twenty first century warming of a large antarctic ice shelf cavity by a redirected coastal current the redirection of warm water under the filchner ronne ice shelf during the second half of this century could cause the ice shelf base to melt at a rate 20 times higher than at present warm ocean currents are known to erode ice shelves from below but changes in currents can be forced by many different mechanisms leading to uncertain outcomes this study highlights the vulnerability to climate change of a small antarctic coastal region which has potentially severe consequences for the mass balance of a large antarctic ice shelf hellmer et al use climate modelling to show that the projected loss of sea ice in the weddell sea east of the antarctic peninsula leads to an increase in wind stress which in turn accelerates a warm ocean current far underneath the vast filchner ronne ice shelf the authors predict that the increased warmth could increase melt by a factor of 20 with possible consequences for ice stream dynamics in the east antarctic ice sheet the antarctic ice sheet loses mass at its fringes bordering the southern ocean at this boundary warm circumpolar water can override the continental slope front reaching the grounding line1 2 through submarine glacial troughs and causing high rates of melting at the deep ice shelf bases3 4 the interplay between ocean currents and continental bathymetry is therefore likely to influence future rates of ice mass loss here we show that a redirection of the coastal current into the filchner trough and underneath the filchner ronne ice shelf during the second half of the twenty first century would lead to increased movement of warm waters into the deep southern ice shelf cavity water temperatures in the cavity would increase by more than 2 degrees celsius and boost average basal melting from 0 2 metres or 82 billion tonnes per year to almost 4 metres or 1 600 billion tonnes per year our results which are based on the output of a coupled ice ocean model forced by a range of atmospheric outputs from the hadcm35 climate model suggest that the changes would be caused primarily by an increase in ocean surface stress in the southeastern weddell sea due to thinning of the formerly consolidated sea ice cover the projected ice loss at the base of the filchner ronne ice shelf represents 80 per cent of the present antarctic surface mass balance6 thus the quantification of basal mass loss under changing climate conditions is important for projections regarding the dynamics of antarctic ice streams and ice shelves and global sea level rise

fluvial response to climate change during and after the last glacial maximum in central anatolia turkey abstract fluvial response to climate change during and after the last glacial maximum lgm included incision aggradation phases recorded in sediment cores from the valley floor of the kizilirmak in central anatolia a numerical chronology was established by ams dating of fluvial sediments and ar ar dating of a basalt sample capping the youngest terrace late pleistocene terrace indicating that the main incision phase was completed at the end of the lgm the succeeding aggradation phase in the valley took place from the end of the lgm onwards it appears that the major climatic transition from the lgm to the late glacial gave rise to aggradation in the fluvial system and this event seems to be consistent with the timing of the regression phase of pluvial lakes and the termination of paleoglacier advances in the high mountains of anatolia this study of fluvial systems in anatolia indicates that the coldest periods are not always characterized by fluvial aggradation

three dimensional inversion of towed streamer electromagnetic data abstract a towed streamer electromagnetic system capable of simultaneous seismic and electromagnetic data acquisition has recently been developed and tested in the north sea we introduce a 3d inversion methodology for towed streamer electromagnetic data that includes a moving sensitivity domain our implementation is based on the 3d integral equation method for computing responses and frechet derivatives and uses the re weighted regularized conjugate gradient method for minimizing the objective functional with focusing regularization we present two model studies relevant to hydrocarbon exploration in the north sea first we demonstrate the ability of a towed electromagnetic system to detect and characterize the harding field a medium sized north sea hydrocarbon target we compare our 3d inversion of towed streamer electromagnetic data with 3d inversion of conventional marine controlled source electromagnetic data and observe few differences between the recovered models second we demonstrate the ability of a towed streamer electromagnetic system to detect and characterize the peon discovery which is representative of an infrastructure led shallow gas play in the north sea we also present an actual case study for the 3d inversion of towed streamer electromagnetic data from the troll field in the north sea and demonstrate our ability to image all the troll west oil and gas provinces and the troll east gas province we conclude that 3d inversion of data from the current generation of towed streamer electromagnetic systems can adequately recover hydrocarbon bearing formations to depths of approximately 2 km we note that by obviating the need for ocean bottom receivers the towed streamer electromagnetic system enables electromagnetic data to be acquired over very large areas in frontier and mature basins for higher acquisition rates and relatively lower cost than conventional marine controlled source electromagnetic methods

and the geophysicist replied which model do you want abstractmarine controlled source electromagnetic csem and magnetotelluric mt soundings were carried out between 1997 and 2003 over the gemini prospect in the gulf of mexico during early development of marine instrumentation the resulting data sets provide a good test bed for examining the effect of the data type and misfit choice on regularized inversion solutions we inverted the data sets individually and jointly for isotropic and anisotropic resistivity at a variety of data misfits we found that multifrequency csem inversions vastly improved structural resolution over single frequency inversions suggesting that variation in skin depth added significant information joint mt and csem inversion appeared to improve resolution over mt only inversions at depths considerably deeper than the csem data can resolve probably by constraining shallow structure in the parts of the model to which the mt data were sensitive the addition of model anisotropy improved data fit but introduced an arbitrary scali

horizontal circulation and volume transports in the weddell gyre derived from argo float data argo floats provide both hydrographic and trajectory data affording the opportunity to investigate surface to mid depth ocean dynamics here argo float data are used to determine the absolute geostrophic velocity field of the upper 50 2000 m of the weddell gyre from which the overall circulation pattern is investigated the weddell gyre plays a pivotal role in the modification of climate by advecting heat towards the antarctic ice shelves and by modifying the water masses that feed into the lowest limb of the global ocean overturning circulation warm deep water the source water mass that delivers heat to the weddell gyre is conveniently located within the upper 2000 m domain covered by the floats we investigate its volume transport as it circulates the gyre full depth volume transports are estimated by applying a quadratic function to extrapolate the relative dynamic height field component to the full ocean depth using ctd profiles from ship based surveys to determine an extrapolation error major new insights are provided by this study there is an established double gyre structure to the circulation with a strong eastern cell and a weaker western cell regional variation of the baroclinic component of the flow field is revealed indicating a northeast to southwest reduction in the baroclinic flow along with a strong meridional gradient of baroclinic flow along the northern limb of the gyre especially east of 25 w the zonal mean gyre strength away from the shelf edge is 32 5 sv 1 sv 1 106 m3 s 1 of which 13 3 sv are associated with the advection of warm deep water there is a considerable amount of recirculation within the gyre interior where water does not traverse the full zonal extent of the gyre the recirculation is stronger in the eastern cell of the observed double gyre structure the interior circulation cells partly explain the large variations in previous gyre strength estimates we provide an extensive review of previous estimates in context of the new results obtained

marine csem of the scarborough gas field part 1 experimental design and data uncertainty we describe the planning processing and uncertainty analysis for a marine csem survey of the scarborough gas field off the northwest coast of australia consisting of 20 transmitter tow lines and 144 deployments positioned along a dense 2d profile and a complex 3d grid the purpose of this survey was to collect a high quality data set over a known hydrocarbon prospect and use it to further the development of csem as a hydrocarbon mapping tool recent improvements in navigation and processing techniques yielded high quality frequency domain data data pseudosections exhibit a significant anomaly that is laterally confined within the known reservoir location perturbation analysis of the uncertainties in the transmitter parameters yielded predicted uncertainties in amplitude and phase of just a few percent at close ranges these uncertainties may however be underestimated we introduce a method for more accurately deriving uncertainties using a line of receivers towed twice in opposite directions comparing the residuals for each line yields a gaussian distribution directly related to the aggregate uncertainty of the transmitter parameters constraints on systematic error in the transmitter antenna dip and inline range can be calculated by perturbation analysis uncertainties are not equal in amplitude and phase suggesting that inversion of these data would be better suited in these components rather than in real and imaginary components one dimensional inversion showed that the reservoir and a confounding resistive layer above it cannot be separately resolved even when the roughness constraint is modified to allow for jumps in resistivity and prejudices are provided indicating that this level of detail is beyond the single site csem data further when range dependent error bars are used the resolution decreases at a shallower depth than when a fixed error level is used

late glacial to mid holocene palaeoclimate development of southern greece inferred from the sediment sequence of lake stymphalia ne peloponnese abstract the sedimentary sequence of lake stymphalia ne peloponnese for the first time sheds light on the palaeoclimate development of southern greece from 15 to 5 ka bp new geochemical data based on high resolution x ray fluorescence scanning provide in situ and continuous analysis of predefined element suites on split core surfaces variations of elements over time were assessed constructing correlation matrices based on the calculation of pearson correlation coefficients the element suite includes al si k ca ti mn fe zn rb sr and zr a major result includes that changes in element behaviour are related to hydrological changes in the catchment precipitation lake level status and evaporation insolation solar activity and are ultimately driven by climate major trends shifts in elemental ratios correspond to the climate development in the eastern mediterranean region based on correlation of rb sr reflecting wet dry climates with foraminiferal proxies of marine core lc21 from the southern aegean sea and the stable oxygen isotope record of soreq cave israel the bolling allerod the younger dryas and the 8 2 ka cold event were identified

itrax description and evaluation of a new multi function x ray core scanner a new automated multi function core scanning instrument named itrax has been developed that records optical radiographic and elemental variations from sediment half cores up to 1 8 m long at a resolution as fine as 200 m an intense micro x ray beam focused through a flat capillary waveguide is used to irradiate samples to enable both x radiography and x ray fluorescence xrf analysis data are acquired incrementally by advancing a split core via a programmable stepped motor drive through the flat rectangular section x ray beam traditional xrf determination of element composition in sediments provides high quality data but it takes a considerable time and normally consumes gram quantities of material that is often only available in limited quantities the itrax core scanner non destructively collects optical and x radiographic images and provides high resolution elemental profiles that are invaluable for guiding sample selection for further destructive detailed sampling this paper presents a description of the construction characteristics and capabilities of the itrax system high resolution itrax data obtained from sediment cores are also presented and compared with results from traditional wavelength dispersive xrf analysis at lower resolution finally some recent technical developments linked to the second generation itrax are presented

the antarctic slope current near 30 e the antarctic slope current flows westward above the continental slope of antarctica entering the weddell sea near 30 e and supplying dense water to the deep overturning cell there and contributing to global antarctic bottom water formation observations from the 2008 i6s hydrographic section are used to investigate the strength of the slope current near 30 e a prominent topographic feature the gunnerus bank diverts the slope current upstream of this longitude and has a large effect on the current s structure splitting it into a coastal and offshore component the bank also enhances water mass mixing and lateral exchange across the slope as part of the 2008 occupation an additional line was made along the crest of the bank forming a closed volume over the western side by combining hydrographic and lowered acoustic doppler current profiler measurements in this box using an inverse method the slope current transport is estimated to be 9 6 2 3 sv the transport associated with the antarctic slope front is 4 0 0 3 sv of which 1 8 0 3 sv enters the weddell gyre as recently formed dense water

casing effects in the sea to borehole electromagnetic method the sea to borehole controlled source electromagnetic csem method has the potential of becoming a useful new exploration and monitoring technique modeling shows that the electromagnetic fields at reservoir depths can be 1 2 orders of magnitude larger than those on the seabed thus opening up the possibility to see deeper or detect and monitor smaller targets in the case of measurements inside metal casing the use of reciprocity to interchange the source and receiver allows the casing conductortobeconsideredasanantenna thisantennaisexcited by a source inside the casing which induces a current flowing along the casing conductor based on the current distribution a casing dipole moment and an equivalent length were derived for thetransversemagnetictmmode inthefrequencyrangeofinterest 0 1 10 hz the increase in field strength resulting from sea to borehole measurements is not lost to the casing attenuation for either the tm or the transverse electric te mode the ratio of the dipole moment of the casing antenna to that of the sourcecurrentcanbeconsideredasthecasingattenuationeffect thisratioisnotfarfromunityforfrequenciessmallerthan1 hz but it decreases rapidly with frequency the equivalent length of the casing antenna can be of the order of a few hundred meters as a consequence the field distribution changes significantly in the presence of casing and the vertical resolution of tm measurementsisdegraded thehorizontalresolutionisnotdegraded significantly measurementofthetmmodehastheadvantageof being sensitive to thin resistive targets and being less affected by sea air interactions in shallow water the te mode measurement having a localized casing effect contributes valuable informationaboutthebackgroundresistivity

mid to late holocene flood frequency changes in the northeastern alps as recorded in varved sediments of lake mondsee upper austria abstract annually laminated varved lake sediments with intercalated detrital layers resulting from sedimentary input by runoff events are ideal archives to establish precisely dated records of past extreme runoff events in this study the mid to late holocene varved sediments of lake mondsee upper austria were analysed by combining sedimentological geophysical and geochemical methods this approach allows to distinguish two types of detrital layers related to different types of extreme runoff events floods and debris flows and to detect changes in flood activity during the last 7100 years in total 271 flood and 47 debris flow layers deposited during spring and summer were identified which cluster in 18 main flood episodes fe 1 18 with durations of 30 50 years each these main flood periods occurred during the neolithic 7100 7050 vyr bp and 6470 4450 vyr bp the late bronze age and the early iron age 3300 3250 and 2800 2750 vyr bp the late iron age 2050 2000 vyr bp throughout the dark ages cold period 1500 1200 vyr bp and at the end of the medieval warm period and the little ice age 810 430 vyr bp summer flood episodes in lake mondsee are generally more abundant during the last 1500 years often coinciding with major advances of alpine glaciers prior to 1500 vyr bp spring summer floods and debris flows are generally less frequent indicating a lower number of intense rainfall events that triggered erosion in comparison with the increase of late holocene flood activity in western and northwestern nw europe commencing already as early as 2800 yr bp the hydro meteorological shift in the lake mondsee region occurred much later these time lags in the onset of increased hydrological activity might be either due to regional differences in atmospheric circulation pattern or to the sensitivity of the individual flood archives the lake mondsee sediments represent the first precisely dated and several millennia long summer flood record for the northeastern ne alps a key region at the climatic boundary of atlantic mediterranean and east european air masses aiding a better understanding of regional and seasonal peculiarities of flood occurrence under changing climate conditions

on the structure and the transport of the eastern weddell gyre abstract the circulation pattern and volume transports in the eastern weddell gyre are estimated on the basis of hydrographic data collected by r v polarstern between 1989 and 1996 in the northeastern edge of the weddell gyre eastward flowing water masses from the antarctic circumpolar current and the weddell sea converge due to the strong effect of topographic constraints on ocean currents in the weakly stratified waters of high latitudes the wedge like structure of the southwest indian ridge can cause the convergence the increased shear leads to instabilities of the current at the eastern end of the ridge which produce an intense mesoscale eddy field between 15 and 30 e in the eddies water from the weddell cold regime and the antarctic circumpolar current waters mix and form the water masses of the weddell warm regime these waters are advected southward and flow towards the westward southern rim current which is driven by the antarctic eastwind band hence there is not a continous flow from the northern to the southern rim but a decay of the mean flow in the northeast and a reformation in the south volume transports across the greenwich meridian estimated on the basis of a combined ctd adcp data set result in an eastward flow of 61 sv in the northern rim current and a westward return flow of 66 sv in the southern part of the gyre the transport is about twice as high as previous estimates between kapp norvegia and the northern tip of the antarctic pensinsula indicating a significant gyre circulation north of 70 s

holocene environmental change and its impact on sediment dynamics in the eastern mediterranean abstract investigators have studied past environmental change in the eastern mediterranean region from a number of perspectives while climate reconstructions and palynological research have focused on forces that drive the geomorphologic system many researchers have attempted to use sediment archive studies to identify periods of change in sediment dynamics due to the large variability in environmental parameters and the variety of landscapes present in the eastern mediterranean region research has focused on sediment archives ranging from small colluvial sites to deltas of large rivers on the mediterranean coast as the cultural record for the region is extremely rich the main goal of palaeo environmental research in the eastern mediterranean has been to identify the relative importance of human impact on the landscape nevertheless sediment archives have significant limitations chronological control for many palaeo environmental records is highly uncertain and rates of landscape change are oftentimes difficult to assess most palaeo environmental research has been conducted on or near archeological sites where direct human impact may obscure the indirect impact on sediment dynamics through land use changes quantification and modeling of sediment dynamics in the eastern mediterranean environment offer one solution when erosion and sediment transport rate analyses are incorporated periods of relatively important change can be identified using multiple approaches the relative importance of the main driving forces climate and land use become distinguishable since field based data from the actual sediment archives remain vital an overview of numerous studies in the eastern mediterranean is provided in order to draw a general picture for different time periods and the relative scale of regional landscape development during the holocene a comparison of sediment dynamics with the record of driving forces indicates that while climate was the main driver of the geomorphic system during the early holocene at some point human impact became widespread and began to dictate sediment dynamics to a large extent from the byzantine period onward soil properties seem to play an increasingly important role as the hillslope soil reservoir in the eastern mediterranean was progressively depleted during the late holocene

eddy overturning of the antarctic slope front controls glacial melting in the eastern weddell sea 1 the eastern weddell sea is characterized by narrow continental shelves and warm deep water wdw is located in close proximity to the ice shelves in this region the exchange of wdw across the antarctic slope front asf determines the rate of basal ice shelf melting here we present a unique data set consisting of 2351 vertical profiles of temperature and salinity collected by southern elephant seals mirounga leonina and a profile beneath the fimbul ice shelf fis obtained via drilling through 395 m of ice this data set reveals variations in salinity and temperature through winter and using a conceptual model of the coastal salt budget we quantify the main exchange processes our data show that modified wdw with temperatures below 1 5 c is advected onto the shelf and into the ice shelf cavities by an eddy overturning of the asf the onshore ekman flux of surface waters during summer is the main source of freshwater that leads to the formation of low salinity shelf waters in the region the modified wdw that reaches beneath the ice shelves is too cold for basal ice shelf melting to create such low salinity water a high resolution model of an idealized asf continental shelf ice shelf system supports the conclusions from the data analysis the inflow of wdw onto the continental shelf and into the ice shelf cavity occurs within a bottom boundary layer where the eddy advection in the model is particularly strong in close agreement with the observed vertical profile of temperature beneath the fis citation nost o a m biuw v tverberg c lydersen t hattermann q zhou l h smedsrud and k m kovacs 2011 eddy overturning of the antarctic slope front controls glacial melting in the eastern weddell sea j geophys res 116 c11014 doi 10 1029 2011jc006965

impregnation method for detecting annual laminations in sediment cores an overview abstract annually laminated sediments can provide an absolute time scale by varve counting and a high resolution palaeoclimate information from varve thickness both types of information may be directly measured from sediment core surfaces in this paper we stress that varve counting and varve thickness measurements derived from fresh core surfaces could not systematically reveal the internal sedimentary structure even if assisted by high resolution image analysis we present an example of a homogeneous sediment core for which the varves were only observable after core impregnation and polishing steps because the impregnation methods are not yet standardized the aim of this paper is to give an updated review of the methodology in this review we present the major critical points during impregnation steps in particular we focus on all of the post treatment sediment disturbances that can alter the laminated micro structure and consequently varve measurements finally we propose a modified impregnation protocol especially adapted for tracking varved intervals in long cores

on the sources of weddell gyre antarctic bottom water in march april 1995 as part of the world ocean circulation experiment section a23 we completed 49 hydrographic stations across the weddell gyre and southern antarctic circumpolar current from the antarctic continental shelf 72 5 s 16 5 w to south georgia 55 s 34 5 w chlorofluorocarbon cfc 11 cfc 12 and cfc 113 data collected at these stations reveal that distinct sources renew the antarctic bottom water defined as waters with potential temperatures less than 0 c of the weddell gyre weddell sea bottom water defined as waters with potential temperatures less than 0 7 c formed in the western weddell sea has cfc concentrations about 5 to 6 times higher in the eastward flowing northern weddell gyre than in the westward flowing southern limb our cfc measurements suggest that distinct sources of weddell sea bottom water exist in the western weddell sea in agreement with previous descriptions based on potential temperature and salinity signals in the northern weddell gyre high cfc concentrations in weddell sea deep water potential temperatures between 0 c and 0 7 c confirm the long recognized sources for this water mass in the western and southwestern weddell sea in the southern weddell gyre at about 20 w and along the antarctic continental slope weddell sea deep water with potential temperatures around 0 45 c shows a deep cfc maximum about 1000 m above the seafloor cfc concentrations in this deep southern core are about 80 of those of new weddell sea deep water in the northern weddell gyre near 30 w the a23 cfc and hydrographic data are not consistent with the hypothesis that weddell sea deep waters are derived from a single source in the western weddell sea instead these tracers suggest that an important portion of the weddell sea deep water in the southern weddell gyre originates outside the western weddell sea probably near the amery basin and environs around 75 e these features of the circulation and renewal of the deep weddell gyre should be carefully considered in simulations dealing with fluxes pathways and formation rates of antarctic bottom water

seismically regularized controlled source electromagnetic inversion marine controlled source electromagnetic csem data can be highly sensitive to the presence of resistive hydrocarbon bearing layers in the subsurface yet due to the relatively poor depth resolution of csem data and the smoothness constraints imposed by electromagnetic em inversion methods the resulting resistivity models are often highly smoothed out typically underestimating the reservoir resistivity and overestimating its thickness conversely seismic full waveform inversion fwi can accurately recover the depths of seismic velocity changes yet is relatively insensitive the presence of hydrocarbons in spite of their low depth resolution csem data have been shown to be highly sensitive to the resistivity thickness product of buried resistive layers suggesting that if the thickness of a target layer can be constrained a priori very accurate resistivity estimates may be obtained we developed a method for leveraging the high depth resolution of fwi into a standard csem inversion algorithm so

cause and effect in mediterranean erosion the role of humans and climate upon holocene sediment flux into a central anatolian lake catchment abstract the debate in historical geomorphological studies about the causes of erosion in regions such as the mediterranean has been long standing the relative roles of climate change and human impacts can be difficult to disentangle in the absence of highly resolved chronologies here we reconstruct the erosion history of a small lake catchment in central anatolia located on the edge of one of the mediterranean s most iconic badland landscapes in cappadocia because these lake sediments are annually laminated precisely dating clastic inwash layers and calculating recurrence intervals and flux rates is possible lake cores have been analysed for xrf elemental geochemistry and via thin sections along with proxies for hydroclimate oxygen isotopes and land cover pollen peaks in titanium along with other detrital elements and changes in clastic layers indicate increased sediment influx into nar lake between 9300 and 8000 cal bp ceramic neolithic when obsidian mining took place nearby and again more importantly during the last 2500 years iron age to modern the latter exhibiting three phases of enhanced catchment erosion multiproxy comparisons show that these phases were related primarily to periods of increased human impact on vegetation and soils around the lake most sediment influx has been in the form of turbidites linked to the presence of a fan delta at the lake edge although this store does not appear to have significantly delayed sediment delivery from eroding hillslopes to the lake bed the marked increase in detrital influx during the late holocene implies that badland development in the lake catchment is recent and largely anthropogenic rather than ancient and of climatic causation and probably involving stream capture the record also shows that sediment influx diminished markedly at times when human land use disintensified which in turn indicates that hillslope degradation is reversible with appropriate land management

a feasibility study of land csem reservoir monitoring in a complex 3 d model summary we carried out a series of numerical simulations in a complex 3 d resistivity model to investigate the feasibility of using controlled source electromagnetics on land for monitoring changes in a hydrocarbon reservoir during production displacement of oil by saline water injection changes the resistivity the modelling allows a comparison of the measured time lapse em signal to various sources of noise that can be expected in a field experiment for instance magnetotelluric signals repeatability errors and near surface resistivity changes caused by seasonal variations our estimates show that land csem monitoring should be feasible though not easily for the example considered here a thick reservoir at a depth of about 1 km the trade off between signal strength and repeatability errors requires the source to be located at some distance from the reservoir measurements in a monitoring well suffer less from surface noise measuring the vertical electric component in a well placed at some distance from the reservoir provides the best result

ten years of marine csem for hydrocarbon exploration marine controlled source electromagnetic csem surveying has been in commercial use for predrill reservoir appraisalandhydrocarbonexplorationfor10 years althougha recent decrease has occurred in the number of surveys and publications associated with this technique the method has become firmly established as an important geophysical tool intheoffshoreenvironment thisisaconsequenceoftwoimportant aspects associated with the physics of the method first it is sensitive to high electrical resistivity which although not an unambiguous indicator of hydrocarbons is an important property of economically viable reservoirs second although the method lacks the resolution of seismic wave propagation it has a much better intrinsic resolution than potential field methods such as gravity and magnetic surveying which until now have been the primary nonseismicdatasetsusedinoffshoreexploration althoughbymany measures marine csem is still in its infancy the reliability and noise floors of the instrument systems have improved significantly over the last decade and interpretation methodology has progressed from simple anomaly detection to 3d anisotropic inversion of multicomponent data using some of theworld sfastestsupercomputers researchdirectionspresently include tackling the airwave problem in shallow water by applying time domain methodology continuous profiling tools and the use of csem for reservoir monitoring during production

reservoir monitoring of steam assisted gravity drainage using borehole measurements this paper presents the results from a research project focusing on permanent crosswell geophysical methods for reservoir monitoring during steam assisted gravity drainage a feasibility study indicated detectable differences in seismic and electrical reservoir properties based on expected changes in temperature and fluid saturation during the production of extra heavy oil as a result of this a permanent cross well system was installed at the leismer demonstration area located in the athabasca oil sands region in alberta canada baseline data sets including cross well seismic three dimensional vertical seismic profiling and cross well electrical resistivity tomography have been acquired comparisons between conventional surface seismic and downhole seismic data show an increase in resolution and frequency content as expected steam assisted gravity drainage induced time lapse effects are clearly visible in the 3d vertical seismic profiling and electrical resistivity tomography data sets even after a few months of oil production in general the 3d vertical seismic profiling images show a higher resolution than the surface seismic data in particular when dealing with vertical positioning of the time lapse events the electrical resistivity tomography baseline shows clear separation between zones of high and low electrical resistivity and during 23 months of electrical resistivity tomography measurements the maximum reduction of resistivity is 85 time lapse observations from acoustic and electrical borehole data correspond well and are also supported by temperature measurements in the two observation wells emerging technologies updated models improved flexibility and reduced costs will allow future reservoir monitoring with surface and borehole data in combination or even with borehole data exclusively key words borehole geophysics resistivity seismics time lapse

synoptic gulf stream velocity profiles through simultaneous inversion of hydrographic and acoustic doppler data data from a shipborne acoustic profiling device have been combined with conductivity temperature depth o 2 sections across the gulf stream to form estimates of the absolute flow fields the procedure for the combination was a form of inverse method the results suggest that at the time of the observations june 1982 the net gulf stream transport off hatteras was 107 11 sv and that across a section near 72 5ow it had increased to 125 6 sv subject to further uncertainty from the definition of the stream the transport of the deep western boundary current was 9 3 sv these and other transport estimates are plausibly close to previous calculations but we do not claim that they represent the temporal mean for comparison purposes we have done an inversion using the hydrographic o 2 data alone as in previously published results and obtained qualitative agreement with the combined inversion inversion of the acoustic measurements alone when corrected for instrument biases leaves unacceptably large mass transport residuals in the deep water our conclusion is that the inversion of the combined data sets produces results much improved over those from using either acoustic or hydrographic chemical constraints in isolation the procedures are close analogues to those which can be used with satellite altimeters and are a procedure for obtaining very accurate geoid slope measurements

eastern mediterranean hydroclimate over the late glacial and holocene reconstructed from the sediments of nar lake central turkey using stable isotopes and carbonate mineralogy there is a lack of high resolution records of hydroclimate variability in the eastern mediterranean from the late glacial and early holocene more knowledge of the speed of climate shifts and the degree to which they were synchronous with changes in the north atlantic or elsewhere is required to understand better the controls on eastern mediterranean climate using endogenic carbonate from a sediment sequence from nar golu a maar lake in central turkey dated by varve counting and uranium thorium methods we present high resolution 25 years oxygen 18o and carbon isotope records supported by carbonate mineralogy data spanning the late glacial and holocene 18ocarbonate at nar golu has been shown previously to be a strong proxy for regional water balance after a dry period i e evaporation far exceeding precipitation in the younger dryas the data show a transition into the relatively wetter early holocene in the early holocene there are two drier periods that appear to peak at 9 3 ka and 8 2 ka coincident with cooling events seen in north atlantic records after this and as seen in other records from the eastern mediterranean there is a millennial scale drying trend through the mid holocene transition the relatively dry late holocene is punctuated by centennial scale drought intervals at the times of 4 2 ka event and late bronze age societal collapse overall we show that central turkey is drier when the north atlantic is cooler throughout this record and at multiple timescales thought to be due to a weakening of the westerly storm track resulting from reduced cyclogenesis in the north atlantic however some features such as the mid holocene transition and the fact the early holocene dry episodes at nar golu are of a longer duration than the more discrete events seen in north atlantic records imply there are additional controls on eastern mediterranean hydroclimate

transient electromagnetic finite difference time domain earth modeling over steel infrastructure including highly conductive steel infrastructure into electromagnetic em earth modeling is motivated by the fact that long metal cased boreholes have the potential to be used as boosting antennas that enable larger source dipole moments and greater signal penetration depths unfortunately geophysical algorithms designed to simulate em responses over rather regional scales are complicated by material property contrasts and structure geometries that are more typical for em engineering applications hence the great majority of earth modeling algorithms that consider em responses from steel cased boreholes use integral equation methods to be able to model complex casing scenarios we revisited the finite difference time domain fdtd method to advance the modeling of transient em field responses from steel cased boreholes a time dependent function that allows for larger fdtd time steps in the dufort frankel method was developed alleviating the generally large computational overhead we compared our method against three different kinds of benchmark solutions to demonstrate the reliability of the fdtd field solutions these test cases were carried out to check the feasibility of a final hydraulic fracturing study images of the electric current distribution in a sheetlike rock fracture were calculated for the cases with and without the presence of a connecting borehole casing demonstrating the casing s potential of illuminating deep target zones

remote sensing of hydrocarbon layers by seabed logging sbl results from a cruise offshore angola detecting and assessing hydrocarbon reservoirs without the need to drill test wells is of major importance to the petroleum industry seismic methods have traditionally been used in this context but the results can be ambiguous another approach is to use electromagnetic sounding methods that exploit the resistivity differences between a reservoir containing highly resistive hydrocarbons and one saturated with conductive saline fluids modeling presented by eidesmo et al 2002 demonstrates that by using seabed logging sbl a special application of frequency domain controlled source electromagnetic csem sounding the existence or otherwise of hydrocarbon bearing layers can be determined and their lateral extent and boundaries can be quantified such information provides valuable complementary constraints on reservoir geometry and characteristics obtained by seismic surveying

a pleistocene pyroclastic poor maar from central anatolia turkey influence of a local fault on a phreatomagmatic eruption in central anatolia the late pleistocene narkoy maar formed on a fault zone a 5 m thick pyroclastic succession erupted from a crater 900 m in diameter the presence of gas fumeroles hot springs and hydrothermal alteration zones indicates that the area is geothermally active the products of the maar are large blocks and lapilli to coarse ash planar bedding and cross stratification are well developed within coarse ash beds the maar deposits were generated by a single period of phreatomagmatic explosion with two episodes the first episode produced wet eruption clouds while the second one was relatively dry in nature the estimate of the volume of pyroclastic ejecta compared with the dimensions of the maar demonstrates a material deficiency which is attributed to a large volume of gas emanated during the phreatomagmatic explosion along a fault presently cross cutting the maar in addition a relatively small volume of magma intruded along the fault and mixed with meteoric water in the fault zone to produce the phreatomagmatic eruption the existence of a hydrothermal system in the fault zone is important in affecting the eruption style and evolution of narkoy maar

remotely induced warming of antarctic bottom water in the eastern weddell gyre 1 four repeat hydrographic sections across the eastern weddell gyre at 30 e reveal a warming by 0 1 c and lightening by 0 02 0 03 kg m 3 of the antarctic bottom water aabw entering the gyre from the indian sector of the southern ocean between the mid 1990s and late 2000s historical hydrographic and altimetric measurements in the region suggest that the most likely explanation for the change is increased entrainment of warmer mid depth circumpolar deep water by cascading shelf water plumes close to cape darnley where the indian sourced aabw entering the weddell gyre from the east is ventilated this change in entrainment is associated with a concurrent southward shift of the antarctic circumpolar current s acc southern boundary in the region this mechanism of aabw warming may affect wherever the acc flows close to antarctica

sensitivity of the eastern mediterranean geomorphic system towards environmental change during the late holocene a chronological perspective alluvial and colluvial sediment deposition provide a vital record of environmental change during the holocene firm chronological control on these archives is necessary to enable us to relate sediment dynamics to human activity and climate variability in the eastern mediterranean such relationships are hard to establish due to the lack of spatially well distributed sediment archives with good chronological control this scarcity is problematic with respect to regional scale reconstructions of the temporal variation of sediment dynamics here we present a radiocarbon database n 178 of geomorphological activity collected from multiple distinct sediment archives within the territory of sagalassos in south western turkey the data were grouped according to their sedimentary facies for analysis using cumulative probability distributions cpds and sedimentation rate sr modelling two small scale colluvial valleys where chronological information was abundant were investigated in more detail results show that sedimentation chronology differs between individual nearby cores as it depends strongly on the local geomorphic situation a generalizing approach combining multiple core results yields more widely valid conclusions high sedimentation rates coincided with the initial major anthropogenic disturbance of the landscape and decreased afterwards probably due to hillslope soil depletion cpd and sr analysis indicates that in general colluvial sedimentation rates did not change much from 2000 bc onwards river floodplain sedimentation in contrast increased markedly during the first millennium bc and during recent times and a significant time lag in enhanced sediment deposition between the upper and lower reaches of the river valleys was observed copyright 2012 john wiley sons ltd

tidally driven vorticity diurnal shear and turbulence atop fieberling seamount abstract fine and microstructure profiles collected over fieberling seamount at 32 26 n in the eastern north pacific reveal a variety of intensified baroclinic motions driven by astronomical diurnal tides the forced response consists of three phenomena coexisting in a layer 200 m thick above the summit plain i an anticyclonic vortex cap of core relative vorticity 0 5f ii diurnal fluctuations of 15 cm s 1 amplitude and 200 m vertical wavelength and iii turbulence levels corresponding to an eddy diffusivity e 10 10 4 m2 s 1 the vortex cannot be explained by taylor proudman dynamics because of its 0 3fn2 negative potential vorticity anomaly the 0 3f fortnightly cycle in the vortex s strength suggests that it is at least partially maintained against dissipative erosion by tidal rectification the diurnal motions are slightly subinertial turning clockwise in time and counterclockwise with depth over the summit plain they also exhibit a fortnightly cycle in their amplitude pointing to

the transport of the weddell gyre across the prime meridian abstract current meter observations from instruments moored from 1996 to 2001 are used to determine the structure and the volume transport of the weddell gyre on the greenwich meridian the record length mean volume transport is 45 sv to the east within the northern and 56 sv to the west within the southern limb of the weddell gyre thus 11 sv must leave the gyre circulation west of the greenwich meridian and enter it east of it the deficit occurs with 8 sv mainly in the circumpolar deep water cdw warm deep water wdw layer surface waters and weddell sea deep water wsdw contribute 2 and 3 sv respectively in contrast to this 3 sv more of weddell sea bottom water wsbw flow in the northern limb to the east than in the southern limb to the west which suggests a wsbw formation rate of about 3 sv in the western weddell sea in the southern boundary of the antarctic circumpolar current acc a volume transport of 35 16 sv was found using geostrophic calculations adjusted with two measurements of the absolute velocity the large heat content of the northern limb points to an extensive heat exchange between the weddell sea and the world ocean west of the prime meridian hence the heat transport as well as the volume transport suggest that the water masses of the weddell gyre are not exclusively replaced in its eastern part but that there is a significant exchange of water masses to the west of the prime meridian

a land based controlled source electromagnetic method for oil field exploration an example from the schoonebeek oil field controlled source electromagnetic csem data are sensitive to the subsurface resistivity distribution but 3d inversion results are ambiguous and in depth interpretation is challenging resolution and sensitivity analysis as well as the influence of noise on resolution have been used to quantify 3d inversion performance based on these numerical studies a land based csem survey was designed and carried out at the schoonebeek oil field the netherlands the acquired data were processed and subsequently inverted for the resistivity distribution the 1d and 3d inversion of horizontal electric field data show the reservoir at the right depth matching well log data without using a priori knowledge about the actual reservoir depth we used a 1d model with fine layering as a starting model for 3d inversion synthetic data inversions and sensitivity tests demonstrate that resistive or conductive bodies inside the reservoir zone may be well detectable with our limited acquisition geometry spatial variations in the reservoir resistivity are visible in the measured data and after inversion by assuming good knowledge of the background resistivity distribution the reservoir resistivity and size however have to be interpreted with care considering the intrinsically low resolution of electromagnetic em which is further reduced by manmade em noise

a high resolution late holocene lake isotope record from turkey and links to north atlantic and monsoon climate a high resolution proxy record of precipitation and evaporation variability through the past 1700 yr from 18o analysis of a varved lake sequence from central turkey shows rapid shifts between dry periods ad 300 500 and ad 1400 1950 and wetter intervals ad 560 750 and ad 1000 1350 changes are consistent with changes in instrumental and proxy records of the indian monsoon dry summers in the eastern mediterranean being associated with periods of enhanced monsoon rainfall in addition major shifts in the record are coherent with changes in north atlantic winter climate with cold wet periods in the alps occurring at times of dry turkish climate

fronts transport and weddell gyre at 30 e between africa and antarctica a detailed description of the frontal structure of major currents and estimates of transport between africa and antarctica at 30 e were made on the basis of a finely resolved hydrographic section made during the 1996 civa 2 cruise particular emphasis was put on a refinement of the eastern boundary of the weddell gyre by analyzing also supplementary hydrographic data from the 1993 civa 1 cruise and the best available historical hydrographic data in the weddell and enderby basins contrary to the general belief our results show that the weddell gyre extends far beyond 30 e reaching at least as far east as the enderby land promontory 53 e from this point westward currents along the antarctic continental margin constitute the gyre s southern boundary thus closing the cyclonic circulation of the gyre at its easternmost end as the most convincing evidence for this refined circulation scheme significant westward transport south of 65 s has been identified from the civa 1 acoustic doppler current profiler data we have shown also using an inertial jet model that the blocked feature of the weddell cold regime 57 s to the west of 25 e is due to the topographic control of flow by local bathymetry during the civa 2 cruise 70 of the antarctic circumpolar current acc was concentrated near the polar front 51 s with surface speeds reaching up to 70 cm s 1 the baroclinic current field in the subpolar area south of the weddell front 58 s for civa 2 and 57 s for civa 1 is featureless 3 cm s 1 but yielding a nonnegligible eastward transport of 15 sv 1 sv 106 m3 s 1 this bottom referenced baroclinic transport is entirely compensated by a substantial westward barotropic transport south of 65 s the acc transport across the 30 e section during the civa 2 cruise is estimated to be 160 sv

historical landscape change in cappadocia central turkey a palaeoecological investigation of annually laminated sediments from nar lake coupled multiproxy indicators pollen stable isotopes and charcoal reconstructed from annually laminated lake sediments from nar ga la in cappadocia central turkey complemented by documentary and archaeological evidence provide a detailed record of environmental changes and their causes from late antiquity ad 300 to the present day stable isotope data indicate marked shifts in the variability in summer drought intensity and winter spring rainfall but these did not coincide in time with changes in vegetation and land use shown by pollen data rather human impacts appear to have been the main driver of landscape ecological changes in cappadocia over the last two millennia pollen and charcoal data indicate four principal land use phases i an early byzantine agrarian landscape characterized by cereals and tree crops and marking the later part of the so called beya ehir occupation phase ii a period of landscape abandonment and the establishment of secondary woodland from ad 670 to 950 coinc

characteristics of sedimentary varve chronologies a review abstract we constructed a varve data base vdb to study the worldwide distribution of varved sediment records and the fidelity of their varve chronologies clusters of lakes with varved sediments exist in central north america in the canadian arctic and in northern and central europe among the 108 sites included in the vdb varved records are typically 200 500 cm long and cover a period of 1000 2000 years their varve chronologies are often based on counting of annual layers from fresh sediment surfaces and photographs or from epoxy embedded sediment blocks and thin sections the vdb indicates that chronological errors associated with counting sedimentary varves fall generally between 1 and 3 but only 57 of published records are providing quantitative error estimations for their chronologies with a careful documentation of varves and by applying radiometric dating methods to surface sediments as well as using historical events as time markers there is the potential of having centennial long varved records with a very precise age depth control however it is unrealistic to expect errors significantly below 1 from several millennia long sections we found no indication that varve chronologies would have been substantially more accurate and precise in some parts of the world than in others or statistically dependent on varve thickness or temporal extension of a varved sequence according to the vdb close to 90 of the published varve chronologies have been cross checked with some independent dating methods

tephrostratigraphy chronology and climatic events of the mediterranean basin during the holocene an overview the identification and characterisation of high frequency climatic changes during the holocene requires natural archives with precise and accurate chronological control which is usually difficult to achieve using only 14c chronologies the presence of time spaced tephra beds in quaternary mediterranean successions represents an additional independent tool for dating and correlating different sedimentary archives these tephra layers are potentially useful for resolving long standing issues in paleoclimatology and can help towards correlating terrestrial and marine paleoclimate archives known major tephras of regional extent derive from central and southern italy the hellenic arc and from anatolia a striking feature of major holocene tephra deposition events in the mediterranean is that they are clustered rather than randomly distributed in time several tephra layers occurred at the time of the s1 sapropel formation between c 8 4 and 9 0 ka bp mercato gabellotto fiumebianco e1 cappadocia and ot

controlled source electromagnetic monitoring of reservoir oil saturation using a novel borehole to surface configuration to advance and optimize secondary and tertiary oil recovery techniques it is essential to know the areal propagation and distribution of the injected fluids in the subsurface we investigate the applicability of controlled source electromagnetic methods to monitor fluid movements in a german oilfield bockstedt onshore northwest germany as injected brines highly saline formation water have much lower electrical resistivity than the oil within the reservoir the main focus of this study is on controlled source electromagnetic simulations to test the sensitivity of various source receiver configurations the background model for the simulations is based on two dimensional inversion of magnetotelluric data gathered across the oil field and calibrated with resistivity logs three dimensional modelling results suggest that controlled source electromagnetic methods are sensitive to resistivity changes at reservoir depths but the effect is difficult to resolve with surface measurements only resolution increases significantly if sensors or transmitters can be placed in observation wells closer to the reservoir in particular observation of the vertical electric field component in shallow boreholes and or use of source configurations consisting of combinations of vertical and horizontal dipoles are promising preliminary results from a borehole to surface controlled source electromagnetic field survey carried out in spring 2014 are in good agreement with the modelling studies

observations of the antarctic slope undercurrent in the southeastern weddell sea 1 the antarctic slope front presents a dynamical barrier between the cold antarctic shelf waters in contact with ice shelves and the warmer subsurface waters offshore two hydrographic sections with full depth current measurements were undertaken in january and february 2009 across the slope and shelf in the southeastern weddell sea southwestward surface intensified currents of 30 cm s 1 and northeastward undercurrents of 6 9 cm s 1 were in thermal wind balance with the sloping isopycnals across the front which migrated offshore by 30 km in the time interval between the two sections a mid depth undercurrent on february 23 was associated with a 130 m uplift of the main pycnocline bringing warm deep water closer to the shelf break this vertical displacement comparable to that caused by seasonal variations in wind speed implies that undercurrents may affect the exchanges between coastal and deep waters near the antarctic continental margins

the marine controlled source electromagnetic response of a steel borehole casing applications for the neptune canada gas hydrate observatory gas hydrates are a potential energy resource a possible factor in climate change and an exploration geohazard the university of toronto has deployed a permanent seafloor time domain controlled source electromagnetic csem system offshore vancouver island within the framework of the neptune canada underwater cabled observatory hydrates are known to be present in the area and due to their electrically resistive nature can be monitored by 5 permanent electric field receivers however two cased boreholes may be drilled near the csem site in the near future to understand any potential distortions of the electric fields due to the metal we model the marine electromagnetic response of a conductive steel borehole casing first we consider the commonly used canonical model consisting of a 100 m 100 m thick resistive hydrocarbon layer embedded at a depth of 1000 m in a 1 m conductive host medium with the addition of a typical steel production casing extending from the seafloor to the resistive zone results show that in both the frequency and time domains the distortion produced by the casing occurs at smaller transmitter receiver offsets than the offsets required to detect the resistive layer second we consider the experimentally determined model of the offshore vancouver island hydrate zone consisting of a 5 5 m 36 m thick hydrate layer overlying a 0 7 m sedimentary half space with the addition of two borehole casings extending 300 m into the seafloor in this case results show that the distortion produced by casings located within a 100 m safety zone of the csem system will be measured at 4 of the 5 receivers we conclude that the boreholes must be positioned at least 200 m away from the csem array so as to minimize the effects of the casings

mediterranean valleys revisited linking soil erosion land use and climate variability in the northern levant abstract this paper presents results of geomorphological and archaeological investigations undertaken in several small drainage basins in the jebel al aqra region of southern turkey by focusing intensive archaeological settlement survey in basins where securely dated sequences of sedimentary valley fills have been recorded spatially and temporally linked high resolution records of land use and soil erosion have been generated sedimentary data show that throughout most of the holocene floodplains remained rather stable allowing deep soils to form but in the past two millennia probably from ad 150 700 a phase of severe soil erosion was initiated and resulted in the deposition of 3 5 5 0 m of alluvial sediments on valley floors archaeological and historical evidence suggest that while these areas were occupied by agrarian communities since at least 2800 bc nearly three millennia of cultivation during the bronze and iron ages had relatively little effect on soil erosion the intensification of settlement throughout the region and the conversion of upland areas to intensive agricultural production during the hellenistic roman and late roman periods 300 bc ad 650 however created the necessary preconditions for severe soil erosion to occur these data are compared against modern and paleoclimate studies of the eastern mediterranean which show an extremely variable precipitation regime and the effects that it can have on erosion a 400 year lag between the initial settlement of upland areas and the first evidence of soil erosion suggest that it may have been the intersection of extreme precipitation events with particular land use conditions of the roman and late roman periods which worked together to drive soil erosion

on the origin of the deep cfc maximum in the eastern weddell sea numerical model results cfc tracer observations indicate that prydz bay in the indian sector of the southern ocean is a region of deep and bottom water formation results of a circum polar ocean circulation model which includes cfc an age tracer and numerical floats indicate prydz bay as being a convection site which contributes to the reservoir of freshly ventilated waters in the weddell sea in contrast to the newly formed weddell sea bottom water captured near bottom water masses of prydz bay origin spread on hori zons which pass the ridges confining the weddell sea there fore contributing directly to the ventilation of the global abyss

the contribution of the weddell gyre to the lower limb of the global overturning circulation the horizontal and vertical circulation of the weddell gyre is diagnosed using a box inverse model constructed with recent hydrographic sections and including mobile sea ice and eddy transports the gyre is found to convey 42 8 sv 1 sv 106 m3 s 1 across the central weddell sea and to intensify to 54 15 sv further offshore this circulation injects 36 13 tw of heat from the antarctic circumpolar current to the gyre and exports 51 23 msv of freshwater including 13 1 msv as sea ice to the mid latitude southern ocean the gyre s overturning circulation has an asymmetric double cell structure in which 13 4 sv of circumpolar deep water cdw and relatively light antarctic bottom water aabw are transformed into upper ocean water masses by mid gyre upwelling at a rate of 2 2 sv and into denser aabw by downwelling focussed at the western boundary 8 2 sv the gyre circulation exhibits a substantial throughflow component by which cdw and aabw enter the gyre from the indian sector undergo ventilation and densification within the gyre and are exported to the south atlantic across the gyre s northern rim the relatively modest net production of aabw in the weddell gyre 6 2 sv suggests that the gyre s prominence in the closure of the lower limb of global oceanic overturning stems largely from the recycling and equatorward export of indian sourced aabw

the antarctic slope current in a changing climate the antarctic slope current asc is a coherent circulation feature that rings the antarctic continental shelf and regulates the flow of water towards the antarctic coastline the structure and variability of the asc influences key processes near the antarctic coastline that have global implications such as the melting of antarctic ice shelves and water mass formation that determines the strength of the global overturning circulation recent theoretical modeling and observational advances have revealed new dynamical properties of the asc making it timely to review earlier reviews of the asc focused largely on local classifications of water properties of the asc s primary front here we instead provide a classification of the current s frontal structure based on the dynamical mechanisms that govern both the along slope and cross slope circulation these two modes of circulation are strongly coupled similar to the antarctic circumpolar current highly variable motions such as dense overflows tides and eddies are shown to be critical components of cross slope and cross shelf exchange but understanding of how the distribution and intensity of these processes will evolve in a changing climate remains poor due to observational and modeling limitations results linking the asc to larger modes of climate variability such as el nino show that the asc is an integral part of global climate an improved dynamical understanding of the asc is still needed to accurately model and predict future antarctic sea ice extent the stability of the antarctic ice sheets and the southern ocean s contribution to the global carbon cycle

holocene environmental change in southwest turkey a palaeoecological record of lake and catchment related changes percentage concentration and accumulation pollen data together with diatom and non siliceous microfossil data are presented for the site of go lhisar go l u 37i8 n 29i36 e elevation 930 m a small intramontane lake in burdur province southwest turkey microfossil assemblages from the longest sediment core gha 813 cm record changes in local and regional vegetation and lake productivity over the last 9500 years pollen spectra indicate that vegetation progressed from an open landscape with an increase in arboreal pollen occurring 8500 bp to mixed forest comprising oak pine and juniper until around 3000 bp cal 1240 bc when a human occupation phase becomes discernible from the pollen spectra this occurs shortly after the deposition of a volcanic tephra layer which originated from the minoan eruption of santorini thera and radiocarbon dated to 3330 70 yr bp cal 1600 bc this human occupation phase is comparable to the beys ehir occupation phase recorded at other sites in southwest turkey and involved forest clearance and the cultivation of fruit trees such as olea juglans castanea and itis together with arable cereal growing and pastoralism the presence of pollen types associated with the beys ehir occupation phase in deposits above the santorini tephra layer confirms a late bronze age early anatolian dark age date for its commencement since 3000 bp notable changes in aquatic ecology associated with tephra deposition and subsequent nutrient and sediment flux from the lake catchment are recorded the beys ehir occupation phase at go lhisar go l u came to an end around 1300 bp cla ad 700 when pine appears to have become the dominant forest tree 1999 elsevier science ltd all rights reserved

tracking the hydro climatic signal from lake to sediment a field study from central turkey palaeo hydrological interpretations of lake sediment proxies can benefit from a robust understanding of the modern lake environment in this study we use nar golu a non outlet monomictic maar lake in central turkey as a field site for a natural experiment using observations and measurements over a 17 year monitoring period 1997 2014 we compare lake water and sediment trap data to isotopic chemical and biotic proxies preserved in its varved sediments nar golu underwent a 3 m lake level fall between 2000 and 2010 18olakewater is correlated with this lake level fall responding to the change in water balance endogenic carbonate is shown to precipitate in isotopic equilibrium with lake water and there is a strong relationship between 18olakewater and 18ocarbonate which suggests the water balance signal is accurately recorded in the sediment isotope record over the same period sedimentary diatom assemblages also responded and conductivity inferred from diatoms showed a rise shifts in carbonate mineralogy and elemental chemistry in the sediment record through this decade were also recorded intra annual changes in 18olakewater and lake water chemistry are used to demonstrate the seasonal variability of the system and the influence this may have on the interpretation of 18ocarbonate we use these relationships to help interpret the sedimentary record of changing lake hydrology over the last 1725 years nar golu has provided an opportunity to test critically the chain of connection from present to past and its sedimentary record offers an archive of decadal to centennial scale hydro climatic change

late quaternary mass movement events in lake el gygytgyn north eastern siberia lake el gygytgyn is situated in a 3ae6 myr old impact crater in north eastern siberia its sedimentary record probably represents the most complete archive of pliocene and quaternary climate change in the terrestrial arctic in order to investigate the influence of gravitational sediment transport on the pelagic sediment record in the lake centre two sediment cores were recovered from the lower western lake slope the cores penetrate a sub recent mass movement deposit that was identified by 3ae5 khz echo sounding in the proximal part of this deposit deformed sediments reflect an initial debris flow characterized by limited sediment mixture above and in front of the debrite a wide massive densite indicates a second stage with a liquefied dense flow the mass movement event led to basal erosion of ca 1 m thick unconsolidated sediments along parts of its flow path the event produced a suspension cloud whose deposition led to the formation of a turbidite the occurrence of the turbidite throughout the lake and the limited erosion at its base mainly suggest deposition by pelagic rain following stokes law very similar radiocarbon dates obtained in the sediments directly beneath and above the turbidite in the central lake confirm this interpretation when applying the depositional model for the late quaternary sediment record of lake el gygytgyn the recovered turbidites allow reconstruction of the frequency and temporal distribution of large mass movement events at the lake slopes in total 28 turbidites and related deposits were identified in two 12ae9 and 16ae6 m long sediment cores from the central lake area covering approximately 300 kyr

detecting hydrocarbon reservoirs from csem data in complex settings application to deepwater sabah malaysia controlled source electromagnetic csem field surveys offer a geophysical method to discriminate between high and low hydrocarbon saturations in a potential reservoir however the same geological processes that create the possible hydrocarbon reservoir may also create topography and near surface variations of resistivity e g shallow gas or hydrates that can complicate the interpretation of csem data in this paper we discuss the interpretation of such data over a thrust belt prospect in deepwater sabah malaysia we show that detailed modeling of the key scenarios can help us understand the contributions of topography near surface hydrates and possible hydrocarbons at reservoir depth complexity at the surface and at depth requires a 3d electromagnetic modeling code that can handle realistic ten million cell models this has been achieved by using an iterative solver based on a multigrid preconditioner finite difference approach with frequency dependent grid adaptation

high resolution x ray fluorescence core scanning analysis of les echets france sedimentary sequence new insights from chemical proxies the les echets sediment sequence has recently been the subject of a high resolution multi proxy study which revealed shifts in lake productivity linked to greenland stadials and interstadials over the last 40 ka wohlfarth et al 2008 rapid ecosystem response to abrupt climate changes during the last glacial period in western europe 40 16 ka geology 36 407 410 here we present new elemental data for this sequence as acquired using an x ray fluorescence core scanning system which provides in situ high resolution continuous multi element analyses it was found that the strength of associations between the studied elements ti rb k zr si ca sr mn and fe varied over time with changes in lake status which are ultimately driven by changes in climate increases in fine grained detrital input as indicated by ti rb k and zr rb overlap with independently established periods of lower lake productivity and are interpreted to represent more arid conditions several of these arid periods are coincident with low diatom concentrations and the timing of heinrich events h4 h3 and h2 the duration of the environmental impacts linked to the h events varied by proxy with elemental data ti and zr rb estimating shorter events than the diatom data periods of lower detrital input and coarser grain sizes agreed in time with periods of higher lake productivity the elemental data provide new insights into hydrological changes and related sediment processes within the catchment and highlight the need for multi element and multi proxy approaches when reconstructing climate change using lacustrine sediment sequences copyright 2011 john wiley sons ltd

mapping thin resistors and hydrocarbons with marine em methods insights from 1d modeling the use of marine controlled source electromagnetic em csem sounding to detect thin resistive layers at depths below the seafloor has been exploited recently to assess the resistivity of potential hydrocarbon reservoirs before drilling we examine the sensitivity of the csem method to such layers with forward and inverse modeling in one and three dimensions the 3d modeling demonstrates that if both source and receivers are over a tabular 3d target 1d modeling predicts the observed response to very high accuracy experimental design can thus be based on 1d analysis in which hundreds of range and frequency combinations can be computed to find the optimal survey parameters for a given target structure modeling in three dimensions shows that the vertical electric field response is largest over the edges of a 3d target the 3d modeling also suggests that a target body needs to have a diameter twice the burial depth to be reliably seen by csem sounding a simple air wave model energy propagating from source to receiver via the atmosphere allows the effects of the target layer and atmosphere to be separated and shows where sensitivity to the target is diminished or lost because of finite water depth as a function of range frequency and seafloor resistivity unlike dc resistivity sounding the marine csem method is not completely t equivalent and in principle can resolve resistivity and thickness separately smooth inversion provides an estimate of the method s resolving power and highlights the fact that although the radial csem fields contain most of the sensitivity to the thin resistive target inverted alone they produce only increasing resistivity with depth inclusion of the radial mode csem data forces the recovery of the thin resistor but magnetotelluric data can be used more effectively to achieve the same result