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

cenomanian turonian carbon isotope events recorded in terrestrial organic matter from northern japan carbon isotopic fluctuations recorded in terrestrial organic matter from the upper cretaceous cenomanian turonian succession of hokkaido japan show a remarkably similar pattern to isotopic fluctuation in carbonate carbon reported from southern england and the italian apennines chronological correlation for the cenomanian turonian section of japan is based on planktonic foraminiferal biostratigraphy with some additional data from macrofossils allowing a detailed comparison of isotope stratigraphies for japan and europe three distinct features of the isotope profile namely a positive spike near the cenomanian turonian boundary a shoulder in the lower middle turonian and a level segment in the middle upper turonian are observed in japan these features are biostratigraphically comparable and correlative with isotope profiles reported from europe the single factor influencing isotopic composition of both terrestrial organic carbon and marine carbonate carbon is isotopic change in the global co2 reservoir of the ocean atmosphere system if these three carbon isotope features are synchronous they may be inferred as having been caused by global phenomena and as providing global high resolution chemo stratigraphic markers carbon isotope stratigraphy could be an important bridge between terrestrial inland sequences and marine sequences

heat flux through sea ice in the western weddell sea convective and conductive transfer processes the heat flux through the snow and sea ice cover and at the ice ocean interface were calculated at five sites in the western weddell sea during autumn and early winter 1992 the ocean heat flux averaged 7 2 w m2 from late february to early june and average ice air heat flux in the second year floes depended on the depth of the snow cover and ranged from 9 to 17 0 8 w m2 in late february three of the five sites had an ice surface which was depressed below sea level resulting at two of the sites in a partially flooded snow cover and a slush layer at the snow ice interface as this slush layer froze to form snow ice the dense brine which was rejected flowed out through brine drainage channels and was replaced by lower salinity nutrient rich seawater from the ocean upper layer we estimate that about half of the second year ice in the region was covered with this slush layer early in the winter as the slush layer froze over a 2 to 3 week period the convection within the ice transported salt from the ice to the upper ocean and increased total heat flux through the overlying ice and snow cover on an area wide basis approximately 10 cm of snow ice growth occurred within second year pack ice primarily during a 2 to 3 week period in february and march this ice growth near the surface of the ice provides a salt flux to the upper ocean equivalent to 5 cm of ice growth despite the thick about 1 m ice cover in addition to the ice growth in the small area less than 5 open water regions

temporal evolution of decaying summer first year sea ice in the western weddell sea antarctica abstract the evolution of the main physico chemical properties of the unflooded 90 cm thick first year sea ice cover at the ice station polarstern ispol clean site is described ispol was an international experiment of the german research icebreaker r v polarstern the vessel was anchored to an ice floe for an observation period of 5 weeks during the early summer melt onset in the western weddell sea the clean site was specially designed and accessed so as to prevent any trace metal contamination of the sampling area observations were made at 5 day intervals during december 2004 in the central part of the main floe results show the succession of two contrasting phases in the behavior of the brine network brine channels pockets and tubes initially brine salinity was higher than that of sea water leading to brine migration and a decrease in the mean bulk salinity of the ice cover this process is highly favored by the already high bulk porosity 14 which ensures full connectivity of the brine network gravity drainage rather than convection seems to be the dominant brine transfer process half way through the observation period the brine salinity became lower than that of the sea water throughout the ice column the brine network therefore switched to a stratified regime in which exchange with sea water was limited to molecular diffusion strongly stabilizing the bulk mean sea ice salinity during the transition between the two regimes and in areas closer to ridges slush water resulting from a mixture of snow meltwater and sea water accumulated at the snow ice interface penetrated through the growing honeycomb like structure and replaced the downward draining brines this resulted in a slight local replenishment of nutrients as indicated by dissolved silicic acid however as a whole the described decaying regime in this globally unflooded location with limited snow cover should be unfavorable to the development of healthy and active surface and internal microbial communities the switch from gravity to diffusion controlled transport mechanisms within the ice column also should affect the efficiency of gas exchange across the sea ice cover the observed late build up of a continuous impermeable superimposed ice layer should further significantly hamper gas exchange statistical estimates of the evolution of the ice thickness during the observation period and salinity trends of the under ice water salinity down to 30 m corroborate model predictions of a moderate bottom melting 5 10 cm from ocean heat fluxes

the sea ice thickness distribution in the northwestern weddell sea we present new data on distribution of snow and sea ice thicknesses in the northwestern weddell sea the data were obtained through direct measurements along 19 profiles each approximately 100 m long on 17 different floes located between 54 46 w and 59 64 s the overall probability density functions pdfs for ice thicknesses reflect the complex mixture of first second and multi year ice to be expected in the outflowing branch of the weddell gyre further differentiation of the data reveals four distinct thickness classes which reflect differences in the formation and subsequent histories of the ice encountered these classes i iv represent strongly deformed first year ice less deformed first and second year ice and deformed second or multi year ice respectively each of the classes is characterized by a specific set of quantities related to ice texture and surface snow characteristics and by distinct pdfs for snow and ice thicknesses in addition geometric surface and bottom roughness characteristics differ significantly for each of the floe classes

sea ice and snow thickness and physical properties of an ice floe in the western weddell sea and their changes during spring warming helicopter borne and ground based electromagnetic em ice thickness and ruler stick snow thickness measurements as well as ice core analyses of ice temperature salinity and texture were performed over a 5 week observation period between november 27 2004 and january 2 2005 on an ice floe in the western weddell sea at approximately 67 s 55 w the study was part of the ice station polarstern ispol expedition of german research icebreaker r v polarstern investigating changes of physical biological and biogeochemical properties during the spring warming as a function of atmospheric and oceanic boundary conditions the ice floe was composed of fragments of thin and thick first year ice and thick second year ice with modal total thicknesses of 1 2 1 3 2 1 and 2 4 2 9 m respectively this included modal snow thicknesses of 0 2 0 5 m on first year ice and 0 75 m on second year ice during the observation period snow thickness decreased by less than 0 2 m there was hardly any ice thinning warming of snow and ice between 0 1 and 1 9 c resulted in decreased ice salinity and increased brine volume direct current dc geoelectric and electromagnetic em induction depth sounding were performed to study changes of electrical ice conductivity as a result of the observed ice warming bulk ice conductivity increased from to 37 to 97 ms m analysis of conductivity anisotropy showed that the horizontal ice conductivity changed from 9 to 70 ms m these conductivity changes have only negligible effects on the thickness retrieval from em measurements

thickness distribution of antarctic sea ice 1 ship based observations are used to describe regional and seasonal changes in the thickness distribution and characteristics of sea ice and snow cover thickness around antarctica the data set comprises 23 373 observations collected over more than 2 decades of activity and has been compiled as part of the scientific committee on antarctic research scar antarctic sea ice processes and climate aspect program the results show the seasonal progression of the ice thickness distribution for six regions around the continent together with statistics on the mean thickness surface ridging snow cover and local variability for each region and season a simple ridge model is used to calculate the total ice thickness from the observations of level ice and surface topography to provide a best estimate of the total ice mass including the ridged component the long term mean and standard deviation of total sea ice thickness including ridges is reported as 0 87 0 91 m which is 40 greater than the mean level ice thickness of 0 62 m analysis of the structure function along north south and east west transects revealed lag distances over which sea ice thickness decorrelates to be of the order of 100 300 km which we use as a basis for presenting near continuous maps of sea ice and snow cover thickness plotted on a 2 5 5 0 grid

in situ measurements of the evolution of young sea ice 1 we present data from in situ measurements of the salinity evolution of young sea ice in the arctic the measurements were carried out with very high vertical and temporal resolution over the course of a few days until the ice had reached a thickness of around 20 cm the measured bulk salinity profiles show that during ice growth sea ice salinity is continuous across the ice ocean interface and that there is no instantaneous loss of salt at the advancing front measured salt fluxes emanating from the ice are as high as 90 g m 2 h 1 during the first few hours of new ice formation and are roughly half as large during later stages of the experiments the bulk salinity within the ice decreases continuously with time from the ocean water salinity to a near steady state value of around 4 parts per thousand ppt these results are interpreted with ideas from mushy layer theory using a rayleigh number to analyze gravity drainage as the driving mechanism for the observed salt loss in our experiments gravity drainage occurs for a critical rayleigh number of around 10 in close agreement with earlier theoretical and experimental studies

the percolation phase transition in sea ice sea ice exhibits a marked transition in its fluid transport properties at a critical brine volume fraction p c of about 5 percent or temperature t c of about 5 c for salinity of 5 parts per thousand for temperatures warmer than t c brine carrying heat and nutrients can move through the ice whereas for colder temperatures the ice is impermeable this transition plays a key role in the geophysics biology and remote sensing of sea ice percolation theory can be used to understand this critical behavior of transport in sea ice the similarity of sea ice microstructure to compressed powders is used to theoretically predict p c of about 5 percent

measurements of salinity and volume of brine excluded from growing sea ice the volume of brine excluded from growing sea ice and its salinity were measured using a brine sampler the measurements were made in both laboratory and field under various growth conditions of the sea ice the salinity of the brine becomes higher and the volume flux decreases as the sea ice growth rate decreases consequently the salt flux of the brine decreases with decreasing growth rate in the case of sea ice growth at a constant rate as the sea ice becomes thicker the salinity of the brine excluded increases while its volume flux decreases however the salt flux is nearly independent of the ice thickness increase at least up to a thickness of 15 cm for sea ice growth rates between 1 7 10 5 and 1 4 10 4 cm s 1 and for a seawater salinity of 33 0 the brine salinity ranged from 42 3 to 92 7 the volume flux ranged from 6 3 10 6 to 3 4 10 5 cc cm 2 s 1 and the salt flux ranged from 6 4 0 7 to 1 5 10 6 g cm 2 s 1

spectral transmission and implications for the partitioning of shortwave radiation in arctic sea ice we present a new set of values for the spectral extinction coefficients k for the interior of first year fy and multi year my arctic sea ice during the summer melt season measured during sheba surface heat budget of the arctic ocean program and at barrow alaska usa results for fy ice are consistent with previously reported values and differences can be understood in terms of variations in the concentration of biological and suspended particulate material the values for the interior of my ice are lower than previously reported for both bare and ponded ice for bare my ice the new kvalues predict a substantial increase in the solar radiation transmitted through the ice into the upper mixed layer ponded my ice is only slightly more transparent than previously reported and fy ice values are generally consistent with previously reported values assuming an asymmetry parameter of 0 94 the extinction coefficients are consistent with a volume scattering coefficient of 77 m 1 that is constant from 400 to at least 720 nm

orbital time scale intra platform basin correlation carbon isotope stratigraphy and sea level history of the cenomanian turonian eastern levant platform jordan two cenomanian turonian boundary ctbe sections kb3 and gm3 of the karak silla intra platform basin of the eastern levant carbonate platform jordan are correlated based on high resolution calcimetry kb3 contains black shales with over 7 wt total organic carbon toc gm3 was deposited at shallower water depth and reveals four conspicuous gypsum beds used for sea level reconstruction spectral analysis of carbonate content and toc reveals forcing mainly by the 100 ka cycle of earth s orbit eccentricity whole rock stable carbon isotope data show a conspicuous positive d13c excursion representing the oceanic anoxic event 2 oae2 the carbon isotope records of kb3 and gm3 correspond well with the cycles in the dc record of the global stratotype gssp at pueblo usa the gssp orbital timescale thus can be applied to the jordan record furthermore all stable isotope events defined in the english chalk reference record are recognized in jordan our orbital model for the jordan sequence stratigraphical framework reveals approximately 1 2 0 2 ma duration of a third order sequence proposed to represent one cycle of the long obliquity 1 2 ma this longterm period is superimposed on three fourth order fluctuations of 400 ka length long eccentricity fourth order sea level fluctuations each of which comprises four carbonate cycles 100 ka eccentricity fifth order sea level fluctuations demise of the levant platform occurred during the phase of decreasing dc values after oae2 in the interval between the cenomanian turonian c t boundary and the end of the early turonian the levant carbonate platform deposits of central jordan represent a textbook like shallow marine platform setting subdivided into intra platform basins during cenomanian turonian c t times kuss et al 2003 the morphological structuring by these basins induced lithologically highly variable successions especially during black shale deposition that preferably occurred in deeper subbasins a correlation of these different successions is possible by means of high resolution calcimetry and stable carbon isotope stratigraphy in this paper we present such a correlation that enables the study of three research aspects a linking different palaeoenvironments over the c t boundary interval b refining the sequence stratigraphic model by constructing an orbital time scale c correlating the successions to the global record exemplified for the well dated c t boundary interval in order to eliminate ambiguities in the local stratigraphy furthermore our data support the global picture and estimates of duration of the c t boundary interval that includes the global oceanic anoxic event 2 oae2 the duration of oae2 has been the matter of many studies in recent years resulting in a range of values from 320 to 960 ka obradovitch 1993 sageman et al 2006 partly caused by considering different intervals an orbital timescale for the pueblo stratotype section was given by sageman et al 2006 providing a precise time measure for the period investigated in our study in addition a comprehensive study of stable carbon isotope records in europe was given by jarvis et al 2006 providing a detailed set of isotope events suitable for global correlation recently an orbital model was also presented for the wunstorf germany section voigt et al 2008 this record correlates well with the present results and can be used to support the new hypothesis put forward in the present paper regarding the orbital trigger of third order sequences

a one dimensional percolation model of flooding and snow ice formation on antarctic sea ice a one dimensional thermodynamic sea ice growth model is developed with emphasis on seawater flooding and snow ice formation on antarctic sea ice to examine the possibility that flooding is the result of brine percolation through a porous ice matrix and the consequences of this percolation on the salinity structure and mass balance of the ice flooding is modeled in a semiheuristic fashion by examining two possible regimes for seawater and brine infiltration through the porous ice into the snowpack a standard model assumes that the upward flow of brine is horizontally homogeneous and brine flow is modeled using a darcian scheme a simple model assumes that the infiltrating brine does not interact with the internal ice brine network but instead percolates upward through cracks or is restricted in spatial extent results of simulations are shown for the climatology in the ross sea and compared to field data from one autumn and one winter cruise aboard the r v nathaniel b palmer in 1995 sensitivity studies are performed to show the effects of variations in climate forcing the dependence of brine percolation and snow ice formation on key thermophysical parameters is investigated results indicate that the mass balance depends very strongly on the brine flow regime in the standard model ice salinities and brine volumes are greatly affected by brine percolation creating a strong feedback between flooding and future snow ice production snow ice formation for the simple model was much more predictable and depended primarily on snow load comparison of results with field data indicate that if brine percolation is the major mechanism for flooding and snow ice formation then there must be either substantial convective redistribution of salt to maintain ice porosity or the flow must be spatially inhomogeneous

influence of the sea ice thickness distribution on polar climate in ccsm3 abstract the sea ice simulation of the community climate system model version 3 ccsm3 t42 gx1 and t85 gx1 control simulations is presented and the influence of the parameterized sea ice thickness distribution itd on polar climate conditions is examined this includes an analysis of the change in mean climate conditions and simulated sea ice feedbacks when an itd is included it is found that including a representation of the subgrid scale itd results in larger ice growth rates and thicker sea ice these larger growth rates represent a higher heat loss from the ocean ice column to the atmosphere resulting in warmer surface conditions ocean circulation most notably in the southern hemisphere is also modified by the itd because of the influence of enhanced high latitude ice formation on the ocean buoyancy flux and resulting deep water formation changes in atmospheric circulation also result again most notably in the southern hemisphere there are indications that the itd also modifies simulated sea

upper cretaceous sequence stratigraphy of the galala plateaux western side of the gulf of suez egypt abstract based on the study of lithology biostratigraphy and analysis of facies this study deduces the occurrence of nine third order upper cretaceous cenomanian maastrichtian depositional sequences which are bounded by eleven sequence boundaries of geographic extent in the galala plateaux situated along the western side of the gulf of suez egypt some of the recorded sequence boundaries e g cenomanian turonian turonian coniacian intra santonian and campanian maastrichtian sequence boundaries are not yet confirmed to eustatic sea level changes fourteen main mixed carbonate siliciclastic facies associations were recognized on a lateral transition between inner to outer ramp settings with apparent subsidence towards the south the tectonic position of the galala plateaux played an important role in the profound complexity of facies changes and the configuration of depositional sequences representing variable time gaps

seasonal variations in the properties and structural composition of sea ice and snow cover in the bellingshausen and amundsen seas antarctica sixty three ice cores were collected in the bellingshausen and amundsen seas in august and september 1993 during a cruise of the r v nathaniel b palmer the structure and stable isotopic composition 18 o 16 o of the cores were investigated in order to understand the growth conditions and to identify the key growth processes particularly the contribution of snow to sea ice formation the structure and isotopic composition of a set of 12 cores that was collected for the same purpose in the bellingshausen sea in march 1992 are reassessed frazil ice and congelation ice contribute 44 and 26 respectively to the composition of both the winter and summer ice core sets evidence that the relatively calm conditions that favour congelation ice formation are neither as common nor as prolonged as the more turbulent conditions that favour frazil ice growth and pancake ice formation both frazil and congelation ice layers have an av erage thickness of 0 12 m in winter evidence that congelation ice and pancake ice thicken primarily by dynamic processes the thermodynamic development of the ice cover relies heavily on the formation of snow ice at the surface of floes after sea water has flooded the snow cover snow ice layers have a mean thickness of 0 20 and 0 28 m in the winter and summer cores respectively and the contribution of snow ice to the winter 24 and summer 16 core sets exceeds most quantities that have been reported previously in other antarctic pack ice zones the thickness and quantity of snow ice may be due to a combination of high snow accumulation rates and snow loads environmental conditions that favour a warm ice cover in which brine convection between the bottom and top of the ice introduces sea water to the snow ice interface and bottom melting losses being compensated by snow ice formation layers of superimposed ice at the top of each of the summer cores make up 4 6 of the ice that was examined and they increase by a factor of 3 the quantity of snow entrained in the ice the accumulation of superimposed ice is evidence that melting in the snow cover on antarctic sea ice floes ran reach an advanced stage and contribute a significant amount of snow to the total ice mass

cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode oceanic anoxic events oaes were episodes of widespread marine anoxia during which large amounts of organic carbon were buried on the ocean floor under oxygen deficient bottom waters oae2 occurring at the cenomanian turonian boundary about 93 5 myr ago is the most widespread and best defined oae of the mid cretaceous although the enhanced burial of organic matter can be explained either through increased primary productivity or enhanced preservation scenarios the actual trigger mechanism corresponding closely to the onset of these episodes of increased carbon sequestration has not been clearly identified it has been postulated that large scale magmatic activity initially triggered oae2 refs 4 5 but a direct proxy of magmatism preserved in the sedimentary record coinciding closely with the onset of oae2 has not yet been found here we report seawater osmium isotope ratios in organic rich sediments from two distant sites we find that at both study sites the marine osmium isotope record changes abruptly just at or before the onset of oae2 using a simple two component mixing equation we calculate that over 97 per cent of the total osmium content in contemporaneous seawater at both sites is magmatic in origin a approximately 30 50 fold increase relative to pre oae conditions furthermore the magmatic osmium isotope signal appears slightly before the oae2 as indicated by carbon isotope ratios suggesting a time lag of up to approximately 23 kyr between magmatism and the onset of significant organic carbon burial which may reflect the reaction time of the global ocean system our marine osmium isotope data are indicative of a widespread magmatic pulse at the onset of oae2 which may have triggered the subsequent deposition of large amounts of organic matter

behaviour of dissolved organic matter and inorganic nutrients during experimental sea ice formation it is well established that during sea ice formation crystals aggregate into a solid matrix and dissolved seawater constituents including inorganic nutrients are rejected from the ice matrix however the behaviour of dissolved organic matter dom during ice formation and growth has not been studied to date dom is the primary energetic substrate for microbial heterotrophic activity in seawater and sea ice and therefore it is at the base of the trophic fluxes within the microbial food web the aim of our study was to compare the behaviour of dom and inorganic nutrients during formation and growth of sea ice experiments were conducted in an indoor basin at 15 c three 1 m3 tanks to which synthetic seawater nutrients and dissolved organic compounds diatom extracted dom had been added were sampled over a period of 5 days during sea ice formation samples were collected throughout the experiment from water underlying the ice and at the end from the ice as well brine was obtained from the ice by centrifuging ice cores inorganic nutrients nitrate and phosphate were substantially enriched in brine in comparison to water and ice phases consistent with the processes of ice formation and brine rejection dissolved organic carbon doc was also enriched in brine but was more variable and enriched in comparison to the dilution line no difference in bacteria numbers was observed between water ice and brine no bacteria growth was measured and therefore had no influence on the doc levels we conclude that the incorporation of dissolved organic compounds in newly forming ice is conservative however since the proportions of doc in the brine were partially higher than those of the inorganic nutrients concentrating effects of doc in brine might be different compared to salts

obliquity forcing of organic matter accumulation during oceanic anoxic event 2 1 an analysis of orbitally influenced climate sensitive sedimentation is conducted across a meridional transect of the proto north atlantic to reconstruct the behavior of the carbon cycle and climate during oceanic anoxic event 2 oae 2 94 ma midlatitude to near equatorial sites spanning deep ocean to shelf environments are evaluated using a new inverse method for the identification and calibration of orbital influence in ancient strata the results yield consistent independent astrochronologies at each location compatible with the recently published radioisotopic astrochronologic time scale at the cenomanian turonian gssp and thus provide a unified high resolution temporal context for evaluation of the event the proto north atlantic astrochronologies document an amplification of obliquity power during oae 2 indicating that obliquity was the dominant pacemaker of organic matter accumulation by the latter portion of the event the strong obliquity signal suggests an influence of high latitude climate processes across midlatitude deep ocean to tropical shelf environments changes in oceanic circulation during oae 2 represent a likely mechanism for the propagation of a high latitude signal and proxy data from demerara rise reveal the development of a new intermediate water mass source synchronous with the record of obliquity amplification we hypothesize that a dense high latitude water mass displaced a pre existing nutrient rich anoxic deep water layer in the proto north atlantic augmented by enhanced volcanism driving an episode of high productivity that lasted 700 800 ka the development and intensification of the new intermediate deep water source was potentially driven by eustatic sea level rise which created expansive seaways in mid to high latitudes

relation of material exchange between sea ice and water to a coupled ice ocean ecosystem at the hokkaido coastal region of the okhotsk sea 1 in this paper the material exchange between the sea ice and the water just below the ice and its relation to the lower trophic ice system are examined using field observations in the hokkaido coastal region of the okhotsk sea and a coupled ice ocean ecosystem model which in detail formulates the material exchange between the ice and the water the accuracy of the model is confirmed by a comparison of the results of the numerical computation with the observations the estimation of the transport of the organic carbon and nutrients based on the computation demonstrates that the physical coupling effect between the ice and water plays a prominent role in supplying the nutrients from the water to the ice ecosystem and in efficiently releasing the organic matter produced by the primary producer in the ice ice algae as a result this study quantitatively clarifies that the physical coupling effect tidal mixing and biological activity in the ice drive the material cycle in the ice and water under the ice

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

diatom induced silicon isotopic fractionation in antarctic sea ice 1 in this study we measure the silicon isotopic composition 29si relative to nbs28 quartz standard of dissolved silicon and biogenic silica collected by sequential melting from spring antarctic pack ice collected near 117 e 64 5 s this work aims to investigate the use of si isotopes to quantify the activity of sea ice diatoms in the different brine structures and the influence of sea ice diatoms on the spring ice edge blooms from three cores with contrasted physico chemical characteristics we report significant isotopic fractionations linked to diatom activity with distinct silicon biogeochemical dynamics between different brine structures the diatoms in snow ice and in brine pockets of frazil or congelation ice have the heavier silicon isotopic composition 0 53 to 0 86 indicating that they grow in a closed system and use a significant fraction of the small dissolved silicon pool available in the brine channels and skeletal layer diatoms display a relatively lower silicon isotopic composition 0 41 to 0 70 although it is still relatively positive compared to expected equilibrium fractionation this suggests that the diatoms have grown in a semi closed system where the dissolved silicon pool i e brine is partially replenished the silicon isotopic composition 0 63 of the sea ice diatoms is much heavier than the one of biogenic silica in the seasonal ice zone mixed layer 0 09 our results suggest that sea ice diatoms either contribute to an insignificant part of the whole diatom biomass in the upper water layer or that they are directly exported below the mixed layer

late cretaceous orbitally paced carbon isotope stratigraphy from the bottaccione gorge italy abstract a refined astronomical tuning of the upper albian lower campanian is proposed from the bottaccione reference section gubbio central italy long term eccentricity cycles filtered from a high resolution 13c record were tuned to the highly stable 405 kyr cycles of the new la2010 astronomical solution for the earth s orbital elements the achieved orbital tuning provides a new precise and accurate age model for dating biostratigraphic magnetostratigraphic and carbon isotope events through a 23 myr long record cycles of 8 0 4 7 3 4 and 2 4 myr modulate the entire 13c record thus extending their detection from the cenozoic to 100 ma and represent primary and stable long term oscillation modes of earth s climate ocean system although an ultimate driver of these long term periodicities is lacking we speculate that specifically the periodicity at 4 7 myr represents a homologue of the present eccentricity grand cycles evolved by the chaotic behaviour of solar system planets during the mesozoic the long term periodicities potentially reflect an unexplored expression of the low frequency response of the carbon cycle to global biogeochemical dynamics of major nutrients particularly phosphorus associated with modulation of inputs to the ocean in turn triggered by high order marine transgressions and formation of highly productive shelf seas this very long term eccentricity control modulated by periodic low energy cycles is suggested to play a crucial role in carbon cycling controlling a chain of climate sensitive global biogeochemical processes on the earth finally these grand cycles provide a potential tool for geological correlation and provide a robust constraint for accurate calculation of the orbital evolution of the solar system

an isotopic study of biogeochemical relationships between carbonates and organic carbon in the greenhorn formation carbon isotopic compositions of total carbonate inoceramid carbonate micritic carbonate secondary cements total organic carbon and geoporphyrins have been measured in 76 different beds within a 17 m interval of a core through the greenhorn formation an interbedded limestone and calcareous shale unit of cretaceous age cenomanian turonian from the western interior seaway of north america results are considered in terms of variations in the processes of primary production which led to the biosynthesis of the molecular precursors of the geoporphyrins and in secondary processes those mediating the transformation of primary organic material into sedimentary total organic carbon it is shown that the porphyrin isotopic record reflects primary isotopic variations more closely than the toc isotopic record and that in these sediments toc is enriched in 13c relative to its primary precursor by 0 6 to 2 8 this enrichment is attributed to isotope effects within the consumer foodweb and is associated with respiratory heterotrophy variations in this secondary enrichment are correlated with variations in the isotopic composition of marine carbonate this correlation is attributed to effects of environmental changes on the marine foodweb these may have included increased atmospheric oxygen associated with the cenomanian turonian oceanic anoxic event the isotopic fractionation associated with fixation of carbon by primary producers is observed to have varied by 1 5 during the interval of deposition it is suggested that this change is due to a variation in the makeup of the community of primary producers and or to a decrease in the atmospheric abundance of co2 during the oceanic anoxic event

link between cyclic eustatic sea level change and continental weathering evidence for aquifer eustasy in the cretaceous abstract cyclic fluctuations in global sea level during epochs of warm greenhouse climate have remained enigmatic because absence or subordinate presence of polar ice during these periods precludes an explanation by glacio eustatic forcing an alternative concept suggests that the water bearing potential of groundwater aquifers is equal to that of ice caps and that changes in the dynamic balance of aquifer charge versus discharge as a function of the temperature related intensity of the hydrological cycle may have driven eustasy during warm climates however this idea has long been neglected for two reasons 1 the large storage potential of subsurface aquifers was confused with the much smaller capacity of rivers and lakes and 2 empirical data were missing that document past variations in the hydrological cycle in relation to eustasy in the present study we present the first empirical evidence for changes in precipitation continental weathering intensity and evaporation that correlate with astronomically long obliquity forced sea level cycles during the warmest period of the cretaceous cenomanian turonian we compare sequence stratigraphic data with changes in the terrigenous mineral assemblage in a low latitude marine sedimentary sequence from the equatorial humid belt at the south tethyan margin levant carbonate platform jordan thereby avoiding uncertainties from land ocean correlations our data indicate covariance between cycles in weathering and sea level predominantly chemical weathering under wet climate conditions is reflected by dominance of weathering products clays in deposits that represent sea level fall aquifer charge discharge conversely preservation of weathering sensitive minerals feldspars epidote and pyroxenes in transgressive sediments reflects decreased continental weathering due to dryer climate aquifer discharge charge based on our results we suggest that aquifer eustasy represents a viable alternative to glacio eustasy as a driver of cyclic 3rd order sea level fluctuations during the middle cretaceous greenhouse climate and it may have been a pervasive process throughout earth history

palaeoenvironmental turnover across the cenomanian turonian transition in oued bahloul tunisia foraminifera and geochemical proxies abstract the integrated analysis of foraminiferal assemblages geochemical proxies and stable isotopes in the oued bahloul section tunisia allowed us to reconstruct the environmental turnover across the cenomanian turonian boundary an increase in palaeoproductivity proxies p ti u al sr al and in 13 c values and a decrease in foraminiferal diversity and 18 o values mark the beginning of the oceanic anoxic event 2 oae2 at the rotalipora cushmani and whiteinella archaeocretacea biozones boundary eutrophic conditions at the seafloor and in the water column are evidenced by high proportions of buliminids and the replacement of planktic oligotrophic specialist rotalipora by eutrophic opportunist hedbergella the enrichment in organic matter and redox sensitive elements together with the abundance of low oxygen tolerant benthic foraminifera indicate dysoxic conditions in the deep water column and at the seafloor higher u aut than mo aut among planktic foraminifera deep and intermediate dwellers disappear rotalipora and globigerinelloides and surface dwellers proliferate hedbergella the persistency of the poorly oxygenated conditions during the w archaeocretacea biozone locally produced euxinic conditions where mo ef and mo aut reach high values diversity presents minimum values and benthic foraminifera temporarily disappear the maximum percentage of heterohelicids indicates a stratified water column with a well developed oxygen minimum zone improved oxygen conditions returned in the upper part of the w archaeocretacea biozone and helvetoglobotruncana helvetica biozone with a slow recovery of foraminiferal assemblages decrease in eutrophic genera heterohelix and increase in mesotrophic genera whiteinella a gradual increase in 18 o values suggests decreased temperatures in surface waters the oae2 has been attributed to global temperature changes and palaeoceanographic reorganization the poor mixing of surface and deep waters and enhanced primary productivity related to global warming associated with increasing continental weathering and nutrient runoff may have favored the eutrophication of the ocean and the expansion of the oxygen minimum zone

thermal evolution of permeability and microstructure in sea ice 1 the fluid permeability k of sea ice constrains a broad range of processes such as the growth and decay of seasonal ice the evolution of summer ice albedo and biomass build up such processes are critical to how sea ice and associated ecosystems respond to climate change however studies of k and its dependence on brine porosity and microstructure are sparse here we present a multifaceted theory for k which closely captures laboratory and field data x ray computed tomography provides an unprecedented look at the brine phase and its connectivity we find that sea ice displays universal transport properties remarkably similar to crustal rocks yet over a much narrower temperature range our results yield simple parameterizations for fluid transport in terms of temperature and salinity and permit more realistic representations of sea ice in global climate and biological models

numerical simulations of the profile properties of undeformed first year sea ice during the growth season a simulation scheme is developed that estimates salinity profiles for first year sea ice during the growth season as a function of the growth history of the ice the model considers the dependence of the initial ice salinity on ice growth velocity and sea water salinity and also the subsequent drainage of brine from the ice the equation for ice growth assumes a linear temperature profile within the ice and is driven by surface heat balance equations that are based on smoothed climatic data for the central arctic basin the estimated salinity profiles are in good agreement with natural profiles although temperature and salinity profiles depend upon the time of the year when ice growth is initiated the brine volume profiles which they specify are essentially a unique function of ice thickness a conclusion that holds even when the insulative effects of snow are considered the temperature and brine volume profiles are then utilized to calculate the ice strength and elastic modulus profiles which in turn specify the composite mechanical properties of the ice sheets through the application of a theory developed by assur 1967 significant differences which are largest for thin ice sheets are observed between ice sheet properties as calculated using composite plate theory and properties calculated from uniform plate theory and average ice properties these results provide a justification for the practice common within the ice modeling community of parameterizing the mechanical behavior of pack ice on the basis of the ice thickness distribution

modeling brine and nutrient dynamics in antarctic sea ice the case of dissolved silica sea ice ecosystems are characterized by microalgae living in brine inclusions the growth rate of ice algae depends on light and nutrient supply here the interactions between nutrients and brine dynamics under the influence of algae are investigated using a one dimensional model the model includes snow and ice thermodynamics with brine physics and an idealized sea ice biological component characterized by one nutrient namely dissolved silica dsi in the model dsi follows brine motion and is consumed by ice algae depending on physical ice characteristics the brine flow is either advective diffusive or turbulent the vertical profiles of ice salinity and dsi concentration are solutions of advection diffusion equations the model is configured to simulate the typical thermodynamic regimes of first year antarctic pack ice the simulated vertical profiles of salinity and dsi qualitatively reproduce observations analysis of results highlights the role of convection in the lowermost 5 10 cm of ice convection mixes saline nutrient poor brine with comparatively fresh nutrient rich seawater this implies a rejection of salt to the ocean and a flux of dsi to the ice in the presence of growing algae the simulated ocean to ice dsi flux increases by 0 115 compared to an abiotic situation in turn primary production and brine convection act in synergy to form a nutrient pump the other important processes are the flooding of the surface by seawater and the percolation of meltwater the former refills nutrients near the ice surface in spring the latter if present tends to expell nutrients from the ice in summer

crystal structure stable isotopes δ18o and development of sea ice in the ross amundsen and bellingshausen seas antarctica the crystal structure and oxygen isotopic composition of ice cores obtained from floes at the end of summer in the eastern ross sea the amundsen sea and the western bellingshausen sea were investigated to determine the ice growth processes and conditions that contribute to sea ice development in the eastern pacific sector of the southern ocean the isotope data indicate that a moderate amount of snow contributes to the development of the sea ice however even the combined use of isotopes and crystal structure analysis does not unambiguously explain the means by which all of the snow is entrained in the ice nevertheless it seems clear that much of the snow is contained in granular snow ice that results from seawater flooding of floes and the base of the snow cover the snow cover in the ross amundsen region was as much as 2 m deep and supported by 7 to 8 m thick floes primarily composed of frazil ice in the bellingshausen region the snow cover and the floes were thinner than in the ross amundsen region the bellingshausen cores were composed primarily of multiple layers of frazil and congelation ice in addition in both regions there were numerous tipped or inclined blocks of congelation ice and layers of rafted nilas in the cores the data indicate that the sea ice develops by multiple mechanisms in a turbulent environment

a non destructive method for measuring the salinity and solid fraction of growing sea ice in situ we describe an instrument developed to make in situ measurements of salinity and solid fraction profiles in growing sea ice the vertical resolution of the measurements is up to a few millimeters with a temporal resolution of up to fractions of a second the technique is based on impedance measurements between platinum wires around which sea ice grows data obtained using this instrument in laboratory experiments are in good agreement with theoretical predictions in a field test in the arctic the bulk salinity of growing sea ice has been measured in situ throughout the whole depth of the ice layer the data are compared with bulk salinities obtained from ice cores and confirm the general understanding that the bulk salinity in ice core studies is significantly underestimated in the lower parts of the cores the approach can also be used in other glaciological applications and for general studies of two phase two component porous media

thermal conductivity of landfast antarctic and arctic sea ice 1 we present final results from a program to measure the thermal conductivity of sea ice with in situ thermistor arrays using an amended analysis of new and previously reported ice temperatures results from landfast first year fy ice near barrow alaska and mcmurdo sound antarctica are consistent with predictions from effective medium models but 10 15 higher than values from the parameterization currently used in most sea ice models we observe no previously reported anomalous near surface reduction which is now understood to have been an artifact nor a convective enhancement to the heat flow although our analysis is limited to temperatures below 5c at which brine percolation is restricted results for landfast multiyear my ice in mcmurdo sound are also consistent with effective medium predictions and emphasize the density dependence we compare these and historical measurements with effective medium predictions and the representation commonly used in sea ice models developed originally for my arctic ice we propose an alternative expression derived from effective medium models appropriate for both my and fy ice that is consistent with

depositional environments and paleogeography of the cretaceous gypsum horizon in west central jordan abstract in the upper cretaceous upper cenomanian gypsum horizon of west central jordan the lithofacies of gypsum limestone and dolomite as well as their sedimentary structures and petrography indicate a coastal intertidal supratidal sabkha environment very much like the persian gulf model 1500 km 2 in area and elongated n s parallel to the dead sea rift fact that this is the second time in the cenomanian of the mujib area that total emergence has happened is taken as an example of synsedimentary tectonics in an unstable area along the not yet existing dead sea rift

global correlation of cenomanian upper cretaceous sequences evidence for milankovitch control on sea level we have investigated the sequence stratigraphy of two widely separated marine cenomanian successions in southeast india and northwest europe and used high resolution ammonite biostratigraphy to demonstrate that sea level changes are globally synchronous and therefore must be eustatically controlled sequence scale sea level changes in the cenomanian were driven by the long eccentricity cycle 400 k y in the milankovitch band we hypothesize that during pre quaternary time the third order sequences of vail and haq are essentially a sediment response to sea level changes driven by the 400 k y cycle construction of a relative sea level curve for the marginal marine succession in india demonstrates that the short term sea level changes are rapid 10 100 m m y and have a magnitude of 2 20 m glacioeustasy is a possible but unproven driving mechanism

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

reconstructing past sea surface temperatures correcting for diagenesis of bulk marine carbonate abstract a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate is used to obtain information on how sea surface temperatures have varied in the past by correcting measured 18o values of bulk carbonate for diagenetic overprinting comparison of bulk carbonate and planktonic foraminiferal 18o records from odp site 677a indicates that the oxygen isotopic composition of bulk carbonate does reflect changes in sea surface temperature and 18o at odp site 690 we calculate that diagenetic effects are small and that both bulk carbonate and planktonic foraminiferal 18o records accurately reflect paleogene warming of high latitude surface oceans biased from diagenesis by no more than 1 c the same is likely to be true for other high latitude sites where sedimentation rates are low at dsdp sites 516 and 525 the effects of diagenesis are more significant measured 18o values of eocene bulk carbonates are more than 2 lower at deeply buried site 516 than at site 525 consistent with the model prediction that the effects of diagenesis should be proportional to sedimentation rate model corrections reconcile the differences in the data between the two sites the resulting paleotemperature reconstruction indicates a 4 c cooling of mid latitude surface oceans since the eocene at low latitudes the contrast in temperature between the ocean surface and bottom makes the carbonate 180 values particularly sensitive to diagenetic effects most of the observed variations in measured 18o values are accounted for by diagenetic effects rather than by sea surface temperature variations we show that the data are consistent with constant equatorial sea surface temperatures through most of the cenozoic with the possible exception of the early eocene when slightly higher temperatures are indicated we suggest that the lower equatorial sea surface temperatures for the eocene and oligocene reported in other oxygen isotope studies are artifacts of diagenetic recrystallization and that it is impossible to reconstruct accurately equatorial sea surface temperatures without explicitly accounting for diagenetic overprinting

brine mixing in the middle devonian of western canada and its possible significance to regional dolomitization abstract the desiccation that most large evaporite basins experienced in their history created large elevation heads these heads must have induced flows of ground or formation waters into the evaporite basins the consequences of such groundwater flows are believed to be 1 provision of the necessary hydrodynamic drive to allow dolomitization of carbonates beneath and adjacent to the evaporite basin and 2 the formation of anomalously distributed evaporites in the basin adjacent to sites of groundwater inflow sites where the groundwaters mixed with marine derived brines such brine mixing may also have been responsible for depleting the marine derived brines of their contained sulfate so explaining later development of sulfate impoverished potash deposits anomalous developments of anhydrite surrounding older carbonate buildups in the distal parts of the middle devonian elk point basin of western canada may represent such products of brine mixing and provide evidence of dolomitization of underlying lower palaeozoic and devonian carbonates coevally with the filling of the evaporite basin regional dolomitization in the williston basin is stratigraphically confined beneath the middle prairie evaporite suggesting a genetic link between the dolomitization and evaporite deposition dolomitization by refluxing brines generated in the evaporite basin appears unlikely because of the presence of an aquitard at the base of the evaporite succession developments of laminar and pisolitic carbonates adjacent to the carbonate buildups are believed to indicate the former presence of subaerial springs that carried calcium rich groundwaters into the evaporite basin anhydrite envelopes around the buildups are interpreted to be reaction products that formed when calcium bearing spring waters mixed with sulfate rich but calcium depleted marine brines the calcium in the spring waters is believed to have entered the groundwaters as a by product of the dolomitization of carbonates underlying the evaporite basin precipitation of gypsum now anhydrite as a consequence of brine mixing must have depleted the sulfate content of the marine derived brines it is possible that the sulfate depleted potash deposits in the prairie evaporite originate by this mechanism on the other hand the stratigraphic position of these deposits lends little support for this hypothesis

orbital scale record of the late cenomanian turonian oceanic anoxic event oae 2 in the tarfaya basin morocco high sedimentation rates up to 12 cm kyear of laminated organic carbon rich biogenic limestones in the tarfaya basin provide an unusually high millennial resolution record of the late cenomanian oceanic anoxic event oae 2 the global positive carbon isotope excursion across the cenomanian turonian corresponds to 11 light dark sedimentary cycles we interpret these cycles as a response to orbital obliquity variation and estimate the duration of the complete excursion as 440 kyear or one long eccentricity cycle on this time scale the main increase in delta 13 c values occurred over a short time interval of less than 20 kyear in the late cenomanian and reached a first maximum approximately 15 kyear prior to the bulk mainly coccoliths delta 18 o derived sea surface maximum temperature that occurs coeval to the extinction of rotalipora cushmani organic carbon accumulation rates follow obliquity cycles reaching a maximum approximately 10 kyear after the last occurrence of r cushmani then slowly decreasing during the early turonian thus the maximum temperature and the maximum organic carbon accumulation in the tarfaya basin lagged by at least 15 kyear behind the global carbon isotope shift and a proposed reduction of atmospheric co 2 content the climate change across the cenomanian turonian boundary probably occurred independent of co 2 levels and may have been controlled by different greenhouse gases water vapour and methane and changes in ocean circulation i e opening of the equatorial atlantic gateway

cenomanian turonian transition in a shallow water sequence of the sinai egypt environmental and depositional changes across the late cenomanian oceanic anoxic event oae2 in the sinai egypt are examined based on biostratigraphy mineralogy 13c values and phosphorus analyses comparison with the pueblo colorado stratotype section reveals the whadi el ghaib section as stratigraphically complete across the late cenomanian early turonian foraminifera are dominated by high stress planktic and benthic assemblages characterized by low diversity low oxygen and low salinity tolerant species which mark shallow water oceanic dysoxic conditions during oae2 oyster biostromes suggest deposition occurred in less than 50 m depths in low oxygen brackish and nutrient rich waters their demise prior to the peak 13c excursion is likely due to a rising sea level characteristic oae2 anoxic conditions reached this coastal region only at the end of the 13c plateau in deeper waters near the end of the cenomanian increased phosphorus accumulations before and after the 13c excursion suggest higher oxic conditions and increased detrital input bulk rock and clay mineralogy indicate humid climate conditions increased continental runoff and a rising sea up to the first 13c peak above this interval a dryer and seasonally well contrasted climate with intermittently dry conditions prevailed these results reveal the globally synchronous 13c shift but delayed effects of oae2 dependent on water depth

desalination processes of sea ice revisited 1 we reexamine five processes that have been suggested to be important for the loss of salt from sea ice these processes are the initial fractionation of salt at the ice ocean interface brine diffusion brine expulsion gravity drainage and flushing with surface meltwater we present results from analytical and numerical studies as well as from laboratory and field experiments that show that among these processes only gravity drainage and flushing contribute to any measurable net loss of salt we show that during ice growth the salinity field is continuous across the ice ocean interface hence there is no immediate segregation of salt at the advancing front

c isotope stratigraphy and paleoenvironmental changes across oae2 mid cretaceous from shallow water platform carbonates of southern mexico the stratigraphic and geochemical record of the mid cretaceous cenomanian turonian oceanic anoxic event 2 oae2 has been studied in numerous tethyan and proto atlantic hemi pelagic pelagic successions but little data comes from nearshore carbonate successions from the proto pacific region here we present the results of a combined stratigraphic and 13c study of c t platform carbonates from southern mexico which were deposited within the proto pacific two scales of sedimentary cyclicity are recognized high frequency peritidal and subtidal cycles 0 4 8 m display little evidence of cycle capping subaerial exposure and are not correlative between sections these relationships suggest that the amplitudes of high frequency sea level changes were minimal during the peak mid cretaceous greenhouse longer term transgressive regressive sequences 18 40 m are correlated between sections and using 13c trends can be correlated with sequences developed in northern europe and india the mexican successions were sampled at a high resolution 10 ky for stable isotopes inorganic organic carbon and oxygen total organic carbon insoluble residues and trace metals the 13ccarb curve matches global trends including 6 distinct isotopic stages permitting identification of oae2 despite the lack of characteristic anoxic facies using the 13ccarb trends we tie the previously identified ammonite planktonic foram and nannofossil biostratigraphy from england and the western interior seaway of colorado into the mexican sections the initiation of oae2 defined by an abrupt positive 3 4 13c shift coincides with a long term sea level rise though the sedimentary expression of the deepening is no greater than that observed for any of the other sea level events across the studied interval oae2 termination transition from gradually decreasing to background 13c values is not associated with a particular sea level trend stratigraphic changes in insoluble residues proxy for continental sediment discharge across oae2 are not correlative between sections and do not show consistent systematic relationships with 13c or sea level variations therefore do not support the hypothesis that oae2 was associated with increased continental derived nutrient influx two peaks in trace metal concentrations coincide with the abrupt increase in 13c ratios onset of oae2 and during the transition from elevated to decreasing 13c values near the c t stage boundary these trends are similar to those recorded in coeval deposits of the western interior seaway and are consistent with the hypothesis that oae2 development was related to the release of reduced metals during the short lived 1 my caribbean oceanic plateau basalt eruption in this scenario oxidation of the metals depleted the existing low dissolved o2 concentrations and thermally buoyant plumes of seawater enriched in biolimiting elements mixed with surface waters stimulated primary productivity and further reduced o2 concentrations leading to widespread anoxia and a large positive 13c shift

frequency modulation reveals the phasing of orbital eccentricity during cretaceous oceanic anoxic event ii and the eocene hyperthermals abstract major advances in our understanding of paleoclimate change derive from a precise reconstruction of the periods amplitudes and phases of the milankovitch cycles of precession obliquity and eccentricity while numerous quantitative approaches exist for the identification of these astronomical cycles in stratigraphic data limitations in radioisotopic dating and instability of the theoretical astronomical solutions beyond 50 myr ago can challenge identification of the phase relationships needed to constrain climate response and anchor floating astrochronologies here we demonstrate that interference patterns accompanying frequency modulation fm of short eccentricity provide a robust basis for identifying the phase of long eccentricity forcing in stratigraphic data one and two dimensional models of sedimentary distortion of the astronomical signal are used to evaluate the veracity of the fm method and indicate that pristine eccentricity fm can be readily distinguished in paleo records apart from paleoclimatic implications the fm approach provides a quantitative technique for testing and calibrating theoretical astronomical solutions and for refining chronologies for the deep past we present two case studies that use the fm approach to evaluate major carbon cycle perturbations of the eocene and late cretaceous interference patterns in the short eccentricity band reveal that eocene hyperthermals etm2 elmo h2 i1 and etm3 x 52 54 myr ago were associated with maxima in the 405 kyr cycle of orbital eccentricity the same eccentricity configuration favored regional anoxic episodes in the mediterranean during the middle and late cenomanian 94 5 97 myr ago the initial phase of the global oceanic anoxic event ii oae ii 93 9 94 5 myr ago coincides with maximum and falling 405 kyr eccentricity and the recovery phase occurs during minimum and rising 405 kyr eccentricity on a myr scale the event overlaps with a node in eccentricity amplitudes both studies underscore the importance of seasonality in pacing major climatic perturbations during greenhouse times

mid latitude terrestrial climate of east asia linked to global climate in the late cretaceous reply the late cretaceous late campanian to maastrichtian was characterized by a variable greenhouse climate with evidence for cooling and or glaciation and warming events most of these climatic signals are derived from marine records and knowledge of the terrestrial climate especially in the mid latitudes is limited due to fragmentary geological records on continents here we report mid latitude terrestrial stable oxygen and carbon isotope data from pedogenic carbonates in the nearly continuous late cretaceous age sk 1 core drilled in the songliao basin northeastern china our data indicate a punctuated mid latitude terrestrial climate in the late cretaceous we interpret the negative excursion of pedogenic carbonate 18o in the early maastrichtian to be the result of decreasing temperature and or strengthened westerlies during global cooling and possible glaciation providing valuable mid latitude terrestrial evidence for this event the negative 13c isotopic excursion ca 66 ma is modeled as higher primary productivity caused by increasing temperature and precipitation in response to a warming climate in the latest cretaceous our continuous stable isotopic records in the songliao basin are in accordance with previously published global late cretaceous records of climate variability from marine and terrestrial regions and demonstrate the sensitivity of mid latitude terrestrial climate in a greenhouse world

the cenomanian turonian oceanic anoxic event i stratigraphy and distribution of organic carbon rich beds and the marine δ13c excursion marine strata deposited during late cenomanian and early turonian time display lithological faunal and geochemical characteristics which indicate that significant parts of the world ocean were periodically oxygen deficient at or very close to the cenomanian turonian boundary between 90 5 and 91 5ma ago oxygen deficiencies were particularly marked over a period of 1ma this short lived episode of oceanic oxygen deficiency has been termed the cenomanian turonian oceanic anoxic event oae the widespread distribution of anoxic sediments deposited synchronously during such a short lived event indicates that such sediments are not simply the product of coincidental local climatic or basinal water mass characteristics but are the result of a global expansion and intensification of the cenomanian turonian oxygen minimum zone related to feedback between sea level rise and regional palaeoceanography the palaeoceanography of the cenomanian turonian oae is discussed in detail in a companion paper by arthur et al 1987 from authors

middle and late cenomanian oceanic anoxic events in shallow and deeper shelf environments of western morocco the response of shallow water sequences to oceanic anoxic event 2 and mid cenomanian events 1a and 1b was investigated along the west african margin of morocco north of agadir azazoul and correlated with the deep water sequence of the tarfaya basin mohammed beach based on biostratigraphy mineralogy phosphorus and stable isotopes in the deeper mohammed beach section results show double peaks in 13corg for mid cenomanian events 1a and 1b rotalipora reicheli biozone lower cc10a biozone the characteristic oceanic anoxic event 2 13c excursion rotalipora cushmani extinction top of cc10a biozone and laminated anoxic black shale in the shallow environment north of agadir a fluctuating sea level associated with dysoxic brackish and mesotrophic conditions prevailed during the middle to late cenomanian as indicated by oyster biostromes nannofossils planktonic and benthonic foraminiferal assemblages anoxic conditions characteristic of oceanic anoxic event 2 for example laminated black shales did not reach into shallow water environments until the maximum transgression of the early turonian climate conditions decoupled along the western margin of morocco between mid cenomanian event 1b and the cenomanian turonian boundary as also observed in eastern tethys north of agadir alternating humid and dry seasonal conditions prevailed whereas in the tarfaya basin the climate was dry and seasonal this climatic decoupling can be attributed to variations in the intertropical convergence zone and in the intensity of the north east trade winds in tropical areas

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

cenomanian turonian carbonate platform deposits in west central jordan we studied upper albian to turonian shallow marine shelf deposits ajlun group of west central jordan along a nne ssw running transect the carbonate dominated succession includes few siliciclastic intercalations claystones and shales and can be subdivided into five formations the naur fuheis and hummar formations of upper albian to upper cenomanian age represent shallow subtidal to supratidal platform environments the uppermost cenomanian to middle turonian shueib formation includes deeper water deposits of the inner mid shelf and locally toc rich black shales shallow marine platform environments once again dominate the wadi as sir formation middle upper turonian a new multibiostratigraphic framework is based on ammonites mainly of the middle cenomanian rhotomagense zone to the middle turonian woollgari zone and calcareous nannofossils biozones cc 9 cc 11 supplemented by benthic and planktonic foraminifers and ostracods it forms the base of a sequence stratigraphic subdivision containing eight sedimentary sequences s1 s8 which are separated by four cenomanian sequence boundaries cejo1 cejo4 and three turonian sequence boundaries tujo1 tujo3 this scheme allows the correlation of the platform succession from distal to proximal shelf areas in contrast to previous correlations using lithologic units furthermore comparisons between the platform successions and sequence patterns of west central jordan and those from neighbouring areas allow to differentiate local regional and global controlling factors of platform development within the study area

cenomanian turonian stable isotope signatures and depositional sequences in northeast egypt and central jordan abstract lithostratigraphic biostratigraphic and microfacies studies of two cenomanian turonian shallow marine siliciclastic carbonate successions at gebel ekma plateau southwestern sinai egypt and wadi karak section central jordan are calibrated with 13c profiles to reveal relative sea level changes within a sequence stratigraphic framework the study provides significantly enhanced stratigraphic resolution and key sections for regional correlation lithofacies are dominated by well developed peritidal to subtidal facies associations indicating deposition in a rimmed carbonate shelf setting biostratigraphic analysis indicates the presence of 6 ammonite zones 3 calcareous nannofossil zones and 3 planktonic foraminiferal zones within the cenomanian to turonian succession six third order depositional sequences bounded by correlatable sequence boundaries can be traced across the african arabian platform comparison with 13c records in deeper water pelagic sequences help to improve the resolution of the boundaries of each depositional sequence recognition of time gaps at the sequence boundaries on the platform recorded in different parts of african arabian platform is attributed to local tectonic activity associated with the change from passive to active margins which are overprinted by the global eustatic signature

growth rate and salinity profile of first year sea ice in the high arctic this paper describes the growth of sea ice and the salinity profiles observed in eclipse sound near pond inlet baffin island canada during the winter of 1977 78 a numerical method of calculation has been developed to incorporate the variations in snow conditions and physical properties of ice and snow during the growth season it is shown that the growth rate can be predicted reasonably well it is also shown that the vertical salinity profile in the ice towards the end of the season provides a record of previous climatological conditions a dependence has been shown between the predicted growth rate and the measured salinity

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

sequence architecture and carbonate platform configuration late cenomanian santonian sinai egypt relative sea level changes on the mixed carbonate siliciclastic platform of sinai are manifested in shifts of distinct facies belts deep water facies highenergy subtidal shallow subtidal lagoon shallow shoreface siliciclastics supratidal and are interpreted in terms of sequence stratigraphy eight sedimentary sequences are recognized for the upper cenomanian to santonian their correlation along a north south transect reveals distinct changes in lithofacies and progradation retrogradation patterns within the individual systems tracts the number and stratigraphy of the sequence boundaries of sinai correlate well with those from adjacent areas patterns of increased subsidence are documented for the central sinai basin since the late cenomanian by increased thickness of the stratal packages post cesin 7 hst post tusin 1 lst and hst post tusin 2 lst and are balanced by varying accumulation rates based on new sedimentological and biostratigraphic data large scale palaeogeographic maps and cross sections show the 1 temporal and spatial evolution of the central sinai basin e g its latest cenomanian initial formation lower turonian deep water facies middle turonian to coniacian synsedimentary subsidence 2 drowning of the cenomanian platform coinciding with the latest cenomanian to early turonian relative sea level rise 3 re establishment of the platform in middle late turonian times and 4 a coniacian basin and swell morphology

relative sea level changes during the cretaceous in israel detailed lithologic microfaunal and biometric investigations using relative abundances diversity indexes and duration charts of ostracods and foraminifera allowed the recognition of sea level changes during the cretaceous of israel three major transgressive regressive sedimentation cycles occur on the northwest margins of the arabian craton these cycles are the neocomian aptian which is mostly terrigenous sediments the albian turonian which is basin marls and platform carbonates and the senonian which is uniform marly chalks the cycles are separated by two major regional unconformities the aptian albian and turonian coniacian boundaries the sedimentary cycles are related to regional tectonic and volcanic events and eustatic changes the paleodepth curve il ustrates the gradual sea level rise reaching its maximum during the late cretaceous with conspicuous advances during the late aptian late albian cenomanian early turonian early santonian and early campanian major lowstands occur at the aptian albian cenomanian turonian turonian coniacian and campanian maastrichtian boundaries this model for israel agrees well with other regional and global sea level fluctuations four anoxic events black shales accompanying transgressions correspond to the cretaceous oceanic record we hypothesize the presence of mature oil shales in the present day eastern mediterranean basin close to allochthonous reef blocks detached from the cretaceous platform

salinity profiles of antarctic sea ice field data and model results in order to describe and compare sea ice salinity distributions which are of interest in the study of physical and biological ice characteristics as well as ice ocean interaction we have computed composite profiles and fitted third degree polynomials to salinity data of 129 cores from the weddell sea four characteristic profile shapes have been recognized and described through the polynomial coefficients c s i and type profiles the field data have been compared with ideal salinity profiles generated by a simulation scheme based on thermodynamic growth under climatological conditions representative of the weddell sea composite salinity profiles agree well with simulations irrespective of the growth mechanism i e frazil or congelation suggesting that ice properties which depend on salinity or porosity may evolve independent of ice growth conditions analysis of salinity and 18o data in conjunction with the simulations demonstrates that apart from meteorological conditions controlling growth velocity and temperature distribution within the ice flooding and upward brine expulsion are important in raising top salinities as frequently observed low top salinities are typical of ice that has undergone retexturing and differential desalination salinity decreases towards the bottom of a floe are a result of high oceanic heat fluxes and snow cover effects as a consequence of these processes the bulk salinity of weddell sea ice cannot be described by a simple linear age thickness relationship as characteristic of arctic first year ice

calcareous nannofossils and mesozoic oceanic anoxic events abstract twenty five years ago mesozoic oceanic anoxic events oaes were documented and formalised as intervals of widespread to global deposition of organic matter the toarcian early aptian oae1a and latest cenomanian oae2 oaes are truly global in nature commonly carbonate poor and typically represented by organic carbon rich black shales in some areas these oaes are also characterised by abundant radiolarian sands and silts they are associated with negative and positive excursions in the 87sr 86sr record in addition to large global carbon isotope anomalies in carbonate and or organic matter caused by a major perturbation of the global carbon budget increased rates of volcanism during the formation of the ontong java and manihiki and caribbean plates and the karoo ferrar traps are believed to have caused the geological responses associated with oae1a oae2 and the toarcian oae respectively excess volcanogenic co2 in the atmosphere most probably turned the climate into a greenhouse mode accelerating continental weathering and increasing nutrient content in oceanic surface waters via river run off higher fertility in the global ocean was also probably triggered directly by submarine igneous events that introduced enormous quantities of biolimiting metals within hydrothermal plumes because mesozoic oaes are often represented by carbonate poor sediments quantitative studies of calcareous nannofossils have been applied to explore a the causes and effects of igneous tectonic events and climate changes relative to nannofloral increases and crises as well as b dissolution events and c diagenetic modifications characterization of calcareous nannofloras in oae intervals can improve our understanding of the marine ecosystem and biological processes such as photosynthesis biological pump and biomineralisation carbonate pump that affect the organic and inorganic carbon cycle as well as adsorption of atmospheric co2 in the oceans types and rates of nannoplankton production and evolution are interpreted to trace the impact of major palaeoceanographic and palaeoclimatic events in selected sections it has been documented that calcareous nannofloras rapidly reacted to new conditions of fertility and higher pco2 by drastically reducing calcification as in the modern oceans during oaes the increase of nutrients and atmospheric co2 induced higher abundances of nannoplankton producing small placoliths and inhibited the deep photic zone nannoconids and schizosphaerellids similarly to the nannoconid crisis preceding deposition of the early aptian oae1a black shales a schizosphaerellid crisis is detected prior to the toarcian oae both oaes are further characterised by a rapid nannofloral speciation beginning approximately 1 5 myr before the oae but without extinctions global changes during the latest cenomanian oae 2 exerted different influences on calcareous nannoplankton that experienced a turnover due to most extreme environmental conditions this event in fact was a time of extinctions followed by originations within calcareous nannofossils precise timing of the events before during and after oae1a oae2 and the toarcian oae indicates that they were intervals of enhanced oceanic productivity and that anoxia dysoxia post dated biotic changes