the posidonia shale lower toarcian of sw germany an oxygen depleted ecosystem controlled by sea level and palaeoclimate abstract the lower toarcian posidonia shale is famous for its excellently preserved fossils and its high amount of organic matter up to 16 both quality of preservation and accumulation of organic matter have been explained by permanent anoxic bottom water conditions high resolution geochemical sedimentological and palaeoecological investigations of various sections of the posidonia shale in sw germany however indicate that oxygen availability was variable and ranged from short oxygenated periods to longer term anoxia the benthic macrofauna consists of nine fossil communities and was used in combination with geochemical data to reconstruct a time averaged oxygen curve anoxic conditions prevailed during the deposition of the toarcian black shales they were however punctuated by various short periods weeks to years with oxygenated bottom water conditions sedimentological e g distinctiveness of microlamination siliciclastic content and geochemical parameters e g organic matter content isotopic signatures 18o and 13c molecular redox parameters pristane phytane ratio arylisoprenoids exhibit a remarkable covariation and seem to be controlled by sea level fluctuations maximum oxygen depletion and an extreme negative shift of 13corg values 34 occurred during the early falciferum zone this is explained by the recycling of 12c enriched carbon derived from remineralization of organic matter on and within the substrate during low sea level stand and a highly elevated redox boundary including photic zone anoxia the subsequent transgression permitted enhanced water exchange with the tethyan ocean and caused improvement of living conditions at the end of the falciferum zone other important factors controlling the depositional environment are the overall palaeogeographic situation and climate the early jurassic is the latest period before break up of pangaea and probably was ruled by a strong meridional atmospheric circulation system with pronounced seasonal changes of prevailing trade and monsoon wind systems an estuarine circulation with a positive water balance and surface water with slightly reduced salinity in the summer alternated with an anti estuarine circulation and a negative water balance in the winter during the summer months a stratified water column with anoxic conditions below the halocline developed 18o data indicate low salinity in the surface water during the monsoon influenced summer high productivity was then located in the photic zone and the corresponding isotopically light 18o signal was fixed in the calcareous nannoplankton during the winter months a saline circulation system brought oxygen to the benthic environment favouring temporary benthic colonization especially during times of relative sea level high stand

magnetostratigraphy of the toarcian stage lower jurassic of the llanbedr mochras farm borehole wales basis for a global standard and implications for volcanic forcing of palaeoenvironmental change the lower jurassic toarcian stage c 183 174 ma is marked by one of the largest global exogenic carbon cycle perturbations of the phanerozoic which is associated with the early toarcian oceanic anoxic event t oae c 183 ma climatic and environmental change at the t oae is reasonably well constrained in the marine realm with marine anoxic or euxinic conditions developing locally across both hemispheres at the same time as the t oae negative carbon isotope excursion however high resolution stratigraphic comparison between different palaeo ocean basins and with the continental realm can be complicated palaeomagnetic reversals can provide a precise and accurate stratigraphic correlation tool between marine and continental sedimentary archives and even between sedimentary and igneous successions here we present a high resolution magnetostratigraphic record for the toarcian stage in the biostratigraphically complete and expanded llanbedr mochras farm borehole cardigan bay basin wales this study provides the first geomagnetic polarity reversal scale that is integrated with high resolution biostratigraphy and carbon isotope stratigraphy for the entire toarcian stage this stratigraphic framework also provides a new precise correlation with the basalt lava sequence of the karoo ferrar large igneous province linking the pliensbachian toarcian boundary and t oae climatic and environmental perturbations directly to this episode of major volcanic activity supplementary material details of the palaeomagnetic data and dip direction are available at https doi org 10 6084 m9 figshare c 4052720

the role of event beds in the preservation of organic carbon in fine grained sediments analyses of the sedimentological processes operating during deposition of the whitby mudstone formation toarcian lower jurassic preserved in northeast england abstract geologists have recently observed that source rocks commonly contain a wide variety of microfabrics including diminutive ripples and burrows the existence of these fabrics challenges the assumption that persistent bottom water anoxia and low energy conditions are necessary prerequisites for enhanced organic carbon preservation in these units in order to enhance our understanding of the depositional and diagenetic processes responsible for organic carbon preservation in these strata the lower jurassic whitby mudstone formation which contains mudstones with up to 14 2 total organic carbon has been investigated using optical electron optical and geochemical methods four thinly bedded mudstone lithofacies were identified a silt bearing clay rich mudstones b clay rich mudstones c clay calcareous nannoplankton and organic carbon bearing mudstones and d cement rich mudstones internally individual beds are typically sharp based and normally graded they are either laminated partially bioturbated or homogenized where depositional fabrics are preserved pellets silt lags ripple lamination shell pavements wave enhanced sediment gravity flows of fluid mud and organo minerallic aggregates have been observed the presence of up to 14 2 toc in units that are sharp based and normally graded suggests that mass flows possibly generated by storms likely influenced sedimentation during deposition of these mudstones the abundant organo minerallic fabrics in these units indicates that at least some of the organic carbon was delivered to the seafloor as marine snow aggregates that likely formed in the water column following phytoplankton blooms homogenization of bed tops indicates that between sediment delivery episodes an infauna was able to colonize the seafloor implying that the bottom waters were at least partly oxygenated during these intervals these fabrics suggest that during deposition of the whitby mudstone formation organic carbon was being preferentially preserved below regions of high primary organic production the close association between sharp based graded beds and organo minerallic aggregates indicates that large volumes of organic carbon were delivered episodically to the seafloor and that conditions at the sediment water interface were episodically dynamic here organic carbon is likely to have been preferentially preserved because the frequency of depositional events was sufficiently high to minimize both oxidant diffusion into the sediment and organic carbon mineralization while bottom water anoxia may have developed during the phytoplankton blooms it was unlikely to have been persistent because the microfabrics present indicate that there was sufficient time and oxygen available for an infauna to disrupt the sediment between deposition events

spatial variability of watermass conditions within the european epicontinental seaway during the early jurassic pliensbachian toarcian in order to constrain spatial variability in watermass conditions within the european epicontinental seaway prior to during and after the toarcian oceanic anoxic event carbon 13cbel 13ccarb and oxygen 18obel 18ocarb isotope records were obtained from three sections in the grands causses basin southern france these data were then compared with similar records along a north south transect across the european epicontinental seaway as the conclusions reached here strongly depend on the reliability of belemnite calcites as archives of palaeoceanographic changes an attempt was made to improve the understanding of isotope signals recorded in belemnite calcite intra rostral carbon and oxygen isotope data from six belemnite specimens belonging to the genus passaloteuthis were collected intra rostral carbon isotopes are influenced by vital effects whereas oxygen isotopes reflect relative changes in temperature and salinity palaeotemperatures calculated from 18obel isotope records from the grands causses basin confirm relatively low temperatures throughout the late pliensbachian similar cool water conditions have previously been shown in germany england spain and portugal a temperature increase of up to 6 c is observed across the pliensbachian toarcian boundary a pronounced negative shift of at least 3 vienna pee dee belemnite is recorded in bulk carbonate carbon during the lower harpoceras serpentinum zone typical of the toarcian oceanic anoxic event before and after the toarcian oceanic anoxic event a good correlation between 13ccarb and 13cbel exists indicating well ventilated bottom waters and normal marine conditions instead data for the toarcian oceanic anoxic event indicate the development of a strong north south gradient in salinity stratification and surface water productivity for the western tethyan realm this study thus lends further support to a pronounced regional overprint on carbon and oxygen isotope records in epicontinental seaways

toarcian carbon isotope shifts and nutrient changes from the northern margin of gondwana high atlas morocco jurassic palaeoenvironmental implications the early toarcian is marked by a global perturbation of the carbon cycle and major marine biological changes these coincide with a general decrease in calcium carbonate production and an increase in organic carbon burial and culminate in the so called toarcian oceanic anoxic event it is believed that the environmental crisis was triggered by the activity of the karoo ferrar large igneous province in order to further document the early toarcian palaeoenvironmental perturbations carbon isotope total organic matter calcareous nannofossils and phosphorus content of the amellago section in the high atlas rift basin of morocco were investigated this section is extremely expanded compared to the well studied european sections its position along the northern margin of the gondwana continent is of critical importance because it enables an assessment of changes of river nutrient input into the western tethyan realm the carbon isotope curve shows two negative excursions of equal thickness and amplitude at the pliensbachian toarcian boundary and at the transition from the polymorphum to the levisoni zone this confirms the supra regional nature of these shifts and highlights the possible condensation of the first boundary shift in european sections phosphorus content is used to trace palaeo nutrient changes and shows that the two negative carbon isotope shifts are associated with increased nutrient levels confirming that these episodes are related to enhanced continental weathering probably due to elevated greenhouse gases in the atmosphere in the high atlas basin the increase in nutrient levels at the pliensbachian toarcian boundary is moreover likely to be the main factor responsible for the coeval demise of the saharan carbonate platform a middle toarcian event centered on the boundary between the bifrons and gradata zones characterized by a positive carbon isotope excursion and nutrient level rise is documented in the amellago section

isorenieratane record in black shales from the paris basin france constraints on recycling of respired co2 as a mechanism for negative carbon isotope shifts during the toarcian oceanic anoxic event the prominent negative stable carbon isotope excursion in both carbonate and organic carbon recorded in organic rich sediments deposited during the toarcian oceanic anoxic event oae has commonly been explained by recycling of 13c depleted co2 the so called kuspert model more recently the massive release of 13c depleted methane or other forms of 13c depleted carbon was also proposed to account for the observed negative 13c excursions in organic carbon of terrigenous as well as of marine origin the occurrence of diagenetic products of the carotenoid isorenieratene isorenieratane and other aryl isoprenoids in toarcian black shales has been regarded as supporting evidence for the kuspert hypothesis as they point to strong stratification of the epicontinental seas a section of a drill core straddling the toarcian of the paris basin cirfontaineen ornois contained intact isorenieratane providing evidence that photosynthetic green sulphur bacteria were present at the time of deposition even prior to the oae however the isorenieratane abundances are very low in the section where the negative 13c excursion in organic carbon and phytane a chemical fossil derived from chlorophyll occurs the abundance of the isorenieratene derivatives increases once the 13c records have shifted to more positive values the 13c of isorenieratane generally circa 13 1 0 5 indicates that the respired co2 contribution at the chemocline was low and is thus not likely to be the main cause of the prominent up to 7 negative 13c shift recorded in toarcian organic carbon records

palaeoclimatic and biotic changes during the aalenian middle jurassic at the southern laurasian seaway basque cantabrian basin northern spain the uppermost toarcian lowermost bajocian deposits have been studied in 10 sections located in the western part of the basque cantabrian basin northern spain the studied 276 successive recorded ammonite assemblages allowed detailed biostratigraphical subdivision and the correlation of the sections at the ammonite zone and subzone scale the foraminifers were studied in 96 samples and 55 diagenetically screened belemnite rostra were analyzed for c and o isotope facies and thickness distribution of the aalenian sediments suggest that deposition took place in a nearly symmetrical sub basin included into an intraplate shallow platform developed over continental crust on which flexure was the main control responsible for subsidence and basin evolution noteworthy negative 13cbel excursions coinciding with seawater temperature changes were recorded during the bradfordensis biochron around the concavum limitatum biochron boundary and around the aalenian bajocian boundary a close relationship between the changes in seawater temperature and the biotic changes observed in the foraminiferal and in the ammonoids assemblages has been evidenced during the comptum biochron the 18obel based palaeotemperature shows a remarkable cooling interval with an average seawater temperature of 15 7 c this cooling favoured the immigration of species of foraminifers that thrived in platforms with colder seawater temperatures located north of the basque cantabrian basin as a consequence a strong increase in the diversity of the foraminiferal assemblages 28 5 of first appearances occurred this interval also coincides with the highest ammonoid abundance recorded during the aalenian a notable increase in temperature with peak values up to 24 3 c was measured during the bradfordensis biochron this warming marks the beginning of progressive loss of foraminifer diversity and the decrease in the abundance of ammonoids however the increase in the relative abundances of some foraminiferal taxa such as the genus spirillina during the warming phase is remarkable some of the foraminiferal species that had their last occurrence during this interval seem to be immigrants from nw europe that arrived during the comptum cooling interval and that did not survive to rise of the seawater temperature another drop in temperature was recorded during the late gigantea and the early concavum biochrons coinciding with this cooling interval nearly 20 of the foraminiferal species disappeared while the ammonoid abundance increased a new and significant warming episode occurred during the latest aalenian limitatum biochron extending to the earliest bajocian discites biochron biotic response to this new t of 2 5 c is remarkable marking one of the most important crises of the aalenian more than 30 of the foraminiferal species disappeared and no new appearances were recorded ammonoids show a decrease in the specimen abundance during the limitatum discites warming preceding a drastic decrease in the species abundance the remarkable biotic changes linked to the variations of seawater temperature recorded in the basque cantabrian basin during the aalenian open the possibility that some of these faunal turnovers specially marked in the benthic foraminifers were of global extent and mainly forced by climate changes

toarcian oceanic anoxic event an assessment of global causes using belemnite c isotope records from black shales markingthe toarcian oceanic anoxic event t oae the first explanation envisions recycling of dissolved inorganiccarbon dic with a light isotopic signature into the photic zone from the lower levels of a salinity stratifiedwater mass essentially requiring a regional paleoceanographic driver of the carbon cycle the second involvesthe rapid and massive dissociation of methane from gas hydrates that effectively renders the t oae a globalperturbation of the carbon cycle we present c isotope records from belemnites d

evidence of terrestrial organic matter deposition across the early toarcian recorded in the northern lusitanian basin portugal abstract the pliensbachian toarcian lower jurassic in the lusitanian basin portugal is particularly well exposed through marl limestone alternations very rich in nektonic and benthonic macrofauna in the general context of toarcian oceanic anoxic event t oae the lower toarcian polymorphum and levisoni ammonite zones marks important sedimentological changes in the marine paleoenvironment to better understand the paleoenvironmental changes that occurred during the latest pliensbachian early toarcian a high resolution study of organic matter was undertaken in the alcabideque section in the northern sector of the basin based on the analysis of 14 samples from a section 20 m thick this study involved organic geochemistry total organic carbon toc sulfur and biomarkers and palynofacies the results confirm that sediments are particularly poor in organic matter with the highest toc values reaching 0 41 wt around the top of polymorphum zone the palynofacies analysis provides evidence that the organic matter largely consists of particles belonging to phytoclasts and palynomorphs groups the phytoclasts present were generally degraded and oxidized with significant representation in the emaciatum and polymorphum zones the palynomorphs were mainly composed by sporomorphs with a sporadic increase in marine palynomorphs mainly dinocysts at the top of the emaciatum and polymorphum zones continental organic matter was predominant at the base of levisoni zone t oae through the deposition of brownish marls chocolate marls which was confirmed by the occurrence of tetrads and polyads pollen grain agglomerates and by biomarkers with the major presence of long chain n alkanes n alkane c17 c20 tricyclic terpane c24 tetracyclic terpane and c29 regular sterane the gammacerane index shows a peak at the top of polymorphum zone clearly associated with the increase of marine palynomorphs and the maximum marine influence in the series

lower jurassic epicontinental carbonates and mudstones from england and wales chemostratigraphic signals and the early toarcian anoxic event sections through lower jurassic epicontinental carbonates from southern britain junction bed and equivalent show a positive carbon isotope excursion 13ccarbonate detectable in bulk rock in the falciferum zone of the lower toarcian isotopic data from organic matter in more clay rich sections from wales and north east england together with determinations on belemnite calcite indicate that highest 13c values are localized in the upper exaratum subzone of the falciferum zone levels of particular enrichment in organic carbon were developed in the early to mid exaratum subzone and hence pre date this 13c maximum these phenomena reflect the impact of the early toarcian oceanic anoxic event in the british area similar isotopic trends have been recorded in other toarcian sections from tethyan europe and are interpreted as reflecting the chemistry of sea water on the assumption of isotopic correlation between the english and tethyan sections the 13c maximum would be everywhere dated as latest exaratum subzone in terms of the north european ammonite scheme absolute oxygen isotope values in carbonates probably reflect both early diagenetic cementation and later temperature related burial diagenesis although a palaeotemperature maximum is tentatively identified as characterizing the early falciferum zone subsequent climatic deterioration may have been triggered by drawdown of co2 related to regional excess carbon burial during the oceanic anoxic event using the positive 13c excursion as a correlative level in sections from different faunal provinces britain italy and spain implies that lower toarcian zonal stratigraphy is diachronous between northern and southern europe there is evidence for partitioning of water masses between the north european shelf and the tethyan continental margin during the early jurassic

soil erosion processes and sediment sorting associated with transport mechanisms on steep slopes summary sediment size distribution greatly affects sediment transport and deposition a better understanding of sediment sorting will improve understanding of erosion and sedimentation processes which in turn will improve erosion modeling to address this issue a total of 12 rainfall simulation experiments were conducted in a 1 m by 5 m box with varying steep slopes 10 15 20 and 25 and the simulated rainfall lasted for 1 h at a rate of 90 mm h 1 for each simulated event runoff and sediment were sampled at 3 min intervals which were performed to study in detail the temporal change in size distribution of the eroded materials these data were used to interpret the real time sequence of transport mechanisms acting in response to the simulated rainfall total soil loss is the sum of suspended saltating and contact loads the proportion of sediment r 2 0 452 p n 120 suspension saltation transports the finer than 0 054 mm size sediment was the most important erosion mechanism during interrill erosion processes however after rill development on hillslopes bed load transport by rolling of medium to large sized sediment particles coarser than 0 152 mm became an increasingly important transport mechanism and it were also enhanced by increased slope overall the study supports a strong relationship between the sediment transport of contact rolling load and stream power the partition of soil loss into these more meaningful components appears to be essential both for initial data interpretation and for subsequent use of such data for soil loss prediction

impact of source depth on coherent underwater acoustic communications a recent paper song et al j acoust soc am 123 856 865 2008 investigated ocean variability impact on coherent underwater acoustic communications 8 16 khz for a single near seafloor transmitter in shallow water during an extended period 27 h this letter extends that investigation to various source depths and receiver subarrays specifically the middle water column source which is either in or out of the thermocline experiences performance variability of 6 7 db in terms of output signal to noise ratio further the source below the thermocline consistently outperforms the source above the thermocline when the receiver subarray is located below the thermocline

high resolution dynamics of early jurassic marine extinctions the case of pliensbachian toarcian ammonites cephalopoda abstract the pliensbachian toarcian interval was marked by major environmental disturbances and by a second order mass extinction here we reappraise the taxonomic spatiotemporal and selective dynamics of extinctions over the whole interval by analysing a high resolution dataset of 772 ammonite species from nw tethyan and arctic domains on average 40 65 of ammonite species disappeared during each subchronozone but higher extinction pulses reaching 70 90 prevailed from the margaritatus to the dispansum chronozone the main extinctions corresponding to the gibbosus pliensbachian toarcian boundary semicelatum bifrons variabilis and dispansum events differed in their dynamics suggesting episodes of ecological stress related to climate change regression disturbance in the carbon cycle or anoxia the multi pulsed volcanic activity in the karoo ferrar province could well have triggered these ecological changes in addition ammonites experienced a morphological bottleneck during the gibbosus event 1 ma before the early toarcian diversity collapse typically drops in richness were related both to high extinctions and to declines in origination rates this feature could result from strengthened ecological stresses related to the temporal overlap of environmental disturbances after the early toarcian crisis the recovery of ammonites was rapid 2 ma and probably influenced by a coeval marine transgression supplementary material figures showing a comparison of extinction and origination patterns based on different datasets and variations of the morphospace occupation are available at http www geolsoc org uk sup18381

paleoenvironmental conditions recorded by 87sr 86sr δ13c and δ18o in late pliensbachian toarcian jurassic belemnites from bulgaria the late pliensbachian toarcian jurassic sedimentological paleontological and geochemical belemnite 87sr 86sr 13c and 18o record is examined in two eastern tethyan bulgarian locations this interval contains the well known early toarcian ocean anoxic event t oae and its manifestation and temporal context is examined in bulgaria many of the features seen in south western europe are identified collapse of carbonate platform productivity at the pliensbachian toarcian boundary the t oae a short pulse of euxinic deposition in the falciferum zone an early toarcian rapid warming event seen in the belemnite 18o record that peaked around the falciferum bifrons zone boundary the long recognized positive 13c excursion in the late falciferum zone is also seen but a precursor sharp 13c negative excursion seen around the tenuicostatum falciferum zone boundary in most organic carbon records is not seen in the belemnite data a curious absence noted from other belemnite records subsequent perturbations in 87sr 86sr 13c and 18o suggest that there may be more global isotopic excursions in the early jurassic on the other hand belemnite sr isotope values from bulgaria are in accord with those recorded in western europe and hence demonstrating its value as a chronostratigraphic tool

long range time reversal communication in deep water experimental results in december 2011 a long range acoustic communication experiment was conducted in deep water west of izu ogasawara islands japan the experiment involved a stationary source 450 550 hz and an 18 element vertical array 102 m aperture both deployed at around the sound channel axis initial analysis of data demonstrates that a data rate of 400 bits s can be achieved over 600 km range in deep water using 16 quadrature amplitude modulation and passive time reversal equalization

numerical evaluation of mechanisms driving early jurassic changes in global carbon cycling the early jurassic early toarcian ca 183 ma carbon cycle perturbation is characterized by aabout 5 parts per thousand delta sup 13 c excursion in the exogenic carbon reservoirs a 1000 ppm rise in atmospheric co sub 2 and a 6 7 degrees warming two proposed explanations for this presumed global carbon cycle perturbation are the liberation of massive amounts of isotopically light ch4 from 1 gondwanan coals by heating during the intrusive eruption of the karoo ferrar large igneous province lip or 2 the thermal dissociation of gas hydrates carbon cycle modeling indicates that the release of ch4 from gondwanan coals synchronous with the eruption of the karoo ferrar lip fails to reproduce the magnitude or timing of the co sub 2 and delta sup 13 c excursions however sensitivity analyses constrained by a marine cyclostratigraphically dated delta sup 13 c record indicate that both features of geologic record can be explained with the huge input of about 15 340 24 750 gt c over about 220 k y a result possibly pointing to the involvement of hydrothermal vent complexes in the karoo basin the simulated release of 6000 gt c from gas hydrates also reproduces aspects of the early toarcian rock record but the large mass involved raises fundamental questionsmore about its formation storage and release less

selective extinction among early jurassic bivalves a consequence of anoxia analyses of taxonomically standardized data sets demonstrate several statistically robust extinction patterns in early jurassic bivalve species from northwest europe and the andean basins of south america in both regions extinction intensities were significantly enhanced in late pliensbachian and early toarcian time as compared to all other time intervals the same intervals except for the early toarcian of south america also represent times of unusual extinction selectivity with infaunal taxa suffering distinctly more than epifaunal forms as infaunal suspension feeders are extremely rare components of early jurassic oxygen controlled macrofaunas these results are entirely compatible with sedimentological and geochemical data suggesting that widespread anoxia was a principal cause of the diversity crisis although many biotic traits that enhance survivorship during background times seem to be irrelevant during major mass extinctions patterns of survivorship selectivity may provide more distinct clues to the causes of less severe mass extinctions

stable isotope records δ18o and δ13c of lower middle jurassic belemnites from the western balkan mountains bulgaria palaeoenvironmental application stable o and c isotope data of 110 upper pliensbachian lower bajocian belemnites have been obtained and used to attempt a reconstruction of palaeotemperature and its variation in two epicontinental depositional environments from the western balkan mountains bulgaria the samples were collected from 3 sections with high resolution ammonite subdivision initially taphonomic cathodoluminescence and geochemical analyses were used for evidence of diagenetic alteration non luminescent parts of the belemnite rostra have been sampled for isotope analyses and 76 samples having d 18 o 0 5 pdb fe 950 ppm and sr mn ratio 80 were used for palaeotemperature interpretations the o and c isotope data generally exhibit little stratigraphical variability with minor fluctuations however there are prominent positive c isotope excursions and coeval negative o isotope shifts detected in the lower toarcian tenuicostatum falciferum and bifrons zones the o isotope data interpreted in terms of palaeotemperature revealed relatively high seawater temperatures during the toarcian aalenian and early bajocian with detectable temperature rises during the early toarcian maximum value of 29 6 c both c isotope maxima and o isotope minima are used as evidence of the early toarcian anoxic event reported from many localities of the same age and in similar facies in western europe in the study the latter is recognized as 3 episodes which are closely related with the seawater temperature maxima this isotope record pattern is considered as a consequence of a global tethyan transgression during the early toarcian 2008 published by elsevier ltd

phanerozoic large igneous provinces lips heatt haline euxinic acidic thermal transgression episodes and mass extinctions abstract the phanerozoic consists of three mutually exclusive climate states icehouse greenhouse and hothouse the greenhouse is the default state representing 70 of the phanerozoic it is characterized by a weak thermal mode pole driven deep water formation with little or no continental sea ice and weakly oxic cool water sinking near the poles nitrogen limitation characterizes greenhouse oceans in which ammonium may be the dominant bioavailable form of nitrogen the steady state greenhouse default must be forced to produce either of the other two states continent continent collision produces the intense chemical weathering that draws down atmospheric co2 and results in the icehouse state that comprises 20 25 of the phanerozoic icehouses have ice caps in contact with the ocean that produce icebergs and foster sea ice formation sea ice formation fills the ocean with highly oxic phosphorus limited icewater except for a thin layer of warm surface water in the tropics of the 23 most conspicuous mass extinctions of the phanerozoic including the late ediacaran 4 are associated with ice volume related regressions and 3 are problematic we suggest that the other 16 mass extinctions occurred when greenhouse climate was forced to hothouse climate large igneous provinces lips can trigger the heatt haline euxinic acidic thermal transgression mechanism which can force greenhouse climate to a hothouse climate state the rapid voluminous co2 emissions of lips cause a series of events that result in very slow but pronounced haline mode circulation mid latitude driven deep water formation that produces warm saline bottom water at very dry hot subtropical and middle latitudes this water upwells at the poles causing warm and moist equable climate hothouse development promotes deep sea anoxia that is generated in concert with co2 buildup and warming the spread of anoxia favors reduced nitrogen over nitrate and limited iron dust curtails nitrogen fixation this leads to dominance of primary productivity by primitive green algae and or cyanobacteria progression to euxinia that reaches the photic zone severely curtails primary productivity via poisoning even as availability of usable nitrogen plummets the result is eukaryotic mass extinction we suggest that the 16 phanerozoic mass extinctions referred to above resulted at least in part from the heatt process evidence for this relationship at 11 of the most severe extinctions is convincing data sets for the other 5 are strongly suggestive of heatt related mass extinction but do not yet have enough documentation to reliably characterize them as heatt episodes

early jurassic schizosphaerellid crisis in cantabria spain implications for calcification rates and phytoplankton evolution across the toarcian oceanic anoxic event 1 the toarcian oceanic anoxic event 183 myr ago represents a global perturbation marked by increasing organic carbon burial and a general decrease in calcium carbonate production likely triggered by elevated carbon dioxide levels in the atmosphere here we present quantitative analyses of calcareous nannofossil diversity and abundance from the castillo de pedroso section in cantabria northern spain we compare these data with geochemical data c and o isotopes obtained from biogenic and bulk carbonate records in order to highlight the response of calcareous phytoplankton to major climatic and paleoceanographic changes the pliensbachian toarcian boundary is characterized by an abrupt decrease in abundance of schizosphaerella punctulata the most important lithogenic contributor to hemi pelagic carbonates in the early jurassic the early toarcian nannofloral assemblages show an increase in abundance of mitrolithus jansae and small sized r selected taxa and a progressive decrease in s punctulata percentages the deep dwellers m jansae and s punctulata experienced a major crisis slightly prior to the deposition of the toarcian black shales that are characterized by high abundances of eutrophic taxa such as lotharingius spp and biscutum spp the return of s punctulata associated with lower percentages of eutrophic taxa was observed just above the toarcian black shales the toarcian episode reveals that high co2 levels and increasing primary productivity probably triggered a shift in abundance from highly calcified nannoliths such as s punctulata and m jansae to small sized r selected coccoliths that overall record a biocalcification crisis at the onset and during the toarcian episode

the response of two tethyan carbonate platforms to the early toarcian jurassic oceanic anoxic event environmental change and differential subsidence chemostratigraphic analyses 87 sr 86 sr d 13 ccarb of limestones from two jurassic platform carbonate sequences in italy trento and campania lucania platforms illustrate previously established trends found in pelagic sediments and skeletal carbonates from biostratigraphically well calibrated sections elsewhere in europe chemostratigraphic correlations between the platform carbonate successions and appropriate intervals from well dated reference sections allow the application of high resolution stratigraphy to these shallow water peritidal carbonates and furthermore elucidate the facies response to the early toarcian oceanic anoxic event oae lower jurassic toarcian levels of the western trento platform southern alps northern italy contain spiculitic cherts that appear where rising carbon isotope values characterize the onset of the oae a palaeoceanographic phenomenon interpreted as driven by increased nutrient levels in near surface waters there is a facies change to more clay rich facies at the level of the abrupt negative carbon isotope excursion also characteristic of the oae higher in the section the campania lucania platform southern apennines southern italy records a change to more clay rich facies where carbon isotope values begin to rise at the beginning of the oae but the negative excursion higher in the section occurs within oolitic facies although in both examples the early toarcian oae can be recognized by a change to more clay rich lithologies this facies development is diachronous and in neither case did the platform drown although the trento platform in the south west sector studied here was adversely affected by the oae it did not drown definitively until late aalenian time the campania lucania platform persisted throughout the jurassic and cretaceous differential subsidence rates which can be calculated using comparative chemostratigraphy are identified as a crucial factor in the divergent behaviour of these two carbonate platforms relatively fast in the case of the trento platform relatively slow in the case of the campania lucania platform it is proposed that where water depths remained as shallow as a few metres during the oae campania lucania platform dissolved oxygen levels remained high nutrient levels relatively low and conditions for carbonate secretion and precipitation remained relatively favourable whereas more poorly ventilated and or more nutrient rich waters trento platform adversely

how contact metamorphism can trigger global climate changes modeling gas generation around igneous sills in sedimentary basins abstract large volumes of greenhouse gases such as ch4 and co2 form by contact metamorphism of organic rich sediments in aureoles around sill intrusions in sedimentary basins thermogenic gas generation and dehydration reactions in shale are treated numerically in order to quantify basin scale devolatilization we show that aureole thicknesses defined as the zone of elevated metamorphism relative to the background level vary within 30 250 of the sill thickness depending on the temperature of the host rock and intrusion besides the sill thickness in shales with total organic carbon content of 5 wt ch4 is the dominant volatile 85 135 kg m3 generated through organic cracking relative to h2o generation from dehydration reactions 30 110 kg m3 even using conservative estimates of melt volumes extrapolation of our results to the scale of sill complexes in a sedimentary basin indicates that devolatilization can have generated 2700 16200 gt ch4 in the karoo basin south africa and 600 3500 gt ch4 in the voring and more basins offshore norway the generation of volatiles is occurring on a time scale of 10 1000 years within an aureole of a single sill which makes the rate of sill emplacement the time constraining factor on a basin scale this study demonstrates that thousands of gigatons of potent greenhouse gases like methane can be generated during emplacement of large igneous provinces in sedimentary basins

the search for the origin of the planktic foraminifera planktic foraminifera are an extremely abundant important and successful group of marine protists they are particularly useful in reconstructing past environments and for biostratigraphic dating despite their importance the origin of the group is uncertain previous work has suggested that they evolved from a benthic ancestor during the triassic or perhaps the mid jurassic bajocian but a reason for their origination has remained unclear here we present evidence from the toarcian early jurassic of nw europe that the origin of the planktic foraminifera may have been one of the results of the early toarcian oceanic anoxic event this event appears to have been associated with a massive dissociation of gas hydrates and other perhaps related water chemistry changes

massive dissociation of gas hydrate during a jurassic oceanic anoxic event in the jurassic period the early toarcian oceanic anoxic event about 183 million years ago is associated with exceptionally high rates of organic carbon burial high palaeotemperatures and significant mass extinction heavy carbon isotope compositions in rocks and fossils of this age have been linked to the global burial of organic carbon which is isotopically light in contrast examples of light carbon isotope values from marine organic matter of early toarcian age have been explained principally in terms of localized upwelling of bottom water enriched in 12c versus 13c refs 1 2 5 6 here however we report carbon isotope analyses of fossil wood which demonstrate that isotopically light carbon dominated all the upper oceanic biospheric and atmospheric carbon reservoirs and that this occurred despite the enhanced burial of organic carbon we propose that as has been suggested for the late palaeocene thermal maximum some 55 million years ago the observed patterns were produced by voluminous and extremely rapid release of methane from gas hydrate contained in marine continental margin sediments

calcareous nannoplankton changes across the early toarcian oceanic anoxic event in the western tethys 1 calcareous nannoplankton were profoundly affected by environmental perturbations coincident with the early toarcian oceanic anoxic event t oae we quantify the abundance of nannofossils across the t oae at three locations in western europe where the event is marked by a prominent negative carbon isotope excursion cie data were treated by statistical analysis and the shannon diversity index was applied in order to describe nannofossil assemblage changes related to paleoenvironmental evolution in the basal toarcian before the t oae high proportions of taxa with an affinity for low temperature e g p liasicus t patulus bussonius occurred this observation is consistent with interpretations of published oxygen isotope records during the t oae the lowest abundance of nannofossils is observed but there is a peak of a coccolith calyculus from an organism that probably thrived in low saline surface waters depleted of nitrate at the end of the perturbation the lowest diversities of nannofossils occurred and assemblages are dominated by crepidolithus crassus a deep dweller this interval corresponded to progressive reoxygenation of deep water and the reoccupation of the deep photic zone by nannoplankton the highest abundance of nannofossils is recorded above the cie and testifies to the recovery of the entire nannoplankton community the t oae was widespread perhaps global and probably linked to major changes in the atmosphere and hydrosphere however the record of this event varies in the basins surrounding the western tethys suggesting regional imprints on the global signal the regional variability may attest to establishment of effective connections between the arctic and tethys oceans which allowed cool low saline water formed at high latitudes to stream toward the western tethys

feasibility of global scale synthetic aperture communications a recent paper higley et al j acoust soc am 118 2365 2372 2005 investigated synthetic aperture communications in shallow water exploiting the relative motion between a source and a receiver this letter presents a feasibility study of synthetic aperture communications at global distances using the 57hz acoustic data from the heard island feasibility test conducted in january 1991 baggeroer and munk phys today 45 22 30 1992 specifically a reception at ascension island about 9200km from the source ship moving at about 3kt near heard island is analyzed by treating the 255 digit m sequence tomography signal as a binary phase shift keying communication signal with an information rate of 11 4bits s the performance using a single receiver combining three consecutive receptions spaced 5 2min 470m apart indicates that synthetic aperture acoustic communications is feasible at global distances

a test of basin scale acoustic thermometry using a large aperture vertical array at 3250 km range in the eastern north pacific ocean broadband acoustic signals were transmitted during november 1994 from a 75 hz source suspended near the depth of the sound channel axis to a 700 m long vertical receiving array approximately 3250 km distant in the eastern north pacific ocean the early part of the arrival pattern consists of raylike wave fronts that are resolvable identifiable and stable the later part of the arrival pattern does not contain identifiable raylike arrivals due to scattering from internal wave induced sound speed fluctuations the observed ray travel times differ from ray predictions based on the sound speed field constructed using nearly concurrent temperature and salinity measurements by more than a priori variability estimates suggesting that the equation used to compute sound speed requires refinement the range averaged ocean sound speed can be determined with an uncertainty of about 0 05 m s from the observed ray travel times together with the time at which the near axial acoustic reception ends used as a surroga

high precision geochronology links the ferrar large igneous province with early jurassic ocean anoxia and biotic crisis abstract apparent synchrony between eruption emplacement of large igneous province lip magmas and mass extinction has led to the implication of magmatism as a primary trigger of global scale environmental change evaluating the efficacy of magmatism as a driver of global change depends on the relative timing of magmatism and environmental change and the magma effusion intrusion rate both of which can be constrained by high precision geochronology early jurassic pliensbachian toarcian global ocean anoxia and acidification carbon isotope perturbations and biotic crisis have been linked to synchronous eruption and emplacement of the karoo and ferrar lips to better constrain the timing and duration of ferrar magmatism we apply the single crystal chemical abrasion u pb id tims method to zircon crystals isolated from twenty ferrar lip sills and lavas and the dufek intrusion dates suggest that both intrusive and extrusive ferrar magmatism occurred over an interval of 349 49 kyr beginning with intrusive magmatism as early as 182 779 0 033 ma lava eruption was synchronous with and in some cases postdates intrusion when coupled with existing geochronology on the karoo province our dates confirm broad synchrony between karoo and ferrar magmatism though karoo magmatism began demonstrably prior to ferrar magmatism starting as early as 183 246 0 045 ma the short lived magmatic history of the ferrar lip makes it a plausible trigger for early jurassic environmental change

warming driven mass extinction in the early toarcian early jurassic of northern and central spain correlation with other time equivalent european sections abstract causes of the major mass extinction recorded during the early toarcian early jurassic are controversial many authors have concluded that the mass extinction is caused by the widespread oceanic anoxia derived from a postulated early toarcian oceanic anoxic event etoae supposedly synchronous in all basins and global in extent another group of papers links the mass extinction with a major climate change that occurred synchronously with the mass extinction the results of the study of five sections of the uppermost pliensbachian and lower middle toarcian deposits located in northern and central spain are presented detailed ammonite based biostratigraphy coupled with stable isotope analysis of belemnite calcite and bulk carbonates as well as total organic carbon toc analyses have been performed in all sections records of the vertical distribution of mainly benthic fossils have been compiled in four of the studied sections results obtained in the spanish outcrops have been compared and correlated with other european sections the excellent mutual relation between the patterns of the early toarcian progressive warming and the concomitant progressive losses of species evidences a cause and effect relationship between the increase of temperature and the mass extinction from an uppermost pliensbachian cooling interval warming started at the lower toarcian tenuicostatum zone increase of average seawater palaeotemperature is associated with a progressive and substantial drawdown in the number of species of nektonic planktonic and benthic organisms representing the extinction interval a prominent increase in seawater temperature occurred around the lower toarcian tenuicostatum serpentinum zonal boundary average temperatures at the serpentinum zone increased about 7 c marking the extinction boundary the high temperatures continued during the middle toarcian bifrons chronozone representing the repopulation interval the anoxia linked to the postulated etoae cannot be the responsible for the mass extinction because it has been synchronously recorded in the oxygenated environments of many european and northern african platforms deposition of laminated organic rich black shale facies above 5 wt toc indicating anoxic environments was mostly confined geographically to the western europe euxinic basin and mainly deposited after the extinction event during the interval of faunal recovery

foraminiferal assemblages extinctions and appearances associated with the early toarcian oceanic anoxic event in the llanbedr mochras farm borehole cardigan bay basin united kingdom abstract the uppermost pliensbachian lower toarcian sediments recovered from llanbedr mochras farm borehole north wales uk were deposited in the cardigan bay basin and mainly consist of alternating marls and marly limestones the current study analyses the foraminiferal assemblages from the cored interval 143 m that has been assigned to the spinatum zone upper pliensbachian to the lower part of the bifrons zone middle toarcian the foraminiferal assemblages are dominated by the suborders lagenina and robertinina four main ecostratigraphic intervals have been identified based on changes in the foraminiferal assemblages that occurred before during and after the toarcian oceanic anoxic event t oae ecostratigraphic interval i upper part of the spinatum zone is characterized by a diverse assemblage with specialist opportunist and intermediate forms this assemblage is interpreted to represent a phase that pre dates the biotic crisis the ecostratigraphic interval ii tenuicostatum zone shows an abrupt increase in opportunist forms such as the genus reinholdella and a facultative opportunist such as paralingulina tenera which was tolerant to oxygen depleted conditions this second interval represents the initial biotic crisis phase in response to decreasing oxygenation the ecostratigraphic interval iii is considered the peak of the biotic crisis coincident with the negative carbon isotopic excursion at the base of the serpentinum zone and characterized by the dominance of the opportunist reinholdella 87 97 of the assemblage and low diversity the ecostratigraphic interval iv upper part of serpentinum zone and lower part of bifrons zone is characterized by an increase of diversity and an abrupt decrease in reinholdella this assemblage is interpreted to reflect the increased availability of oxygen from deep infaunal to epifaunal microhabitats and the return to normal conditions at the sea bottom ecostratigraphic fluctuations in the mochras foraminiferal assemblages across the t oae event are comparable with those from other parts of the uk the lusitanian basin portugal the umbria marche basin italy and the atlassic basin north africa in addition a foraminiferal turnover is evident across the pliensbachian toarcian boundary and the t oae and reflects the effects of the early jurassic biotic crisis on benthic foraminifera controlling factors of the biotic crisis are discussed regarding that anoxic conditions do not necessarily have a lethal effect on all foraminiferal species and other oceanographic and environmental factors need consideration fragmentation of epicontinental platforms sea level changes crisis of carbonate productivity and temperature changes

a carbon isotope perturbation at the pliensbachian toarcian boundary evidence from the lias group ne england a perturbation in the carbon isotope record at the time of the pliensbachian toarcian boundary 184 ma in the early jurassic is reported based on new data from yorkshire england two sharp 13 c org negative excursions each with a magnitude of 2 5 and reaching minimum values of 28 5 are recorded in the bulk organic matter record in sediments of latest pliensbachian to earliest toarcian age a similar pattern of negative carbon isotope excursions has been observed at the stage boundary in the sw european section at peniche portugal in 13 c carbonate 13 c wood and 13 c brachiopod records the isotopic excursion is of interest when considering the genesis and development of the later toarcian oceanic anoxic event oae as well as the second order global extinction event that spans the stage boundary furthermore the isotope excursion potentially provides a chemostratigraphic marker for recognition of the stage boundary which is currently achieved on the basis of different ammonite faunas in the nw european and tethyan realms

expression of the early toarcian negative carbon isotope excursion in separated carbonate microfractions jurassic paris basin abstract the causes of the pronounced negative excursion in carbon isotope values that was recorded during the early toarcian oceanic anoxic event t oae are still under debate particularly with regard to the local versus global pattern of the excursion and the extent to which recorded signals are under a diagenetic control in this study we employ a novel microseparation technique in order to investigate the isotopic and mineralogical characteristics of different size fractions of the carbonate content from a toarcian section recovered from the sancerre couy borehole southern paris basin beyond the recognition of a 6 13 c excursion in the bulk carbonate content our data also demonstrate that biogenic particles such as coccoliths and inorganic grains precipitated as early diagenetic phases including dolomite both record the excursion with the same magnitude although several black shales occur through the paris basin toarcian section it is only that associated with the onset of the oae that coincides with a large negative carbon isotope excursion taken together these observations indicate that during this event the entire water column was characterized by homogeneous carbon isotope values such a pattern is incompatible with the idea that the negative excursion was generated simply through the upwelling of bottom waters enriched in re mineralized organic carbon cf the kuspert model since this would have required a strong vertical gradient in the water column additionally the paris basin data show that the decrease in carbonate 13 c values during the oae occurred in several discrete steps each of some 2 as has previously been found for organic carbon substrates in other european sections the stepped nature of the isotopic profile which is part of a stratigraphic signature previously ascribed to milankovitch forcing is compatible with regular pulsed input of light carbon into the whole atmosphere ocean system from a climatically sensitive source such as gas hydrate or from thermal methanogenesis of organic rich sediments in the karoo ferrar large igneous province contrasts in the amplitude of the negative carbon isotope excursion on a regional scale remain an important unexplained aspect of the toarcian record

long range acoustic communication in deep water using a towed array in september 2010 a long range acoustic communication lrac10 experiment was carried out in deep water off the southern california coast the experiment involved two mobile components 1 a source towed slowly at a speed of 2 3 knots at 75 m depth and 2 a horizontal line array towed at 3 5 knots at a depth of 200 m phase coherent communication sequences were transmitted in the frequency band of 200 300 hz at various ranges 100 700 km initial analysis of the lrac10 data demonstrates that an information rate of 50 bits s can be achieved over 550 km range using quadrature phase shift keying qpsk modulation and error correction coding combined with beamforming

sedimentary and biological response to sea level and palaeoceanographic changes of a lower middle jurassic tethyan platform margin southern alps italy abstract the sediment succession formed at the platform to basin transition along the western margin of a jurassic tethyan carbonate platform records a cyclicity in the order of 3 10 my these cycles are interpreted as due to sea level fluctuations associated to palaeoceanographic changes of the surface waters as inferred by the evolutionary dynamics of the calcareous nannofossils overimposed to these variations the skeletal composition of the platform succession records a longer term order of 50 my trend of progressive environmental deterioration related to the break up of pangea our case study deals with the venetian platform margin and the lombardian basin of the southern alps italy a lower to middle jurassic platform basin system of the western tethys four depositional sequences have been recognized in the lower to middle jurassic the local sea level curve derived from sequence analysis records a short lived on the venetian platform the skeletal sediment composition of the carbonate platform changed from sinemurian domerian photozoan to toarcian heterozoan assemblages dominated by suspension feeders this change appears due to increased trophic resources the older event of platform demise correlates to the sea level drop of the latest domerian the final drowning of the venetian platform occurred after the early aalenian drop in the sea level among the basin biota calcareous nannofossils represent the major pelagic carbonate producer since the beginning of the jurassic nevertheless the sinemurian bajocian deep sea carbonates of the lombardian basin consist mainly of allochthonous mud exported off platform with a low nannoplanktonic contribution moreover the platform demise correlates with condensation gaps and mass flows in the basin this relationship suggests that the growth history of the carbonate platform directly controlled the carbonate sedimentation in the adjacent basin the nannofloras recorded in the lower and middle jurassic successions of the lombardian basin consist of two different taxonomic groups the genus schizosphaerella a group of uncertain systematic affinity and several genera of coccolithophorids an inverse correlation between the abundance of schizospheres and coccoliths has been recorded throughout the whole interval investigated moreover during periods of platform and sea level fall schizosphaerella spp dropped in abundance whereas rates of coccolith diversification calculated according to roth s equations reached peak values our evidence shows that schizospheres could be oligotrophic forms while coccolithophorids on the contrary probably diversified during periods of increased nutrient resources the observed sea level falls are in phase with increased trophic resources and holds on up to the transgressive interval the biological response includes a dramatic drop of the platform carbonate productivity and increased corg accumulation on the sea floor the long term evolution of the sedimentary system records increasing eutrophication from liassic to dogger as reflected by the compositional changes of the carbonate producers

basin scale time reversal communications during november 1994 broadband acoustic signals were transmitted from a 75 hz source to a 20 element 700 m vertical array at approximately 3250 km range in the eastern north pacific ocean as part of the acoustic engineering test aet of the acoustic thermometry of ocean climate atoc program worcester et al j acoust soc am 105 3185 3201 1999 the aet tomography signal can be treated as a binary phase shift keying bpsk communication signal with an information rate of 37 5 bits s with the multipath arrivals spanning 5 8 s this data represents an extreme case of intersymbol interference isi the aet array data are processed using time reversal combined with frequent channel updates to accommodate channel variations over the 20 min long reception followed by a single channel decision feedback equalizer dfe the almost error free performance using all 20 array elements demonstrates the feasibility of time reversal communications further comparable performance of single receive element

organic geochemistry of the lower toarcian posidonia shale in nw europe abstract a suite of core and outcrop samples of the lower toarcian posidonia shale and time equivalent deposits was collected from multiple locations including southern germany swabian alb and franconian alb northern germany the east coast of great britain the netherlands and luxembourg in order to study major differences and similarities with respect to depositional environment and redox potential based on molecular geochemical data all samples are immature or in the early oil window with the highest thermal maturity occurring in the profile from great britain about 0 7 vitrinite reflectance molecular geochemical maturity parameters were used to quantify maturation in detail during shale deposition in the west cleveland basin great britain h 2 s was immediately consumed in the water column by terrigenous input supplying abundant reactive iron to form pyrite these samples are characterized by low dibenzothiophene phenanthrene ratios 95 of 2 and h 2 s in contrast sulfidic euxinic bottom waters possibly with enhanced salinity and stratified water column prevailed due to a more restricted iron supply in luxembourg northern germany and the franconian alb of southern germany a more oxygenated dysoxic bottom water column associated with anoxic sediments i e anoxic dysoxic boundary close to the sediment water interface prevailed in the swabian alb of southern germany despite observed changes within each vertical profile at each site large scale regional trends in depositional conditions can be clearly identified for the early toarcian

impact of ocean variability on coherent underwater acoustic communications during the kauai experiment kauaiex during the july 2003 acoustic communications experiment conducted in 100 m deep water off the western side of kauai hawaii a 10 s binary phase shift keying signal with a symbol rate of 4 kilosymbol s was transmitted every 30 min for 27 h from a bottom moored source at 12 khz center frequency to a 16 element vertical array spanning the water column at about 3 km range the communications signals are demodulated by time reversal multichannel combining followed by a single channel decision feedback equalizer using two subsets of array elements whose channel characteristics appear distinct 1 top 10 and 2 bottom 4 elements due to rapid channel variations continuous channel updates along with doppler tracking are required prior to time reversal combining this is especially true for the top 10 elements where the received acoustic field involves significant interaction with the dynamic ocean surface the resulting communications performance in terms of output signal to noise ratio exhibits significant change over the 27 h transmission duration this is particularly evident as the water column changes from well mixed to a downward refracting environment

astronomical forcing and chronology of the early toarcian early jurassic oceanic anoxic event in yorkshire uk 1 during the early toarcian 183 ma ago a high rate of organic carbon burial globally over a brief interval of time has led to the recognition of a major oceanic anoxic event oae a pronounced negative excursion in the carbon isotope composition of marine organic matter marine carbonate and terrestrial plant material is a key feature of this event but the precise timescale and cause s of this isotopic anomaly are debated associated with the negative carbon isotope excursion is evidence for a coeval rise in seawater palaeotemperature an increase in continental weathering rates and the mass extinction of marine invertebrate species the early toarcian oae provides evidence for the earth s response during rapid climate change and critical to our understanding of the event is a high resolution timescale that allows us to quantify the rates duration and lead lag times of environmental processes in this study we present 2743 new high resolution organic carbon sulphur and carbonate concentration data from samples of well preserved organic rich mudrocks spanning the early toarcian oae in yorkshire uk we have used these data to document the geochemical changes and significantly extend and refine the astronomical timescale across this event our detailed analysis of the relationship between astronomical forcing and carbon isotope changes in both yorkshire and a section from peniche portugal indicates that astronomical forcing paced the timing of major shifts in 13c and hence climate in both sections our analyses also demonstrate that there was a marked increase in the relative strength of astronomical forcing recorded at the onset of the oae and that the recorded nature of astronomical forcing changed during the event both the yorkshire and peniche cyclostratigraphies suggest that one astronomical forcing parameter paced environmental change through the 13c event and that this parameter was obliquity or precession

calibrating the magnitude of the toarcian carbon cycle perturbation sedimentary rocks recording the toarcian oceanic anoxic event t oae are marked by a negative carbon isotope excursion cie reaching up to 7 and ranking among the largest known in the phanerozoic these records suggest a dramatic perturbation of the carbon cycle that has been linked to the transfer of juvenile carbon from the endogenic to the exogenic reservoirs nevertheless the magnitude of the toarcian cie varies significantly from one substrate to another hence complicating mass balance evaluation of the potential driving mechanisms here we show using high resolution paired records of 13ctotal organic carbon toc and hydrogen index from the denkingen core and dotternhausen quarry germany that the amplitude of the negative cie in marine organic matter is considerably exaggerated by changes in organic matter sourcing our corrected 3 4 cie implies a constant carbon isotope fractionation between organic and carbonate carbon across the t oae and may point to a prominent role of cyanobacteria as organic matter producers during the early jurassic these results also suggest that the difference between inorganic and organic carbon isotope values in marine strata constitutes a poor proxy of pco2 levels across the t oae moreover this corrected 3 4 cie together with evidence for 5 c seawater warming across the t oae point to the input of 25 000 gt c with much more 13c enriched signature than previously modeled our results thus allow reconciling inorganic and organic 13c records of the t oae and have important implications for the evaluation of their causal mechanisms

transarctic acoustic telemetry on april 9 and 13 1999 two arctic climate observation using underwater sound tomography signals were transmitted from a 20 5 hz acoustic source moored at the franz victoria strait to an eight element 525 m vertical array at ice camp aplis in the chukchi sea at a distance of 2720 km the transmitted signal was a 20 min long 255 digit m sequence that can be treated as a binary phase shift keying communication signal with a data rate of 2 bits s the almost error free performance using either spatial diversity three elements for a single transmission or temporal diversity two transmissions with a single element demonstrates the feasibility of ice covered trans arctic acoustic communications

carbon cycle dynamics following the end triassic mass extinction constraints from paired δ13ccarb and δ13corg records 1 constraining the carbon isotopic changes associated with the end triassic mass extinction is key to understanding the causes of the extinction and dynamics of recovery from it yet the pattern and timing of 13c variation surrounding the extinction remain poorly constrained here we present close to 1000 new 13c measurements from six newly sampled sections in italy we observe a sharp negative excursion in 13ccarb coincident with the disappearance of the triassic fauna and two positive excursions above it the negative 13ccarb excursion in these sections does not occur in 13corg suggesting a possible diagenetic origin in contrast the interval of elevated 13c occurs in both carbonate and organic carbon suggesting that it is likely to be a primary feature the positive excursions in the lombardy basin southern alps and mt cefalo southern apennines appear to be time correlative on the basis of their position above the disappearance of characteristically triassic biota however it is less certain that they are time correlative with positive excursions in other sections worldwide as few options exist that honor both bio and chemostratigraphy nonetheless similarity to other events that are interpreted as global as well as carbon cycle considerations suggest that the isotopic enrichment is best interpreted to reflect a shift in the isotope composition of the global surface carbon reservoir our data indicate that perturbation of the global carbon cycle was not confined to the immediate vicinity of the extinction interval but rather persisted for substantial length of geologic time afterwards

osmium isotope evidence for two pulses of increased continental weathering linked to early jurassic volcanism and climate change large igneous provinces lips are proposed to have caused a number of episodes of abrupt environmental change by increasing atmospheric co2 levels which were subsequently alleviated by drawdown of co2 via enhanced continental weathering and burial of organic matter here the sedimentary records of two such episodes of environmental change the toarcian oceanic anoxic event t oae and preceding pliensbachian toarcian pl to event both possibly linked to the karoo ferrar lip are investigated using a new suite of geochemical proxies that have not been previously compared stratigraphic variations in osmium isotope 187os 188os records are compared with those of mercury hg and carbon isotopes 13c in samples from the mochras core llanbedr farm cardigan bay basin wales these sedimentary rocks are confirmed as recording an open marine setting by analysis of molybdenum uranium enrichment trends indicating that the os isotope record in these samples reflects the isotopic composition of the global ocean the os isotope data include the first results across the pl to boundary when seawater 187os 188os increased from 0 40 to 0 53 in addition to new data that show elevated 187os 188os from 0 42 to 0 68 during the t oae both increases in 187os 188os correlate with negative carbon isotope excursions and increased mercury concentrations supporting an interplay between terrestrial volcanism weathering and climate that was instrumental in driving these distinct episodes of global environmental change these observations also indicate that the environmental impact of the karoo ferrar lip was not limited solely to the t oae

globally enhanced mercury deposition during the end pliensbachian extinction and toarcian oae a link to the karoo ferrar large igneous province the mesozoic era featured emplacement of a number of large igneous provinces lips formed by the outpouring of millions of cubic kilometres of basaltic magma the radiometric ages of several mesozoic lips coincide with the dates of oceanic anoxic events oaes as a result of these coincidences a causal link has been suggested but never conclusively proven this study explores the use of mercury as a possible direct link between the karoo ferrar lip and the coeval toarcian oae t oae mercury is emitted to the atmosphere as a trace constituent of volcanic gas and may be distributed globally before being deposited in sediments modern marine deposits show a strong linear correlation between mercury and organic matter content results presented here indicate departures from such a simple linear relationship in sediments deposited during the t oae and also during the pliensbachian toarcian transition an event that saw elevated benthic extinctions and carbon cycle perturbations prior to the t oae a number of depositional settings illustrate an increased mercury concentration in sediments that record one or both events suggesting a rise in the depositional flux of this element complications to this relationship may arise from very organic rich sediments potentially overprinting any hg toc signal whereas environments preserving negligible organic matter may leave no record of mercury deposition however the global distribution of coevally elevated hg rich levels suggests enhanced atmospheric mercury availability during the early toarcian potentially aided by the apparent affinity of hg for terrestrial organic matter although the relative importance of aquatic vs terrestrial fixation of hg in governing these enrichments remains uncertain a perturbation in atmospheric hg is most easily explained by enhanced volcanic output it is suggested that extrusive igneous activity caused increased mercury flux to the early toarcian sedimentary realm supporting the potential of this element as a proxy for ancient volcanism this interpretation is consistent with a relationship between lip formation and a perturbed carbon cycle during the pliensbachian toarcian transition and t oae the recording of these two distinct hg excursions may also indicate that the karoo ferrar lip released volatiles in temporally distinct episodes due either to multiple phases of magmatic emplacement or sporadic release of thermogenic gaseous products from intrusion of igneous material into volatile rich lithologies

reply to the comment by boulila and hinnov towards chronology of the early toarcian environmental crisis in the lorraine sub basin ne paris basin by w ruebsam p munzberger and l schwark earth and planetary science letters 404 2014 273 282

elemental and oxygen isotope composition of early jurassic belemnites salinity vs temperature signals well preserved calcitic belemnite samples from the basque cantabrian basin of northern spain have been analyzed to improve our current understanding of the chemistry of seawater as an index of paleoceanographic changes during the early jurassic a period punctuated by times of oceanic anoxia and global mass extinctions because the oxygen isotope composition of calcite depends not only on temperature but also on salinity we present here a combination of sr ca mg ca and 18o analyses that helped us to evaluate both effects separately comparison between the temporal records and cross plots of these geochemical parameters shows a good correlation of mg ca with 18o and a weak correlation of sr ca with 18o comparison of our belemnite 18o record with coeval o isotope profiles from other paleogeographic domains suggests the existence despite differences in the absolute isotopic values of a major negative shift during the serpentinus zone that is regionally reproducible this event is linked to the early toarcian ocean anoxic event oae and suggests the existence of global changes in paleoclimatic and paleoceanographic conditions that are reflected largely in the geochemical composition of seawater compared to our results however other early toarcian 18o data reported from northern european basins are generally depleted 1 3 1 6 in contrast mg ca ratios display similar values these differences in 18o data suggest a salinity component for the northern european data and provide evidence for a north to south salinity gradient within the north european interior boreal seaway during the early jurassic this study suggests that the secular variation of mg ca is a useful proxy for discriminating between temperature and salinity effects on the oxygen isotope composition of fossil shells and highlights the prospect of using the mg ca ratios of belemnite calcite to calculate paleotemperatures independently of salinity the findings of our study may help to calibrate 18o curves in other basins by removing the salinity component of their 18o records which may help to calculate water density gradients between the jurassic seas of northern and southern europe

organic accumulation in lacustrine rift basin constraints from mineralogical and multiple geochemical proxies the lunpola basin in the central tibet is the highest petroliferous basin in the world the basin is a cenozoic lacustrine rift basin with widespread oil shale depositions which provide a valuable example for understanding the mechanisms of organic accumulation thirty five samples of oil shale and mudstone were collected from one of the organic rich oil shale intervals in the lunpola basin to discuss the controlling factors of organic enrichment in the investigated oil shale interval many redox proxies including v v ni ratios mo u covariations and pyrite framboid size distribution suggest anoxic conditions however the almost consistent variation patterns of toc p and mo contents indicate that organic matter accumulation was controlled mainly by primary productivity the relatively low sr ba average 0 74 and sr cu ratios average 4 75 suggest a warm humid climate during the oil shale deposition these conditions are suitable for living of organisms which would raise the initial productivity of lake and in turn could have led to the oxygen depleted conditions the detrital input together with fast sedimentary rate during the oil shale deposition would result in dilution of organic matter

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

molybdenum isotope evidence for global ocean anoxia coupled with perturbations to the carbon cycle during the early jurassic relatively brief periods of severe paleoenvironmental change during the jurassic and cretaceous were associated with the widespread accumulation of organic rich marine deposits termed oceanic anoxic events oaes these intervals involved abrupt global warming of 5 10 c higher rates of continental weathering elevated extinction rates and large scale perturbations to the global carbon cycle the major oaes also overlapped temporally the emplacement of large igneous provinces however despite being known as oaes the extent of seawater anoxia at those times is undefined and the causative processes remain unclear here we show how changes in seawater molybdenum isotope ratios a proxy for seawater anoxia during the toarcian early jurassic oae define the onset and expansion of oxygen deficient conditions our data also place constraints on the areal extent of marine anoxia during the event and demonstrate that anoxia expanded and contracted periodically broadly in line with precession driven changes in 13 corg despite their intermittent occurrence over geological history oaes have an important contemporary relevance because the magnitude and high rates of environmental change then were broadly similar to those occurring at the present day