improving the interpretability of air gun seismic reflection data using deterministic filters a case history from offshore cape leeuwin southwest australia to identify drilling targets for an integrated ocean drilling program project to investigate high latitude black shales required reinterpretation of legacy seismic data the original processing had identified the major structures but was of insufficient resolution to map the more subtle markers at the top of the shale sequence by reprocessing these 2004 vintage 2d air gun marine seismic reflection data we show that the application of filters determined from deepwater data yields subbottom geological imaging superior to statistical methods and arguably better than modeled source deconvolution methods particularly for recovery of low frequencies the data were acquired to the southwest of australia in an area with swells that are typically 2 4 m and cause distortions to the predicted source and receiver response functions these distortions cannot be incorporated in an idealized modeled source function hence we have opted to design the deterministic filters from the seismic data we applied the deconvolution in two steps a prestack filter to suppress the air gun bubble pulse signal and a poststack filter to suppress the notches in the amplitude spectrum caused by the free surface reflections at the source and the receiver through this strategy we expanded the seismic data bandwidth at the low and high frequencies and improved resolution the tie with the single borehole in the area was significantly improved and has enabled a more confident interpretation of the shale horizons

deep sea records of the continental weathering and erosion response to east asian monsoon intensification since 14 ka in the south china sea we analyzed sediment from ocean drilling program odp site 1144 in the northern south china sea to examine the weathering response of se asia to the strengthening of the east asian monsoon eam since 14 ka our high resolution record highlights the decoupling between continental chemical weathering physical erosion and summer monsoon intensity mass accumulation rates ti ca k rb hematite goethite and sr 87 sr 86 show sharp excursions from 11 to 8 ka peaking at 10 ka clay minerals show a shorter lived response with a higher kaolinite illite chlorite ratio at 10 7 9 5 ka however not all proxies show a clear response to environmental changes magnetic susceptibility rises sharply between 12 and 11 ka grain size becomes finer from 14 to 10 ka and then coarsens until similar to 7 ka but is probably controlled by bottom current flow and sealevel sr and nd isotopes show that material is dominantly eroded from taiwan with a lesser flux from luzon while clay mineralogy suggests that the primary sources during the early holocene were reworked via the shelf in the taiwan strait rather than directly from taiwan erosion was enhanced during monsoon strengthening and caused reworking of chemically weathered pleistocene sediment largely from the now flooded taiwan strait which was transgressed by similar to 8 ka cutting off supply to the deep water slope none of the proxies shows an erosional response lasting until similar to 6 ka when speleothem oxygen isotope records indicate the start of monsoon weakening although more weathered sediments were deposited from 11 to 8 ka when the monsoon was strong these are reworked and represent more weathering during the last glacial maximum lgm when the summer monsoon was weaker but the shelves were exposed c 2012 elsevier b v all rights reserved

long term cooling drying record of north china since the middle pleistocene from geochemical evidence of a 150 m deep drill core beijing plain china the quaternary strata in north china primarily consist of fluvial sediments which react strongly to east asian monsoon circulation however the records of the quaternary climate change history in terms of these fluvial sedimentations were limited which impeded understanding the east asian monsoon evolution in north china thus a 150 m deep drill core was collected from changping in the beijing plain to reconstruct the quaternary palaeoenvironmental changes the core was chronologically well constrained using palaeomagnetic and thermoluminescence dating the magnetostratigraphic result indicated that the brunhes matuyama boundary is at 134 2 m 0 78 ma and the age at the bottom of the core is 1 07 ma the thermoluminescence tl dating of the upper sand at similar to 2 m was 10 4 ka the chemical weathering history since the middle pleistocene in beijing plain was reconstructed by using geochemical proxies including selected major element pairs chemical index of alteration and al2o3 cao na2o k2o diagrams the cia value of the changping core ranged from 50 3 to 69 4 average 59 2 which indicated that the sediment has experienced incipient to intermediate chemical weathering during the middle pleistocene the result of a cn k figure shows a high plagioclase to k feldspar ratio in the source which would be indicative of a granodiorite gd source from jundu mountains north of the beijing plain all the geochemical results revealed a long term gradual decrease of weathering since the middle pleistocene which implied a long term increasing aridification cooling in the beijing plain c 2014 elsevier ltd and inqua all rights reserved

uncertainty analysis of depth predictions from seismic reflection data using bayesian statistics estimating the depths of target horizons from seismic reflection data is an important task in exploration geophysics to constrain these depths we need a reliable and accurate velocity model here we build an optimum 2d seismic reflection data processing flow focused on pre stack deghosting filters and velocity model building and apply bayesian methods including gaussian process emulation and bayesian history matching bhm to estimate the uncertainties of the depths of key horizons near the borehole dsdp 258 located in the mentelle basin south west of australia and compare the results with the drilled core from that well following this strategy the tie between the modelled and observed depths from dsdp 258 core was in accordance with the 2 posterior credibility intervals and predictions for depths to key horizons were made for the two new drill sites adjacent the existing borehole of the area the probabilistic analysis allowed us to generate multiple realizations of pre stack depth migrated images these can be directly used to better constrain interpretation and identify potential risk at drill sites the method will be applied to constrain the drilling targets for the upcoming international ocean discovery program iodp leg 369

velocity depth ambiguity of reflection traveltimes the conversion of time horizons to depth is fundamental to exploration geophysics the interval velocity used in the conversion is often estimated from the stacking velocity assuming that each layer s interval velocity is homogeneous however even for one laterally inhomogeneous layer above a flat reflector the stacking velocity can swing violently about its average and conventional methods of velocity estimation fail i show that violent swings in the stacking velocity are a symptom of a long wavelength ambiguity between the burial depth to an interface and interval velocity lateral variations in seismic velocity with a spatial wavelength of about 2 7 d where d is the depth to the reflecting horizon cannot be unambiguously resolved from traveltime measurements the spatial wavelength of this ambiguous component varies from 2 57 d for very small source receiver separations to 2 86 d for source receiver separations equal to d spectral components of the stacking velocity at wavelengths shorter than

linkage between lake xingkai sediment geochemistry and asian summer monsoon since the last interglacial period in this study we present the element geochemical data of core xk08 a2 drilled from lake xingkai khanka northeast china the study aims to examine the changes of sediment provenance and geochemical composition in response to asian summer monsoon variability since the last interglacial period major elemental analyses on lacustrine samples and sand samples from lake xingkai and the surrounding sandy ridges in northeast china indicate that their abundance varied in relatively narrow ranges the samples had only undergone the primary stage of chemical weathering similar ti al and k al ratios between the lacustrine samples from lake xingkai and the loess paleosol samples in north china were observed which suggests that they come from broadly similar desert sources due to the significant dependence on grain size and influence of sediments recycling chemical index of alteration of the lacustrine sediments could not be regarded as sensitive indicators of source regions weathering on the glacial interglacial timescale alternatively the geochemical proxies of the lacustrine sediments could be linked to the asian summer monsoon through the development of runoff and physical erosion in the catchment weakened asian summer monsoon caused more fine particles transported to the lake basin by reduced runoff in the last glacial period in contrast coarser and less weathered detritus are transported into the lake accompanying strengthened asian summer monsoon during the warm periods

the ti al molar ratio as a new proxy for tracing sediment transportation processes and its application in aeolian events and sea level change in east asia abstract ti al molar ratios of sediments in various sedimentary environments are used to explain sediment transportation from source regions to sink areas samples were collected from outcrops soils fluvial lake and marine sediment environments initial ti al molar ratios of sediments are controlled by those of parent soils or rocks these ratios tend to decline gradually as a result of heavy mineral gravity fractionation during transportation sedimentary ti al molar ratios in sink areas such as lakes and pelagic environments are lower than those in source regions in this study for the changjiang river huanghe river and kaoping river ti al molar ratios decline considerably from downstream to estuary environments additionally well sorted aeolian sands have extremely low ti al molar ratios in northern china the ti al molar ratios of aerosol particles found in taiwan and the east china sea show reduced ratios as a result of asia dust storm episodes furthermore lower ti al molar ratios in deep ocean sediments were discovered by tracing the distribution of sedimentary ti al molar ratios in the south china sea when sea levels dropped during glacial periods the river estuary was closer to deep marine areas and carried more terrestrial sediments into deep marine environments the closer estuary with relatively higher ti al ratio would lead increase of ti al molar ratios in deep sea sediments in this study ti al molar ratio is promoted as a new proxy to help with understanding changes in sedimentary environments

controls on the erosion of cenozoic asia and the flux of clastic sediment to the ocean rates of continental erosion may be reconstructed from variations in the rate of accumulation of clastic sediment most of which lies offshore global rates of marine sedimentation are usually considered to have reached a maximum after 3 4 ma driven by enhanced erosion in a variable glacial interglacial climate however a new compilation of seismic data from the marginal seas of asia now shows that only the red river reached its historic peak after 4 ma sediment flux from asia first peaked in the early middle miocene 24 11 ma well before the initiation of a glacial climate indicating that rock uplift and especially precipitation are the key controls on erosion at least over long periods of geologic time reconstructions of weathering in east asia show that faster erosion correlates with more humid warm climates in the early middle miocene changing to less erosive drier climates after 14 ma when antarctic glaciation begins average rates of sedimentation on most east asian continental margins since 1 8 ma are 5 6 times less than the modern fluvial flux implying that the flux to the oceans varies sharply on short timescales and is not always buffered over timescales of 10 4 yr by storage in flood plains

seismic attenuation of atlantic margin basalts observations and modeling paleogene basalts are present over much of the northeastern atlantic european margin in regions containing significant thicknesses of layered basalt flows conducting seismic imaging within and beneath the volcanic section has proven difficult largely because the basalts severely attenuate and scatter seismic energy we use data from a vertical seismic profile vsp from well 164 07 1 that penetrated 1 2 km of basalt in the northern rockall trough west of britain to measure the seismic attenuation caused by the in situ basalts the effective quality factor qeff of the basalt layer is found from the vsp to be 15 35 which is considerably lower more attenuative than the intrinsic attenuation measured on basalt samples in the laboratory we then run synthetic seismogram models to investigate the likely cause of the attenuation full waveform 1d modeling of stacked sequences of lava flows based on rock properties from the same well indicates that much of the seismic attenuation observed from the vsp can b

high resolution osl dating of a late quaternary sequence from xingkai lake ne asia chronological challenge of the mis 3a mega paleolake hypothesis in china in this paper a combined osl 49 samples and 14c 14 samples dating study was conducted on a sediment core from xingkai lake ne asia a single aliquot regenerative dose protocol was used to determine the equivalent dose dede of the extracted fine grained fg quartz fraction the suitability of the measurement procedure was confirmed by a set of luminescence tests e g preheat plateau and dose recovery measurements in addition a post ir infrared stimulated luminescence protocol at 290 c pirir290 was applied to the polymineral fg fraction of seven samples our results can be summarized as follows 1 the uppermost sample was dated to 110 a indicating that the osl signal of fg quartz has been well bleached this has been further confirmed by the consistency of osl ages and pirir290 ages within 80 ka the resulting osl ages generally increased with depth and the lowermost samples of core xk08 reached back to the last interglacial although the pirir290 dating suggested that the quartz osl ages likely begin to be underestimated beyond 80 ka 2 the comparison of osl and 14c ages suggested that the radiocarbon dating technique may significantly underestimate the age of sediments for samples older than 30 cal ka bp corresponding to 25 14c ka bp and thus it is necessary to pay attention when using such old 14c dates for paleoclimatic archaeological interpretation 3 this study challenges the radiocarbon based chronology of the mis 3a mega paleolake hypothesis which had been reiterated for many years and extensively reported across northern and western china and 4 the current high resolution osl dating record one age 5 10 cm showed clear sedimentation rate changes down the core the identified variations in the sedimentation processes at the orbital timescale may be related to regional global climatic changes during the past 130 ka and the high sedimentation rate during the last 0 4 ka has probably been caused by intensified human activities in the xingkai lake catchment

lake qinghai sediment geochemistry linked to hydroclimate variability since the last glacial abstract geochemistry of basin sediments from semi arid regions is valuable to understand past hydroclimatic changes here we investigate the links of sedimentary geochemistry rb sr ca zr toc and caco 3 carbonate mineralogy and ostracod shell 18 o of lake qinghai a basin proximal to major dust production centers at mid latitudes of the northern hemisphere to changes in depositional conditions and hydroclimate during the past 32 ka surface lacustrine sediments are characterized by low rb high sr low rb sr high caco 3 and high ca zr values in contrast to the chemical compositions of eolian loess high rb low sr high rb sr low caco 3 and low ca zr a direct comparison of soluble ca and sr in two short cores with instrumental water discharge data suggests that lacustrine precipitates in lake qinghai are dominated by authigenic aragonite formed under ca 2 limited water conditions and that the accumulation rate of aragonite dominantly depends on solute fluxes into the lake during the rainy seasons late may to september our high resolution down core records show that sediments during the last glacial 32 19 8 ka had high rb low sr low caco 3 and low ca zr indicating eolian dust loess accumulation in a desiccated basin under dry glacial conditions further supported by grain size and pollen results this type of sedimentation was maintained during the last deglacial 19 8 11 5 ka but interrupted by episodic lacustrine precipitates with high sr high caco 3 high ca zr and low rb at 11 5 ka sedimentary rb sr ca zr caco 3 and toc show dramatic and permanent changes implying an abrupt shift in the atmospheric circulation at the onset of the holocene in the lake qinghai region lacustrine precipitates have persisted throughout the holocene with a maximum during the early to mid holocene 10 5 8 0 ka since 8 0 ka the gradual and significant decreases in aragonite and sr accumulations in tandem with increasing dust deposit and more positive ostracod 18 o may be linked to a weakening of asian summer monsoons during the mid to late holocene overall our records appear to show a high sensitivity of sediment development and geochemistry in lake qinghai to the regional hydroclimate changes since the last glacial

extracting seismic uncertainties from tomographic velocity inversion and their use in reservoir risk analysis structural information in subsurface seismic images is critical for reservoir delineation reserve estimation and well planning however by its very nature it is also uncertain one cause of the image uncertainty is the migration velocity model that directly affects the position of migrated events both laterally and vertically the term velocity is meant in the broad sense i e it also includes the anisotropy parameters we present a method that accounts for uncertainties in a velocity model estimated by tomography and translates them into the migrated domain standard deviation attributes on target horizon positions or layer thicknesses are extracted the method includes quality controls for validating the estimated uncertainty attributes before integration with other downstream or interpretative information the method is demonstrated on a north sea area covered by data from multiple seismic surveys we observe that uncertainties increase with model complexity or depth and decrease as the illu

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

pre breakup continental extension in east gondwanaland and the early opening of the eastern indian ocean abstract extension of continental crust by up to 360 km on a north northeast azimuth in the great australian bight occurred prior to the middle cretaceous 96 ma onset of seafloor spreading between australia and antarctica this large amount of continental extension is constrained to the late jurassic 160 ma middle cretaceous interval about a pole estimated to lie about 40 southeastward of southeastern australia using bathymetric data combined with seismic and magnetic determinations of the continent ocean boundaries off australia india and antarctica we determine a revised fit of east gondwanaland prior to continental extension and at various stages thereafter in the first stage from 160 to 132 5 ma m11 india australia rotated from antarctica with continental crustal extension between australia and antarctica and largely transform motion between the coromandel coast margin of india and the kron prins olav kyst margin of antarctica in the second stage from 132 5 to 96 ma india rotated northwestward away from australia antarctica producing m10 and younger magnetic anomalies along the western margin of australia continental extension was greatest between australia and antarctica during this stage the newly determined 132 5 96 ma rotation between india and australia provides an improved fit between the orientation of observed m10 m0 magnetic anomalies and the southward decrease in spreading rate off the western australian margin together with bathymetry the new rotation parameters lead to identification of the abandoned 96 ma spreading ridge along the lost dutchmen and dirck hartog ridges the naturaliste fracture zone is found to lie nearly parallel to the early cretaceous transform direction between india and antarctica suggesting that slow seafloor spreading required between australia and antarctica to accommodate the continental extension further east occurred between naturaliste fracture zone and the m4 m0 anomalies adjacent to the naturaliste plateau the revised fit of india in east gondwanaland reduces the eastward extent of greater india to 95 e but does not change its extent as far north as the cape range fracture zone the new pole determined for the early cretaceous rotation between india and australia antarctica lies within 15 of the southern tip of india significantly closer than in previous determinations thereby reducing the amount of seafloor spreading generated between africa and antarctica by the india antarctica rotation and thus offering a possible solution to the perceived spreading rate problems between m11 and m0 in the somali mozambique and antarctic basins

weathering and global denudation a negative correlation between sediment yield and weathering history as measured by the chemical alteration cia of the suspended sediment is observed for many of the world s major rivers and other regions of denudation the weathering history is a first order control on the sediment yield of such areas termed equilibrium denudation regions for other areas data scatter with either apparent increases or decreases of sediment yield for given cia values these areas are termed nonequilibrium denudation regions low sediment yields can be attributed to moderated erosion either natural or human induced and or the incorporation of unweathered glacial debris accelerated erosion resulting in high sediment yield is primarily human induced and results from cultivation and other land use each of these effects has a profound influence on global sediment discharge from the continents pre human suspended sediment discharge from the continents is estimated to be 12 6 times 10 15 g yr or about 0 6 the

modeling fracture propagation and seafloor gas release during seafloor warming induced hydrate dissociation the stability of marine methane hydrates and the potential release of methane gas to the ocean and atmosphere have received considerable attention in the past decade sophisticated hydraulic thermodynamic models are increasingly being applied to investigate the dynamics of bottom water warming hydrate dissociation and gas escape from the seafloor however these models often lack geomechanical coupling and neglect how overpressure development and fracture propagation affect the timing rate and magnitude of methane escape in this study we integrate a geomechanical coupling into the widely used tough hydrate model it is shown that such coupling is crucial in sediments with permeability 10 16 m2 as fracture formation dramatically affects rates of dissociation and seafloor gas release the geomechanical coupling also results in highly nonlinear seafloor gas release which presents an additional mechanism for explaining the widely observed episodic nature of gas flares from seafloor sediments in a variety of tectonic and oceanographic settings

chemical weathering of monsoonal eastern china implications from major elements of topsoil major element compositions of 36 bulk samples and 41 clay samples which were obtained from 47 topsoils collected in monsoonal eastern china were investigated with conventional wet chemistry and x ray fluorescence xrf spectrometry respectively based on major element analyses the mobility of major elements and latitudinal distributions of sio2 al2o3 ratio chemical index of alteration cia chemical index of weathering ciw and weathering index of parker wip were analyzed meanwhile the suitability of these chemical weathering indices to topsoils in monsoonal eastern china and its controls were discussed these investigations indicate that na k ca mg and si are relatively depleted while mn p fe and ti are relatively enriched in topsoils of the study area by comparison with their contents in the upper continent crust ucc and that alkali metal na k and alkaline earth metal ca mg elements are generally easier to be depleted from their parent materials than other major elements during chemical weathering the latitudinal distributions of cia ciw and wip show that they are suitable to both bulk and clay samples but sio2 al2o3 is only suitable to clay samples not suitable in bulk ones all these investigations indicate a significant dependence of grain size in major element abundance and latitudinal distributions of sio2 al2o3 cia ciw and wip but parent rock type has little effect on them except its impact on the latitudinal distribution of wip in clay samples the significant grain size dependence probably indicates the presence of unaltered minerals in bulk samples thus we suggest that clay samples are more suitable to investigating chemical weathering of sediments on continents than bulk samples the trivial effect of parent rock type probably indicates a relatively uniform chemical weathering on various parent rocks correlation analyses indicate that climate is the dominant control of chemical weathering of topsoils in the study area and the significant latitude effect indicated by the spatial distributions of chemical weathering indices actually reflect the climate control on chemical weathering of topsoils chemical weathering indices actually reflect the integrated weathering history in the study area besides the dominant control of climate other factors like tectonics parent rock biology landform and soil depth and age might also have some effect on the chemical weathering of topsoils in the study area which needs further research c 2013 elsevier ltd all rights reserved

ocean warming and gas hydrate stability on the mid norwegian margin at the storegga slide abstract the sensitivity of oceanic gas hydrates and submarine slope stability to the combined forcing of sea level changes and bottom water perturbation is a critical issue for risk assessment in the storegga slide area on the mid norwegian margin evidence for the existence of gas hydrates both inside and outside the storegga slide complex comes from reflection seismic profiles where a bottom simulating reflection marks today s base of the gas hydrate stability zone paleo bottom water temperatures show a relatively fast increase at approximately 12 5 10 ka calendar years following the younger dryas while stable warm water conditions have prevailed since then despite sea level rise this warm water inflow caused a major reduction in the thickness of the gas hydrate stability zone along the upper slope of the mid norwegian margin modelling results indicate that critical hydrate stability conditions and consequently the maximal potential pore pressure build up occur at the location of the storegga slide headwall although the major phase of hydrate melting predates the storegga slide event dated at 8 2 ka calendar years reduced hydrate stability conditions could have facilitated or contributed to sub marine slope failure additionally the bottom simulating reflections within the slide complex seem to have nearly adjusted to new equilibrium conditions highlighting the dynamics of hydrate stability in continental margin sediments under environmental changes climate change geohazards

dynamic response of oceanic hydrate deposits to ocean temperature change the dynamic response of oceanic hydrate deposits to ocean temperature change matthew t reagan and george j moridis earth sciences division lawrence berkeley national laboratory 1 cyclotron rd berkeley ca 94720 usa

addressing anisotropy in 3 d prestack depth migration a case study from the southern north sea this is a case study of a 3 d anisotropic prestack depth migration apsdm of data from block l10 of the dutch sector of the north sea producing gas reservoirs in l10 are typical of the area in that they are contained in horst and tilted fault blocks of the rotliegend formation imaging these fault blocks is made difficult by a complex overburden greatly influenced by salt tectonics in particular the overburden includes chalk characterized by fast velocities and a strong vertical velocity gradient

chemical weathering since the little ice age recorded in lake sediments a high resolution proxy of past climate because of the different geochemical behaviour of rubidium and strontium in earth surface processes variations of the rb sr ratios in lake sediments were used as a geochemical proxy of chemical weathering and past climate in a single watershed low magnetic susceptibility low caco3 low sr concentration and hence high rb sr ratio in the lake sediments indicate weak chemical weathering under a cold but wet climate during the little ice age lia in the closed daihai lake watershed the concordant change in both sr and caco3 concentrations with 18o values in the dunde ice core suggests that weak chemical weathering during the wet lia was controlled by air temperature after the lia however precipitation played a dominant role in chemical weathering copyright 2001 john wiley sons ltd

modelling methane hydrate stability changes and gas release due to seasonal oscillations in bottom water temperatures on the rio grande cone offshore southern brazil abstract the stability of methane hydrates on continental margins worldwide is sensitive to changes in temperature and pressure conditions it has been shown how gradual increases in bottom water temperatures due to ocean warming over post glacial timescales can destabilize shallow oceanic hydrate deposits causing their dissociation and gas release into the ocean however bottom water temperatures bwt may also vary significantly over much shorter timescales including due to seasonal temperature oscillations of the ocean bottom currents in this study we investigate how a shallow methane hydrate deposit responds to seasonal bwt oscillations with an amplitude of up to 1 5 c we use the tough hydrate code to model changes in the methane hydrate stability zone mhsz using data from the rio grande cone in the south atlantic ocean off the brazilian coast in all the cases studied bwt oscillations resulted in significant gaseous methane fluxes into the ocean for up to 10 years followed by a short period of small fluxes of gaseous methane into the ocean until they stopped completely on the other hand aqueous methane was released into the ocean during the 100 years simulated for all the cases studied during the temperature oscillations the mhsz recedes continuously both horizontally and in a smaller scale vertically until a permanent and a seasonal region in mhsz are defined sensitivity tests were carried out for parameters of porosity thermal conductivity and initial hydrate saturation which were shown to play an important role on the volume of methane released into the ocean and on the time interval in which such release occurs overall the results indicate that in a system with no gas recharge from the bottom seasonal temperature oscillations alone cannot account for long term gas release into the ocean

ambiguity in analysis of velocity and depth velocity analysis methods generally involve an analysis of the traveltime moveout of seismic events to investigate ambiguities for such methods we can start with a simple single layer model and investigate the uncertainty in the estimation of velocity and reflector depths this analysis will show that the velocity depth ambiguity is dependent on the offset depth ratio and on the accuracy of traveltime picks

systematics of time migration errors even if the correct velocity is used time migration mispositions events whenever the velocity changes laterally these errors increase with lateral velocity variation depth of burial and dip angle our analyses of two model types one with an implicit gradient and one with an explicit gradient yield simple rules of thumb for these errors to first order in the lateral gradient the x error is a 1 3tan2 and the z error is 2atan3 where the quantity a a x z contains the information about depth of burial and magnitude of lateral gradient these rules can be used to determine when depth migration is needed further analysis also shows that the image ray correction to time migration is accurate only at small dip for dipping events the image ray correction must be supplemented by a shift in x of the form 3atan2 and a shift in z given by 2atan3 these time migration corrections take the same form for both the models we have studied suggesting a general scheme for correcting time migration w

methane release from warming induced hydrate dissociation in the west svalbard continental margin timing rates and geological controls 1 hundreds of plumes of methane bubbles first observed in 2008 emanate from an area of the seabed off west svalbard that has become 1 c warmer over the past 30 years the distribution of the plumes lying close to and upslope from the present upper limit of the methane hydrate stability zone indicates that methane in the plumes could come from warming induced hydrate dissociation a process commonly invoked as contributing to rapid climate change we used numerical modeling to investigate the response of hydrate beneath the seabed to changes in bottom water temperature over periods of up to 1000 years b p the delay between the onset of warming and emission of gas resulting from the time taken for thermal diffusion hydrate dissociation and gas migration can be less than 30 years in water depths shallower than the present upper limit of the methane hydrate stability zone where hydrate was initially several meters beneath the seabed and fractures increase the effective permeability of intrinsically low permeability glacigenic sediment at the rates of warming of the seabed that have occurred over the past two centuries the enthalpy of hydrate dissociation limits the rate of gas release to moderate values cycles of warming and cooling can create and sustain hydrate close to the seabed

tracing bottom water oxygenation with sedimentary mn fe ratios in lake zurich switzerland abstract redox dynamics of manganese mn were studied in the sediment of lake zurich using precise sediment core age models monthly long term oxygen o 2 monitoring data of the water column 1936 2010 and high resolution xrf core scanning the age models were based on bi annual lamination and calcite precipitation cycles if present mn exhibits distinct maxima which coincide with the annual maximum deep water o 2 concentrations in spring according to the monitoring data in contrast the iron fe signal is mainly the result of calcite dilution as indicated by a strong negative correlation between fe and calcium ca xrf data the mn fe ratio in the core from the maximum lake depth zh10 15 137 m revealed a moderate correlation with o 2 measurements in the lake bottom water confirming the successful application of the mn fe ratio to semi quantitatively reconstruct bottom water oxygenation in the lake mostly low ratios were observed between 1895 and the mid 1960s as a result of eutrophication however geochemical focusing and sedimentological factors can reduce the applicability of the mn fe ratio in reconstructing o 2 concentrations in the bottom water of lakes

a 2000 year dust storm record from lake sugan in the dust source area of arid china 1 arid northwestern china is considered to be a major source of atmospheric dust supply to the northern hemisphere however dust storm evolution and dust emission processes in the past remain unclear due to the scarcity of geologic archives in this region hydrologically closed lakes in dust source areas act as a trap providing the opportunity to trace the history of dust emission or eolian activity here we present the results of dust storm proxies and a dust storm history from lake sugan in the qaidam basin a dust source area on the northern qinghai tibetan plateau grain size analyses of the materials deposited during modern dust storms and of the lake surface sediments demonstrate that the coarse component of the lake sediments was transported primarily by ambient winds when dust storms occurred in combination with a sediment chronology generated by counting annual laminations a 2000 year dust storm history was reconstructed on the basis of changes in the coarse component and magnetic susceptibility of the lake sediments frequent and or intensive dust storms occurred during the intervals ad 300 500 ad 1180 1240 and ad 1500 1700 the occurrence of dust storms largely coincided with the strengthening of the siberian high with colder air masses from high latitudes such as during the little ice age frequently encroaching into the dust source areas in northwestern china our results suggest that wind strength plays an important role in dust emissions in arid source areas however dust storms in the late 20th century are most likely associated with disturbance of the ground surface caused by petroleum exploitation in the qaidam basin

variations in 87sr 86sr ratios of calcites in chinese loess a proxy for chemical weathering associated with the east asian summer monsoon abstract 87sr 86sr ratios of loess paleosol calcites of luochuan in china over the past 130 ka display a regular change with increasing trend of 87sr 86sr ratios in the following order loess calcite weakly pedogenetic paleosol calcite paleosol calcite pure secondary calcite the observed variations in the 87sr 86sr record of loess paleosol calcites correlate closely with the records of the magnetic susceptibility coarse grain fraction content in the same profile an et al chin sci bull 39 1994 182 184 and the specmap stacked 18o record of global ice volume imbrie et al in berger et al eds milankovitch and climate part i reidel boston 1984 pp 269 305 strata from the last glacial consist mostly of loesses and weakly developed paleosols and have lower 87sr 86sr ratios averaging 0 71079 paleosols which developed during the last interglacial have higher 87sr 86sr ratios averaging 0 71131 the four periods ca 125 110 98 90 80 75 and 9 5 ka b p of increased summer monsoonal rainfall coincide with the four peaks in 87sr 86sr values a series of 87sr 86sr high frequency high amplitude fluctuations is superimposed on the last glacial interglacial cycle over the past 130 ka occurring on millennium timescales with an average time span of about 3 ka during the last glacial the fluctuations of the 87sr 86sr ratios of the luochuan loess paleosol calcites lie in the range 0 71036 0 71176 for the past 130 ka the study shows that the sr isotopic system in loess paleosol calcites may therefore be an excellent proxy of chemical weathering on continents associated with the east asian summer monsoon

natural gas hydrates in the rio grande cone brazil a new province in the western south atlantic the rio grande cone is a large scale fanlike feature in the continental slope of the pelotas basin southern brazil where ubiquitous world class bottom simulating reflectors bsrs are readily observed in seismic records with the purpose of searching for natural gas hydrate deposits in the cone area four oceanographic cruises were carried out between may 2011 and july 2013 leading to the discovery of two pockmark fields active faults and gas hydrates in shallow sediments multichannel seismic multibeam echo sounder side scan sonar and sub bottom profiler records were used to map the shallow section and select sites for piston core sampling gas hydrates were recovered in several piston cores within muddy sediments collected inside pockmarks displaying high backscatter in the multibeam and side scan sonar data we present two representative piston cores where numerous levels of gas hydrates occur along with degassing features authigenic carbonate and soupy sediments gas dissociated from gas hydrate samples is dominantly methane 99 78 with minor quantities of ethane the chemical and isotopic compositions of the gas strongly suggest a biogenic origin for the analyzed samples these new findings are regarded as strong enough evidence to consider the rio grande cone as a new gas hydrate province

interpretation of velocity estimates from coherency inversion velocity estimation by coherency inversion provides a velocity depth macro model of the subsurface the accuracy of this model is critical for imaging techniques such as depth migration and inversion therefore the reliability of seismic interpretation is strongly dependent on the accuracy of the derived model uncertainties in the velocity and depth estimates for the model can be calculated using a combination of the response surface technique and the dix equation in the layer stripping strategy the method takes into account the local errors connected mainly to the current layer and the global errors connected to the derived overburden examples using synthetic and real data show that the coherency inversion produces accurate macro models

glacial interglacial indian summer monsoon dynamics the modern indian summer monsoon ism is characterized by exceptionally strong interhemispheric transport indicating the importance of both northern and southern hemisphere processes driving monsoon variability here we present a high resolution continental record from southwestern china that demonstrates the importance of interhemispheric forcing in driving ism variability at the glacial interglacial time scale as well interglacial ism maxima are dominated by an enhanced indian low associated with global ice volume minima in contrast the glacial ism reaches a minimum and actually begins to increase before global ice volume reaches a maximum we attribute this early strengthening to an increased cross equatorial pressure gradient derived from southern hemisphere high latitude cooling this mechanism explains much of the nonorbital scale variance in the pleistocene ism record