neoproterozoic snowball earth simulations with a coupled climate ice sheet model ice sheets may have reached the equator in the late proterozoic era 600 800 myr ago according to geological and palaeomagnetic studies possibly resulting in a snowball earth but this period was a critical time in the evolution of multicellular animals posing the question of how early life survived under such environmental stress here we present computer simulations of this unusual climate stage with a coupled climate ice sheet model to simulate a snowball earth we use only a reduction in the solar constant compared to present day conditions and we keep atmospheric co2 concentrations near present levels we find rapid transitions into and out of full glaciation that are consistent with the geological evidence when we combine these results with a general circulation model some of the simulations result in an equatorial belt of open water that may have provided a refugium for multicellular animals

application of stochastic simulation to co2 flux from soil mapping and quantification of gas release 1 conditional sequential gaussian simulations sgs have been applied for the first time to the study of soil diffuse degassing from different volcanic and nonvolcanic systems the application regards five data sets of soil co2 fluxes measured with the accumulation chamber methodology at the volcanic areas of solfatara of pozzuoli italy vesuvio cone italy nisyros greece and horseshoe lake california and at the nonvolcanic degassing area of poggio dell olivo italy the sgs algorithm was used to generate 100 realizations of co2 flux for each area probabilistic summaries of these simulations together with the information given by probability plots were used 1 to draw maps of the probability that co2 fluxes exceed thresholds specific for a background flux i e to define the probable extension of the degassing structures 2 to calculate the total co2 output and 3 to quantify the uncertainty of the estimation the results show that the sgs is a suitable tool to model soil diffuse degassing producing realistic images of the distribution of the co2 fluxes that honor the histogram and variogram of the original data moreover the relation between the sample design and the uncertainty of estimation was investigated leading to an empirical relation between uncertainty and the sampling density that can be useful for the planning of future co2 flux surveys

dynamics of carbon dioxide emission at mammoth mountain california mammoth mountain a dormant volcano in the eastern sierra nevada california has been passively degassing large quantities of cold magmatic co2 since 1990 following a 6 month long earthquake swarm associated with a shallow magmatic intrusion in 1989 a search for any link between gas discharge and volcanic hazard at this popular recreation area led us to initiate a detailed study of the degassing process in 1997 our continuous monitoring results elucidate some of the physical controls that influence dynamics in flank co2 degassing at this volcano high coherence between variations in co2 efflux and variations in atmospheric pressure and wind speed imply that meteorological parameters account for much if not all of the variability in co2 efflux rates our results help explain differences among previously published estimates of co2 efflux at mammoth mountain and indicate that the long term annual co2 degassing rate has in fact remained constant since 1997 discounting the possibility of large meteorologically driven temporal variations in gas efflux at other volcanoes may result in spurious interpretations of transients that do not reflect actual geologic processes

sedimentary challenge to snowball earth evidence from the magnetic field fossilized in sedimentary rocks suggests that more than 600 million years ago ice occupied tropical latitudes a popular explanation for these findings the snowball earth concept envisages a fully frozen earth for millions of years caused by a runaway ice albedo feedback a rapid catastrophic meltback at very high levels of atmospheric carbon dioxide is thought to have ended this extreme climatic state however sedimentary rocks deposited during these cold intervals indicate that dynamic glaciers and ice streams continued to deliver large amounts of sediment to open oceans throughout the glacial cycle the sedimentary evidence therefore indicates that despite the severity of glaciation some oceans must have remained ice free significant areas of open ocean have important implications for the survival and diversification of life and for the workings of the global carbon cycle the snowball earth concept envisages a fully frozen earth for millions of years several times during the neoproterzoic era between 1 000 and 542 million years ago however the sedimentary evidence suggests that despite the severity of glaciation some oceans must have remained ice free

diffuse carbon dioxide emissions from hidden subsurface structures at asama volcano japan we measured diffuse carbon dioxide co2 flux and soil temperature around the summit of asama volcano japan to assess the diffuse degassing structure around the summit area soil co2 flux was measured using an accumulation chamber method and the spatial distributions of co2 flux and soil temperature were derived from the mean of 100 sequential gaussian simulations results show that soil co2 flux was high on the eastern flank of kamayama cone and the eastern rim of maekake crater the outer cone these areas mostly correspond to high temperature anomalies the average emission rate of diffuse co2 was calculated to be 12 6 t day 1 12 2 14 6 t day 1 such diffuse emissions account for 12 of the total diffuse and plume co2 emissions from the summit area the diffuse co2 anomalies probably reflect permeable zones controlled by local topography and hidden fractures bordering maekake crater the permeable zones are connected to the low electrical resistivity zone inferred to indicate both a hydrothermal fluid layer and an upper sealed layer made of clay minerals magmatic gas from the main conduit ascends to the volcano surface through this fluid layer and the permeable zones these insights emphasize that the pathways and the connection between the pathways and the source of diffuse co2 combine to create the pattern of heterogeneous diffuse co2 emission seen at the surface only by using a combination of gas measurements and geophysical tools can we begin to understand the dynamics of this system as a whole

how to remove the seasonal atmospheric effect an application on a surface volcanic temperature at nisyros active volcano hellenic volcanic arc abstract surface temperature at a volcanic system is the result of a mixture of two heat sources originating one from above and another from below the ground surface the atmosphere significantly affects the surface s temperature of the volcano and removal of the atmospheric effect is required for meaningful interpretations prior to any characterization of anomalous volcanic activity time series of meteorological data were acquired from the closest weather station to nisyros volcano and surface volcanic temperature from the southern part of nisyros caldera were analyzed time series analysis took place at different time scales through a decomposition method the decomposition of the time series into long seasonal and short term components was performed by the application of the kolmogorov zurbenko kz filter to separate the noise that appears on the obtained data the time series regression tsr model was applied in all time scales the long and the short term components of the surface volcanic temperature show no significant correlation with the atmospheric variables while the seasonal term indicates a very strong association with an r2 equal with 99 after the removal of the atmospheric effect our model indicates that there is a normal activity of the seasonal heat emission in nisyros with no anomalous signals in the temperature residuals during our survey this methodology may facilitate the process of filtering a seasonal atmospheric effect and better comprehend the heat emission of a volcano hydrothermal system from temperature surface readings

spectroscopic evidence for a lava fountain driven by previously accumulated magmatic gas the eruption of mount etna in 2000 was notable for an exceptional series of 64 periodic lava fountains propelling lava fragments to heights of up to 900 metres it has been difficult to determine which of two suggested sources of power gas release from the magma itself during its rapid ascent or a build up of pressure from gas accumulated at depth is the driving force for these dramatic jets but one of the etna fountains provided volcanologists with the opportunity to use remote sensing not that remote see picture on the following page to determine the infrared spectra of the gas phase this revealed the chemical composition of the gas that powered this fountain as consistent with an origin in an accumulated gas layer lava fountains are spectacular continuous gas jets propelling lava fragments to heights of several hundred metres which occasionally occur during eruptions of low viscosity magmas1 2 3 4 5 whether they are generated by the effervescent disruption of fast rising bubbly melt2 3 4 5 or by the separate ascent of a bubble foam layer accumulated at depth6 7 still remains a matter of debate8 no field measurement has yet allowed firm discrimination between these two models a key insight into the origin of lava fountains may be gained by measuring the chemical composition of the driving gas phase this composition should differ markedly depending on whether the magma degassing occurs before or during eruption9 10 here we report the analysis of magmatic gas during a powerful 250 600 m high lava fountain measured with fourier transform infrared spectroscopy11 12 13 14 on mount etna sicily the abundances of volcanic gas species determined from absorption spectra of lava radiation reveal a fountain gas having higher co2 s and s cl ratios than other etnean emissions14 15 16 17 18 and which cannot derive from syn eruptive bulk degassing of etna basalt19 20 instead its composition suggests violent emptying of a gas bubble layer previously accumulated at about 1 5 km depth below the erupting crater

comparative soil co2 flux measurements and geostatistical estimation methods on masaya volcano nicaragua we present a comparative study of soil co2 flux f rm co 2 measured by five groups groups 1 5 at the iavcei ccvg eighth workshop on volcanic gases on masaya volcano nicaragua groups 1 5 measured f rm co 2 using the accumulation chamber method at 5 m spacing within a 900 m2 grid during a morning am period these measurements were repeated by groups 1 3 during an afternoon pm period measured f rm co 2 ranged from 218 to 14 719 g m 2 day 1 the variability of the five measurements made at each grid point ranged from 5 to 167 however the arithmetic means of fluxes measured over the entire grid and associated total co2 emission rate estimates varied between groups by only 22 all three groups that made pm measurements reported an 8 19 increase in total emissions over the am results based on a comparison of measurements made during am and pm times we argue that this change is due in large part to natural temporal variability of gas flow rather than to measurement error in order to estimate the mean and associated co2 emission rate of one data set and to map the spatial f rm co 2 distribution we compared six geostatistical methods arithmetic and minimum variance unbiased estimator means of uninterpolated data and arithmetic means of data interpolated by the multiquadric radial basis function ordinary kriging multi gaussian kriging and sequential gaussian simulation methods while the total co2 emission rates estimated using the different techniques only varied by 4 4 the f rm co 2 maps showed important differences we suggest that the sequential gaussian simulation method yields the most realistic representation of the spatial distribution of f rm co 2 but a variety of geostatistical methods are appropriate to estimate the total co2 emission rate from a study area which is a primary goal in volcano monitoring research

shrimp u pb dating of coesite bearing zircon from the ultrahigh pressure metamorphic rocks sulu terrane east china this paper provides further evidence for the ongoing discussion as to whether the dabie uhpm belt formed in triassic or palaeozoic time and whether the sulu uhpm belt formed in triassic or neoproterozoic time combined use of laser raman spectrometer lr cathodoluminescence imaging cl and ion probe u pb in situ dating shrimp provided accurate ages of uhpm from rocks collected from weihai ne sulu uhpm belt lr was used to identify coesite and other uhp minerals as inclusions in zircon separates from an amphibolized peridotite and an eclogite cl was used to examine the zoning structure of these zircon and shrimp dating was performed on specific spots on zircon to obtain ages of different geological events an age of 221 12 ma was obtained for coesite bearing zircon from the amphibolized peridotite an age of 228 29 ma for eclogite was obtained from the lower intercept of a concordia plot these ages are interpreted as the time of uhpm in the weihai region ultramafic rocks to the east of weihai yield a magmatic age at 581 44 ma the zircon in the ultramafic rocks possibly also records a thermal event at c 400 ma but no independent geological evidence for this event has been found the eclogite protolith formed in the middle proterozoic 1821 19 ma which is similar to the age of country rock gneisses of 1847 1744 ma the new geochronological data confirm that uhpm occurred in the triassic in the sulu area when subduction took the ultramafic body and the eclogite protolith together with the adjacent supracrustal rocks to mantle depths

glacial flow of floating marine ice in snowball earth 1 simulations of frigid neoproterozoic climates have not considered the tendency of thick layers of floating marine ice to deform and spread laterally we have constructed a simple model of the production and flow of marine ice on a planetary scale and determined ice thickness and flow in two situations when the ocean is globally ice covered hard snowball and when the tropical waters remain open soft snowball in both cases ice flow strongly affects the distribution of marine ice flowing ice probably carries enough latent heat and freshwater to significantly affect the transition into a snowball earth climate we speculate that flowing marine ice rather than continental ice sheets may be the erosive agent that created some neoproterozoic glacial deposits

constraints on timing of peak and retrograde metamorphism in the dabie shan ultrahigh pressure metamorphic belt east central china using u th pb dating of zircon and monazite abstract the dabie shan ultrahigh pressure metamorphic uhpm belt occupies the suture between the yangtze and sino korean blocks in east central china the timing of uhpm in the dabie belt is controversial and most recent data come from dating of zircons monazite has recently been recognized as useful for dating of multiple tectonic events due to its preservation of multiple growth zones and monazite growth has been documented to occur during prograde peak and retrograde metamorphism zircons and monazites from uhp mafic rocks from maowu and a uhp jadeite quartzite from shuanghe were imaged in thin sections and in mineral separates and dated using a high resolution ion microprobe maowu mafic rocks are unique in that they contain high light rare earth element concentrations and therefore contain abundant monazite maowu eclogites and garnet pyroxenites contain zircons with mean 206 pb 238 u age of 230 4 ma and monazites from a clinopyroxenite have 208 pb 232 th ages of 209 4 ma multiple lines of evidence suggest that the measured ages represent the timing of new growth and recrystallization and are not cooling ages i e they do not correspond to the cessation of diffusional pb loss as rocks cooled below the closure temperature during exhumation shuanghe jadeite quartzites contain zircons with cores that define a discordia with an upper intercept age 1921 22 ma and lower intercept age of 236 32 ma interpreted to represent the ages of the source rocks and of peak metamorphism respectively zircon rims contain jadeite inclusions that restrict growth to pressures greater than 1 5 gpa their pooled age of 238 3 ma agrees well with the lower intercept defined by cores suggesting that pb loss from cores and growth of new rims occurred during uhpm at 235 240 ma monazite records multiple events during retrograde metamorphism maowu clinopyroxenite and shuanghe jadeite quartzite experienced monazite growth at 209 ma interpreted to reflect regional amphibolite facies overprinting resulting from pervasive retrograde fluid infiltration only the jadeite quartzite records growth at 223 1 ma estimated exhumation rates for maowu are 7 8 km ma

mudball surface dust and snowball earth deglaciation 1 recent modeling results have raised doubts about the ability to deglaciate from a global glaciation at atmospheric carbon dioxide levels that are realistic for a neoproterozoic snowball earth here we argue that over the lifetime of a snowball event ice dynamics should lead to the development of a layer of continental and volcanic dust at the ice surface in the tropics that would significantly lower the tropical surface albedo and encourage deglaciation this idea leads to the prediction that clay drapes found on top of neoproterozoic glaciations should be thicker in tropical than extratropical regions we test this idea by running the foam general circulation model gcm with an added tropical dust layer of different sizes and albedos and find that the tropical dust layer causes snowball deglaciation at pco2 0 01 0 1 bar in a reasonable regime of these parameters we find similar though more nuanced results from a limited number of test cases using national center for atmospheric research s cam gcm

carbon dioxide emissions from vegetation kill zones around the resurgent dome of long valley caldera eastern california usa abstract a survey of diffuse co2 efflux soil temperature and soil gas chemistry over areas of localized vegetation kill on and around the resurgent dome of long valley caldera california was performed to evaluate the premise that gaseous and thermal anomalies are related to renewed intrusion of magma some kill sites are long lived features and others have developed in the past few years total anomalous co2 emissions from the thirteen areas average around 8 7 t per day but the majority of the emissions come from four sites west of the casa diablo geothermal power plant geochemical analyses of the soil gases from locations west and east of the plant revealed the presence of isobutane related to plant operations the 13c values of diffuse co2 range from 5 7 to 3 4 similar to values previously reported for co2 from hot springs and thermal wells around long valley at many of the vegetation kill sites soil temperatures reach boiling at depths 20 cm soil temperature depth profiles at two of the high emissions areas indicate that the conductive thermal gradient in the center of the areas is around 320 c m 1 we estimate total heat loss from the two areas to be about 6 1 and 2 3 mw given current thinking on the rate of hydrothermal fluid flow across the caldera and using the co2 concentration in the thermal fluids the heat and co2 loss from the kill areas is easily provided by the shallow hydrothermal system which is sourced to the west of the resurgent dome we find no evidence that the development of new areas of vegetation kill across the resurgent dome are related to new input of magma or magmatic fluids from beneath the resurgent dome our findings indicate that the areas have developed as a response to changes in the shallow hydrologic system some of the changes are likely related to fluid production at the power plant but at distal sites the changes are more likely related to seismicity and uplift of the dome

magmatic inflation at a dormant stratovolcano 1996 1998 activity at mount peulik volcano alaska revealed by satellite radar interferometry 1 a series of ers radar interferograms that collectively span the time interval from july 1992 to august 2000 reveal that a presumed magma body located 6 6 0 5 km beneath the southwest flank of the mount peulik volcano inflated 0 051 0 005 km3 between october 1996 and september 1998 peulik has been active only twice during historical time in 1814 and 1852 and the volcano was otherwise quiescent during the 1990s the inflation episode spanned at least several months because separate interferograms show that the associated ground deformation was progressive the average inflation rate of the magma body was 0 003 km3 month from october 1996 to september 1997 peaked at 0 005 km3 month from 26 june to 9 october 1997 and dropped to 0 001 km3 month from october 1997 to september 1998 an intense earthquake swarm including three ml 4 8 5 2 events began on 8 may 1998 near becharof lake 30 km northwest of peulik more than 400 earthquakes with a cumulative moment of 7 15 1017 n m were recorded in the area through 19 october 1998 although the inflation and earthquake swarm occurred at about the same time the static stress changes that we calculated in the epicentral area due to inflation beneath peulik appear too small to provide a causal link the 1996 1998 inflation episode at peulik confirms that satellite radar interferometry can be used to detect magma accumulation beneath dormant volcanoes at least several months before other signs of unrest are apparent this application represents a first step toward understanding the eruption cycle at peulik and other stratovolcanoes with characteristically long repose periods

oxygen isotope equilibrium between eclogite minerals and its constraints on mineral sm nd chronometer abstract sm nd and oxygen isotope analyses were carried out for mineral separates of ultrahigh pressure eclogites from the sulu terrane in eastern china the results show a direct correspondence in equilibrium or disequilibrium state between the oxygen and sm nd isotope systems of eclogite minerals the omphacite garnet pairs of oxygen isotope equilibrium at eclogite facies conditions yield meaningful triassic sm nd isochron ages whereas those of oxygen isotope disequilibrium give non triassic ages of geological meaninglessness this can be reasonably interpreted by the fact that the rates of oxygen diffusion in garnet and pyroxene are lower than or close to those of nd diffusion and thus attainment of isotopic equilibrium in the omphacite garnet o system suggests achievement of nd isotope equilibrium in the same mineral pairs the presence or absence of fluid in the eclogite protoliths is a major rate controlling factor for isotopic equilibration during high grade metamorphism it appears that the state of oxygen isotope equilibrium between cogenetic minerals can provide a critical test for the validity of the sm nd mineral chronometer in addition the exact timing of the ultrahigh pressure metamorphism in the dabie sulu terranes is constrained at early triassic rather than late triassic

nd and sr systematics in an eclogite xenolith from tanzania evidence for frozen mineral equilibria in the continental lithosphere combined isotopic nd sr and petrographic analyses are reported for an eclogitic xenolith from the vissury mine tanzania an exceedingly large difference in measured nd values in garnet and clinopyroxene 200 units suggest a major mineral equilibration at 1 75 0 014 ga nd isotopic heterogeneities are demonstrated in different generations of garnet and zonation in sr and nd isotope compositions is present within the clinopyroxene the variation in measured nd isotope compositions in different generations of garnet corresponds to 16 units exsolution of garnet from clinopyroxene occurred in an essentially closed system with respect to sr and nd petrographically different generations of garnet are present one garnet with rutile inclusions as well as the rims of clinopyroxene are clearly off the isochron features like this can originate either if a system is not closed e g affected by a migrating fluid or if a remanent isotopic heterogeneity survived the homogenisation at 1 75 ga the subsolidus partitioning of sm and nd between garnet and clinopyroxene results in higher fractionation of the smnd ratio in garnet than in the liquid crystal partitioning since the closure temperature for the sm nd exchange between garnet and clinopyroxene may be around 850 c in a dry system many of the lithospheric ultramafic rocks may exhibit frozen mineral equilibria the isotopic data suggest that this eclogite was emplaced at 1 75 ga into the lithosphere mantle at temperatures of about 1040 c and then cooled as a closed system at a rate of 6 50 c my down to 840 c where all the exchange reactions were efficiently frozen in at 1 75 ga ago the coincidence of the emplacement of granites 1 7 1 8 ga into the central part of the tanzanian craton with the age of the eclogite suggests that lower crustal melting was triggered by a thermal event in the upper lithosphere

explosive eruptive record in the katmai region alaska peninsula an overview at least 15 explosive eruptions from the katmai cluster of volcanoes and another nine from other volcanoes on the alaska peninsula are preserved as tephra layers in syn and post glacial last glacial maximum loess and soil sections in katmai national park ak about 400 tephra samples from 150 measured sections have been collected between kaguyak volcano and mount martin and from shelikof strait to bristol bay 8 500 km2 five tephra layers are distinctive and widespread enough to be used as marker horizons in the valley of ten thousand smokes area and 140 radiocarbon dates on enclosing soils have established a time framework for entire soil tephra sections to 10 ka the white rhyolitic ash from the 1912 plinian eruption of novarupta caps almost all sections stratigraphy distribution and tephra characteristics have been combined with microprobe analyses of glass and fe ti oxide minerals to correlate ash layers with their source vents microprobe analyses typically 20 50 analyses per glass or oxide sample commonly show oxide compositions to be more definitive than glass in distinguishing one tephra from another oxides from the kaguyak caldera forming event are so compositionally coherent that they have been used as internal standards throughout this study other than the novarupta and trident eruptions of the last century the youngest locally derived tephra is associated with emplacement of the snowy mountain summit dome 6 ka two tephras 3 700 and 2 700 14c years b p and a summit scoria cone with a crater still steaming today mount katmai has three times produced very large explosive plinian to sub plinian events in 1912 12 16 ka and 23 ka and many smaller pyroclastic deposits show that explosive activity has long been common there mount griggs fumarolically active and moderately productive during postglacial time mostly andesitic lavas has three nested summit craters two of which are on top of a holocene central cone only one ash has been found that is tentatively correlated with the most recent eruptive activity on griggs 3 460 14c years b p eruptions from other volcanoes ne and sw beyond the katmai cluster represented in this area include 1 coignimbrite ash from kaguyak s caldera forming event 5 800 14c years b p 2 the climactic event from fisher caldera 9 100 14c years b p tentatively correlated 3 at least three eruptions most likely from mount peulik 700 7 700 and 8 500 14c years b p and 4 a phreatic fallout most likely from the gas rocks 2 300 14c years b p most of the radiocarbon dating has been done on loess soil and peat enclosing this tephra ash correlations supported by stratigraphy and microprobe data are combined with radiocarbon dating to show that variably organics bearing substrates can provide reliable limiting ages for ash layers especially when data for several sites is available

geochronology and isotopic character of ultrahigh pressure metamorphism with implications for collision of the sino korean and yangtze cratons central china the collision zone between the sino korean and yangtze cratons in central china is marked by subduction related metamorphic rocks composed of crustal protoliths these range in metamorphic grade from ultrahigh pressure eclogite to low greenschist facies the paragenesis of the ultrahigh pressure rocks coesite and diamond bearing indicates subduction to depths greater than 120 km as a result of continental collision despite extreme metamorphic conditions zircons have not undergone pb loss but rather illustrate two periods of growth crystallization between 700 and 800 ma and ultrahigh pressure metamorphism at 218 2 5 ma previous studies have predicted a time transgressive collision but age data presented in this study indicate that the collision was approximately coeval along the length of the suture u pb zircon ages of these ultrahigh pressure metamorphic rocks are 218 4 2 5 ma and 217 1 8 7 ma for the dabie mountains and shandong peninsula respectively the similar ages imply that the tan lu fault which offsets the ultrahigh pressure metamorphic rocks is a secondary feature not related to collision or subduction whole rock isotopic data show that both rb sr and u pb were open systems during metamorphism but that sm nd probably remained closed nd initial isotopes display crustal signatures indicating that the crust subducted as a coherent slab rather than becoming intercalated with mantle material at depth sm nd data in conjunction with u pb zircon dating indicate that the ultrahigh pressure rocks are not typical yangtze craton basement 2 9 ga but that they originally crystallized in a rift environment between 700 and 800 ma discrepancies between 40ar 39ar plateaus sm nd isochrons and u pb zircon ages render calculation of a p t t path unrealistic

timing of collision of the north and south china blocks controversy and reconciliation the qinling orogen was formed by the joining of the north and south china blocks but the timing of their integration has been debated for more than a decade the controversies obviously stem from different approaches to reconstruction of the integration history two contrasting lines of evidence yield two different ages for collision of the north and south china blocks middle paleozoic and late triassic the shangdan suture within the qinling was regarded in previous studies as the trace along which the north and south china blocks collided our studies however demonstrate that there are two sutures within the qinling the well documented shangdan suture and the newly discovered mianlue suture we show in this paper that the late proterozoic to early mesozoic evolution of the qinling involved interactions between the north china block the north and south qinling orogens and the south china block the middle paleozoic collision along the shangdan suture as constrained by some evidence accreted only the south qinling orogen to the southern part i e the north qinling of the north china block contemporaneous rifting of the south china block and subsequent drifting separated the south qinling from the south china block during the middle to late paleozoic the separation of the south from the north china blocks is supported by other evidence in particular geomagnetic data evidently it was the late triassic collision of the south china block with the south qinling orogen along the mianlue suture that led to final integration of the north and south china blocks

ocean acidification in the aftermath of the marinoan glaciation boron isotope patterns preserved in cap carbonates deposited in the aftermath of the younger cryogenian marinoan ca 635 ma glaciation confirm a temporary ocean acidification event on the continental margin of the southern congo craton namibia to test the significance of this acidification event and reconstruct earth s global seawater ph states at the cryogenian ediacaran transition we present a new boron isotope data set recorded in cap carbonates deposited on the yangtze platform in south china and on the karatau microcontinent in kazakhstan our compiled 11b data reveal similar ocean ph patterns for all investigated cratons and confirm the presence of a global and synchronous ocean acidification event during the marinoan deglacial period compatible with elevated postglacial p co2 concentrations differences in the details of the ocean acidification event point to regional distinctions in the buffering capacity of ediacaran seawater

integrated geophysical and geological methods to investigate the inner and outer structures of the quaternary mýtina maar w bohemia czech republic the m tina maar is the first known quaternary maar in the bohemian massif based on the results of mrlina et al j volcanol geother res 182 97 112 2009 a multiparametric geophysical electrical resistivity tomography gravimetry magnetometry seismics and geological petrochemical research study had been carried out the interpretation of the data has provided new information about the inner structure of the volcanic complex 1 specification of the depth of post volcanic sedimentary fill up to 100 m and 2 magnetic and resistivity signs of one or two hidden volcanic structures interpreted as intrusions or remains of a scoria cone the findings at the outer structure of the maar incorporate the 1 evidence of circular fracture zones outside the maar 2 detection and distribution of volcanic ejecta and tephra fall deposits at the surface and 3 indications from electrical resistivity tomography and gravity data in the area between the m tina maar and elezna h rka scoria cone interpreted as a palaeovalley filled by volcaniclastic rocks and aligned along the strike line nw se of the tachov fault zone these findings are valuable contributions to extend the knowledge about structure of maar volcanoes in general because of ongoing active magmatic processes in the north east part of the cheb basin ca 15 30 km north of the investigation area the m tina maar diatreme volcano and surroundings is a suitable key area for research directed to reconstruction of the palaeovolcanic evolution and assessment of possible future hazard potential in the bohemian massif

the oxygen geochemical cycle dynamics and stability abstract the first and possibly only major rise of atmospheric oxygen from p o 2 0 1 pal the present atmospheric level to p o 2 10 pal appears to have occurred sometime before 2 ga ago although the exact time of and the cause s for the rise have been hotly debated equally important questions on the atmospheric oxygen concern its stability especially the mechanisms regulating the atmospheric p o 2 level and the causes and magnitude of p o 2 variations since the first major rise of atmospheric oxygen previous efforts to model the p o 2 variation during the phanerozoic time have typically relied on secondary information such as the carbon and sulfur isotopic records of sedimentary rocks and on simple dynamics of the geochemical cycles of o c s and p based on box type models as a result many kinetic questions about the variation and stability of atmospheric oxygen could not have been answered here we quantitatively evaluate the dynamics and stability of atmospheric o 2 and co 2 using recent experimental data field observations and a new model for the c o coupled geochemical cycles we examine the change with time in the fluxes of various compounds o 2 co 2 phosphate organic c carbonate c c bearing reduced volcanic gases and c free reduced volcanic gases among the various reservoirs atmosphere soil surface ocean deep ocean the lower crust and mantle and upper crust under a variety of scenarios our model does not assume steady state fluxes for any of the reservoirs rather the model incorporates the kinetic experimental data on oxidation of coal a proxy for kerogen the dynamics of soil formation and erosion the kinetics of decomposition of organic matter in the oceans by aerobic and anaerobic bacteria the equilibrium ocean atmosphere carbonate model the observed relationships among the organic burial flux dissolved o 2 content of deep ocean and sedimentation rates and the three box model ocean the important parameters that strongly influence the dynamics of atmospheric o 2 are found to be a the total area of soil formation on earth b the average soil depth c the average rate of physical erosion of soils which is linked to the average rate of accumulation of clastic sediments in the oceans d the composition and flux of volcanic gas and e the level of atmospheric co 2 we develop kinetic equations linking these parameters to the production and consumption fluxes of atmospheric oxygen and also to stable p o 2 values considering the likely ranges of variations in these parameters in geologic history we suggest that the atmospheric p o 2 level is likely to have stayed within a very narrow range of 0 6 2 pal and that the entire ocean except for local euxinic basins is likely to have been basically oxygenated since the first major rise of atmospheric oxygen more than 2 ga ago

a post eruption study of gases and thermal waters at okmok volcano alaska abstract we report here on the first focused study of gas discharges and thermal spring waters at okmok volcano since the 2008 phreatomagmatic eruptions results include the first compositional gas data from okmok with minimal air contamination and the first data on magmatic carbon in okmok spring waters chemical and isotopic analyses of the waters and gases are used to assess the character of okmok fluids eight years after the eruptions ceased gases from vents on intracaldera cone c have high concentrations of h2 and contain h2s rather than so2 demonstrating the influence of a hydrothermal system while isotope values of carbon 10 2 to 8 9 and helium 8 ra confirm the presence of magma derived volatiles estimates of equilibrium temperatures for the cone c gas are 230 30 c a much cooler reservoir with a maximum temperature of 55 c feeds the intracaldera warm springs based on discharge measurements of creeks draining the caldera the total heat output of the warm springs is estimated to be about 32 mw gas data from a single location of steaming ground at the geyser bight geothermal area southwest of the okmok caldera are given the gas is typical of geothermal gases with high concentrations of h2s and an air corrected helium isotope ratio of 7 15 ra

triple oxygen isotopes in biogenic and sedimentary carbonates abstract the 17 o anomaly 17 o of natural waters has been shown to be sensitive to evaporation in a way analogous to deuterium excess with evaporated bodies of water e g leaf waters lake waters animal body waters tending to have lower 17 o than primary meteoric waters in animal body water 17 o relates to the intake of evaporated waters evaporative effluxes of water and the 17 o value of atmospheric o 2 which itself carries signatures of global carbon cycling and photochemical reactions in the stratosphere carbonates have the potential to record the triple oxygen isotope compositions of parent waters allowing reconstruction of past water compositions but such investigations have awaited development of methods for high precision measurement of 17 o of carbonate we describe optimized methods based on a sequential acid digestion reduction fluorination approach that yield 17 o data with the high precision 0 010 1 needed to resolve subtle environmental signals we report the first high precision 17 o dataset for terrestrial carbonates focusing on vertebrate biogenic carbonates and soil carbonates but also including marine invertebrates and high temperature carbonates we determine apparent three isotope fractionation factors between the o 2 analyte derived from carbonate and the parent waters of the carbonate these in combination with appropriate temperature estimates from clumped isotope thermometry or known or estimated body temperatures are used to calculate the 18 o and 17 o of parent waters the clearest pattern to emerge is the strong 17 o depletion in avian dinosaurian and mammalian body water from analyses of eggshell and tooth enamel relative to meteoric waters following expected influences of evaporated water e g leaf water and atmospheric o 2 on vertebrate body water parent waters of the soil carbonates studied here have 17 o values that are similar to or slightly lower than global precipitation our results suggest that 17 o will have useful application to paleoenvironmental studies of continental environments where the effects of evaporation are important and where vertebrate body water may record an isotopic signal of evaporated water sources and atmospheric oxygen

the sea level fingerprint of a snowball earth deglaciation cap dolostones are thought to represent deposition from seas transgressing over formerly glaciated continental margins during marinoan snowball deglaciation nevertheless facies associations within some cap dolostones indicate that an episode of regional regression punctuated these transgressive sequence tracts to date inferences of sea level change during and after the marinoan snowball deglaciation have been interpreted using simple qualitative arguments in the present study we explore the full spatio temporal variability of sea level change during snowball deglaciation and its aftermath using a gravitationally self consistent theory that accounts for the deformational gravitational and rotational perturbations to sea level on a viscoelastic earth model the theory is applied to model marinoan snowball deglaciation on a generalized ediacaran paleogeography with a synthetic continental ice sheet distribution we find that sea level change following a synchronous rapid 2 kyr collapse of snowball ice cover will exhibit significant geographic variability including site specific histories that are characterized by syn deglacial sea level fall or stillstand moreover some sites that experience syn deglacial transgression will continue to experience transgression in the post deglacial phase taken together these results suggest that sea level change recorded by strata capping snowball glaciogenic units may reflect a more complicated trajectory than previously thought including deposition that was not limited to the deglaciation phase these simulations as well as others that explore the response to asynchronous melting and deglaciation phases of longer duration demonstrate that an episode of regional regression interrupting a cap dolostone transgressive sequence tract may reflect one of several processes or their combination 1 near field adjustment associated with rapid local melting during an otherwise global hiatus in deglaciation 2 post glacial uplift of sites during a period of slowing deglaciation and 3 a transition at some sites from a sea level fall dominated by post glacial uplift to a phase of sea level rise due to eustasy and peripheral bulge subsidence throughout an extended order 50 kyr or greater snowball deglaciation

origin of carbon in fumarolic gas from island arcs abstract we have measured 3 he 4 he ratios 13c values and co 2 3 he ratios of fumaroles and hot spring gases in three volcanic areas in japan the 3 he 4 he ratios 13c values and co 2 3 he ratios vary from 02 05 ratm 9 7 to 2 7 and from 7 74 109 to 1 18 1011 respectively based on these data and those in the literature we present the first quantitative estimates of the upper mantle sediment and limestone including slab components in co2 of volcanic and hydrothermal fluids from subduction zones taking compiled c isotopic data of limestone and organic sediment assuming that the co 2 3 he ratio and 13c value of mid ocean ridge basalt morb are representative of the upper mantle component and that later isotopic and elemental fractionations are minimal it is possible to deconvole each fraction of c on the basis of simple mixing equations up to 20 of the carbon in high temperature volcanic gases in subduction zones is derived from a morb type source while the major fraction of the gases is attributable to co2 produced by decarbonation of subducted marine limestone and slab carbonate

ferromanganese crusts as recorders of marine dissolved oxygen abstract the distinct triple oxygen isotope composition of tropospheric o2 relative to seawater is the result of biogeochemical reactions e g primary productivity respiration exchange with the stratosphere and the relative size of different oxygen containing reservoirs namely o2 o3 and co2 this difference in isotopic composition gives tropospheric o2 utility as a record of biogeochemical and atmospheric processes and may also be used for determining where in the rock record isotopic fingerprints of tropospheric oxygen may be preserved the isotopic record of tropospheric oxygen in previous studies is largely limited to analyses of gas trapped in continental glaciers and a patchwork of other proxies most notably the triple oxygen signature of sulfate here we show the uppermost layers of hydrogenetic deep ocean ferromanganese crusts from each of the major ocean basins have a triple oxygen isotope composition consistent with the direct incorporation of dissolved oxygen the range of 18o and 17o in ferromanganese crusts suggests the mn oxide endmember contains a near 50 50 mixture of oxygen from water and dissolved o2 our data indicate this signal also persists into older layers of the crusts potentially preserving near 75 million years of the oxygen isotopic composition of the lower troposphere and subsequent deep ocean respiration our analysis of oxygen isotope values bulk chemistry and estimated local dissolved oxygen for crust top samples reveals that variations in bulk chemistry ultimately exhibit more influence on the oxygen mass balance than changes in dissolved oxygen presenting a challenge for unambiguous determination of local dissolved oxygen although analytical challenges remain these widespread layered deposits of ferromanganese crust may offer a viable path for future interrogation of the history or relative history of the oxygen cycle of the troposphere and deep ocean millions of years into the past

the dole effect and its variations during the last 130 000 years as measured in the vostok ice core we review the current understanding of the dole effect the observed difference between the delta sup 18 o of atmospheric o sub 2 and that of seawater and its causes extended the record of variations in the dole effect back to 130 kyr before present using data on the delta sup 18 o of o sub 2 obtained from studying the vostok ice core and discuss the significance of temporal variations the dole effect reflects oxygen isotope fractionation during photosynthesis respiration and hydrologic processes evaporation precipitation and evapotranspiration our best prediction of the present day dole effect 20 8 per thousand is considerably lower than the observed value 23 5 per thousand and we discuss possible causes of this discrepancy during the past 130 kyr the dole effect has been 0 05 per thousand lower than the present value on average the standard deviation of the dole effect from the mean has been only per thousand and the dole effect is nearly unchanged between glacial maxima and interglacial periods the small variability in the dole effect suggests that relative rates of primary production in the land and marine realms have been relatively constant most periodic variability in the dole effect is in the precession band suggesting that changes in this global biogeochemical termmore reflects variations in low latitude land hydrology and productivity or possibly variability in low latitude oceanic productivity 65 refs 4 figs 3 tabs less

biological oxygen productivity during the last 60 000 years from triple oxygen isotope measurements during isotope exchange between o2 and co2 in the stratosphere the relative rates of biologic o2 production and stratospheric processing determine the relationship between d 17 o and d 18 oo f o2 in the atmosphere variations of this relationship thus allow us to estimate changes in the rate of mass dependent o2 production by photosynthesis versus the rate of o2 co2 exchange in the stratosphere with about equal fractionations of d 17 o and d 18 o in this study we reconstruct total oxygen productivity for the last glacial the last glacial termination and the early holocene from the triple isotope composition of atmospheric oxygen trapped in ice cores with a box model we estimate that total biogenic productivity was only 76 83 of today for the glacial and was probably lower than today during the glacial interglacial transition and the early holocene depending on how reduced the oxygen flux from the land biosphere was during the glacial the oxygen flux from the glacial ocean biosphere was 88 140 of its present value index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4870 oceanography biological and chemical stable isotopes 1615 global change biogeochemical processes 4805 0315 atmospheric composition and structure biosphere atmosphere interactions keywords gisp2 siple ice cores oxygen isotopes past oxygen productivity stratospheric isotope exchange respiration

fluid inclusions in coesite bearing eclogites and jadeite quartzite at shuanghe dabie shan china fluid inclusions in coesite bearing eclogites and jadeite quartzite at shuanghe in dabie shan east central china have preserved remnants of early prograde and or peak metamorphic fluids reset during post uhp ultrahigh pressure metamorphic uplift inclusions occur in several minerals e g omphacite epidote notably as isolated primary inclusions in quartz included in various host minerals two major fluid types have been identified non polar fluid species n2 or co2 and aqueous the latter is by far the most predominant aqueous fluids cover a wide range of salinity from halite bearing brines to low salinity fluids for non polar fluids few n2 inclusions occur in undeformed eclogite whereas a number of co2 rich inclusions have been found in microshear zones of eclogite or jadeite quartzite in close proximity to marble occurrences the primary character of n2 and high salinity aqueous inclusions indicates that they are remnants from uhp metamorphic fluids and for some there is the distinct possibility that they are ultimately derived from pre metamorphic fluids this conclusion is supported by the preservation in some samples of microdomains containing synchronous inclusions of variable salinities which tend to relate to the chemical composition of the host crystal carbonic fluids may be derived from neighbouring rocks notably marble and carbonate bearing metasediments during post metamorphic uplift during post uhp exhumation a limited decrease of the fluid density has occurred with formation of new sets of fluid inclusions fluid movements however remained exceedingly limited at the scale of the enclosing crystal

zinc isotope variations in deep sea carbonates from the eastern equatorial pacific over the last 175 ka the carbonate fraction of sediment core odp 849 leg 138 located in the eastern equatorial pacific mostly consisting of coccoliths was separated and analyzed for its zn isotopic composition the overall variation in zn isotopic composition as determined by multiple collector magnetic sector inductively coupled plasma mass spectrometry was found to be on the order of 1 expressed in 66zn where xzn xzn 64zn sample xzn 64zn standard 1 103 and x 66 67 or 68 over the last 175 ka the analytical precision was 0 04 and the overall reproducibility was usually better than 0 07 the zn isotopic composition signal exhibits several marked peaks and a high frequency variability a periodogram of the 66zn signal showed two periodicities of 35 2 and 21 2 ka we suggest that the latter is caused by the precession of the earth s axis of rotation the periodogram exhibits a minimum at 41 1 ka thus showing that the zn isotopic composition is independent of the obliquity in the eastern equatorial pacific the range of 66zn values observed for the carbonate fraction of odp 849 overlaps with the range observed for fe mn nodules in the world s oceans which suggests that seawater carbonate zn isotope fractionation is weak we therefore assume that most of the zn isotope variability is a result of the selective entrainment of the light isotopes by organic matter in the surface ocean the odp 849 66zn record seems to follow the changes in the insolation cycles changes in the late summer fall equatorial insolation modulate the intensity of the equatorial upwelling hence the mixing between deep and surface waters we propose that during decreased summer fall equatorial insolation when a steep thermocline can develop el nino like conditions the surface waters cannot be replenished by deep waters and become depleted in the lighter zn isotopes by biological activity thus resulting in the progressive increase of the 66zn values of the carbonate shells presumably in equilibrium with surface seawater

sedimentary constraints on the duration of the marinoan oxygen 17 depletion mosd event the 635 ma marinoan glaciation is marked by dramatic earth system perturbations deposition of nonmass dependently 17o depleted sulfate so42 in worldwide postglacial sediments is thus far unique to this glaciation it is proposed that an extremely high pco2 atmosphere can result in highly 17o depleted atmospheric o2 or the marinoan oxygen 17 depletion mosd event this anomalous 17o signal was imparted to sulfate of oxidative weathering origin however 17o depleted sulfate occurs in limited sedimentary intervals suggesting that earth surface conditions conducive to the mosd had a finite duration an mosd duration can therefore provide much needed constraint on modeling earth system responses at that time unfortunately the sulfate 17o record is often sparse or lacks radiometric dates here we report 11 barite layers from a post marinoan dolostone sequence at wushanhu in the south china block the 17o depletion fluctuates in magnitude in lower layers but is persistently absent up section providing the most confident first and last sedimentary appearance of the anomaly 13c chemostratigraphy is used to correlate the wushanhu section to two proximal sections on the same shallow platform that lack barite layers but have published u pb dates that occur in dolostone and shale assuming a similar pattern and rate for carbonate and shale deposition among the different sections we estimate the mosd duration at 0 0 99 my this number can be further constrained by new radiometric dates from equivalent sequences worldwide thus underpinning models on the nonsteady state earth system response in the immediate aftermath of the marinoan meltdown

two billion year old evaporites capture earth s great oxidation major changes in atmospheric and ocean chemistry occurred in the paleoproterozoic era 2 5 1 6 billion years ago increasing oxidation dramatically changed earth s surface but few quantitative constraints exist on this important transition this study describes the sedimentology mineralogy and geochemistry of a two billion year old and 800 m thick evaporite succession from the onega basin in russian karelia the deposit consists of a basal unit dominated by halite 100 m followed by anhydrite magnesite 500 m and dolomite magnesite 200 m dominated units the evaporite minerals provide a robust constraint that marine sulfate concentrations were at least 10 mmol kg representing an oxidant reservoir equivalent to over 20 of the modern ocean atmosphere oxidizing capacity these results show that substantial amounts of surface oxidant accumulated during this critical transition in earth s oxygenation

abundance of zinc isotopes as a marine biogeochemical tracer 1 the zn isotopic compositions of ferromanganese nodules sediment trap samples sediments and organic reference samples have been analyzed by multiple collector inductively coupled plasma mass spectrometry icp ms the range of isotopic variations 1 for 66zn 64zn is significant with respect to the analytical precision 0 04 at the 95 confidence level marine argillaceous sediments show rather constant values consistent with those of continental shales and loess and with the value of a basalt from reunion island we infer that the depletion of the light zn isotopes in marine particles and in ferromanganese nodules presumably equilibrated with seawater results from biological activity in the upper water column the 66zn values of sediment trap samples collected near the upwelling off the coast of mauritania central atlantic show a seasonal isotopic fluctuation consistent with biological pumping during the high productivity period higher values of 66zn in nodules appear to be associated with the amplitude of seasonal variations rather than with the mean values of the biological productivity

origin and age of the lake nyos maar cameroon abstract lake nyos occupies a young maar crater in the precambrian granitic terrane of northwest cameroon the lake is partly surrounded by poorly consolidated ultramafic nodule bearing pyroclastic surge deposits that were explosively ejected from the nyos crater at the time of its formation radiocarbon dates show that the maar probably formed about 400 years ago field evidence suggests that carbon dioxide could have been the principal volatile involved in the formation of the nyos maar and that the role of water may have been minor the formation of the nyos maar was preceded by a brief period of effusive basaltic volcanism but the maar itself may have largely formed by cold dry explosive processes carbon dioxide may still be trapped interstitially in a diatreme inferred to underlie lake nyos its gradual release into the waters of lake nyos may have set the stage for the tragic gas release event of august 21 1986 only young maar lakes such as nyos may pose a danger of future lethal gas releases

diffuse gas emissions at the ukinrek maars alaska implications for magmatic degassing and volcanic monitoring abstract diffuse co 2 efflux near the ukinrek maars two small volcanic craters that formed in 1977 in a remote part of the alaska peninsula was investigated using accumulation chamber measurements high co 2 efflux in many places exceeding 1000 g m 2 d 1 was found in conspicuous zones of plant damage or kill that cover 30 000 50 000 m 2 in area total diffuse co 2 emission was estimated at 21 44 t d 1 gas vents 3 km away at the gas rocks produce 0 5 t d 1 of co 2 that probably derives from the ukinrek maars basalt based on similar 13 c values 6 3 he 4 he ratios 5 9 7 2 r a and co 2 3 he ratios 1 2 10 9 in the two areas a lower 3 he 4 he ratio 2 7 r a and much higher co 2 3 he ratio 9 10 10 in gas from the nearest arc front volcanic center mount peulik ugashik provide a useful comparison the large diffuse co 2 emission at ukinrek has important implications for magmatic degassing subsurface gas transport and local toxicity hazards gas water rock interactions play a major role in the location magnitude and chemistry of the emissions

distribution and significance of extraneous argon in uhp eclogite sulu terrain china insight from in situ 40ar 39ar uv laser ablation analysis in situ 40ar 39ar uv laser ablation analyses of garnet omphacite epidote phengite barroisite and symplectite in a sample of uhp eclogite from qinglongshan sulu terrain china reveal extremely heterogeneous argon isotopic ratios results from the 220 240 ma eclogite indicate a significant and variable extraneous argon signature that is restricted to the early formed phengite and epidote and later formed barroisite individual compositionally zoned phengite grains record a large variation in 40ar 39ar dates 300 1100 ma that are positively correlated with celadonite content these data are consistent with retrograde chemical exchange and argon isotopic repartitioning in response to decreasing partial pressures of argon during decompression consistent with the observation of atmospheric argon ratios in garnet omphacite and symplectite these data support an interpretation that the extraneous ar was incorporated early in the crystallization history of the eclogite and not from a late infiltrating fluid the ultimate source of the extraneous argon remains speculative however on the basis of supporting stable oxygen and hydrogen isotope data from this locality which support a closed isotopic system it is inferred to have been inherited from the protolith of the uhp eclogite

a new model for atmospheric oxygen over phanerozoic time a mathematical model has been constructed that enables calculation of the level of atmospheric o2 over the past 570 my from rates of burial and weathering of organic carbon c and pyrite sulfur s burial rates as a function of time are calculated from an assumed constant worldwide clastic sedimentation rate and the relative abundance and c and s contents of the three rock types marine sandstones and shales coal basin sediments and other non marine clastics red beds arkoses by our model values of o2 versus time using a constant total sedimentation rate agree with those for variable sedimentation derived from present day rock abundances and estimates of erosional losses since deposition this agreement is the result of our reliance on the idea that any increase in total worldwide sediment burial with consequently faster burial of c and s and greater o2 production must be accompanied by a corresponding increase in erosion and increased exposure of c and s on the continents to o2 consumption via weathering it is the redistribution of sediment between the three different rock types and not total sedimentation rate that is important in o2 control to add stability to the system negative feedback against excessive o2 fluctuation was provided in the modeling by the geologically reasonable assignment of higher weathering rates to younger rocks resulting in rapid recycling of c and s we did not use direct o2 negative feedback on either weathering of c and s or burial of c because weathering rates are assumed to be limited by uplift and erosion and the burial rate of c limited by the rate of sediment deposition the latter assumption is the result of modern sediment studies which show that marine organic matter burial occurs mainly in oxygenated shallow water and is limited by the rate of supply of nutrients to the oceans by rivers results of the modeling indicate that atmospheric o2 probably has varied appreciably over phanerozoic time during the late carboniferous and permian periods o2 was higher than previously because of the rise of vascular land plants and the widespread burial of organic matter in vast coal swamps a large decrease in o2 during the late permian was due probably to the drying up of the coal swamps and deposition of a large proportion of total sediment in c and s free continental red beds sensitivity study shows that major parameters affecting results are the mean c concentration in coal basins and the relative sizes of the reservoirs of young rapidly recycled versus old rocks less sensitivity was found for changes over time in total land area undergoing weathering and the use of direct o2 negative feedback on marine carbon burial good agreement for rates of c burial calculated via our model and via independent models which are based on the use of stable carbon isotopes indicates that the dominant factor that has brought about changes in atmospheric o2 level and the isotopic composition of dissolved inorganic carbon in seawater over phanerozoic time is sedimentation and not weathering or higher temperature phenomena such as basalt seawater reaction

co2 and he degassing at el chichon volcano chiapas mexico gas flux origin and relationship with local and regional tectonics during 2007 2008 three co2 flux surveys were performed on el chichon volcanic lake chiapas mexico with an additional survey in april 2008 covering the entire crater floor including the lake the mean co2 flux calculated by sequential gaussian simulation from the lake was 1 190 march 2007 730 december 2007 and 1 134 g m 2 day 1 april 2008 with total emission rates of 164 9 5 march 2007 59 2 5 december 2007 and 109 6 6 t day 1 april 2008 the mean co2 flux estimated from the entire crater floor area was 1 102 g m 2 day 1 for april 2008 with a total emission rate of 144 5 9 t day 1 significant change in co2 flux was not detected during the period of survey and the mapping of the co2 flux highlighted lineaments reflecting the main local and regional tectonic patterns the 3he 4he ratio as high as 8 1 ra for gases in the el chichon crater is generally higher than those observed at the neighbouring transmexican volcanic belt and the central american volcanic arc the co2 3he ratios for the high 3he 4he gases tend to have the morb like values 1 41 109 and the co2 3he ratios for the lower 3he 4he gases fall within the range for the arc type gases the high 3he 4he ratios the morb like co2 3he ratios for the high 3he 4he gases and high proportion of morb co2 m 25 15 at el chichon indicate a greater depth for the generation of magma when compared to typical arc volcanoes

quantification of gas fluxes from the subcontinental mantle the example of laacher see a maar lake in germany abstract vertical and horizontal distributions of helium and neon isotopes were measured in the water of laacher see a maar lake in the east eifel volcanic field in germany neon is in approximate atmospheric equilibrium throughout the lake but the concentrations of both helium isotopes increase with depth and reach values of up to 10 4 he and 50 3 he times the atmospheric equilibrium concentration the isotopic ratio of the helium excess r ex 3 he ex 4 he ex is 7 42 0 03 10 6 i e r ex r a 5 36 0 02 where r a 1 384 10 6 is the isotopic ratio in air this indicates the presence of mantle derived helium laacher see is thermally stratified during the summer it acts as an almost perfect trap for injected gases the helium concentration in the hypolimnion deep water approximately doubled from may to september 1991 yielding a mean 4 he flux of 10 2 10 12 atoms m 2 s 1 this value is 30 times smaller than in lake nyos cameroon but 20 times larger than in crater lake usa release of bubbles of nearly pure co 2 99 observable in shallow waters at the eastern shore as well as detected by divers in about 30 m depth was identified as an important source of the helium excess in the lake if carefully sampled by divers to avoid air contamination the bubbles exhibit mantle influenced isotopic signatures not only for helium but also for neon and argon 20 ne 22 ne 9 92 0 03 40 ar 36 ar 391 4 based on the elemental ratios of carbon neon and argon to 3 he the fluxes of volatiles from the mantle into laacher see are determined as 7 4 10 7 atoms m 2 s 1 for 3 he 13 10 7 atoms m 2 s 1 for 20 ne 26 10 7 atoms m 2 s 1 for 361 ar and 6 4 10 17 molecules m 2 s 1 for co 2 non atmospheric neon was also found in the well wallenborn in the west eifel volcanic field with a 20 ne 22 ne ratio as high as 11 21 0 06

a carbon isotope challenge to the snowball earth the snowball earth hypothesis contends that most of the planet was covered with thick ice for millions of years about three quarters of a billion years ago a dramatic warming event thought to have been fuelled by high atmospheric carbon dioxide levels eventually defrosted earth a new isotopic analysis of rocks that were laid down after the initial glaciation challenges the idea of a hard snowball earth the data are consistent with a rather low partial pressure of atmospheric co2 not the orders of magnitude above current levels that would provide the extreme warming necessary for escape from snowball earth this supports the idea that the initial glaciation was much less severe than has been proposed the snowball earth hypothesis postulates that the planet was entirely covered by ice for millions of years in the neoproterozoic era in a self enhanced glaciation caused by the high albedo of the ice covered planet in a hard snowball picture the subsequent rapid unfreezing resulted from an ultra greenhouse event attributed to the buildup of volcanic carbon dioxide co2 during glaciation1 high partial pressures of atmospheric co2 from 20 000 to 90 000 p p m v in the aftermath of the marinoan glaciation 635 myr ago have been inferred from both boron and triple oxygen isotopes2 3 these values are 50 to 225 times higher than present day levels here we re evaluate these estimates using paired carbon isotopic data for carbonate layers that cap neoproterozoic glacial deposits and are considered to record post glacial sea level rise1 the new data reported here for brazilian cap carbonates together with previous ones for time equivalent units4 5 6 7 8 provide estimates lower than 3 200 p p m v and possibly as low as the current value of 400 p p m v our new constraint and our re interpretation of the boron and triple oxygen isotope data provide a completely different picture of the late neoproterozoic environment with low atmospheric concentrations of carbon dioxide and oxygen that are inconsistent with a hard snowball earth

comment on paleozoic ages and excess 40ar in garnets from the bixiling eclogite in dabieshan china new insights from 40ar 39ar dating by stepwise crushing by qiu and wijbrans 2006 abstract qiu and wijbrans qiu h n and wijbrans j r 2006 paleozoic ages and excess 40 ar in garnets from the bixiling eclogite in dabieshan china new insights from 40 ar 39 ar dating by stepwise crushing geochim cosmochim acta 70 2354 2370 present three ar ar age spectra for fluid inclusions in garnet from eclogite at bixiling in the dabie orogen east central china these paleozoic ages of 427 20 to 444 10 ma are interpreted to represent the first formation of dabie ultrahigh pressure uhp eclogite and thus require subduction of yangtze crust to have started much earlier than previously accepted however no petrographic evidence such as mineral inclusions in the garnet relating to the particular metamorphic conditions is presented to substantiate the proposed uhp metamorphic event because garnet growth is not uniquely responsible for uhp eclogite facies metamorphism a distinction between uhp and high pressure hp metamorphic events must be made in the interpretation of geochronological results available data from mineral sm nd and zircon u pb dating of eclogites from the same area have firmly established that the uhp eclogite facies metamorphism took place at triassic neither the age of uhp metamorphism nor the timing of continental collision is reliably constrained by their presented data the fluid inclusions in garnet must contain inherited 40 ar from uhp eclogite precursor without considerable resetting of the ar ar isotopic system during triassic uhp metamorphism therefore their data are either meaningless or at best viewed as the age of garnet growth by low t hp blueschist eclogite facies metamorphism of the uhp eclogite precursor during arc continent collision in the early paleozoic furthermore it is critical for metamorphic geochronology to substantiate the timing of uhp metamorphic event by means of zircon u pb in situ dating on coesite bearing domains of metamorphically grown zircon

tracing and quantifying magmatic carbon discharge in cold groundwaters lessons learned from mammoth mountain usa abstract a major campaign to quantify the magmatic carbon discharge in cold groundwaters around mammoth mountain volcano in eastern california was carried out from 1996 to 1999 the total water flow from all sampled cold springs was 1 8 10 7 m 3 yr draining an area that receives an estimated 2 5 10 7 m 3 yr of recharge suggesting that sample coverage of the groundwater system was essentially complete some of the waters contain magmatic helium with 3 he 4 he ratios as high as 4 5 times the atmospheric ratio and a magmatic component in the dissolved inorganic carbon dic can be identified in virtually every feature sampled many waters have a 14 c of 0 5 pmc a 13 c near 5 and contain high concentrations 20 50 mmol l of co 2 aq but are otherwise dilute specific conductance 100 300 s cm with low ph values between 5 and 6 such waters have previously escaped notice at mammoth mountain and possibly at many other volcanoes because co 2 is rapidly lost to the air as the water flows away from the springs leaving neutral ph waters containing only 1 3 mmol l hco 3 the total discharge of magmatic carbon in the cold groundwater system at mammoth mountain is 20 000 t yr as co 2 ranging seasonally from about 30 to 90 t day several types of evidence show that this high discharge of magmatic dic arose in part because of shallow dike intrusion in 1989 but also demonstrate that a long term discharge possibly half this magnitude 10 000 t yr predated that intrusion to sustain a 10 000 t yr dic discharge would require a magma intrusion rate of 0 057 km 3 per century assuming complete degassing of magma with 0 65 wt co 2 and a density of 2 7 t m 3 the geochemical data also identify a small

zn isotope evidence for immediate resumption of primary productivity after snowball earth the ediacaran period began with the deglaciation of the ca 635 ma marinoan snowball earth and the deposition of cap dolostones on continental shelves worldwide during post glacial sea level rise these carbonates sharply overlie glacial sediments deposited at low paleolatitudes and preserve negative carbon isotope excursions the snowball earth hypothesis invokes an almost complete cessation of primary productivity in the surface ocean because assimilatory uptake of zn appears to fractionate its isotopes zn isotope ratios measured in carbonate precipitated in the surface ocean should track fluctuations in primary productivity here we report the first zn isotopic data together with carbon and oxygen isotopic profiles from a neoproterozoic cap dolostone the nuccaleena formation in the flinders ranges south australia we interpret the zn isotopic data in terms of a two stage evolution of the deglacial ocean slightly 66 zn enriched values at the base of the cap dolostone indicate immediate resumption of the biological pump upon melting of the surface ocean but this signal was diluted by intense surface runoff that drove 66 zn 66 zn 64 zn versus the jmc lyon reference values down to the composition of continentally derived zn a subsequent rise in 66 zn records a vigorous increase in primary production and export from a nutrient laden surface ocean

the snowball earth aftermath exploring the limits of continental weathering processes article i nfo carbonates capping neoproterozoic glacial deposits contain peculiar sedimentological features and geochemical anomalies ascribed to extraordinary environmental conditions in the snowball earth aftermath it is commonly assumed that post snowball climate dominated by co2 partial pressures several hundred times greater than modern levels would be characterized by extreme temperatures a vigorous hydrological cycle and associated high continental weathering rates however the climate in the aftermath of a global glaciation has never been rigorously modelled here we use a hierarchy of numerical models from an atmospheric general circulation model to a mechanistic model describing continental weathering processes to explore characteristics of the earth system during the supergreenhouse climate following a snowball glaciation these models suggest that the hydrological cycle intensifies only moderately in response to the elevated greenhouse indeed constraints imposed by the surface energy budget sharply limit global mean evaporation once the temperature has warmed sufficiently that the evaporation approaches the total absorbed solar radiation even at 400 times the present day pressure of atmospheric co2 continental runoff is only 1 2 times the modern runoff under these conditions and accounting for the grinding of the continental surface by the ice sheet during the snowball event the simulated maximum discharge of dissolved elements from continental weathering into the ocean is approximately 10 times greater than the modern flux consequently it takes millions of years for the silicate weathering cycle to reduce post snowball co2 levels to background neoproterozoic levels regarding the origin of the cap dolostones we show that continental weathering alone does not supply enough cations during the snowball melting phase to account for their observed volume

geologic framework and tectonic evolution of the qinling orogen central china abstract the geologic framework of the qinling orogen was built up through interplay of three blocks the north china block including the north qinling the south qinling and the south china block separated by the shangdan and mianlue sutures the shangdan suture resulted from middle paleozoic collision of the north china block and the south qinling the mianlue suture resulted from late triassic collision of the south qinling and the south china block present upper crust of the qinling is structured dominantly by thrust fold systems the north qinling displays thick skinned deformation with crystalline basement involved whilst the south qinling is characterized by thin skinned thrusts and folds detached above the lower sinian two types of precambrian basement crystalline and transitional are defined according to lithology and metamorphic grade and different in age stratigraphic and sedimentary architecture is characterized by distinct zonation the qinling orogen experienced a prolonged continental divergence and convergence between blocks during the period from late neoproterozoic to early paleozoic times the south qinling was the northern margin of the south china block and the north qinling was the southern margin of the north china block separated by a proto tethyan qinling ocean the north qinling evolved into an active margin when the proto tethyan qinling ocean subducted northward during ordovician time collision of the south and north qinling took place in middle paleozoic along the shangdan suture synchronous with the collision rifting occurred at the southern rim of the south qinling and was followed by the opening of the paleo tethyan qinling ocean during the late paleozoic resulting in the splitting of the south china block from the south qinling collision of the south qinling and the south china block came about in the late triassic along the mianlue suture the late triassic collisional orogeny caused extensive fold and thrust deformation and granitoid intrusions throughout the qinling and led to final amalgamation of the north and south china blocks

linking the ukinrek 1977 maar eruption observations to the tephra deposits new insights into maar depositional processes abstract the ukinrek maars erupted 30 march to 9 april 1977 forming two maars a line of small pit craters and a tephra blanket extending to 2 km from the vents we combine photographic and written observations with stratigraphic analysis to reconstruct the eruption the eruption began with very low a few meters high fountaining from small craters above an inferred east west trending dike creating local scoria spatter agglomerate ramparts with a sandy matrix the eruption very quickly in minutes to hours centered on the west maar the west maar eruption lasted 1 2 days starting and ending with phreatomagmatic explosions with weak phreato strombolian activity in between initial explosions formed a 30 m wide crater enlarged by crater wall collapse and columns as high as 6500 m phreato strombolian activity produced 72 of the erupted volume including a small spatter cone and a scoria blanket around the vent a final explosion series emplaced a lithic rich breccia as ballistic blocks possibly as the northern half of the final crater collapsed into the southern vent area the east maar formed over the last nine days of the eruption and represents 93 of the total volume 4 6 106 m3 of the ukinrek eruption initial explosions were probably shallower than 10 20 m but most of the eruption occurred from explosions at 50 60 m below the pre eruptive surface with evidence of explosions to 90 m depth only at the very end of the eruption the east maar eruption mostly produced columns of lapilli ash and steam and the deposits are mostly fallout winds blew fallout mostly to the north for the first 5 6 days and to the south for the last three days of the eruption wind directed pyroclastic density currents collapsed from the column producing fines rich layers within the coarser fallout sporadic explosions produced weak density currents in the first few days and lithic and juvenile block rich breccias in the last few days of the eruption we interpret that collapse of the crater walls made a slurry that in part provided the water for phreatomagmatic interaction explosions came from depths

orbitally forced ice sheet fluctuations during the marinoan snowball earth glaciation the presence of dynamic ice sheets during snowball earth glaciations is controversial geological evidence and ice sheet modelling suggest that ice sheets may have responded to orbital forcing when pco2 reached a certain threshold

a red algal bloom in the aftermath of the marinoan snowball earth organic matter from the cap dolostones overlying the marinoan age glacigenic diamictites of the araras group amazon craton has been studied to reconstruct the post glacial ecosystem molecular fossils indicate that the post marinoan ecosystem was marked by an apparent decline in marine algal diversity the proliferation of red algae may be explained by environmental changes such as a massive nutrient input accompanying continental weathering after the ice thaw and a dimer light penetrating sea water due to the drowning of the platform in addition the presence of green sulphur bacteria indicates that sea water was stratified with an anoxic possibly euxinic i e sulphidic layer at the water sediment interface sulphur cycling probably occurred at the redox boundary as suggested by the recognition of active sulphate reduction this observation supports a microbially induced model for the formation of the cap dolostones

deciphering the atmospheric signal in marine sulfate oxygen isotope composition abstract atmospheric o2 and co2 levels inform us of the changes in chemical and biological environments yet the history of atmospheric compositions and po2 in particular is not well constrained the triple oxygen isotope 16 17 18o composition of marine so 4 2 has been proposed to directly record the ratio po2 pco2 in the contemporaneous atmosphere to resolve this atmospheric signal both a precise measurement of the 17o composition of sulfate and a model with which to interpret the measurement are needed here we present precise measurements of the triple oxygen isotope composition of modern marine sulfate and then forward a novel sulfur cycle model that deconvolves the potential atmospheric and microbial inputs to this signal our interpretation of marine sulfate oxygen isotope composition provides a framework for calculating atmospheric composition relative rates of biogeochemical activity and can be applied to geologic records of marine sulfate to constrain the po2 pco2 ratio over time

snowball earth ice thickness on the tropical ocean 1 on the tropical oceans of a neo proterozoic snowball earth snow free ice would have existed in regions of net sublimation photosynthesis could have continued beneath this bare ice if it was sufficiently thin and sufficiently clear the steady state ice thickness is determined by the necessity to balance the upward conduction of heat with three subsurface heating rates the heat flux from the ocean to the ice base the latent heat of freezing to the ice base and the solar energy absorbed within the ice a preliminary study using a broadband model for solar radiation and assuming a large freezing rate had indicated that tropical ice might be only a few meters thick here we show that the vertical throughput of ice by surface sublimation and basal freezing would be too slow to keep the ice thin and that the broadband model had exaggerated the absorption depth of sunlight we use a spectral model for solar absorption computing radiative transfer at 60 wavelengths considering absorption by the ice and scattering by bubbles with the spectral model the computed ice thickness is much greater for a solar flux of 320 w m 2 at the equatorial surface and expected albedo of 0 5 for bare sea ice we find that surface temperatures below 12 c generate ice layers too thick for photosynthesis 100 m if the albedo were as low as 0 4 thick ice would occur only for surface temperatures below 25 c but such low temperatures would be difficult to maintain with such low albedo for surface temperatures warmer than these limits the ice becomes thin 1 m and is unlikely to represent a coherent ice layer however glacial deformation of thick floating ice from nearby oceanic regions may preclude the existence of thin or ice free patches

syn and posteruptive hazards of maar diatreme volcanoes abstract maar diatreme volcanoes represent the second most common volcano type on continents and islands this study presents a first review of syn and posteruptive volcanic and related hazards and intends to stimulate future research in this field maar diatreme volcanoes are phreatomagmatic monogenetic volcanoes they may erupt explosively for days to 15 years above the preeruptive surface a relatively flat tephra ring forms below the preeruptive surface the maar crater is incised because of formation and downward penetration of a cone shaped diatreme and its root zone during activity both the maar crater and the diatreme grow in depth and diameter inside the diatreme which may penetrate downwards for up to 2 5 km fragmented country rocks and juvenile pyroclasts accumulate in primary pyroclastic deposits but to a large extent also as reworked deposits ejection of large volumes of country rocks results in a mass deficiency in the root zone of the diatreme and causes the diatreme fill to subside thus the diatreme represents a kind of growing sinkhole due to the subsidence of the diatreme underneath the maar crater is a subsidence crater and also grows in depth and diameter with ongoing activity as long as phreatomagmatic eruptions continue the tephra ring grows in thickness and outer slope angle syneruptive hazards of maar diatreme volcanoes are earthquakes eruption clouds tephra fall base surges ballistic blocks and bombs lahars volcanic gases cutting of the growing maar crater into the preeruptive ground formation of a tephra ring fragmentation of country rocks thus destruction of area and ground changes in groundwater table and potential renewal of eruptions the main hazards mostly affect an area 3 to possibly 5 km in radius distal effects are comparable to those of small eruption clouds from polygenetic volcanoes syneruptive effects on infrastructure people animals vegetation agricultural land and drainage are pointed out posteruptive hazards concern erosion and formation of lahars inside the crater a lake usually forms and diverse types of sediments accumulate in the crater volcanic gases may be released in the crater compaction and other diagenetic processes within the diatreme fill result in its subsidence this posteruptive subsidence of the diatreme fill and thus crater floor is relatively large initially but will decrease with time it may last millions of years various studies and monitoring are suggested for syn and posteruptive activities of maar diatreme volcanoes erupting in the future the recently formed maar diatreme volcanoes should be investigated repeatedly to understand more about their syneruptive behaviour and hazards and also their posteruptive topographic limnic and biologic evolution and potential posteruptive hazards for future maar diatreme eruptions a hazard map with four principal hazard zones is suggested with the two innermost ones having a joint radius of up to 5 km areas that are potentially endangered by maar diatreme eruptions in the future are pointed out

dynamic model constraints on oxygen 17 depletion in atmospheric o2 after a snowball earth a large perturbation in atmospheric co2 and o2 or bioproductivity will result in a drastic pulse of 17o change in atmospheric o2 as seen in the marinoan oxygen 17 depletion mosd event in the immediate aftermath of a global deglaciation 635 mya the exact nature of the perturbation however is debated here we constructed a coupled four box and quick response biosphere atmosphere model to examine both the steady state and dynamics of the mosd event our model shows that the ultra high co2 concentrations proposed by the snowball earth hypothesis produce a typical mosd duration of less than 106 y and a magnitude of 17o depletion reaching approximately 35 both numbers are in remarkable agreement with geological constraints from south china and svalbard moderate co2 and low o2 concentration e g 3 200 parts per million by volume and 0 01 bar respectively could produce distinct sulfate 17o depletion only if postglacial marine bioproductivity was impossibly low our dynamic model also suggests that a snowball in which the ocean is isolated from the atmosphere by a continuous ice cover may be distinguished from one in which cracks in the ice permit ocean atmosphere exchange only if partial pressure of atmospheric o2 is larger than 0 02 bar during the snowball period and records of weathering derived sulfate are available for the very first few tens of thousands of years after the onset of the meltdown in any case a snowball earth is a precondition for the observed mosd event

life geology and snowball earth according to the snowball earth hypothesis a series of global glaciations occurred 750 580 million years ago each lasting for millions of years and ending in a scorching heat caused by an extreme enrichment of atmospheric greenhouse gases hyde et al 1 have used climate models to simulate this global glaciation finding in one case an alternative climate scenario in which a partially frozen earth has ice free oceans equatorward of 25 latitude we do not believe that this slushball earth is consistent with the most striking geological and palaeomagnetic observations explained by the snowball earth hypothesis

geochemical precursors of the activity of an open conduit volcano the stromboli 2002 2003 eruptive events 1 marked increases of co2 h2 and he dissolved in thermal waters and changes in the dissolved carbon isotopic composition were observed at stromboli before the 28 december 2002 eruption and before a violent explosive paroxysm occurred on 5 april 2003 high anomalous co2 flux values were recorded at the crater rim since a week before the eruption onset the first anomalies in the thermal waters dissolved co2 amount appeared some months before the eruption when magma column rose at a very high level in the conduit high peaks of dissolved h2 and he were recorded a few days before the paroxysm carbon isotopic composition indicates a magmatic origin of the dissolved co2 whose increase together with those of h2 and he is attributed to an increasing output of deep gases likely produced by depressurization of a rising batch of a deep gas rich magma whose fragments have been emitted during the explosion

carboniferous and triassic eclogites in the western dabie mountains east central china evidence for protracted convergence of the north and south china blocks shrimp u pb dating and laser ablation icp ms trace element analyses of zircon from four eclogite samples from the north western dabie mountains central china provide evidence for two eclogite facies metamorphic events three samples from the huwan shear zone yield indistinguishable late carboniferous metamorphic ages of 312 5 307 4 and 311 17 ma with a mean age of 309 3 ma one sample from the hong an group 1 km south of the shear zone yields a late triassic age of 232 10 ma similar to the age of ultra high pressure uhp metamorphism in the east qinling dabie orogenic belt ree and other trace element compositions of the zircon from two of the huwan samples indicate metamorphic zircon growth in the presence of garnet but not plagioclase namely in the eclogite facies an interpretation supported by the presence of garnet omphacite and phengite inclusions zircon also grew during later retrogression zircon cores from the huwan shear zone have ordovician to devonian 440 350 ma ages flat to steep heavy ree patterns negative eu anomalies and in some cases plagioclase inclusions indicative of derivation from north china block igneous and low pressure metamorphic source rocks cores from hong an group zircon are neoproterozoic 780 610 ma consistent with derivation from the south china block in the western dabie mountains the first stage of the collision between the north and south china blocks took place in the carboniferous along a suture north of the huwan shear zone the major triassic continent continent collision occurred along a suture at the southern boundary of the shear zone the first collision produced local eclogite facies metamorphism in the huwan shear zone the second produced widespread eclogite facies metamorphism throughout the dabie mountains sulu terrane and a lower grade overprint in the shear zone

the role of the aquifer in soil co 2 degassing in volcanic peripheral areas a case study of stromboli island italy abstract the peripheral area of stromboli island italy named scari was continuously studied between january 2009 and december 2010 data on soil co 2 flux and the partial pressure of co 2 pco 2 in equilibrium with the thermal aquifer linked to the magmatic system are presented soil co 2 fluxes range from 20 to 370 g m 2 d 1 and have been strongly affected by soil temperature variations soil co 2 flux data were filtered with respect to the soil temperature and the calculated values called residuals were considered to detect changes induced by the magmatic system the pco 2 values change in a wide range from 0 03 to 0 6 atm showing rapid variations the results of this study show that in the volcanic peripheral area the degassing process of soil co 2 is determined not only by the co 2 released directly from the magma but also by gas water interactions in the aquifer the aquifer is able to dissolve the high amount of co 2 discharged by the magmatic system moreover the residuals of co 2 flux diffused from the soil show a delay on the order of 1 month with respect to the pco 2 in equilibrium with the aquifer the soil co 2 flux is therefore not directly linked to the uprising of magmatic co 2 but instead depends on the co 2 discharged from the aquifer which buffers and modulates the volatile changes released by the magmatic system

stretching the envelope of past surface environments neoproterozoic glacial lakes from svalbard the oxygen isotope composition of terrestrial sulfate is affected measurably by many earth surface processes during the neoproterozoic severe snowball glaciations would have had an extreme impact on the biosphere and the atmosphere here we report that sulfate extracted from carbonate lenses within a neoproterozoic glacial diamictite suite from svalbard with an age of similar to 635 million years ago falls well outside the currently known natural range of triple oxygen isotope compositions and indicates that the atmosphere had either an exceptionally high atmospheric carbon dioxide concentration or an utterly unfamiliar oxygen cycle during deposition of the diamictites

discussion of the article by a c lasaga and h ohmoto on the oxygen geochemical cycle dynamics and stability geochim cosmochim acta 66 361 381 2002

modeling atmospheric o2 over phanerozoic time a carbon and sulfur isotope mass balance model has been constructed for calculating the variation of atmospheric o2 over phanerozoic time in order to obtain realistic o2 levels rapid sediment recycling and o2 dependent isotope fractionation have been employed by the modelling the dependence of isotope fractionation on o2 is based for carbon on the results of laboratory photosynthesis experiments and for sulfur on the observed relation between oxidation reduction recycling and s isotope fractionation during early diagenetic pyrite formation the range of fractionations used in the modeling agree with measurements of phanerozoic sediments by others results derived from extensive sensitivity analysis suggest that there was a positive excursion of o2 to levels as high as 35 during the permo carboniferous high o2 at this time agrees with independent modeling based on the abundances of organic matter and pyrite in sediments and with the occurrence of giant insects during this period the cause of the excursion is believed to be the rise of vascular land plants and the consequent increased production of o2 by the burial in sediments of lignin rich organic matter that was resistant to biological decomposition

resolved snowball earth clouds abstractrecent general circulation model gcm simulations have challenged the idea that a snowball earth would be nearly entirely cloudless this is important because clouds would provide a strong warming to a high albedo snowball earth gcm results suggest that clouds could lower the threshold co2 needed to deglaciate a snowball by a factor of 10 100 enough to allow consistency with geochemical data here a cloud resolving model is used to investigate cloud and convection behavior in a snowball earth climate the model produces convection that extends vertically to a similar temperature as modern tropical convection this convection produces clouds that resemble stratocumulus clouds under an inversion on modern earth which slowly dissipate by sedimentation of cloud ice there is enough cloud ice for the clouds to be optically thick in the longwave and the resulting cloud radiative forcing is similar to that produced in gcms run in snowball conditions this result is robust to large changes in the clo