oak leaves as biosensors of late neogene and early pleistocene paleoatmospheric co2 concentrations abstract complementary to the interpretation of 13 c values of biogenic carbonate and sedimentary organic carbon in marine sediments paleoatmospheric co 2 levels can be estimated by considering the inverse relationship between atmospheric co 2 concentration and stomatal parameters frequency size on leaves of land plants in woody plants the significance of this species specific physiological response to changing co 2 regimes is now repeatedly confirmed both experimentally and from historical sequences of leaves collected since the onset of industrialization a corollary of this relationship is that analysis of stomatal parameters on fossil leaves has the potential of determining changes in paleoatmospheric co 2 levels at different time scales well preserved cuticle remains of oak leaves from late miocene pliocene and early pleistocene sediments of the lower rhine embayment germany the netherlands give promise of extending the record of stomatal frequency response to the last 10 ma during intervals with warm temperate to subtropical climatic conditions oak leaves are characterized by a high stomatal resistance or low conductance to co 2 diffusion and low stomatal frequencies during cooler intervals we observe an opposite picture comparison with historical relations between co 2 concentration and stomatal properties suggests that paleoatmospheric co 2 concentrations were not significantly higher than during the last 200 years and fluctuated several times between 280 and 370 ppmv in covariation with contrasting regional climatic conditions on a global scale intervals with reduced co 2 levels match glacial pulses characterized by the occurrence of ice rafted detritus in high latitude oceanic sediments

the role of carbon dioxide during the onset of antarctic glaciation earth s modern climate characterized by polar ice sheets and large equator to pole temperature gradients is rooted in environmental changes that promoted antarctic glaciation 33 7 million years ago onset of antarctic glaciation reflects a critical tipping point for earth s climate and provides a framework for investigating the role of atmospheric carbon dioxide co2 during major climatic change previously published records of alkenone based co2 from high and low latitude ocean localities suggested that co2 increased during glaciation in contradiction to theory here we further investigate alkenone records and demonstrate that antarctic and subantarctic data overestimate atmospheric co2 levels biasing long term trends our results show that co2 declined before and during antarctic glaciation and support a substantial co2 decrease as the primary agent forcing antarctic glaciation consistent with model derived co2 thresholds

cretaceous pco2 estimation from stomatal frequency analysis of gymnosperm leaves of patagonia argentina abstract stomatal frequency of fossil conifers and ginkgoals cuticles were considered as potential indicators of the p co 2 values in the patagonian palaeoatmosphere during the cretaceous samples are from continental deposits of early upper aptian age anfiteatro de tico and punta del barco formations and upper albian lower cenomanian age kachaike formation both outcropping in andean and extra andean portions of santa cruz province argentina it can be inferred that the co 2 atmospheric content was similar during both stages or was slightly higher toward the late albian early cenomanian the co 2 content estimated from the conifers is between 700 and 1400 ppmv or lower from the mid aptian ginkgoals this co 2 range is consistent with those predicted worldwide by previous studies stomatal indices biogeochemical models and carbon isotopes and implies a co 2 content 2 3 4 0 times higher than present the high atmospheric co 2 content during the middle aptian and late albian early cenomanian was probably linked to a warming process at high latitudes during these times this is consistent with the floristic development recorded during both stages in patagonia

a method for computing shallow ice core depths sipre style hand augers usually recover core sections whose bottom is somewhat shallower than the drill depth a procedure for calculating the range of possible core depths is presented in the field the drill barrel is lowered down the hole by means of a series of rigid extension rods the apparatus is then rotated to drill through debris left behind by the prior run and into fresh firn or ice care is taken to ensure that the total penetration of debris and firn does not exceed about half the length of the drill barrel otherwise the barrel s capacity for core and chips will be exceeded and the drill likely jammed the entire apparatus is then recovered the workers record the run number the total drill length barrel and extensions the exposed length of extensions above the hole top at the end of drilling and the length of recovered core the cycle is then repeated an example is shown in table i these data are then used to calculate drill depth which is drill length minus the exposed length plus an adjustment if drilling is from the base of a pit distance drilled is then obtained by comparison with the drill depth of the prior run the apparent core loss is the distallce drilled minus the length of recovered core the actual core loss is not readily calculated it is the sum of true core loss ground up core and the collapse of friable strata and the amount of core

carbon isotopes in continental weathering environments and variations in ancient atmospheric co2 pressure abstract abundance and carbon isotope data from an fe co3 oh component in apparent solid solution in oolitic goethites have been used to infer ancient atmospheric co2 pressures a test of the validity of these estimates might be comparisons of the carbon isotope compositions of fe co3 oh in oolitic goethites with time equivalent pedogenic calcites temporal trends of the oolitic goethite and pedogenic calcite 13c values are generally similar but time equivalent samples from each of these two groups are not common in the existing data to facilitate discussion of the concept comparisons were made of available goethite and calcite samples even though ages of the compared samples in each pair were not identical in four out of the five comparisons fe co3 oh abundance and 13c data were combined with pedogenic calcite 13c data to calculate physically reasonable soil co2 concentrations for the ancient calcitic soids this suggests that the compared oolitic goethite and pedogenic calcite systems were responding to the same global scale phenomenon i e atmospheric co2 atmospheric pco2 as determined from the goethites in these four well behaved cases ranged from values indistinguishable from modern within analytical uncertainty to values up to approximately 16 time modern modern atmospheric pco2 was taken to be 10 3 5 atm one interpretation of the fifth anomalous comparison is that atmospheric co2 levels increased from about 3 times modern to about 18 times modern from the triassic into the early jurassic this inferred value for the pco2 of the early jurassic atmosphere is not uniquely constrained by the existing data and needs to be substantiated however even considerably lower early jurassic atmospheric pco2 values of 6 to 9 times modern i e 1 3 to 1 2 of the estimated value of 18 times modern would still indicate significant differences between the global carbon cycles then and now these results highlight the need for more research on the behavior of the atmosphere during and after the triassic jurassic transition

the early toarcian anoxic event in the westernmost tethys subbetic paleogeographic and paleobiogeographic significance a positive delta 13 c excursion reveals an oceanic anoxic event in the subbetic corresponding to the westernmost end of the tethys during the early jurassic this positive delta 13 c excursion exists in five stratigraphic sections consisting of lower and middle toarcian pelagic sediments the positive delta 13 c excursion in the subbetic is located in the upper part of the early toarcian serpentinus approx falciferum biozone while in other tethyan regions alps apennines and dinarides it has been found in the lower part of the same biozone the most significant positive delta 13 c excursion detected in the subbetic is therefore about half a million years younger although other relative peaks had been detected this isotopic anomaly can be correlated with a maximum transgression that occurred earlier in the regions closer to the open sea of the tethys ocean other features of the anoxic event faunal crises and black shale deposits appear at different ages related t

a latest pleistocene and holocene glacial history and paleoclimate reconstruction at three sisters and broken top volcanoes oregon u s a abstract at least three sets of moraines mark distinct glacial stands since the last glacial maximum lgm in the three sisters region of the oregon cascade range the oldest stand predates 8 1 ka defined here as post lgm followed by a second between 2 and 8 ka neoglacial and a third from the little ice age lia advance of the last 300 years the post lgm equilibrium line altitudes were 260 100 m lower than that of modern glaciers requiring 23 9 increased winter snowfall and 1 4 0 5 c cooler summer temperatures than at present the lia advance had equilibrium line altitudes 110 40 m lower than at present implying 10 4 greater winter snowfall and 0 6 0 2 c cooler summer temperatures

regional significance of an early holocene moraine in enchantment lakes basin north cascade range washington abstract the upper enchantment lakes basin in the north cascade range of washington displays two moraine belts each recording an episode of glacier advance after the end of the last glaciation the inner belt the brynhild 0 1 to 0 5 km beyond existing glaciers postdates mount st helens wn tephra 450 yr old which lies only beyond the moraines the morainal surface is only slightly weathered is almost barren of lichens and is devoid of soil evidence suggesting that the brynhild moraines are no more than a century old the outer moraine the brisingamen 0 3 to 0 7 km beyond existing glaciers is weathered and is covered with large lichens on and behind the brisingamen moraine the mazama ash 6900 yr old is present beneath the mount st helens yn and wn tephras despite more than 7 millennia of weathering the rock surface behind the brisingamen moraine is measurably less weathered than the surface beyond which was last glaciated during the rat creek advance about 13 000 yr ago the age of the brisingamen moraine therefore is probably early holocene the brisingamen moraine evidently correlates with moraines near glacier peak near mount rainier in northeastern and central oregon in the southern canadian rockies and in the northern u s rocky mountains these regional effects suggest that a climatic episode of cooling or increased snowfall affected the entire region some time during the early holocene

stomatal evidence for a decline in atmospheric co2 concentration during the younger dryas stadial a comparison with antarctic ice core records a recent high resolution record of late glacial co2 change from dome concordia in antarctica reveals a trend of increasing co2 across the younger dryas stadial gs 1 these results are in good agreement with previous antarctic ice core records however they contrast markedly with a proxy co2 record based on the stomatal approach to co2 reconstruction which records a ca 70 ppm mean co2 decline at the onset of gs 1 to address these apparent discrepancies we tested the validity of the stomatal based co2 reconstructions from kru akenes by obtaining further proxy co2 records based on a similar approach using fossil leaves from two independent lakes in atlantic canada our late glacial co2 reconstructions reveal an abrupt ca 77 ppm decrease in atmospheric co2 at the onset of the younger dryas stadial which lagged climatic cooling by ca 130 yr furthermore the trends recorded in the most accurate high resolution ice core record of co2 from dome concordia can be reproduced from our stomatal based co2 records when time averaged by the mean age distribution of air contained within dome concordia ice 200 to 550 yr if correct our results indicate an abrupt drawdown of atmospheric co2 within two centuries at the onset of gs 1 suggesting that some re evaluation of the behaviour of atmospheric co2 sinks and sources during times of rapid climatic change such as the late glacial may be required copyright 2002 john wiley sons ltd journal of quaternary science

floral changes across the triassic jurassic boundary linked to flood basalt volcanism one of the five largest mass extinctions of the past 600 million years occurred at the boundary of the triassic and jurassic periods 201 6 million years ago the loss of marine biodiversity at the time has been linked to extreme greenhouse warming triggered by the release of carbon dioxide from flood basalt volcanism in the central atlantic ocean in contrast the biotic turnover in terrestrial ecosystems is not well understood and cannot be readily reconciled with the effects of massive volcanism here we present pollen spore and geochemical analyses across the triassic jurassic boundary from three drill cores from germany and sweden we show that gymnosperm forests in northwest europe were transiently replaced by fern and fern associated vegetation a pioneer assemblage commonly found in disturbed ecosystems the triassic jurassic boundary is also marked by an enrichment of polycyclic aromatic hydrocarbons which in the absence of charcoal peaks we interpret as an indication of incomplete combustion of organic matter by ascending flood basalt lava we conclude that the terrestrial vegetation shift is so severe and wide ranging that it is unlikely to have been triggered by greenhouse warming alone instead we suggest that the release of pollutants such as sulphur dioxide and toxic compounds such as the polycyclic aromatic hydrocarbons may have contributed to the extinction

mesozoic ecosystems climate and biotas this issue of palaeogeography palaeoclimatology palaeoecology is devoted to papers on mesozoic ecosystems and is an outcome of the international geoscience program igcp 632 igcp is a joint opera

late early cretaceous climate and pco2 estimates in the liupanshan basin northwest china abstract the extinct conifer family cheirolepidiaceae especially pseudofrenelopsis is commonly used to reconstruct the atmospheric palaeo co2 concentration pco2 during the cretaceous period in recent years many pseudofrenelopsis specimens have been collected from the uppermost stratum of the naijiahe formation in the liupanshan basin ningxia hui autonomous region northwest china the stomatal parameters such as stomatal density stomatal index stomatal pore length and stomatal pore depth and the stable carbon isotope composition of the present pseudofrenelopsis were analyzed the palaeo co2 levels of the liupanshan basin during the late early cretaceous late albian were reconstructed using stomatal ratio sr and mechanistic model approaches the sr method yielded a semi quantitative pco2 estimate of 620 ppmv on the basis of the recent standardization and 1030 ppmv on the basis of the carboniferous standardization which show similarities with other sr based and geochemical based reconstructions for the late early cretaceous the pco2 was about 670 ppmv on the basis of mechanistic model method similar to the estimated pco2 values recovered by the sr method corrected with the recent standardization based on comparative studies of previously published pco2 results of the early cretaceous pco2 levels varied during the early cretaceous and pco2 was relatively stable during the late early cretaceous furthermore environmental conditions of the liupanshan basin during the late early cretaceous were studied the stable carbon isotope composition of pseudofrenelopsis leaves ranged from 21 5 to 24 3 with an average of 22 8 indicating an arid semi arid and high evaporation climate during the late early cretaceous in the liupanshan basin these environmental conditions were also supported by palynological lithological and geochemical evidence

late glacial vegetation and climate change in western oregon abstract pollen records from two sites in western oregon provide information on late glacial variations in vegetation and climate and on the extent and character of younger dryas cooling in the pacific northwest a subalpine forest was present at little lake central coast range between 15 700 and 14 850 cal yr b p a warm period between 14 850 and 14 500 cal yr b p is suggested by an increase inpseudotsugapollen and charcoal the recurrence of subalpine forest at 14 500 cal yr b p implies a return to cool conditions another warming trend is evidenced by the reestablishment ofpseudotsugaforest at 14 250 cal yr b p increased haploxylonpinuspollen between 12 400 and 11 000 cal yr b p indicates cooler winters than before after 11 000 cal yr b p warm dry conditions are implied by the expansion ofpseudotsuga a subalpine parkland occupied gordon lake western cascade range until 14 500 cal yr b p when it was replaced during a warming trend by a montane forest a rise inpinuspollen from 12 800 to 11 000 cal yr b p suggests increased summer aridity pseudotsugadominated the vegetation after 11 000 cal yr b p other records from the pacific northwest show an expansion ofpinusfrom ca 13 000 to 11 000 cal yr b p this expansion may be a response either to submillennial climate changes of younger dryas age or to millennial scale climatic variations

modern glacier characteristics as a basis for inferring former climates with particular reference to the loch lomond stadial abstract studies of the mass balance of modern glaciers have indicated that the equilibrium line altitude ela is the most critical parameter in the link between glaciers and climate average accumulation on a glacier includes components derived from direct precipitation on the glacier surface as well as wind drifting and avalanching of snow and approximates closely to accumulation at the equilibrium line ablation is most usefully predicted by mean summer temperature and there is a close non linear relationship between accumulation and mean summer temperature at the equilibrium line following discussion of methods of reconstructing former glaciers and calculating their equilibrium line altitudes the application of the above relationships to the loch lomond readvance glaciers of highland britain is considered and an outline of the precipitation pattern and the mean summer temperature of the loch lomond stadial is given

early pliensbachian early jurassic c isotope perturbation and the diffusion of the lithiotis fauna insights from the western tethys abstract high resolution carbonate carbon isotope stratigraphy of lower jurassic marine shallow water limestones are compared with the distribution of the lithiotis fauna on the trento platform southern alps italy the lithiotis fauna is the first example of globally distributed mound building bivalves in the geological record and experienced global diffusion in the early jurassic a set of carbonate carbon isotope excursions of 2 3 illustrating three distinct negative shifts followed by positive rebounds are recorded in the isotope stratigraphy and can be correlated with the global negative 13 c shift of the sinemurian pliensbachian boundary event s p event and to the subsequent phase of c isotope perturbation that characterized the lower pliensbachian in the studied stratigraphic sections the s p event likely triggered eutrophic conditions illustrated by the presence of organic rich facies and by fossil associations characteristic of poorly oxygenated waters after the eutrophic phase the amelioration of environmental conditions was marked by a positive 3 rebound of the 13 c carb values and by the occurrence of marine stenotypic faunas on the trento platform the stabilization of the 13 c carb values coincided with the appearance of the lithiotis fauna that subsequently became widely distributed in the entire range of platform environments and thrived in the late pliensbachian when metric scale bivalve mounds were generated during the same time the maximum proliferation of the lithiotis fauna is recorded both in the tethyan and panthalassa regions hence the reported relationships between the 13 c carb data and the distribution and ecological characteristics of the genera contained in the lithiotis fauna suggest that the s p event and its aftermath possibly coupled with the undergoing coeval continent reorganization that led to the opening of the hispanic corridor could have set the stage for the rapid diffusion of these unusual bivalves across many parts of the globe

holocene and latest pleistocene glacial chronology glacier national park montana moraines of two different age groups have been identified fronting the present day glaciers and snowfields in glacier national park montana the subdued vegetated moraines of the older group have been found at 25 sites mainly in the central part of the lewis range these older moraines are in places overlain by the mazama ash although the exact age of the moraines has not been determined by radiocarbon dating vegetative evidence and correlation with other pre altithermal age moraines in the rocky mountains suggest that these older moraines date from 10 000 bp or earlier whether these moraines are the product of a separate advance after the end of the wisconsin glaciation or are simply the product of the last advance or stillstand of wisconsin glaciers before final deglaciation is not known moraines of the younger group consisting of fresh bouldery rubble are common throughout glacier park tree ring analyses indicate that some of these younger moraines were deposited by advances that culminated du

integrated seismic interpretation of the carlsberg fault zone copenhagen denmark summary we locate the concealed carlsberg fault zone along a 12 km long trace in the copenhagen city centre by seismic refraction reflection and fan profiling the carlsberg fault is located in a nnw sse striking fault system in the border zone between the danish basin and the baltic shield recent earthquakes indicate that this area is tectonically active a seismic refraction study across the carlsberg fault shows that the fault zone is a low velocity zone and marks a change in seismic velocity structure a normal incidence reflection seismic section shows a coincident flower like structure we have recorded seismic signals in a fan geometry from shots detonated both inside the low velocity fault zone and up to 500 m away from the fault zone the seismic energy was recorded on three receiver arrays 1 5 to 2 4 km long arcs across the expected location of the 400 to 700 m wide fault zone at distances of up to 7 km from the shots shots detonated inside the fault zone result in 1 weak and delayed first arrivals on the receivers located inside the fault zone compared to earlier and stronger first arrivals outside the fault zone 2 strong guided p and s waves as well as surface waves inside the fault zone the fault zone is a shadow zone to shots detonated outside the fault zone finite difference wavefield modelling supports the interpretations of the fan recordings our fan recording approach facilitates cost efficient mapping of fault zones in densely urbanized areas where seismic normal incidence and refraction profiling are not feasible

tetrapod biostratigraphy and biochronology of the triassic jurassic transition on the southern colorado plateau usa abstract nonmarine fluvial eolian and lacustrine strata of the chinle and glen canyon groups on the southern colorado plateau preserve tetrapod body fossils and footprints that are one of the world s most extensive tetrapod fossil records across the triassic jurassic boundary we organize these tetrapod fossils into five time successive biostratigraphic assemblages in ascending order owl rock rock point dinosaur canyon whitmore point and kayenta that we assign to the ascending order revueltian apachean wassonian and dawan land vertebrate faunachrons lvf in doing so we redefine the wassonian and the dawan lvfs the apachean wassonian boundary approximates the triassic jurassic boundary this tetrapod biostratigraphy and biochronology of the triassic jurassic transition on the southern colorado plateau confirms that crurotarsan extinction closely corresponds to the end of the triassic and that a dramatic increase in dinosaur diversity abundance and body size preceded the end of the triassic

geocarbsulf a combined model for phanerozoic atmospheric o2 and co2 abstract a model for the combined long term cycles of carbon and sulfur has been constructed which combines all the factors modifying weathering and degassing of the geocarb iii model berner r a kothavala z 2001 geocarb iii a revised model of atmospheric co2 over phanerozoic time am j sci 301 182 204 for co2 with rapid recycling and oxygen dependent carbon and sulfur isotope fractionation of an isotope mass balance model for o2 berner r a 2001 modeling atmospheric o2 over phanerozoic time geochim cosmochim acta 65 685 694 new isotopic data for both carbon and sulfur are used and new feedbacks are created by combining the models sensitivity analysis is done by determining 1 the effect on weathering rates of using rapid recycling rapid recycling treats carbon and sulfur weathering in terms of young rapidly weathering rocks and older more slowly weathering rocks 2 the effect on o2 of using different initial starting conditions 3 the effect on o2 of using different data for carbon isotope fractionation during photosynthesis and alternative values of oceanic 13c for the past 200 million years 4 the effect on sulfur isotope fractionation and on o2 of varying the size of o2 feedback during sedimentary pyrite formation 5 the effect on o2 of varying the dependence of organic matter and pyrite weathering on tectonic uplift plus erosion and the degree of exposure of coastal lands by sea level change 6 the effect on co2 of adding the variability of volcanic rock weathering over time berner r a 2006 inclusion of the weathering of volcanic rocks in the geocarbsulf model am j sci 306 in press results show a similar trend of atmospheric co2 over the phanerozoic to the results of geocarb iii but with some differences during the early paleozoic and for variable volcanic rock weathering lower co2 values during the mesozoic atmospheric oxygen shows a major broad late paleozoic peak with a maximum value of about 30 o2 in the permian a secondary less broad peak centered near the silurian devonian boundary variation between 15 and 20 o2 during the cambrian and ordovician a very sharp drop from 30 to 15 o2 at the permo triassic boundary and a more or less continuous rise in o2 from the late triassic to the present

extent timing and climatic implications of glacier advances mount rainier washington u s a at the pleistocene holocene transition abstract the north atlantic younger dryas climatic reversal did not cause a glacier advance on mount rainier the glaciers on mount rainier seem to have advanced in response to regional or local shifts in climate however the younger dryas climatic reversal may have affected the mount rainier area causing a cold but dry climate unfavorable to glacier advances glaciers in the vicinity of mount rainier advanced twice during late glacial early holocene time radiocarbon dates obtained from lake sediments adjacent to the corresponding moraines are concordant indicating that the ages for the advances are closely limiting the first advance occurred before 11 300 14c yr bp 13 200 cal yr bp during the north atlantic younger dryas event between 11 000 and 10 000 14c yr bp 12 900 and 11 600 cal yr bp glaciers retreated on mount rainier probably due to a lack of available moisture but conditions may have remained cold the onset of warmer conditions on mount rainier occurred around 10 000 14c yr bp 11 600 cal yr bp organic sedimentation lasted for at least 700 years before glaciers readvanced between 9800 and 8950 14c yr bp 10 900 and 9950 cal yr bp

early jurassic late pliensbachian co2 concentrations based on stomatal analysis of fossil conifer leaves from eastern australia the stomatal index a measure of stomatal density of an extinct australian early jurassic araucariacean conifer species allocladus helgei jansson is used to reconstruct the atmospheric carbon dioxide concentration pco 2 in the early jurassic the fossil leaves are preserved in a single bed palynologically dated to late pliensbachian similar to 185 183 mya atmospheric pco 2 is estimated from the ratios between the stomatal index of a helgei and the stomatal indices of three modern analogs nearest living equivalent plants co2 concentration in the range of similar to 750 975 ppm was calibrated from the fossil material with a best estimated mean of similar to 900 ppm the new average pco 2 determined for the late pliensbachian is thus similar to although similar to 10 lower than previously inferred minimum concentrations of similar to 1000 based on data from the northern hemisphere but may help constrain pco 2 during this period our results are the first pco 2 estimates produced using jurassic leaves from the southern hemisphere and show that i paleo atmospheric pco 2 estimates are consistent at a global scale though more investigations of southern hemisphere material are required and ii the stomatal proxy method can now be used without the context of relative change in pco 2 when applying the correct methodology c 2014 the authors published by elsevier b v on behalf of international association for gondwana research less

terrestrial and marine extinction at the triassic jurassic boundary synchronized with major carbon cycle perturbation a link to initiation of massive volcanism mass extinction at the triassic jurassic tr j boundary occurred about the same time 200 ma as one of the largest volcanic eruptive events known that which characterized the central atlantic magmatic province organic carbon isotope data from the uk and greenland demonstrate that changes in flora and fauna from terrestrial and marine environments occurred synchronously with a light carbon isotope excursion and that this happened earlier than the tr j boundary marked by ammonites in the uk the results also point toward synchronicity between extinctions and eruption of the first central atlantic magmatic province lavas suggesting a causal link between loss of taxa and the very earliest eruptive phases the initial isotopic excursion potentially provides a widely correlatable marker for the base of the jurassic a temporary return to heavier values followed but relatively light carbon dominated the shallow oceanic and atmospheric reservoirs for at least 600 k y

high precision u pb geochronology and a new chronostratigraphy for the canadon asfalto basin chubut central patagonia implications for terrestrial faunal and floral evolution in jurassic abstract the fluvial lacustrine and tuffaceous sedimentary succession of the canadon asfalto continental basin exposed in the argentinean chubut province of central patagonia preserves an extraordinary record of jurassic fauna and flora that marks key events in the evolution of dinosauria early mammals and major south american plant groups however basin wide correlation of the fossiliferous units is complicated by fault displacements unconformities and repetitive lithofacies new u pb analyses of zircon ca tims method from five primary tuff beds interstratified with the lacustrine strata establish a new chronostratigraphic framework for the sedimentary and volcanic units of canadon asfalto basin constraining ca 33 m y of depositional history and biotic evolution that spans nearly all three epochs of the jurassic five major vertebrate and plant rich stratigraphic intervals have been identified and are being actively investigated that range in age from pliensbachian to kimmeridgian or younger our combined biostratigraphic and high precision geochronologic results indicate that the major faunal turnover of the sauropodomorph dinosaurs which led to the rise of the eusauropods took place in the early jurassic earlier than previously recognized similarly the first successful radiation of the ornithischian dinosaurs heterodontosaurids as well as the evolutionary diversifications of the araucarian conifers and the osmundaceous ferns all occurred before the end of the early jurassic the diverse palynofloral assemblage of the canadon calcareo formation that was once considered to be early cretaceous in age is now entirely constrained to the late jurassic

the heterogeneous upper mantle low velocity zone abstract the upper mantle low velocity zone lvz is a depth interval with slightly reduced seismic velocity compared to the surrounding depth intervals the zone is present below a relatively constant depth of 100 km in most continental parts of the world both in cratonic areas with high average velocity and tectonically active areas with low average velocity evidence for the low velocity zone arises from controlled and natural source seismology including studies of surface waves and of primary and multiple reflections of body waves from the bounding interfaces calculations of receiver functions and absolute velocity tomography the available data indicates a more pronounced reduction in seismic velocity and q value for s waves than p waves as well as high electrical conductivity in the lvz seismic waves are strongly scattered by the zone which demonstrates the existence of small scale heterogeneity the depth to the base of the lvz is systematically shallower in cold stable cratonic areas than in hot active regions of the world because of its global occurrence below a relative constant depth of 100 km the lvz cannot be explained by metamorphic or compositional variation and rheological changes calculated upper mantle temperatures indicate that the rocks are close to the solidus in an interval with variable thickness below 100 km depth provided that the rocks contain water and carbon dioxide the presence of even small amounts of such fluids in the mantle rocks will lower the solidus by several hundred degrees and introduce a characteristic kink on the solidus curve around 80 100 km depth the seismic velocities and q values are significantly reduced of rocks which are close to the solidus or contain small amounts of partial melt hence the lvz may be explained by upper mantle temperatures being close to the solidus in a depth interval below 100 km assuming that the rocks contain only limited amounts of fluids this mechanism may explain the low velocities q values and resistivity as well as the intrinsic scattering and the characteristic variation in thickness of the low velocity zone

tephrochronology of late wisconsin deglaciation and holocene glacier fluctuations near glacier peak north cascade range washington abstract tephra layers near glacier peak in the north cascade range provide limiting dates for four periods of alpine glacier advance field relations suggest that late wisconsin alpine glaciers last advanced prior to the eruption of tephra layers from glacier peak about 11 250 yr b p late wisconsin deglaciation in the central north cascades was complete prior to the glacier peak tephra eruptions glaciers again expanded in the early holocene about 8400 8300 yr b p soil formed in alpine meadows during an episode of mild climate in the middle holocene prior to at least two intervals of glacier expansion an older episode between 5100 and 3400 yr b p and a younger episode within the last 1000 yr

stomatal proxy record of co2 concentrations from the last termination suggests an important role for co2 at climate change transitions a new stomatal proxy based record of co2 concentrations co2 based on betula nana dwarf birch leaves from the hasseldala port sedimentary sequence in south eastern sweden is presented the record is of high chronological resolution and spans most of greenland interstadial 1 gi 1a to 1c allerod pollen zone greenland stadial 1 gs 1 younger dryas pollen zone and the very beginning of the holocene preboreal pollen zone the record clearly demonstrates that i co2 were significantly higher than usually reported for the last termination and ii the overall pattern of co2 evolution through the studied time period is fairly dynamic with significant abrupt fluctuations in co2 when the climate moved from interstadial to stadial state and vice versa a new loss on ignition chemical record used here as a proxy for temperature lends independent support to the hasseldala port co2 record the large amplitude fluctuations around the climate change transitions may indicate unstable climates and that tippingpoint situations were involved in last termination climate evolution the scenario presented here is in contrast to co2 records reconstructed from air bubbles trapped in ice which indicate lower concentrations and a gradual linear increase of co2 through time the prevalent explanation for the main climate forcer during the last termination being ocean circulation patterns needs to re examined and a larger role for atmospheric co2 considered

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

age of the crowfoot advance in the canadian rocky mountains a glacial event coeval with the younger dryas oscillation a suite of sediment core samples was recovered from two lakes crowfoot and bow lakes that are adjacent to the crowfoot moraine type locality to identify and radiocarbon date sediments related to the crowfoot advance the crowfoot moraine system widely recognized throughout northwestern north america represents a glacial advance that is post wisconsin and pre mazama tephra in age an interval of inorganic sediments bracketed by accelerator mass spectrometry radiocarbon ages of ca 11 330 and 10 100 sup 14 c yr b p is associated with the crowfoot moraine the crowfoot advance is therefore approximately synchronous with the european younger dryas cold event ca 11 000 10 000 sup 14 c yr b p furthermore the termination of the crowfoot advance also appears to have been abrupt these findings illustrate that the climatic change responsible for the european younger dryas event extended beyond the northern atlantic basin and western europe equilibrium line altitude ela depressions associated with the crowfoot advance are similar to those determined for the little ice age advance whereas younger dryas ela depressions in europe significantly exceed little ice age ela depressions 26 refs 3 figs 1 tab

changing co2 conditions during the end triassic inferred from stomatal frequency analysis on lepidopteris ottonis goeppert schimper and ginkgoites taeniatus braun harris abstract end triassic fluctuations in atmospheric carbon dioxide co2 concentration were reconstructed by the use of stomatal frequency analysis on a single plant species the seedfern lepidopteris ottonis goeppert schimper stomatal index showed no distinct intra and interpinnule variation which makes it a suitable proxy for past relative co2 changes records of decreasing stomatal index and density from the bottom to the top of the rhaetian hettangian wustenwelsberg section bavaria germany indicate rising co2 levels during the triassic jurassic transition additionally stomatal frequency data of fossil ginkgoalean leaves ginkgoites taeniatus braun harris suggest a maximum palaeoatmospheric co2 concentration of 2750 ppmv for the latest triassic

fine structure of p wave velocity distribution along the atotsugawa fault central japan abstract a seismic experiment with five explosive sources and 396 seismic stations was conducted in august 2005 in the atotsugawa fault area central japan the 396 seismic stations were located on a survey line with a length of 47 km the profile line was located along the atotsugawa fault the average spacing of the seismic stations was about 119 m the spatially high density linear array was used to reveal the seismic structure of the fault zone the fine structure along the atotsugawa fault was obtained at depths shallower than 6 km a large lateral variation of p wave velocity which was consistent with the geological structure was found at the shallowest layer the heterogeneous variation with a velocity range of 5 7 km s 6 2 km s was obtained at the second layer the second layer was divided into three parts the western part of the research area was determined to be high velocity the low velocity area was detected at the central part at the east end of the profile line the p wave velocity was higher than that of the central part the low velocity area coincided with a low seismicity area the depth section of the reflection profile showed a boundary located at a depth of around 13 km the boundary was roughly consistent with the cut off depth of the seismicity of the microearthquakes the high seismic activity area was characterized to be reflective

pliensbachian environmental perturbations and their potential link with volcanic activity swiss and british geochemical records abstract the mechanisms leading to environmental and climate change prior to and anticipating the well studied toarcian oceanic anoxic event are not completely understood specifically the role of the continuing break up of pangea associated palaeogeographic rearrangements and the influence of volcanic activity are less well known therefore we studied the pliensbachian interval in the open marine hemipelagic section of the breggia gorge in southern switzerland to elucidate the potential impact of these major changes on the environment and climate we identified carbon isotope excursions towards lower values in whole rock carbonates dated from the sinemurian pliensbachian boundary davoei margaritatus and spinatum zones and possibly from the pliensbachian toarcian boundary using the whole rock oxygen isotope record and phosphorus content we associated these events with phases of increased runoff possibly related to climate warming we also established the first mercury hg record for the entire pliensbachian and in order to verify its validity we analysed an additional section located along the dorset coast in southern england the presence of hg spikes common in both sections may indicate the influence of episodes of increased volcanic activity the hg spike during the earliest pliensbachian may coincide with a late phase of the central atlantic magmatic province and or increased rifting linked with the opening of the hispanic corridor further significant maxima in hg contents are observed within the davoei and margaritatus zones and both phases may correspond to early volcanic activity of the karoo ferrar large igneous province further analyses are however needed to corroborate this interpretation and evaluate the importance of organic matter scavenging and detrital input in comparison to volcanic activity

mount mazama eruption calendrical age verified and atmospheric impact assessed geochemical identification of mount mazama ash in the greenland ice sheet project 2 gisp2 ice core gives a calendrical age of 7627 150 cal yr b p 5677 150 b c for the eruption thus providing a more accurate early holocene stratigraphic time line than previously available the gisp2 record of volcanically derived sulfate suggests a total stratospheric aerosol loading between 88 and 224 mt spread over an 6 yr period following the eruption of mount mazama taking into account the likelihood of some tropospheric aerosol transport to greenland realistic estimates of the resulting atmospheric optical depth range from 0 6 to 1 5 these values may have produced a temperature depression of 0 6 to 0 7 c at mid to high northern latitudes for 1 3 yr after the eruption these results indicate that the 5677 b c eruption of mount mazama was one of the most climatically significant volcanic events of the holocene in the northern hemisphere we also calculate a maximum stratospheric cl release of 8 1 mt by the eruption which may have led to substantial stratospheric ozone depletion

multi proxy record of holocene glacial history of the spearhead and fitzsimmons ranges southern coast mountains british columbia abstract evidence from glacier forefields and lakes is used to reconstruct holocene glacier fluctuations in the spearhead and fitzsimmons ranges in southwest british columbia radiocarbon ages on detrital wood and trees killed by advancing ice and changes in sediment delivery to downstream proglacial lakes indicate that glaciers expanded from minimum extents in the early holocene to their maximum extents about two to three centuries ago during the little ice age the data indicate that glaciers advanced 8630 8020 6950 6750 3580 2990 and probably 4530 4090 cal yr bp and repeatedly during the past millennium little ice age moraines dated using dendrochronology and lichenometry date to early in the 18th century and in the 1830s and 1890s limitations inherent in lacustrine and terrestrial based methods of documenting holocene glacier fluctuations are minimized by using the two records together

early jurassic microbial mats a potential response to reduced biotic activity in the aftermath of the end triassic mass extinction event wrinkle structures are microbially induced sedimentary structures miss formed by cyanobacteria and are common in pre cambrian and cambrian siltstones and sandstones but are otherwise rare in the phanerozoic geological record this paper reports the first discovery of mesozoic wrinkle structures from sweden these are preserved in fine grained and organic rich heterolithic strata of the lower jurassic hettangian hoganas formation in skane southern sweden the strata formed in a low energy shallow subtidal setting in the marginal parts of the danish rift basin palynological analyses of fine grained sandstones hosting the wrinkle structures show that the local terrestrial environment probably consisted of a wetland hosting ferns cypress and the extinct conifer family cheirolepidaceae palynostratigraphy indicates a hettangian age still within the floral recovery phase following the end triassic mass extinction event the finding of wrinkle structures is significant as the presence of microbial mats in the shallow subtidal zone in a deeper setting compared to where modern epibenthic microbial mats grow suggests decreased benthic biodiversity and suppressed grazing in shallow marine environments in the early aftermath of the end triassic mass extinction event

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

seismic reflections from the near vertical san andreas fault major near vertical strike slip faults should reflect seismic energy due to velocity contrasts within and across the fault zone analogous to sub horizontal faults commonly imaged by both multichannel and wide angle reflection surveys an increase of velocity with depth in the upper crust allows such reflections to be detected in surface seismic surveys we have observed fault reflection events from both sides of the san andreas fault in long offset common receiver gathers acquired near san francisco the events can be traced to the known surface position of the fault and provide constraints on the subsurface position to 3 7 km depth such reflections can be used to find the geometry of major near vertical faults even in areas without active seismicity providing information crucial to the understanding of the tectonics and seismic hazards of strike slip faulting

latest pleistocene alpine glacier advances in the sawtooth mountains idaho usa reflections of midlatitude moisture transport at the close of the last glaciation mountain glaciers in the sawtooth mountains responded strongly to reinvigorated atmospheric moisture transport following the last ice sheet maximum the glaciers constructed an extensive moraine belt in the southeastern sawtooth mountains allowing determination of a detailed radiocarbon chronology from lake and marsh cores moraine morphometry and soil data indicate construction of seven to nine moraines in each of four valleys during two main late pleistocene ice advances a basal radiocarbon date from marsh cores in the alturas valley documents that the maximum advance during marine oxygen isotope stage 2 occurred shortly before ca 16 900 calibrated cal yr b p minimum limiting dates on glacial lacustrine sediment in lake and marsh cores from three valleys clustered around 13 950 cal yr b p document the maintenance or reestablishment of extensive ice volume during early late glacial time the ca 16 900 cal yr b p advance postdates the last ice sheet maximum by 4000 yr and is broadly correlative with maximum advances of the north yellowstone outlet glacier and the puget lobe of the cordilleran ice sheet and a near maximum advance of wallowa mountain glaciers these synchronous advances indicate response of a variety of ice systems to reinvigorated moisture transport following the ice sheet maximum as does the subsequent sawtooth advance during early late glacial time together these responses indicate strong sensitivity of certain ice systems to moisture delivery fluctuations

a speleothem record of younger dryas cooling klamath mountains oregon usa awell dated d 18 o record in a stalagmite from a cave in the klamath mountains oregon with a sampling interval of 50 yr indicates that the climate of this region cooled essentially synchronously with younger dryas climate change elsewhere in the northern hemisphere the d 18 o record also indicates significant century scale temperature variability during the early holocene the d 13 c record suggests increasing biomass over the cave through the last deglaciation with century scale variability but with little detectable response of vegetation to younger dryas cooling d 2005 university of washington all rights reserved

on the long term context for late twentieth century warming 1 previous tree ring based northern hemisphere temperature reconstructions portray a varying amplitude range between the medieval warm period mwp little ice age lia and present we describe a new reconstruction developed using largely different methodologies and additional new data compared to previous efforts unlike earlier studies we quantify differences between more traditional std and regional curve standardization rcs methodologies concluding that rcs is superior for retention of low frequency trends continental north american versus eurasian rcs series developed prior to merging to the hemispheric scale cohere surprisingly well suggesting common forcing although there are notable deviations e g fifteenth to sixteenth century results indicate clear mwp warm lia cool and recent warm episodes direct interpretation of the rcs reconstruction suggests that mwp temperatures were nearly 0 7c cooler than in the late twentieth century with an amplitude difference of 1 14c from the coldest 1600 1609 to warmest 1937 1946 decades however we advise caution with this analysis although we conclude as found elsewhere that recent warming has been substantial relative to natural fluctuations of the past millennium we also note that owing to the spatially heterogeneous nature of the mwp and its different timing within different regions present palaeoclimatic methodologies will likely flatten out estimates for this period relative to twentieth century warming which expresses a more homogenous global fingerprint therefore we stress that presently available paleoclimatic reconstructions are inadequate for making specific inferences at hemispheric scales about mwp warmth relative to the present anthropogenic period and that such comparisons can only still be made at the local regional scale

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

on the nature of methane gas hydrate dissociation during the toarcian and aptian oceanic anoxic events the magnitude and timing of a major rapid negative carbon isotope excursion recorded in marine and terrestrial matter through the early toarcian early jurassic and early aptian early cretaceous oceanic anoxic events oaes have been proposed to be the result of large methane gas hydrate dissociation events here we develop and evaluate a global carbon isotope mass balance approach for determining the responses of each component of the exogenic carbon cycle terrestrial biosphere atmosphere and ocean the approach includes a dynamic response of the terrestrial carbon cycle to methane related co2 increases and climatic warming our analyses support the idea that both the early toarcian and early aptian isotopic curves were indicative of large episodic methane releases 5000 and 3000 gt respectively promoting warm greenhouse conditions in the mesozoic these events are calculated to have increased the atmospheric co2 concentration by 900 and 600 ppmv respectively and land surface temperatures by 2 5 to 3 0 c however we show that much of the methane released from oceanic sediments is rapidly sequestered by terrestrial and marine components in the global carbon cycle and this effect strongly attenuated the potential for ancient methane gas hydrate dissociation events to act as major amplifiers in global warming an increase in oceanic carbon sequestration is consistent with the deposition of globally distributed black shales during these oaes our analyses point to the urgent need for high resolution marine and terrestrial carbon isotope records to better characterize the nature of the toarcian and aptian events and improve our interpretation of their consequences for the global carbon cycle

ocean acidification during the early toarcian extinction event evidence from boron isotopes in brachiopods this project was funded by the european union s horizon 2020 research and innovation program under the marie sklodowska curie grant agreement and project base line earth 643084 and by the slovak research and development agency apvv17 0555 and the slovak scientific grant agency vega 0169 19

variable responses of western u s glaciers during the last deglaciation cosmogenic 10 be exposure ages from moraines in the wallowa mountains oregon identify two maximal late pleistocene glaciations at 21 1 6 0 4 ka and 17 0 6 0 3 ka and a minor glacial event at 10 2 6 0 6 ka our new high resolution chronology integrated with other well dated glacial records from the western united states demonstrates sub stantial differences in the synoptic responses of western u s glaciers to climate forcing associated with the global last glacial maximum and subsequent millennial scale events originating in the north atlantic region these variable synoptic glacier responses identify large changes in the relative contributions of regional to global controls on the climate of the western united states that accompanied the deglaciation

early jurassic carbon and oxygen isotope records and seawater temperature variations insights from marine carbonate and belemnite rostra pieniny klippen belt carpathians abstract new carbon and oxygen isotope records and discussion of the main variations in seawater temperature through the sinemurian aalenian of the pieniny klippen basin northern tethys ocean are presented herein comparison of the recorded changes in stable isotope compositions of bulk carbonate and belemnite rostra from an open marine environment with previously documented predominantly restricted epicontinental data enables determination of major climatic events that were most likely of worldwide extent a slight positive 13c shift is recorded in the lowermost upper pliensbachian a significant positive excursion in carbonate carbon isotope values is documented in the lower toarcian serpentinum zone furthermore the 13c values display a falling trend in the lower upper toarcian and relatively constant values in the aalenian temperatures inferred from the 18o values of well preserved belemnite rostra suggest rather cool seawater conditions 10 13 c in the pieniny klippen basin during the late sinemurian warming by 4 c in the early pliensbachian and then cooling by 8 c in the late pliensbachian the seawater temperature rose once more in the early toarcian and began to fall again during the middle toarcian in the middle late aalenian seawater temperatures oscillated between 10 and 13 c

no causal link between terrestrial ecosystem change and methane release during the end triassic mass extinction profound changes in both marine and terrestrial biota during the end triassic mass extinction event and associated successive carbon cycle perturbations across the triassic jurassic boundary t j 201 3 ma have primarily been attributed to volcanic emissions from the central atlantic magmatic province and or injection of methane here we present a new extended organic carbon isotope record from a cored t j boundary succession in the danish basin dated by high resolution palynostratigraphy and supplemented by a marine faunal record correlated with reference c isotope and biotic records from the uk it provides new evidence that the major biotic changes both on land and in the oceans commenced prior to the most prominent negative c isotope excursion if massive methane release was involved it did not trigger the end triassic mass extinction instead this negative c isotope excursion is contemporaneous with the onset of floral recovery on land whereas marine ecosystems remained perturbed the decoupling between ecosystem recovery on land and in the sea is more likely explained by long term flood basalt volcanism releasing both so2 and co2 with short and long term effects respectively

location of the carlsberg fault zone from seismic controlled source fan recordings 1 we locate the concealed carlsberg fault zone in the city of copenhagen from seismic fan recordings the fault is part of a fault system close to the border between the danish basin and the baltic shield recent earthquakes indicate that this area is tectonically active the fault zone is a seismic low velocity zone fan shots were recorded on three receiver arrays 1 5 2 4 km long arcs across the fault sources were placed inside and up to 500 m away from the 400 700 m wide fault zone at offsets of up to 7 km shots inside the fault zone show 1 weak delayed first arrivals inside the fault zone 2 stronger first arrivals outside the fault zone 3 guided waves inside the fault zone the fault is a shadow zone for shots detonated outside the fault zone our approach facilitates fault mapping in densely urbanized areas where seismic profiling is not feasible

climatic and sea level control of jurassic pliensbachian clay mineral sedimentation in the cardigan bay basin llanbedr mochras farm borehole wales

high resolution climatic evolution of coastal northern california during the past 16 000 years holocene and latest pleistocene oceanographic conditions and the coastal climate of northern california have varied greatly based upon high resolution studies ca every 100 years of diatoms alkenones pollen caco 3 and total organic carbon at ocean drilling program odp site 1019 41 682 n 124 930 w 980 m water depth marine climate proxies alkenone sea surface temperatures ssts and caco 3 behaved remarkably like the greenland ice sheet project gisp 2 oxygen isotope record during the balling allerod younger dryas yd and early part of the holocene during the yd alkenone ssts decreased by 3 c below mean bolling allerod and holocene ssts the early holocene ca 11 6 to 8 2 ka was a time of generally warm conditions and moderate caco 3 content generally 4 the middle part of the holocene ca 8 2 to 3 2 ka was marked by alkenone ssts that were consistently 1 2 c cooler than either the earlier or later parts of the holocene by greatly reduced numbers of the gyre diatom pseudoeunotia doliolus 10 and by a permanent drop in caco 3 to 3 starting at ca 5 2 ka coastal redwood and alder began a steady rise arguing for increasing effective moisture and the development of the north coast temperate rain forest at ca 3 2 ka a permanent ca 1 c increase in alkenone sst and a threefold increase in p doliolus signaled a warming of fall and winter ssts intensified higher amplitude and more frequent cycles of pine pollen alternating with increased alder and redwood pollen are evidence that rapid changes in effective moisture and seasonal temperature enhanced el nino southern oscillation enso cycles have characterized the site 1019 record since about 3 5 ka

greenhouse crises of the past 300 million years proxies of past co 2 and climate over the past 300 m y now reveal multiple global climate change events in unprecedented detail evidence for past co 2 spikes comes from expanded and refined data on stomatal index of fossil ginkgo and related leaves new evidence for synchronous climatic change comes from paleosols in montana utah and neighboring states each co 2 spike was coeval with unusually clayey red and decalcified paleosols which can be traced throughout the colorado plateau spikes in atmospheric co 2 also were coeval with increases in paleosol alkali depletion as an indication of high temperature and spikes in paleosol base depletion and depth to calcic horizons as indications of high precipitation in the colorado plateau times of warmer climate were also more humid perhaps due to greater moisture potential of warmer air seasonality of climate did not increase during warm wet spikes the mesozoic greenhouse was not persistently hot with cool spells but warm with hot flashes these data furnish power laws predicting the sensitivity and magnitude of change in mean annual temperature mat and mean annual precipitation map due to rising co 2 in a mid latitude mid continental region the magnitude of the coming anthropogenic greenhouse pales in comparison with past greenhouse spikes at times of global mass extinctions

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

an inter comparison study of three stomatal proxy methods for co2 reconstruction applied to early jurassic ginkgoales plants abstract the inverse relationship between concentrations of co2 in the atmosphere pco2 and the stomatal index of vascular plant has been widely used to estimate ancient levels of atmospheric co2 however some atmospheric concentration of co2 in the geological past paleo co2 estimates show little congruence because they are derived using different correlative methods or from different fossil plant species with different calibration approaches here we apply three methods including 1 the empirical method of mcelwain 1998 2 the empirical method of barclay and wing 2016 and 3 the mechanistic method of franks et al 2014 to a single fossil ginkgo species ginkgoites marginatus to track and assess their consistency of pco2 estimates for the early jurassic by using an inter comparison of three methods a high degree of consistency in pco2 estimates and trends has been observed in two empirical proxy methods in addition the mechanistic method and both the empirical methods also show generally good consistent paleo co2 estimates at the bed level to test the congruence of paleo co2 estimates we also apply all three methods to one additional ginkgoalean fossil species sphenobaiera huangii all three methods show species dependent uncertainty in paleo co2 estimates when applied to different ginkgalean fossil species collected from the same fossiliferous bed moreover considering the potential effect of guard cell size to the mechanistic method the genome size of fossil and living ginkgo taxa was analyzed based on the significant positive relationship between genome size and guard cell size the result demonstrates that a likely occurrence of polyploidy in sphenobaiera huangii may result in underestimated paleo co2 when applying mechanistic method due to an increase in the size of the stomatal complex

cosmogenic 3he and 10be chronologies of the late pinedale northern yellowstone ice cap montana usa cosmogenic 3 he and 10 be ages measured on surface boulders from the moraine sequence deposited by the northern outlet glacier of the yellowstone ice cap indicate that the outlet glacier reached its terminal position at 16 5 6 0 4 3 he ka and 16 2 6 0 3 10 be ka respectively concordance of these ages supports the scaled production rates used for 3 he 118 6 6 6 6 atoms g 21 y r 21 and 10 be 5 1 6 0 3 atoms g 21 y r 21 62s at high latitudes at sea level two recessional moraines upvalley from the terminal moraine have mean ages of 15 7 6 0 5 10 be ka and 14 0 6 0 4 10 be ka respectively and a late glacial flood bar was deposited at 13 7 6 0 5 10 be ka these cosmogenic chronologies identify a late pinedale glacial maximum in northern yellowstone that is significantly younger than previously thought and they suggest deglaciation of the yellowstone plateau by 14 10 be ka

synchrony between early jurassic extinction oceanic anoxic event and the karoo ferrar flood basalt volcanism a well known second order mass extinction took place during the pliensbachian and toarcian stages of the early jurassic first recognized as a minor pliensbachian peak in the global extinction rate it has alternatively been interpreted as a regional response to the early toarcian oceanic anoxic event detailed studies established it as a global long term event spanning five successive ammonoid zones here we present a revised time scale based on highprecision u pb ages resolved to the zone level which suggests that elevated extinction rates were sustained for about 4 m y and peak extinction occurred at 183 ma recent isotopic dating of flood basalts from the southern gondwanan karoo and ferrar provinces documents a culmination in volcanic activity ca 183 ma the onset of volcanism is recorded as an inflection and start of a rapid rise of the seawater 87 sr 86 sr curve the synchrony of voluminous flood basalt eruptions and biotic crises as already noted for three of the major mass extinctions permits a causal relationship which in this case may be mediated by widespread oceanic anoxia

extinction trajectories of benthic organisms across the triassic jurassic boundary abstract we analysed diversity and abundance patterns of benthic organisms across the triassic jurassic t j boundary based on the paleobiology database pbdb which compiles palaeontological collection data on a global scale while sepkoski s sepkoski j j jr 2002 a compendium of fossil marine animal genera bulletins of american paleontology 363 1 563 compendium on the stratigraphic ranges of marine animal genera suggests that the dominant macrobenthic groups of the late triassic experienced significant extinctions prior to the t j boundary a significant end triassic extinction peak is evident from pbdb s data this rhaetian extinction peak is found in both an analysis of the raw data of stratigraphic ranges and a sample standardized analysis of occurrence data 41 of all mesobenthic and macrobenthic genera crossing the norian rhaetian boundary became extinct within the rhaetian although this rate suffices to characterize the end triassic extinction as a true mass extinction against a middle triassic to middle jurassic background significantly reduced rhaetian origination rates add to the strong diversity depletion in the earliest jurassic as for other mass extinctions evidence for selective extinction is meagre when the analysis is limited to the boundary interval alone and when focused on taxonomic and ecological characteristics of individual genera when taxa are separated by environmental preferences however several determinants of extinction risk become evident suggesting that reef dwellers had a significantly higher extinction risk than level bottom dwellers taxa with an inshore preference were more strongly affected than offshore taxa taxa preferring carbonate substrates were more strongly hit than taxa preferring siliciclastic substrates and taxa preferentially inhabiting low latitudes had higher extinction rates than taxa more common at intermediate and high latitudes much of this selectivity is not independent and also seen in the intervals of background extinctions suggesting that the end triassic mass extinction represents an intensification of background extinctions but not a qualitatively different macroevolutionary regime one possible exception is related to preferences for depositional environments suggesting a selective rhaetian extinction in reefs and inshore settings

extracting a climate signal from 169 glacier records i constructed a temperature history for different parts of the world from 169 glacier length records using a first order theory of glacier dynamics i related changes in glacier length to changes in temperature the derived temperature histories are fully independent of proxy and instrumental data used in earlier reconstructions moderate global warming started in the middle of the 19th century the reconstructed warming in the first half of the 20th century is 0 5 kelvin this warming was notably coherent over the globe the warming signals from glaciers at low and high elevations appear to be very similar

fault zone guided waves from explosions in the san andreas fault at parkfield and cienega valley california fault zone guided waves were successfully excited by near surface explosions in the san andreas fault zone both at parkfield and cienega valley central california the guided waves were observed on linear three component seismic arrays deployed across the fault trace these waves were not excited by explosions located outside the fault zone the amplitude spectra of guided waves show a maximum peak at 2 hz at parkfield and 3 hz at cienega valley the guided wave amplitude decays sharply with observation distance from the fault trace the explosion excited fault zone guided waves are similar to those generated by earthquakes at parkfield but have lower frequencies and travel more slowly these observations suggest that the fault zone wave guide has lower seismic velocities as it approaches the surface at parkfield we have modeled the waveforms as s waves trapped in a low velocity wave guide sandwiched between high velocity wall rocks resulting in love type fault zone guided waves while the results are nonunique the parkfield data are adequately fit by a shallow wave guide 170 m wide with an s velocity 0 85 km sec and an apparent q 30 to 40 at cienega valley the fault zone wave guide appears to be about 120 m wide with an s velocity 0 7 km sec and a q 30

disrupted vegetation as a response to jurassic volcanism in southern sweden central skane scania in southern sweden hosts evidence of extensive jurassic volcanism in the form of mafic volcanic plugs and associated volcaniclastic deposits that entomb wellpreserved macro plant and spore pollen assemblages palynological assemblages recovered from the hoor sandstone are of hettangian pliensbachian age and those from the overlying lahar deposits are dated as pliensbachian early toarcian palynomorph assemblages from these units reveal significantly different ecosystems particularly with respect to the gymnospermous components that represented the main canopy plants both palynofloras are dominated by osmundacean marattiacean and cyatheacean fern spore taxa but whereas the hoo r sandstone hosts abundant chasmatosporites spp pollen produced by plants related to cycadophytes the volcanogenic deposits are dominated by cypress family pollen perinopollenites with an understorey component rich in putative erdtmanithecales or possibly gnetales and collectively representing vegetation of disturbed habitats permineralized conifer wood attributed to protophyllocladoxylon sp belonging to plants that probably produced the abundant perinopollenites grains is abundant in the volcanigenic strata and shows sporadic intraseasonal and multi year episodes of growth disruption together with the relatively narrow but marked annual growth rings and the annual and mean sensitivity values that span the complacent sensitive domains these features suggest growth within mediterranean type biomes subject to episodic disturbance less

extremely elevated co2 concentrations at the triassic jurassic boundary abstract although progress has been made in recent years in reconstructing the environmental conditions at the triassic jurassic boundary tjb published records of atmospheric co 2 concentrations have been of low resolution and or based on multi taxon estimates this is addressed here by reconstructing co 2 concentrations across the tjb using stomatal frequencies of four phylogenetically and ecologically distinct plant groups from two depositionally geographically and taphonomically separate boundary sections in east greenland and northern ireland with stomatal proxy methods and regression analysis the resulting co 2 records then are compared with an additional existing tjb record from a geological section in sweden the final results indicate that pre tjb rhaetian the co 2 concentration was approximately 1000 ppm that it started to rise steeply pre boundary and had doubled to around 2000 2500 ppm at the tjb the co 2 concentration then remained elevated for some time post boundary before returning to pre tjb levels in the hettangian these results are in very good accordance with published c isotope fire and leaf dissection records and clearly indicate steeply rising and lingering co 2 concentration at the tjb

extreme southwestern margin of late quaternary glaciation in north america timing and controls well preserved latero frontal moraines in the eastern san bernardino mountains of southern california provide evidence for several glacial advances during the late quaternary and mark the southwesternmost limit of glaciation in the western cordillera using geomorphology and 10be cosmogenic radionuclide dating a succession of moraines from three glaciated valleys is dated to 18 20 ka last glacial maximum 15 16 ka heinrich event 1 12 13 ka younger dryas stade and 5 9 ka early middle holocene these ages substantiate the view that glaciation throughout the american cordilleras was synchronous during the late quaternary furthermore these data show that glacial advances in southern california occur when a significant decrease in summer temperature is coupled with an increase in moisture flux producing high winter snowfall this allows for perennial snow accumulation that may under appropriate conditions persist to form glacial ice

timing and significance of late glacial and holocene cirque glaciation in the sierra nevada california mapping and radiocarbon dates of cirque moraines in the sierra nevada demonstrate that the last significant pre little ice age glacier advance in the range the recess peak resulted from snowline lowering roughly twice that of the matthes little ice age advance and that the recess peak advance is late pleistocene in age we mapped recess peak and matthes deposits in 64 cirques along a profile of the main sierran crest that spans the north south limits of neoglacial deposits in the range equilibrium line altitudes for the reconstructed recess peak glaciers vary greatly but coherently with those of the matthes advance the variability of both sets of deposits reflects strong topographic influences on snow accumulation and ablation patterns in their deep cirques tephrochronology and radiocarbon dates from lake sediment cores provide limits on the timing of the two advances previous work documenting the absence of a young regionally extensive tephra on matthes moraines in the central sierra demonstrates that they formed after 700 14c years bp 650 cal years bp the age of the recess peak advance has been less certain we therefore collected and dated sediment cores from lakes dammed behind terminal moraines correlating to the recess peak advance in four widely separated drainages along the sierran crest north to south south fork american river lee vining creek middle fork san joaquin river and bishop creek twenty three high precision ams radiocarbon dates on gyttja peat and macrofossils from the cores are internally consistent and demonstrate that the recess peak advance previously thought to be of late holocene age 2500 years bp ended before 11 190 70 14c years bp 13 100 85 cal years bp recess peak is therefore late pleistocene in age and probably predates the north atlantic younger dryas climatic reversal the absence of any glacial deposits on the bedrock between the recess peak and matthes deposits indicates that 1 any advance related to the younger dryas event in central california was smaller than the matthes advance 2 the matthes advance was the most extensive and possibly the only neoglacial event in the range and 3 climate in the sierra between 13 000 cal years bp and 650 cal years bp was apparently too warm and or dry to support glaciers larger than those of the little ice age other mapping indicates that the recess peak is the first significant glacier advance after retreat of tioga local late wisconsin maximum glaciers these results suggest a regionally variable climate in western north america during the younger dryas event because glaciers appear to have expanded in the canadian rockies at that time the new recess peak age limits combined with other dated lake cores indicate that the sierra was essentially deglaciated by 14 000 15 000 cal years bp 12 000 13 000 14c years bp substantially earlier than previously estimated this finding indicates that current production rates of some in situ cosmogenic nuclides calibrated on an assumed deglaciation of the range at 11 000 cal years bp 10 000 14c years bp may be systematically too high by as much as 20

climate change driven black shale deposition during the end triassic in the western tethys abstract several new triassic jurassic boundary sections from the eiberg basin northern calcareous alps austria have been studied at high resolution we present integrated geochemical and biological proxy data from this western tethys shelf basin high resolution correlation of kuhjoch the global boundary stratotype section and point gssp for the base of the jurassic hochalplgraben and tiefengraben shows that the initial and main carbon isotope excursions cie are contemporaneous with first and last occurrences of boundary defining macro and microfossils we focus on the end triassic initial cie at the transition from the limestones of the kossen formation to the marls of the kendlbach formation this change coincides with a dramatically increased influx of conifer cheirolepidiaceae pollen and increased total organic carbon toc values succeeded by an acme of green algae cymatiosphaera we present a model in which increased terrestrial organic matter influx is related to enhanced seasonality and increased erosion of the hinterland reduced salinity of the surface waters led to the mass occurrence of green algae stratification of the water column may have caused anoxic bottom water conditions and black shale deposition during the initial cie at the base of the kendlbach fm

carbon sequestration activated by a volcanic co 2 pulse during ocean anoxic event 2 ninety four million years ago during ocean anoxic event 2 there was a marked increase in the burial of organic carbon in marine sediments measurements of stomata in fossil leaves show that the two main pulses of carbon burial were associated with a decline in atmospheric co2 levels of up to 26 the cretaceous ocean anoxic event 2 about 94 million years ago is thought to be linked to extensive volcanism which triggered a biogeochemical chain of events that eventually led to widespread marine anoxia and a remarkable increase in carbon burial in marine sediments1 2 3 it has been suggested that the event was accompanied by a substantial decrease in atmospheric co2 concentrations4 but the quantification of the drawdown remains controversial5 6 here we reconstruct atmospheric co2 concentrations throughout the ocean anoxic event from counts of the stomata in fossil leaves and use terrestrial carbon isotopes to link the reconstruction to marine records of the event7 8 we find that before the onset of ocean anoxia atmospheric co2 concentrations increased by 20 over background levels of 370 100 70 ppm this was part of a long term rise in atmospheric co2 levels presumably caused by volcanism which reached a peak of 500 400 180 ppm however two pulses of extensive carbon burial during the ocean anoxic event as indicated by positive carbon isotope excursions are associated with decreased atmospheric co2 concentrations we conclude that the sequestration of marine organic carbon led to a decrease in atmospheric co2 concentration of up to 26 during ocean anoxic event 2

a new cordaitean pollen cone and pollen grains in situ from the early permian of hexi corridor and its geotectonic significance a new species of cordaitean pollen cone is described and diagnosed from early permian strata in gansu province northwestern china the gross morphology and well preserved features of the species named cordaianthus yongchangensis z x wang et b n sun sp nov have been studied in detail the current fossil has helically arranged bracts and secondary fertile shoots the bract longer and wider than in other known fossils diverges at approximately 90 from the axis the secondary fertile shoots are obovate with scales on individual shoots and fertile scales concentrated near the apex of the secondary fertile shoots more than five pollen sacs are clustered on the fertile scales which number 8 13 as the current species differs from any known species in the fossil records it is considered as a new species of cordaianthus the species with its microstructure of bracts and scales in situ pollen sacs and pollen grains provides important clues on the evolution of cordaitopsida based on the known reproductive organs of cordaitean plants we discovered that the current fossil with its wide bracts that protect the helically arranged secondary fertile shoots is similar to modern conifer cones suggesting that the current fossil is an evolutionally advanced species in comparisons with cordaitean fossils the leaves of cordaitean plants from the alt alashan terrane during the early permian presented mixed leaf features of specimens from the ncb north china block and scb south china block in conclusion the alt was already located between the ncb and scb in the early permian c 2016 elsevier b v all rights reserved

seismic guided waves trapped in the fault zone of the landers california earthquake of 1992 a mobile seismic array of seven stations was deployed at 11 sites along the fault trace of the m7 4 landers earthquake of june 28 1992 with a maximum offset of 1 km from the trace we found a distinct wave train with a relatively long period following the s waves that shows up only when both the stations and the events are close to the fault trace this wave train is interpreted as a seismic guided wave trapped in a low velocity fault zone to study the distribution of amplitude of the guided waves with distance from the fault trace and also their attenuation with travel distance along the fault zone we eliminated source and recording site effects by the coda normalization method the normalized amplitudes of guided waves show a spectral peak at 3 4 hz which decays sharply with distance from the fault trace spectral amplitudes at high frequencies 8 15 hz show an opposite trend increasing with distance from the fault trace the normalized amplitudes of guided waves at 3 4 hz also show a systematic decrease with hypocentral distance along the fault zone from which we infer an apparent q of 50 in order to confirm the existence of the guided waves a dense array of 31 stations was deployed at one of the 11 sites the resultant records revealed unequivocal evidence for the existence of guided waves associated with the fault zone by modeling the waveforms as s waves trapped in a low velocity waveguide sandwiched between two homogeneous half spaces with velocity vs 3 0 km s we infer a waveguide width of about 180 m a shear velocity of 2 0 2 2 km s and a q of 50 hypocenters of aftershocks with clear guided waves show a systematic distribution both laterally and with depth delineating the extent of the low velocity fault zone in three dimensions we find that the zone extends to a depth of at least 10 km this zone apparently continues to the south across the pinto mountain fault because guided waves are observed at stations north of the pinto mountain fault for earthquakes with epicenters south of it on the other hand the zone appears to be discontinuous at the fault bend located about 20 km north of the mainshock epicenter guided waves were observed for stations and epicenters which are located on the same sides of the fault bend but not for those on the opposite sides

global trends of pco2 across the cretaceous paleogene boundary supported by the first southern hemisphere stomatal proxy based pco2 reconstruction reliable reconstructions of atmospheric carbon dioxide concentrations pco2 are required at higher resolution than currently available to help resolve the relationship between mass extinctions and changes in palaeo pco2 levels such reconstructions are needed 1 at a high temporal resolution for constraining the pre and post extinction atmospheres and 2 at a sufficient spatial resolution to constrain potential inter hemispheric differences here we estimate pco2 based on fossil lauraceae leaf cuticle specimens derived from three localities with strata spanning the latest cretaceous to the mid paleocene including a new cretaceous paleogene boundary k pg locality in new zealand we use two independent methods of stomatal density based pco2 reconstructions a transfer function calibrated using herbarium material and the stomatal ratio method producing three calibration sets our results based on the mean values of each of the three calibration methods indicate pco2 ranging between ca 460 and 650 ppm during the latest cretaceous falling precipitously to average values between ca 360 and 430 ppm across the k pg boundary and further to ca 305 320 ppm in the mid paleocene a spike of extremely high pco2 at the k pg could not be confirmed but our results are nonetheless consistent with previously published pco2 records from the northern hemisphere and show that stomatal density worldwide was responding to significant changes in pco2 across the k pg

was the younger dryas triggered by a flood draining of a huge lake into the northern atlantic may have triggered a cold period 12 900 years ago the route taken by the flood waters remains unknown

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

late glacial and early holocene variations in atmospheric co2 concentration indicated by high resolution stomatal index data data from ice cores suggest that late glacial and early holocene atmospheric co2 variations were rather conservative the most important change being a gradual younger dryas increase by contrast palaeo co2 records based on the inverse relationship between co2 partial pressure and stomatal frequency of terrestrial plant leaves reflect a more dynamic co2 evolution including an abrupt decrease at the allerod younger dryas transition here we present a late glacial and early holocene co2 record based on stomatal index data from leaves preserved in the sediments of a small lake in southwestern sweden three independent records constructed from stomatal index data of salix polaris salix herbacea and betula nana leaves were combined to form a high resolution co2 reconstruction for the period 12 800 10 800 cal yr bp atmospheric co2 concentrations were found to have decreased rapidly from c 260 ppmv to 210 215 ppmv within 200 years during the allerod gi 1 younger dryas gs 1 transition after 100 200 years co2 concentration started to gradually increase to 270 290 ppmv at the end of the younger dryas stadial gs 1 co2 concentrations were relatively stable during the early holocene except for a short lived period of lower 240 250 ppmv values c 11350 11200 cal yr bp this late glacial and early holocene co2 evolution partly resembles previous stomatal based co2 reconstructions and the overall trend is almost identical to that seen in ice core records the amplitude of change is however markedly higher in the swedish stomatal based record compared to the ice cores this difference may partly be accounted for by the inherent smoothing of ice core co2 records caused by diffusion but a major part of the difference in amplitude between ice core and stomatal based records still remains to be explained based on our reconstruction atmospheric co2 may have played an important role in climate dynamics during the last deglaciation c 2003 elsevier b v all rights reserved less

synchronous records of pco2 and δ14c suggest rapid ocean derived pco2 fluctuations at the onset of younger dryas just before the onset of the younger dryas yd cold event several stomatal proxy based pco2 records have shown a sharp increase in atmospheric co2 concentration pco2 of between ca 50 and 100 ppm followed by a rapid decrease of similar or even larger magnitude here we compare one of these records a high resolution pco2 record from southern sweden with the intcal13 record of radiocarbon d 14 c the two records show broadly synchronous fluctuations at the yd onset specifically the intcal13 record documents decreasing d 14 c just before the yd onset when pco2 peaks consistent with a source of old co2 from the deep ocean we propose that this fluctuation occurred due to a major ocean flushing event the cause of the flushing event remains speculative but could be related to the hypothesis of the glacial ocean as a thermobaric capacitor we confirm that the earth system can produce such large multidecadal timescale fluctuations in pco2 through simulating an artificial ocean flushing event with the genie earth system model we suggest that sharp transitions of pco2 may have remained undetected so far in ice cores due to inter firn gas exchange and time averaging the stomatal proxy record is a powerful complement to the ice core records for the study of rapid climate change

deep time evidence of a link between elevated co2 concentrations and perturbations in the hydrological cycle via drop in plant transpiration the physiological effects of high co 2 concentrations i e co 2 on plant stomatal responses may be of major importance in understanding the consequences of climate change by causing increases in runoff through suppression of plant transpiration radiative forcing by high co 2 has been the main consideration in models of global change to the exclusion of plant physiological forcing but this potentially underestimates the effects on the hydrological cycle and the consequences for ecosystems we tested the physiological responses of fossil plants from the triassic jurassic boundary transition tr j succession of east greenland this interval marks a major high co 2 driven environmental upheaval with faunal mass extinctions and significant floral turnover our results show that both stomatal size expressed in fossil material as sl the length of the stomatal complex opening and stomatal density sd the number of stomata per mm 2 decreased significantly during the tr j we estimate using a leaf gas exchange model that the decreases in sd and sl resulted in a 50 60 drop in stomatal and canopy transpiration at the tr j we also present new field evidence indicating simultaneous increases in runoff and erosion rates we propose that the consequences of stomatal responses to elevated co 2 may lead to locally increased runoff and erosion and may link terrestrial and marine biodiversity loss via the hydrological cycle

carbon isotope anomaly and other geochemical changes at the triassic jurassic boundary from a marine section in hungary most mass extinctions are linked with carbon isotope excursions implying that biotic crises are coupled with changes in the global carbon cycle the isotopic evolution during the end triassic extinction is far less documented than that for the other major phanerozoic extinctions here we report a sharp and short lived 23 5 excursion in carbon isotope values for carbonate d 13 ccarb corresponding to a 22 excursion in the isotopic composition of marine organic matter d 13 corg and other geochemical

late quaternary vegetation and climate history near little lake central coast range oregon pollen and plant macrofossils recovered from little lake oregon provide the first record of late quaternary climate and vegetation changes in oregon9s central coast range the pollen data suggest that the period from ca 42 000 to 24 770 yr b p featured an open forest of western white pine western hemlock and fir the inferred climate was cooler and wetter than today the full glacial period was characterized by a parkland of spruce lodgepole pine and mountain hemlock which suggests that the climate was colder and possibly drier than today the oregon coast range was not a glacial refugium for temperate conifers as has been proposed by 16 000 yr b p the pollen and plant macrofossil data suggest the development of a montane forest composed of pine fir western hemlock and mountain hemlock temperate taxa were present in the vegetation at 13 500 yr b p during a period of climatic amelioration a reversal in this warming trend may have occurred between 11 000 and 10 500 yr b p when pine western and mountain hemlock and spruce were slightly more abundant early holocene forests featured douglas fir red alder and bracken fern implying more severe summer drought and more frequent fires after 5600 yr b p douglas fir western hemlock and western red cedar dominated the record marking the introduction of the present day cool moist climate however during the past 2800 yr increased douglas fir and decreased cedar suggest the possibility of reduced effective moisture at little lake

temporal and spatial distribution patterns of the marine brackish water bivalve waagenoperna in china and its implications for climate and palaeogeography through the triassic jurassic transition abstract waagenoperna was a genus of epi byssate marine to brackish water littoral bivalves it used to be regarded as late permian late triassic in age however a review of the genus reveals that it did not occur until the late triassic and in the early jurassic some species of waagenoperna i e w lilingensis w mytiloides and w cf lilingensis had a wide distribution in the areas southwest of the shanghai altay mountain range including parts of southern china the sediments hosting these bivalves are intercalated with non marine strata including coal the geographic and stratigraphic distribution patterns of waagenoperna can not only aid in the correlation of the non marine coal bearing strata spanning the triassic jurassic transition and constrain their age but also particularly demonstrate a history of transgressions flooding the areas southwest of shanghai altay during the sinemurian these extensive transgressions influenced the climate and changed the palaeo topography of southwestern shanghai altay they ensured a humid climate and resulted in the formation of marsh and even paralic swamp environments these environments allowed the flora and fauna to thrive and led to the accumulation of large quantities of organic matter that eventually formed coal and probably oil as well

high resolution shear wave seismics across the carlsberg fault zone south of copenhagen implications for linking mesozoic and late pleistocene structures abstract the carlsberg fault zone cfz is a nnw sse striking structure close to the transition zone between the danish basin and the baltic shield we examine the fault evolution by combining very high resolution onshore shear wave seismic data one conventional onshore seismic profile and marine reflection seismic profiles the faulting geometry indicates a strong influence of triassic subsidence and rifting in the central european basin system growth strata within the cfz surrounding hollviken graben reveal syntectonic sedimentation in the lower triassic indicating the opening to be a result of triassic rifting in the upper cretaceous growth faulting documents continued rifting these findings contrast the late cretaceous to paleogene inversion tectonics in neighboring structures such as the tornquist zone the high resolution shear wave seismic method was used to image faulting in quaternary and danian layers in the cfz the portable compact vibrator source elvis iii s8 was used to acquire a 1150 m long seismic section on the island amager south of copenhagen the shallow subsurface in the investigation area is dominated by quaternary glacial till deposits in the upper 5 11 m and danian limestone below in the shear wave profile we imaged the uppermost 30 m of the western part of cfz the complex fault zone comprises normal block faults and one reverse block fault the observed faults cut through the danian as well as the quaternary overburden hence there are strong indicators for ongoing faulting like mapped faulting in quaternary sediments and ongoing subsidence of the eastern block of the cfz as interpreted by other authors the lack of earthquakes localized in the fault zone implies that either the frequency of occurring earthquakes is too small to be recorded in the observation time span or that the movement of the shallow sub surface layers may be due to other sources than purely tectonic processes

time scale for adjustment of glaciers to changes in mass balance the length of time tm over which a glacier responds to a prior change in climate is investigated with reference to the linearized theory of kinematic waves and to results from numerical models we show the following tm may in general be estimated by a volume time scale describing the time required for a step change in mass balance to supply the volume difference between the initial and final steady states the factor f in the classical estimate of m l u where i is glacier length and u is terminus velocity has a simple geometrical interpretation ft is the ratio of thickness change averaged over the full length i to the change at the terminus although both u and f relate to dynamic processes local to the terminus zone the ratio f u and therefore tm are insensitive to details of the terminus dynamics in contrast to conclusions derived from some simplified kinematic wave models a more robust estimate of tm independent of terminus dynamics is given by tm h b where h is a thickness scale for the glacier and b is the mass balance rate negative at the terminus we suggest that tm for mountain glaciers can be substantially less than the 1o2 103 years commonly considered to be theoretically expected

a global perturbation to the sulfur cycle during the toarcian oceanic anoxic event abstract the mesozoic era was punctuated by intervals of widespread anoxia within the ocean termed oceanic anoxic events or oaes the chemostratigraphy of these intervals also contains evidence of transient perturbations to many biogeochemically important elemental cycles here we present high resolution sulfur isotope data from three stratigraphic sections spanning the toarcian oceanic anoxic event t oae of the early jurassic all sections show a similar increase in the sulfur isotope ratio of sulfate parallel to an overall positive excursion in carbon isotopes during the oae interval based on forward box modeling the sulfate s isotope excursion can be generated by transiently increasing the burial rate of pyrite in marine sediments likely deposited under euxinic i e anoxic and sulfidic conditions in the water column in addition modeling shows that prolonged recovery of the 34 s of seawater sulfate at least 8 ma after the initial rise associated with the oae was due to the relatively long residence time of sulfate in the jurassic ocean estimates from our modeling put the toarcian marine sulfate concentrations at 4 to 8 mm the similarity of the sulfur isotope records from the north european epicontinental or epeiric sea and tethyan continental margin suggests that local modification of the marine sulfur isotope signal was minimal a point explored with isotope mixing models importantly our results indicate that the sulfur isotope excursion reflects a globally significant perturbation in the sulfur cycle and that pyrite burial in the north european epeiric seaway alone cannot account for the excursion this study along with recent work from other phanerozoic intervals of widespread marine oxygen deficiency confirms that the sulfur cycle can be perturbed significantly by enhanced pyrite burial during periods of prolonged oceanic anoxia euxinia

significant transient pco2 perturbation at the new zealand oligocene miocene transition recorded by fossil plant stomata abstract the reorganisation of earth s climate system from the oligocene to the miocene was influenced by complex interactions between tethyan tectonics orbital parameters oceanographic changes and carbon cycle feedbacks with climate modelling indicating that pco2 was an important factor oscillating episodes of climate change during the oligocene miocene transition omt have however been difficult to reconcile with existing pco2 records here we present a new pco2 record from the omt into the early miocene reconstructed using the stomatal proxy method with a database of fossil lauraceae leaves from new zealand the leaf database derives from three relatively well dated sites located in the south island of new zealand foulden maar mataura river and grey lake atmospheric pco2 values were obtained based on four separate calibrations with three nearest living equivalents using the stomatal ratio method as well as transfer functions our results based on the mean values of each of the four calibrations indicate pco2 ranging 582 732 ppm average 650 ppm at the omt falling precipitously to mean values of 430 538 ppm average 492 ppm for the earliest miocene and 454 542 ppm average 502 ppm in the early miocene the much higher values of pco2 at the omt indicate that pco played an important role in climate dynamics during this time potentially including the abrupt termination of glaciations