asia both deepen the east asian trough in fall and induces vigorous tropical extratropical exchange of air mass and heat which enhances the cold air outbreak and initiation of the psac through exciting descending rossby waves the el nino induced indonesian subsidence generates low level anticyclonic vorticity over south asia which is advected by mean monsoon westerly instigating the anomalous psac the iso interacting with the underlying ocean plays a critical role in the abrupt establishment of psac the wind evaporation entrainment feedback tends to amplify suppress iso before after winter northeasterly monsoon commences suggesting the roles of atmosphere ocean inter action and the seasonal march of background winds in changing the philippine sea iso intensity and maintaining psac

orographically anchored el nino effect on summer rainfall in central china abstractyear to year variations in summer precipitation have great socioeconomic impacts on china historical rainfall variability over china is investigated using a newly released high resolution dataset the results reveal summer mean rainfall anomalies associated with enso that are anchored by mountains in central china east of the tibetan plateau these orographically anchored hot spots of enso influence are poorly represented in coarse resolution datasets so far in use in post el nino summers an anomalous anticyclone forms over the tropical northwest pacific and the anomalous southwesterlies on the northwest flank cause rainfall to increase in mountainous central china through orographic lift at upper levels the winds induce additional adiabatic updraft by increasing the eastward advection of warm air from tibet in post el nino summers large scale moisture convergence induces rainfall anomalies elsewhere over flat eastern china which move northward from june to august and amount to little in

paleoceanographic changes at the northern tethyan margin during the cenomanian turonian oceanic anoxic event oae 2 abstract the late cenomanian early turonian oceanic anoxic event oae 2 represents major paleoceanographic and faunal perturbations samples from the northern tethyan margin rehkogelgraben eastern alps were investigated in order to trace the paleoceanographic processes paleoecologic conditions were reconstructed by combining the results of assemblage counts of indicative microfossil groups foraminifera and radiolaria assemblages size distributions and abundances show a tripartite subdivision for surface and bottom waters 1 oligotrophic surface conditions and oxic bottom waters with a reasonably high food supply for the late cenomanian interval 2 an oae period with black shales characterized by very low numbers but high diversities and a lack of high productivity indicators among planktic foraminifera low abundances of small sized benthic foraminifera indicate low oxic dysoxic conditions at the seafloor 3 post oae assemblages are characterized by mesotrophic planktic species and benthic foraminifera suggest oxic bottom waters it took about 300 ky to re establish a pelagic carbonate producing regime the semi enclosed basin situation of the penninic ocean is thought to be responsible for differences between the high productivity in the world ocean during the oae 2 and the overall absence of high productivity indicators and high foraminiferal diversities at rehkogelgraben the penninic ocean may have even served as a refuge during the environmental crisis

calcareous nannofossil evidence for the existence of the gulf stream during the late maastrichtian 1 upper maastrichtian calcareous nannofossil assemblages from eight cores on the south carolina coastal plain onshore set and three deep sea drilling sites from the continental slope and abyssal hills offshore set were analyzed by correlation and principal component analysis to examine the ancient surface water thermal structure in addition a temperature index derived from independently published paleobiogeographic information was applied to the sample data all three methods indicate a strong separation of the samples into onshore and offshore sets with the offshore data set exhibiting significantly warmer paleotemperatures the great disparity between these two sample sets indicates that there was a strong thermal contrast between the onshore and offshore surface water masses that persisted throughout the late maastrichtian despite evident short term changes in fertility productivity and community structure this suggests the gulf stream was present as a major oceanographic feature during the late maastrichtian

the expression of the cenomanian turonian oceanic anoxic event in tibet the gongzha section of tibet china is located at the northern margin of the indian plate se tethys and is characterized by hemipelagic grey marls and marly limestones light grey limestones and silty limestones but no organic rich sediments high resolution biostratigraphy reveals an expanded cenomanian turonian ct boundary interval and the 13c record includes the main features of the classical positive carbon isotope excursion that characterizes the ct oceanic anoxic event the biotic response inferred from the foraminifera suggests that oxic to dysoxic conditions prevailed except for a short interval marked by peak abundance of heterohelix that indicates a significantly dysoxic environment during the 13c b peak excursion the overall decreasing trend in redox sensitive trace elements rste during the maximum 13c excursion confirms the absence of significant longer lasting anoxia in the gongzha section enrichments in rste are linked to phases of increased detrital input chemical weathering indices suggest that the upper cenomanian sediments accumulated under an increasingly hot and humid climate that culminated near the ct boundary in the early turonian lower weathering indices suggest a warm drier climatic regime with reduced continental runoff phosphorus mass accumulation rates show a significant peak at the onset of the positive 13c excursion followed by a decrease up to the basal turonian this pattern is positively correlated with the long term decrease in detrital index as also observed in numerous other ct boundary sections e g eastbourne pueblo and whadi el ghaib sinai long term phosphorus accumulation in the gongzha section is therefore associated with changes in detrital input the overall decreased detrital input can be explained by the increasingly remote continental sources due to the major transgression at the end of cenomanian coupled with changes in continental weathering intensity linked to increasingly more arid climate conditions

carbon and oxygen isotope stratigraphy of the english chalk and italian scaglia and its palaeoclimatic significance a detailed carbon and oxygen isotope stratigraphy has been generated from upper cretaceous coastal chalk sections in southern england east kent culver cliff isle of wight eastbourne and seaford head sussex norfolk coast and the british geological survey bgs trunch borehole norfolk data are also presented from a section through the scaglia facies exposed near gubbio italian apennines wherever possible the sampling interval has been one metre or less both the chalk and scaglia carbon isotopic curves show minor positive excursions in the mid cenomanian mid and high turonian basal coniacian and highest santonian lowest campanian there is a negative excursion high in the campanian in chalk sections that span that interval the well documented cenomanian turonian boundary spike is also well displayed as is a broad positive excursion centred on the upper coniacian a number of these positive excursions correlate with records of organic carbon rich deposition in the atlantic ocean and elsewhere the remarkable similarity in the carbon isotope curves from england and italy enables cross referencing of macrofossil and microfossil zones and pinpoints considerable discrepancy in the relative positions of the turonian coniacian and santonian stages the oxygen isotope values of the various chalk sections although showing different absolute values that are presumably diagenesis dependent show nonetheless a consistent trend the east kent section which is very poorly lithified indicates a warming up to the cenomanian turonian boundary interval then cooling thereafter regional organic carbon burial documented for this period is credited with causing drawdown of co 2 and initiating climatic deterioration inverse greenhouse effect data from other parts of the world are consistent with the hypothesis that the cenomanian turonian temperature optimum was a global phenomenon and that this interval represents a major turning point in the climatic history of the earth

a mechanism for decadal changes of enso behavior roles of background wind changes this study explains why a number of el nino properties period amplitude structure and propagation have changed in a coherent manner since the late 1970s and why these changes had almost concurred with the pacific decadal climate shift evidence is presented to show that from the pre shift 1961 1975 to the post shift 1981 1995 epoch significant changes in the tropical pacific are found in the surface winds and temperature whereas changes in the thermocline are uncertain numerical experiments with the cane and zebiak model demonstrate that the decadal changes in the surface winds qualitatively reproduce the observed coherent changes in el nino properties the fundamental factor that altered the model s el nino is the decadal changes of the background equatorial winds and associated upwelling the annual cycle is also necessary for the mean state to modulate el nino from the pre to post shift epoch the changes in the background winds and upwelling modify the structure of the coupled mode eastward displacement of the equatorial westerly anomalies by reallocating anomalous atmospheric heating and sst gradient along the equator this structural change amplifies the enso cycle and prolongs the oscillation period by enhancing the coupled instability and delaying transitions from a warm to a cold state or vice versa the changes in the mean currents and upwelling reduce the effect of the zonal temperature advection while enhance that of the vertical advection thus the prevailing westward propagation is replaced by eastward propagation or standing oscillation our results suggest a critical role of the atmospheric bridge that rapidly conveys the influences of extratropical decadal variations to the tropics and the possibility that the pacific climate shift might have affected el nino properties in the late 1970s by changing the background tropical winds and the associated equatorial upwelling

patterns of local and global redox variability during the cenomanian turonian boundary event oceanic anoxic event 2 recorded in carbonates and shales from central italy careful evaluation of the local geochemical conditions in past marine settings can provide a window to the average redox state of the global ocean during episodes of extensive organic carbon deposition these comparisons aid in identifying the interplay between climate and biotic feedbacks contributing to and resulting from these events well documented examples are known from the mesozoic era which is characterized by episodes of widespread organic carbon deposition known as oceanic anoxic events this organic carbon burial typically leads to coeval positive carbon isotope excursions geochemical data are presented here for several palaeoredox proxies cr ti v mo zn mn fe speciation i ca and sulphur isotopes from a section exposed at furlo in the marche umbrian apennines of italy that spans the cenomanian turonian boundary here oceanic anoxic event 2 is represented by a ca 1 m thick radiolarian rich millimetre laminated organic rich shale known locally as the bonarelli level iron speciation data for thin organic rich intervals observed below the bonarelli level imply a local redox shift going into the oceanic anoxic event with ferruginous conditions i e anoxic with dissolved ferrous iron transiently developed prior to the event and euxinia i e anoxic and sulphidic bottom waters throughout the event itself pre oceanic anoxic event enrichments of elements sensitive to anoxic water columns were due to initial development of locally ferruginous bottom waters as a precursor to the event however the greater global expanse of dysoxic to euxinic conditions during the oceanic anoxic event greatly reduced redox sensitive trace metal concentrations in seawater pyrite sulfur isotopes document a positive shift leading into the oae carbonate i ca ratios were generally low suggesting locally reduced bottom water oxygen conditions preceding the event and relatively increased o2 concentrations post event combined the furlo geochemical data suggest a redox stratified water column with oxic surface waters and a shallow chemocline overlying locally ferruginous bottom waters preceding the event globally widespread euxinic bottom waters during the oceanic anoxic event followed by chemocline shallowing but sustained local redox stratification following the event this article is protected by copyright all rights reserved

decadal change in the south tropical pacific in a global assimilation analysis using an ocean general circulation model that incorporates data assimilation we show that the northward flowing portion of the subtropical gyre in the south pacific undergoes a well defined decadal variation the maximum variability of ocean temperature is located at around 10 degrees s and is largest in the western side of the basin with a vertical extension of up to 1000 m the anomalous temperature shows a rapid warm to cold transition in the late 1970s with a peak to peak value of more than 1 degrees c coupled with this change is a strengthened circulation in the northern portion of the subtropical gyre further analysis indicates that the decadal change in the south tropical pacific is linked to increased ekman suction induced by enhanced cyclonic wind stress curl in the region

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

upper cretaceous carbon and oxygen isotope stratigraphy of hemipelagic carbonate facies from southern tibet china a high resolution carbon isotope curve derived from upper cretaceous hemipelagic sediments cropping out at tingri southern tibet shows similarities to patterns established on other continents notably in the presence of a well defined positive excursion across the cenomanian turonian boundary where 13 c values exceed 3 5 from the upper turonian to the lower campanian 13 c values generally decline apart from a minor positive excursion in the middle coniacian a trend that departs from that recorded from europe relatively low 13 c values c 1 at the santonian campanian and campanian maastrichtian boundaries in tibet define a prominent broad positive excursion centred in the middle campanian and terminated by an abrupt fall towards the close of the stage when compared with data from europe and north africa the 13 c values of the tibetan section are generally lower by c 1 5 except for the middle campanian positive excursion where values 13 c c 2 are comparable with those documented from europe and north africa these differences are interpreted as reflecting variable mixing of water masses carrying different carbon isotope signatures such that areas close to the major sinks of marine organic carbon recorded higher 13 c values than those located in more distal regions oxygen isotope ratios albeit affected by diagenesis may record a palaeotemperature signal

improved extended reconstruction of sst 1854 1997 abstract an improved sst reconstruction for the 1854 1997 period is developed compared to the version 1 analysis in the western tropical pacific the tropical atlantic and indian oceans more variance is resolved in the new analysis this improved analysis also uses sea ice concentrations to improve the high latitude sst analysis and a modified historical bias correction for the 1939 41 period in addition the new analysis includes an improved error estimate analysis uncertainty is largest in the nineteenth century and during the two world wars due to sparse sampling the near global average sst in the new analysis is consistent with the version 1 reconstruction the 95 confidence uncertainty for the near global average is 0 4 c or more in the nineteenth century near 0 2 c for the first half of the twentieth century and 0 1 c or less after 1950

foraminiferal response to mid cenomanian upper cretaceous palaeoceanographic events in the anglo paris basin northwest europe we have analysed the sedimentology macrofossil event horizons including pulse faunas and foraminiferal succession 80 samples from an 8 m succession in the upper lower and lower middle cenomanian upper cretaceous at folkestone southeast england comparative sedimentological analysis of successions in southern and northeastern england indicates the presence of three hierarchies of cycle 20 kyr productivity chalk marl couplets cycles attributed to the milankovitch precession cycle 100 kyr sea level cycles attributed to the milankovitch eccentricity cycle and l myr cycles attributed to longer term sea level cycles previously recognised macrofossil pulse faunas occur preferentially at the bases of the 100 kyr eccentricity cycles we analysed the foraminiferal fauna across the lower middle cenomanian boundary at abbott s cliff folkestone in great detail 80 samples in 8 m the foraminiferal succession is also intricately related to the 1 myr sea level and 100 kyr eccentricity cycles changes related to the long term cycles include variations in the abundance of the benthic foraminifera tritaxia gyroidinoides lingulogavelinella and dorothia and an increase in benthic diversity in the transgressive deposits changes related to the 100 kyr eccentricity cycles include the presence of rotalipora ex gr reicheli in the lower part and rarely upper part of cycles the abundance of planktics both absolute and relative in the middle to upper part of cycles an increase in the proportion of gavelinella berthelini and g reussi in the upper part of cycles we present a stratified water column model to explain the changes related to the 100 kyr scale cycle 1998 elsevier science b v

midlatitude shelf seas in the cenomanian turonian greenhouse world temperature evolution and north atlantic circulation 1 an 8 million year record of subtropical and midlatitude shelf sea temperatures derived from oxygen isotopes of well preserved brachiopods from a variety of european sections demonstrates a long term cenomanian temperature rise 16 20 c midlatitudes that reached its maximum early in the late turonian 23 c midlatitudes superimposed on the long term trend shelf sea temperatures vary at shorter timescales in relation to global carbon cycle perturbations in the mid cenomanian and the late turonian two minor shelf sea cooling events 2 3 c coincide with carbon cycle perturbations and times of high amplitude sea level falls although this evidence supports the hypothesis of potential glacioeustatic effects on cretaceous sea level the occurrence of minimum shelf sea temperatures within transgressive beds argues for regional changes in shelf sea circulation as the most plausible mechanism the major carbon cycle event in the latest cenomanian oceanic anoxic event 2 is accompanied by a substantial increase in shelf sea temperatures 4 5 c that occurred 150 kyr after the commencement of the 13c excursion and is related to the spread of oceanic conditions in western european shelf sea basins our oxygen isotope record and published 18o data of pristinely preserved foraminifera allow the consideration of north atlantic surface water properties in the cenomanian along a transect from the tropics to the midlatitudes on the basis of fossil derived 18o estimated w ranges and modeled salinities temperature salinity density ranges were estimated for tropical subtropical and midlatitude surface waters accordingly the cenomanian temperate shelf seas waters have potentially the highest surface water density and could have contributed to north atlantic intermediate to deep waters in the preopening stage of the equatorial atlantic gateway

record of albian to early cenomanian environmental perturbation in the eastern sub equatorial pacific the present paper documents and discusses a new albian early cenomanian carbon isotope 13ccarb and 13corg curve from the subequatorial eastern pacific in peru chemostratigraphic evidences for the expression of the oae1b set and for oae1c and oae1d are presented this dataset is relevant inasmuch as previous work is strongly biased towards study sites in north america western interior basin in europe tethys and the pacific realm a comparison of the carbon isotope stratigraphy obtained in peru with published sections from the central and western pacific the western atlantic and northern and western tethys reveals an overall good agreement supporting the global nature of the isotope patterns described here the 13c from peru record is constrained by biostratigraphic evidence and 87sr 86sr isotope stratigraphy using well preserved oyster shells furthermore we document the development of a heterozoan epeiric neritic mixed carbonate siliciclastic ramp in the western platform of peru and its corresponding sedimentary facies associations this dataset was used to elucidate the complex interplay of climatic changes nutrient supply and platform drowning leading to the following conclusions i an upper aptian lower albian major change from siliciclastic dominated to carbonate sedimentation coincided with the impact of the kilian level ii a lower albian incipient platform drowning linked to the impact of the paquier level iii a lower middle albian major demise of neritic carbonate production that coincides with the leenhardt level followed by middle albian condensed sedimentation that reports prominent negative values in 13ccarb prior to the onset of oae1c and iv finally renewed carbonate ramp production during the upper albian lower cenomanian the data shown here represent the foundation for future work documenting the mid cretaceous of peru and its implications for the palaeoceanography of the se subequatorial pacific

carbon isotope stratigraphy recorded by the cenomanian turonian oceanic anoxic event correlation and implications based on three key localities we present new detailed carbon isotope records for bulk carbonate total organic carbon toc and phytane from three key sections spanning the cenomanian turonian boundary interval eastbourne england gubbio italy tarfaya morocco with the purpose of establishing a common chemostratigraphic framework for oceanic anoxic event oae 2 isotope curves from all localities are characterized by a positive carbon isotope excursion of c 4 for toc and phytane and c 2 5 for carbonate although diagenetic overprinting appears to have obliterated the primary carbonate carbon isotope signal in at least part of the tarfaya section stratigraphically peak 13 c values for all components are followed by intervals of high near constant 13 c in the form of an isotopic plateau recognition of an unambiguous return to background 13 c values above the plateau is however contentious in all sections hence no firm chemostratigraphic marker for the end point of the positive isotopic excursion can be established the stratigraphically consistent first appearance of the calcareous nannofossil quadrum gartneri at or near the cenomanian turonian boundary as established by ammonite stratigraphy in conjunction with the end of the 13 c maximum characteristic of the isotopic plateau provides a potentially powerful tool for delimiting the stratigraphic extent and duration of oae 2 this oceanic anoxic event is demonstrated to be largely if not wholly confined to the latest part of the cenomanian stage

orbitally modulated black shale deposition in the upper albian amadeus segment central italy a multi proxy reconstruction abstract the upper albian amadeus segment which falls within oceanic anoxic event 1c exhibits cyclical alternations of marls black shales and carbonate rich beds that record evidence of orbital climate and sedimentary dynamics a combined micropalaeontological planktic and benthic foraminifera and palynomorphs and geochemical stable isotopes clay mineralogy and major element distribution investigation allowed recognition of a remarkable influence of continental material within the black shales moreover the palaeoproductivity record is characterised by a non linear response to the orbital forcing the micropalaeontological and geochemical record suggests that upper albian bedded cycles in the marne a fucoidi formation resulted from interplay of changes in atmospheric and hydrological parameters of the western tethys and its drainage basin in particular deposition of the black shales occurred during precession minima in times of increased precipitation enhanced continental runoff and stratification of the upper water column in this respect the black shales of the amadeus segment share similarities with the neogene eastern mediterranean sapropels

reconstruction of short term palaeoceanographic changes during the formation of the late albian niveau breistroffer black shales oceanic anoxic event 1d se france the niveau breistroffer black shale succession in the vocontian basin se france is the regional equivalent of the widely distributed late albian oceanic anoxic event 1d the studied black shale rich interval at the col de palluel section is 6 28 m thick and comprises four black shale units with up to 2 5 wt total organic carbon toc intercalated with marlstones calcareous nannofossil palynomorph planktic foraminifera and stable isotopic data from the niveau breistroffer succession suggest that short term climate changes influenced its deposition with relatively warm and humid climate during black shale formation in comparison with relatively cool and dry climatic conditions during marlstone deposition an increase in the terrigenous marine ratio of palynomorphs indicates enhanced humidity and higher runoff during black shale formation a nutrient index based on calcareous nannofossils and the abundance pattern of small 63 125 m hedbergellid foraminifera show short term changes in the productivity of the surface water surface water productivity was reduced during black shale formation and increased during marlstone deposition a calcareous nannofossil temperature index and bulk rock oxygen isotope data indicate relative temperature changes with warmer surface waters for black shale samples at these times warm humid climate and reduced surface water productivity were accompanied by greater abundances of subsurface dwelling calcareous nannofossils nannoconids and planktic foraminifera rotaliporids these taxa presumably indicate more stratified surface water conditions we suggest that the formation of the niveau breistroffer black shales occurred during orbitally induced increase in monsoonal activity that led to increasing humidity during periods of black shale formation this in turn caused a decrease in low latitude deep water formation and probably an increase in surface water stratification the combination of these two mechanisms caused depleted o 2 concentrations in the bottom water that increased the preservation potential of organic matter

principal modes of rainfall sst variability of the asian summer monsoon a reassessment of the monsoon enso relationship abstract using global rainfall and sea surface temperature sst data for the past two decades 1979 98 the covariability of the asian summer monsoon asm and el nino southern oscillation enso was investigated the findings suggest three recurring rainfall sst coupled modes characterized by a pronounced biennial variability the first mode is associated with generally depressed rainfall over the western pacific and the maritime continent stemming from the eastward shift of the walker circulation during the growth phase of el nino the associated sst pattern consists of an east west sst seesaw across the pacific and another seesaw with opposite polarity over the indian ocean the second mode is associated with a growing la nina comprising mixed regional and basin scale rainfall and sst variability with abnormally warm water in the vicinity of the maritime continent and western pacific it possesses a pronounced low level west pacific anticyclone wpa near the philippines and exhibits large sub

chemostratigraphy versus biostratigraphy data from around the cenomanian turonian boundary a detailed isotopic profile is presented for a stratigraphically expanded cenomanian turonian boundary section in chalk facies exposed at eastbourne sussex and compared with data from pueblo colorado in both sections macro and micropalaeontological markers first appearances and disappearances are well constrained and their relative positions and relationship to the structure of the carbon isotope curve are identical this consistent relationship between two independent phenomena one geochemical the other biostratigraphical is taken as evidence for the likely synchroneity of both the biostratigraphical markers and the carbon isotope excursion in these two areas this interpretation contrasts with suggestions made recently by other authors whose data have been taken to imply a lack of correlation between the carbon isotope excursion in europe and north america

interdecadal changes in the major modes of asian australian monsoon variability strengthening relationship with enso since the late 1970s abstract the present paper develops an integral view of the year to year variability across the entire asian australian monsoon a am system which covers one third of the global tropics between 40 and 160 e using season reliant empirical orthogonal function s eof analysis the authors identified two major modes of variability for the period 1956 2004 the first exhibits a prominent biennial tendency and concurs with the turnabout of el nino southern oscillation enso providing a new perspective of the seasonally evolving spatiotemporal structure for tropospheric biennial oscillation the second mode leads enso by one year the remote el nino forcing the monsoon warm pool ocean interaction and the influence of the annual cycle are three fundamental factors for understanding the behavior of the first mode the monsoon ocean interaction is characterized by a positive feedback between the off equatorial convectively coupled rossby waves and the underlying sea surface temperature sst dipole anoma

sea surface temperature variability in the subpolar atlantic over the last two millennia 1 a decadal resolution time series of sea surface temperature sst spanning the last two millennia is reconstructed by combining a proxy record from a new sediment sequence with previously published data from core md99 2275 north of iceland the alkenone based sst reconstruction is validated with historic observational data and compared to a new similar temporal resolution reconstruction obtained from sediment core rapid21 3k in the subpolar north atlantic the two sst paleorecords show consistent multidecadal scale coolings throughout the interval and similar expressions during the contrasted climatic periods colloquially known as the medieval climatic anomaly mca and little ice age lia in order to further understand the temporal and spatial sst variations and investigate the influence of natural forcings on the observed sst changes during the last millennium we compare our time series to simulations using the institut pierre simon laplace ipslcm4 v2 climate model this comparison highlights the potential importance of volcanism as a natural forcing driving coherent abrupt cooling events captured in the subpolar north atlantic records

secular variation in late cretaceous carbon isotopes a new δ13c carbonate reference curve for the cenomanian campanian 99 6 70 6 ma carbon stable isotope variation through the cenomanian santonian stages is characterized using data for 1769 bulk pelagic carbonate samples collected from seven chalk successions in england the sections show consistent stratigraphic trends and 13c values that provide a basis for highresolution correlation positive and negative 13cexcursions and inflection points on the isotope profiles are used to define 72 isotope events key markers are provided by positive 13c excursions of up to 2 the albian cenomanianboundary event mid cenomanian event i thecenomanian turonian boundary event the bridgewick hitch wood and navigation events of late turonian age and the santonian campanian boundary event isotope events are isochronous within a framework provided by macrofossil datum levels and bentonite horizons an age calibrated composite 13c reference curve and an isotope event stratigraphy are constructed using data from the english chalk the isotope stratigraphy is applied to successions in germany france spain and italy correlation with pelagic sections at gubbio central italy demonstrates general agreement between biostratigraphic and chemostratigraphic criteria in the cenomanian turonian stages confirming established relationships between tethyan planktonic foraminiferal and boreal macrofossil biozonations correlation of the coniacian santonian stages is less clear cut magnetostratigraphic evidence for placing the base of chron 33r near the base of the upper santonian is in good agreement with the carbon isotope correlation but generates significant anomalies regarding the placement of the santonian and campanian stage boundaries with respect to tethyan planktonic foraminiferal and nannofossil zones isotope stratigraphy offers a more reliable criterion for detailed correlation of cenomanian santonian strata than biostratigraphy with the addition of campanian 13c data from one of the english sections a composite cenomanian campanian age calibrated reference curve is presented that can be utilized in future chemostratigraphic studies the cenomanian campanian carbon isotope curve is remarkably similar in shape to supposedly eustatic sea level curves increasing 13c values accompanying sea level rise associated with transgression and falling 13c values characterizing sea level fall and regression the correlation between carbon isotopes and sea level is explained by variations in epicontinental sea area affecting organic matter burial fluxes increasing shallow sea floor area and increased accommodation space accompanying sea level rise allowedmore efficient burial ofmarine organic matter with the preferential removal of 12c from the marine carbon reservoir during sea level fall reduced seafloor area marine erosion of previously deposited sediments and exposure of basin margins led to reduced organiccarbon burial fluxes and oxidation of previously deposited organic matter causing falling 13c values additionally drowning of carbonate platforms during periods of rapid sea level rise may have reduced the global inorganic relative to the organic carbon flux further enhancing 13c values while renewed platform growth during late transgressions and highstands prompted increased carbonate deposition variations in nutrient supply changing rates of oceanic turnover and the sequestration or liberation of methane from gas hydrates may also have played a role in controlling carbon isotope ratios

the middle cenomanian event in the equatorial atlantic the calcareous nannofossil and benthic foraminiferal response abstract in addition to oceanic anoxic event 2 oae2 other perturbations of the carbon cycle occurred during the cenomanian and turonian of which the middle cenomanian event mce is the most prominent one in palaeoecological publications however this event is strongly underrepresented in contrast to the well studied oae2 in order to fill this gap we have studied early cenomanian to late turonian calcareous nannofossil and benthic foraminiferal assemblages of ocean drilling program site 1260 at demerara rise western equatorial north atlantic in order to decipher biotic changes throughout this interval and especially across the mce our data show distinctive changes in the relative abundance of certain calcareous nannofossil taxa and a drastic decrease in benthic foraminiferal diversities and abundances associated with the mce in the lower part of the studied section and prior to the mce a mixed water column with high nutrient availability in the upper photic zone is suggested based on very high relative abundances of the mesotrophic eutrophic nannofossil species biscutum constans around the mce interval certain nannofossil taxa e g rhagodiscus asper show a distinctive decrease in relative abundance while others become more dominant taxa which increase in relative abundance after the mce e g eprolithus floralis are interpreted as either having favoured less eutrophic surface waters or having inhabited deeper parts of the photic zone in a well stratified water column this interpretation is supported by published oxygen isotope and tex86 data which suggest increased water column stratification starting with the mce and lasting to the end of the cenomanian stage as a result of the implementation of a saline intermediate to deep water mass during this interval our study shows that the mce was a significant biotic event in the cenomanian turonian equatorial atlantic characterised by a lasting change of surface and bottom water ecosystems

blake nose stable isotopic evidence against the mid cenomanian glaciation hypothesis detailed multitaxon stable isotope 18 o and 13 c data from blake nose western north atlantic argue against a mid cenomanian glaciation event during the mid cretaceous greenhouse results generated are precisely correlated to sea level changes inferred from european sequence stratigraphy using the twin 13 c excursions mid cenomanian event mce ia and mce ib microfossils analyzed surface dwelling to deep dwelling planktonic foraminifera benthic foraminifera coccoliths show remarkably consistent intertaxon 18 o and 13 c offsets comparative scanning electron microscope and sr ca analyses allow some 18 o data to be eliminated because of selective diagenesis across mce ia the proposed interval of major glacioeustatic regression the planktonic 18 o values are constant for each taxon the absence of a mean seawater 18 o shift contradicts predictions for the mid cenomanian glaciation episode the benthic 18 o records show significant fluctuations during mce i implying short term variability in north atlantic intermediate water and deep water circulation patterns and or sources at that time

major and trace element characterization of oceanic anoxic event 1d oae 1d insight from the umbria marche basin central italy abstract the pialli level in the umbria marche basin central italy correlates with the lowermost part of the positive carbon isotopic excursion characterizing the late albian early cenomanian oceanic anoxic event 1d oae 1d high resolution litho bio and chemostratigraphic data from the monte petrano and le brecce sections allow for a bed by bed comparison of the two successions and discriminate local from basin scale signals we present new x ray fluorescence icp ms and toc data for both the limestones and the pialli level shales integrated with available carbonate carbon isotopes and nannofossil temperature and nutrient indices data indicate a homogenous background sedimentation dominated by pelagic carbonates biogenic silica with little contribution by clays the limited variation in lithogenic elements points to an essentially homogeneous detrital source area with limited fluvial terrigenous input higher mn concentrations coupled with low enrichments in redox sensitive elements such as u fe s re mo ag suggest that the pialli level shales represent temporary suboxia without reaching anoxia furthermore p authigenic ba cd and ni enrichments together with nannofossil nutrient index indicate generally low primary productivity conditions along the entire succession with only minor increases for some of the black to dark grey shales of the pialli level the nannofossil temperature index highlights a warm climate during the oae 1d with the warmest conditions experienced during the deposition of the pialli level shales during the late albian the warm and humid climate was interrupted by brief episodes of relatively warmer and less saline surface waters ensuring slower rates of bottom water renewal and producing temporary suboxic conditions such paleoceanographic dynamics would be the continuation of episodic warmer and humid pulses characterizing the late albian interval in the umbria marche basin as such the pialli level can be considered the result of a last episode closing a cycle before the establishment of a steadier climate during the early cenomanian

origin of rhythmic albian black shales piobbico core central italy calcareous nannofossil quantitative and statistical analyses and paleoceanographic reconstructions 1 the mid cretaceous 120 90 ma was a time of excess atmospheric co2 greenhouse climate and widespread o2 deficiency in the ocean the albian is punctuated by brief intermittent episodes of anoxia dysoxia recorded as cyclic black shales in the western tethys and atlantic oceans the albian section of the piobbico core central italy contains 30 m 10 ma of rhythmic black shales that were sampled at a high resolution and examined for calcareous nannofossil assemblages and c and o stable isotopes unlike oceanic anoxic events productivity was not the primary factor controlling the deposition of albian rhythmic black shales it is suggested that during warm humid climatic cycles higher temperatures and or increased precipitation and runoff produced density stratification at a regional scale recurrent lowered salinity in the early albian and warming in the late albian are credited with causing development of a pycnocline resulting in slower rates of deep water renewal and consequent anoxia

different evolutions of the philippine sea anticyclone between the eastern and central pacific el nino possible effects of indian ocean sst abstractthe authors examine different evolution features of the low level anticyclone over the tropical northwestern pacific between eastern pacific ep el nino events and central pacific cp el nino events during ep el nino the low level anticyclone shows an eastward movement from the northern indian ocean to the east of the philippines during cp el nino however the anticyclone is mostly confined to the west of the philippines it is weaker exhibits a shorter lifetime and lacks eastward movement compared to the philippine sea anticyclone psac during ep el nino investigation into the possible impact of indian ocean io sea surface temperature sst on the evolution of the low level anticyclone during ep and cp el nino indicates that both sst and low level atmospheric circulation over the io are related more strongly with ep el nino than with cp el nino the io sst tends to exert a more prominent influence on psac during ep el nino than during cp el nino during the developing summer and autum