helium and carbon fluxes in lake nyos cameroon constraint on next gas burst on 21 august 1986 a lethal gas burst issued from lake nyos in cameroon western africa killing at least 1700 people although the consensus is that the victims died of asphyxiation by co2 of magmatic origin the frequency of such catastrophic degassing events is still unknown the co2 flux at the bottom of lake nyos is estimated based on the measurement of3he4he and4he20ne ratios and the chemical composition of gases exsolved from the lake water the calculated co2 flux at the bottom of lake nyos is 4 4 2 3 1013cm3stp year combined with the estimated release in the august 1986 event of 8 2 1014 cm3 stp the co2 flux suggests that the gas burst may happen about once in18 10 years although the significant uncertainty should be taken into account for the frequency resulting from assumptions such as steady state fluxes in the lake and small fractionization of the c he ratio during the degassing event several yearly measurements of hypolimnetic fluxes and seasonal measurements of epilimnetic fluxes are needed to constrain better the recurrence interval in addition the results of a regional3he4he survey of carbonated mineral springs in northwestern cameroon are discussed in the context of the regional geotectonics

gas hazard assessment at the monticchio crater lakes of mt vulture a volcano in southern italy geochemical investigations have shown that there is a considerable inflow of gas into both crater lakes of monticchio southern italy these lakes are located in two maars that formed 140 000 years ago during mt vulture volcanos last eruptive activity isotopic analyses suggest that co2 and helium are of magmatic origin the latter displays 3 he 4 he isotope ratios similar to those measured in olivines of the maar ejecta in spite of the fact that the amount of dissolved gases in the water is less than that found in lake nyos cameroon both the results obtained and the historical reports studied indicate that these crater lakes could be highly hazardous sites even though they are located in a region currently considered inactive this could be of special significance in very popular tourist areas such as the monticchio lakes which are visited by about 30 000 people throughout the summer for the most part on sundays

mantle helium flux from the bottom of lake mashu japan abstract most of the 52 water samples from lake mashu hokkaido japan show large anomalies in their3he 4he ratios up to 4 6 times the atmospheric ratio and4he 20ne ratios indicating continuous injection of mantle he due to hot spring activity at the lake bottom the3he 4he ratio of the injected mantle he is estimated at3he 4he 9 43 0 17 10 6 which is close to the highest value reported for volcanic gases from the japanese islands accumulation of mantle he in the near bottom water can be reasonably explained by a diffusion process with a constant he flux from the lake bottom off4he 9 2 107 atoms cm2 s andf3he 8 7 102 atoms cm2 s the heat 3he ratio 1 7 10 7j atom falls in the range of values reported for submarine hydrothermal systems 0 4 26 10 7 j atom whereas the c3he ratio 1 8 1011 is about two orders of magnitude higher than the morb average 2 109 the mantle he injected from the lake bottom has a fairly short mean residence time in the lake water and is estimated at about 2 4 years overturn of the lake water which occurs twice a year probably plays an important role in the rapid transportation of the mantle he from the bottom to the surface

erosional response of south china to arc rifting and monsoonal strengthening a record from the south china sea abstract ocean drilling program sampling of the distal passive margin of south china at sites 1147 and 1148 has yielded clay rich hemipelagic sediments dating to 32 ma oligocene just prior to the onset of seafloor spreading in the south china sea the location of the drill sites offshore the pearl river suggests that this river or its predecessor may have been the source of the sediment in the basin which accounts for only 1 8 of the total neogene sediment in the asian marginal seas a mean erosion depth of 1 km over the current pearl river drainage basin is sufficient to account for the sediment volume on the margin two dimensional backstripping of across margin seismic profiles shows that sedimentation rates peaked during the middle miocene 11 16 ma and the pleistocene since 1 8 ma nd isotopic analysis of clays yielded nd values of 7 7 to 11 0 consistent with the south china block being the major source of sediment more positive nd values during and shortly after rifting compared to later sedimentation reflect preferential erosion at that time of more juvenile continental arc rocks exposed along the margin as the drainage basin developed and erosion shifted from within the rift to the continental interior nd values became more negative a rapid change in the clay mineralogy from smectite dominated to illite dominated at 15 5 ma synchronous with middle miocene rapid sedimentation mostly reflects a change to a wetter more erosive climate evidence that the elevation of the tibetan plateau and erosion in the western himalaya both peaked close to this time supports the suggestion that the asian monsoon became much more intense at that time much earlier than the 8 5 ma age commonly accepted

noble gases in hydrothermal plumes of loihi seamount abstract seawater samples from hydrothermal plumes of loihi seamount show very high 3 he 4 he ratios up to 15 8 10 6 and 4 he 20 ne ratios higher than that of air saturated seawater assw the 3 he 4 he ratio in the source from which the helium is released into the seawater is estimated as 23 1 2 3 10 6 from the correlation plot of 3 he 20 ne vs 4 he 20 ne the 3 he heat ratio at loihi is 5 49 times higher than that at the galapagos rift and at 21 n epr the difference may be attributed to the differences in the structure of the mantle beneath hot spots and the mid ocean ridge the former representing the deeper mantle region and the latter the shallower depleted mantle these observations are consistent with the view that helium in hydrothermal plumes of loihi seamount was derived from a deeper mantle region via a hot spot where more primordial helium is still preserved

quaternary palaeoceanographic changes in the northern south china sea odp site 1146 radiolarian evidence the abundance and accumulation rates of siliceous microfossils in the northern south china sea including radiolarians diatoms and sponge spicules increased during most glacial intervals within the past 1100 kyr similar trends are observed in the index of thermocline surface radiolarians tsr diatom accumulation rates dar charcoal accumulation rates car and the abundance of radiolarian species cycladophora davisiana davisiana decreasing sea surface temperature accompanied by increased seasonality since 900 ka is indicated by a decline in the tropical radiolarian assemblage including tetrapyle octacantha and octopyle stenozona and by an increase in the subtropical assemblage including pterocotys zancleus peromelissa phalacra and ommatartuts tetrathalamus tetrathalamus rapid increases at about 800 to 700 ka of siliceous microfossils charcoal subsurface and intermediate radiolarians as well as the tsr index and the dar imply a fundamental shift in climate and a shoaling thermocline although these fundamental changes in the silicious fauna and flora of the south china sea take place within the context of a developing 100 kyr cycle they do not change in step with changing sea level as indicated by marine delta 18 o this is most clearly illustrated by the step like increase in silica accumulation radiolaria diatoms and sponge spicules at 680 ka rather these fundamental changes probably reflect intensified surface productivity associated with enhanced east asian winter monsoon circulation copyright c 2003 john wiley sons ltd

astronomically tuned plio pleistocene benthic δ 18 o record from south china sea and atlantic pacific comparison based on benthic foraminiferal n 18 o from odp site 1143 a 5 myr astronomical timescale for the west pacific plio pleistocene was established using an automatic orbital tuning method the tuned brunhes matuyama paleomagnetic polarity reversal age agrees well with the previously published age of 0 78 ma the tuned ages for several planktonic foraminifer bio events also agree well with published dates and new ages for some other bio events in the south china sea were also estimated the benthic n 18 o from site 1143 is highly coherent with the earth s orbit etp both at the obliquity and precession bands for the last 5 myr and at the eccentricity band for the last 2 myr in general the 41 kyr cycle was dominant through the plio pleistocene although the 23 kyr cycle was also very strong the 100 kyr cycle became dominant only during the last 1 myr a comparison of the benthic n 18 o between the atlantic odp 659 and the east and west pacific 846 and 1143 reveals that the atlantic pacific benthic oxygen isotope difference ratio vn 18 oatlpac displays an increasing trend in three time intervals 3 6 2 7 ma 2 7 2 1 ma and 1 5 0 25 ma each of the intervals begins with a rapid negative shift in vn 18 oatlpac followed by a long period with an increasing trend corresponding to the growth of the northern hemisphere ice sheet this means that all three intervals of ice sheet growth in the northern hemisphere were accompanied at the beginning by a rapid relative warming of deep water in the atlantic as compared to that of the pacific followed by its gradual relative cooling this general trend superimposed on the frequent fluctuations with glacial cycles should yield insights into the processes leading to the boreal glaciation cross spectral analyses of the vn 18 oatlpac with the earth s orbit suggests that after the initiation of northern hemisphere glaciation at about 2 5 ma obliquity rather than precession had become the dominant force controlling the vertical structure or thermohaline circulation in the paleo ocean a 2002 elsevier science b v all rights reserved

alteration assemblages in the nakhlites variation with depth on mars secondary mineral assemblages in the nakhlite meteorites lafayette governador valadares gv nakhla yamato y 000593 y 000749 have been studied using scanning electron microscopy transmission electron microscopy and electron probe micro analysis the different nakhlites have distinctive secondary assemblages in their olivine grains and mesostases showing compositional fractionation correlated with their relative depths below the martian surface fracture filled veins in lafayette at the bottom of the pile consist of a siderite phyllosilicate fe oxide hydrated silicate gel assemblage corresponding veins in nakhla and gv further up the pile are predominantly a siderite gel assemblage with additional evaporites including gypsum y 000593 y 000749 veins are dominated by gel the gel s mg mg fe ratio decreases from lafayette 0 37 to gv 0 32 nakhla 0 24 and y 000593 0 15 we suggest that hydrothermal fluid flowed up this depth profile initiated by melting of buried h2o co2 ice our results show a complex mix of fe rich phyllosilicate within the veins and mesostasis of lafayette with d spacings of 0 7 1 1 nm suggesting a mixture of smectite and serpentine the phyllosilicate formed at close to neutral ph 150 c we also suggest that water rock ratios w r of 1 10 occurred in lafayette with smaller values for the other nakhlites this is reflected in the volume of alteration minerals 10 of olivine in lafayette to 3 in nakhla textural evidence of rapid cooling together with the w r and likely fluid velocities suggest that the secondary assemblages formed quickly e g within months a model is proposed in which the secondary assemblages formed in an impact induced hydrothermal system terminated by precipitation of the gel and evaporation of soluble salts

the geology and mineralogy of ritchey crater mars evidence for post noachian clay formation widespread detection of phyllosilicates clay minerals in noachian 3 5 ga terrains on mars and their paucity in younger terrains have led to the hypothesis that noachian conditions were more clement than the colder drier conditions that have since followed however recent clay detections in several hesperian impact craters suggest that fluvial transport and alteration were possible after the posited early era of phyllosilicate formation here we present evidence that rocks within hesperian age ritchey crater 28 5 s 51 w record a period of post noachian fluvial transport and in situ alteration this resulted in the transport of clays from the crater wall to the crater floor and the formation of hydrated silica and fe mg smectite in ritchey s central uplift clay minerals associated with central uplifts are commonly interpreted to represent preexisting clays excavated from depth potentially providing insight into older crustal clay forming processes here we present detailed geomorphic and mineralogic maps and show that the clays in ritchey s central peak formed after or as a direct result of the impact and are thus hesperian or younger clays on the crater wall were either preexisting clays exposed by the impact or formed in situ through postimpact water rock interaction in either scenario some of these clays were likely subsequently transported to the crater floor by fluvial alluvial processes in a source to sink system in this context the hydrated phases in ritchey indicate several different formation and transport mechanisms and provide further evidence that near surface clay mineral formation and thus habitable conditions existed on mars after the noachian

astronomical forcing of the east asian monsoon mirrored by the composition of pliocene south china sea sediments abstract high precision major and minor element records of pliocene core intervals from ocean drilling program odp site 1145 located in the northern part of the south china sea were generated at a 5 cm approximately 2 kyr resolution from the geochemical data distinct proxies those indicating changes in detrital matter provenance as well as those indicating productivity variations could be derived both the terrigenous input to the northern south china sea k si and variations in productivity ba al show a response to insolation forced monsoon variability while the fluvial input k si responds to changes in the summer monsoon productivity increases as documented by ba enrichments seem to reflect variations in winter monsoon intensity a stronger winter monsoon may have increased nutrient availability via dust input and or upwelling phenomena according to our geochemical proxy records summer and winter monsoons are approximately 180 out of phase this may imply forcing of the winter monsoon through southern hemisphere summer insolation maxima the k si ratio shows a linear correlation with the la90 1 0 5 northern hemisphere summer insolation record and has therefore been used to create an astronomical timescale for the investigated sediments of odp site 1145 carbonate contents and corresponding color reflectances display 41 and 100 kyr cycles we propose that these do not reflect glacial cycles but are rather the result of an interference signal of dilution by fluvial and eolian terrigenous material and carbonate production burial flux a sudden onset of gradual changes in sediment composition occurs after 3 0 ma this is also documented by an increase in sedimentation rates and may be caused by enhanced fluvial input from the pearl river due to intensified weathering rates on the asian continent this may be linked to tectonic processes around the himalayan tibetan complex and its consequences regarding land sea heating and atmospheric circulation

bottomwater formation due to hydrothermal activity in frolikha bay lake baikal eastern siberia hydrothermal water enters frolikha bay a well known site of high geothermal heat flux in the northern part of lake baikal at 400 m depth on the basis of ctd profiles the hydrothermal water is identified as forming an anomalous bottom layer with a higher temperature 0 15 c and salinity 2 5 mg kg 1 than the overlying water due to the entrainment of lake water a distinct dense water layer up to 40 m thick stabilised by its slightly higher salinity becomes established close to the bottom of the bay the density current thus generated flows out of the bay towards the deeper parts of the basin since helium isotope analysis shows that the geochemical characteristics of the hydrothermal water are similar to those of water from nearby hot springs on land the bottomwater of frolikha bay is easily interpreted in terms of the mixing of ordinary fresh water from the lake and hydrothermal water carrying isotopically heavy he from the continental crust because of its high crustal he content a similar hydrothermal component may even be identified in the open water of the northern basin

pliocene pleistocene stable isotope and paleoceanographic changes in the northern south china sea abstract based on the stable isotopic analysis of planktonic and benthic foraminifers from ocean drilling program core 1148 of the northern south china sea scs pliocene pleistocene isotope stratigraphy and events have been reconstructed the benthic foraminiferal 18o record shows that the pacific intermediate water had a greater influence upon the scs or the pacific deep water above 2600 m was warmer before 3 2 ma than at present after that the benthic 18o conspicuously increased during the 3 2 2 5 ma period in correspondence to the formation of the northern hemisphere ice sheet whereas the planktonic 18o signal suggests a stepwise overall decrease of sea surface temperature during the 2 2 0 9 ma period compared to the equatorial pacific records the decrease in planktonic globigerinoides ruber 13c during the 3 2 2 2 ma period is particularly striking suggesting that fertility of surface water increased noticeably according to the modern 13c distribution of g ruber in the northern scs it is inferred that the east asian winter monsoon strengthened during this interval afterwards there were several conspicuous decreases of g ruber 13c at 1 7 1 3 0 9 0 45 and 0 15 ma bp that is about every 0 4 ma suggesting that the east asian winter monsoon became episodically stronger this is confirmed by changes in relative abundance of planktonic foraminifer species neogloboquadrina dutertrei a typical east asian winter monsoon proxy the deep water 13c of the scs is close to that of the pacific but lighter than that of the atlantic implying that the pattern of deep water originating mainly from the atlantic and through the pacific entering the scs existed at least since the early pliocene after 1 4 ma the benthic 13c signal decreased conspicuously but with a periodicity of 100 ka suggesting that the deep water ventilation of the scs was reduced probably corresponding to a decrease of the north atlantic deep water and or further isolation of the scs deep basin from the pacific during glaciations

deep alteration between hellas and isidis basins abstract recent investigations of alteration of martian crustal outcrops suggest putative crustal hydrothermal systems which are favorable environments for the emergence of life in this study we perform an analysis of the crism targeted observations covering crustal outcrops in the region between the hellas and isidis basins with the goal of investigating the alteration phases over the wide studied region we detect the presence of possible serpentines chlorites smectites and carbonates these detections occur within ejecta blankets crater walls and central uplifts of impact craters we investigate the relation between the observed associations of minerals and the ages of the impact craters assessed by crater count no clear relation is observed we also investigate the relationship between the group of detected mineral and the pre impact depth of the studied outcrops assessed from the size of the impact craters this method allows us to reconstruct the pre impact cross section we suggest that alteration of the first 7 km of the crust between the hellas and isidis basins may have undergone alteration processes

helium 3 emission from nevado del ruiz volcano colombia high helium 3 helium 4 ratios up to 6 6ratm 6 6 times the atmospheric ratio of 1 40 10 6 were observed in nine samples of gases and hot waters from seven sites located around the volcano nevado del ruiz colombia the values of the ratio decrease with distance from the crater such a tendency coincides well with the pattern first reported from the volcano ontake central japan and suggests a general signature of helium isotope ratios around individual volcanoes the corrected helium 3 helium 4 ratios at one gas vent sampled twice over six months increased this is interpreted to mean that the mantle contribution of helium may have increased with time

helium 3 emission related to volcanic activity the helium 3 helium 4 ratio in bubbling gases from ten hot springs located around mount ontake an active volcano in central japan ranges from 1 71 r sub atm 1 71 times the atmospheric ratio of 1 40 x 10 sup 6 to 6 15 r sub atm the value of the ratio decreases with distance from the central cone of the volcano such a tendency may be a characteristic of helium 3 emission in volcanic areas and suggests more primitive helium 3 is carried with fluid flowing through a conduit during volcanic activity 6 references 1 figure 1 table

geochemical insight into differences in the physical structures and dynamics of two adjacent maar lakes at mt vulture volcano southern italy 1 we report on the first geochemical investigation of the monticchio maar lakes mt vulture volcano southern italy covering an annual cycle that aimed at understanding the characteristic features of the physical structures and dynamics of the two lakes we provide the first detailed description of the lakes based on high resolution conductivity temperature depth ctd profiles chemical and isotopic h and o compositions of the water and the amounts of dissolved gases e g he ar ch4 and co2 the combined data set reveals that the two lakes which are separated by less than 200 m exhibit different dynamics one is a meromictic lake where the waters are rich in biogenic and mantle derived gases while the other is a monomictic lake which exhibits complete turnover of the water in winter and the release of dissolved gases our data strongly suggest that the differences in the dynamics of the two lakes are due to different density profiles affected by dissolved solutes mainly fe which is strongly enriched in the deep water of the meromictic lake a conceptual model of water balance was constructed based on the correlation between the chemical composition of the water and the hydrogen isotopic signature gas rich groundwaters that feed both of the lakes and evaporation processes subsequently modify the water chemistry of the lakes our data highlight that no further potential hazardous accumulation of lethal gases is expected at the monticchio lakes nevertheless geochemical monitoring is needed to prevent the possibility of vigorous gas releases that have previously occurred in historical time

quantifying the flux of hydrothermal fluids into mono lake by use of helium isotopes in mono lake concentrations of 3 he and 4 he are greater than atmospheric equilibrium values indicating a subsurface helium source this assertion is supported by vertical concentration profiles that show maximum d 3 he values 168 occurring within the pycnocline the slope of the regression between 3 he and 4 he concentrations is near 2 8 ra ra is the atmospheric helium isotope ratio indicating that the subsurface source has a component of mantle helium hydrothermal springs and gas vents from paoha island have similar ratios which suggests that discharge from this thermal system is the most important source a 3 he mass balance indicated that below the deep pycnocline at 17 m 25 cc stp of 3 he accumulates each year 90 from the influx of hydrothermal water and 10 from the in situ decay of tritium although it is not retained because of gas transfer across the air water interface 70 cc stp of 3 he is injected each year into the upper 17 m when 3 he is used as a tracer the influx of hydrothermal water below the deep pycnocline was estimated to be 0 045 6 0 025 m 3 s 21 because the hydrothermal water is fresher than mono lake this influx causes the salinity of the monimolimnion to decrease by 0 1 salinity units per year and may play a small but important role in the salinity budget of this layer which is presently denser than and isolated from the surface water the isotopes of helium 3 he and 4 he have become important tracers for continental fluids for a number of reasons first helium isotope ratios vary significantly between the different reservoirs in the geosphere the 3 he 4 he isotope ratio of the atmosphere 1 4 3 10 26 lies between that of the deep crust 5 3 10 28 and that of the upper mantle 10 25 second continental fluids retain in their helium isotopes a record of the different reservoirs they have contacted hence in bodies of water such as lakes that receive the influx of water from many sources the helium isotope signature can be used to identify the different sources third the isotopic composition of helium can change as a result of the production of

magnetic signature of environmental changes in the last 1 2 myr at odp site 1146 south china sea abstract a detailed magnetic analysis has been done on the upper 145 m of the splice of odp site 1146 drilled during leg 184 in the south china sea first a magnetostratigraphic record was obtained the bruhnes matuyama reversal preceded by a precursor and the two jaramillo reversals were identified at 115 133 and 137 5 mcd meter composite depth respectively several known excursions during the brunhes period as well as the kamikatsura event during the matuyama chron were also identified coupled with the oxygen isotope record obtained from benthic foraminifera this allows us to establish a precise age model showing that the studied interval extends to 1 18 myr long term and short term variations have been documented in the magnetic parameters which appear at least in part related to changes in monsoon activity on the long term trend three main intervals with different magnetic trends were identified 1 2 0 7 0 7 0 2 and the most recent 0 2 myr during the oldest period the magnetic content decreases while the grain size of the magnetic mineral increases with large fluctuations the coercivity of the magnetic minerals also increases consistently with data obtained by other authors from pacific cores during the following 500 kyr all the magnetic properties are rather uniform with rather low abundance and relatively large grain sizes and low s ratio this probably illustrates a period of enhanced winter monsoon then in the most recent period the magnetic grain size decreases again with pronounced fluctuations on the short term scale a 23 kyr component is identified by power spectrum analysis in all magnetic parameters in the bottom part of the studied interval this component is correlated with the oxygen isotope record as shown by coherence analysis except for the most recent 200 kyr where the pattern changes cold warm periods coincide with low high magnetic content and magnetic grains are coarser during cold stages and finer during warm periods this is consistent with the clay mineral analysis and illustrates changes in the balance between arid humid periods corresponding to dominant winter summer monsoon and giving rise to physical erosion and wind blowing chemical weathering in the main fluvial plains and transport by oceanic current

development of east asian summer monsoon environments in the late miocene radiolarian evidence from site 1143 of odp leg 184 abundant radiolarians are preserved in the relatively complete upper miocene section of odp site 1143 three radiolarian zones rn6 rn7 and rn8 are recognized on the basis of diartus petterssoni total range in rn6 6 7 ma variations in the abundance of radiolarians especially pyloniid forms radiolarian flux and species diversity are good proxies of upwelling which similar to today s was likely driven by summer monsoons these radiolarian paleomonsoon proxies indicate that the east asian summer monsoon first initiated close to the middle late miocene boundary at similar to 12 11 ma and reached a maximum strength at similar to 8 24 ma therefore the initiation of the east asian summer monsoon was likely earlier than the first indian monsoon which appeared similar to 8 myr ago c 2003 elsevier b v all rights reserved

helium isotope evidence for magmatic gases in lake nyos cameroon we have measured he 4he and 4he 20ne ratios of gas samples collected at lake nyos where a toxic gas disaster occurred on august 21 1986 and at lake monoun in cameroon west africa the he 4he ratios corrected for air contamination are 5 39 5 75 ratm where ratm is the atmospheric ratio of 1 40 10 6 for lake nyos and 3 56 ratm for lake monoun the data suggest a significant contribution of mantle derived helium in these cameroon volcanic crater lakes the origin of co2 gas erupted during lake nyos disaster is inferred to be of magmatic origin based on the high he 4he ratio

hotspot tracks and the early rifting of the atlantic abstract many hotspot tracks appear to become the locus of later rifting as though the heat of the hotspot weakens the lithosphere and tens of millions of years later the continents are split along these weakened lines examples are the west coast of greenland east coast of labrador madeira hotspot the south coast of mexico north coast of honduras guyana hotspot and the south coast of west africa north coast of brazil st helena hotspot a modern day analog of a possible future rift is the snake river plain where the north american continent is being pre weakened by the yellowstone hotspot track this conclusion is based on reconstructions of the motions of the continents over hotspots for the past 200 million years the relative motions of the plates are determined from magnetic anomaly isochrons in the oceans and the motion of one plate is chosen ad hoc to best fit the motions of the plates over the hotspots however once the motion of this one plate is chosen the motions of all the other plates are prescribed by the relative motion constraints in addition to the correlation between the predicted tracks and sites of later continental breakup exposed continental shields correlate with the tracks their exposure may be the result of hotspot induced uplift which has led to erosion of their former platform sediment cover

evidence for magma carbonate interaction beneath syrtis major mars 1 we used three methods spectral index mapping linear spectral mixture analysis and factor analysis and target transformation to determine if carbonate decomposition products including lime cao periclase mgo portlandite ca oh 2 and brucite mg oh 2 are present on the surface of mars using an expanded spectral library that includes decomposition products of calcite and magnesite we deconvolved a binned emissivity data set from the mars global surveyor thermal emission spectrometer mgs tes the deconvolution model indicates that anhydrous carbonates are not present at kilometer scales above the tes detection limit however carbonate decomposition products may be present at or above the tes detection limit in northeast syrtis major and several other small regions on mars the model results are supported by spectral index mapping and factor analysis and target transformation of tes data in this region the volcanic setting of the detections may indicate the interaction of syrtis major lavas with subsurface carbonates or alternatively the eruption of carbonate bearing lavas that were subsequently devolatilized by impacts or later lava flows

perchlorate induced low temperature carbonate decomposition in the mars phoenix thermal and evolved gas analyzer tega 1 simulated thermal evolved gas analyzer tega analyses have shown that a co2 release detected between 400 c and 680 c by the phoenix lander s tega instrument may have been caused by a reaction between calcium carbonate and hydrated magnesium perchlorate in our experiments a co2release beginning at 385 12 c was attributed to calcite reacting with water vapor and hcl gas from the dehydration and thermal decomposition of mg perchlorate the release of co2 is consistent with the tega detection of co2 released between 400 and 680 c with the amount of co2increasing linearly with added perchlorate x ray diffraction xrd experiments confirmed cacl2 formation from the reaction between calcite and hcl these results have important implications for the mars science laboratory msl curiosity rover heating soils may cause inorganic release of co2 therefore detection of organic fragments not co2 alone should be used as definitive evidence for organics in martian soils

the evolution of thermal structure and water chemistry in lake nyos abstract we collected a time series of physical and chemical data to gain a better understanding of the dynamics of lake nyos measurements of water and gas chemistry and temperature made during january march and may 1987 are compared to data taken in september 1986 just after the initial co 2 gas release there is no pattern of change in overall heat content of the lake although heat input to bottom waters 185 208 m has occurred at a rate of 1600 mw m 2 this increase in heat content translates to a change from 23 38 to 24 12 c at 200 m and can be explained by geothermal heat flow and addition of thermal spring water concentrations of ca 2 mg 2 na k fe 2 and alkalinity have increased only in bottom waters in situ lake processes such as sulfate and iron reduction are unable to account for the changes in alkalinity observed chemical changes are consistent with a scenario where slightly thermal soda water is being input to the bottom of the lake measurements of p co 2 at depth ranged from 18 to 28 of saturation and exhibited horizontal variability overall recharge of co 2 in bottom waters is negligible mainly because of increasing ion concentrations in bottom water total stability of the water column increased 33 from 48 800 j m 2 in september 1986 to 64 700 j m 2 in may 1987 as long as co 2 concentrations remain the same this level of stability is higher than could be disrupted by common limnologic or meteorologic processes there is thermal and chemical evidence that a buildup of dissolved iron and co 2 in bottom waters must have preceded the august 1986 gas release in addition a survey of all crater lakes in cameroon indicates that only lakes nyos and monoun contain high concentrations of dissolved iron and co 2 thus there is a low probability of any other cameroonian lake releasing a substantial volume of co 2

nitrogen isotope and chlorin paleoproductivity records from the northern south china sea remote vs local forcing of millennial and orbital scale variability abstract variations in nitrogen isotopic composition 15n and total chlorin accumulation rate ar are employed as proxies to reconstruct oceanic nitrate inventory the balance between denitrification and n fixation and paleoproductivity in a rapidly accumulating sediment drift deposit beneath the western pacific warm pool for the last 145 kyr subsurface and deep waters of the northern south china sea scs are sourced from the shallow kuroshio current kc and pacific intermediate water respectively their relative importance in determining sedimentary 15n and paleoproductivity have been altered by changes in equatorial circulation summer and winter monsoon intensity and relative sea level the location and basin configuration of the marginal scs renders it especially sensitive to such changes assuming complete annual nitrate utilization low 15n values during glacial stages are interpreted as a reflection of reduced remote denitrification in the eastern tropical north pacific etnp source waters while much of marine isotope stage mis 3 and the last interglacial were characterized by high denitrification however intervals of anomalously low 15n values are interpreted as reflecting the contribution from regional n fixation in west pacific surface waters transmitted to the site by the shallow kc unusually the holocene is characterized by declining 15n values and an inverse correlation with organic matter content since ca 8 2 ka millennial scale variations during mis 3 indicate higher frequency variations in both etnp denitrification and local n fixation which may be coherent with a hemispheric response to dansgaard oeschger events recorded at high latitudes for much of the last 145 kyr paleoproductivity was decoupled from 15n and instead seems to reflect the extent of the global nitrate inventory stimulated by elevated dust fertilization and regional mixed layer deepening associated with the relative intensity of the se asian winter monsoon despite evaluation of possible conflicting influences on the record of each proxy we interpret our data as clear evidence of glacial interglacial changes in marine nutrient inventory across the whole of the north pacific with a corresponding biogeochemical response and important implications for global co2 drawdown via an invigorated biological pump the relative importance of local regional and global contributions to our records appears to be strongly modulated by relative sea level controlling trans and extra basinal circulation in the scs

gas buildup in lake nyos cameroon the recharge process and its consequences the gases dissolved in lake nyos cameroon were quantified recently december 1989 and september 1990 by two independent techniques in situ measurements using a newly designed probe and laboratory analyses of samples collected in pre evacuated stainless steel cylinders the highest concentrations of co2 and ch4 were 0 30 mol kg and 1 7 mmol kg respectively measured in cylinders collected 1 m above lake bottom probe measurements of in situ gas pressure at three different stations showed that horizontal variations in total dissolved gas were negligible total dissolved gas pressure near the lake bottom is 1 06 mpa 10 5 atm 50 as high as the hydrostatic pressure of 2 1 mpa 21 atm comparing the co2 profile constructed from the 1990 data to one obtained in may 1987 shows that co2 concentrations have increased at depths to below 150 m based on these profiles the average rate of co2 input to bottom waters was 2 6 108 mol a increased deep water temperatures require an average heat flow of 0 32 mw into the hypolimnion over the same time period the transport rates of co2 heat and major ions into the hypolimnion suggest that a low temperature reservoir of free co2 exists a short distance below lake bottom and that convective cycling of lake water through the sediments is involved in transporting the co2 into the lake from the underlying diatreme increased ch4 concentrations at all depths below the oxycline and a high14c content 41 modern in the ch4 4 m above lake bottom show that much of the ch4 is biologically produced within the lake the ch4 production rate may vary with time but if the co2 recharge rate remains constant co2 saturation of the entire hypolimnion below 50 m depth would require 140a given present day concentrations

spatial distribution and flux of terrigenic he dissolved in the sediment pore water of lake van turkey abstract in this study the largest ever carried out to measure noble gases in the pore water of unconsolidated sediments in lakes the emission of terrigenic he through the sediment column of lake van was successfully mapped on the local scale the main input of he to the water body occurs at the borders of a deep basin within the lake which is probably the remains of a collapsed caldera the 3 he 4 he ratio identifies the he injected into the sedimentary column of lake van as a mixture of he released from a mantle source and radiogenic he of crustal origin 3 he 4 he 2 6 4 1 10 6 during passage through the pore space terrigenic he seems to be further enriched in radiogenic he that is most likely produced in the sediment column in fact two distinct trends in isotopic composition can be distinguished in the he injected from the lake basement into the sediments one of these characterizes samples from the shallow water the other characterizes samples from the deep basin however both of these trends are related to the same source of terrigenic he the he fluxes determined seem to be characteristic of each sampling location and might be considered as a proxy for the fluid permeability of the deep sediment column these new findings provide insight into the process of fluid transport within the sediments and into the process of formation of the lake basin moreover the isotopic signature of the he that emanates into the water column of lake van is strongly affected by the mixing conditions prevailing in the overlying water body this fact misled previous studies to interpret the terrigenic he in lake van as being solely of mantle origin 3 he 4 he 10 5

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

mantle co2 degassing at mt vulture volcano italy relationship between co2 outgassing of volcanoes and the time of their last eruption abstract mantle volatiles are mainly lost from the earth to the atmosphere through subaerial and submarine volcanism recent studies have shown that degassing of mantle volatiles also occurs from inactive volcanic areas and in tectonically active areas a new challenge in earth science is to quantify the mantle derived flux of volatiles e g co2 which is important for understanding such diverse issues as the evolution of the atmosphere the relationships between magma degassing and volcanic activity gas pressure and seismogenic processes and the hazards posed by volcanic lakes here we present a detailed study of mantle derived co2 budget from mt vulture volcano in the apennines italy whose latest eruption occurred 141 11 kyr ago the relationship between 13cco2 and total dissolved carbon at mt vulture volcano indicates that the emitted co2 is a mixture of a biogenic end member with an average 13cco2 of about 17 and a mantle derived co2 end member with 13cco2 values from 3 to 2 these values of mantle derived 13cco2 are in the range of those for gas emitted from active volcanoes in the mediterranean we calculated the contribution of individual components co2 in groundwater in lakes and from main pools to the total co2 budget in the area we used new measurements of water flow combined with literature data to calculate the co2 flux associated with groundwater and measured the gas flux from the main pools on the volcanic edifice finally we calculated the co2 flow in the lakes based on the gradient concentration and eddy diffusivity the total mantle derived co2 budget in the area is 4 85 10 8 mol yr 1 which is more than double previous estimates this is higher than those observed in younger volcanic systems elsewhere thereby supporting the existence of actively degassing mantle melts below mt vulture volcano a structural map highlights the tectonic control on co2 flow across the mt vulture volcanic edifice indeed the tectonic discontinuities that controlled the magma upwelling during the most recent volcanic activity are still the main active degassing structures the new estimate of co2 budget in the mt vulture area together with literature data on co2 budget from historically active and inactive italian volcanoes suggests a power law functional relationship between the age of the most recent volcanic eruption and both total discharged co2 r 2 0 73 and volcano size normalized co2 flux r 2 0 66 this relation is also valid by using data from worldwide volcanoes highlighting that deep degassing can occur over very long time too in turn the highlighted relation provides also an important tool to better evaluate the state of activity of a volcano whose last activity occurred far in time finally our study highlights that in the southern apennines an active degassing of mantle derived volatiles i e he co2 occurs indiscriminately from west to east this is in contrast to the central northern apennine which is characterized by a crustal radiogenic volatile contribution which increases eastward coupled to a decrease in deep co2 flux this difference between the two regions is probably due to lithospheric tears which control the upwelling of mantle melts their degassing and the transport of volatiles through the crust

deep sea pollen from the south china sea pleistocene indicators of east asian monsoon abstract a high resolution pollen record sampling interval averages 820 years has been obtained from odp site 1144 water depth 2037 m northern south china sea the 504 m sequence in composition length covers the last 1 03 million years according to micropaleontological and isotopic stratigraphy the pollen assemblages are characterized by high proportions of pinus and herb pollen and by their frequent alternations based on these alternations 29 pollen zones have been recognized that are closely correlated to the marine oxygen isotope stages mis 1 29 pinus dominant pollen zones correspond to interglacial periods with lighter 18o values while herb marked ones relate to the heavier 18o stages assigned to glacials judging from the pollen data the exposed northern continental shelf of the south china sea during the glacials was covered by grassland and the extensive northern shelf has formed only since mis 6 ca 150 ka probably as a result of tectonic subsidence tree pollen influx values are indicative of winter monsoon which began to intensify 600 ka ago the summer monsoon variations can be approximated by the fern percentage within the total pollen and spore abundance and the result shows high values in general occurring at interglacials with the maxima at mis 15 5e and 1 the relatively high fern percentage with smaller amplitude in variations before 600 ka might suggest more stable humid conditions before the intensification of winter monsoon

changes in terrestrial ecosystem since 30 ma in east asia stable isotope evidence from black carbon in the south china sea a 30 m y stable isotopic record of marine deposited black carbon from regional ter restrial biomass burning from the northern south china sea reveals photosynthetic path way evolution for terrestrial ecosystems in the late cenozoic this record indicates that c3 plants negatively adjusted their isotopic discrimination and c 4 plants appeared grad ually as a component of land vegetation in east asia since the early miocene a long time before sudden c4 expansion occurred during the late miocene to the pliocene the changes in terrestrial ecosystems with time can be reasonably related to the evolution of east asian monsoons which are thought to have been induced by several intricate mechanisms during the late cenozoic and could contribute significantly to the post miocene marine carbonate isotope decline

clay mineral assemblages in the northern south china sea implications for east asian monsoon evolution over the past 2 million years abstract clay mineral assemblages at odp site 1146 in the northern south china sea are used to investigate sediment source and transport processes and to evaluate the evolution of the east asian monsoon over the past 2 myr clay minerals consist mainly of illite 22 43 and smectite 12 48 with associated chlorite 10 30 kaolinite 2 18 and random mixed layer clays 5 22 hydrodynamic and mineralogical studies indicate that illite and chlorite sources include taiwan and the yangtze river that smectite and mixed layer clays originate predominantly from luzon and indonesia and that kaolinite is primarily derived from the pearl river mineral assemblages indicate strong glacial interglacial cyclicity with high illite chlorite and kaolinite content during glacials and high smectite and mixed layer clay content during interglacials during interglacials summer enhanced monsoon southwesterly currents transport more smectite and mixed layer clays to site 1146 whereas during glacials enhanced winter monsoon northerly currents transport more illite and chlorite from taiwan and the yangtze river the ratio smectite mixed layers illite chlorite was adopted as a proxy for east asian monsoon variability higher ratios indicate strengthened summer monsoon winds and weakened winter monsoon winds during interglacials in contrast lower ratios indicate a strongly intensified winter monsoon and weakened summer monsoon during glacials spectral analysis indicates the mineral ratio was dominantly forced by monsoon variability prior to the development of large scale glaciation at 1 2 myr and by both monsoon variability and the effects of changing sea level in the interval 1 2 myr to present

soluble sulfate in the martian soil at the phoenix landing site 1 sulfur has been detected by x ray spectroscopy in martian soils at the viking pathfinder opportunity and spirit landing sites sulfates have been identified by omega and crism in valles marineris and by the spectrometers on the mer rovers at meridiani and gusev the ubiquitous presence of sulfur has been interpreted as a widely distributed sulfate mineralogy one goal of the wet chemistry laboratory wcl on nasa s phoenix mars lander was to determine soluble sulfate in the martian soil we report here the first in situ measurement of soluble sulfate equivalent to 1 3 0 5 wt as so 4 in the soil the results and models reveal so 4 predominately as mgso 4 with some caso 4 if the soil had been wet in the past epsomite and gypsum would be formed from evaporation the wcl derived salt composition indicates that if the soil at the phoenix site were to form an aqueous solution by natural means the water activity for a dilution of greater than 0 015 g h 2 o g soil would be in the habitable range of known terrestrial halophilic microbes

the lake nyos gas disaster chemical and isotopic evidence in waters and dissolved gases from three cameroonian crater lakes nyos monoun and wum abstract to better understand the cause of the nyos gas disaster of august 21 1986 we conducted geochemical and limnological surveys in october 1986 of three lakes nyos monoun and wum which are located in the cameroon volcanic zone that is characterized by a prevalence of young alkaline basalts and basanitoids lake wum was studied as a non active control co2 is dissolved in significant concentrations about 1 5 of saturation in gas active lakes nyos and monoun but is virtually absent in lake wum stable isotopic ratios of total dissolved carbon 13c 3 for nyos and 5 5 for monoun and of helium 5 7 ratm for nyos and 3 6 ratm for monoun indicate a mantle origin of these gases however so42 and cl concentrations are found to be very low concentrations of dissolved chemical species like fe2 mg2 ca2 and hco3 are high in the two gas active lakes whereas they are very low in the gas inactive lake high salinities in the gas active lakes are probably due to dissolution of indigenous mafic rocks and transported lateritic soil in acidic co2 rich warm water the gas active lakes are characterized by increasing temperature and salinity with increasing depth indicating an active influx of heat and dissolved materials at the bottom density estimates show that the lake water is stably stratified in spite of the inverse temperature profile of the lakes on account of dissolved chemical species the concentrations of dissolved carbonate species co2 aq and hco3 are positively correlated with those of ionic dissolved species indicating their common occurrence in the bottom water the august 1986 gas bursts from lake nyos were most likely caused by rapid exsolution of dissolved co2 within the lake an explosive process such as a phreatic eruption or a co2 gas jetting from beneath the bottom is unlikely because of low concentrations of cl and so42 no oxygen isotopic shift low turbidity and no reported perturbation of the bottom sediments exsolution of co2 bubbles could occur if co2 saturated bottom water was displaced upwards by an increased influx of high salinity water from the bottom during the rainy season exsolution of co2 at the upper layers was possibly accelerated by upwelling of a two phase fluid co2 bubbles and solution a mechanism known as a pneumatic lift pump resulting in discharge of a large amount of co2 gas the h2s concentration in the gas cloud must have been kept far below the lethal level because of a high fe2 concentration of the lake water

hydrous minerals on mars as seen by the crism and omega imaging spectrometers updated global view 1 the surface of mars has preserved the record of early environments in which its basaltic crust was altered by liquid water these aqueous environments have survived in the form of hydrological morphologies and alteration minerals including clays and hydrated salts because these minerals probe on earth aqueous environments compatible with biotic activity understanding their formation processes on mars is of great exobiological relevance and also offers insight into earth s now erased ancient water environments using remote sensing we conducted a large scale investigation of the distribution composition age and geomorphic settings of hydrous minerals on mars providing a sharpened global view of the early aqueous environments and their evolution with time aqueous alteration seems to have produced clays on a planetary scale but these are found to be restricted to the oldest observable terrains on mars 4 gyr however very diverse aqueous environments have also been found which suggest widespread complex aqueous settings from the surface to kilometric depths and spanning over 1 gyr by building a robust statistical sample of detections the global trends inferred here attempt to provide a broad view of our current understanding of hydrous minerals on mars and provide context for more localized in depth analyses collectively these trends suggest that at least transient conditions have existed on mars which may have been favorable for pre biotic to biotic activity

distribution of helium and tritium in lake baikal the 3 h 3 he age of a water mass is a measure of the time that has passed since the water mass was last in contact with the atmosphere between 1992 and 1995 a detailed study of 3 h 3 he ages was conducted in lake baikal the deepest and largest lake by volume on earth to investigate deep water renewal in its three major basins maximum 3 h 3 he ages are 14 17 years in the southern basin 16 18 years in the central basin and 10 11 years in the northern basin rates of renewal of deep water with surface water deduced from volume weighted mean 3 h 3 he ages below 250 m depth are about 10 yr 1 in the southern and central basins and 15 yr 1 in the northern basin in the southern basin the mean 3 h 3 he age below 250 m depth increased steadily from 9 6 years in 1992 to 11 years in 1995 indicating a slight diminution in deep water renewal during this time bottom water renewal by large scale advection was estimated from the mass balance of 3 he in the 200 m thick bottom layer of each basin bottom water renewal rates in the northern basin were found to be between 80 and 150 km 3 yr 1 and in the central basin between 10 and 20 km 3 yr 1 whereas in the southern basin they were practically zero correlating oxygen and dissolved helium 4 concentrations with 3 h 3 he age allowed us to determine the mean hypolimnetic oxygen depletion rate in the water column 4 5 mol l 1 yr 1 as well as mean helium fluxes from the lake bottom 2 8 x 10 11 atoms m 2 s 1 in the northern basin and 1 3 x 10 11 atoms m 2 s 1 in the central and southern basins the helium isotope ratio of the terrigenic helium component injected from the lake bottom determined from measurements of water from hydrothermal springs in the vicinity of the lake was found to be 2 2 x 10 7

accumulation of mantle gases in a permanently stratified volcanic lake lac pavin france abstract lac pavin is a volcanic crater lake in the massif central france characterized by a permanent vertical density stratification resulting from a strong and persistent chemocline between about 60 and 70 m depth the deep water below the chemocline forms the monimolimnion in which most dissolved ions as well as helium carbon dioxide and methane are strongly enriched the 3he 4he isotope ratio of the excess helium is 9 09 0 01 10 6 or 6 57 0 01 ra these findings clearly indicate a flux of mantle derived magmatic gases into the monimolimnion in order to derive the fluxes of magmatic volatiles into lac pavin it is essential to understand the hydrologic characteristics of the lake previously published two box models have assumed groundwater input at the lake bottom a short residence time in the monimolimnion and biogenic origin of the co2 we propose an alternative model with a flux of magmatic gases but not of water into the monimolimnion and a weak diffusive coupling between the monimolimnion and the overlying mixolimnion which leads to a long deep water residence time 70 yr we reassess the carbon budget of the lake and conclude that the major part of the accumulated co2 in the monimolimnion is of magmatic origin from the model derived water exchange rates we calculated a mantle 4he flux of 6 2 1011 atoms m 2 s 1 this value lies near the lower end of the range found in comparable volcanic lakes the flux of magmatic co2 is estimated as 1 2 0 4 10 7 mol m 2 s 1 which is also comparatively low the monimolimnion appears to be in steady state with respect to these fluxes therefore no further potentially hazardous accumulation of co2 takes place

investigating the history of east asian monsoon and climate during the last glacial interglacial period 0 140 000 years mineralogy and geochemistry of odp sites 1143 and 1144 south china sea abstract monsoon climate is an important component of the global climatic system a comprehensive understanding of its variability over glacial interglacial time scales as well as of its effects on the continent and in the ocean is required to decipher links between climate continental weathering and productivity a detailed multiproxy study including bulk and clay mineralogy grain size analysis phosphorus geochemistry sedex extraction organic matter characterization and nitrogen stable isotopes was carried out on samples from odp sites 1143 and 1144 leg 184 south china sea covering the past 140 000 years we tentatively reconstruct the complex sedimentation and climatic history of the region during the last glacial interglacial cycle when sea level variations linked to the growth and melting of ice caps interact with monsoon variability during interglacial periods of high sea level summer monsoon was strong and humid and warm climate characterized the adjacent continent and islands clay minerals bear signals of chemical weathering during these intervals high calcite and reactive phosphorus mass accumulation rates mars indicate high productivity especially in the southern region of the basin during glacial intervals strong winter monsoon provided enhanced detrital input from the continent as indicated by high detrital mar glacial low sea level resulted in erosion of sediments from the exposed sunda shelf to the south and clay mineral variations indicate that warm and humid conditions still prevailed in the southern tropical areas enhanced supply of nutrients from the continent both by river and eolian input maintained high primary productivity reduced circulation during these periods possibly induced active remobilization of nutrients such as phosphorus from the sediments intense and short cold periods recorded during glacial and interglacial stages correlate with loess records in china and marine climatic records in the north atlantic confirming a teleconnection between low and high latitude climate variability

geochemical and nd isotopic variations in sediments of the south china sea a response to cenozoic tectonism in se asia secular variations in geochemistry and nd isotopic data have been documented in sediment samples at odp site 1148 in the south china sea major and trace elements show significant changes at ca 29 5 ma and 26 23 ma whereas ond values show a single change at ca 26 23 ma increases in al ti al k rb sr and la lu ratios and a decrease in the th la ratio of the sediments beginning at 29 5 ma are consistent with more intense chemical weathering in the source region the abrupt change in nd isotopes and geochemistry at ca 26 23 ma coincides with a major discontinuity in the sedimentology and physical properties of the sediments implying a drastic change in sedimentary provenance and environment at the drill site comparison of the nd isotopes of sediments from major rivers flowing into the south china sea suggests that pre 27 ma sediments were dominantly derived from a southwestern provenance indochina sunda shelf and possibly northwestern borneo whereas post 23 ma sediments were derived from a northern provenance south china this change in provenance from southwest to north was largely caused by ridge jumping during seafloor spreading of the south china sea associated with a southwestward expansion of the ocean basin crust and a global rise in sea level thus the geochemical and nd isotopic changes in the sediments at odp site 1148 are interpreted as a response to a major plate reorganization in se asia at ca 25 ma b 2003 elsevier science b v all rights reserved

injection of mantle type helium into lake van turkey the clue for quantifying deep water renewal helium neon and tritium concentrations have been measured to study long term vertical mixing and deep water renewal in lake van eastern turkey the largest soda lake on earth helium excesses were found in the water column of lake van although neon concentrations were close to air saturation the excesses of both isotopes are strictly correlated and increase with depth in the bottom water 4he supersaturation is about 20 and the corresponding 3he concentration is 2 5 times the air saturation value the mean excess 3he 4he ratio of 1 1 2 10 5 is slightly higher than the morb ratio found in lake nemrut a neighbouring volcanic crater lake in which a large input of mantle helium was detected mantle helium accounts for the majority of the helium excesses in lake van although part of the 3he excess is attributed to the presence of tritium a one dimensional lake model was used which describes tritium input vertical mixing and gas exchange to reconstruct the evolution of the helium isotopes and the tritium as a conclusion the model based on the measured 3he and 4he profiles shows that 1 the vertical exchange of deep water occurs within 1 2 yr 2 the flux of mantle helium into the lake averaged over the total cross section of lake van is 0 23 0 35 cm3 stp m 2 yr 1 2 3 1011 atoms m 2 s 1 the present estimate of the global mantle helium flux averaged over the total surface area of the earth is 3 9 109 atoms m 2 s 1 the flux into lake van would account for at least 0 04 0 06 of this

recent ph and co2 profiles at lakes nyos and monoun cameroon implications for the degassing strategy and its numerical simulation abstract in situ ph profiles are reported for the first time for lakes nyos and monoun the ph profiles were converted to co2 profiles using hco3 profiles calculated from conductivity data recent observations 1993 1996 at lake nyos indicates that co2 still accumulates below 180 m depth at a rate of 125 mmol year 1 at lake monoun the majority of co2 is present below a depth of 60 m only 25 m below the saturation depth consequently a potential danger of gas explosion is high at both lakes and artificial degassing of the lakes should be performed as soon as possible a system for industrial degassing of the lakes is proposed the system based on the self sustained gas lift principle consists of multiple pipes 14 cm in diameter with different intake depths 12 pipes for lake nyos four each at 185 195 and 205 m and three pipes for lake monoun at 70 80 and 90 m the stepped degassing at different depths is intended to keep the maximum stability of the lakes the proposed degassing operation was simulated using the dyresm code for both lakes in 5 years approximately 50 of currently dissolved co2 in lake nyos and 90 in lake monoun will be removed the expected changes in the thermal and chemical structures of the lakes as degassing proceeds will be most easily monitored with a carefully calibrated ctd equipped with a ph sensor the simulation indicates that the discharged degassed water will sink to a level of neutral buoyancy i e to a maximum of 70 m at lake nyos and 35 m at lake monoun there would be no possibility of triggering a gas explosion by this plunge of discharged water because the water present there would have already been replaced by water at lower co2 concentration during the degassing from shallower pipes

orbital evidence for more widespread carbonate bearing rocks on mars carbonates are key minerals for understanding ancient martian environments because they are indicators of potentially habitable neutral to alkaline water and may be an important reservoir for paleoatmospheric co 2 previous remote sensing studies have identified mostly mg rich carbonates both in martian dust and in a late noachian rock unit circumferential to the isidis basin here we report evidence for older fe and or ca rich carbonates exposed from the subsurface by impact craters and troughs these carbonates are found in and around the huygens basin northwest of hellas in western noachis terra between the argyre basin and valles marineris and in other isolated locations spread widely across the planet in all cases they cooccur with or near phyllosilicates and in huygens basin specifically they occupy layered rocks exhumed from up to 5 km depth we discuss factors that might explain their observed regional distribution arguments for why carbonates may be even more widespread in noachian materials than presently appreciated and what could be gained by targeting these carbonates for further study with future orbital or landed missions to mars

he n and c isotopes and fluxes in aira caldera comparative study of hydrothermal activity in sakurajima volcano and wakamiko crater kyushu japan abstract we investigate the degassing activity of an active submarine crater wakamiko and an active sub aerial volcano sakurajima both located in aira caldera southern kyushu japan we provide 3he 4he 13c co2 and 15n data for 15 hot springs wells and bubbling gas from sakurajima volcano along with 3he 4he from seawater at four different sites for both kagoshima bay and wakamiko crater we find a common magmatic 3he 4he ratio for sakurajima and wakamiko 7 2 0 8 ra which is consistent with 1 a mixing between air saturated water asw and morb type he and 2 a common magmatic source located in the center of aira caldera corrected 3he 4he 13c co2 and ch4 3he data for sakurajima are correlated with the distance from the volcanic vent showa crater which we attribute to crustal contamination and biogenic reaction the low 13c co2 values 10 1 0 2 to 13 7 0 3 observed at sakurajima may result from the addition of carbon from organic matter from basement rocks in magmatic source after correction for air derived nitrogen we find 15nc values range between 1 7 and 4 3 which indicates that magmatic n is dominated by a sedimentary derived component up to 65 8 we calculate wakamiko fluxes of 4he 975 228 mol y 3he 0 011 0 003 mol y co2 184 43 t d and heat 195 22 mw our helium and heat fluxes are the first in situ fluxes ever reported for wakamiko crater all these wakamiko fluxes are at least one order of magnitude lower than those observed for sakurajima co2 1800 t d 3he 0 71 mol y heat 2100 mw degassing at sakurajima volcano is much stronger than that at wakamiko crater the variation of sakurajima co2 flux with time source minamidake or showa crater and eruptive activity appears not to significantly affect the co2 flux at wakamiko crater which is much more stable 132 307 t d during the last 30 years this indicates that there is no link between sakurajima and wakamiko degassing activity despite having the same magmatic source

carbon reservoir changes preceded major ice sheet expansion at the mid brunhes event the beginning of the mid brunhes event ca 430 ka coincided with the largest amplitude change in d 18 o in the global ocean over the past 6 m y this large d 18 o change recorded a major ice sheet expansion that cannot be explained by small changes in orbital forcing our recent studies at ocean drilling program site 1143 from the south china sea show that this large d 18 o change was preceded by a significant negative d 13 c shift a global survey of long deep sea records has revealed periodic d 13 cmax episodes i e maximum positive values of d 13 c and both major ice sheet expansion events in the pleistocene the mid brunhes event and the middle pleistocene revolution were preceded by d 13 cmax ep isodes followed by negative d 13 c shifts this new finding suggests that disturbance in carbon reservoirs leads to major growth of ice sheet size and challenges the prevalent concept of arctic control of glacial cycles because earth is now passing again through a d 13 cmax episode it is crucial to understand the causal relationship between the successive d 13 c changes and ice sheet growth events