the roles of co2 and orbital forcing in driving southern hemispheric temperature variations during the last 21 000 yr abstract transient climate model simulations covering the last 21 000 yr reveal that orbitally driven insolation changes in the southern hemisphere combined with a rise in atmospheric pco2 were sufficient to jump start the deglacial warming around antarctica without direct northern hemispheric triggers analyses of sensitivity experiments forced with only one external forcing component greenhouse gases ice sheet forcing or orbital forcing demonstrate that austral spring insolation changes triggered an early retreat of southern ocean sea ice starting around 19 18 ka bp the associated sea ice albedo feedback and the subsequent increase of atmospheric co2 concentrations helped to further accelerate the deglacial warming in the southern hemisphere implications for the interpretation of southern hemispheric paleoproxy records are discussed

climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

origin of the lethal gas burst from lake monoun cameroun abstract on 15 august 1984 a lethal gas burst issued from a submerged 96 m deep crater in lake monoun in cameroun western africa killing 37 people the event was associated with a landslide from the eastern crater rim which slumped into deep water waters below 50 m are anoxic dominated by high fe 2 600 mg l and hco 3 1900 mg l anoxic and supersaturated with siderite which is a major component of the crater floor sediments the unusually high fe 2 levels are attributed to reduction of laterite derived ferric iron gradually brought into the lake as loess and in river input sulfur compounds are below detection limits in both water and gas gases effervescing from depressurized deep waters are dominantly co 2 with minor ch 4 having 13 c of 7 18 and 54 8 per mil respectively bacterial decomposition of organic matter may account for the methane but 14 c of lake water indicates that only 10 of the carbon is modern giving an apparent age of 18 000 years the dominant source of carbon is therefore attributed to long term emission of co 2 as volcanic exhalation from vents within the crater which led to gradual build up of hco 3 in the lake the density stratification of the lake may have been upset by an earthquake and underwater landslide on 15 august which triggered overturn of the lake and caused nucleation of co 2 in the deep water the resultant ebullition of co 2 from deep lake waters led to a gas burst at the surface and locally generated a water wave up to 5 m high people travelling through the gas cloud were asphyxiated presumably from co 2 and suffered skin discoloration from unidentified components

hydrothermal hydrocarbon gases in the sediments of the king george basin bransfield strait antarctica thermogenic hydrocarbons formed by the thermal alteration of organic matter are encountered in several piston core stations in the king george basin anatarctica these hemipelagic sediments are being deposited in an area of active hydrothermalism associated with the back arc spreading in the bransfield strait the lateral extent of sediments infiltrated by the hydrothermally influenced interstitial fluids is characterized by basalt diapirix intrusions and is delineated by an acoustically turbid zone in the sediments of the eastern part of the basin iron sulphide bearing veins and fractures cut across the sediment in several cores they appear to be conduits for flow of hydrothermally altered fluids these zones have the highest c2 and ethene contents the thermogenic hydrocarbons have molecular c1 c2 c3 ratios typically 50 and 13ch4 values between 38 and 48 indicating an organic source which has undergone strong thermal stress several sediment cores also have mixed gas signatures which indicate the presence of substantial amounts of bacterial gas predominantly methane hydrocarbon generation in the king george basin is thought to be a local phenomenon resulting from submarine volcanism with temperatures in the range 70 150 c there are no apparent seepages of hydrocarbons into the water column and it is not believed that significant accumulation of thermogenic hydrocarbons reside in the basin

boundary scavenging at the east atlantic margin does not negate use of 231pa 230th to trace atlantic overturning abstract the 231 pa 230 th method is a promising tool to reconstruct ocean circulation over the past glacial interglacial cycle however marine particle flux may constrain the applicability of this ratio as a direct quantitative proxy for the strength of atlantic meridional overturning circulation amoc by influencing the fractionation between the in situ produced 231 pa and 230 th in ocean water here we present 231 pa 230 th down core profiles from high particle flux areas off namibia and senegal covering the past 35 ka the 231 pa 230 th profiles at these sites show very different responses to temporal variations of particle fluxes and to changes in water masses our results show that sedimentary 231 pa 230 th in the eastern atlantic margin is linked to particle flux but controlled primarily by the mode of the amoc our data suggest that during the past 30 ka the high productivity eastern margin was not capable of importing and storing significant amounts of 231 pa from the open ocean consequently the applicability of the 231 pa 230 th proxy to reconstruct past ocean circulation is not hampered by this potentially additional 231 pa sink

foraminiferal mg ca evidence for southern ocean cooling across the eocene oligocene transition constraining the magnitude of high latitude temperature change across the eocene oligocene transition eot is essential for quantifying the magnitude of antarctic ice sheet expansion and understanding regional climate response to this event to this end we constructed high resolution stable oxygen isotope 18o and magnesium calcium mg ca records from planktic and benthic foraminifera at four ocean drilling program odp sites in the southern ocean planktic foraminiferal mg ca records from the kerguelen plateau odp sites 738 744 and 748 show a consistent pattern of temperature change indicating 2 3 c cooling in direct conjunction with the first step of a two step increase in benthic and planktic foraminiferal 18o values across the eot in contrast benthic mg ca records from maud rise odp site 689 and the kerguelen plateau odp site 748 do not exhibit significant temperature change the contrasting temperature histories derived from the planktic and benthic mg ca records are not reconcilable since vertical 18o gradients remained nearly constant at all sites between 35 0 and 32 5 ma based on the coherency of the planktic mg ca records from the kerguelen plateau sites and complications with benthic mg ca paleothermometry at low temperatures the planktic mg ca records are deemed the most reliable measure of southern ocean temperature change we therefore interpret a uniform cooling of 2 3 c in both deep surface thermocline waters and intermediate deep waters of the southern ocean across the eot cooling of southern ocean surface waters across the eot was likely propagated to the deep ocean since deep waters were primarily sourced on the antarctic margin throughout this time interval removal of the temperature component from the observed foraminiferal 18o shift indicates that seawater 18o values increased by 0 6 0 15 across the eot interval corresponding to an increase in global ice volume to a level equivalent with 60 130 modern east antarctic ice sheet volume

fractionation processes affecting the stable carbon isotope signature of thermal waters from hydrothermal volcanic systems the examples of campi flegrei and vulcano island southern italy abstract the carbon isotopic composition of dissolved c bearing species is a powerful tool to discriminate the origin of carbon in thermal waters from volcanic and hydrothermal systems however the 13 c values of dissolved co 2 and tdic total dissolved inorganic carbon are often different with respect to the isotopic signature that characterizes the potential carbon primary sources i e deep hydrothermal reservoirs magmatic gases and organic activity the most commonly invoked explanation for such isotopic values is related to mixing processes between deep and shallow end members nevertheless experimental and empirical investigations demonstrated that isotopic fractionation due to secondary processes acting on the uprising fluids from the hydrothermal reservoirs is able to reproduce the measured isotopic values in this paper we investigated the chemistry of thermal waters collected at campi flegrei and vulcano island southern italy whose origin is related to interaction processes among magmatic gases meteoric water seawater and hosting rocks a special focus was dedicated to the 13 c values of dissolved co 2 13 c co2 aq and total dissolved inorganic carbon 13 c tdic the 13 c co2 aq and 13 c tdic values in the water samples from both these systems ranged from i those measured in fumarolic gases likely directly related to the deep hydrothermal magmatic reservoir and ii those typically characterizing biogenic co 2 i e produced by microbially driven degradation of organic matter a simple mixing model of the two end members apparently explaining these intermediate carbon isotopic values contrasts with the chemical composition of the dissolved gases on the contrary isotopic fractionation due to secondary processes such as calcite precipitation affecting hydrothermal fluids during their underground circulation seems to exhaustively justify both the chemical and isotopic data if not recognized these processes which frequently occur in volcanic and hydrothermal systems may lead to an erroneous interpretation of the carbon source causing an underestimation of the contribution of the hydrothermal magmatic fluids to the dissolved carbon species these results pose extreme caution in the interpretation of intermediate 13 c co2 aq and 13 c tdic values for the assessment of the carbon budget of hydrothermal volcanic systems

geochemistry of some gases in hydrothermal fluids from the southern juan de fuca ridge five samples of hydrothermal fluids from two vent areas on the southern juan de fuca ridge were analyzed for dissolved gases concentrations in the end member hydrothermal fluid of h2 270 527 mol kg ch4 82 118 mol kg and co2 3920 4460 mol kg are well above values in ambient seawater and are similar to concentrations reported for other ridge crest hydrothermal systems the carbon isotopic ratios of the ch4 13c 17 8 to 20 8 and co2 13c 3 6 to 4 7 suggest that at least some of the ch4 and co2 in the fluids is basalt derived the range of 13c values for the basalt derived co2 is 6 8 to 9 7 calculated by assuming conservation of recharge co2 during hydrothermal circulation apparent temperatures of equilibration between the ch4 and the basalt derived co2 range from 640 c to 750 c small amounts of ethane c2h6 ch4 0 9 10 3 2 2 10 3 propane and butane detected in the samples may also have formed in the basalt one sample of almost pure 95 5 hydrothermal fluid contained a significant fraction up to 63 and 74 respectively of the recharge ar and n2 this suggests that the fluid has not undergone extensive vapor liquid phase separation

effect of thermal non equilibrium seafloor topography and fluid advection on bsr derived geothermal gradient abstract the seafloor and bottom simulating reflectors bsrs are interpreted from the 3d seismic data acquired in krishna godavari kg offshore basin in the vicinity of sites drilled cored during national gas hydrate program nghp expedition 01 the shallow structures such as inner toe thrust fault system regional and local linear fault systems and mass transport deposits are inferred from attributes of seafloor time structure as well as from the seismic profiles the geothermal gradient is estimated from the depths and temperatures of the seafloor and the bsr the temperature at the bsr depth is estimated from the methane hydrate and seawater salinity phase boundary assuming that the bsr represents the base of the gas hydrate stability zone the spatial variations in geothermal gradient gtg show a strong correlation with seafloor topography in the kg basin the gtg decreases by 13 30 over the topographic mounds formed due to inner toe thrust faults and recent mass transport deposits the gtg decreases by only 5 10 over the mounds likely due to defocusing of heat flux based on one dimensional topographic modeling hence the gtg perturbation due to topography alone cannot explain the observed gtg anomaly the temperature profile beneath these mounds may not be in equilibrium with the surroundings either due to the recent upliftment of sediments along the inner toe thrust faults or rapid deposition of sediments due to slumping sliding in contrast an increase in gtg by 10 15 is observed in the vicinity of major fault systems we presume that the likely mechanism for the increase in gtg is fluid advection from a deeper part of the basin a detailed thermal modeling involving the effect of surface topography high sedimentation rates fluid advection and sediment thickening due to tectonics is required to understand the thermal profile in kg offshore basin

millennial scale variability in antarctic ice sheet discharge during the last deglaciation two well dated high resolution records of iceberg rafted debris are presented that document variability in antarctic ice sheet discharge during the last deglaciation global sea levels have risen by more than 100 metres since the last glacial maximum around 20 000 years ago with several meltwater pulses of several metres or more in the most dramatic of these meltwater pulse 1a sea level rose by about 16 metres at 14 600 years ago this magnitude of sea level rise strongly suggests major antarctica contributions but to date there has been no firm physical evidence now michael weber and colleagues present a record of iceberg rafted debris from the scotia sea and show clear signals of pulsed iceberg release from antarctica as early as 19 000 years ago the largest iceberg release occurred during meltwater pulse 1a providing the long sought confirmation of antarctic contributions to this major jump in sea level rise our understanding of the deglacial evolution of the antarctic ice sheet ais following the last glacial maximum 26 000 19 000 years ago 1 is based largely on a few well dated but temporally and geographically restricted terrestrial and shallow marine sequences2 3 4 this sparseness limits our understanding of the dominant feedbacks between the ais southern hemisphere climate and global sea level marine records of iceberg rafted debris ibrd provide a nearly continuous signal of ice sheet dynamics and variability ibrd records from the north atlantic ocean have been widely used to reconstruct variability in northern hemisphere ice sheets5 but comparable records from the southern ocean of the ais are lacking because of the low resolution and large dating uncertainties in existing sediment cores here we present two well dated high resolution ibrd records that capture a spatially integrated signal of ais variability during the last deglaciation we document eight events of increased iceberg flux from various parts of the ais between 20 000 and 9 000 years ago in marked contrast to previous scenarios which identified the main ais retreat as occurring after meltwater pulse 1a3 6 7 8 and continuing into the late holocene epoch the highest ibrd flux occurred 14 600 years ago providing the first direct evidence for an antarctic contribution to meltwater pulse 1a climate model simulations with ais freshwater forcing identify a positive feedback between poleward transport of circumpolar deep water subsurface warming and ais melt suggesting that small perturbations to the ice sheet can be substantially enhanced providing a possible mechanism for rapid sea level rise

orbitally driven insolation forcing on holocene climate trends evidence from alkenone data and climate modeling a global spatial pattern of long term sea surface temperature sst trends over the last 7000 years is explored using a comparison of alkenone derived sst records with transient ensemble climate simulations with a coupled atmosphere ocean circulation model under orbitally driven insolation forcing the spatial trend pattern both in paleo sst data and in model results shows pronounced global heterogeneity generally the extratropics cooled while the tropics experienced a warming during the middle to late holocene we attribute these divergent holocene climate trends to seasonally opposing insolation changes furthermore climate mode changes similar to the arctic north atlantic oscillation are superimposed on the prevalent pattern it is concluded that nonlinear changes in the entire seasonal cycle of insolation played a dominant role for the temporal evolution of holocene surface temperatures for understanding of marine proxy data apart from the dominance of summer insolation in high latitudes a notable shift in the maximum insolation of the year in low latitudes has to be taken into account which may influence timing of phytoplankton production and thus alters the seasonal origin of temperature signals recorded in the proxies

variability of southwest indian summer monsoon precipitation during the bolling allerod we have generated a high resolution 20 yr 2 3 0 th dated stalagmite oxygen isotope record from timta cave in the western himalaya in india that documents southwest indian summer monsoon ism precipitation variations during the bolling allerod interstadial from 15 2 to 11 7 ka compared with the glacial and younger dryas ism precipitation was enhanced during the bolling allerod ism precipitation was apparently coupled to variations in the east asian monsoon and north atlantic climate on millennial and multicentennial time scales during the deglaciation analyses of a high growth rate interval 2 5 yr resolution encompassing the late bolling early alterod suggest that multidecadal monsoon variability was an important aspect of ism behavior at that time the frequency spectrum of ism precipitation during this time interval is similar to that of the 1 4 c record and other ism precipitation records during the latest holocene this raises the hypothesis that multidecadal climate dynamics during the late boiling early allerod may have been similar to those that operated during the last several millennia even though the boundary conditions of these two time intervals were very different

on the definition of seasons in paleoclimate simulations with orbital forcing 1 orbital forcing is a major driver of climate variability on timescales of 10 000 to 100 000 years changes in the orbital parameters cause variations in the length of the seasons by several days consequently models using a fixed present day calendar result in biased paleoseasons especially in boreal autumn when the vernal equinox is used as an anchor point the bias is estimated for temperatures and precipitation in a transient model simulation over the last 21 000 years and an accelerated simulation over the last 129 000 years the largest differences of up to 4 k occur over the continents in high latitudes precipitation estimates are mostly affected in the low latitudes the time dependent bias is large enough to modify the temporal characteristics of temperature and precipitation indices it is discussed to what extent the bias in one season is distorting comparisons between models and paleoproxies the bias has minor implications for proxy model comparisons in general however proxies of monsoon activity should be compared with fixed angular seasons for process studies and climate sensitivity studies the use of fixed angular seasons is imperative

the 41 kyr world milankovitch s other unsolved mystery 1 for most of the northern hemisphere ice ages from 3 0 to 0 8 m y global ice volume varied predominantly at the 41 000 year period of earth s orbital obliquity however summer or summer caloric half year insolation at high latitudes which is widely believed to be the major influence on high latitude climate and ice volume is dominated by the 23 000 year precessional period thus the geologic record poses a challenge to our understanding of climate dynamics here we propose that variations in the insolation gradient between high and low latitudes control high latitude climate and ice volume during the late pliocene and early pleistocene the differential heating between high and low latitudes driven by obliquity controls the atmospheric meridional flux of heat moisture and latent energy which may exert the dominant control on high latitude climate on milankovitch timescales in the two dimensional zonal energy balance models typically used to study the long term evolution of climate the meridional atmospheric moisture flux is usually kept fixed the hypothesis that insolation gradients control the poleward energy fluxes precipitation and ice volume at high latitudes has never been directly examined within the context of an ice sheet model in light of what we know about modern energy fluxes and their relative influence on high latitude climate this possibility should be examined

horizontal mixing in lakes horizontal mixing in the upper hypolimnion of lakes far from the boundaries was studied in lake basins with surface areas between 5 and 220 km 2 by observing the growth of the concentration distribution of the fluorescent dye sodium fluorescein uranin in each of the eight experiments between 0 2 and 2 kg of uranin was instantaneously released into the lake in the appropriate depth between 15 and 25 m in such a way to keep the initial cloud size as small as possible the horizontal extension of the cloud was repeatedly determined by integration of numerous vertical profiles these surveys served to test theoretical models for horizontal mixing the temporal development of the size and of the variances along the principal axes of the tracer concentration distribution was the main property considered here the experiments cover a range of cloud sizes between 3 x 10 2 and 3 x 10 5 m 2 none of them support the hypothesis that cloud size grows with elapsed time raised to the power of 3 as predicted by the inertial subrange turbulence model first applied to dispersion by batchelor 1950 the shear diffusion model of carter and okubo 1965 was found to provide a good description of the development of cloud size with time this model also accounts for the fact that the tracer distributions were not radially symmetric effective horizontal diffusivities lie between 0 02 and 0 3 m 2 s 1 reevaluation of published data from experiments in lake ontario e g murthy 1976 and in the ocean e g okubo 1971 supports both the applicability of the shear diffusion model and the doubts raised against the appropriateness of the inertial subrange model for scales up to 1000 m

hydrothermal activity in the northern tanganyika rift east africa abstract hydrothermal fluids from sub lacustrine and sub aerial sites were sampled in the north tanganyika rift during the 1991 tanganydro expedition two types of hydrothermal end member fluids a na hco 3 type and a na cl type have been identified within the sample set the na hco 3 hydrothermal fluids are emitted at the level of the sub lacustrine pemba and sub aerial kabezi and mashuzi sites which are located in the northernmost bujumbura sub basin the na cl hydrothermal fluid vents at the level of the sub lacustrine cape banza field on the southeastern edge of the ubwari ridge the two types of hydrothermal fluids display isotopic and chemical evidence of interaction with magmatic volatiles the magmatic effects are strongest in the fluid discharging on the pemba hydrothermal field where abundant co 2 bubbling accompanies fluid emission the 13 c values of the co 2 gas sampled at pemba and at cape banza indicate a magmatic origin the pemba fluid shows the highest alkalinity and boron content and the lowest ph of the hydrothermal end member fluids and it has equilibrated at depth at the highest temperature 214 7 c in addition the sulfide mineralizations associated with the pemba hydrothermal vents are enriched in as and tl which similarly to b can be transported as volatiles in magmatic fluids the northern tanganyika na hco 3 fluids are similar to the na hco 3 fluid of the geothermal system of lake bogoria in the eastern branch of the east african rift and they can be compared with the na hco 3 hydrothermal water that is inferred to flow into lake kivu the cape banza na cl fluids may derive from the mixing between meteoric water and a deep seated basement brine similar to the ones found in old continental shields such as the canadian shield the high equilibrium temperatures and the geochemistry of the north tanganyika rift hydrothermal fluids suggest that degassing magmatic bodies are present at depth in the area these magmatic bodies may be either the southern expression of the south kivu magmatism or a more recent activity not yet expressed as surface volcanism the hydrothermal sites are located along major active rift bounding faults which can be associated with deep and strong seismicity as in the case of the pemba field such deep fractures may have favoured the uprise of the magmatic bodies that are the source of heat and volatiles to the hydrothermal systems the circulation of hydrothermal fluids within the tanganyika lacustrine sedimentary pile could play an important role in the maturation of the organic matter enclosed in the lake sediments and the subsequent oil generation and migration

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

occurrence of faecal pellet filled simple and composite burrows in cold seep carbonates a glimpse of a complex benthic ecosystem abstract ichnofossils preserved in marine sedimentary records provide unique information on various activities feeding dwelling excretion etc of benthic organisms here we report faecal pellet filled tubular simple and composite burrow casts from cold seep carbonate layers 16 18 mbsf deposited at least 46 58 kyr ago in the krishna godavari basin bay of bengal india deposition of these chemosynthetic clam bearing authigenic carbonate sediments with highly depleted carbon stable isotope ratios indicates methane expulsion that resulted in the development of a cold seep ecosystem although cold seep communities are extensively reported from the rock record and modern seep sites hardly any information is available on burrowing activity of the seep biota our findings open up a window for future investigation of the ecological significance of such burrows

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

sulphur eruptions at volcan poas costa rica since the recent desiccation of the crater lake at volcan poas costa rica vigorous fumarolic activity on the exposed lake bed has been associated with the manifestation of miniature sulphur volcanoes sulphur flows and sulphur pools in this paper observations of 2 3 m high active sulphur volcanoes are reported and mechanisms for their formation proposed and discussed their ejecta composed of milled particles crystals and accretionary lapilli of sulphur are unlike previously described pyroclastic sulphur deposits and probably form from a spray of crystallised sulphur forced to the surface by fumarolic gases passing upwards through shallow bodies of liquid sulphur while much of the erupted material is recycled the reservoir of molten sulphur can also be replenished by influxing magmatic hydrothermal fluids 34s isotope ratios of several samples of native sulphur collected at poas range between 9 4 and 12 3 cdt these are among the isotopically lightest volcanic deposits of elemental sulphur reported although this pronounced depletion is readily explained by the likely formation of the sulphur under the acidic conditions of the aqueous lake and hydrothermal system the total amount of native sulphur deposits contained within lake sediments at poas and perhaps at other active volcanoes with crater lakes is potentially substantial a large explosive eruption could by volatilisation and oxidation of this sulphur inject large volumes of sulphur dioxide into the atmosphere the greenish colouration of the sulphur reminiscent of other documented terrestrial sulphur eruptions is probably due to impurities this emphasises the point that interpretation of spectral reflectances of the jovian moon io regarding the possible contribution of sulphur cannot rely on extrapolation of laboratory data for pure materials

progress in paleoclimate modeling this paper briefly surveys areas of paleoclimate modeling notable for recent progress new ideas including hypotheses giving a pivotal role to sea ice have revitalized the low order models used to simulate the time evolution of glacial cycles through the pleistocene a prohibitive length of time for comprehensive general circulation models gcms in a recent breakthrough however gcms have succeeded in simulating the onset of glaciations this occurs at times most recently 115 kyr b p when high northern latitudes are cold enough to maintain a snow cover and tropical latitudes are warm enhancing the moisture source more generally the improvement in models has allowed simulations of key periods such as the last glacial maximum and the mid holocene that compare more favorably and in more detail with paleoproxy data these models now simulate enso cycles and some of them have been shown to reproduce the reduction of enso activity observed in the early to middle holocene modeling studies have demonstrated that the reduction is a response to the altered orbital configuration at that time an urgent challenge for paleoclimate modeling is to explain and to simulate the abrupt changes observed during glacial epochs i e dansgaard oescher cycles heinrich events and the younger dryas efforts have begun to simulate the last millennium over this time the forcing due to orbital variations is less important than the radiance changes due to volcanic eruptions and variations in solar output simulations of these natural variations test the models relied on for future climate change projections they provide better estimates of the internal and naturally forced variability at centennial time scales elucidating how unusual the recent global temperature trends are

sensitivity of paleoclimate simulation results to season definitions according to the milankovitch theory slow variations of the earth s orbital parameters change the amplitude of the seasonal cycle of insolation and are considered to be the main forcing mechanism of glacial interglacial cycles because of the precession and changes in eccentricity the length of seasons also varies no absolute phasing is then possible between the insolation curves of two different periods various solutions to compare different periods have been given either for astronomical computations e g berger and loutre 1991 laskar et al 1993 or for model simulations e g kutzbach and otto bliesner 1982 mitchell et al 1988 but the sensitivity of model results to the different possible solutions has never been quantified our results based on simulations of the last interglacial climate 126 kyr b p where changes in the length of the seasons are large clearly show that phase leads or lags between the various solutions used introduce biases in the analysis of insolation and climate change of the same order of magnitude as the milankovitch forcing our main conclusions are that 1 when comparing various model simulations the date of the vernal equinox i e the phasing of the seasonal cycle of insolation as well as the definition of seasons must be the same for all models in order to avoid artificial differences 2 seasons based on astronomical positions are preferred to seasons defined with the same lengths as today since they better account for the phasing of insolation curves however insolation is not the only forcing in most atmospheric general circulation model simulations we also discuss the impact of the calendar hidden behind the definition of the seasonal cycle of the other boundary conditions such as sea ice or sea surface temperatures

multiproxy approach for the reconstruction of the glacial ocean surface margo michal kucera antoni rosell mele ralph schneider claire waelbroeck mara weinelt department of geology royal holloway university of london egham tw20 0ex uk icrea and institute of environmental science and technology universitat autonoma de barcelona 08193 bellaterra catalonia spain departement de geologie et oceanographie umr5805 epoc cnrs universite de bordeaux1 33405 talence cedex france laboratoire des sciences du climat et de l environnement laboratoire mixte cnrs cea f 91198 gif sur yvette france institute for geosciences university of kiel olshausen strasse 40 d 24098 kiel germany

the high pco2 caprese reservoir northern apennines italy relationships between present and paleo fluid geochemistry and structural setting abstract the chemical and isotopic compositions of i co2 rich fluids exploited from the 5 000 m deep pieve santo stefano 1 pss1 borehole located in the upper tiber basin northern apennines italy and ii natural gas seeps located in its surroundings mainly in the mt fungaia ophiolitic bearing complex ligurian unit are presented and discussed deep seismic profiles have allowed to identify a thrust related antiform caprese antiform a regional geological structure trapping the pressurized deep fluids fluids from the caprese reservoir cr consist of a co2 n2 rich gas phase sourced by both mantle degassing and thermal degradation of carbonate rocks and organic rich sediments of the umbro tuscan sedimentary series and a na cl saline up to 82 g l of tds brine gases naturally discharging in the study area are related to those present in the cr these gases during their uprising toward the surface mix with shallow aquifers addition of i h2 and h2s derived by the interaction with ophiolite bearing ligurian units and ii thermogenic hydrocarbons originated from the degradation of organic matter contained in the turbiditic sandstone rich formations cervarola falterona unit was also evidenced fluid inclusions trapped in calcite and quartz crystals from the pss1 drill core at the depth of 3864 to 3867 m contain co2 n2 and h2o nacl phases the different paleo co2 n2 contents and densities found with respect to the fluids currently exploited from the cr have been related to the evolution of the reservoir throughout the time compositional data of fluids exploited from pss1 borehole provide a unique opportunity to better characterize chemical physical processes and source regions of past and present deep fluids circulating in northern apennines

simulation of the last 21 000 years using accelerated transient boundary conditions abstract the earth system model of intermediate complexity ecbilt clio has been used for transient simulations of the last deglaciation and the holocene the forcing effects of the ice sheets greenhouse gas concentrations and orbital configurations are prescribed as time varying boundary conditions in this study two key aspects of the transient simulations are investigated which are of broader relevance for long term transient paleoclimate modeling the effect of using accelerated boundary conditions and of uncertainties in the initial state simulations with nonaccelerated boundary conditions and an acceleration factor 10 were integrated these simulations show that the acceleration can have a significant impact on the local climate history in the outcropping regions of the high southern latitudes and the convective regions in the north atlantic the acceleration leads to damped and delayed temperature response to the boundary conditions furthermore uncertainties in the initial state can strongly

lake bogoria hot springs kenya geochemical features and geothermal implications abstract many boiling springs and fumaroles are present along the shores of lake bogoria which is a closed basin alkaline saline lake typical of african rifts two different geothermal waters both of na hco3 type have been recognized the first discharged by the boiling springs located along the western shores of the lake comes from a shallow steam heated thermal aquifer its temperature is close to 100 c as indicated by chalcedony solubility while the chloride content of these waters is slightly higher than 200 mg l 1 the second recognizable in the southernmost boiling springs is representative of a deeper and hotter geothermal reservoir the occurrence of mixing and boiling processes complicates the interpretation of geochemical data nevertheless a chloride content of about 660 mg l 1 an equilibrium temperature close to 170 c and a high carbon dioxide partial pressure at least 10 20 bar have been estimated for the deep geothermal reservoir

petrology and geochemistry of the nyamuragira volcano zaire abstract nyamuragira volcano in the western rift of the east africa rift valley is characterized by violent volcanic eruptions the most recent of which occurred in 1967 1971 1976 1977 1980 and 1981 1982 its extrusives consist of a highly potassic suite of olivine basanite tephritic phonolites among which phonolitic tephrite is the commonest the petrographic features of the whole suite such as phenocryst and groundmass mineral assemblages and modal variations are rather simple major elements vary smoothly from olivine basanite to phonolitic interstitial glass without any abrupt change with increasing k 2 o in addition the typical incompatible trace elements ba ce f nb rb and sr increase continuously with the increase of k 2 o these suggest that chemical variations were controlled mainly by the effective fractionation of olivine and clinopyroxene associated with plagioclase and titanomagnetite furthermore in the k 2 o incompatible trace element diagrams trend lines extrapolated to zero converge on the coordinate axes of the vertical and horizontal lines this suggests that these incompatible elements were preferentially moved toward the primitive basaltic magma during the partial melting of metasomatized upper mantle peridotites furthermore these elements are concentrated almost completely in residual liquids during fractional crystallization

millennial to orbital scale variations of drought intensity in the eastern mediterranean abstract millennial to orbital scale rainfall changes in the mediterranean region and corresponding variations in vegetation patterns were the result of large scale atmospheric reorganizations in spite of recent efforts to reconstruct this variability using a range of proxy archives the underlying physical mechanisms have remained elusive through the analysis of a new high resolution sedimentary section from lake van turkey along with climate modeling experiments we identify massive droughts in the eastern mediterranean for the past four glacial cycles which have a pervasive link with known intervals of enhanced north atlantic glacial iceberg calving weaker atlantic meridional overturning circulation and dansgaard oeschger cold conditions on orbital timescales the topographic effect of large northern hemisphere ice sheets and periods with minimum insolation seasonality further exacerbated drought intensities by suppressing both summer and winter precipitation

decreasing capability of the degassing systems at lakes nyos and monoun cameroon a new gas removal system applied to lake monoun to prevent a future limnic eruption

global ocean response to orbital forcing in the holocene 1 global upper ocean evolution in the holocene is studied in two coupled ocean atmosphere models under orbital forcing conditions at 3 6 8 and 11 ka the annual mean sea surface temperature sst changes in the early to mid holocene are found to be forced mainly by the annual mean insolation forcing with an overall symmetric response of colder equator 1 c in the arctic this sst change is consistent with a synthesis of mid holocene paleo sst records in contrast the temperature response in the thermocline is dominated by an antisymmetric pattern with a cooling warming in the northern southern hemisphere midlatitudes the thermocline response is determined predominantly by surface water subduction and ultimately the insolation forcing in local late winter

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

orbital forcing of arctic climate mechanisms of climate response and implications for continental glaciation progress in understanding how terrestrial ice volume is linked to earths orbital configuration has been impeded by the cost of simulating climate system processes relevant to glaciation over orbital time scales 10 3 10 5 years a compromise is usually made to rep resent the climate system by models that are averaged over one or more spatial dimensions or by three dimensional models that are limited to simulating par ticular snapshots in time we take advantage of the short equilibration time 310 years of a climate model consisting of a three dimensional atmosphere coupled to a simple slab ocean to derive the equilibrium climate response to accelerated variations in earths orbital configuration over the past 165 000 years prominent decreases in ice melt and increases in snowfall are sim ulated during three time intervals near 26 73 and 117 thousand years ago ka when aphelion was in late spring and obliquity was low there were also significant decreases in ice melt and increases in snowfall near 97 and 142 ka when eccentricity was relatively large aph elion was in late spring and obliquity was high or near its long term mean these glaciation friendly time intervals correspond to prominent and secondary phases of terrestrial ice growth seen within the marine d 18 o record both dynamical and thermal effects contribute to the increases in snowfall during these periods through increases in storm activity and the fraction of precipi tation falling as snow the majority of the mid to high latitude response to orbital forcing is organized by the properties of sea ice through its influence on radiative feedbacks that nearly double the size of the orbital forcing as well as its influence on the seasonal evolution of the latitudinal temperature gradient

a combined electron microprobe emp and raman spectroscopic study of the alteration products in martian meteorite mil 03346 1 we examine the secondary alteration products in mil 03346 using raman spectroscopic and electron microprobe traverses discussion focuses on the single olivine in 177 supplemented with observations from 168 and 169 traverses start at the rim and progress into the interior dark brown nearly opaque laihunite fe2 fe3 2 sio4 2 is present as overgrowths and 20 50 m veins of reddish brown stilpnomelane k na ca 4 ti0 1 al2 3 fe3 35 5 mn0 8 mg9 3 si63al9 o oh 206 n h2o occur inside the olivine stilpnomelane crosscuts and postdates the laihunite veins are in sharp contact with the host olivine but lined by 5 m films of jarosite kfe3 3 so4 2 oh 6 from a later generation of alteration an interstitial laihunite also hosts stilpnomelane the most recent secondary phases are gypsum and bassanite in our x ray maps of 168 and 169 ca sulfates were not observed in x ray maps of 177 but were detected in our raman point count all sulfates are believed to be martian the groundmass of mil indicates rapid cooling from elevated temperatures with fo2 near qfm reports of laihunite synthesis by olivine oxidation at elevated temperatures 100 800 c suggest the overgrowths formed during consolidation in terrestrial rocks stilpnomelane is a product of late diagenesis to garnet grade metamorphism in mil stilpnomelane appears to be a secondary phase formed at the lower end of this stability range at conditions akin to diagenesis raman spectra indicate that the stilpnomelane jarosite and ca sulfates are hydrated the stilpnomelane contains cl and was followed by jarosite a product of acid alteration and the deposition of ca sulfates and halide salts from more neutral chloride solutions

northern hemisphere forcing of southern hemisphere climate during the last deglaciation changes in ocean circulation are the most plausible explanation for the early southern hemisphere deglacial warming and its lead over northern hemisphere temperature milankovitch theory which was developed to explain the relationship between earth s movement and the climate holds that glacial cycles are ultimately controlled by variations in northern hemisphere summer insolation exposure to the sun s rays spectral analyses of palaeoclimate records support this theory but a mechanistic test has been elusive other lines of evidence also show that climate changes in the southern hemisphere may have led those in the northern hemisphere casting doubt on the main theory here feng he and colleagues use a coupled ocean atmosphere model to show that the last deglaciation was indeed triggered by northern hemisphere insolation changes amplified by albedo co2 and ocean circulation changes according to the milankovitch theory changes in summer insolation in the high latitude northern hemisphere caused glacial cycles through their impact on ice sheet mass balance1 statistical analyses of long climate records supported this theory but they also posed a substantial challenge by showing that changes in southern hemisphere climate were in phase with or led those in the north2 although an orbitally forced northern hemisphere signal may have been transmitted to the southern hemisphere3 insolation forcing can also directly influence local southern hemisphere climate potentially intensified by sea ice feedback4 5 6 suggesting that the hemispheres may have responded independently to different aspects of orbital forcing signal processing of climate records cannot distinguish between these conditions however because the proposed insolation forcings share essentially identical variability7 here we use transient simulations with a coupled atmosphere ocean general circulation model to identify the impacts of forcing from changes in orbits atmospheric co2 concentration ice sheets and the atlantic meridional overturning circulation amoc on hemispheric temperatures during the first half of the last deglaciation 22 14 3 kyr bp although based on a single model our transient simulation with only orbital changes supports the milankovitch theory in showing that the last deglaciation was initiated by rising insolation during spring and summer in the mid latitude to high latitude northern hemisphere and by terrestrial snow albedo feedback the simulation with all forcings best reproduces the timing and magnitude of surface temperature evolution in the southern hemisphere in deglacial proxy records8 9 amoc changes associated with an orbitally induced retreat of northern hemisphere ice sheets10 is the most plausible explanation for the early southern hemisphere deglacial warming and its lead over northern hemisphere temperature the ensuing rise in atmospheric co2 concentration provided the critical feedback on global deglaciation9 11

discovery of sublacustrine hydrothermal activity and associated massive sulfides and hydrocarbons in the north tanganyika trough east african rift massive sulfides and carbonate mineral deposits associated with sublacustrine thermal springs were recently discovered along the zaire side of the north tanganyika trough western branch of the east african rift this hydrothermal activity investigated by scuba diving at a maximum depth of 20 m is located at the intersection of major north south normal faults and northwest southeast faults belonging to the tanganyika rukwa malawi trm strike slip fault zone the preliminary results presented here come from analyses of sulfide deposits hydrothermal fluids and associated hydrocarbons that result from geothermal activity in this part of the east african rift filled by a thick pile of sediment the north tanganyika trough

time dependent co2 variations in lake albano associated with seismic activity lake albano alban hills volcanic complex central italy is located in a densely populated area near rome the deep lake waters have significant dissolved co2 concentrations probably related to sub lacustrine fluid discharges fed by a pressurized co2 rich reservoir the analytical results of geochemical surveys carried out in 1989 2010 highlight the episodes of co2 removal from the lake the total mass of dissolved co2 decreased from 5 8 107 kg in 1989 to 0 5 107 kg in 2010 following an exponential decreasing trend calculated values of both dissolved inorganic carbon and co2 concentrations along the vertical profile of the lake indicate that this decrease is caused by co2 release from the epilimnion at depth 9 m combined with 1 water circulation at depth 95 m and 2 co2 diffusion from the deeper lake layers according to this model lake albano was affected by a large co2 input that coincided with the last important seismic swarm at alban hills in 1989 suggesting an intimate relationship between the addition of deep originated co2 to the lake and seismic activity in the case of a co2 degassing event of an order of magnitude larger than the one that occurred in 1989 the deepest part of lake albano would become co2 saturated resulting in conditions compatible with the occurrence of a gas outburst these results reinforce the idea that a sudden co2 input into the lake may cause the release of a dense gas cloud presently representing the major volcanic threat for this densely populated area

chemocline collapse in lake kivu as an analogue for nitrogen cycling during oceanic anoxic events abstract one of the outstanding issues in the study of nutrient dynamics during oceanic anoxic events oaes is the preservation of 15n depleted nitrogen isotope signals which are not observed in analogous modern environments the favored mechanism for 15 n values below 0 is utilization of excess ammonium derived from underlying anoxic waters by primary producers however there are few modern examples available for testing this hypothesis due to the overall well oxygenated state of modern oceans here we present sedimentary 13 corg and 15 nbulk data as well as pigment biomarker ratios from the sediments of lake kivu a meromictic lake in east africa this system serves as a potential analogue for the development of strongly depleted 15 nbulk in oae black shales we focus on intervals of organic carbon enrichment sapropels that are interpreted to have been the result of lake water column mixing events sediment 13 corg and 15 nbulk decrease by up to 6 and 4 respectively near the base of sapropel layers these negative excursions provide evidence for the mixing of 13c depleted dissolved inorganic carbon and ammonium in excess of photosynthetic need derived from the deeper anoxic basin of the lake support of this model is also provided by photosynthetic pigment biomarkers which show significant fluctuations in phototrophic ecology consistent with water column mixing and changes in nutrient status further evidence for the shallowing of the chemocline during sapropel deposition is found in the presence of bacteriochlorophyll derivatives produced by phototrophic sulfide oxidizers

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

homogeneous climate variability across east antarctica over the past three glacial cycles recent ice core studies have raised the disturbing possibility that glacial interglacial climate changes may be non uniform across antarctica1 2 these findings have been confined to records from the ross sea sector of the continent but significant deviations in other areas would call into question the widely assumed validity of the climate record obtained from vostok east antarctica on large spatial scales3 here we present an isotopic profile from a core drilled at dome fuji4 5 situated 1 500 km from vostok in a different sector of east antarctica the two records show remarkable similarities over the past three glacial cycles the extent of the dome fuji record in both large amplitude changes such as terminations interglacials and interstadials and more subtle glacial events even when the origin of precipitation is accounted for our results indicate that antarctic climate is essentially homogeneous at the scale of the east antarctic plateau possibly as a consequence of the symmetry of the plateau and the adjacent ocean

environmental processes of the ice age land oceans glaciers epilog knowledge of the state of the earth at the last glacial maximum lgm an interval around 21 000 years ago is an important benchmark for understanding the sensitivity of global environmental systems to change much progress in understanding climates of the lgm has occurred in the 20 years since the end of the climap project of the 1970s climate long range investigation mapping and prediction here we review this progress based on presentations and discussion at a rst open science meeting of the epilog project environmental processes of the ice age land oceans glaciers held in delmenhorst germany may 1999 we outline key controversies and document protocols for epilog contributions so that a new synthesis of the lgm earth can emerge as an open project of the world s community of scientists 2001 elsevier science ltd all rights reserved

oxygen deficiency in lake sihetun formation of the lower cretaceous liaoning fossillagerstatte china the redox state of lake sihetun represented by the lower cretaceous yixian formation western liaoning china is evaluated to understand the formation of this konservat lagerstatte lake evolution is subdivided into four phases of which phases 2 and 3 exhibit excellent fossil preservation exceptional preservation and mass mortality events within phase 2 were previously attributed to synsedimentary volcanism and oxygen deficiency however the volcanic trigger for mass mortality events remains enigmatic and distinction between anoxia and dysoxia has not been put forward so far to resolve the redox state of the lake during phase 2 5394 diameters of pyrite framboid pseudomorphs in 29 thin sections from three localities have been measured framboid size distributions reveal that lake sihetun was governed by dysoxic bottom waters with spells of anoxia recording pronounced environmental stress hence holomictic eutrophic conditions were episodically replaced by meromictic interludes spatial variations in redox state were common and oxic conditions were detected in two of the three studied localities concentrated iron sulphide layers resulted from biofilms at the lake floor or the development of microenvironments around organic remains which preserved highly reactive organic compounds in contrast sediments of phase 3 record oxic conditions and an entirely holomictic lake

water and dissolved gas geochemistry at coatepeque ilopango and chanmico volcanic lakes el salvador central america abstract coatepeque on the e slope of santa ana volcano ilopango inside ilopango caldera and chanmico associated with san salvador volcano are volcanic lakes in el salvador showing a thermocline at a relatively shallow depth from 30 to 40 m from 20 to 40 m and from 5 to 15 m depth respectively and anoxic conditions below 33 24 and 4 m depth respectively the na cl composition of the coatepeque and ilopango lakes displaying tds values up to 1226 and 1216 mg l respectively is likely due to hydrothermal fluids that feed these two lakes as also confirmed by cl br molar ratios 650 high as b li and si contents and cl so42 ratio 1 the mg2 hco3 water composition of lake chanmico whose tds values were between 566 and 856 mg l suggests water rock interaction processes with mafic ultramafic rocks variably affected by serpentinization processes which produced high mg2 si and b concentrations waters at depth were characterized by the presence of co2 from an extra lacustrine source as suggested by 13c co2 values significantly less negative than those typically related to biogenic processes albeit this gas was found in smaller quantities when compared to those recorded in other meromictic lakes hosted in quiescent volcanic systems e g lake kivu in drc monticchio albano and averno lakes in italy hule and rio cuarto lakes in costa rica lake pavin in france the occurrence of ch4 whose concentrations in lake chanmico were up to two orders of magnitude higher than those recorded in coatepeque and ilopango lakes suggests bacterial methanogenesis

response of lake kivu stratification to lava inflow and climate warming during the eruption of nyiragongo volcano in january 2002 about 10 6 m 3 of lava entered lake kivu the high concentrations of co2 and ch4 dissolved in the deep waters of lake kivu raised serious concerns about a potential gas outburst with catastrophic consequences for the population in the kivu tanganyika region therefore 3 weeks after the volcanic eruption we performed an ad hoc lake survey of the stability of the water column stratification vertical profiles of temperature and turbidity revealed signatures of the lava which had penetrated to 100 m depth however there was no substantial warming or destratification of the gas containing deep layers below the deep double diffusive structures also remained unaltered based on these observations we conclude that a thermally driven gas outburst in lake kivu is not to be expected from future eruptions of comparable dimensions in addition the recent measurements allowed for an update and gave new insight into the stratification and double diffusive mixing phenomena in lake kivu a comparison with former measurements revealed a warming of the upper part of the lake of up to 0 58c within the last 30 yr which could be attributed to climate variability

synchronous climate changes in antarctica and the north atlantic central greenland ice cores provide evidence of abrupt changes in climate over the past 100 000 years many of these changes have also been identified in sedimentary and geochemical signatures in deep sea sediment cores from the north atlantic confirming the link between millennial scale climate variability and ocean thermohaline circulation it is shown here that two of the most prominent north atlantic events the rapid warming that marks the end of the last glacial period and the bolling allerod younger dryas oscillation are also recorded in an ice core from taylor dome in the western ross sea sector of antarctica this result contrasts with evidence from ice cores in other regions of antarctica which show an asynchronous response between the northern and southern hemispheres

composition and origin of authigenic carbonates in the krishna godavari and mahanadi basins eastern continental margin of india abstract the mineralogical and stable isotopic composition of authigenic carbonates from the krishna godavari kg and mahanadi basin provide a deeper insight into the processes inducing carbonate formation in the sediments of the eastern continental margin of india in the bay of bengal authigenic carbonate cements micro nodules bioturbation casts and tubes from 12 core locations drilled during the indian national gas hydrate program nghp expedition 01 were investigated for this study three main processes responsible for authigenic carbonate precipitation are identified organoclastic sulfate reduction anaerobic oxidation of methane and methanogenesis evidence of vigorous methane seepage is indicated in carbonates recovered at sites 7 10 12 kg basin and 19 mahanadi basin these methane derived carbonates display typical paragenetic carbonate mineralogies aragonite high mg calcite with 15 mol mgco 3 ca rich dolomite two separate horizons of methane derived carbonates are correlated between 4 drill holes up to 16 km apart the upper horizon has been dated with 14 c 40 100 51 600 a bp 1950 and clearly indicates that methane seepage has been much more vigorous in the past possibly due to the effect of lower sea level on the gas hydrate stability zone across the margin

the late pleistocene and holocene stratigraphy and paleolimnology of lakes kivu and tanganyika abstract evidence from diatoms chemistry and sedimentology shows that lakes kivu and tanganyika experienced late pleistocene low stands 86 to 300 m for kivu and 250 to 350 m for tanganyika both lakes had higher 2 10 fold sedimentation rates prior to 11 500 yr b p about 9900 yr b p upwelling became important in southern lake tanganyika which had been deepening for at least several millenia by 9400 yr b p kivu had become deep and dilute with overflow via the ruzizi river to lake tanganyika southern lake tanganyika became more stably stratified about 5200 yr b p volcanism and hydrothermal activity in kivu began about 5000 yr b p and the salinity reached 3 ppt and the lake became strongly stratified the ruzizi river outflow was interrupted from 3500 yr b p until recently the sedimentary record implies that sudden hydrothermal activity and sublacustrine volcanism in kivu has probably been the cause of its impoverished fauna these results show that high lake levels in the eastern rift of africa from 10 000 to 7000 yr b p were paralleled in the western rift given the great volumes of these lakes climate has not caused great variations in salinity the diatom floras however have been remarkably sensitive to changes in stratification and nutrient supply volcanism has been a major force in the limnological and biological evolution of lake kivu while both kivu and tanganyika have responded to changes in precipitation and wind stress

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

modeling obliquity and co2effects on southern hemisphere climate during the past 408 ka abstractthe effect of obliquity and co2 changes on southern hemispheric climate is studied with a series of numerical modeling experiments using the earth system model of intermediate complexity loch vecode ecbilt clio agism model loveclim and a coupled general circulation model model for interdisciplinary research on climate miroc it is shown in time slice simulations that phases of low obliquity enhance the meridional extratropical temperature gradient increase the atmospheric baroclinicity and intensify the lower and middle troposphere southern hemisphere westerlies and storm tracks furthermore a transient model simulation is conducted with loveclim that covers the greenhouse gas ice sheet and orbital forcing history of the past 408 ka this simulation reproduces reconstructed glacial interglacial variations in temperature and sea ice qualitatively well and shows that the meridional heat transport associated with the orbitally paced modulation of middle troposphere westerlies and storm tr

monsoon influenced variation in productivity and lithogenic sediment flux since 110 ka in the offshore mahanadi basin northern bay of bengal abstract the indian monsoon drives seasonal changes in precipitation and weathering across india as well as circulation and productivity in the northern indian ocean variation in paleo monsoon intensity and its effect on productivity and lithogenic fluxes is poorly constrained in the bay of bengal in this paper we present analysis of a sediment record from the offshore mahanadi basin recovered during the indian national gas hydrate program expedition 01 site nghp 01 19b we reconstruct variation in biogenic and lithogenic components during the last 110 kyr using measurements of total organic carbon toc total nitrogen tn toc tn caco3 biogenic silica bsi 13toc 15tn bulk mineralogy from x ray diffraction bulk and lithogenic grain size distribution magnetic susceptibility bulk density and ca br and zr rb from x ray fluorescence xrf the mass accumulation rate mar of caco3 a function of marine productivity drastically increased between 70 and 10 ka and is correlated to previously documented elevated asian dust fluxes and increased bay of bengal salinity during a weakened southwest monsoon decreased freshwater input over this period likely diminished stratification allowing for increased mixing and nutrient availability thus enhancing productivity despite weaker southwest monsoon winds the mar of lithogenic material is highest during the holocene suggesting that sediment supply driven by monsoon intensity is a stronger control on margin sedimentation than sea level at the mahanadi basin over the entire record magnetic susceptibility and xrf zr rb are strongly correlated with caco3 suggesting higher primary mineral input under a weakened southwest monsoon toc tn and 13toc also increase under glacial conditions suggesting higher relative input of terrestrial c4 organic matter these results highlight the mahanadi basin as a supply dominated margin where terrigenous sedimentation is strongly influenced by monsoon intensity and that productivity is limited by variation in monsoon driven stratification on glacial interglacial timescales rather than a direct response to monsoon winds

new precipitation and accumulation maps for greenland annual total precipitation and the annual accumulation on the greenland ice sheet are evaluated and presented in two maps the maps are based on accumulation measurements of 25 1 pits and cores obtained from the upper accumulation zone and precipitation measurements made at 35 meteorological stations in the coastal region to construct the accumulation map the annual precipitation was split into solid and liquid precipitation components annual total precipitation exceeding 2500 mm w e occurs on the southeastern tip of greenland while the minimum precipitation is estimated to occur on the northeastern slope of the ice sheet the mean annual precipitation for all of greenland is 340 mm w e the largest annual accumulation of about 1500 mm w e is found on the glaciers in the southeastern corner of greenland while the smallest accumulation is found on the northeastern slope of the ice sheet west of danmarkshavn the mean accumulation on the greenland ice sheet is estimated at 310 mm w e the regional difference in accumulation is examined with respect to the 850 hpa m bar level circulation the present surface topography is found to play an important role in determining regional accumulation on the ice sheet

isotope geochemistry of carbonate sediments from lake kivu east central africa isotopic investigations of carbonates from lake kivu show that most of the carbonate in the main basin is precipitated in isotopic equilibrium with the lake water bicarbonate near isotopic equilibrium with the atmosphere however aragonite precipitated from the surface water of the separate bukavu basin was periodically enriched in 13c delta 13c up to 13 6 per mille sign due to a preferential removal of 12c enriched sedimentary organic matter this occurred during times of low water level stands when the bukavu basin was isolated from the main lake and its waters were chemically stratified

modeling the time dependent response of the asian summer monsoon to obliquity forcing in a coupled gcm a phasemap sensitivity experiment to study the time dependent response of the asian summer monsoon to obliquity forcing we analyze a 284 000 year long transient simulation produced by a fully coupled global climate model gcm using a new phase mapping phasemap approach here we focus on understanding the phase response of monsoonal circulation to insolation forcing at the earth orbital obliquity band 41 kyr our results show that the east asian summer monsoon easm can be divided into two geographic regions the north east asian summer monsoon neasm and the south east asian summer monsoon seasm the indian summer monsoon ism and the seasm are in phase at the obliquity band strengthened with an increase in obliquity from obliquity minima omin to obliquity maxima omax the neasm is out of phase with the ism and seasm weakened with an increase in obliquity from omin to omax we hypothesize that the inverse phase between the neasm and the ism at the obliquity band results from an ism neasm teleconnection linked to the formation mechanism of the bonin high

holocene carbon cycle dynamics based on co2 trapped in ice at taylor dome antarctica a high resolution ice core record of atmospheric co2 concentration over the holocene epoch shows that the global carbon cycle has not been in steady state during the past 11 000 years analysis of the co2 concentration and carbon stable isotope records using a one dimensional carbon cycle model uggests that changes in terrestrial biomass and sea surface temperature were largely responsible for the observed millennial scale changes of atmospheric co2 concentrations

physical and biogeochemical limits to internal nutrient loading of meromictic lake kivu lake kivu is one of the large african rift lakes situated between the democratic republic of the congo and rwanda in its permanently stratified hypolimnion unusually high methane concentrations have increased further in recent decades because methanogenesis is in part dependent on supply of organic material from the photic zone it is necessary to quantify upward nutrient fluxes from the saline nutrient rich deep waters these upward fluxes are mainly driven by advection caused by subaquatic springs biogenic calcite precipitation drives surface water depletion and deep water enrichment of ca2 s r 2 and ba2 methane is mainly oxidized aerobically at the redox interface at 60 m with a small contribution of anaerobic methane oxidation a subaquatic spring that sustains the major chemocline at 250 m depth was depleted of n p and ch4 and concentrations of major ions were slightly lower than in the lake water of the same depth enrichment of the deep waters with nutrients and ch4 are driven by mineralization of settling organic material whereas sio2 is influenced by uptake and mineralization of diatoms and inputs through subaquatic springs dissolved inorganic phosphorus and si fluxes supplied by internal loading through upwelling were found to be lower than the estimations for lakes malawi and tanganyika in contrast n flux was within the lower range for lake malawi whereas it was assumed to be totally lost by denitrification in lake tanganyika in lake kivu nutrient uptake by primary production is three times higher than nutrient upward fluxes

palaeomagnetic and mineral magnetic studies of sediment from ball s cavern schoharie u s a abstract two sediment sequences from a cave near schoharie n y have been sampled for palaeomagnetic measurements the nature of the palaeomagnetic records obtained was found to be similar to other north american records a correlation can be made with lake sediment records back to 13 000 yr b p and with a sediment record from bessette creek in canada for the period between 23 000 and 30 000 yr b p during both periods the dominant long term trend of the vgp path has been that of anticlockwise motion but during the last 13 000 years there has been more superimposed short term clockwise motion than during the earlier period magnetic properties of the sediments suggest that magnetite is the dominant magnetic mineral and this is confirmed by the mossbauer spectra of both the sediments and magnetic extracts mossbauer measurements on the magnetic extracts also detected the presence of a small amount of haematite

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

basalt weathering across scales abstract weathering of silicate minerals impacts many geological and ecological processes for example the weathering of basalt contributes significantly to consumption of atmospheric carbon dioxide co2 and must be included in global calculations of such consumption over geological timeframes here we compare weathering advance rates for basalt wd where d and indicate the scale at which the rate is determined and surface area measured respectively from the laboratory to the watershed scales data collected at the laboratory weathering rind soil profile and watershed scales show that weathering advance rate of basalt is a fractal property that can be described by a fractal dimension dr 2 3 by combining the fractal description of rates with an arrhenius relationship for basalt weathering we derive the following equation to predict weathering advance rates at any spatial scale from weathering advance rates measured at the bet scale w d k 0 a d r 2 e e a r t here k0 is the pre exponential factor 1 29 107 mm3 mm 2 yr 1 ea is the activation energy 70 kj mol 1 and a is a spatial constant related to the scale of measurement of bet surface area 10 7 mm the term a d r 2 is the roughness the roughness fractal dimension can be conceptualized as a factor related to both the thickness of the reaction front and the specific surface area within the reaction front however the above equation can also be written in terms of a surface fractal dimension and the hypothetical average grain radius these fractal dimensions provide insight into reaction front geometry and should vary with lithology once the surface area discrepancy has been accounted for using this method we find a one to two order of magnitude range in weathering advance rates measured at any scale or temperature that can be attributed to factors such as changes in erosional regime parent lithology mechanism climate composition of reacting fluid and biological activity our scaled equation when used to predict global basalt co2 consumption based upon global lithologic maps yields an uptake flux 1 75 1013 mol co2 yr 1 within the predicted error of fluxes estimated based upon riverine measurements

gas hydrates in india potential and development abstract the shallow sediments along the indian continental margin are good hosts for gas hydrates and the methane within gas hydrates has been prognosticated as more than 1500 times of india s present natural gas reserve production of even 10 from this natural reserve is sufficient to meet country s vast energy requirement for about a century hence it was felt necessary to map the most prospective zones of gas hydrates and evaluate their energy potential along the indian margin first of all we have updated the gas hydrates stability thickness map along the indian shelf to provide the spatial and depth domains within which gas hydrates can be looked for we have identified the bottom simulating reflectors bsrs the main marker for gas hydrates in the krishna godavari kg mahanadi andaman kerala konkan and saurashtra regions respectively the total organic carbon content toc sediment thickness and rate of sedimentation indicate that the cauvery and kerala laccadive basins are also prospective for gas hydrates seismic attenuation q 1 reflection strength instantaneous frequency and blanking have been computed to characterize the sediments containing gas hydrates and free gas the faulting or gas chimneys have also been used for the identification of gas hydrates we have developed several approaches based on seismic traveltime tomography full waveform inversion amplitude versus offset avo modeling and avo attributes each coupled with rock physics modeling and utilized them for the quantification of gas hydrates a large volume of multi channel and ocean bottom seismic data have been acquired in 2010 between 500 to 2500 m water depths in kg and mahanadi basins the new data exhibit wide spread occurrences of bsrs reveal new prospective zones of gas hydrates and are being modeled for the delineation of sediments hosting gas hydrates and evaluation of their resource potential efforts are on to develop suitable technology for exploitation we anticipate that free gas lying below gas hydrate bearing sediments can be produced economically in near future however it may take longer time to retrieve gas from gas hydrates

increased seasonality in middle east temperatures during the last interglacial period the last interglacial period about 125 000 years ago is thought to have been at least as warm as the present climate owing to changes in the earth s orbit around the sun it is thought that insolation in the northern hemisphere varied more strongly than today on seasonal timescales which would have led to corresponding changes in the seasonal temperature cycle here we present seasonally resolved proxy records using corals from the northernmost red sea which record climate during the last interglacial period the late holocene epoch and the present we find an increased seasonality in the temperature recorded in the last interglacial coral today climate in the northern red sea is sensitive to the north atlantic oscillation a climate oscillation that strongly influences winter temperatures and precipitation in the north atlantic region from our coral records and simulations with a coupled atmosphere ocean circulation model we conclude that a tendency towards the high index state of the north atlantic oscillation during the last interglacial period which is consistent with european proxy records contributed to the larger amplitude of the seasonal cycle in the middle east

borehole versus isotope temperatures on greenland seasonality does matter new simulation results obtained with the hamburg atmosphere general circulation model echam 4 under maximum glacial boundary lgm conditions confirm the paleotemperatures on greenland determined by borehole thermometry the disagreement between 18o isotope based temperatures and the borehole temperatures of the lgm is not only reproduced by the model but the simulation results provide a plausible explanation paleotemperatures inferred from 18o measurements in ice cores are biased by a substantially increased seasonality of precipitation over greenland during the lgm during the glacial winter a much more zonal circulation prevents the effective transport of moisture to the greenland ice sheet and therefore reduces the contribution of isotopically strongly depleted winter snow to the annual mean isotope signal

vostok ice core climatic response to co2 and orbital forcing changes over the last climatic cycle vostok climate and co2 records suggest that co2 changes have had an important climatic role during the late pleistocene in amplifying the relatively weak orbital forcing the existence of the 100 kyr cycle and the synchronism between northern and southern hemisphere climates may have their origin in the large glacial interglacial co2 changes

evaluation of recent precipitation studies for greenland ice sheet the retrieval of an accurate spatial and temporal record of contemporary greenland precipitation is a uniquely challenging task because of the extreme variability in both atmospheric processes and the resulting precipitation distribution over relatively small spatial scales a comparison of precipitation data sets composed of monthly mean values from recent studies shows a convergence on the general features of the long term spatial patterns but substantial disagreement on the temporal variability both regionally and for all of greenland there is general agreement on a long term greenland average of about 35 cm yr 1 and on long term values for regional scales although differences for outlying data sets exceed 50 of the observed glaciological estimate for particular regions a fundamental problem is the inadequate topographic representation of greenland in the numerical analyses nearly all of the data sets are overly dry for high elevation areas as seen from comparisons with glaciological observations from summit the east central region of greenland is found to be particularly susceptible to the temporal discontinuities in data sets which employ operational analyses in contrast there is strong agreement among all methods on the temporal variability for the west central region over a 15 year period from the comparison it is concluded that none of the data sets is able to capture all of the regional scale features in general however the deficiencies of each data set are readily identifiable from comparison and evaluation in the context of circulation features agreement among the methods on particular regions and timescales gives increased confidence in drawing conclusions related to aspects of greenland s precipitation climatology in particular an enhanced precipitation retrieval method is found to be less susceptible to data artifacts than other methods using operational analyses in the north anomalously high precipitation is associated with cyclonic development near the fram strait for west central greenland the close agreement among methods is related to the dominant contribution of the mean circulation

anatomy of a river drainage reversal in the neogene kivu nile rift abstract the neogene geological history of east africa is characterised by the doming and extension in the course of development of the east african rift system with its eastern and western branches in the centre of the western rift rise rwanda is situated on proterozoic basement rocks exposed in the strongly uplifted eastern rift shoulder of the kivu nile rift segment where clastic sedimentation is largely restricted to the rift axis itself a small volcanically and tectonically controlled depository in northwestern rwanda preserved the only neogene sediments known from the extremely uplifted rift shoulder those pliocene to pleistocene holocene fluvio lacustrine muds and sands of the palaeo nyabarongo river record the influence of virunga volcanism on the major drainage reversal that affected east africa in the plio pleistocene when the originally rift parallel upper nile drainage system became diverted to the east in order to enter the nile system via lake victoria sedimentary facies development heavy mineral distributions and palaeobiological controls including hominid artefacts signal a short time interval of

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

formation of methane related authigenic carbonates in a highly dynamic biogeochemical system in the krishna godavari basin bay of bengal abstract we report the abundant occurrence of authigenic fe rich carbonate high mg calcite hmc and low mg calcite from 11 cores recovered from the krishna godavari basin k g basin bay of bengal the cores were collected as part of the indian gas hydrate exploration program on board r v marion dufresne md 161 may 2007 in different environments including mounds mud diapirs mass flows and hemipelagic sediments over a range of water depths from 647 to 2079 m authigenic carbonates range in size from 1 mm to 12 cm and display various morphologies like roundish or platy micro nodules and tube like forms from the cores 173 carbonate samples have been investigated for their depth distribution mineralogy geochemical and stable isotopic composition the stable carbon isotopic composition of 46 out of 88 measured carbonate samples are around 50 which allows the differentiation into methane related carbonates hmc especially at sites 8 and 15 but also in low abundance at sites 1 5 9 and 12 results indicate that the carbonates at site 8 and 15 represent paleo methane seepage locations the fe rich carbonates occur abundantly at many sites in the k g basin their varying carbon isotopic composition indicates that probably not only sulfate reduction through organic matter degradation but also methanogenesis are the responsible processes for their formation

bacterial response to contrasting sediment geochemistry in the central indian basin in order to investigate whether geochemical physiographic and lithological differences in two end member sedimentary settings could evoke varied microbe sediment interactions two 25 cm long sediment cores from contrasting regions in the central indian basin have been examined site tvbc 26 in the northern siliceous realm 10 s 75 5 e is organic c rich with 0 3 0 09 total organic carbon site tvbc 08 in the southern pelagic red clay realm 16 s 75 5 e located on the flank of a seamount in a mid plate volcanic area with hydrothermal alterations of recent origin is organic c poor 0 1 0 07 significantly higher bacterial viability under anaerobic conditions generally lower microbial carbon uptake and higher numbers of aerobic sulphur oxidizers at the mottled zones characterize core tvbc 26 in the carbon poor environment of core tvbc 08 a doubling of the 14 c uptake a 250 times increase in the number of autotrophic nitrifiers a fourfold lowering in the number of aerobic sulphur oxidizers and an order higher of denitrifiers exist when compared to core tvbc 26 this suggests the prevalence of a potentially autotrophic microbial community in core tvbc 08 in response to hydrothermal activity microbial activity at the northern tvbc 26 is predominantly heterotrophic with enhanced chemosynthetic activity restricted to tangreen mottled zones the southern tvbc 08 is autotrophic with increased heterotrophic activity in the deepest layers notably the bacterial activity is generally dependent on the surface productivity in tvbc 26 the carbon rich core and mostly independent in tvbc 08 the carbon poor hydrothermally influenced core the northern sediment is more organic sink controlled and the southern more hydrothermal source controlled hydrothermal activity and associated rock alteration processes may be more relevant than organic matter delivery in these deep sea sediments thus this study highlights the relative importance of hydrothermal activity versus organic delivery in evoking different microbial response in the central indian basin sediments

early pleistocene glacial cycles and the integrated summer insolation forcing long term variations in northern hemisphere summer insolation are generally thought to control glaciation but the intensity of summer insolation is primarily controlled by 20 000 year cycles in the precession of the equinoxes whereas early pleistocene glacial cycles occur at 40 000 year intervals matching the period of changes in earth s obliquity the resolution of this 40 000 year problem is that glaciers are sensitive to insolation integrated over the duration of the summer the integrated summer insolation is primarily controlled by obliquity and not precession because by kepler s second law the duration of the summer is inversely proportional to earth s distance from the sun

water and gas chemistry at lake kivu drc geochemical evidence of vertical and horizontal heterogeneities in a multibasin structure 1 waters and dissolved gases collected along vertical profiles in the five basins main kabuno bay kalehe ishungu and bukavu forming the 485 m deep lake kivu democratic republic of the congo were analyzed to provide a geochemical conceptual model of the several processes controlling lake chemistry the measured horizontal and vertical variations of water and gas compositions suggest that each basin has distinct chemical features produced by 1 different contribution from long circulating fluid system containing magmatic co2 responsible of the huge co2 ch4 rich reservoir hosted within the deep lake water 2 spatial variations of the biomass distribution and or speciation and 3 solutes from water rock interactions the kabuno bay basin is characterized by the highest rate of magmatic fluid input accordingly this basin must be considered the most hazardous site for possible gas outburst that could be triggered by the activity of the nyiragongo and nyamulagira volcanoes located a few kilometers north of the lake

lithofacies characterization of gas hydrate prospects discovered during the national gas hydrate program expedition 02 offshore krishna godavari basin india abstract lithofacies of host sediments associated with gas hydrate reservoirs may have a significant influence on the formation of hydrates the type of sediments and the depositional processes responsible for the gas hydrate bearing sediments along the eastern margin of the india have been studied by integrating core data and logging while drilling downhole logs borehole data correlated with seismic data were used for the interpretation of geological process responsible for gas hydrate formation the acquired seismic profiles were correlated with the downhole logs by identifying the shape of the well logs curves that indicate finning up and blocky patterns turbidite sands and debris flows were also identified from the log and core sediment studies this study identified two prominent types of depositional systems 1 turbidity currents and 2 debris flows were mainly responsible for the deposition of gas hydrate bearing reservoirs in the study area based on these studies two well developed gas hydrate systems have been identified in the krishna godavari basin and hydrates were determined to be distributed mostly in sand dominated facies fine grained sand in the identified turbidite deposits were shown to be a good hydrate reservoir the hydrate bearing sediments in the central part of the krishna godavari basin area c in d6 block consist of mostly debris flows which is consistent with scattered gravel and sand silt sized grains in channel levee systems

a combined geochemical and isotopic study of the fluids discharged from the montecatini thermal system nw tuscany italy abstract the thermo mineral fluids discharges of montecatini terme northern apennines tuscany italy have been exploited since the roman times and despite the fact that this thermal complex is one of the biggest in europe the most recent geochemical investigations were published almost 40 years ago to fill this gap in this paper a detailed geochemical and isotopic investigation on the main thermal springs and wells from the montecatini thermal system mts is presented the chemical and isotopic features of the montecatini waters suggested that they are mainly controlled by water rock interaction processes between meteoric water permeating at depth from the surrounding reliefs up to 800 m a s l and the triassic evaporites burano formation belonging to the tuscan sedimentary series the local stratigraphic and tectonic framework favors an efficient recharge of the hydrothermal reservoir by the meteoric precipitation from a large catchment area and this aspect plays a fundamental role for the longevity of the montecatini thermal spas notwithstanding the huge amount of thermal water exploited the 3h values indicated that the thermal waters are likely related to a relatively long 50 years fluid circulation pattern approaching the surface thermal and saline waters mix with cold and low tds total dissolved solids waters hosted in short shallow aquifer s whose chemistry is dictated by the interaction of rain waters with silico clastic rocks of low solubility geothermometric estimations in the f so42 hco3 system suggested the occurrence of a main fluid reservoir at t 80 95 c and pco2 0 5 bars such co2 pressure is consistent with values estimated for other thermal springs from central southern tuscany being co2 basically supplied by a deep source nevertheless 13c co2 and 13c tdic values were lower than those expected for a mantle thermometamorphic co2 source this can be explained by i isotopic fractionation occurring during calcite precipitation and or ii mixing with biogenically derived gases occurring at relatively shallow depth