westward propagation of latitudinal asymmetry in a coupled ocean atmosphere model abstract hemispheric asymmetries of continental geometry have long been speculated to be the cause of the northern hemisphere position of the intertropical convergence zone over the central and eastern pacific it is unknown however how the effects of continental asymmetries are transmitted to and felt by the central pacific thousands of kilometers away this paper proposes a transmitter mechanism by investigating the response of a coupled ocean atmospheric model to a symmetry breaking force by the american continents the model treats land forcing implicitly as an eastern boundary condition in the absence of oceanic feedback the model response to the eastern boundary forcing is tightly trapped and confined to a small longitudinal extent off the coast whereas the climate over the interior ocean is symmetric about the equator ocean atmosphere coupling greatly enhances the transmissibility of the effects of the land forcing establishing large latitudinal asymmetry over a great zonal extent a westwar

the equatorial atlantic oscillation and its response to enso an internal equatorial atlantic oscillation has been identified by analyzing sea surface temperature sst observations the equatorial atlantic oscillation can be viewed as the atlantic analogue of the el nino southern oscillation enso phenomenon in the equatorial pacific but it is much less vigorous the equatorial atlantic oscillation is strongly influenced by the pacific enso with the equatorial atlantic sea surface temperature lagging by about six months this lag can be explained by the dynamical adjustment time of the equatorial atlantic to low frequency wind stress variations and the seasonally varying background state which favours strongest growth of perturbations in summer results of an extended range simulation with a coupled ocean atmosphere gcm support this picture

organic matter composition and sulfate reduction intensity in oman margin sediments abstract petrographical and geochemical studies of neogene marine sediments from the oman sea leg 117 sites 720 724 726 and 730 show a close relationship between the nature and amount of the organic matter and the degree of degradation of organic matter by sulfate reduction i e pyritization petrographically three major pyritization types were observed 1 finely dispersed pyrite framboids in sediments from oman margin and indus fan enriched in autochthonous marine organic matter 2 infilling of pores by massive pyrite crystals in oman margin sediments with a low toc and a high microfossil content 3 pyrite mineralization of lignaceous fragments in organic depleted sediments from the indus fan leading to more massive pyrite geochemically we can define a sulfate reduction index sri as the percentage of initial organic carbon versus that of residual organic carbon finely laminated pliocene pleistocene sediments from the oman margin exclusively contain organic matter deriving from organic phytoplankton for which the quantity toc positively correlates with the geochemical quality hydrogen index we think that the occurrence of this residual organic matter is linked mainly to a high primary paleo productivity the intensity of sulfate reduction is constant for sediments with toc up to 2 and becomes more important when organic input decreases this degradation process can destroy up to 50 of the initial organic matter but is not sufficient to explain some of the encountered very low toc values it can be seen that sharp increases of certain plankton species with mineral skeletons are responsible for a pronounced degradation of organic matter due to increased sulfate reduction in that case the organic matter may be strongly degraded high sri although deposited in an oxygen depleted environment conversely miocene pliocene sediments contain an autochthonous organic matter that is typical of both low productivity and oxic processes their very low sulfate reduction index indicates that very little metabolizable organic matter was initially present

simple climatic indices for the tropical atlantic ocean and some applications two indices related to the sea surface temperature sst variability in the tropical atlantic are proposed one index describes the sst averaged over the whole basin 30 n to 20 s 60 w to 15 e and the other illustrates a meridional dipole between the northern and southern hemispheres the computational method for obtaining these indices is intentionally kept simple the objective being to reproduce the signature of the main results previously provided from more complicated statistical analyses monthly time series for both indices are produced from 1964 up to the present time the whole basin index exhibits principally a sustained warming which has intensified since about 1975 and it has a significant periodicity close to that of the quasi biennial oscillation the dipole index exhibits a decadal scale variation and its building up seems to be related to other worldwide climatic changes as for instance el nino southern oscillation extreme episodes rainfall variabilities over the brazilian nordeste and african sahel

relationship between the equatorial and meridional modes of climatic variability in the tropical atlantic the tropical atlantic ocean exhibits two primary modes of interannual climate variability an equatorial mode analogous to but weaker than the pacific el nino phenomenon and a meridional mode that does not have a pacific counterpart the equatorial mode is responsible for warm and cold sea surface temperature sst events mainly in the gulf of guinea and is identifiable by abnormal changes in the equatorial thermocline slope resulting from zonal wind anomalies in the western tropical atlantic the meridional mode is characterized by a north south interhemispheric gradient of sst anomalies here it is shown using observed surface and subsurface oceanic temperatures that the meridional mode is linked to the equatorial mode at both decadal and short interannual 1 2 years time scales both modes involve north south displacements of the itcz as in the annual response

why the itcz is mostly north of the equator abstract although the distribution of sunshine is symmetrical about the equator the earth s climate is not climatic asymmetries are prominent in the eastern tropical pacific and atlantic oceans where the regions of maximum sea surface temperature convective cloud cover and rainfall are north of the equator this is the result of two sets of factors interactions between the ocean and atmosphere that are capable of converting symmetry into asymmetry and the geometries of the continents that determine in which longitudes the interactions are effective and in which hemisphere the warmest waters and the intertropical convergence zone are located the ocean atmosphere interactions are most effective where the thermocline is shallow because the winds can readily affect sea surface temperatures in such regions the thermocline happens to shoal in the eastern equatorial pacific and atlantic but not in the eastern indian ocean because easterly trade winds prevail over the tropical atlantic and pacific wher

a climate change event detected in visean oil shales from devon island arctic canada abstract important depositional characteristics indicative of climate change has been discovered in 50 m sedimentary succession consisting of oil shales with a marlstone and carbonate matrix of the visean shales from the lower carboniferous emma fiord formation on devon island canada s arctic archipelago older carboniferous tournaisian shales are however absent from devon island but elsewhere such as big marsh nova scotia tournaisian shales show no comparable evidence for climate change the techniques used include reflected light microscopy rockeval analyses instrumental neutron activation analysis inaa for elemental concentration indeed visean shales from the lower part the emma fiord formation from devon island have a marlstone matrix with abundant algal matter the matrix also has low carbonate 32 and total organic carbon toc content between 33 3 and 55 6 moreover the toc show a positive correlation with authigenic uranium and mo which suggests a high productivity due to the high rain deeper water lacustrine depositional environment other visean oil shales from the emma fiord formation on devon island have somewhat different characteristics from those with marlstone matrix indeed they have a high 75 carbonate content with calcified algal matter and low toc 1 14 17 4 a very low correlation between toc and authigenic u and mo most importantly very high oil generation 98 413 l t potential of marlstones as compared to low yield of carbonate mudstones 4 1 17 0 l t shows a dramatic climatic shift to low precipitation and much dryer conditions such a drastic climatic condition has not been detected for the tournaisian oil shales

relationship between zonal and meridional modes in the tropical atlantic the tropical atlantic displays two main modes of variability the meridional or dipole mode and the equatorial zonal mode it was proposed recently that these two modes are correlated and are both forced within the tropics by latitudinal displacements of the itcz this modeling study shows that while the two modes are correlated for limited record lengths prior to and after 1976 the correlation falls apart when longer time series from 1949 to 2000 are considered the 1976 climate shift also occurred in the tropical atlantic seen as a thermocline shift similar to the pacific forced dynamically within the tropics the first eof of the simulated thermocline depth captures the inter decadal mode with the 1976 shift the first eof of sst anomalies prior to after 1976 represents the meridional zonal mode consistent with the previous finding that the relation between the eastern pacific and atlantic itcz is stronger in the 1980 90 s

how ubiquitous is the dipole relationship in tropical atlantic sea surface temperatures several kinds of analysis are applied to sea surface temperature anomalies ssta 1856 1991 to determine the degree to which ssta of opposite sign in the tropical north and south atlantic occur antisymmetric dipole configurations of ssta on basin scales are not ubiquitous in the tropical atlantic unless the data are stratified by both season and frequency inherent dipole behavior cannot be demonstrated upon removing the global el nino southern oscillation signal in ssta which is symmetric between the north and south atlantic from the data the regions north or south of the intertropical convergence zone have qualitatively different temporal variabilities and are poorly correlated dipole configurations do occur infrequently 12 15 of the time but no more so than expected by chance for stochastically independent variables nondipole configurations that imply significant meridional ssta gradients occur much more frequently nearly half of the time cross spectral analysis of seasonally averaged ssta indices for the north and south atlantic show marginally significant coherence with antisymmetric phase in two period bands 8 12 years for the boreal winter spring and 2 3 years for the boreal summer fall antisymmetric coherence is optimal for a small subregion west of angola in the south atlantic with respect to ssta of basin scale in the tropical north atlantic dipole variability even where optimal explains only a small fraction of the total variance in tropical atlantic ssta 7

prediction of tropical atlantic sea surface temperatures using linear inverse modeling the predictability of tropical atlantic sea surface temperature on seasonal to interannual timescales by linear inverse modeling is quantified the authors find that predictability of caribbean sea and north tropical atlantic sea surface temperature anomalies sstas is enhanced when one uses global tropical sstas as predictors compared with using only tropical atlantic predictors this predictability advantage does not carry over into the equatorial and south tropical atlantic indeed persistence is a competitive predictor in those regions to help resolve the issue of whether or not the dipole structure found by applying empirical orthogonal function analysis to tropical atlantic ssts is an artifact of the technique or a physically real structure the authors combine empirically derived normal modes and their adjoints to form influence functions maps highlighting the geographical areas to which the north tropical atlantic and the south tropical atlantic ssts are most sensitive at specified lead times when the analysis is confined to the atlantic basin the 6 month influence functions in the north and south tropical atlantic tend to be of the opposite sign and evolve into clear dipoles within 6 months when the analysis is performed on global tropical ssts the 6 month influence functions are connected

land atmosphere ocean interactions in the southeastern atlantic interannual variability land atmosphere ocean interactions in the southeastern south atlantic and their connections to interannual variability are examined using a regional climate model coupled with an intermediate level ocean model in austral summer zonal displacements of the south atlantic subtropical high sash can induce variations of mixed layer currents in the benguela upwelling region through surface wind stress curl anomalies near the namibian coast and an eastward shifted sash is related to the first pacific south american mode when the sash is meridionally displaced mixed layer vertically integrated ekman transport anomalies are mainly a response to the change of alongshore surface wind stress the latitudinal shift of the sash tends to dampen the anomalous alongshore wind by modulating the land sea thermal contrast while opposed by oceanic diffusion although the position of the sash is closely linked to the phase of el nino southern oscillation enso and the southern annular mode sam in austral summer an overall relationship between benguela upwelling strength and enso or sam is absent during austral winter variations of the mixed layer ekman transport in the benguela upwelling region are connected to the strength of the sash through its impact on both coastal wind stress curl and alongshore surface wind stress compared with austral summer low level cloud cover change plays a more important role although wintertime sea surface temperature fluctuations in the equatorial atlantic are strong and may act to influence variability over the northern benguela area the surface heat budget analysis suggests that local air sea interactions dominate

relationships between low frequency variability in the southern hemisphere and sea surface temperature anomalies abstract long term trends and interannual variations of circulation anomalies in the southern hemisphere are examined using the national centers for environmental prediction national center for atmospheric research reanalysis from 1949 to 1998 the changes in planetary circulation regimes are linked to global sea surface temperature anomalies sstas empirical orthogonal function eof analysis was performed on 500 hpa height anomalies the leading mode eof1 shows a strong zonal symmetry with a phase reversal between height anomalies in high and midlatitudes apart from zonal symmetry a zonal wavenumber 3 is evident with three centers located in three southern oceans in the low frequency band with fluctuations longer than 60 months eof1 is associated with the second rotated eof mode of sstas with positive loadings over three southern oceans and negative loadings in the north pacific and the north atlantic the next two modes are the pacific south american psa patterns they depict wave 3 patterns in

molybdenum accumulation in cariaco basin sediment over the past 24 k y a record of water column anoxia and climate molybdenum mo concentrations in a sediment core from the cariaco basin on the venezuelan continental shelf can be partitioned between a marine fraction and a terrigenous fraction the accumulation rate of the marine fraction of mo increased abruptly 15 000 calendar years ago 15 ka from 2 yr 1 to 4 g cm 2 yr 1 and then decreased abruptly at 9 ka the accumulation rate remained high throughout this 6 k y period but exhibited maxima at 15 14 and 12 5 ka corresponding in time to meltwater pulse ia into the gulf of mexico and the onset of the younger dryas cold event respectively the marine fraction of mo is interpreted in terms of redox conditions of bottom water as dictated by both the flux of settling organic matter and bottom water residence time correspondence between geochemical extremes in this core with changes in sea level and global climate demonstrates the high degree to which this ocean margin basin has responded to the paleoceanographic regime throughout the past 24 k y

the permo triassic extinction the end permian mass extinction brought the palaeozoic great experiment in marine life to a close during an interval of intense climatic tectonic and geochemical change improved knowledge of latest permian faunas coupled with recent advances in isotopic studies and biostratigraphy have greatly enhanced our understanding of the events of 250 million years ago and have begun to provide answers to many questions about the causes of extinction

an early carboniferous visean lacustrine oil shale in canadian arctic archipelago the lower carboniferous visean emma fiord formation in the canadian arctic archipelago is an oil shale of lacustrine origin composed of black carbonaceous shale siltstone and marlstone with interbedded sandstone conglomerate and oolitic and algal limestones at kleybolte peninsula on ellesmere island the emma fiord formation was deposited on the tectonically active northwestern rim of the sverdrup basin it is now thermally overmature and well beyond the dry gas zone of organic maturation vitrinite reflectance approx 5 0 in contrast the emma fiord sequence on grinnell peninsula devon island near the southern edge of the sverdrup basin is immature to marginally mature vitrinite reflectance 0 26 0 44 and is composed predominantly of liptinite rich oil sha e these kerogen rich rocks contain a high volume of microcrystalline calcite and compositionally are marlstones the emma fiord lake system probably was a closed basin and may have been thermally and chemically stratified meromictic seasonal or continuous high organic productivity by phytoplankton and bacteria in the epilimnion resulted in accumulation of lipid rich calcareous sediment below an anoxic hypolimnion the emma fiord oil shales on grinnell peninsula contain both autochthonous and allochthonous organic material two types of oil shales are recognized in this sequence 1 alginite rich oil shales with a clay carbonate matrix in which liptinite content may be as high as 93 of the organic matter the hydrogen oxygen index indicates kerogen of intermediate composition between types i and ii these oil shales are hydrogen rich and oxygen poor 2 alginite poor oil shale with a carbonate matrix relatively hydrogen poor and oxygen rich the hydrogen oxygen index indicates kerogen of intermediate composition between types ii and iii the emma fiord oil shales were deposited in lakes formed immediately prior to or possibly synchronous with the initiation of rifting in the sverdrup basin syntectonic red bed conglomerates derived from uplifted horst blocks directly overlie the emma fiord rocks a few beds of conglomerate and sandstone in the upper part of the emma fiord formation possibly record the onset of faulting the formation closely resembles contemporaneous sequences in northern alaska yukon territory greenland and spitsbergen clearly similar tectonic and paleoclimatic factors influenced sedimentation over this area in the early carboniferous with the sverdrup basin locations lying within 10 15 of the paleoequator

simulations of the atmospheric response to south atlantic sea surface temperature anomalies abstract the sensitivity of the atmospheric circulation to sea surface temperature sst anomalies in the tropical and subtropical south atlantic ocean is studied by means of simulations with an atmospheric general circulation model gcm two types of prescribed sst anomalies are used motivated by previous analyses of data the first occurs during austral summers in association with a strengthening of the south atlantic convergence zone sacz and consists of cold sst anomalies over the subtropical south atlantic the second is the leading seasonally varying empirical orthogonal function of sst consisting of warm basin scale anomalies with maximum amplitude in the subtropics during january march and at the equator in june an ensemble of about 10 seasonal simulations is made using each type of anomaly focusing on the january march period in the first case and the january june seasonal evolution in the second during january march both experiments yield a statistically significant baroclinic response o

the timing and extent of the eruption of the siberian traps large igneous province implications for the end permian environmental crisis we present new high precision 40ar 39ar ages on feldspar and biotite separates to establish the age duration and extent of the larger siberian traps volcanic province samples include basalts and gabbros from noril sk the lower tunguska area on the siberian craton the taimyr peninsula the kuznetsk basin vorkuta in the polar urals and from chelyabinsk in the southern urals most of the ages except for those from chelyabinsk are indistinguishable from those found at noril sk cessation of activity at noril sk is constrained by a 40ar 39ar age of 250 3 1 1 ma for the uppermost kumginsky suite the new 40ar 39ar data confirm that the bulk of siberian volcanism occurred at 250 ma during a period of less than 2 ma extending over an area of up to 5 million km2 the resolution of the data allows us to confidently conclude that the main stage of volcanism either immediately predates or is synchronous with the end permian mass extinction further strengthening an association between volcanism and the end permian crisis a sanidine age of 249 25 0 14 ma from bed 28 tuff at the global section and stratotype at meishan china allows us to bracket the p tr boundary to 0 58 0 21 myr and enables a direct comparison between the 40ar 39ar age of the traps and the permo triassic boundary section younger ages 243 ma obtained for basalts from chelyabinsk indicate that volcanism in at least the southern part of the province continued into the triassic

evolution of interannual warm and cold events in the southeast atlantic ocean extreme warm episodes in the southeast atlantic ocean known as benguela ninos have devastating envi ronmental impacts and have been shown to be remotely forced to place these extreme events into perspective the investigation is here extended to minor warm events as well as to cold episodes to this end different sets of observations have been combined with outputs from a numerical simulation of the tropical atlantic for the period 1982 99 it is shown that both warm and cold surface events develop regularly in the same specific region along the coast of angola and namibia some cold events compete in magnitude with major warm episodes local sea air heat flux exchanges do not seem to precondition the sea surface in the angola benguela region prior to the arrival of an event most warm and cold episodes are large scale events despite their limited surface signature they appear to be generated by wind anomalies in the western and central equatorial atlantic in the same way as benguela ninos seasonal fluctuations of the depth and shape of the tropical thermocline seem partly to control the way subsurface anomalies eventually impact the surface during austral summer surface anomalies create an identifiable pool centered near 158s whereas in winter they show an elongated pattern along the coast stretching toward the equator local upwelling or downwelling favorable wind regimes as well as local net heat fluxes may modulate the surface expression of events

the influence of atlantic sea surface temperature anomalies on the north atlantic oscillation abstract the influence of atlantic sea surface temperature sst anomalies on the atmospheric circulation over the north atlantic sector during winter is investigated by performing experiments with an atmospheric general circulation model these consist of a 30 yr run with observed sst anomalies for the period 1961 90 confined geographically to the atlantic ocean and of a control run with climatological ssts prescribed globally a third 30 yr integration with observed ssts confined to the south atlantic is made to confirm present findings the simulated interannual variance of 500 hpa wintertime geopotential heights over the north atlantic attains much more realistic values when observed atlantic ssts are prescribed circulation patterns that resemble the positive phase of the north atlantic oscillation nao become more pronounced in terms of the leading eof of winter means and a cluster analysis of daily fields the variance of an interannual nao index increases by fivefold over its control value atl

displacement fields due to the 1946 nankaido earthquake in a laterally inhomogeneous structure with the subducting philippine sea plate a three dimensional finite element approach abstract the displacement fields associated with the 1946 nankaido earthquake have been investigated in detail taking into account the configuration of the philippine sea plate subducting beneath southwest japan we used a three dimensional finite element method for the elastic problem to examine the effects of three dimensionally inhomogeneous structure some differences in the displacement patterns between homogeneous and inhomogeneous media have been identified the amounts of displacements are large in low rigidity portions such as in the crust and mantle wedge and are small in a high rigidity portion composed of the subducting plate the inhomogeneity affects horizontal displacements at the earth s surface more than vertical displacements if the rigidity and the poisson ratio given here to southwest japan are appropriate the fault parameters of the earthquake which have been estimated from simple dislocation models in a homogeneous semi infinite medium need to be modified somewhat the present computations indicate that larger dip angles and smaller fault slips are more appropriate fault parameters when structural inhomogeneity is taken into account this suggests that the discrepancy in the obtained total seismic moment between the geodetic and seismic models of the nankaido earthquake could be reduced

evidence for interannual and interdecadal climate variability in the south atlantic a singular value decomposition svd analysis is used to determine the coupled modes of variability of monthly sea surface temperature sst and sea level pressure slp data from the south atlantic region for the period 1953 1992 we find that the three leading svd modes respectively account for 63 20 and 6 of the total square covariance the first mode represents an approximately 15 year period oscillation in the strength of the subtropical anticyclone accompanied by fluctuations of a north south dipole structure in the sst it appears to be linked to the global scale interdecadal 15 year joint mode in sst and slp recently studied by mann and park the second mode is characterized by east west displacements of the anticyclone center in association with strong 6 to 7 year period fluctuations of sst off the coast of africa the third mode is characterized by north south displacements of the anticyclone and 4 year period fluctuations in the sst in a broad band across the central south atlantic this mode is strongly correlated with enso

gas emissions due to magma sediment interactions during flood magmatism at the siberian traps gas dispersion and environmental consequences we estimate the fluxes of extremely reduced gas emissions produced during the emplacement of the siberian traps large igneous province due to magma intrusion in the coaliferous sediments of the tunguska basin using the results of a companion paper iacono marziano et al submitted to epsl and a recent work about low temperature interaction between magma and organic matter svensen et al 2009 we calculate co ch4 dominated gas emission rates of 7 1015 2 1016 g yr for a single magmatic volcanic event these fluxes are 7 to 20 times higher than those calculated for purely magmatic gas emissions in the absence of interaction with organic matter rich sediments we investigate by means of atmospheric modelling employing present geography of siberia the short and mid term dispersion of these gas emissions into the atmosphere the lateral propagation of co and ch4 leads to an important perturbation of the atmosphere chemistry consisting in a strong reduction of the radical oh concentration as a consequence both co and ch4 lifetimes in the lower atmosphere are enhanced by a factor of at least 3 at the continental scale as a consequence of 30 days of magmatic activity the short term effect of the injection of carbon monoxide and methane into the atmosphere is therefore to increase the residence times of these two species and in turn their capacity of geographic expansion the estimated co and ch4 volume mixing ratios i e the number of molecules of co or ch4 per cm3 divided by the total number of molecules per cm3 in the low atmosphere are 2 5 ppmv at the continental scale and locally higher than 50 ppmv the dimension of the area affected by these high volume mixing ratios decreases in the presence of a lava flow accompanying magma intrusion at depth complementary calculations for a 10 year duration of the magmatic activity suggest i an increase in the mean ch4 volume mixing ratio of the whole atmosphere up to values 3 to 15 times higher than the current one and ii recovery times of 100 years to bring back the atmospheric volume mixing ratio of ch4 to the pre magmatic value thermogenic methane emissions from the siberian traps has already been proposed to crucially contribute to end permian early triassic global warming and to the negative carbon isotopic shift observed globally in both marine and terrestrial sediments our results corroborate these hypotheses and suggest that concurrent high temperature co emissions also played a key role by contributing to increase i the radiative forcing of methane and therefore in its global warming potential and ii the input of isotopically light carbon into the atmosphere that generated the isotopic excursion we also speculate a poisoning effect of high carbon monoxide concentrations on end permian fauna at a local scale

decadal and interannual sst variability in the tropical atlantic ocean abstract the mechanisms regulating interannual and decadal variations of sea surface temperature sst in the tropical atlantic are examined observed variations of sea surface temperature are typically in the range of 0 3 0 5 c and are linked to fluctuations in rainfall on both the african and south american continents the authors use a numerical model to simulate the observed time series of sea surface temperature for the period 1960 1989 based on the results experiments are conducted to determine the relative importance of heat flux and momentum forcing two dominant timescales for variability of sst are identified a decadal timescale that is controlled by latent heat flux anomalies and is primarily responsible for sst anomalies off the equator and an equatorial mode with a timescale of 2 5 years that is dominated by dynamical processes the interhemispheric gradient of anomalous sst the sst dipole is primarily linked to the former process and thus results from the gradual strengthening and weak

characteristics of low frequency sea surface temperature fluctuations in the tropical atlantic abstract sea surface temperature anomalies in the tropical atlantic ocean are reexamined to investigate an apparent low frequency oscillation that has been described as a fluctuating dipole structure with poles north and south of the equator and a node near the itcz using principal components rotated by the varimax method and simple correlations of area averaged temperatures we show that during the 1964 88 interval sst anomalies north and south of the itcz are not significantly correlated therefore the low frequency variation with an apparent decadal period observed in the sst gradient across the itcz during 1964 88 does not arise from temporally coherent and out of phase fluctuations in each hemisphere and cannot be characterized as a dipole

spatial correlations of interdecadal variation in global surface temperatures we have analyzed spatial correlation patterns of interdecadal global surface temperature variability from an empirical perspective using multi taper coherence estimates from 140 yr records we find that correlations between hemispheres are significant at 95 confidence for non randomness for most of the frequency band 0 06 f 0 24 cyc yr coherence estimates of pairs of 100 yr grid point temperature data series near 5 yr period reveal teleconnection patterns consistent with known patterns of enso variability significant correlated variability is observed near 15 year period with the dominant tele connection pattern largely confined to the northern hemisphere peak to peak t 0 5 with simultaneous warming and cooling of discrete patches on the earth s surface a global average of this pattern would largely cancel

an integrated assessment of a type euxinic deposit evidence for multiple controls on black shale deposition in the middle devonian oatka creek formation an integrated lithologic paleontologic and multi proxy geochemical study of the middle devonian oatka creek formation a black shale in the northern appalachian basin indicates that a number of different factors contributed to organic carbon rich black shale deposition conditions leading to this organic rich sedimentary deposit were ultimately controlled by a relative sealevel rise dominantly eustatic but with possible contributions from local tectonics which cut off the supply of carbonate to the basin geochemical proxy evidence such as mo ti fe ti corg spy and 34spy suggests that as sealevel continued to rise after the carbonate supply was cut off a threshold was crossed at which point conditions in the basin shifted from dominantly anoxic to dominantly euxinic anoxic sulfidic bottom waters concurrent with the shift to dominantly euxinic conditions the supply of siliciclastic sediments was cut off resulting in a condensed horizon as evidenced by the elemental ratios of si al and k fe mg and the relative concentration of eolian silt as determined petrographically and from scanning electron microscopy sediment starvation in the basin appears to have facilitated the biogeochemical re cycling of c n and p specifically the elemental ratios of c n and p and the stable carbon isotope composition of organic matter suggest that the preferential regeneration of p under anoxic conditions and of n during the oxic phase of oxic anoxic oscillation led to enhanced primary production in surface waters thereby maintaining euxinic conditions in the bottom waters through respiration of settling organic matter finally it is observed that though conditions in the basin seem to have remained consistently anoxic sulfidic for some time after the initial shift to euxinic conditions a progressive increase in siliciclastic sedimentation led to a corresponding decrease in the enrichment of various redox related elements illustrating the overriding control that sedimentation can have on geochemical proxy records

decadal variability of the tropical atlantic ocean surface temperature in shipboard measurements and in a global ocean atmosphere model abstract numerous analyses of relatively short 25 30 years in length time series of the observed surface temperature of the tropical atlantic ocean have indicated the possible existence of decadal timescale variability it was decided to search for such variability in 100 yr time series of sea surface temperature sst measured aboard ships and available in the recently published global ocean surface temperature atlas gosta fourier and singular spectrum analyses of the gosta sst time series averaged over 11 subregions each approximately 1 106 km2 in area show that pronounced quasi oscillatory decadal 8 20 yr and multidecadal 30 40 yr timescale variability exists in the gosta dataset over the tropical atlantic motivated by the above results sst variability was investigated in a 200 yr integration of a global model of the coupled oceanic and atmospheric general circulations developed at the geophysical fluid dynamics laboratory gfdl the second 100 yr of sst in the coupled model s tropical

a southern hemisphere wave response to enso with implications for southern africa precipitation ensemble gcm simulations with an imposed idealized warming of the eastern pacific ocean reveal two wave anomalies in the southern hemisphere one in the eastern and one in the western hemisphere both are statistically significant at the 99 confidence level application of a steady state linear model and a rossby wave source analysis is used to diagnose the causes of the waves the western hemisphere wave is forced by the advection and stretching of planetary vorticity by the divergent flow from the southern hemisphere component of the central pacific twin anticyclones that straddle the equator during warm events the eastern hemisphere wave is a result of the northeastward shift of the south indian convergence zone sicz that in turn is forced from the upper troposphere by convergence to the north an upper level convergence maximum over the equatorial indian ocean induces divergence to the south encouraging vertical motion and precipitation to the northeast of the sicz s normal position the resulting anomalous upper level convergence in the climatological position of the sicz as well as the anomalous vorticity flux convergence by the transients associated with an equatorward shift of the storm track behind the sicz force the eastern hemisphere rossby wave since a shift of the sicz is a fairly robust observed consequence of enso events these results suggest the mechanism by which drought conditions develop over southern africa at the height of many warm events seasonal prediction capabilities in this region can be improved by monitoring and understanding the details and consequences of the adjustment of the walker circulation near the equator outside of the pacific ocean basin

atmosphere ocean coupled variability in the south atlantic abstract the climate variability of the south atlantic region is determined from 40 yr 1953 92 of comprehensive ocean atmosphere data set monthly sea surface temperature sst and sea level pressure slp data using the empirical orthogonal function eof and the singular value decomposition svd analysis methods the eof method is applied to each field separately whereas the svd method is applied to both fields simultaneously the significance of the atmosphere ocean interaction is revealed by a strong resemblance between individual eof and coupled svd modes of sst and slp the three leading modes of coupled variability on interannual and interdecadal timescales are discussed in some detail the first coupled mode which accounts for 63 of the total square covariance represents a 14 16 yr period oscillation in the strength of the subtropical anticyclone accompanied by fluctuations of a north south dipole structure in the sst the atmosphere ocean coupling is strongest during the southern summe

interactions between sea surface temperature over the south atlantic ocean and the south atlantic convergence zone 1 interactions between the sea surface temperature sst over the south atlantic ocean 40 s equador and the south atlantic convergence zone sacz were studied through numerical experiments with an atmospheric general circulation model agcm and an ocean general circulation model ogcm the agcm experiments showed that warm sst anomalies over the south atlantic tend to intensify the sacz and shift it northward while cool sst anomalies over the south atlantic tend to weaken the sacz the ogcm experiments on the other hand showed that the intensification of the sacz contributes to cool the underlying ocean through the reduction of incident shortwave solar radiation causing the appearance of cold sst anomalies or the weakening of pre existing warm sst anomalies the most important finding in this work was the predominance of the cloud shortwave sst negative thermodynamic feedback between the atmosphere and the ocean over the southwest tropical atlantic this is one order of magnitude larger than the dynamic feedback associated with ekman pumping the latter was verified only during strong sacz events the results suggest that negative sst anomalies often observed underlying the sacz represent an ocean response to atmospheric forcing

structure of interannual to decadal climate variability in the tropical atlantic sector abstract a search for coupled modes of atmosphere ocean interaction in the tropical atlantic sector is presented previous studies have provided conflicting indications of the existence of coupled modes in this region the subject is revisited through a rotated principal component analysis performed on datasets spanning the 36 yr period 1958 93 the analysis includes four variables sea surface temperature oceanic heat content wind stress and atmospheric diabatic heating the authors find that the first rotated principal component is associated with fluctuations in the subtropical wind system and correlates with the north atlantic oscillation nao while the second and third modes which are the focus of interest are related to tropical variability the second mode is the atlantic nino mode with anomalous sea surface temperature and anomalous heat content in the eastern equatorial basin wind stress weakens to the west of anomalously warm water while convection is shifted south and eastward surface

geochemistry of recent toc rich sediments from the gulf of california and the black sea major and minor elements incl ag as ba cd co cr cu mn mo ni pb sr v zn have been determined in recent sediments from the gulf of california upwelling area and black sea sapropels in order to reinterpret their chemical composition in view of reliable seawater and plankton data the chemistry of the gulf of california sediments reflects regeneration processes which occur in the water column i e only a small fraction 10 of elements like cd which in seawater are coupled to the labile nutrients c n p is buried in the sedimentary column in contrast elements like the more resistant nutrients si undergo a deeper regeneration cycle ba several trace metals which are present in comparatively higher concentrations in seawater as mo u v and at the same time are reactive under reducing conditions and or are able to form stable sulfides are fixed in the sediments during early diagenesis the early diagenetic behavior of ba is closely related to bacterial sulfate reduction the formation of barite concretions is discussed anoxic conditions in the water column act as ideal traps for a number of redox sensitive and or stable sulfide forming elements a simple trace metal balance calculation shows that the chemical composition of black sea sapropels is controlled by fluvial and mediterranean seawater element input and the accumulation rate of terrigenous detrital material

massive volcanism at the permian triassic boundary and its impact on the isotopic composition of the ocean and atmosphere abstract bulk carbonate and conodonts from three permian triassic p t boundary sections at guryul ravine kashmir abadeh central iran and pufels bula bulla italy were investigated for 13 c and 18 o carbon isotope data highlight environmental changes across the p t boundary and show the following features 1 a gradual decrease of 4 to more than 7 starting in the late permian changhsingian c bachmanni zone with two superimposed transient positive excursions in the c meishanensis h praeparvus and the m ultima s mostleri zones 2 two 13 c minima the first at the p t boundary and a higher occasionally double minimum in the lower i isarcica zone it is unlikely that the short lived phenomena such as a breakdown in biological productivity due to catastrophic mass extinction a sudden release of oceanic methane hydrates or meteorite impact s could have been the main control on the latest permian carbon isotope curve because of its prolonged 0 5 ma duration gradual decrease and the existence of a 1 positive shift at the main extinction horizon the p t boundary 13 c trend matches in time and magnitude the eruption of the siberian traps and other contemporaneous volcanism suggesting that volcanogenic effects such as outgassed co 2 from volcanism and even more thermal metamorphism of organic rich sediments as the likely cause of the negative trend

tropical atlantic sea surface temperature variability and its relation to el nino southern oscillation past analyses of tropical atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics across the intertropical convergence zone itcz by analyzing an improved 43 year 1950 1992 record of sst smith et al 1996 and other data derived from the comprehensive ocean atmosphere data set coads it is shown that the regions north and south of the itcz are statistically independent of each other at the seasonal to interannual timescales dominating the data confirming the conclusions of houghton and tourre 1992 some dipole behavior does develop weakly during the boreal spring season when there is a tendency for sst anomaly west of angola to be opposite of that in the tropical north atlantic it is further shown that tropical atlantic sst variability is corre lated with pacific e1 nifio southern oscillation enso variability in several regions the ma jor region affected is the north atlantic area of ne trades west of 40ow along 10on 20on and extending into the caribbean there about 50 80 of the anomalous sst variability is associ ated with the pacific enso with atlantic warmings occurring 4 5 months after the mature phases of pacific warm events an analysis of local surface flux fields derived from coads data shows that the enso related atlantic warmings occur as a result of reductions in the surface ne trade wind speeds which in turn reduce latent and sensible heat losses over the region in ques tion as well as cooling due to entrainment this enso connection is best developed during the boreal spring following the most frequent season of maximum enso anomalies in the pacific a region of secondary covariability with enso occurs along the northern edge of the mean itcz position and appears to be associated with northward migrations of the itcz when the north at lantic warmings occur although easterly winds are intensified in the western equatorial atlantic in response to pacific warm events they do not produce strong local changes in sst contrary to expectations from studies based on equatorial dynamics these teleconnected wind anomalies do not give rise to significant correlations of sst in the gulf of guinea with the pacific enso as the teleconnection sequence matures strong se trades at low southern latitudes follow the de velopment of the north atlantic sst anomaly and precede by several months the appearance of weak negative sst anomalies off angola and stronger positive anomalies extending eastward from southern brazil along 15o 30os

tropical atlantic air sea interaction and its influence on the nao an atmospheric general circulation model agcm is forced with a prescribed sst dipole anomaly in the tropical atlantic to investigate the cause of cross equatorial sst gradient cesg variability and its teleconnection to the extratropics the model response bears a striking resemblance to observations in both the tropics and extratropics the tropical response is robust and can act to reinforce the prescribed sst anomalies through wind induced evaporation a new feedback mechanism involving low level stratiform clouds in the subtropics is also identified in the model and observations the tropical sst dipole forces a barotropic teleconnection into the extratropics that projects onto the north atlantic oscillation nao it further induces the extratropical portion of the north atlantic sst tripole when the agcm is coupled with an ocean mixed layer model cesg variability thus appears to be the centerpiece of a pan atlantic climate pattern observed to extend from the south atlantic to greenland

latest permian chars may derive from wildfires not coal combustion the permian triassic boundary extinction event was the largest biological crisis of the phanerozoic one of the principle triggers for the mass extinction is thought to be greenhouse warming resulting from the release of ch 4 from basalt coal interaction during the extensive siberian traps russia eruptions observations of organic matter interpreted to be coal combustion products fly ash in latest permian marine sediments have been used to support this hypothesis however this interpretation is dependent upon vesicular chars being fly ash coal combustion derived and not formed by alternative mechanisms here we present reflectance microscopy images of vesicular chars from russian permian coals and chars from modern tundra peatland and boreal forest fires to demonstrate that despite a difference in precursor fuels wildfires are capable of generating vesicular chars that are morphologically comparable to end permian fly ash these observations coupled with extensive global evidence of wildfires during this time interval call into question the contribution of coal combustion to the end permian extinction event

catastrophic dispersion of coal fly ash into oceans during the latest permian extinction the eruption of the siberian trap flood basalts resulted in the heating and combustion of coals and organic rich sediments at the time of the permian mass extinction the presence of char in distant lake sediments linked to the eruption suggests that fly ash could have been generated by the coal combustion and then dispersed globally creating toxic marine conditions

spells of low frequency oscillations and weather regimes in the northern hemisphere abstract the low frequency variability in the midlatitudes is described through an analysis of the oscillatory phenomena in order to isolate nearly periodic components of the atmospheric flow the multichannel version of the singular spectrum analysis m ssa is developed and applied to an nmc 32 year long set of 700 hpa geopotential heights in the same way that principal component analysis identifies the spatial patterns dominating the variability m ssa identifies dynamically relevant space time patterns and provides an adaptive filtering technique three major low frequency oscillations lfos are found with periods of 70 days 40 45 days and 30 35 days the 70 day oscillation consists of fluctuations in both position and amplitude of the atlantic jet with a poleward propagating anomaly pattern the 40 45 day oscillation is specific to the pacific sector and has a pronounced pacific north american pna structure in its high amplitude phase the 30 35 day mode is confined over the atlantic region

methane release from igneous intrusion of coal during late permian extinction events abstract unusually large and locally variable carbon isotope excursions coincident with mass extinctions at the end of the permian period 253 ma and guadalupian epoch 260 ma can be attributed to methane outbursts to the atmosphere methane has isotopic values 13c low enough to reduce to feasible amounts the carbon required for isotopic mass balance the duration of the carbon isotopic excursions and inferred methane releases are here constrained to 10 000 yr by counting annual varves in lake deposits and by estimating peat accumulation rates on paleogeographic maps the most marked carbon isotope excursions form linear arrays back to plausible methane sources end permian siberian traps and longwood bluff intrusions of new zealand and end guadalupian emeishan traps of china intrusion of coal seams by feeder dikes to flood basalts could create successive thermogenic methane outbursts of the observed timing and magnitude but these are unreasonably short times for replenishment of marine or permaf

dominant modes of variability in the south atlantic a study with a hierarchy of ocean atmosphere models using an atmosphere model of intermediate complexity and a hierarchy of ocean models the dominant modes of interannual and decadal variability in the south atlantic ocean are studied the atmosphere simplified parameterizations primitive equation dynamics speedy model has t30l7 resolution the physical package consists of a set of simplified physical parameterization schemes based on the same principles adopted in the schemes of state of the art agcms it is at least an order of magnitude faster whereas the quality of the simulated climate compares well with those models the hierarchy of ocean models consists of simple mixed layer models with an increasing number of physical processes involved such as ekman transport wind induced mixing and wind driven barotropic transport finally the atmosphere model is coupled to a regional version of the miami isopycnal coordinate ocean model micom covering the south atlantic with a horizontal resolution of 1 and 16 vertical layers the coupled modes of mean sea level pressure and sea surface temperature simulated by speedy micom strongly resemble the modes as analyzed from the ncep ncar reanalysis indicating that this model configuration possesses the required physical mechanisms for generating these modes of variability using the ocean model hierarchy the authors were able to show that turbulent heat fluxes ekman transport and wind induced mixing contribute to the generation of the dominant modes of coupled sst variability the different roles of these terms in generating these modes are analyzed variations in the wind driven barotropic transport mainly seem to affect the sst variability in the brazil malvinas confluence zone the spectra of the mixed layer models appeared to be too red in comparison with the fully coupled speedy micom model due to the too strong coupling between sst and surface air temperatures sats resulting from the inability to advect and subduct sst anomalies by the mixed layer models in speedy micom anomalies in the southeastern corner of the south atlantic are subducted and advected toward the north brazilian coast on a time scale of about 6 yr

atmospheric response to south atlantic sst dipole 1 recent analyses of historical data and output of numerical models have suggested a dipolar mode of decadal variability in the south atlantic in this work the the atmospheric response to such anomalous sst dipole in the south atlantic is investigated with a numerical model the results show a deep baroclinic response over the equatorward pole and a shallow equivalent barotropic response over the poleward pole the baroclinic response is strongest during the austral summer it affects the meridional circulation over the tropical atlantic with anomalous downward motion north of the itcz and anomalous ascending motion southward of it resulting in a southward shift of the itcz the itcz response is enhanced due to a positive feedback induced by anomalous low level convergence of moisture changes in cloud cover counteract the variations in latent heat flux north of the itcz thereby prohibiting the generation of an ssta of opposite sign as suggested by the wind evaporation sst wes feedback

atlantic sst gradient and the influence of enso 1 the relationship between the boreal winter el nino sst anomaly and boreal spring tropical atlantic sst gradient north atlantic minus south atlantic is investigated using a long detrended sst record for both el nino and la nina concordant cases same sign for nino3 index and atlantic sst gradient slightly dominate over discordant ones reflecting the fact that the nino3 index correlates more strongly with the north atlantic than the south atlantic sst anomaly the ratio of the numbers of concordant and discordant cases is 4 3 overall indicating strong non enso influences on the atlantic sst gradient the composite of the concordant cases shows an sst anomaly in the north atlantic with the same sign as nino3 and an opposite signed anomaly off the southwest coast of africa resembling benguela nino that of the discordant cases is dominated by a pre existing sst anomaly with the same sign as nino3 in the south central south atlantic

contrasting sulfur geochemistry and fe al and mo al ratios across the last oxic to anoxic transition in the cariaco basin venezuela an abrupt transition from oxic to anoxic sulfidic euxinic marine bottom waters occurred in the cariaco basin in response to increasing productivity resulting from the late pleistocene post glacial rise in sea level and corresponding increase in surface water nutrient availability the microlaminated sediments of the euxinic interval which span the last f14 5 ky suggest a predominance of water column syngenetic pyrite formation based on 1 high pyrite sulfur spy concentrations in the surficial sediment layers 2 values for degree of pyritization dop that generally do not increase appreciably with increasing burial 3 ratios of total iron fet to al that are elevated above the continental baseline recorded in the underlying oxic sediments and 4 spy isotope trends that largely mimic the d 34 shsof the modern water column intermediate dop values in the microlaminated deposits and fet al ratios that are slightly above continental levels indicate an iron reservoir controlled by scavenging during syngenetic pyrite formation in combination with intermediate rates of fe bearing siliciclastic accumulation as predicted from the relative rates of siliciclastic delivery fet al and dop data lie between end member values observed in the modern black sea as viewed broadly fet al and dop relationships in euxinic sediments reflect the balance between syngenetic fe scavenging and temporal and spatial gradients in siliciclastic input pyrite concentrations are generally low in the underlying oxic marine deposits because of limitations in the supply of organic carbon corg however the upper 80 cm of the fe rich corg poor bioturbated sediment show evidence for a strong diffusional hsoverprint from the overlying fe limited euxinic marine environment this post glacial transition manifests in pyrite overprints that are strongly 34 s depleted relative to those in restricted presently euxinic marine settings elsewhere in the world such as the black sea where the sedimentary sequence spanning the last glacial interglacial transition begins with a shift from freshwater to corg poor oxic marine deposition and thus dominantly sulfate diffusion trends for mo al ratios in the microlaminated sediments suggest that mo is enriched by roughly two orders of magnitude above the continental levels recorded in the oxic deposits organic matter plays a role by enhancing hsproduction and or by providing a substrate for mo scavenging significant mo enrichment via diffusion into the upper portion of the bioturbated zone was not observed despite hs rich pore waters as recorded in the heavy iron sulfide overprint we have

a quasi biennial oscillation in the equatorial atlantic ocean a quasi biennial oscillation with features characteristic of equatorial coupled modes is found in the equatorial atlantic ocean the origins of the phenomenon are investigated by using a coupled atmosphere ocean general circulation model in which the fully coupled domain is restricted to the tropical atlantic 20 s 30 n the simulations capture a similar oscillation regardless of whether sea surface temperatures prescribed outside the coupled domain correspond to the observed or the climatology i e lack year to year variability it is concluded that the equatorial atlantic hosts a quasi biennial oscillation generated by coupled atmosphere ocean interactions internal to the basin with little influence from remote events even from el nino southern oscillation

south atlantic variability arising from air sea coupling local mechanisms and tropical subtropical interactions abstract interannual variability in the southern and equatorial atlantic is investigated using an atmospheric general circulation model agcm coupled to a slab ocean model som in the atlantic in order to isolate features of air sea interactions particular to this basin simulated covariability between sea surface temperatures ssts and atmosphere is very similar to the observed non enso related covariations in both spatial structures and time scales the leading simulated empirical coupled mode resembles the zonal mode in the tropical atlantic despite the lack of ocean dynamics and is associated with baroclinic atmospheric anomalies in the tropics and a rossby wave train extending to the extratropics suggesting an atmospheric response to tropical sst forcing the second non enso mode is the subtropical dipole in the sst with a mainly equivalent barotropic atmospheric anomaly centered on the subtropical high and associated with a midlatitude wave train consistent with atmospheric forcing of the sub

geochemical study of organic matter rich cycles from the kimmeridge clay formation of yorkshire uk productivity versus anoxia abstract in this contribution we study two meter scale cycles from the kimmeridge clay formation cored near marton yorkshire which shows cyclic organic matter om distribution our aim is to try to understand the factors responsile for om accumulation the first cycle called lower cycle shows a total organic carbon toc content between 1 and 10 whereas the second called upper cycle shows a toc content varying between 5 and 35 the geochemical composition major elements and trace elements the organic geochemistry toc hi palynofacies and mineralogy of the sediments have been determined in both cycles the cyclicity is expressed through variations in the nature and in the relative abundance of the various types of organic matter constituents furthermore dilution effects by inorganic components of the sediment cannot account for the toc cyclicity for lower cycle the mo v and u content is low and little variable as is the intensity of the oxidation which om suffered from this indicates that variations in phytoplanktonic productivity may be held responsible for the cyclicity in steady and mildly reducing redox conditions in the upper cycle cyclicity also appears to depend on productivity but variations in the concentration of mo v and u and in the oxidation state of the om suggest the environment was temporarily more reducing it is proposed that larger amounts of h 2 s were released into marine bottom waters as a result of initial om decomposition forced the oxic anoxic boundary to rise in the water column and thus favoured om storage the main driving force for variations in the om concentration was the productivity of organic matter walled phytoplankton redox conditions of the depositional environment could have had a positive action but only by acting as a positive feedback effect

explosive eruption of coal and basalt and the end permian mass extinction the end permian extinction decimated up to 95 of carbonate shell bearing marine species and 80 of land animals isotopic excursions dissolution of shallow marine carbonates and the demise of carbonate shell bearing organisms suggest global warming and ocean acidification the temporal association of the extinction with the siberia flood basalts at approximately 250 ma is well known and recent evidence suggests these flood basalts may have mobilized carbon in thick deposits of organic rich sediments large isotopic excursions recorded in this period are potentially explained by rapid venting of coal derived methane which has primarily been attributed to metamorphism of coal by basaltic intrusion however recently discovered contemporaneous deposits of fly ash in northern canada suggest large scale combustion of coal as an additional mechanism for rapid release of carbon this massive coal combustion may have resulted from explosive interaction with basalt sills of the siberian traps here we present physical analysis of explosive eruption of coal and basalt demonstrating that it is a viable mechanism for global extinction we describe and constrain the physics of this process including necessary magnitudes of basaltic intrusion mixing and mobilization of coal and basalt ascent to the surface explosive combustion and the atmospheric rise necessary for global distribution

variability of the tropical ocean surface temperatures at decadal multidecadal timescales part i the atlantic ocean abstract gridded time series from the global ocean surface temperature atlas were analyzed with a variety of techniques to identify spatial structures and oscillation periods of the tropical atlantic sea surface temperature sst variations at decadal timescales and to develop physical interpretations of statistical patterns of decadal sst variations each time series was 110 yr 1882 1991 long the tropical atlantic sst variations were compared with decadal variations in a 74 yr long 1912 85 north nordeste brazil rainfall time series and a 106 yr long 1886 1991 tropical atlantic cyclone activity index time series the tropical atlantic sst variations were also compared with decadal variations in the extratropical atlantic sst multiyear to multidecadal variations in the cross equatorial dipole pattern identified as a dominant empirical pattern of the tropical atlantic sst variations in earlier and present studies are shown to be variations in the approximately north south gradient of sst anomalies

observed decadal midlatitude and tropical atlantic climate variability two common indicators of atlantic climate variability viz the north atlantic oscillation nao and the cross intertropical convergence zone itcz sea surface temperature sst gradient are examined for their frequency characteristics and midlatitude tropical links sst anomalies north and south of the itcz are found to be uncorrelated on all time scales while the sea level pressure slp fluctuations associated with the nao display a coherent seesaw between iceland and the azores this out of phase relationship spans a broad range of time scales but is particularly strong in the 5 10 year period band strong broadband coherence between the nao and the tropical atlantic cross itcz sst difference is found in the 8 20 year period band suggesting a significant midlatitude tropical interaction moreover tropical atlantic ssts on both sides of the itcz separately exhibit significant coherence with the nao index and slp variability over iceland and the azores based on these findings we hypothesize that the tropical atlantic ta ocean atmosphere interaction is affecting north atlantic climate variability

siberian gas venting and the end permian environmental crisis abstract the end of the permian period is marked by global warming and the biggest known mass extinction on earth the crisis is commonly attributed to the formation of the siberian traps large igneous province although the causal mechanisms remain disputed we show that heating of tunguska basin sediments by the ascending magma played a key role in triggering the crisis our conclusions are based on extensive field work in siberia in 2004 and 2006 heating of organic rich shale and petroleum bearing evaporites around sill intrusions led to greenhouse gas and halocarbon generation in sufficient volumes to cause global warming and atmospheric ozone depletion basin scale gas production potential estimates show that metamorphism of organic matter and petroleum could have generated 100 000 gt co2 the gases were released to the end permian atmosphere partly through spectacular pipe structures with kilometre sized craters dating of a sill intrusion by the u pb method shows that the gas release occurred at 252 0 0 4 million years ago overlapping in time with the end permian global warming and mass extinction heating experiments to 275 c on petroleum bearing rock salt from siberia suggests that methyl chloride and methyl bromide were significant components of the erupted gases the results indicate that global warming and ozone depletion were the two main drivers for the end permian environmental crisis we demonstrate that the composition of the heated sedimentary rocks below the flood basalts is the most important factor in controlling whether a large igneous provinces causes an environmental crisis or not we propose that a similar mechanism could have been responsible for the triassic jurassic 200 ma global warming and mass extinction based on the presence of thick sill intrusions in the evaporite deposits of the amazon basin in brazil

warm events in the tropical atlantic abstract sea surface temperature in the eastern equatorial atlantic ocean undergoes anomalous warming events of 1 2 c every few years the warm anomalies reach their maximum strength in northern hemisphere summer when equatorial upwelling normally brings cold thermocline water to the surface by compositing surface observations from a 28 year record we are able to identify consistent features in anomalies of sst and winds the composites show that the sst anomalies in northern summer are confined to the eastern equatorial region with reduced zonal winds to the west and reduced northward trade winds to the east accompanying these changes in winds are enhanced convection near the equator caused by a southward shift and intensification of the intertropical convergence zone later in the year sst south of the equator becomes elevated as a result by spring of the year following the equatorial anomaly convection in the western side of the basin is much higher than normal to understand the ocean dynami