marsis remote sounding of localized density structures in the dayside martian ionosphere a study of controlling parameters enhanced topside electron densities in the dayside martian ionosphere have been repetitively observed in areas of near radial crustal magnetic fields for periods of tens of days indicating their long term spatial and temporal stability despite changing solar wind conditions we perform a statistical study of these density structures using the ionospheric mode of the mars advanced radar for subsurface and ionosphere sounding marsis onboard mars express we estimate the apparent extents of these structures relative to the altitude of the surrounding ionosphere the apex of the density structures often lies higher than the surrounding ionosphere median vertical extent of 18 km which indicates upwellings these structures are much wider than they are high with latitudinal scales of several degrees the radar reflector regions are observed above both moderate and strong magnetic anomalies and their precise locations and latitudinal extents match quite well with the locations and latitudinal extents of magnetic structures of given magnetic polarity oblique to vertical fields which happen to be regions where the field lines are open part of the time the majority of the density structures occur in regions where ionospheric plasma is dominant indicating closed field regions shielded from shocked solar wind plasma

dynamics of a stepped carbon isotope excursion ultra high resolution study of early toarcian environmental change abstract in the toarcian early jurassic 183 myr ago the ocean atmosphere system was subject to one of the largest perturbations of the carbon cycle in the last 250 myr known as the toarcian oceanic anoxic event t oae this event was accompanied by a 6 negative carbon isotope excursion cie caused by massive injection of isotopically light carbon into the ocean atmosphere system possibly from destabilisation of gas hydrates this study reveals the pacing and sequence of events leading up to the cie and to widespread deposition of organic rich sediments the very high resolution isotopic record from exceptionally well preserved carbonate and organic matter from the paris basin enables recognition of increased co 2 levels 130 kyr in advance of the major negative cie an accelerated increase in the p co 2 is registered 25 kyr before the onset of this negative excursion and was so rapid and so intense that it led to a water column undersaturated with respect to calcium carbonate in the paris basin undersaturation is expressed as a dramatic drop in the accumulation of the biogenic calcite produced by the surface dwelling calcifiers these environmental perturbations representing precursor phases of co 2 injection predate the first step towards relatively light carbon isotopes in carbonate and organic matter and are tentatively attributed to karoo ferrar magmatism this negative shift was registered slightly earlier in terrestrial carbon than marine carbonate subsequent global warming is credited with liberating isotopically light carbon and ultimately fostered anoxia in the paris basin the response of these cumulative inputs of carbon to the earth system isotopic and sedimentological evidence indicates continuously elevated phytoplanktonic productivity throughout the first step of the negative cie suggesting that the biological pump accelerated the drawdown of excess carbon leading to temporary recovery of carbonate sedimentation 45 kyr after the first step of the cie this re establishment of the saturation state of the water column was only fleeting before the later stepwise release of isotopically light carbon

oblique reflections in the mars express marsis data set stable density structures in the martian ionosphere the mars advanced radar for subsurface and ionospheric sounding marsis onboard the european space agency s mars express mex spacecraft routinely detects evidence of localized plasma density structures in the martian dayside ionosphere such structures likely taking the form of spatially extended elevations in the plasma density at a given altitude give rise to oblique reflections in the active ionospheric sounder data these structures are likely related to the highly varied martian crustal magnetic field in this study we use the polar orbit of mex to investigate the repeatability of the ionospheric structures producing these anomalous reflections examining data taken in sequences of multiple orbits which pass over the same regions of the martian surface under similar solar illuminations within intervals lasting tens of days presenting three such examples or case studies we show for the first time that these oblique reflections are often incredibly stable indicating that the underlying ionospheric structures are reliably reformed in the same locations and with qualitatively similar parameters the visibility or lack thereof of a given oblique reflection on a single orbit can generally be attributed to variations in the crustal field within the ionosphere along the spacecraft trajectory we show that within these examples oblique reflections are generally detected whenever the spacecraft passes over regions of intense near radial crustal magnetic fields i e with a cusp like configuration the apparent stability of these structures is an important feature that must be accounted for in models of their origin

shapes of magnetically controlled electron density structures in the dayside martian ionosphere nonhorizontal localized electron density structures associated with regions of near radial crustal magnetic fields are routinely detected via radar oblique echoes on the dayside of mars with the ionospheric sounding mode of the mars advanced radar for subsurface and ionospheric sounding marsis radar onboard mars express previous studies mostly investigated these structures at a fixed plasma frequency and assumed that the larger apparent altitude of the structures compared to the normal surrounding ionosphere implied that they are bulges however the signal is subjected to dispersion when it propagates through the plasma so interpretations based on the apparent altitude should be treated with caution we go further by investigating the frequency dependence i e the altitude dependence of the shape of 48 density structure events using time series of marsis electron density profiles corrected for signal dispersion four possible simplest shapes are detected in these time series which can give oblique echoes bulges dips downhill slopes and uphill slopes the altitude differences between the density structures and their edges are in absolute value larger at low frequency high altitude than at high frequency low altitude going from a few tens of kilometers to a few kilometers as frequency increases bulges dominate in numbers in most of the frequency range finally the geographical extension of the density structures covers a wide range of crustal magnetic fields orientations with near vertical fields toward their center and near horizontal fields toward their edges as expected transport processes are suggested to be a key driver for these density structures

paleoceanographic changes of the late pliensbachian early toarcian interval a possible link to the genesis of an oceanic anoxic event abstract secular records of the elemental and isotopic composition of belemnite calcite were studied in pliensbachian and toarcian sections from the yorkshire coast uk and southern germany to investigate oceanographic change during an interval prior to and including the toarcian oceanic anoxic event oae records from southern germany are correlated to the uk stratigraphy using strontium isotope stratigraphy the geochemical trends measured from belemnite calcite are consistent between the two sections and are interpreted in terms of temperature and salinity of the northwest european epi continental sea the data suggest that a dramatic environmental change coincided with the toarcian oae belemnite mg ca sr ca and na ca ratios increase by a factor of between 1 7 and 2 coincident with a 3 negative shift in 18o from the mid tenuicostatum zone until the lower falciferum zone of the uk ammonite biostratigraphy a period of 0 6 0 7 myr taken at face value the mg ca and 18o data argue for an abrupt warming of 6 7 c and substantial freshening during this interval global warming accompanied by an accelerated hydrological cycle and increased runoff is proposed to explain these changes prior to these events data from lower in the yorkshire section suggest a possible cooling accompanied by a shift to more saline waters during the period from the upper pliensbachian margaritatus zone to the toarcian lower tenuicostatum zone this earlier event may also have been important in causing density stratification in the northwest european epi continental sea

effects of magnetic anomalies discovered at mars on the structure of the martian ionosphere and solar wind interaction as follows from radio occultation experiments the slopes of the electron density profiles obtained by radio occultation experiments at mars revealed different variations with solar zenith angle in comparison with behavior of the electron density profiles in the magnetic field free ionosphere of venus the results obtained by the mars global surveyor mgs spacecraft show the existence of highly variable and very localized magnetic fields of crustal origin at mars addressing the difference between the ionosphere at venus and mars the scale heights of electron density profiles obtained by radio occultation methods onboard mariner 9 and viking 1 are analyzed at altitudes higher than the topside boundary of the photoequlibrium region in the magnetic field free ionosphere the local increase of the mean scale height in the altitude region 180 250 km is assumed to be either an effect of a nonhorizontal magnetic field associated with the magnetic anomalies or diffusive equilibrium in the magnetic field free ionosphere the areas where the scale height of electron density profile is increased in comparison with average one have been selected the angle between the magnetic field measured by mgs mag er at altitudes 120 250 km and local zenith direction is investigated throughout these selected areas

duration of the early toarcian carbon isotope excursion deduced from spectral analysis consequence for its possible causes abstract the marked 3 8 negative carbon isotope excursion associated with the early toarcian oceanic anoxic event oae 183 myr ago in the early jurassic period is thought to represent one of the most important perturbations of the c cycle in the last 200 myr however the origin of this excursion remains strongly debated primarily due to uncertainties in the estimation of its duration which ranges from 200 kyr to 1 myr here we present a new orbital calibration of the early toarcian carbon isotope excursion based on spectral analyses of two independent datasets generated from the sedimentary record of two hemipelagic sections from portugal peniche and sw germany dotternhausen in order to better constrain the timescale and hence the origin of this excursion these analyses reveal that orbital cycles exert a strong influence on both the calcium carbonate content in portugal and on the greyscale of black shales in germany which allow us to propose a duration of 1 9 myr for the early toarcian and of 900 kyr for the entire carbon isotope excursion the shift towards lower carbon isotope values lasted 150 kyr and carbon isotope values remained low for 450 kyr the subsequent increase of carbon isotope values lasted 300 kyr this calibration suggests that the sustained input of isotopically light carbon at the origin of the excursion occurred over 600 kyr and thus dismisses causal mechanisms implying relatively small source reservoirs such as the massive dissociation of methane hydrates in the light of our new cyclostratigraphic timescale the massive input of isotopically light carbon associated with the emplacement of the karoo ferrar basaltic province appears as the most likely cause of the toarcian global carbon isotope excursion we also show that the c isotope perturbation coincided with a transition from precession eccentricity dominated cycles to obliquity eccentricity dominated cycles suggesting that the oae was marked by a fundamental change in the response of the climate system which allowed the obliquity signal normally better recorded at high latitudes to be a dominant forcing factor of short term sedimentary cycles at tropical latitudes

multiproxy geochemical analysis of a panthalassic margin record of the early toarcian oceanic anoxic event toyora area japan abstract the early toarcian oceanic anoxic event oae was a significant palaeoenvironmental perturbation that led to marked changes in ocean chemistry and climate and which also had a long lasting impact on marine ecosystems the global significance of the event has been recognised from the widespread occurrence of a 3 7 negative excursion in the carbon isotope 13 c composition of marine organic and inorganic matter and terrestrial plant material this feature of the event is indicative of a pronounced perturbation to the global carbon cycle an inference further supported by widespread evidence for seawater deoxygenation and elevated rates of organic carbon burial nevertheless the precise palaeoenvironmental impacts of this event from sections outside of the boreal and tethyan realms are uncertain here we present the results of a multiproxy geochemical study of an expanded record of the early toarcian event from the northwest panthalassa ocean margin exposed in southwest japan toyora area yamaguchi prefecture our results indicate that in the studied succession organic matter enrichment persisted through the early toarcian event but elemental redox proxies do not support persistent seawater anoxia analyses of terrigenously derived major and trace element abundances coupled with sedimentological observations reveal an increase in coarse grained sediment close to the onset of a 4 excursion in 13 c org and coincident with an inferred increase in terrestrial organic matter flux these observations are consistent with previously published evidence for a marked strengthening of hydrological cycling and increased runoff that occurred contemporaneously with abrupt warming at the onset of the carbon isotope event

tectonic evolution of the satpura mountain belt a critical evaluation and implication on supercontinent assembly abstract the satpura mountain belt also referred as central indian tectonic zone in recent literature forms an important morphotectonic unit in the central part of india some of the recent workers have reported an orogenic event at 1000 900 ma termed sausar orogeny which led to amalgamation of the north indian block and the south indian block and formation of the satpura mountain belt in this model the stratigraphic relations of two important lithostratigraphic units on either side of the satpura mountain belt the sausar group in the south and the vindhyan supergroup on the north are suggested to be revised from previously held ideas critical analyses of available published work in the region to assess the status of the sausar group vis a vis the vindhyan supergroup was carried out it is found that the ideas proposed by the recent workers stem from an earlier interpretation that the sausar group has monocyclic evolution and the earliest fabric in the sausar group is marked by a schistosity with ew strike re mapping of the gneissic rocks and adjacent matasedimentary rocks of khawasa deolapar and kandri mansar areas revealed presence of gneissic rocks and granulites of two generations and of four phases of superposed deformations in the metasediments and gneisses the older gneisses and granulites constitute the basement over which the rocks of the sausar group were deposited and the younger gneisses developed by metamorphism and migmatisation of the rocks of the sausar group the latter types are found in the khawasa ramakona areas contrary to the belief of the recent workers that no volcanic activity is present in the sausar group volcanic rocks marked by amygdular basic flows and tuffs have been mapped from different parts of the sausar group migmatisation and metamorphism of these volcanic rocks of the sausar group have given rise to amphibolites and granulites in khawasa and ramakona areas therefore the use of fabric patterns in these areas to suggest that the granulite facies metamorphism in the ramakona katangi granulite domain was pre sausar in age is debatable available geochronological data of the satpura mountain belt and its eastward continuation into the chhotanagpur gneiss terrain indicate that the basement and cover rocks of these areas were subjected to multiple deformation and metamorphic episodes of similar style and nature the earliest deformation and metamorphism of the rocks of the sausar group and its equivalent rocks to the east took place at 2100 1900 ma the regional ew trend of the belt developed during the second deformation at 1800 1700 ma and again at 1600 1500 ma this deformation was accompanied by migmatisation and granulite facies metamorphism in the northern domain of the sausar belt and in the chhotanagpur gneiss region late phase low intensity deformations in the region were associated with thermal events at 1100 1000 ma and 900 800 ma the ew trending fabric referred as satpura orogenic trend in indian literature marks a major compressional tectonic event developed during the second deformation of the sausar group this has its counter part in western australia as the capricorn orogeny 1780 1830 ma the development of the satpura mountain belt during the grenvillian orogeny is ruled out from the synthesis of event stratigraphic data of the region and from its comparison with the western australian craton

carbon isotope record of the early jurassic toarcian oceanic anoxic event from fossil wood and marine carbonate lusitanian basin portugal thetoarcianoceanicanoxicevent oae intheearlyjurassic 183maago wascharacterizedbywidespreadnear synchronous deposition of organic rich shales in marine settings as well as perturbations to several isotopic systems characteristically two positive carbon isotope excursions in a range of materials are separated by an abrupt negative shift carbon isotope profiles from toarcian fossil wood collected in england and denmark have previously been shown to exhibit this large drop 7 i n 13 c values interpreted as due to an injection of isotopically light co2 into the ocean atmosphere system however the global nature of this excursion has been challengedonthebasisofcarbon isotopedatafromnektonicmarinemolluscs belemnites whichexhibitheavierthanexpectedcarbonisotope values here we present new data principally from fossil wood and bulk carbonate collected at centimetre scale from a hemipelagic section at peniche coastal portugal this section is low in organic carbon average toc 0 5 and the samples should not have suffered significant diagenetic contamination by organic carbon of marine origin the carbon isotope profile based on wood shows two positive excursions separated by a large and abrupt negative excursion which parallels exactly the profile based on bulk carbonate samples from the same section albeit with approximately twice the amplitude 8 in wood versus 3 5 in carbonate these data indicate thatthe negative carbon isotope excursion affected the atmosphereand by implication the global ocean as well the difference in amplitude between terrestrial organic and marine carbonate curves can be explained by greater water availability in the terrestrial environment during the negative excursion for which there is independent evidence from marine osmiumisotope records and plausibly changes in atmospheric co2 content for which independent evidence is also available the peniche succession is also notable for the occurrence of re deposited sediments their lowest occurrence coincides with the base of the negative excursionandtheirhighestoccurrencecoincideswithitstop thus slopeinstabilityandsedimentsupplycouldhavebeenstronglylinked to the global environmental perturbation an association that may misleadingly simulate the effects of sea level fall

a case study of a density structure over a vertical magnetic field region in the martian ionosphere one of the discoveries made by the radar sounder on the mars express spacecraft is the existence of magnetically controlled structures in the ionosphere of mars which result in bulges in the ionospheric electron density contours these bulges lead in turn to oblique echoes which show up as hyperbola shaped features in the echograms a hyperbola shaped feature observed over an isolated region of strong crustal magnetic field is associated with a plasma cavity in the upper ionosphere and a corresponding density enhancement in the lower levels of the ionosphere we suggest that along open magnetic field lines the solar wind electrons are accelerated downward and the ionospheric ions are accelerated upward in a manner similar to the field line driven auroral acceleration at earth this heating due to precipitating electrons may cause an increase in the scale height and may drive a loss of ionospheric plasma at high altitudes

osmium isotope evidence for the regulation of atmospheric co2 by continental weathering the long term stability of earth9s climate throughout the phanerozoic stands in marked contrast to the dramatic fluctuations that have taken place on time scales as short as a few years reflecting the high efficiency of longer term climate regulation through negative feedbacks a fundamental mechanism is thought to involve control of co 2 in the ocean atmosphere system through continental weathering although unambiguous high resolution data supporting this hypothesis have hitherto not been available organic rich mud rocks from yorkshire england which were deposited during the toarcian oceanic anoxic event ca 181 ma early jurassic contain evidence of an exceptionally large excursion in the 187 os 188 os ratio of contemporaneous seawater from 0 4 to 1 0 the most likely explanation for this excursion is that it resulted from a transient increase in global continental weathering rates of 400 800 the os isotope excursion coincided with a well documented global 13 c excursion of 6 that affected all the major biospheric reservoirs of the time higher mean global temperatures caused global chemical weathering rates to increase substantially while in turn chemical weathering was very effective in reducing the elevated levels of atmospheric co 2 and the high temperatures to preexcursion levels

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

radar soundings of the ionosphere of mars we report the first radar soundings of the ionosphere of mars with the marsis mars advanced radar for subsurface and ionosphere sounding instrument on board the orbiting mars express spacecraft several types of ionospheric echoes are observed ranging from vertical echoes caused by specular reflection from the horizontally stratified ionosphere to a wide variety of oblique and diffuse echoes the oblique echoes are believed to arise mainly from ionospheric structures associated with the complex crustal magnetic fields of mars echoes at the electron plasma frequency and the cyclotron period also provide measurements of the local electron density and magnetic field strength

nitrogen isotope evidence for water mass denitrification during the early toarcian jurassic oceanic anoxic event bulk sedimentary nitrogen isotope 15ntot data have been generated from lower jurassic black carbon rich shales in the british isles and northern italy deposited during the early toarcian oceanic anoxic event a pronounced positive 15ntot excursion through the exaratum subzone of the falciferum zone defined by characteristic ammonites in the british isles broadly correlates with a relative maximum in weight percent total organic carbon and in some sections with a negative 13corg excursion upwelling of a deoxygenated water mass that had undergone partial denitrification is the likely explanation for relative enrichment of 15ntot and parallels may be drawn with quaternary sediments of the arabian sea gulf of california and northwest mexican margin the development of early toarcian suboxic water masses and consequent partial denitrification is attributed to increases in organic productivity approximately coincident phenomena include the following a relative climatic optimum realignment of major oceanic current systems and a possible release of methane gas hydrates from continental margin sediments early in the history of the oceanic anoxic event

magnetically controlled structures in the ionosphere of mars 1 the ionospheric sounding data obtained by the marsis mars advanced radar for subsurface and ionospheric sounding instrument on the mars express spacecraft show that the dayside ionosphere has considerable structure over regions of strong crustal magnetic fields this structure is typically seen as a hyperbola shaped trace in a display of echo intensity versus apparent altitude and time the hyperbola shapes are consistent with oblique reflections from regions of enhanced electron density that are fixed with respect to mars comparisons with the cain et al 2003 model for the crustal magnetic field of mars show that the apexes of the hyperbolas which identify the closest approach to the regions of enhanced electron density usually coincide with regions where the crustal magnetic field is strong and nearly vertical the electron density enhancements which extend as much as 50 km above the surrounding ionosphere are believed to arise from increases in the scale height of the ionosphere possibly due to heating of the ionosphere by solar wind electrons that reach the base of the ionosphere along the nearly vertical open magnetic field lines statistical analyses of the apparent altitudes of the apexes of the hyperbolas as well as analyses of repeated passes over the same region indicate that the electron density enhancements usually consist of horizontal cylinder like structures rather than isolated hemispherical structures in many cases the axes of the cylindrical density structures are aligned with the symmetry axes of adjacent cylindrical magnetic field structures with opposite polarity

magnetically controlled density structures in the topside layer of the martian ionosphere magnetically controlled density structures in the main layer of the martian ionosphere are regularly detected by the mars advance radar for subsurface and ionospheric sounder marsis on board the mars express spacecraft when it passes over the regions of strong crustal magnetic fields these structures appear as oblique echoes in an ionogram and as hyperbola shaped feature in a radargram for the first time we observed such oblique echoes from the topside layer of the martian ionosphere comparison with a crustal magnetic field model suggests that these echoes mostly occur in regions close to magnetic field anomalies the marsis ionograms that show these oblique echoes are limited in number one reason for such limited occurrence is the fact that these echoes occur at the low frequency end of an ionogram where local plasma frequency lines and electron cyclotron lines make it difficult to discern these echoes in one case however we observed the topside layer with oblique echoes on several continuous ionograms and a hyperbola shaped feature on a radargram the apex of the hyperbola falls in the region of vertical magnetic fields unlike the main layer the recurrent occurrence of the topside layer at the same location is not common more importantly the oblique echoes from the topside layer are always associated with those from the main layer of the ionosphere but not vice versa the simultaneous observation of oblique echoes from the main and topside layers are explained by considering the formation of ionization bulges at the respective layer altitudes

calcium isotope evidence for dramatic increase of continental weathering during the toarcian oceanic anoxic event early jurassic abstract the early toarcian was punctuated by pulses of massive carbon injection that are thought to have triggered through increased greenhouse conditions elevated continental discharge and nutrient input marine anoxia seawater acidification and species extinctions nevertheless the mode and tempo of changes in continental weathering across this interval remains highly debated leading to considerable uncertainty about the main causes of these perturbations in this study we present calcium isotope measurements 44 40ca of well preserved brachiopods and bulk rock samples from the hemipelagic strata of pliensbachian toarcian age of peniche in portugal in order to constrain changes in the calcium cycle and hence changes in continental weathering during the early toarcian the data reveal a similar trend as carbon isotope data from the same section and show negative excursions of about 0 5 at the pliensbachian toarcian transition pl to and at the base of the toarcian oceanic anoxic event t oae interval the comparison of 44 40ca ratios recorded in brachiopods and bulk rock corrected for variable dolomite contribution indicates that these excursions reflect changes in the global isotopic composition of seawater rather than changes in the dominant mineralogy of calcifying organisms or in hydrological budget of the considered basin box modeling results suggest that the pl to and t oae 44 40ca excursions can be explained by a transient 90 decrease of carbonate accumulation due to seawater acidification followed by a 500 increase in continental weathering rates the sharp increases in continental weathering inferred from the 44 40ca ratios seem overall consistent with lower toarcian sedimentological and biotic records that document rapid crises in carbonate production followed by episodes of increased calcium carbonate burial nevertheless the maximum of carbonate burial recorded by most nw european basinal successions occurs several hundreds of kyrs after that predicted by box modeling results this mismatch either implies that the european records of carbonate accumulation do not reflect global trends or that the fundamental processes related to the removal of excess alkalinity caused by increased continental weathering are more complex than previously appreciated based on the amount of ca input simulated by box modeling the injection of tens of thousands of gigatons of carbon with an isotopic composition 13c comprised between 6 and 14 appears as the most likely causes of the 13c excursions characterizing these two events these results indicate that environmental and biotic changes of the pl to and t oae were mainly caused a cascade of environmental changes triggered by the massive carbon emissions from the karoo ferrar volcanism

toarcian extreme warmth led to tropical cyclone intensification abstract models predict that tropical cyclone intensity should increase on a warming planet observing this relationship remains however a difficult task since no clear trend is yet emerging from the anthropogenic record the geological past offers the opportunity to study this relationship by looking at episodes of extreme warmth such as the toarcian oceanic anoxic event t oae early jurassic ca 181 ma in this study we document an increase in the occurrence of storm related deposits during the onset of the t oae in the tide dominated high atlas basin of morocco associated with a drastic deepening of the mean storm weather wave base the palaeolatitude of the high atlas basin 18 north during the early jurassic rules out winter storms as the driving mechanism behind the formation of these deposits and points to a dramatic intensification of tropical cyclone intensity during the t oae global warming these new results combined with the previously reported ubiquitous appearance of storm deposits during the t oae in tropical seas of the western tethyan area support the concept that the globally averaged intensity of tropical cyclones will increase in the coming century due to the anthropogenic climate change

hydrothermal venting of greenhouse gases triggering early jurassic global warming abstract the climate change in the toarcian early jurassic was characterized by a major perturbation of the global carbon cycle the event lasted for approximately 200 000 years and was manifested by a global warming of 6 c anoxic conditions in the oceans and extinction of marine species the triggering mechanisms for the perturbation and environmental change are however strongly debated here we present evidence for a rapid formation and transport of greenhouse gases from the deep sedimentary reservoirs in the karoo basin south africa magmatic sills were emplaced during the initial stages of formation of the early jurassic karoo large igneous province and had a profound influence on the fate of light elements in the organic rich sedimentary host rocks total organic carbon contents and vitrinite reflectivity data from contact aureoles around the sills show that organic carbon was lost from the country rocks during heating we present data from a new type of geological structures termed breccia pipes rooted in the aureoles within the shale of the western karoo basin the breccia pipes are cylindrical structures up to 150 meters in diameter and are mainly comprised of brecciated and baked black shale thousands of breccia pipes were formed due to gas pressure build up during metamorphism of the shales resulting in venting of greenhouse gases to the toarcian atmosphere mass balance calculations constrained by new aureole data show that up to 1800 gt of co2 was formed from organic material in the western karoo basin about 15 times this amount of co2 27 400 gt may have formed in the entire basin during the intrusive event u pb dating of zircons from a sill related to many of the pipes demonstrates that the magma was emplaced 182 5 0 4 million years ago this supports a causal relationship between the intrusive volcanism the gas venting and the toarcian global warming

oblique reflections of mars express marsis radar signals from ionospheric density structures raytracing analysis mars advanced radar for subsurface and ionosphere sounding marsis radar sounder on board the mars express spacecraft revealed oblique reflections coming systematically from apparently stable dens

astronomical calibration of the toarcian stage implications for sequence stratigraphy and duration of the early toarcian oae the toarcian oceanic anoxic event t oae of the early jurassic period involves one of the largest perturbations of the carbon cycle in the past 250 ma recorded by a pronounced negative carbon isotope excursion cie numerous studies have focused on potential causes of the t oae and cie but are hampered by an uncertain timescale here we present high resolution 2 kyr magnetic susceptibility ms measurements from the marine marls of the sancerre couy drill core southern paris basin spanning the entire toarcian stage the ms variations document a rich series of sub milankovitch to milankovitch frequencies precession obliquity and eccentricity with the periodic g2 g5 405 kyr and quasi periodic g g 2 4 myr cenozoic mean periodicity eccentricity terms being the most prominent the ms related g g variation reflects third order eustatic sequences and constrains the sequence stratigraphic framework of the toarcian stage in addition ms variations reveal a modulation of g g by g g eccentricity related cycles suggesting that sea level change was the main control on the deposition of the toarcian sancerre marls in tune with the astro climatic frequencies the stable 405 kyr cyclicity constrains a minimum duration of the toarcian stage to 8 3 myr and the well documented cie associated with the t oae to 300 to 500 kyr the 405 kyr ms timescale calibrates the periodicity of the prominent high frequency c cycles that occur in the decreasing part of the cie to 30 to 34 kyr consistent with the toarcian obliquity period predicted for an earth experiencing sustained tidal dissipation

reply to the discussion on carbon and oxygen isotope systematic of a paleoproterozoic cap carbonate sequence from the sausar group central india by anupam chattopadhyay 2015 published in palaeogeography palaeoclimatology palaeoecology 433 156 157 abstract the discussion on our paper on paleoproterozoic glaciation arises out of the failure of previous geological mapping in the sausar belt to identify many features which were reported earlier and to examine the outcrops critically for evidence of volcanism and glaciation in central india the details of these are given in this reply

interpreting mars ionospheric anomalies over crustal magnetic field regions using a 2 d ionospheric model the spatially inhomogeneous small scale crustal magnetic fields of mars influence the escape of planetary atmospheric species and the interaction of the solar wind with the ionosphere understanding the plasma response to crustal magnetic field regions can therefore provide insight to ionospheric structure and dynamics to date several localized spatial structures in ionospheric properties that have been observed over regions of varying magnetic field at mars have yet to be explained in this study a two dimensional ionospheric model is used to simulate the effects of field aligned plasma transport in regions of strong crustal magnetic fields resulting spatial and diurnal plasma distributions are analyzed and found to agree with observations from several spacecraft and offer compelling interpretations for many of the anomalous ionospheric behaviors observed at or near regions of strong crustal magnetic fields on mars

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

sedimentary evidence for enhanced hydrological cycling in response to rapid carbon release during the early toarcian oceanic anoxic event abstract a pronounced excursion in the carbon isotope composition of biospheric carbon and coeval seawater warming during the early toarcian 183 ma has been linked to the large scale transfer of 12c enriched carbon to the oceans and atmosphere a european bias in the distribution of available data means that the precise pattern tempo and global expression of this carbon cycle perturbation and the associated environmental responses remain uncertain here we present a new cm scale terrestrial dominated carbon isotope record through an expanded lower toarcian section from japan that displays a negative excursion pattern similar to marine and terrestrial carbon isotope records documented from europe these new data suggest that 12c enriched carbon was added to the biosphere in at least one rapid millennial scale pulse sedimentological analysis indicates a close association between the carbon isotope excursion and high energy sediment transport and enhanced fluvial discharge together these data support the hypothesis that a sudden strengthening of the global hydrological cycle occurred in direct and immediate response to rapid carbon release and atmospheric warming

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

stepwise atmospheric carbon isotope excursion during the toarcian oceanic anoxic event early jurassic polish basin abstract during the mesozoic 250 64 ma intervals of about 0 5 myr were subject to severe environmental changes including high sea surface temperature and very low oxygen content of marine water these oceanic anoxic events or oaes occurred simultaneously with profound disturbance to the carbon cycle the carbon isotope anomaly in the early jurassic that marks the toarcian oceanic anoxic event t oae at 182 ma is characterized in marine sections by a series of dramatic steps towards lighter values herein we present new carbon isotope data from terrestrial organic matter phytoclast separates collected through a late pliensbachian middle toarcian coastal and marginal marine succession in the polish basin a setting where hinterland climate and sea level change are well recorded the results show that the shift to light carbon isotope values in the woody organic matter and therefore also in atmospheric carbon dioxide similarly occurred in major steps the steps are here correlated with those identified from marine organic matter where they have previously been attributed to 100 kyr eccentricity forcing of climate the results provide strong support for orbitally and climatically controlled release of isotopically light carbon from gas hydrates into the ocean atmosphere system in a series of rapid bursts additionally a link between the carbon isotope steps and shoreline movements can be demonstrated individual peaks of the negative excursion are mostly associated with facies indicative of sea level rise flooding surfaces however at the same time inferred higher atmospheric carbon dioxide content may be expected to have resulted in increased rainfall and temperature leading to accelerated weathering and erosion and consequently increased sediment supply progradation and regression causing some mismatches between isotope shifts and inferred sea level changes enhanced abundance of megaspores derived from hydrophilic plant groups and marked increase in kaolinite are coincident with the overall development of the negative isotope excursion the combined data suggest that each 100 kyr cycle in carbon isotope values was characterized by increasingly severe palaeoclimatic change culminating in extremely hot and humid conditions co incident with the peak of the final most negative carbon isotope excursion the chemostratigraphic correlation allows very precise dating of the late pliensbachian middle toarcian coastal and marginal marine sedimentary succession in the polish basin

chronology of the early toarcian environmental crisis in the lorraine sub basin ne paris basin abstract early toarcian jurassic 183 ma sediments recorded profound environmental changes including mass extinction global warming marine transgression as well as widespread bottom water anoxia and organic matter accumulation on the western tethyan shelf enhanced organic matter accumulation was accompanied by a positive carbon isotope excursion cie in pelagic carbonate which marks the toarcian oceanic anoxic event these environmental changes were accompanied by a major perturbation of the global carbon cycle expressed by negative cie interrupting the positive trend the duration of the carbon cycle perturbation is still debated with estimates for the negative cie range from 200 to 600 kyr here we present ultra high resolution 555 kyr for the tenuicostatum zone and 1310 kyr for the serpentinum zone the durations of the elegantulum and falciferum subzones can be estimated to 790 kyr and 520 kyr respectively a change in the orbital response from eccentricity to obliquity forcing evident from other locations is well expressed in the lorraine sub basin and occurred within the cie interval the strong impact of the obliquity component in post event deposits hints to processes most effective at high latitudes such as the waxing and waning of polar ice paleogeographic features of the western tethyan shelf supported the tele connection of higher to lower latitude processes via water exchange through the viking corridor

wave enhanced sediment gravity flows and mud dispersal across continental shelves reappraising sediment transport processes operating in ancient mudstone successions recent studies of marine shelf sediment dispersal show that wave enhanced sediment gravity flows are widespread phenomena and can transport large volumes of fluid mud rapidly across low gradient shelves flow evolution is controlled by sediment supply seabed gradient and spatial distribution of wave energy at the seabed using existing flow models we predict that such flows in mud dominated sediments will develop a three part microstratigraphy produced by changing flow conditions beginning with wave induced turbulent resuspension then development of a wave enhanced sediment gravity flow prior to lutocline collapse and suspension settling petrographic examination of modern flow deposits collected from the eel shelf reveals that resultant beds possess a microstratigraphy consistent with our hypothesis a silt rich basal subunit with curved ripple laminae abruptly overlain by a subunit composed of continuous intercalated silt clay laminae and an upper clay rich drape analyses of beds from ancient mud rich outer shelf and basinal successions cleveland ironstone jurassic uk and mowry shale cretaceous united states show that they too contain beds with this three part organization suggesting that such flows were active in these ancient settings too recognition of these microstructures in these ancient mud dominated successions demonstrates that sediment in these settings was commonly reworked and transported advectively downslope by high energy events contrasting with previous interpretations of these units that deposition was dominated by quiescent suspension settling identification of these recognition criteria now allows the products of this newly recognized sediment dispersal mechanism to be identified in other shale dominated successions

early toarcian early jurassic oceanic anoxic event recorded in the shelf deposits in the northwestern panthalassa evidence from the nishinakayama formation in the toyora area west japan abstract the early toarcian oceanic anoxic event t oae was marked by the worldwide burial of organic rich black shales and a coincident pronounced negative carbon isotope excursion of carbonates organic matter and fossil wood this characteristic carbon isotope perturbation and other geochemical records have been recognized in many sections in the european domain and in selected sections in the central and eastern panthalassa but not in the western panthalassa we present herein for the first time data of carbon isotope ratios of organic carbon total organic carbon toc contents and sedimentary fabrics from the uppermost pliensbachian to the lower toarcian sequence in the sakuraguchi dani valley toyora area west japan that was deposited in the shelf basin of the northwestern panthalassa the carbon isotope profile displays a similar trend to those in contemporaneous strata in the tethys and in the eastern and central panthalassic regions which is characterized by a distinct negative excursion around the tenuicostatum falciferum zone boundary in the early toarcian this evidence suggests that the widely recognized negative carbon isotope excursion represents a nature of the global carbon cycle perturbation analyses of total organic carbon contents and sedimentary fabrics in the study section reveal that accumulation of organic carbon occurred and anoxic bottom water was prevalent during the early toarcian the most organic rich strata and bottom water anoxia described in the study section however exist in the interval showing the carbon isotope positive recovery after the abrupt negative shift and this fact suggests that the accumulation of organic matters and development of marine anoxia were globally diachronous even though the negative cie was interpreted as a synchronous event our study also demonstrates that the early toarcian anoxia in the northwestern panthalassic basin was not a single and continuous anoxic event but was interrupted by episodic short term oxygenation events