nutrients as the dominant control on the spread of anoxia and euxinia across the cenomanian turonian oceanic anoxic event oae2 model data comparison 1 the cenomanian turonian oceanic anoxic event oae2 is characterized by large perturbations in the oxygen and sulfur cycles of the ocean potentially resulting from changes in oxygen supply via oxygen solubility and ocean circulation and in marine productivity we assess the relative impact of these mechanisms comparing model experiments with a new compilation of observations for seafloor dysoxia anoxia and photic zone euxinia the model employed is an intermediate complexity earth system model which accounts for the main ocean dynamics and biogeochemistry of the cretaceous climate the impact of higher temperature and marine productivity is evaluated in the model as a result of higher atmospheric carbon dioxide and oceanic nutrient concentrations the model shows that temperature is not alone able to reproduce the observed patterns of oceanic redox changes associated with oae2 observations are reproduced in the model mainly via enhanced marine productivity due to higher nutrient content responsible for 85 of the change higher phosphate content could have been sustained by increased chemical weathering and phosphorus regeneration from anoxic sediments which in turn induced an enhanced nitrogen nutrient content of the ocean via nitrogen fixation the model also shows that the presence of seafloor anoxia as suggested by black shale deposition in the proto north atlantic ocean before the event might be the result of the silled shape and lack of deep water formation of this basin at the late cretaceous overall our model data comparison shows that oae2 anoxia was quasi global spreading from 5 of the ocean volume before the event to at least 50 during oae2

molybdenum behavior during early diagenesis insights from mo isotopes 1 we present molybdenum isotope and concentration data from 14 sites in the eastern pacific from the central california to the peru margin the environments studied have been chosen to represent a broad range in oxidation reduction redox potential which provide a framework for the behavior of this redox sensitive element manganese rich hemipelagic sediments from the eastern tropical pacific have a mean characteristic mo isotope signature 98 95mo 0 49 0 04 two times the standard deviation of the mean 2 sdom with n 14 that reflects fractionation between ocean water and authigenic mo associated with mn oxides authigenic fe mo s deposits from reducing continental margin settings also have a characteristic mo isotopic signature 98 95mo 1 64 0 04 2 sdom with n 136 both of these values are in contrast to highly sulfidic 11 m h2saq restricted basin environments which contain mo isotope values analytically indistinguishable from seawater in terms of the mo isotope composition the modern oceanic mo sink is dominated by continental margin type environments where 98 95mo 1 6 and mn rich sediments where 98 95mo approximately 0 5 with a minor contribution from euxinic settings where h2saq 11 m

palaeotemperatures still exist in the greenland ice sheet the temperature distribution through the greenland ice sheet at the dye 3 borehole is a record of the past climatic changes in the arctic the numerical model of the temperature distribution now presented reproduces the observed temperature distribution within 0 03 k and shows that the basal ice is still cooled 5 k by the cold ice age climate the results suggest a mean ice age temperature of 32 2 c which is 12 k colder than the present temperature and a precipitation rate 50 25 of the present rate calculations of a more detailed temperature history through the present inter glacial period reveal evidence of the ad 1920 50 maximum the little ice age and the atlantic period

the anatomy of last glacial maximum climate variations in south westland new zealand derived from pollen records abstract we present pollen records from three sites in south westland new zealand that document past vegetation and inferred climate change between approximately 30 000 and 15 000 cal yr bp detailed radiocarbon dating of the enclosing sediments at one of those sites galway tarn provides a more robust chronology for the structure and timing of climate induced vegetation change than has previously been possible in this region the kawakawa oruanui tephra a key isochronous marker affords a precise stratigraphic link across all three pollen records while other tie points are provided by key pollen stratigraphic changes which appear to be synchronous across all three sites collectively the records show three episodes in which grassland interpreted as indicating mostly cold subalpine to alpine conditions was prevalent in lowland south westland separated by phases dominated by subalpine shrubs and montane lowland trees indicating milder interstadial conditions dating expressed as a bayesian estimated single best age followed in parentheses by younger older bounds of the 95 confidence modelled age range indicates that a cold stadial episode whose onset was marked by replacement of woodland by grassland occurred between 28 730 29 390 28 500 and 25 470 26 090 25 270 cal yr bp years before ad 1950 prior to the deposition of the kawakawa oruanui tephra milder interstadial conditions prevailed between 25 470 26 090 25 270 and 24 400 24 840 24 120 cal yr bp and between 22 630 22 930 22 340 and 21 980 22 210 21 580 cal yr bp separated by a return to cold stadial conditions between 24 400 and 22 630 cal yr bp a final episode of grass dominated vegetation indicating cold stadial conditions occurred from 21 980 22 210 21 580 to 18 490 18 670 17 950 cal yr bp the decline in grass pollen indicating progressive climate amelioration was well advanced by 17 370 17 730 17 110 cal yr bp indicating that the onset of the termination in south westland occurred sometime between ca 18 490 and ca 17 370 cal yr bp a similar general pattern of stadials and interstadials is seen to varying degrees of resolution but generally with lesser chronological control in many other paleoclimate proxy records from the new zealand region this highly resolved chronology of vegetation changes from southwestern new zealand contributes to the examination of past climate variations in the southwest pacific region the stadial and interstadial episodes defined by south westland pollen records represent notable climate variability during the latter part of the last glaciation similar climatic patterns recorded farther afield for example from antarctica and the southern ocean imply that climate variations during the latter part of the last glaciation and the transition to the holocene interglacial were inter regionally extensive in the southern hemisphere and thus important to understand in detail and to place into a global context

uv induced mass independent sulfur isotope fractionation in stratospheric volcanic sulfate 1 sulfuric acid aerosols produced in the stratosphere following massive volcanic eruptions possess a mass independent sulfur isotopic signature acquired when volcanic so2 experiences uv photooxidation the volcanic data are consistent with laboratory so2 photooxidation experiments using uv light at 248 nm maximum absorption of ozone whereas sulfur isotopic anomalies previously observed in archean samples are consistent with photodissociation at 190 220 nm a mechanism of so2 photooxidation occurring in the early stage of a stratospheric volcanic plume in the range of 220 320 nm weak band absorption of so2 is also proposed since mass independent sulfur isotope anomalies in stratospheric volcanic sulfate appear to depend on the exposure of so2 to uv radiation their measurements might therefore offer the possibility to determine the degree of uv penetration in the ozone absorption window for the present and past atmospheres they can also be used to determine the stratospheric or tropospheric nature of volcanic eruptions preserved in glaciological records offering the possibility to reassess the climatic impact of past volcanic eruptions

enhanced productivity led to increased organic carbon burial in the euxinic north atlantic basin during the late cenomanian oceanic anoxic event 1 three cenomanian turonian c t 93 5 ma black shale sections along a northeast southwest transect in the southern part of the proto north atlantic ocean were correlated by stable carbon isotope stratigraphy using the characteristic excursion in 13c values of both bulk organic matter om and molecular fossils of algal chlorophyll and steroids all three sites show an increase in marine organic carbon oc accumulation rates during the c t oceanic anoxic event oae the occurrence of molecular fossils of anoxygenic photosynthetic green sulfur bacteria lack of bioturbation and high abundance of redox sensitive trace metals indicate sulfidic conditions periodically reaching up into the photic zone before as well as during the c t oae during the c t oae there was a significant rise of the chemocline as indicated by the increase in concentrations of molecular fossils of green sulfur bacteria and mo al ratios the presence of molecular fossils of the green strain of green sulfur bacteria indicates that euxinic conditions periodically even occurred at very shallow water depths of 15 m or less during the c t oae however bottom water conditions did not dramatically change as indicated by more or less constant v al and zn al ratios at site 367 this suggests that the increase in oc burial rates resulted from enhanced primary productivity rather than increased anoxia which is supported by stable carbon isotopic evidence and a large increase in ba al ratios during the c t oae the occurrence of the productivity event during a period of globally enhanced organic carbon burial rates i e the c t oae points to a common cause possibly related to the formation of a deep water connection between north and south atlantic basins

single particle mineralogy of microparticles from himalayan ice cores using sem edx and atr ftir imaging techniques for identification of volcanic ash signatures abstract in this study insoluble microparticles from four discrete layers of ice cores drilled out from the east rongbuk glacier of the himalayas were characterized on a single particle basis by scanning electron microscopy coupled with energy dispersive x ray spectrometry sem edx and attenuated total reflectance fourier transform infrared atr ftir imaging the combined application of the two single particle analytical techniques for the analysis of the same individual particles provided complementary information i e their elemental compositions and morphology by sem edx and their molecular species functional groups and crystallinity by atr ftir imaging which is crucial for the definite identification of the mineral species including their polymorphs the results showed that the integrated signatures of volcanic ash va involving their mineralogical characteristics for silica polymorphs vitreous nature of silica and silicate particles chemical heterogeneity within the micrometer sized particles and unique morphology can be used to clearly differentiate micrometer sized va from the mineral dust of a soil origin on a single particle basis the different mineralogical characteristics among the volcanic samples would be due to their association with different volcanic eruptions

characteristics and possible source of a 1479 a d volcanic ash layer in a greenland ice core abstract a microparticle concentration peak in a gisp2 ice core contains volcanic glass shards of rhyolitic composition that correspond in age to the 1479 1480 a d mt st helens wn eruption these glass shards are compositionally similar to the wn tephra and constitute 83 of the total particle population the shards are very coarse grained up to 40 m diameter suggesting rapid transport from their source to greenland a major sulfate peak in the ice occurs approximately 4 months after deposition of the glass shards this difference in depositional timing suggests primarily tropospheric transport of the ash and stratospheric transport of the sulfate aerosol large scale climatic perturbations following this eruption were evidently negligible glaciochemical seasonal indicators suggest a late fall to early winter 1479 a d eruption

volcanic triggering of late pliocene glaciation evidence from the flux of volcanic glass and ice rafted debris to the north pacific ocean abstract mass accumulation rates mar of different components of north pacific deep sea sediment provide detailed information about the timing of the onset of major northern hemisphere glaciation that occurred at 2 65 ma an increase in explosive volcanism in the kamchatka kurile and aleutian arcs occurred at this same time suggesting a link between volcanism and glaciation sediments recovered by piston coring techniques during odp leg 145 provide a unique opportunity to undertake a detailed test of this possibility here we use volcanic glass as a proxy for explosive volcanism and ice rafted debris ird as a proxy for glaciation the mar of both glass and ird increase markedly at 2 65 ma further the flux of the volcanic glass increased just prior to the flux of ice rafted material suggesting that the cooling resulting from explosive volcanic eruptions may have been the ultimate trigger for the mid pliocene glacial intensification

past volcanism and climate revealed by greenland ice cores abstract a new method is outlined for estimating the annual injection of volcanic acids mainly sulphuric into the upper troposphere and the stratosphere the potentiality of the method is demonstrated by data on a number of historically well known eruptions analyses of annual layers in a mid greenland ice core reveal a continuous year by year record of the volcanic activity north of 20 s back to a d 553 comparison with various climatic records suggests that periods of frequent and violent eruptions usually coincide with cold climatic conditions for example the highest volcanic activities since a d 553 occurred in a d 1250 1500 and a d 1550 1700 i e in the initial and the culminating phases of the little ice age

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

a new particulate mn fe p shuttle at the redoxcline of anoxic basins abstract pelagic redoxclines of anoxic basins and deeps form the suboxic transition between oxygenated surface and anoxic or even sulfidic bottom waters intense element cycling favoured by elevated microbial activity causes steep gradients of physico chemical parameters nutrients and redox sensitive trace metals this study presents a conceptual model for authigenic particle formation at pelagic redoxclines which is based on the tight coupling of mn fe and p cycles besides the well known occurrence of mn oxides textural sem edx and geochemical icp oes icp ms analyses of particles from the redoxclines of the black sea and the baltic sea gotland basin landsort deep evidence the existence of earlier postulated fe oxyhydroxo phosphates and emphasize mixed phases consisting of mn oxides and fe oxyhydroxo phosphates as a new solid species most of the analyzed particles are star shaped of about 5 m in size and occur as single particles or aggregates without any morphological differences between mn oxides fe oxyhydroxo phosphates and mixed phases throughout the redoxcline these minerals show a general succession with maximum abundance of mn oxides above the redoxcline followed by mixed phases and almost pure fe phosphates within and below the redoxcline respectively molar fe p ratios of single particles argue against the formation of known pure fe phosphates like vivianite or strengite at the lower end of the redox transition zone but are consistent with recent experimental findings for colloidal p bearing hydrous ferric oxides moreover morphological similarities suggest the formation of irregular fe oxyhydroxo coatings due to oxidation of upward diffusing fe 2 by oxygen and stepwise replacement of mn iv by fe iii on sinking mno x particles followed by immediate adsorption or even co precipitation of phosphate batch type experiments using biogenic mno x particles demonstrate the efficient potential of fe 2 oxidation by sinking mno x particles when entering sulfidic waters mno x particles are progressively reduced leading to an increasing relative abundance of fe and p rich particles in deeper parts of the water column these particles are also reductively dissolved thereby releasing fe 2 and phosphate to the water column this mn fe p shuttle likely affects phosphate transport throughout the water column and thus impacts primary production at least over longer time scales furthermore the particulate mn fe p shuttle must have played an important role for the cycling of p and certain trace metals in ancient ocean basins e g during certain periods of cretaceous black shale formation and should be considered in future mass balances and modeling approaches dealing with oxic anoxic interfaces of aquatic ecosystems

new la icp ms cryocell and calibration technique for sub millimeter analysis of ice cores ice cores provide a robust reconstruction of past climate however development of timescales by annual layer counting essential to detailed climate reconstruction and interpretation on ice cores collected at low accumulation sites or in regions of compressed ice is problematic due to closely spaced layers ice core analysis by laser ablation inductively coupled plasma mass spectrometry la icp ms provides sub millimeter scale sampling resolution on the order of 100 m in this study and the low detection limits ng l 1 necessary to measure the chemical constituents preserved in ice cores we present a newly developed cryocell that can hold a 1m long section of ice core and an alternative strategy for calibration using ice core samples from central greenland we demonstrate the repeatability of multiple ablation passes highlight the improved sampling resolution verify the calibration technique and identify annual layers in the chemical profile in a deep section of an ice core where annual layers have not previously been identified using chemistry in addition using sections of cores from the swiss italian alps we illustrate the relationship between ca na and fe and particle concentration and conductivity and validate the la icp ms ca profile through a direct comparison with continuous flow analysis results

determination of molybdenum isotope fractionation by double spike multicollector inductively coupled plasma mass spectrometry 1 molybdenum isotopic compositions are precisely determined by mc icp ms measurements using a mo double spike the double spike is added prior to chemical purification so that laboratory and instrumental mass fractionations are separated from natural mass dependent fractionation fractionation is determined on four mo mass ratios providing an internal consistency check the external standard reproducibility is at 0 06 per mil on the 98mo 95mo ratio 2 standard deviation using a normal microconcentric nebuliser with a cyclonic spray chamber the minimum quantity of mo is 1 g for high precision results a hydrothermal molybdenite shows fractionation of 0 3 per mil on the 98mo 95mo ratio relative to our standard johnson matthey 1000 g ml 0 3 icp standard solution lot 602332b fine grained sediments show fractionation of 0 1 and 0 3 per mil on the 98mo 95mo ratio the observed mo isotope fractionation is small but resolvable with the presented high resolution technique

volcanic ash layers from the last glacial termination in the ngrip ice core the tephrochronological record of the 1400 1640 m depth 10 000 16 000 calendar ice core years before present of the ngrip ice core has been established by particle screening of selected samples ash was identified in 20 samples correlation with ice marine and terrestrial records from volcanic source regions in the northern hemisphere positively identifies the saksunarvatn ash and the vedde ash ash zone 1 major element chemistry of the remaining identified ash layers mainly points towards an icelandic origin this tephrochronological record provides new important marker horizons for correlating the timing of the climatic changes associated with the last glacial termination within the north atlantic region as well as outlining more details concerning the frequency and composition of volcanic eruptions occurring at this deglaciation copyright 2005 john wiley sons ltd

synchronous deposition of volcanic ash and sulfate aerosols over greenland in 1783 from the laki eruption iceland 1 sulfate aerosols from the 1783 1784 a d laki eruption are widely used as a reference horizon for constraining greenland ice core time scales yet the timing of the arrival of the sulfate remains under discussion two ice cores from western greenland analyzed with high temporal resolution confirm that sulfate aerosols arrived over greenland late in 1783 concomitant with the tephra elevated concentrations of cd bi and tl all indicators of volcanic emissions and with a short lived rare earth elements anomaly thereafter sulfate deposition declined rapidly very modest concentrations of sulfate in 1784 snowfall evident in six greenland cores suggest a relatively short less than 1 year atmospheric residence time and an injection height limited to the lower stratosphere an improved estimate of the associated stratospheric sulfate burden is calculated and provides an important input for models assessing climatic impacts of this volcanic eruption

molybdenum isotope fractionation during adsorption by manganese oxides the isotopic composition of mo 97 95mo in seawater is 2 heavier than mo in marine ferromanganese crusts and nodules barling et al earth planet sci lett 193 2001 447 457 siebert et al earth planet sci lett 211 2003 159 171 to explore this phenomenon we have conducted an experimental investigation into the mass dependent fractionation of mo isotopes during adsorption onto mn oxyhydroxide two series of experiments were carried out a time series in which adsorption proceeded for 2 96 h and a ph series in which ph varied from 6 5 to 8 5 the extent of mo adsorption by mn oxyhydroxides decreases with increasing ph a trend typical of anion adsorption and takes 48 h to reach steady state lighter mo isotopes are preferentially adsorbed experimentally determined fractionation factors soln mnox exhibit no systematic variation with either time or experimental ph the mean soln mnox for all experiments is 1 0018 0 0005 2 s d comparison of the mo isotopic data for experimental solutions and mo adsorbed to mn oxyhydroxide with predictions for closed system equilibrium and rayleigh fractionation models indicates that isotope fractionation occurs as a result of closed system equilibrium exchange between dissolved and adsorbed mo the isotopic offset between dissolved and adsorbed mo is comparable to that observed between mo in seawater and mo in ferromanganese nodules and crusts it is therefore likely that adsorption of mo to mn oxyhydroxides is a significant factor in the fractionation of mo isotopes in the oceans

atmospheric aerosol loading and transport due to the 1783 84 laki eruption in iceland interpreted from ash particles and acidity in the gisp2 ice core abstract glass shards from the a d 1783 laki fissure eruption in iceland have been identified in the gisp2 ice core from summit greenland at a level just preceding the major acidity sulfate peak detailed reconstruction of ice stratigraphy coupled with analyses of solid particles from filtered samples indicate that a small amount of laki ash was carried via atmospheric transport to greenland in the summer of 1783 whereas the main aerosol precipitation occurred in the summer and early fall of 1784 sulfate concentrations in the ice increase slightly during late summer and fall of 1783 and remain steady throughout the winter due to slow oxidation rates during this season in the arctic the sulfate concentration rises dramatically in the spring and summer of 1784 producing a massive sulfate peak previously believed to have accumulated during the summer of 1783 and commonly used as the marker horizon in greenland ice core studies the chronology of ash and acid fallout at the gisp2 site suggests that a significant portion of the laid eruption plume penetrated the tropopause and that aerosol generated from it remained aloft for at least 1 yr after the eruption based on comparisons with other glaciochemical seasonal indicators abnormally cool conditions prevailed at summit during the summer of 1784 this further supports the claim that a significant volume of sulfate aerosol remained in the arctic middle atmosphere well after the eruption had ceased

long range transport of volcanic ash to the greenland ice sheet betzer et al 1 reported the surprising discovery of giant 75 m mineral particles transported more than 10 000 km from their source we have found volcanic ash containing glass shards as large as 300 m in a section of wisconsinian ice from the dye 3 core in greenland which is similarly unexpected and raises interesting questions concerning the long range aeolian transport of particulate matter as the volcanic ash correlates well with similar ash in deep sea sediment cores from the atlantic it also allows us to date the ice with some confidence

heterogeneous oxygenation states in the atlantic and tethys oceans during oceanic anoxic event 2 abstract the cenomanian turonian boundary ca 93 5 ma is marked by an episode of profound environmental change including a major perturbation of the carbon cycle and an oceanic anoxic event oae 2 here we present molybdenum mo isotope variations within the oae 2 interval for four sections from the western tethys furlo and la contessa and the north atlantic odp site 1276 and dsdp site 367 the main target of this study is to investigate the extent of reducing conditions truly global in extent or restricted to poorly ventilated restricted deep basins with particular reference to the relationship between the change in the oxygenation state of the ocean and the link to global perturbations of the carbon cycle recorded in carbon isotopes all four sections show fluctuations in the redox sensitive trace metal rste distribution suggesting rapid variations in local redox conditions ranging from anoxic to euxinic the rste enrichment factors efs also suggest different depositional conditions and paleoceanographic processes in the western tethys versus the north atlantic whereas the north atlantic sites show evidence of weak watermass restriction associated with the action of a particulate shuttle within the water column the efs of the tethyan sections are characteristic of unrestricted marine systems mo isotopes show surprisingly negative values through the tethyan sections at the onset of oae 2 an increasing trend in mo 98 is observed with values ranging from 0 6 to 0 6 during the second half of oae 2 the mo 98 curve shows a progressive shift towards more negative values in the north atlantic mo 98 signatures from odp site 1276 show a similar behaviour as observed in the western tethys at dsdp site 367 mo isotopes are generally heavier during oae 2 fluctuating around an average value of 1 1 this is consistent with fully euxinic conditions and the black shales deposited may have recorded the seawater signature during oae 2 the mo isotope signature is lighter than the modern ocean value 2 3 and suggests a higher proportion of bottom water euxinia 10 although this estimate is greater than the euxinic fraction in the modern ocean our results challenge the suggestion of a globally euxinic deep waters during oae 2 the variations in mo toc ratios within the north atlantic and tethys oceans are in good agreement with a general drawdown of mo within the oae interval suggesting a general increase in anoxic conditions during oae 2 our results highlight the role of local parameters in the development of euxinia even during period of widespread anoxia such as oaes

trace element abundances in the rock canyon anticline pueblo colorado marine sedimentary section and their relationship to caribbean plateau construction and oxygen anoxic event 2 1 rapid eruption of submarine lava flows during formation of the caribbean plateau correlates closely with ocean anoxic event 2 oae2 which bracketed the cenomanian turonian boundary 93 5 ma these events also correspond with a positive excursion in carbon isotopic composition of seawater hydrothermal activity associated with large scale submarine volcanism may have been responsible for this abrupt change in ocean chemistry we determined the distribution of major minor and trace element abundances in the rock canyon marine sedimentary section pueblo colorado after normalizing element concentrations to zr to remove the variable contribution of terrigenous material to these sediments we detected an interval of concentrated metal abundance anomalies that coincides with the abrupt beginning of the positive 13c isotope excursion the metal abundance anomalies indicate that intermittent hydrothermal activity in the form of both water rock exchange and magmatic degassing introduced large concentrations of trace metals into the cretaceous ocean at the same time that extinctions of benthic species turnover in plankton communities and increases in isotopically light organic carbon burial occurred the stratigraphic position of this interval of trace metal anomalies matches events associated with oae2 and indicates that intermittent hydrothermal activity on a massive scale triggered abrupt changes in carbon burial and deep ocean oxygen contents

basinal restriction black shales re os dating and the early toarcian jurassic oceanic anoxic event 1 profiles of mo total organic carbon toc through the lower toarcian black shales of the cleveland basin yorkshire united kingdom and the posidonia shale of germany and switzerland reveal water mass restriction during the interval from late tenuicostatum zone times to early bifrons zone times times which include that of the putative early toarcian oceanic anoxic event the degree of restriction is revealed by crossplots of mo and toc concentrations for the cleveland basin which define two linear arrays with regression slopes ppm of 0 5 and 17 the slope of 0 5 applies to sediment from the upper semicelatum and exaratum subzones this value which is one tenth of that for modern sediments from the black sea mo toc regression slope 4 5 reveals that water mass restriction during this interval was around 10 times more severe than in the modern black sea the renewal frequency of the water mass was between 4 and 40 ka the mo toc regression slope of 17 applies to the overlying falciferum and commune subzones the value shows that restriction in this interval was less severe and that the renewal frequency of the water mass was between 10 and 130 years the more restricted of the two intervals has been termed the early toarcian oceanic anoxic event but is shown to be an event caused by basin restriction local to nw europe crossplots of re os and mo against toc show similar trends of increasing element concentration with increase in toc but with differing slopes together with modeling of 187 os 188 os and d 98 mo the element toc trends show that drawdown of re os and mo was essentially complete during upper semicelatum and exaratum subzone times mo toc regression slope of 0 5 drawdown sensitized the restricted water mass to isotopic change forced by freshwater mixing so that continental inputs of re os and mo via a low salinity surface layer created isotopic excursions of up to 1 3 in d 98 mo and up to 0 6 for 187 os 188 os restriction thereby compromises attempts to date toarcian black shales and possibly all black shales using re os chronology and introduces a confounding influence in the attempts to use d 98 mo and initial 187 os 188 os for palaeo oceanographic interpretation