timing of recovery from the end permian extinction geochronologic and biostratigraphic constraints from south china four volcanic ash beds bracket the early middle triassic boundary as defined by conodont biostratigraphy in a stratigraphic section in south china high precision u pb dates of single zircons allow us to place the early to middle triassic olenekian anisian boundary at 247 2 ma magnetic reversal stratigraphy allows global correlation the new dates constrain the early triassic interval characterized by delayed biotic recovery and carbon cycle instability to 5 m y this time constraint must be considered in any model for the end permian extinction and subsequent recovery

geochemical implications of sulfate in sedimentary carbonates abstract sulfate content reaches maximum partitioning in inorganically deposited mn calcite from aqueous solution when the carbonate contains 4 wt mno similar partitioning was also found for sr which rises to a maximum when calcite sediments contain 0 5 wt mno the behavior of the sulfate is explicable in terms of substitution of co 2 3 by so 2 4 this argument for the distribution of so 2 4 in inorganically formed carbonates is also consistent for sulfate in marine carbonates ir spectra of recent biogenic carbonates revealed no organic but only inorganic sulfate indicating that the sulfate occupies lattice sites in the carbonates total sulfate content of recent calcitic marine carbonates and pleistocene limestones increases with increasing mg content up to a maximum near 2 3 wt mg and decreases at larger mg contents this decrease in the sulfate content of these marine carbonates from that incorporated originally into the carbonate lattices is attributed to gradual exsolution during diagenesis in subaerial fresh water or on the sea floor in low so 2 4 waters the sulfate in coralline algae apparently increases the mg content above that predicted from observed shifts in the x ray diffraction peaks based upon so 2 4 free calcites

evidence for warmer interglacials in east antarctic ice cores reconstructions of temperature variations from antarctic ice cores rely on the assumption that the relationship between hydrogen and oxygen isotopic ratios and temperature are stable in space and time sime et al analyse three 340 000 year old ice cores from east antarctica and use an isotope enabled general circulation model to show that instead the relationship is nonlinear during warm periods the ratios are less sensitive to temperature so previous estimates of interglacial temperatures are likely to be about 3 c too low this is consistent with peak antarctic interglacial temperatures at least 6 c higher than today this work suggests that there are serious deficiencies in our understanding of climates that are warmer than today s reconstructions of temperature variations from antarctic ice cores rely on the assumption that the relationship between hydrogen and oxygen isotope ratios and temperature are stable in space and time three east antarctic ice core records are now analysed alongside input from general circulation models to reveal that during warmer interglacial periods the isotope ratios are less sensitive to temperature than during colder interglacials consequently previous estimates of interglacial temperatures are probably too cold stable isotope ratios of oxygen and hydrogen in the antarctic ice core record have revolutionized our understanding of pleistocene climate variations and have allowed reconstructions of antarctic temperature over the past 800 000 years 800 kyr refs 1 2 the relationship between the d h ratio of mean annual precipitation and mean annual surface air temperature is said to be uniform 10 over east antarctica3 and constant with time 20 refs 3 5 in the absence of strong independent temperature proxy evidence allowing us to calibrate individual ice cores prior general circulation model gcm studies have supported the assumption of constant uniform conversion for climates cooler than that of the present day3 5 here we analyse the three available 340 kyr east antarctic ice core records alongside input from gcm modelling we show that for warmer interglacial periods the relationship between temperature and the isotopic signature varies among ice core sites and that therefore the conversions must be nonlinear for at least some sites model results indicate that the isotopic composition of east antarctic ice is less sensitive to temperature changes during warmer climates we conclude that previous temperature estimates from interglacial climates are likely to be too low the available evidence is consistent with a peak antarctic interglacial temperature that was at least 6 k higher than that of the present day approximately double the widely quoted 3 1 5 k refs 5 6

early triassic seawater sulfate drawdown abstract the marine sulfur cycle is intimately linked to global carbon fluxes atmospheric composition and climate yet relatively little is known about how it responded to the end permian biocrisis the largest mass extinction of the phanerozoic here we analyze carbonate associated sulfate cas from three permo triassic sections in south china in order to document the behavior of the c s cycle and its relationship to marine environmental changes during the mass extinction and its aftermath we find that 34 s cas varied from 9 to 44 at rates up to 100 myr 1 during the griesbachian smithian substages of the early triassic we model the marine sulfur cycle to demonstrate that such rapid variation required drawdown of seawater sulfate concentrations to 4 mm and a reduction in its residence time to 200 kyr this shorter residence time resulted in positive covariation with 13 c carb due to strong coupling of the organic carbon and pyrite burial fluxes carbon and sulfur isotopic shifts were associated with contemporaneous changes in climate marine productivity and microbial sulfate reduction rates with negative shifts in 13 c carb and 34 s cas linked to warming decreased productivity and reduced sulfate reduction sustained cooling during the spathian re invigorated oceanic overturning circulation reduced marine anoxia and limited pyrite burial as seawater sulfate built to higher concentrations during the spathian the coupling of the marine c and s cycles came to an end and a general amelioration of marine environmental conditions set the stage for a recovery of invertebrate faunas variation in seawater sulfate during the early triassic was probably controlled by climate change possibly linked to major eruptive phases of the siberian traps

carbon isotope record of the p t boundary and the lower triassic in the southern alps evidence for rapid changes in storage of organic carbon abstract the carbonate carbon isotope record of lower triassic shelf sediments was investigated in the pufels and l om picol uomo sections of the western central dolomites to derive a complete record from the permian triassic transition to the uppermost lower triassic from the western tethys the carbon isotope record shows the well studied decrease at the permian triassic boundary ptb followed by an increase to about 1 5 at the dienerian smithian boundary the 13c values increase to a pronounced 6 maximum a steady rapid drop until the upper smithian below 2 follows this 13c peak at the smithian spathian transition a steep rise to positive values is documented the positive carbon isotope peak is interpreted to reflect an interval of enhanced burial of organic carbon whereas the isotopic minima provide evidence of periods of oxidation of organic matter and or release of isotopically light carbon this may be ascribed to quickly changing environmental conditions which have already been postulated by paleontologists due to the delayed biotic recovery from the permian triassic extinction event because of the short time interval these positive isotope excursions represent their generation by burial of organic carbon in periods of high productivity and or anoxia appears plausible concurrent carbon isotopic excursions are reported from iran pakistan and oman as well as from southern china which indicate an at least tethys wide event if the excursion proves to be of global significance dark shale deposited in the pelagic panthalassa ocean may have acted as sink for organic carbon supporting the hypothesis of a periodically stratified ocean in the lower triassic

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

early triassic conodont palynological biostratigraphy of the meishan d section in changxing zhejiang province south china the lower triassic consisting of the yinkeng fm helongshan fm and the lower part of the nanlinghu fm is well developed at the meishan d section of changxing county zhejiang province south china based on detailed study of the conodont biostratigraphy from the interval of the permian triassic boundary and the lower triassic in the meishan d section 8 conodont zones are recognized in ascending order as follows the neogondolella changxingensis yini hindeodus praeparvus zone beds 24a 24e top of the changxing fm the neogondolella meishanensis meishanensis hindeodus eurypyge zone beds 25 27b base of the yinkeng fm the hindeodus parvus zone beds 27c 27d first conodont zone of triassic the global index for the base of triassic the isarcicella staeschei zone beds 28 29a lower part of the yinkeng fm i isarcica zone beds 29b 51 lower part of the yinkeng fm the neogondolella tulongensis n planata zone beds 52 72 from upper part of the yinkeng fm to lower part of the helongshan fm the neospathodus kummeli zone beds 73 92 middle part of the helongshan fm and the neospathodus cristagalli n dieneri zone beds 93 111 from upper part of the helongshan fm to the base of the nanlinghu fm at the meishan d section the palynological biostratigraphy is also studied herein the palynological assemblage of lundbladispora taeniaesporites equisetosporites is found in the intervals which contain the conodont isarcicella isarcica zone and the lower part of the neogondolella tulongensis n planata zone

investigating the 8 2 ka event in northwestern madagascar insight from data model comparisons abstract the 8 2 ka event is a well known cooling event in the northern hemisphere but is poorly understood in madagascar here we compare paleoclimate data and outputs from paleoclimate simulations to better understand it records from madagascar suggest two distinct sub events 8 3 ka and 8 2 ka that seem to correlate with records from northern high latitude this could indicate causal relationships via changes in the atlantic meridional overturning circulation amoc with changes in moisture source s 18o and changes in the mean position of the inter tropical convergence zone itcz as climate modelling suggests these two sub events are also apparent in other terrestrial records but the climatic signals are different the prominent 8 2 ka sub event records a clear antiphase relationship between the northern and southern hemisphere monsoons whereas such relationship is less evident during the first 8 3 ka sub event data model comparison have also shown a mismatch between the paleoclimate data and the model outputs the causes of which are more or less understood and may lie in the proxies in the model or in both data and model knowing that paleoclimate proxies and climate models produce different sets of variables further research is needed to improve the data model comparison approach so that both paleoclimate data and paleoclimate models will better predict the likely climate status of a region during a specified time in the past with minimal uncertainties

contrasting patterns of hydrological changes in europe in response to holocene climate cooling phases the quantitative reconstruction of climatic parameters from pollen and lake level data obtained at saint jorioz lake annecy eastern france gives evidence for cooler and wetter conditions during the 8 2 ka cold event a comparison of these regional data with other hydrological records reconstructed in europe for the same period suggests as a working hypothesis that mid latitudes between ca 50 and 43 underwent wetter conditions in response to the cooling whereas northern and southern europe were marked by drier climate in the latter case leading to an interruption of the sapropel 1 formation in the mediterranean a similar hydrological tri partition of europe can be observed during other holocene cooling phases associated with north atlantic ird events data indicate that the middle zone characterised by wetter climate conditions could have had a more extended latitudinal amplitude during phases of climate cooling weaker than the 8 2 ka event the differences in expansion of the wet mid european zone depending on holocene climate cooling phases could reflect variations in the strength of the atlantic westerly jet in relation with the thermal gradient between high and low latitudes

the major ion composition of permian seawater abstract the major ion mg2 ca2 na k so42 and cl composition of permian seawater was determined from chemical analyses of fluid inclusions in marine halites new data from the upper permian san andres formation of texas 274 272 ma and salado formation of new mexico 251 ma analyzed by the environmental scanning electron microscopy esem x ray energy dispersive spectrometry eds method along with published chemical compositions of fluid inclusions in permian marine halites from north america two formations of different ages and the central and eastern european basins eight formations of four different ages show that permian seawater shares chemical characteristics with modern seawater including so42 ca2 at the point of gypsum precipitation evolution into mg2 na k so42 cl brines and mg2 k ratios 5 permian seawater however is slightly depleted in so42 and enriched in ca2 although modeling results do not rule out ca2 concentrations close to those in present day seawater na and mg2 in permian seawater are close to slightly below their concentrations in modern seawater permian and modern seawater are both classified as aragonite seas with mg2 ca2 ratios 2 conditions favorable for precipitation of aragonite and magnesian calcite as ooids and cements the chemistry of permian seawater was modeled using the chemical composition of brine inclusions for three periods lower permian asselian sakmarian 296 283 ma lower permian artinskian kungurian 283 274 ma and upper permian tatarian 258 251 ma parallel changes in the chemistry of brine inclusions from equivalent age evaporites in north america central europe and eastern europe show that seawater underwent secular variations in chemistry over the 50 million years of the permian modeled so42 concentrations are 20 mmol per kg h2o mmolal and 19 mmolal in the asselian sakmarian and artinskian kungurian with higher concentrations in the upper permian tatarian 23 mmolal modeled ca2 is at or above its concentration in modern seawater throughout the permian mg2 is close to slightly below its concentration in modern seawater 55 mmolal in the asselian sakmarian 52 mmolal and tatarian 52 mmolal but slightly higher than modern seawater in the artinskian kungurian 60 mmolal mg2 ca2 ratios are 3 5 total range 2 7 to 5 5 in the lower permian and rose slightly to 3 7 total range 3 1 to 5 8 in the upper permian primarily due to decreases in ca2 these results are consistent with models that predict oscillations in the major ion composition of phanerozoic seawater on the basis of changes in the midocean ridge river water flux ratio driven by changes in the rate of midocean ridge crust production the permian was characterized by low sea levels icehouse conditions and southern hemisphere glaciation such conditions analogous to the present ice age and the similarities between permian seawater and modern seawater all suggest that general phanerozoic supercycles driven by mantle convection and global volcanicity also control the major ion chemistry of seawater

sequence stratigraphy of carbonate evaporite basins models and application to the upper permian zechstein of northeast england and adjoining north sea the successions of carbonate evaporite basins which are periodically cut off from the world ocean are considered in terms of their sequence stratigraphy two basin types are distinguished those where incomplete drawdown takes place and those showing complete drawdown and wholesale basin desiccation it is argued that following relative sea level falls sequences begin with the evaporites precipitated as marginal lowstand gypsum wedges in the first basin type and as lowstand basin centre halite fills in the second the evaporites pass up into carbonate sediments which are mainly deposited on shallow water platforms around the basin during transgressive and highstand systems tracts the concepts and models developed are applied to the zechstein upper permian strata of northeast england and adjoining north sea seven sequences are proposed with some containing thin parasequences the sequence approach to carbonate evaporite basins which considers both basin margin and basin centre facies gives a more encompassing perspective of sedimentation than the traditional cycle concept with its emphasis on the basin centre

changes in the global carbon cycle occurred as two episodes during the permian triassic crisis coeval records of ocean atmosphere and terrestrial change are crucial to understanding the pattern and causes of global mass extinction across the permian triassic boundary ptb however relationships among changes in different settings remain largely unclear primarily due to the challenges associated with the correlation among disparate records here we compare marine carbon isotopic records with marine and terrestrial environmental and biotic events recorded in sediments from the meishan ptb section of south china time scaled carbonate carbon isotopes exhibit two gradual major shifts across the ptb at meishan and these are duplicable elsewhere around the tethys ocean the two shifts are associated with two episodes of enhanced terrestrial weathering indicated by an increased abundance of 13 c enriched moretanes relative to hopanes and an elevated abundance of black carbon fragments key marine events previously reported for the ptb including photic zone euxinia faunal mass extinction and cyanobacterial expansion also occur as two episodes coinciding with both of the progressive shifts to negative 13 c values and enhanced weathering the temporal sequence of the duplicable events suggests that the biotic crisis was a consequence of prolonged and episodic changes in the marine and continental systems and argues against an extraterrestrial impact as the main cause

a sulfur isotope event at the end of the permian abstract a hypothesis of light sulfur injection to the ocean atmosphere system at the end of the permian was presented by kaiho et al kaiho k kajiwara y nakano t miura y kawahata h tazaki k ueshima m chen z q shi g r 2001 end permian catastrophe by a bolide impact evidence of a gigantic release of sulfur from the mantle geology 29 815 818 based on a negative shift of 34 s 32 s ratio of carbonate associated sulfate in south china this hypothesis was discussed in some papers with additional data in other areas however the cause and distribution of the negative shift has not been clarified here we show that a significant decrease in the 34 s 32 s ratio of carbonate associated sulfate occurred simultaneously in south china and hungary at the end of the permian coincident with the end permian mass extinction the cause of the abrupt negative shift of 34 s 32 s in these two distant sites is the injection of light sulfur to the surface ocean from the deep ocean rich in h 2 s or deposits rich in sulfide or the mantle this sulfur isotope event was likely caused by either an abrupt warming a bolide impact to the ocean mantle plume induced volcanism or a harmonizing of these possible direct causes are 1 massive release of h 2 s gas from the euxinic surface and intermediate waters due to abrupt warming by volcanic co 2 or impact shock wave in the ocean 2 a huge volcanism penetrated sediments or ore rich in sulfide 3 an extraterrestrial impact to sulfide rich sediments or ore deposit and 4 release of mantle origin sulfur by an impact of 70 km asteroid to the ocean these are four possible causes for a mass extinction there is also a possibility of a local oceanic event only in the tethys

ensemble water isotope enabled coupled general circulation modeling insights into the 8 2 ka event 1 freshwater forcing has long been postulated as a catalyst for abrupt climate change because of its potential to interfere with thermohaline circulation thc the most recent example may have occurred about 8 2 ka ago with the sudden drainage of glacial lakes agassiz and ojibway into the hudson bay we perform an ensemble of simulations for this freshwater release using the fully coupled atmosphere ocean general circulation model goddard institute for space studies modele r in all cases simulated effects include reduced ocean heat transport and enhanced atmospheric heat transport in the atlantic increased surface albedo through greater low cloud and sea ice cover and local cooling of up to 3 c our suite of ensemble experiments allows us to examine the importance of the initial ocean state in particular the presence or absence of labrador sea water in controlling the magnitude and length of the climate response water isotope tracers included in this model provide an improved means for direct comparisons of the modeled tracer response to water isotope based climate proxy data comparison of model simulations to data implies that there was an abrupt approximate halving of atlantic thc hence providing strong support for the hypothesis that the 8 2 ka event was caused by an abrupt release of fresh water into the north atlantic

modeling the effect of freshwater pulses on the early holocene climate the influence of high frequency climate variability freshwater 4 67 10 14 m 3 into the labrador sea at three different constant rates 1 5 sv 1 sv 1 10 6 m 3 s 1 i n 10 years 0 75 sv in 20 years and 0 3 sv in 50 years for each rate five ensemble experiments have been performed varying in initial conditions the freshwater pulses produce a weakening of the thermohaline circulation the perturbed state is in agreement with proxy evidence for the 8 2 ka event two types of recovery of the thermohaline circulation occurred differing in time scale 1 200 years and 2 200 years in the experiments with 10 year and 20 year pulses both types of recovery were observed this suggests that the model response is unpredictable in the range of parameters studied here it is hypothesized that the unpredictability is associated with annual to decadal climate variability our results demonstrate that several types of recovery may exist with the same kind of perturbation the interpretation of events observed in proxy data may be thus more complex than realized until now since the magnitude and duration of climatic events caused by freshwater pulses is likely to depend strongly on nonlinear dynamics inside the coupled atmosphere sea ice ocean system index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4255 oceanography general numerical modeling 4532 oceanography physical general circulation 4215 oceanography general climate and interannual variability 3309 9325 information related to geographic region atlantic ocean keywords holocene thermohaline circulation predictability meltwater coupled climate model

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

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

sulfur cycle in buried evaporites sulfur isotopes are potent indicators of the way in which sulfur behaves chemically during diagenesis we have studied sulfur isotope ratios 34s 32s from a number of minerals and compounds across the permian triassic boundary in the khuff formation abu dhabi the 34s in dissolved marine sulfate increased by 10 from the late permian to the early triassic despite precipitation of gypsum from permian and triassic seawater and its subsequent dehydration to anhydrite at depths greater than about 1000 m the primary marine stratigraphic sulfur isotope variation has been preserved in anhydrite in the khuff formation a combination of biostratigraphic and absolute age data show that this 10 shift occurred over 2 m y gypsum dehydration to anhydrite has not involved significant isotopic fractionation or diagenetic redistribution of material in the subsurface the sulfur isotope variation across the permian triassic boundary is also present in elemental sulfur and h2s at depths greater than 4300 m formed by reaction of anhydrite with hydrocarbons via thermochemical sulfate reduction this demonstrates that sulfate reduction has not led to isotope fractionation it also demonstrates that significant mass transfer has not occurred at least in the vicinity of the permian triassic boundary even though elemental sulfur and h2s are both fluid phases at depths greater than 4300 m thus despite two major diagenetic processes that converted the sulfur in gypsum into elemental sulfur and h2s by 4300 m burial and the potentially mobile nature of some of the reaction products the primary differences in sulfur isotopes have been preserved in the rocks and fluids all reactions occurred in situ there was no significant sulfur isotope fractionation and only negligible sulfur was added subtracted or moved internally within the system

terrestrial impact of abrupt changes in the north atlantic thermohaline circulation early holocene uk abrupt cooling events are features of holocene climate and may recur in the future we use lake records from hawes water nw england to quantify the impact of two prominent early holocene climatic events subdecadal oxygen isotope records from sedimentary carbonate 18 oc dated using thermal ionization mass spectrometry tims u series analyses provide evidence for abrupt cold events lasting 50 and 150 yr at 9350 and 8380 yr ago which correlate with the 9 3 ka and 8 2 ka events recognized in greenland ice cores at hawes water mean july air temperatures inferred from chirono mid assemblages decreased by 1 6 c during each event calculations show that the isotopic excursions were dominantly caused by decreases in the isotopic composition of meteoric precipitation 18 op by 1 3 this is interpreted as a direct downstream response to cooling and freshening of northeast atlantic surface water by melting ice sheets intermediate in magnitude between events observed in greenland and central europe the effects are consistent with a partial shutdown of the north atlantic thermohaline circulation

the carbon and sulfur cycles and atmospheric oxygen from middle permian to middle triassic the results of a theoretical isotope mass balance model are presented for the time dependence of burial and weathering plus degassing fluxes within the combined long term carbon and sulfur cycles averaged data for oceanic 13c and 34s were entered for every million years from 270 to 240 ma middle permian to middle triassic to study general trends across the permian triassic boundary results show a drop in the rate of global organic matter burial during the late permian and a predominance of low values during the early to middle triassic this overall decrease with time is ascribed mainly to epochs of conversion of high biomass forests to low biomass herbaceous vegetation resulting in a decrease in the production of terrestrially derived organic debris additional contributions to lessened terrestrial carbon burial were increased aridity and a drop in sea level during the late permian which led to smaller areas of low lying coastal wetlands suitable for coal and peat deposition mirroring the drop in organic matter deposition was an increase in the burial of sedimentary pyrite and a dramatic increase in the calculated global mean ratio of pyrite s to organic c high s c values resulted from an increase of deposition in marine euxinic basins combined with a decrease in the burial of low pyrite associated terrestrial organic matter the prediction of increased oceanic anoxia during the late permian and early triassic agrees with independent studies of the composition of sedimentary rocks weathering plus burial fluxes for organic carbon and pyrite sulfur were used to calculate changes in atmospheric oxygen the striking result is a continuous drop in o2 concentration from 30 to 13 over a twenty million year period this drop was brought about mainly by a decrease in the burial of terrestrially derived organic matter but with a possible contribution from the weathering of older organic matter on land it must have exerted a considerable influence on animal evolution because of the role of o2 in respiration some examples are the extinction of many vertebrates loss of giant insects and amphibians and the restriction of animals to low elevations it is concluded that the extinction of plants may have contributed to the extinction of animals

the 8 2 ka bp event in north eastern north america first combined oxygen and hydrogen isotopic data from peat in newfoundland finding direct evidence for atmospheric circulation change in terrestrial records of holocene climate variability remains a fundamental challenge here we present the first combined stable oxygen and hydrogen isotopic palaeorecord from a peatland core in newfoundland canada sphagnum cellulose samples were isolated from a core from nordan s pond bog newfoundland and analysed for d values combined with existing 18o data the resulting d 18o bi plot correlates directly with existing measurements of the modern late 20th century isotopic composition of precipitation from gnip stations in nova scotia and labrador implying a close relationship between the estimated isotopic composition of source water used by the mosses and that of the source precipitation we use the relative variations between the two isotope records to test the hypothesis that atmospheric circulation changed in the millennium following the 8 2 ka bp climate event the data reveal a secondary complex isotopic response 200 years 8250 8050 a bp after a primary oxygen isotopic event that is widespread in the north atlantic region this secondary event is characterized by a divergence in oxygen and hydrogen isotope records that can most plausibly be explained by the augmentation of precipitation moisture from a more distant and more continental vapour source

the early triassic ammonoid recovery paleoclimatic significance of diversity gradients ammonoids recovered much faster than other marine shelly invertebrates after the end permian mass extinction based on a refined global data set at the basin level we investigate the paleobiogeographical global latitudinal and longitudinal diversity patterns in terms of climatic changes during the early triassic such analysis differs from already published qualitative or quantitative studies in that it estimates faunal patterns and endemicity at an ecologically meaningful level of spatial resolution i e at the basin level during the early triassic the global first order trend in increasing ammonoid diversity was accompanied by a progressive change from cosmopolitan to latitudinally restricted distributions this led to the emergence of a clear latitudinal diversity gradient during most of the smithian and spathian stages which entails increased steepness of the sea surface temperature gradient during the late early triassic however two brief episodes of ammonoid cosmopolitanism combined with low global diversity interrupted the first order increasing trend at the very beginning of the smithian and at its very end the longitudinal analysis of smithian distributions indicates a westward decrease of diversity within the tethys which faded away during the spathian analysis of endemicity indicates a rapid biogeographical maturing and structuring of faunas concomitant with the edification of the latitudinal diversity gradient

recovery tempo and pattern of marine ecosystems after the end permian mass extinction high resolution sampling of more than 10 000 microfossils from seven late permian middle triassic paleoequatorial sections in south china refutes claims for a 5 m y recovery delay after the end permian mass extinction we show that level bottom seafloor diversity began to recover in the early smithian little more than 1 m y after the mass extinction while recovery of reef building metazoans began 4 m y later in the anisian a further mass extinction in the late smithian identified in the pelagic fossil record is weakly manifest as a temporary pause in diversification among benthic communities in the early triassic of south china the offshore diversity increase began before then in shallower settings the recovery from the end permian mass extinction in south china was therefore significantly more rapid and environmentally more complex than hitherto known

a neogene seawater sulfur isotope age curve from calcareous pelagic microfossils abstract until now our knowledge of the sulfur isotopic composition of seawater through geologic time has depended on stable isotopic analysis of sulfate from evaporites owing to the sporadic occurrence of evaporites through time the secular sulfur isotope age curve contains many gaps with little or no data in order to fill in some of these gaps particularly the neogene we have analyzed the sulfur isotopic composition of carbonate associated sulfate in carbonate tests of planktonic foraminifera other investigators have shown that sulfate may occur in biogenic calcites either lattice bound as micro fluid inclusions in adsorbed phases or as protein polysaccharides whatever the origin the sulfur isotopic composition of this sulfate appears to be representative of that of the water in which the organism lived as shown by results on recent calcareous foraminifera and macrofossils using this approach for study of miocene to recent pelagic marine sediments supplemented by new data for miocene marine evaporites from the gulf of suez we have found that the 34 s of seawater has decreased about 2 5 over the past 25 m y and that most of the decrease has occurred over the past 5 m y parallelling a decrease in the 13 c of dissolved oceanic bicarbonate from the same interval sedimentary redox models based on isotope records suggest that organic carbon and sulfide burial have both decreased over the past 5 m y alternatively an increase in weathering rates over the past 5 m y would not require a decrease in organic carbon or sulfide burial as long as the isotopic effect of the increased river input exceeds the isotopic effect of the burial of the reduced species in either case the net result would be a decrease in atmospheric p o 2

carbon oxygen and strontium isotopes in paleozoic carbonate components an evaluation of original seawater chemistry proxies abstract brachiopods trilobites cements and whole rock matrix material were evaluated for their reliability as proxies of original seawater carbon oxygen and strontium isotope chemistry in this process coeval material was evaluated from individual horizons of formations spanning the permian to cambrian unaltered shells of low mg calcite articulated brachiopods retain original seawater oxygen carbon and strontium isotope compositions as old as late ordovician assessments of older specimens are hampered by a lack of suitable material coeval brachiopod whole rock sets a definitive assessment of cement marine chemistry is difficult due to the paucity of material but despite this caveat cements hold some promise for retaining original carbon and possibly strontium isotope seawater values in contrast the potential of whole rock material as a proxy of original seawater chemistry is quite complex in some but not all instances the carbon isotopic composition of whole rock after detailed scrutiny and evaluation appears to represent an original seawater chemistry signal in a few instances their oxygen isotope compositions reflect original seawater values unlike the stable isotope compositions the strontium isotopes of all studied whole rock material permian to upper cambrian appear not to reflect original seawater chemistry values thus the potential for retaining original seawater isotope chemistry and serving as specific proxies in order of decreasing reliability are 1 unaltered low mg calcite brachiopods c o and sr isotopes 2 pristine marine cements c and sr isotopes and 3 whole rock material c isotopes carbon oxygen and strontium isotope compositions of ordovician trilobites mirror those of coeval unaltered brachiopods cambrian trilobites hold significant promise as an important proxy of original seawater isotope chemistry but further studies are needed to ascertain their full potential the survey of isotopes in some ordovician and cambrian intermediate low mg calcite trilobites demonstrates their potential as an important proxy of original seawater chemistry

model support for forcing of the 8 2 ka event by meltwater from the hudson bay ice dome previous model experiments of the 8 2 ka event forced by the drainage of lake agassiz often do not produce climate anomalies as long as those inferred from proxies in addition to the agassiz forcing there is new evidence for significant amounts of freshwater entering the ocean at 8 2 ka from the disintegration of the laurentide ice sheet lis we use the community climate system model version 3 ccsm3 to test the contribution of this additional meltwater flux similar to previous model experiments we find that the estimated freshwater forcing from lake agassiz is capable of sustaining ocean and climate anomalies for only two to three decades much shorter than the event duration of 150 years in proxies using new estimates of the lis freshwater flux 0 13 sv for 100 years from the collapse of the hudson bay ice dome in addition to the agassiz drainage the ccsm3 generates climate anomalies with a magnitude and duration that match within error those from proxies this result is insensitive to the duration of freshwater release a major uncertainty if the total volume remains the same an analysis of the modeled north atlantic freshwater budget indicates that the agassiz drainage is rapidly transported out of the north atlantic while the lis contribution generates longer lasting freshwater anomalies that are also subject to recirculation by the subtropical gyre back into the north atlantic thus the meltwater flux originating from the lis appears to be more important than the agassiz drainage in generating 8 2 ka climate anomalies and is one way to reconcile some model data discrepancies

isotope fractionation by sulfate reducing natural populations and the isotopic composition of sulfide in marine sediments isotope fractionations during sulfate reduction by natural bacterial populations were measured in seven different marine sediments and compared with the isotopic composition of solid phase sulfides in the same sediments the measured fractionations during sulfate reduction could explain only between 41 and 85 of the 34s depletion in the sedimentary sulfides this result directly demonstrates that the depletion of 34s in solid sulfides is an expression of the combined activity of sulfate reducing organisms with additional fractionations accumulated during the oxidative part of the sulfur cycle the only known process to significantly augment the fractionations created during sulfate reduction is the microbial disproportionation of the intermediate sulfur compounds elemental sulfur thiosulfate and sulfite in a simple model we show how important each of these disproportionation processes could be in generating the isotopic composition of sedimentary sulfides the sulfate reduction rates in the sediments studied varied by a factor of 1000 and did not correlate with the fractionation during sulfate reduction by contrast a correlation was observed between sulfate reduction rate and the extent of 34s depletion into sedimentary sulfides the most 34s depleted sulfides found in sediments supporting the lowest rates of sulfate reduction thus the fractionations imposed during the disproportionating processes are better expressed in sediments with low sulfate reduction rates the direct phototrophic oxidation of sulfide to sulfate with minimal fractionation may have been important in the sediments that had a high sulfate reduction rate

a 7000 year record of environmental change including early farming impact based on lake sediment geochemistry and pollen data from county sligo western ireland detailed chronologically tightly constrained lake sediment based geochemical and pollen records have enabled local changes in soil erosion woodland cover and composition and prehistoric farming impact to be reconstructed in considerable detail the profile opens shortly after 7800 bc when tall canopy trees were well established and presumably in equilibrium with their environment a distinct perturbation that involved an increase in pine and birch a decrease in oak and a minor opening up of the woodland is regarded as the local expression of the 8 2 ka climate anomaly lack of response in the geochemical erosional indicators is interpreted as evidence for drier conditions a short lived over compensation in climate recovery followed the 8 2 ka event neolithic farming impact is clearly expressed in both the pollen and geochemical data both datasets indicate that neolithic impact was concentrated in the early neolithic 3715 3440 bc in the interval 3000 2700 bc there appears to have been a break in farming activity the pollen data suggest substantially increased farming impact both arable and pastoral in the bronze age with maximum farming and woodland clearances taking place in the late bronze age 1155 935 bc these developments are poorly expressed in the geochemical record possibly due to within lake changes

association of 34s depleted pyrite layers with negative carbonate δ13c excursions at the permian triassic boundary evidence for upwelling of sulfidic deep ocean water masses 1 a marine permian triassic boundary ptb section at nhi tao vietnam contains a series of at least 9 pyritic horizons characterized by concurrent decreases in pyrite s 34spy and carbonate c isotopic compositions 13ccarb the first and largest of the events that precipitated these pyritic horizons was coincident with the late permian mass extinction while subsequent events were generally smaller and occurred at quasiperiodic intervals of 20 to 30 ka a near complete lack of organic carbon to drive bacterial sulfate reduction in sediment pore waters among other considerations argues against a diagenetic control for these relationships rather the covariant patterns documented herein are most easily explained as the product of recurrent upwelling of anoxic deep ocean waters containing 34s depleted hydrogen sulfide and 13c depleted dissolved inorganic carbon the sulfide 34s record of the study section represents a mixture of a small amount of isotopically heavy authigenic pyrite formed via in situ bacterial sulfate reduction with a generally larger quantity of isotopically light syngenetic pyrite precipitated within the water column during upwelling episodes although upwelling of toxic deepwaters has been invoked in earlier studies as a mechanism for the late permian marine mass extinction this is the first study to 1 document patterns of pyrite 13ccarb covariation that strongly support upwelling as a major process at the ptb and 2 provide evidence of multiple quasiperiodic upwelling events that may reflect reinvigoration of global ocean overturn following a prolonged interval of late permian deep ocean stagnation

the 8k event cause and consequences of a major holocene abrupt climate change abstract a prominent abrupt climate event about 8200 years ago brought generally cold and dry conditions to broad northern hemisphere regions especially in wintertime in response to a very large outburst flood that freshened the north atlantic changes were much larger than typical climate variability before and after the event with anomalies up to many degrees contributing to major displacement of vegetative patterns this 8k event provides a clear case of cause and effect in the paleoclimatic realm and so offers an excellent opportunity for model testing the response to north atlantic freshening has the same general anomaly pattern as observed for older events associated with abrupt climate changes following north atlantic freshening and so greatly strengthens the case that those older events also reflect north atlantic changes the north atlantic involvement in the 8k event helps in estimating limits on climate anomalies that might result in the future if warming caused ice melt and hydrologic cycle intensification at high latitudes lead to major changes in north atlantic circulation few model experiments have directly addressed the 8k event and most studies of proxy records across this event lack the time resolution to fully characterize the anomalies so much work remains to be done

sulfur and oxygen isotopes in italian marine sulfates of permian and triassic ages evaporitic sulfates of permian and triassic ages from italian occurrences were analyzed for sulfur and oxygen isotopes in order to supplement the corresponding isotope age curves and to use isotopic data to trace the origin of the sulfate in hydrologic systems the sulfur isotopic composition age relationships obtained in this study generally agree with those found throughout the world in two cases i e in samples from the carniola di bovegno formation bergamo and brescia alps and from the lower part of the gracilis formation recoaro vicenza sulfur isotopes suggest different ages for the rocks than the formerly ascribed ones oxygen isotopic compositions show the same range from 10 5 to 18 5 without any consistent relationship with sulfur these ranges of values are almost identical to those published previously for sulfates of permian and triassic ages from other locations

surface and deep ocean interactions during the cold climate event 8200 years ago evidence from a north atlantic deep sea sediment core reveals that the largest climatic perturbation in our present interglacial the 8200 year event is marked by two distinct cooling events in the subpolar north atlantic at 8490 and 8290 years ago an associated reduction in deep flow speed provides evidence of a significant change to a major downwelling limb of the atlantic meridional overturning circulation the existence of a distinct surface freshening signal during these events strongly suggests that the sequenced surface and deep ocean changes were forced by pulsed meltwater outbursts from a multistep final drainage of the proglacial lakes associated with the decaying laurentide ice sheet margin

freshwater outbursts to the oceans from glacial lake agassiz and their role in climate change during the last deglaciation abstract lake agassiz was the largest lake in north america during the last deglaciation as the laurentide ice sheet lis retreated large volumes of water stored in this proglacial lake were episodically released into the oceans these waters were variably routed to the gulf of mexico arctic ocean north atlantic ocean and hudson bay during this period the three largest cooling events in the northern hemisphere closely followed 4 of the 5 largest outbursts from lake agassiz 1 the younger dryas which was preceded by a release of 9500 km 3 2 the preboreal oscillation preceded by releases of 9300 km 3 and 5900 km 3 and 3 the 8 2 ka cold event preceded by a 163 000 km 3 outburst these are respectively fluxes of 0 30 sv 0 29 sv 0 19 sv and 5 2 sv if released in 1 year because the influx of freshwater reaching the north atlantic ocean can inhibit thermohaline circulation partly depending on whether the ocean was in a glacial interglacial or transitional mode of circulation we believe that at least these large outbursts from lake agassiz may have provided the triggers for changes in ocean circulation and in turn for widespread climate change

british late glacial and holocene climatic history reconstructed from land snail assemblages gations have enabled refinement of the stratigraphic scheme as shells of land snails occur in quantity throughout the sequence preece 1998 they provide a detailed mollusk succession from the beginning of the late glacial until the present day the late glacial assemblages are dominated by species of open country and marsh but shadeintolerant species are replaced by a succession of woodland species during the early part of the holocene following forest clearances during the neolithic and bronze age 5000 3000 yr b p these closed forest communities show a reversion to grassland assemblages with only minor indications of scrub fig 2 a detailed chronology for this succession is provided by a series of

age assessment and implications of late quaternary periglacial and paraglacial landforms on muckish mountain northwest ireland based on schmidt hammer exposure age dating shd abstract schmidt hammer exposure age dating shd was applied to a variety of late quaternary periglacial and paraglacial landforms composed of coarse rock debris on muckish mountain northwest ireland landform ages were determined using a linear high precision age calibration curve derived from young and old control surfaces of known age on the same rock type the shd ages represent maximum estimates of the time elapsed since the boulders stabilised and the landforms became inactive most ages are also minimum estimates for the start of landform development because older boulders are buried beneath the sampled surface boulders ages and 95 confidence intervals obtained for blockfield boulder lobes and talus indicate these features were likely active during several of the early holocene cold events evidenced in greenland ice cores and north atlantic sediment records activity ceased at different times 9 7 ka bp these landforms are the first indication of a geomorphological response to early holocene cooling in the oceanic mountains of ireland late holocene ages obtained for rock slope failure run out debris and debris cone boulders overlap with shifts to cooler and or wetter conditions including the little ice age geomorphological impacts associated with these changes in climate have not previously been recorded in the irish uplands the shd results indicate that previously implied timings for the stabilisation of some accumulations of coarse rock debris on mountain slopes are in need of revision

geochemical evidence from bio apatite for multiple oceanic anoxic events during permian triassic transition and the link with end permian extinction and recovery abstract a detailed 20 myr redox history of permian to triassic oceans changhsingian to carnian stages has been constructed using ce anomaly ce and th u ratios from conodont albid crown apatite material the results show that the well established phenomenon of intense ocean anoxia coincident with the end permian mass extinction is faithfully recorded in conodont ce and th u data extending this conodont redox record shows that end permian anoxia persisted possibly into the earliest dienerian stage and that two intense oceanic anoxic events also occurred later in the early triassic earliest smithian earliest spathian and middle spathian followed by a weaker manifestation of anoxia in the anisian stage seen in ce data marine benthic radiation following the end permian mass extinction began after the smithian earliest spathian anoxic event suggesting a suppression of evolution prior to this due to these inimical conditions the failure of the middle spathian anoxic event to retard the evolutionary rebound implies shallow shelf seas remained well ventilated at this time even if the oceans did not other attributes of the early triassic record also closely coincide with redox fluctuations phases of anoxia intensification saw the proliferation of microbial carbonates and major negative carbon isotope swings that can be attributed to chemocline shallowing causing alkalinity pulses and enrichment in light remineralised carbon and or indicate a trigger meachnaims related to increased fluxes of light c from siberian volcanic sources

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

isotopic evidence for an anomalously low oceanic sulfate concentration following end permian mass extinction abstract the cataclysmic end permian mass extinction was immediately followed by a global expansion of microbial ecosystems as demonstrated by widespread microbialite sequences disaster facies in shallow water settings here we present high resolution carbonate carbon 13 c carb and carbonate associated sulfate sulfur isotope 34 s cas records from the microbialite in the cili permian triassic p tr section in south china a stepwise decline in 13 c carb begins in the underlying skeletal limestone predating the main oceanic mass extinction and the first appearance of microbialite and reaches its nadir in the upper part of the microbialite layer the corresponding 34 s cas in the range of 17 4 to 27 4 is relatively stable in the underlying skeletal limestone and increases gradually from 2 m below the microbialite rising to a peak at the base of the microbialite two episodes of positive and negative shifts occurred within the microbialite layer and exhibit a remarkable co variance of sulfur and carbon isotope composition the large amplitude of the variation in 34 s cas as high as 7 per 100 kiloyears suggests a small oceanic sulfate reservoir size at this time furthermore the 13 c carb and 34 s cas records co vary without phase lag throughout the microbialite interval implying a marine driven c cycle in an anoxic ocean with anomalously low oceanic sulfate concentrations on the basis of a non steady state box model we argue that the oceanic sulfate concentration may have fallen to less than 15 perhaps as low as 3 of that in the modern oceans low oceanic sulfate concentration likely was the consequence of evaporite deposition and widespread anoxic sulfidic conditions prior to the main mass extinction by promoting methanogenesis and a build up of atmospheric ch 4 and co 2 low oceanic sulfate may have intensified global warming exacerbating the inimical environmental conditions of the latest permian

lake isotope records of the 8200 year cooling event in western ireland comparison with model simulations the early holocene cooling which occurred around 8200 calendar years before present was a prominent abrupt event around the north atlantic region here we investigate the timing duration magnitude and regional coherence of the event as expressed in carbonate oxygen isotope records from three lakes on northwest europe s atlantic margin in western ireland namely loch avolla loch gealain and lough corrib an abrupt negative oxygen isotope excursion lasted about 200 years comparison of records from three sites suggests that the excursion was primarily the result of a reduction of the oxygen isotope values of precipitation which was likely caused by lowered air temperatures possibly coupled with a change in atmospheric circulation comparison of records from two of the lakes loch avolla and loch gealain which have differing bathymetries further suggests a reduction in evaporative loss of lake water during the cooling episode comparison of climate model experiments with lake sediment isotope data indicates that effective moisture may have increased along this part of the northeast atlantic seaboard during the 8200 year climatic event as lower evaporation compensated for reduced precipitation

paleohydraulics of the last outburst flood from glacial lake agassiz and the 8200 bp cold event abstract during the last deglaciation of north america huge proglacial lakes formed along the southern margin of the laurentide ice sheet the largest of these was glacial lake agassiz which formed about 11 7 14 c kyr and drained into hudson bay about 7 7 14 c kyr 8 45 cal kyr overflow from these lakes was variably directed to the mississippi st lawrence and mackenzie drainage systems and it is thought that switches in routing were accompanied by a response in ocean circulation that produced abrupt climate events when the ice dam across hudson bay finally was breached a massive flood drained lake agassiz which was routed through hudson strait to the labrador sea in terms of stored water volume the largest reservoir was associated with the kinojevis level of lake agassiz for this maximum filling the impounded water volume available to produce floods is estimated as 40 000 151 000 km 3 depending on the location of the ice margin and route used the timing of this rapid release of stored freshwater just precedes the early holocene cooling event at 8 2 cal kyr bp we use the spring hutter theory to simulate flood hydrographs for floods that originate in subglacial drainage conduits and find that flood magnitude and duration are 5 sv and 0 5 yr multiple fillings and floods are possible as are single floods having a complex multipulse structure modelling results suggest that the outburst flood from lake agassiz may have terminated before the lake surface elevation dropped to sea level and that the flood ended when a stable drainage channel was established connecting lake agassiz to the tyrrell sea

environmental responses to the 9 7 and 8 2 cold events at two ecotonal sites in the dovre mountains mid norway abstract we found strong signals of two cooling events around 9700 and 8200 cal yrs bp in lakes store finnsjoen and flafattjonna at dovre mid norway analyses included pollen in both lakes and c n ratio biomarkers e g alkanes and br gdgts and xrf scanning in finnsjoen the positions of these lakes close to ecotones upper forest lines of birch and pine respectively reduced their resilience to cold events causing vegetation regression at both sites the global 8 2 event reflects the collapse of the laurentide ice sheet the 9 7 event with impact restricted to scandinavia and traced by pollen at dovre only reflects the drainage of the baltic ancylus lake more detailed analysis in finnsjoen shows that the events also caused increased allochtonous input k ca increased sedimentation rate and decreased sediment density and aquatic production br gdgt based temperatures indicate gradual cooling through the early holocene in finnsjoen ca 3100 maxima minima couplets in sediment density along the analysed sequence of ca 3100 calibrated years show the presence of varves for the first time in norway impact of the 9 7 and 8 2 events lasted ca 60 and 370 years respectively pine pollen percentages were halved and re established in less than 60 years indicating the reduction of pine pollen production and not vegetative growth during the 9 7 event the local impact of the 8 2 event sensu lato ca 8420 8050 cal yrs bp divides the event into a precursor an erosional phase and a recovery phase at the onset of the erosional phase summer temperatures increased

unsteady diagenetic processes and sulfur biogeochemistry in tropical deltaic muds implications for oceanic isotope cycles and the sedimentary record abstract sedimentary s cycling is usually conceptualized and interpreted within the context of steadily accreting 1 d transport reaction regimes unsteady processes however are common in many sedimentary systems and can result in dramatically different s reaction balances and diagenetic products than steady conditions globally important common examples include tropical deltaic topset and inner shelf muds such as those extending from the amazon river 1600 km along the guianas coast of south america these deposits are characterized by episodic reworking of the surface seabed over vertical depths of 0 1 3 m reworked surface sediments act as unsteady suboxic batch reactors unconformably overlying relict anoxic often methanic deposits and have diagenetic properties largely decoupled from net accumulation of sediment despite well oxygenated water and an abundant reactive organic matter supply physical disturbance inhibits macrofauna and benthic communities are dominated by microbial biomass across immense areas in the surficial suboxic layer molecular biological analyses tracer experiments sediment c s fe compositions and 34s 18o of pore water so 4 2 indicate close coupling of anaerobic c s and fe cycles 18o so 4 2 can increase by 2 3 during anaerobic recycling without net change in 34s so 4 2 demonstrating so 4 2 reduction coupled to complete anaerobic reoxidation to so 4 2 and a 18o so 4 2 reduction reoxidation fractionation factor 12 summed magnitudes s reoxidation must be coupled to fe oxide reduction contributing to high dissolved fe2 1 mm and fe mobilization export the reworking of amazon guianas shelf muds alone may isotopically alter 18o so 4 2 equivalent in mass to 25 of the annual riverine delivery of so 4 2 to the global ocean unsteady conditions result in preservation of unusually heavy 34s isotopic compositions of residual cr reducible s ranging from 0 to 30 in physically reworked deposits in contrast bioturbated facies adjacent to physically reworked regions accumulate isotopically light s 34s to 20 in otherwise similar decomposition regimes the isotopic patterns of both physically and biologically reworked regions can be simulated with simple diagenetic models heavy s isotopic signatures are largely a consequence of unsteady diffusion and progressive anaerobic burndown into underlying deposits whereas isotopically depleted bioturbated deposits predominantly reflect biogenic diffusive scaling and isotopic distillation diffusive pumping associated with reoxidation in burrow walls immediately adjacent to reduced zones the s isotopic transition from unsteady physically controlled regions of the amazon delta moving laterally into bioturbated facies mimics the transition of s isotopic patterns temporally in the geologic record during the rise of bioturbation no special role for s disproportionation is required to explain these differences the potential role of unsteady suboxic diagenesis and dynamic reworking of sediments has been largely ignored in models of the evolution of surficial elemental cycling and interpretations of the geologic record

climatic and biotic upheavals following the end permian mass extinction the recovery from the end permian mass extinction was slow and prolonged a temperature reconstruction shows that further biotic crises during the recovery were associated with extreme warmth

structure of the 8200 year cold event revealed by a speleothem trace element record abrupt first order shifts in strontium and phosphorus concentrations in stalagmite calcite deposited in western ireland during the 8200 year event the major cooling episode 8200 years before the present are interpreted as responses to a drier climate lasting about 37 years both shifts are centered on 8330 80 years before the present coinciding with a large oxygen isotope anomaly and a change in the calcite petrography in this very high resolution monthly record antipathetic second order oscillations in phosphorus and strontium reveal decreased growth rates and increased rainfall seasonality growth rate variations within the event reveal a two pronged structure consistent with recent model simulations

evidence of holocene surface and near surface palaeofires in karst caves and soils abstract black deposits covering speleothems cave walls and floors in postojna cave and predjama cave sw slovenia and charcoal found in soil outside the postojna cave were studied in order to establish their origin and age sem eds analysis of these deposits from both caves indicated that they are charred plant remains very similar to oxidised charcoal in soil stable carbon isotope 13 c values of 29 41 crna jama p1 26 9 predjama and 25 1 charcoal in soil confirm their origin from biomass burning radiocarbon dating from postojna cave crna jama p1 8394 35 cal yr b p and pisani rov 8235 25 cal yr b p suggests that the oldest analysed black deposits formed in the early holocene mesolithic the age is consistent with soil charcoal found at 1 m depth in the surrounding area black deposits from predjama were dated to 4095 25 cal yr b p eneolithic and were caused by burning fires at the cave entrance as supported by archaeological remains prehistoric 2375 20 cal yr b p charcoal from the upper part of the soil profile 0 5 to 0 6 m and historic 1240 29 cal yr b p or 745 cal yr ce black deposits from postojna cave crna jama p2 are related to forest fires which are most likely human induced we interpret the oldest dated black deposits in postojna cave as traces of early holocene natural forest fires since fire activity inside crna jama and pisani rov is not supported by archaeological remains favourable cave entrance morphology and microclimate allowed smoke to enter the cave during the winter period and deposit on speleothems but an anthropogenic cause of forest fires cannot be excluded since there are well documented mesolithic archaeological cave sites located close to the area the study shows that black deposits on speleothems in caves are an important palaeoenvironmental record and proxy for holocene climate

terrestrial marine teleconnections in the collapse and rebuilding of early triassic marine ecosystems abstract the latest permian mass extinction lpe just prior to the permian triassic boundary at 252 ma resulted in the disappearance of 90 of skeletonized marine taxa and the replacement of the paleozoic fauna by the modern fauna in the immediate aftermath of the extinction shallow marine ecosystems were dominated by microbial communities and diminutive disaster taxa lilliput faunas and the post crisis period in general was characterized by high abundance low diversity marine communities occupying a reduced ecological space the recovery of marine ecosystems was a protracted process lasting throughout the 5 myr long early triassic some clades failed to recover and subsequently went extinct dead clades walking while others recovered only to suffer secondary crises during the early triassic profound environmental changes accompanied these biotic developments deep oceans experienced sustained hypoxia or anoxia for at least several million years following the boundary event anoxia was also widespread in shallow marine areas especially at the time of the lpe but it was more episodic and abated more rapidly than in the deep ocean making it an unlikely factor in the delayed recovery of early triassic marine ecosystems the development of anoxia was due at least in part to a sharp temperature rise following the lpe but may have been stimulated by changes in marine nutrient inventories and productivity rates as well these conditions may have been the result of a concurrent increase in subaerial weathering rates that was sustained into the early triassic in addition to increasing nutrient fluxes to marine areas rapid weathering caused a massive influx of sediment to shallow marine systems subjecting marine biotas to siltation stress this scenario implies close teleconnections between terrestrial and marine environments during the permian triassic boundary crisis with perturbations of the terrestrial realm contributing to the marine crisis

pyrite framboids in the permian triassic boundary section at meishan china evidence for dysoxic deposition pyrite framboid evidence from the permian triassic global stratotype at meishan china indicates the late permian mass extinction is closely associated with a dramatic decline of benthic oxygen levels sizes and abundances of the framboids were determined from acid residues and in situ on polished sections of the samples the framboids are abundant in the thin pyrite lamina on the top of bed 24e the upper layer of bed 24 and beds 25 26 and 29 rare in bed 24e and bed 28 but absent in bed 27 they have narrow size distributions with average diameters from 4 6 mu m to 8 7 mu m which are similar to those formed under anoxic dysoxic conditions the abundances and mean diameters of the pyrite framboids indicate redox conditions of deposition changing from upper dysoxia bed 24e and lower dysoxia pyrite lamina beds 25 and 26 to oxygenation bed 27 and again to upper dysoxia bed 28 and lower dysoxia bed 29 our discovery confirms a worldwide dysoxic marine event during the permian triassic transition suggestive of a direct relationship with the permian triassic marine mass extinction c 2007 elsevier b v all rights reserved

evidence for higher than average air temperatures after the 8 2 ka event provided by a central european δ 18 o record the so called 8 2 ka event represents one of the most prominent cold climate anomalies during the holocene warm period accordingly several studies have addressed its trigger mechanisms absolute dating and regional characteristics so far however knowledge about subsequent climate recovery is still limited although this might be essential for the understanding of rapid climatic changes here we present a new sub decadally resolved and precisely dated oxygen isotope o record for the interval between 7 7 and 8 7 ka bp 10 calendar years before ad 1950 derived from the calcareous valves of benthic ostracods preserved in the varved lake sediments of pre alpine mondsee austria besides a clear reflection of the 8 2 ka event showing a good agreement in timing duration and magnitude with other regional stable isotope records the high resolution mondsee lake sediment record provides evidence for a 75 year long interval of higher than average o values directly after the 8 2 ka event possibly reflecting increased air temperatures in central europe this observation is consistent with evidence from other proxy records in the north atlantic realm thus most probably reflecting a hemispheric scale climate signal rather than a local phenomenon as a possible trigger we suggest an enhanced resumption of the atlantic meridional overturning circulation amoc supporting assumptions from climate model simulations

centennial scale climate cooling with a sudden cold event around 8 200 years ago the extent of climate variability during the current interglacial period the holocene is still debated temperature records derived from central greenland ice cores show one significant temperature anomaly between 8 200 and 8 100 years ago which is often attributed to a meltwater outflow into the north atlantic ocean and a slowdown of north atlantic deep water formation this anomaly provides an opportunity to study such processes with relevance to present day freshening of the north atlantic anomalies in climate proxy records from locations around the globe are often correlated with this sharp event in greenland but the anomalies in many of these records span 400 to 600 years start from about 8 600 years ago and form part of a repeating pattern within the holocene more sudden climate changes around 8 200 years ago appear superimposed on this longer term cooling the compounded nature of the signals implies that far field climate anomalies around 8 200 years ago cannot be used in a straightforward manner to assess the impact of a slowdown of north atlantic deep water formation and the geographical extent of the rapid cooling event 8 200 years ago remains to be determined

early triassic calcimicrobial mounds and biostromes of the nanpanjiang basin south china stanley s model 1988 proposed that a permiantype reef fauna survived the early triassic reefless period in yet undiscovered refuges in the ancestral pacific ocean and then reappeared as the builders of middle triassic reefs flugel 1994 in contrast suggested that the middle triassic reefbuilding fauna are not holdovers from the permian but bear only a superficial resemblance to permian fossils recent publications reflect a consensus that the early triassic lacked reefs and reef mounds although some authors acknowledged the possibility that reef like structures may have existed in poorly explored areas such as south china and russia senowbari daryan et al 1993 flugel 1994 it is shown herein that calcimicrobial framework mounds and biostromes existed in the early triassic in the nanpanjiang basin of south china organic framework in this paper refers to a three dimensional biologically constructed network of calcified fossils that forms a rigid mass and supports an interconnected network of internal cavities that were open during accumulation although the calcimicrobial frameworks discussed herein are much smaller than frameworks of modern metazoan reefs the term framestone is more appropriate for these fabrics than other reef rock terms such as bindstone or bafflestone embry and klovan 1971 these calcimicrobial mounds and biostromes are important as the first organic framestones documented from the early triassic

the end permian regression in south china and its implication on mass extinction abstract records of more than 20 permian triassic boundary ptb sections from south china show that widespread end permian regression took place in whole south china timing of the low ebb of this regression was pinpointed to the clarkina meishanensis and hindeodus changxingensis zones biostratigraphic and paleogeographic studies at conodont zonation level reveal that the yangtze carbonate platform and isolated small carbonate platforms in the hunan guizhou guangxi hgg basin experienced sedimentary hiatus during these two zones which lasted about 50 100 kya meanwhile the basinal areas namely the northern marginal basin of yangtze platform and the hunan guizhou guangxi basin have continuous conodont zonation with silicious and ashbed deposits the basinal areas show two negative 13c shifts during the ptb interval from clarkina yini zone to isarcicella isarcica zone while on the platforms there is usually only one negative shift because the early shift at c meishanensis zone was lost during hiatus the end permian regression and successive rapid transgression taking place at the ptb casted important effects to the pattern and process of the ptb mass extinction the depositional hiatus hitherto underestimated will necessitate reassessment of some interpretations on the causes and results of that extinction

simulation of the cold climate event 8200 years ago by meltwater outburst from lake agassiz meltwater pulse is assumed to have a volume of 1 6 10 14 m 3 and a period of discharge of 2 years on the basis of glaciological modeling of the decay of the laurentide ice sheet lis we present a possible mechanism which can explain the centennial duration of the 8 2 ka cold event the mechanism is related to the existence of an additional equilibrium climate state with reduced north atlantic deep water nadw formation and a southward shift of the nadw formation area hints at the additional climate state were obtained from the largely varying duration of the pulse induced cold episode in response to overlaid random freshwater fluctuations in monte carlo simulations the model equilibrium state was attained by releasing a weak multicentury freshwater flux through the st lawrence pathway completed by the meltwater pulse the existence of such a climate mode appears essential for reproducing climate anomalies in close agreement with paleoclimatic reconstructions of the 8 2 ka event the results furthermore suggest that the temporal evolution of the cold event was partly a matter of chance index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4255 oceanography general numerical modeling 4532 oceanography physical general circulation 4215 oceanography general climate and interannual variability 3309 9325 information related to geographic region atlantic ocean

the sulphur isotopic composition of trace sulphates in carboniferous brachiopods implications for coeval seawater correlation with other geochemical cycles and isotope stratigraphy the carboniferous 34s record based on the analysis of structurally substituted sulphate sss in brachiopod shells is characterized by a significant decline from values around 21 1 in the tournaisian to 12 1 in the gzelian superimposed on this broad evolution is a higher order structure with a relative minimum in the late visean followed by a maximum in the bashkirian on the 107 year time scale 34s is positively correlated with 13ccarb in contrast to the long term negative linkage between sulphur and carbon observed for the entire phanerozoic this indicates that mechanisms other than the redox balance control the carbon and sulphur cycles on this time scale the 87sr 86sr and 34s records display parallel trends during the tournaisian to moscovian this positive correlation suggests that tectonics may be of importance for the evolution of 34s on time scales of 107 years a possible scenario to explain the co evolution of the isotope systems and their linkage to tectonism and palaeoclimate invokes an increased nutrient supply to the oceans during periods of enhanced uplift and continental weathering this nutrient flux may have resulted in increased burial of organic matter and enhanced bacterial sulphate reduction

do storms cause long term beach erosion along the u s east barrier coast abstract in a few hours or days scores of meters of beach width can be lost due to a severe storm however newly available shoreline data from the u s east coast show that beaches recover after storms to positions consistent with their long term 100 yr trend even the largest storms such as the ash wednesday storm of 1962 considered to be the most damaging in the twentieth century appear to have had little effect on the long term trend the gradual recession of beaches along the u s east coast is mainly controlled by other factors such as sea level rise and variations of sediment supply therefore it follows that barrier beaches in a coastal plain setting would not experience long term erosion in response to storm impact if the sea were to stop rising and sediment supply did not change

lake agassiz final drainage event in the northwest north atlantic 1 the 8 2 ka climate event recorded in greenland ice cores is subject of debates with respect to causal linkage with a collapse of the atlantic meridional overturning due to the drainage of the late glacial lake agassiz here we present records from the nw north atlantic down current the flood discharge route showing that the 9 5 8 ka interval was marked by a succession of events the drainage itself corresponds to a twin layer of carbonate rich turbidites deposited within the calibrated 8 35 8 5 ka interval proxies of sea surface and deep current conditions do not indicate significant concomitant changes in the nw north atlantic the dataset however supports the concept that the 8 2 ka climate event may represent one of the manifestations of climate instability during an interval with major changes of land drainage in ne america due to the collapse of the laurentide ice sheet subsequent fast sea level rise and large scale reorganization of the north atlantic thermohaline circulation pattern

modeling the stable water isotope expression of el nino in the pliocene implications for the interpretation of proxy data the el nino southern oscillation enso drives interannual climate variability hence its behavior over a range of climates needs to be understood it is therefore important to verify that the paleoarchives used for pre instrumental enso studies can accurately record enso signals here we use the isotope enabled hadley centre general circulation model hadcm3 to investigate enso signals in paleoarchives from a warm paleoclimate the mid pliocene warm period mpwp 3 3 3 0ma continuous e g coral and discrete e g foraminifera proxy data are simulated throughout the tropical pacific and enso events suggested by the pseudoproxy data are assessed using modeled enso indices hadcm3 suggests that the ability to reconstruct enso from coral data is predominantly dependant on location however since modeled enso is slightly stronger in the mpwp than the preindustrial enso is slightly easier to detect in mpwp aged coral hadcm3 also suggests that using statistics from a number of individual foraminifera individual foraminifera analysis ifa generally provides more accurate enso information for the mpwp than for the preindustrial particularly in the western and central pacific however a test case from the eastern pacific showed that for some locations the ifa method can work well for the preindustrial but be unreliable for a different climate the work highlights that sites used for paleo enso analysis should be chosen with extreme care in order to avoid unreliable results although a site with good skill for preindustrial enso will usually have good skill for assessing mpwp enso this is not always the case

climatic change recorded by stable isotopes and trace elements in a british holocene tufa combined stable isotope d18o and d13c and trace element mg sr geochemistry from bulk tufa calcite and ostracod shell calcite from an early holocene british tufa reveal clear records of holocene palaeoclimatic change variation in d18o is caused principally by change in the isotopic composition of holocene rainfall recharge itself caused mainly by change in air temperature the d13c variability through much of the deposit reflects increasing influence of soil zone co2 owing to progressive woodland soil development bulk tufa mg ca and sr ca are controlled by their concentrations in the spring water importantly mg ca ratios are not related to d18o values and thus show no temperature dependence first order sympathetic relationships between d13c values and mg ca and sr ca are controlled by aquifer processes residence times co2 degassing and calcite dissolution reprecipitation and probably record intensity of palaeorainfall recharge effects stable isotope records from ostracod shells show evidence of vital effects relative to bulk tufa data the ostracod isotopic records are markedly spiky because the ostracods record snapshots of relatively short duration years whereas the bulk tufa samples record averages of longer time periods probably decades the d18o record appears to show early holocene warming a thermal maximum at ca 8900 cal yr bp and the global 8200 yr bp cold event combined d13c mg ca and sr ca data suggest that early holocene warming was accompanied by decreasing rainfall intensity the mg ca data suggest that the 8200 yr bp cold event was also dry warmer and wetter conditions were re established after the 8200 yr bp cold event until the top of the preserved tufa sequence at ca 7100 cal yr bp

sulfur isotopic evidence for chemocline upward excursions during the end permian mass extinction the latest permian was a time of major change in ocean chemistry accompanying the greatest mass extinction of the phanerozoic to examine the nature of these changes samples from two well studied marine sections that span the permian triassic boundary have been analyzed the meishan and shangsi sections located in southern china isotopic analysis of the carbonate associated sulfate in these samples provides a detailed record of several isotopic shifts in 34scas approaching and across the ptb ranging from 30 to 15 vcdt with repeated asynchronous fluctuations at the two locations we interpret the patterns of isotopic shifts in conjunction with other data to indicate a shallow unstable chemocline overlying euxinic deep water which periodically upwelled into the photic zone these chemocline upward excursion events introduced sulfide to the photic zone stimulating a bloom of phototrophic sulfur oxidizing bacteria we hypothesize that elemental sulfur globules produced by these organisms and 34s depleted pyrite produced in the euxinic water column were deposited in the sediment later oxidation led to incorporation as cas this created the large changes to the 34scas observed in the latest permian at these locations

the 8 2 kyr bp event simulated by a global atmosphere sea ice ocean model seven freshwater perturbation experiments were performed with a global atmosphere sea ice ocean model to study the mechanism behind the 8 2 kyr bp holocene cooling event these experiments differed in initial state and duration of the applied freshwater pulse while the amount of freshwater was kept constant 4 67x10 14 m 3 one of the scenarios with freshwater added to the labrador sea at a rate of 0 75 sv during 20 years resulted in weakening of the north atlantic thermohaline circulation during 320 years and surface cooling varying from 1 to 5 degreesc over adjacent continents this result is consistent with proxy data suggesting that a meltwater induced weakening of the thermohaline circulation caused the event moreover our results indicate that the time scale of the meltwater release and the initial state are important as both have a strong effect on the magnitude and duration of the produced model response

impact of floods versus routing events on the thermohaline circulation 1 the last deglaciation was interrupted by three major cooling events the younger dryas the preboreal oscillation and the 8 2 ka cold event as the laurentide ice sheet retreated different outlets from lake agassiz became available causing the proglacial lake to drain to a new level in a rather short timescale flood and divert continental runoff over hundreds of years routing here we use an earth system model to investigate the impact of floods short term high amplitude versus routing events long term low amplitude on the thermohaline circulation and the resulting climate change we show that the initial outbursts of freshwater are not strong enough to influence large scale climate and can therefore not be the cause of millennial scale climate variability however routing events have the potential of weakening the thermohaline circulation and therefore causing a cool event in the northern hemisphere

the permian triassic boundary at nhi tao vietnam evidence for recurrent influx of sulfidic watermasses to a shallow marine carbonate platform the permian triassic boundary at nhi tao cao bang province vietnam was sampled in a 7 5 m thick outcrop section at high resolution 5 cm intervals for chemostratigraphic and magnetic susceptibility analysis the section consists entirely of slightly argillaceous limestone representing shallow marine facies of the jinxi platform one of several large carbonate platforms within the nanpanjiang basin located on the southern margin of the south china craton upper permian strata beds 1 7 are mainly dark gray cherty fossiliferous wackestones and packstones containing a diverse open marine fauna whereas uppermost permian and lower triassic strata beds 9 and higher are medium gray calcimicrobial framestones containing rare macrofossils these facies are separated by a 12 cm thick oolitic pisolitic grainstone bed 8 that coincides with the disappearance of most late permian faunal elements as well as with the first appearance of various geochemical anomalies that continue into the lower triassic part of the section this late permian event horizon is characterized by 1 an abrupt decline in total organic carbon to near zero values 2 the onset of a sustained decline in carbonate 13c and 3 the first of eight concentration peaks in pyrite sulfur significantly each sulfide peak is associated with lower pyrite 34s values as well as with the onset of a negative carbonate 13c excursion or the acceleration of an excursion already in progress these chemostratigraphic relationships are consistent with multiple episodes of upwelling of sulfidic 34s and 13c depleted deep ocean waters onto the jinxi platform the first upwelling event was the most intense and caused a drastic reduction in primary productivity and the demise of the late permian fauna subsequent episodes were less intense but may have contributed to a delay in recovery of early triassic marine ecosystems a ten fold increase in magnetic susceptibility in bed 9 may record the influx of fine detrital particles following destruction of terrestrial ecosystems and massive soil erosion the terrestrial signal of the end permian catastrophe thus follows the marine signal with a 12 cm lag which may reflect the time of transit of soil derived particles across the nanpanjiang basin suggesting that the marine and terrestrial crises in the nhi tao region occurred more or less synchronously these observations suggest a model in which renewal of global ocean overturn followed a prolonged interval of deep ocean stagnation during the late permian with upwelling intensity modulated by short term 20 kyr climate cyclicity

parallel trends in organic and inorganic carbon isotopes across the permian triassic boundary stable carbon isotope ratios in both inorganic and organic reservoirs have been widely applied to model environmental and sedimentological changes on a global scale most studies dealing with major extinction events have used the record of inorganic carbon in this paper the authors report the relation between shifts in carbon 13 content of organic matter and coexisting carbonate fractions at a major extinction event the permian triassic boundary they found that both delta sup 13 c sub carb and delta sup 13 c sub org of the surface ocean varied dramatically across the boundary but the fractionation delta sup 13 c between organic matter and carbonate remained constant this result appreciably restricts the interpretation of changes in the carbon cycle during this critical interval the new data are best explained by a combination of two mechanisms for variation in delta sup 13 c sub carb 1 burial and erosion of organic carbon with a long time constant and 2 sequestration of organic carbon into shallow and deep oceanic reservoirs with a shorter time constant for application to their case the first mechanism is limited by possible buildup of marine pco sub 2 which would increase the isotopic fractionation factor the second mechanism is limited in application to short term transient variations in delta sup 13 c modelingmore of the carbon cycle and its variations of delta sup 13 c must take both mechanisms into account less

the lower triassic of south china abstract the permian triassic boundary of south china has been well known and well studied for decades but what is relatively less noticed is that there are also many excellent marine lower triassic sequences in the region covering various paleogeographic lithofacies this paper presents an outline of the various lower triassic stratigraphic sequences in south china and provides a reference to the application of the lower triassic subdivision and stages the early triassic marine basin of south china is subdivided into five sedimentary provinces cathaysia lower yangtze upper yangtze youjiang and lijiang provinces each province has an interrelated distribution of lithofacies and stratigraphy the lower triassic biostratigraphic sequences of bivalves ammonoids and conodonts are summarized in the various sedimentary facies and provinces of south china the chinese twofold subdivision of the lower triassic is primarily demonstrated as well in this paper

stable carbon isotope stratigraphy across the permian triassic boundary in shallow marine carbonate platforms nanpanjiang basin south china a distinct negative 13c excursion is documented in two permian triassic sections heping and taiping in shallow marine carbonate platform deposits in the nanpanjiang basin south china these sections span from the changhsingian to the dienerian and are characterized by a distinct marine boundary facies change from massive skeletal lime packstone in the changhsingian to distinctive calcimicrobial framestone in the griesbachian hindeodus parvus zone the 13corg and 13ccarb excursions occur directly after the onset of the calcimicrobial framestone herein termed the permian triassic boundary event and before the first occurrence of h parvus the isotope shifts are associated with a sharp drop in species abundance and diversity and coincide with a decrease in total organic carbon toc content the shift towards depleted values in 13corg and 13ccarb at the permian triassic boundary event together with low toc contents persists throughout the griesbachian h parvus zone these data document a corresponding negative shift of 13corg and 13ccarb values and low toc contents with the onset of growth of calcified microbial framestones a postextinction disaster facies immediately below the base of the griesbachian h parvus zone based on paleontological evidence the first occurrence of the disaster facies follows the extinction event which implies that the 13c depleted values above this facies postdate the event this suggests that two separate events had to account for the initiation of the extinction and the 13c excursion however the consequences that led to the negative isotopic shift might be linked to the intriguing recovery lag of early triassic ecosystems based on data from ptb sections worldwide of a greater 13c offset in high compared with low latitudes we propose that methane eruptions from thermal destabilization of high latitude clathrate deposits may have led to the negative 13c shift and may have caused long term adverse ecological conditions

modeling oxygen isotopes in the pliocene large scale features over the land and ocean the first isotope enabled general circulation model gcm simulations of the pliocene are used to discuss the interpretation of 18o measurements for a warm climate the model suggests that spatial patterns of pliocene ocean surface 18o 18osw were similar to those of the preindustrial period however arctic and coastal regions were relatively depleted while south atlantic and mediterranean regions were relatively enriched modeled 18osw anomalies are closely related to modeled salinity anomalies which supports using 18osw as a paleosalinity proxy modeled pliocene precipitation 18o 18op was enriched relative to the preindustrial values but with depletion of 2 over some tropical regions while usually modest 4 the enrichment can reach 25 over ice sheet regions in the tropics 18op anomalies are related to precipitation amount anomalies although there is usually a spatial offset between the two this offset suggests that the location of precipitation change is more uncertain than the amplitude when interpreting 18op at high latitudes 18op anomalies relate to temperature anomalies however the relationship is neither linear nor spatially coincident a large 18op signal does not always translate to a large temperature signal these results suggest that isotope modeling can lead to enhanced synergy between climate models and climate proxy data the model can relate proxy data to climate in a physically based way even when the relationship is complex and nonlocal the 18o climate relationships identified here from a gcm could not be determined from transfer functions or simple models

isotopic composition and speciation of sulfur in the miocene monterey formation reevaluation of sulfur reactions during early diagenesis in marine environments the timing and pathways of early diagenetic sulfur transfer from dissolved species in pore waters to solid inorganic and organic compounds in sediments have been studied in the miocene monterey formation santa maria basin onshore california correlation between concentrations of total organic carbon toc and total sulfur ts in addition to concentrations of titanium aluminum total iron and reactive iron have been used to infer organic matter reactivity redox conditions and relative rates of clastic and biogenic input for each lithofacies isotopic compositions of six sulfur species acid volatile disulfide kerogen bitumen sulfate and elemental have provided information regarding relative timing of sulfur incorporation sulfate diffusivity in the upper centimeters of the sediments and the sources of sulfur for individual species isotopically the disulfide species expresses the greatest fractionation relative to estimated values of miocene seawater sulfate 22 cdt on average disulfide is depleted in 34s by 10 4 relative to kerogen and by 9 9 relative to acid volatile sulfide the 34s of bitumen shows no systematic change relative to 34skeregon suggesting the presence of migrated bitumen isotopic similarity of sulfate and elemental sulfur to sulfides and bitumen indicates that sulfate and elemental sulfur are chemical and or biological oxidation products derived from sulfides and bitumen consistent ordering of isotopic values for sulfur species disulfide acid volatile sulfide kerogen indicates that pyrite precipitated nearest to the sediment water interface under mildly reducing conditions and with little or no decrease in sulfate concentration relative to seawater enrichment of 34s in acid volatile sulfide and kerogen sulfur resulted from formation of these species at greater depths or in restricted micro environments under more reducing conditions and with low concentrations of porewater sulfate the formation of acid volatile sulfide after pyrite but during early diagenesis is significant because it implies more strongly reducing conditions than are generally recognized in deep water marine sediments

paleoredox biotic and sulfur isotopic changes associated with the end permian mass extinction in the western tethys abstract detailed cm scale s toc total organic carbon 34ssulfide and pyrite morphological analysis of the permian triassic boundary beds at the bulla section northern italy suggests that marine waters at this site saw the influx of two dysoxic euxinic intervals that mark the end permian extinction event this suggests reduced oxygen conditions and the presence of h2s is the cause of the end permian extinction the bulla section also shows three troughs in 34ssulfate of which the latter two coincide with the dysoxic euxinic intervals this suggests that the latter two 34ssulfate troughs are the result of h2s oxidation in surface waters but the first trough is the result of a different mechanism we propose that h2s was oxidized in another region either to low 34ssulfate water or elemental s which then moved to the bulla area at the balvany section hungary there are two 34ssulfate troughs near the extinction and no evidence of euxinia a similar mechanism to the first bulla 34ssulfate trough is proposed with the suggestion that these waters were also depleted in oxygen in order to effect the extinction at balvany

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

behavior of carbonate associated sulfate during meteoric diagenesis and implications for the sulfur isotope paleoproxy abstract although carbonate associated sulfate cas is used widely as a proxy for the sulfur isotope composition of ancient seawater little is known about the effects of diagenesis on retention of primary 34 s signals our case study of the key largo limestone pleistocene florida is the first systematic assessment of the impact of meteoric diagenesis on cas properties geochemical and petrographic data show that meteoric diagenesis has affected the exposed coralline facies to varying degrees yielding differences now expressed as sharp reaction fronts between primary and secondary carbonate minerals within individual coral heads specifically analyses across high resolution transects in the key largo limestone show that concentrations of strontium and sodium decrease across the recrystallization front from original aragonite to meteoric low magnesium calcite by factors of roughly 5 and 10 respectively predictably 18 o values decrease across these same fronts the 13 c relationships are more complex with the most depleted values observed in the latest formed calcite such trends likely reflect carbon isotope buffering capacity that decreased as reaction progressed as well as protracted development of soil profiles and the associated terrestrial biomass and thus depleted 13 c during sea level lowstand conversely 34 s values of cas vary within a narrow buffered range from 20 6 to 22 6 compared to 20 8 22 0 of coeval pleistocene seawater across the same mineralogical transition despite sulfate concentrations that drop in the diagenetic calcite by an average factor of 12 collectively these data point to robust preservation of primary 34 s for carbonates that have experienced intense meteoric diagenesis which is encouraging news for those using the isotopic composition of cas as a paleoceanographic proxy at the same time the vulnerability of cas concentrations to diagenetic resetting is clear

high isotope fractionations during sulfate reduction in a low sulfate euxinic ocean analog a detailed record of the early earth sulfur s cycle is chronicled by the s isotope values of sulfide and sulfate preserved in the rock record interpretation of this record rests on our understanding of sulfur cycling in modern systems experiments and the resulting isotopic signatures very large fractionations in 34s of 70 are commonly measured between sulfide and sulfate in modern systems and in ancient sediments theoretical calculations suggest that sulfate reducing prokaryotes are capable of producing such large fractionations during the reduction of sulfate to sulfide although they have only been demonstrated to generate fractionations up to 48 here we report the first direct determination of 60 70 fractionations by natural populations of sulfate reducers these high fractionations occur under the relatively low sulfate conditions 1 1 2 mm of meromictic lago di cadagno in switzerland the major and minor isotopic composition of sulfide and sulfate in the lake water is consistent with sulfide produced by sulfate reduction with little evidence for modification by further oxidative sulfur cycling these observations help us to constrain the evolution of seawater sulfate concentrations

environmental and diagenetic variations in carbonate associated sulfate an investigation of cas in the lower triassic of the western usa an integrated stable isotope elemental and petrographic analysis of early triassic spathian carbonates and evaporites along a proximal to deep environmental transect reveals significant variations in 34s composition of carbonate associated sulfate cas the variations in the 34s of cas are strongly correlated with the ca mg composition of carbonates suggesting that the variations are driven by the degree of dolomitization the 34s of dolostones and evaporites are similar to one another and exhibit lower 34s values than limestones from all localities three hypotheses may explain the differences in 34s between proximal dolostones evaporites and inner middle shelf limestones 1 limestones experienced anaerobic sulfate reduction and subsequent incorporation of 34s enriched sulfate into cas during diagenesis while dolostones did not this is unlikely because of the lack of correlation between 34scas and toc as well as other indicators of diagenesis 2 dolomitization controlled the 34scas in proximal paleoenvironments where the source of the 34s depleted fluids was either continentally derived or the result of rayleigh distillation during evaporite formation and 3 a 34s depth gradient existed during the early triassic such that limestones formed in distal waters are more enriched in 34s versus evaporites and dolostones formed in proximal settings we do not favor this hypothesis because the strong correlation between ca mg and 34scas implies that dolomitization controls the 34scas in these samples results from subtidal well preserved non dolomitized limestones suggest that the 34s of spathian seawater sulfate may have been heavier than previously suggested from analyses of evaporite deposits alone